13. NATURAL SOURCE MAGNETOTELLURICS

Transcription

1 13. NATURAL SOURCE MAGNETOTELLURICS 13.1 INTRODUCTION FIXED FUNCTION KEYS MT/AMT PROGRAM OPERATION... 5 MAIN DISPLAY...5 HEADER...7 FOOTER...8 LINE SETUP...8 ACQUISITION CONFIGURATION...9 CHANNEL TABLE...10 SOFT FUNCTION KEYS...11 ARCHIVE SUBMENU...12 SCREEN: CHANNEL TABLE DISPLAY SCREENS...13 SCREEN: SETUP...13 SCREEN: RESULTS...15 SCREEN: GRAPH...16 SCREEN: STACKS...17 JOB_INFO SUBMENU...18 SAV_GAIN FUNCTION...18 SCOPE FUNCTION BOARD CALIBRATION SUBMENU GATHERING DATA PROGRAM START UP...25 DATA ACQUISITION...25 STOP ACQUISITION...26 ACQUISITION ERRORS VIEWING DATA TIME SCHEDULE TIME SCHEDULE HEADER...31 TIME SCHEDULE TABLE...32 ARCHIVE FILE NAMING...34 STARTING A NON-REPEATING TIME SCHEDULE...35 STARTING A REPEATING TIME SCHEDULE CACHE FILE GDP October 2014

2 GDP INSTRUCTION MANUAL 13.9 A NOTE ON VARIABLE A-SPACING A NOTE ON PHASE A NOTE ON SCALING CASCADE DECIMATION OVERVIEW RESTRICTIONS NOTES ON FIELD CONFIGURATIONS FIELD CONFIGURATIONS SINGLE STATION MT...49 LOCAL REMOTE REFERENCE MT...50 LOCAL REMOTE REFERENCE MT...51 MT MEASUREMENT CLUSTERS METHOD TO FIELD-CHECK MAGNETIC SENSORS. 53 October 2014 Section 13, Page 2 GDP-32 24

3 13.1 INTRODUCTION NATURAL SOURCE MAGNETOTELLURICS Natural source magnetotellurics (MT) or audio-frequency magnetotellurics (AMT) is a frequency domain EM program that uses naturally occurring random noise as the signal source. This data acquisition system uses cascade decimation and stacking and averaging of Fourier transformed cross and auto-power spectra of the 6th and 8th harmonics, to obtain amplitude and phase measurements of the electric and magnetic fields. The frequency range of the MT/AMT program is from (6/8192) to 8192 Hz, and is divided into three groups as shown below, with the 6th and 8th harmonics displayed: Low band Medium band High band (SR = 32 Hz) (SR = 1024 Hz) (SR = Hz) 3. Hz 4. Hz High Mid Low The Low band is further divided into Low, Mid, and High ranges. Data for all bands are acquired on a continuous basis, with the filtering, decimation and Fourier transforms being done after data are collected. Data acquired for the Low bands are saved to the flash drive on a real-time basis. Data collected using the Time Schedule feature are not processed by the GDP. Both electric field (Ex, Ey, Ez) measurements and magnetic field (Hx, Hy, Hz) measurements are utilized with this method. A calibrate buffer is provided for the magnetic antenna calibrates, and is saved as XAMTANT.CAL on the GDP C:\ drive. An older file format, ANTAMT.CAL, is also recognized if the new file is not found. The standard board calibrate buffer is saved as 24BRDAMT.CAL on the GDP C:\ drive. Board calibration data can be viewed in the Calibration menu of the AMT program. If no calibrate files are found, empty files are created with 1.0 magnitude and 0.0 phase values. SELECT UP SELECT DN Home End All selectable fields can be modified using and keys. Numeric fields can be incremented or decremented using the same keys. Some numeric fields, such as Gain/Atn can only be modified to allowable values. Go to Section 6 for information concerning calibration, synchronization and generic operation of all programs. Go to the end of this AMT Instruction Manual for suggestions on connecting the receiver for field measurements. GDP Section 13, Page 3 October 2014

4 GDP INSTRUCTION MANUAL Note: Some numeric or alphanumeric values are not registered in GDP memory until you exit PREV FIELD Pg Up Pg Dn Enter the parameter field by pressing,, or The exceptions to this behavior are the frequency band and the powerline notch filters. Frequency band is used as the sample rate selection. Whenever you change the frequency the sample rate is automatically changed through the timing card. However, the anti-alias filter is not changed until just prior to data acquisition. Enter Upon pressing to gather data or set gains, the receiver will automatically set the antialias filter as defined by internal look-up tables FIXED FUNCTION KEYS NEXT FIELD Six fixed function keys are located below the six soft function keys ( through ) at the bottom edge of the LCD. Enter the 24AMT.CAC cache and view data. Data can be viewed as time-series or apparent resistivity plots vs. frequency. Exit the AMT program and return to the main menu for selection of other data acquisition programs. Enter the calibrate and system checking sub-menu. See GDP Section 6.1, Calibration for more details. Perform a one-time gaining of the channels that are currently On and for the currently selected BAND. (This key has no function in older versions of this program) Perform a one-time buck out any self-potential (SP) or amplifier offset, for all channels that are currently on. (This key has no function in older versions of this program) Measure the contact resistance or coil output resistance. See GDP Section 6.3, Measuring Contact Resistance for more details. October 2014 Section 13, Page 4 GDP-32 24

5 NATURAL SOURCE MAGNETOTELLURICS 13.3 MT/AMT PROGRAM OPERATION One of the differences between the GDP and its predecessor, the GDP-32 II, is that there is no longer a menu structure at the start of each acquisition program. Each program will now start in the main user interface menu. There are sub-menus that the user may use to enter programspecific entries. These sub-menus vary between the different programs. Instead of cumbersome menu levels which force a sequence of data entry, the operator can use the following guideline: 1. Start by filling in the parameters in the JOB_INFO submenu. 2. Back on the Main Menu, set A-Space and other Line Setup parameters. 3. Set Acquisition Configuration parameters and configure the channels in the Channel Table. 4. Acquire data. 5. Review the data, and finally 6. Archive the data cache file. These steps are all accessed from the Main Menu, and its various screens and submenus, as described in this manual. Note: The order of these steps is not required, however due to some features of the program, changing some fields can cause other fields to be updated. This can cause some values, particularly in the Channel Table, to be modified after the user has already set them. MAIN DISPLAY The screen provides 80 characters on 30 lines. The entire screen is visible on the Color display. However, 60 characters on 20 lines are visible on the Monochrome display. Use the and one of the quadrant keys to shift the display to another area: + SELECT UP PREV FIELD Home Pg Up SELECT DN NEXT FIELD key End Pg Dn SELECT DN End Home For example, shift the display down by using, and back up with. Only the first diagram below shows the entire screen. MOST OF THE OTHER SCREENS IN THIS MANUAL DISPLAY ONLY 60 characters BY 20 lines. The AMT Main Display has three areas for data entry: Acquisition Configuration, Line Setup, and the Channel Table. A Header line shows current conditions and a Footer area shows status and messages. Below this, the lower left screen shift area is an area for historical Error and Warning messages. These are generally common with all of the GDP programs. The key moves the cursor directly to some of the main input areas of the display. SELECT UP GDP Section 13, Page 5 October 2014

6 GDP INSTRUCTION MANUAL <1303a_24AMT_MainAreas> Full display screen showing defined areas. October 2014 Section 13, Page 6 GDP-32 24

7 NATURAL SOURCE MAGNETOTELLURICS <1303a_24AMT_MainAreas> Display showing 60 characters and 20 lines. (the colors are for this illustration only) AREAS COMMON TO ALL PROGRAMS HEADER The Header line contains the following information: 28 Block number. AMT2.24j BAT 14.4 Sats 0 27 Jun 2014 Date. Program name and version. Battery Level in Volts. Number of GPS satellites (when GPS sync option is available). 0 13: 7:45 Time (Schedule days elapsed 0-2, Hours, Minutes, Seconds). GDP Section 13, Page 7 October 2014

8 FOOTER GDP INSTRUCTION MANUAL The Footer area contains several lines of information: The STATUS: line indicates the general status of the program or progress during data acquisition. Below this is a Help line that displays warnings, requests user confirmation or acquisition progress steps. The third line contains labels for the soft function keys. These change depending on the SCREEN and field that the cursor is in. The last ten lines of the display are a history of messages, not generally visible in smaller LCD screens unless it is shifted by pressing the start of each new acquisition period. SELECT DN End. These historical messages are cleared at LINE SETUP The operator should first fill in the Line Setup area of the screen. Entries in this part of the screen can automatically update other fields, especially in the Channel Table. These input fields are not usually changed after a survey has started, therefore they are located in the lower half of the screen. Although there is no required sequence for editing the input fields, it is suggested that these fields be entered first. The following list of input fields is in the suggested order of data entry. A-SPACE E-field dipole size in meters or feet (a-spacing). Notice that entering a value in this field causes all the values of the Asp column of the Channel Table to be modified to match. Variable a-spacing can later be configured by modifying values in the Asp column of the Channel Table as discussed later. Ft / M LINE Specifies units of length, Feet or Meters, for all length and space entries. Informative user defined alphanumeric identification. Direction Informative selection for line direction. Selections are: N, NE, E, SE, S, SW, W, NW, DH (drill hole), SET (any user defined set). X-AZ Informative azimuth of the X direction of the line (0 to +/-360). SPREAD TX LOC LINE Y: RX LOC Informative 2-character user-defined identification. Informative transmitter location, along line (X). The field for Tx designation is NNNNNNN with a floating decimal point. This field is not used for AMT calculations, but could be used as a location or survey designator. Informative transmitter location, across line (Y). The field for Line designation is NNNNNNN with a floating decimal point. This field is not used for AMT calculations, but could be used as a location or survey designator. Receiver location, along line (X). The field for Rx is NNNNNNN with a floating decimal point. For multiple E-field surveys, we normally set Rx equal to the station location at which the receiver is set up. October 2014 Section 13, Page 8 GDP-32 24

9 ACQUISITION CONFIGURATION NATURAL SOURCE MAGNETOTELLURICS The Acquisition Configuration area of the screen contains the following fields: BAND Frequency band selected. Band selection changes sample rate and the number of points collected. Options are: High band Mid Band Low 1 Band Low 2 Band Low 3 Band While making selections, the GDP will evaluate the memory and disk space required, based upon BAND and STACKS settings, and inform the operator if sufficient space is available to successfully record all of the data. STACKS The total number of time series records specified to be acquired and processed for the frequency band. If the entered value would cause acquisition memory of flash disk space to be exceeded, the value will be adjusted down in order to have successful data acquisition. The STATUS: field will show a message INSUFFICIENT DISK SPACE for ACQUISITION or INSUFFICIENT MEMORY for ACQUISITION. GAIN Switch for setting the method the GDP will use for setting gains. Options are ALWAYS Automatic gaining, with SP bucking, will occur before each stack. ONCE DONE Automatic gaining, with SP bucking, will occur only for the first stack. After the first stack, this option will change to DONE. No gaining will occur on subsequent stacks. Changes to some fields will cause this selection to revert to ONCE. MEM_SP A stored memory gain will be recalled, SP bucking will be performed for all stacks. Refer to the SAV-GAIN function key described later. MEMORY A stored memory gain and SP will be recalled. Refer to the SAV-GAIN function key described later. SPONLY SP bucking will be performed for all stacks. The gain values currently set in the Channel Table will not be altered. MAN MODE The gain and SP values currently set in the Channel Table will not be altered. The selections for MODE are STANDARD and NOISY, and describe the electrical environment in which the data are being acquired. This configures the auto gaining algorithm. STANDARD mode will result in a generally higher gain factor. The NOISY mode will result in a lower gain factor in order to minimize the chances of saturating the input signal which would reduce the accuracy in measuring the earth response. GDP Section 13, Page 9 October 2014

10 GDP INSTRUCTION MANUAL NOTCH Powerline notch filter switch. Users have several possible selections here, depending upon the hardware configuration of your receiver. OUT - All notch filters bypassed and 180 Hz notch filters enabled , 180, 300 and 540 Hz notch filters enabled , 300 and 540 Hz notch filters enabled. Other standard selections are: and 150 Hz notch filters enabled , 150, 250 and 450 Hz notch filters enabled. 50/60-50, 150, 60 and 180 Hz notch filters enabled. Note: All powerline notch filters inject noise into the system, and should only be used when absolutely necessary. More information on Notch Filter design can be found in Chapter 16 of this manual. HIPASS Function that allows the user to disable the High Pass filters built into the GDP Information on the High Pass filters can be found in chapter 6. METHOD There are three choices: Vector (Scalar is a subset of vector) Tensor and NoCheck. These are not used in GDP calculations. This value, along with the channel component types, are for post processing. NoCheck instructs the program to not verify that electrode and antenna configurations are sufficient to perform Vector or Tensor data acquisition and processing. CHANNEL TABLE The channel table refers to a separate section of the main menu where metadata pertaining to a specific channel are contained and results for that channel are displayed. The general area of the channel table is highlighted in this sections display. The table is a distinct grouping of fields which can be accessed by pressing the button. There are four SCREEN selections that configure the Channel Table. Press through: SETUP, RESULTS, GRAPH, and STACKS, as described below. to cycle October 2014 Section 13, Page 10 GDP-32 24

11 NATURAL SOURCE MAGNETOTELLURICS SOFT FUNCTION KEYS The function keys through are considered soft function keys because they may perform different functions not only in different programs, but their functionality can change within a program depending on the menu, submenu, input field or Channel Table column the cursor is in. Each key's functionality is identified by its label on the bottom line of the display screen. While the Main Menu is displayed, the keys perform the following functions: ARCHIVE: Start the Archive submenu used to rename the current cache file and initiate a new file. The Archive submenu is described below. SCREEN: Cycle through Channel Table display screens. JOB_INFO: Job Information submenu used to enter survey job information. CH_OFF/ON and SAV_GAIN: When the cursor is in the Channel Table, this key toggles channels Off or On. When the cursor is not in the table, this key stores gain settings used with the MEMORY, and MEM_SP gain modes. SCOPE: Real time scope display of a channel's input signal. It functions only when the cursor is in the Channel Table and in the row of a channel that is currently On. TIMESCH: Time Schedule submenu, which allows viewing, editing and starting time schedules. The Time Schedule submenu is described in the TIME SCHEDULE section. GDP Section 13, Page 11 October 2014

12 GDP INSTRUCTION MANUAL ARCHIVE SUBMENU The Archive submenu is accessed by the key, and allows the user to rename the current cache data file and initialize a new empty file. The renamed cache file is archived to the C:\DATA directory. The screen displays the number of blocks in the current cache file. Only the 8-character file name can be changed. The default name will start with the prefix AMT, followed by 2-character day-of-the-month and 2-character hour. The last character is sequenced to ensure that a unique name is used. The file extension is always.cac. <1303b_24AMT_Archive> Enter If the cache archive name is acceptable, press. If there is a name conflict, an error will occur and allow the name to be changed. When successful, the archive name will be displayed to the operator. When finished, press any key to return to the Main Menu. To cancel archiving Escape the cache file, press. The name of the current cache file to which data is written is always 24AMT.CAC. A new empty file will be initialized when the old cache data have been archived, and the stack/block number has been reset. October 2014 Section 13, Page 12 GDP-32 24

13 NATURAL SOURCE MAGNETOTELLURICS SCREEN: CHANNEL TABLE DISPLAY SCREENS Cycle through the Channel Table screens by using. SCREEN: SETUP The SETUP screen is the initial Channel Table configuration displayed. <1303c_24AMT_Setup> In the SETUP screen, the column entry fields are: Comp Typ, Stn/Ant, Gain Atn, Pre Amp, SPmv and Asp. Non editing fields are: Ch, Calibration Found, Saturated Reading, and CRES. Ch Cal The channel and card cage slot number for the A-D Card. If proper board calibration or antenna calibration records are not found in the calibration caches an exclamation point (!) is displayed next to the channel number. Data acquisition can be completed without the proper calibration record loaded into the cache, and the data displayed on the GDP screen will use calibration values of 1.0 mag and 0.0 phase, and thus will not accurately represent the actual earth response. Calibration caches for the antennas and boards are ASCII files. Comp Typ Channel component type selection. Any selection other than OFF will turn the channel ON. While the cursor is on a channel, the key is used to turn a channel Off or On. This key is the only way an operator can turn off a channel. Refer to the CH_OFF/ON function key described later. An Off channel can also be turned on by selecting a component type. Ex, Ey Electric field designators Hx, Hy, Hz Magnetic field designators. (Antenna types are listed in Section 18.9 ANTENNA DESIGNATIONS ) GDP Section 13, Page 13 October 2014

14 Sat STN/ANT GDP INSTRUCTION MANUAL Hxr, Hyr, Hzr Reference Magnetic field designators (for local remote reference applications only). This field also indicates empty slots and cards not supported by the AMT program such as NanoTEM cards. When the inputs to the channel, after applying the gain and attenuate, saturate the A-D converter, this will indicate. Data acquisition can be completed, but the data acquired by the GDP will not accurately represent the actual earth response. Saturation is detected while gaining, and in real time during data acquisition Dual usage field: 1) E-field designator: Identifies the station number for multiple E-field measurements. 2) H-field designator: Identifies the magnetic field antenna used for that channel. The number in this field must have an exact matching number in the antenna calibrate cache. Antenna identifiers use the format NNNC where NNN is the antenna designator or serial number and C is the antenna type or filter designator. For example: 50 ANT/1 antenna (0), serial number MT antenna, serial number MT/AMT antenna, serial number Single channel TEM/3 (9), serial number 18. GAIN ATN Gain settings for stages 0 and 1 (in powers of 2). The attenuator settings are separated by a dash and have four stages when auto gaining, 0, -1, -2 and -3. An attenuator setting of -4 can be made manually. More information about the gain stages can be found in chapter 16 of this manual. PRE AMP This column allows for input of preamplifier gains, such as the SC-8. Note: The design of the GDP is such that Zonge no longer advises the use of the SC-8 Signal Conditioning Box for most AMT/MT applications. SPmv Self Potential or offset in millivolts. Initially set to Asp This field is for defining A-space, or the length of the dipole. Channels with Hx, Hy and Hz fields will ignore this field. Note: A-space values can also be entered in the A-SPACE field. The entry in the Channel Table is the value used for the apparent resistivity calculation. Entries in the table can be changed when a variable A-space value is needed due to conditions on the ground.. Entries in the A- SPACE field outside of the Channel Table will reset all previous entries made inside the table. CRES Contact Resistance is measured in Ohms. Press the key. October 2014 Section 13, Page 14 GDP-32 24

15 NATURAL SOURCE MAGNETOTELLURICS SCREEN: RESULTS The Results screen can be reached by cycling the key. The program also displays the RESULTS screen automatically after collecting a stack of data unless the operator has selected the STACKS screen. <1303d_24AMT_Results> The RESULTS screen displays the columns MAG 6 th, CC/dPH, and Cagniard Rho. The column entry fields, Comp Typ, Stn/Ant, and the non-editing fields, Ch, Calibration Found, Saturated Reading, are described in the SETUP screen description above. The values displayed at the end of each acquisition stack are for the lowest frequency component in the selected BAND. MAG 6th The square root of the auto-power of each component. The E-field channels are not normalized, so the units are volts. The H-field channels are normalized by the antenna calibrate, and the resultant units are microteslas. CC/dPh Cagniard Rho Coherency coefficient between the orthogonal E- and H-components of the 6th harmonic on the E-field lines, or phase difference in milliradians on the H-field lines. Cagniard or apparent resistivity in ohmmeters for the 6th harmonic. The top value for RHOxy is calculated using ExHy * /HyHy *, the bottom value is ExEx * /HyEx *. The same logic is used for EyHx. GDP Section 13, Page 15 October 2014

16 SCREEN: GRAPH GDP INSTRUCTION MANUAL The GRAPH view allows the user to graphically examine the Cagniard Resistivity data plotted vs. frequency immediately after data are acquired. The plot shows the 12 frequencies calculated from one stack of data. Plotting at this time is very basic. There are no scales for either frequency or resistivity. Users can enter the channel table and then cycle up and down through the E field channels to view the EH apparent resistivity values for that channel. <1303e_24AMT_Graph> October 2014 Section 13, Page 16 GDP-32 24

17 NATURAL SOURCE MAGNETOTELLURICS SCREEN: STACKS The STACKS screen can be displayed by cycling. This screen displays the selected results for the last 5 stacks of data as each stack is being acquired. When this screen is displayed, the cursor is moved to the results selector field. The selections are: Mag, CC, and Rho. Note that while data are being collected, this selection cannot be changed. When data acquisition has finished, cycling this field will update the Channel Table display with the selected results for the last 5 stacks. The STACKS Channel Table is cleared at the start of an acquisition. <1303f_24AMT_Stacks> GDP Section 13, Page 17 October 2014

18 GDP INSTRUCTION MANUAL JOB_INFO SUBMENU The Job Information submenu can be accessed by pressing from the main menu. Entries in this menu are saved as metadata in the data cache and in the 24COMMON.INI file so that users do not have to re-enter these fields every time any of the acquisition programs are started. Entries in these fields carry into Zonge data processing programs. <1303g_24AMT_JobInfo> GDP OPERATOR User defined identification. Alphanumerics permitted. JOB NAME User defined identification. Alphanumerics permitted. JOB FOR User defined identification. Alphanumerics permitted. JOB BY User defined identification. Alphanumerics permitted. JOB NUMBER User defined identification. Alphanumerics permitted. TX SN User defined identification. Alphanumerics permitted. SAV_GAIN FUNCTION The Save Gain function allows the operator to save the gain, attenuate and SP values in memory, for each of the BAND selections, and have them recalled by the MEMORY, and MEM_SP gain settings during data acquisition. When is pressed, the gain, attenuator, SP, and values in the Channel Table will be saved in memory for all of the channels and for the current band. During data acquisition, if the GAIN setting is MEMORY, the gain, attenuator and SP values for all the channels will be recalled for the current band, just prior to data acquisition. If the GAIN setting is MEM_SP, then only the gain and attenuator values will be recalled, and the receiver will perform SP buckout prior to data acquisition. This functionality can be used during manual or Time Schedule controlled acquisition whenever greater control over gain settings is required. October 2014 Section 13, Page 18 GDP-32 24

19 SCOPE FUNCTION NATURAL SOURCE MAGNETOTELLURICS The Scope function allows the operator to see a real time graphical representation of the input signals to individual channels. When the cursor is in the Channel Table and in the row of an On channel, pressing the key will bring up a Scope display of the input signal to that channel. Moving the cursor to the row of another On channel will cause the Scope to display that input signal. Moving out of the Channel Table or to the row of an Off channel, will not affect the Scope. Pressing again, pressing Escape, or starting data acquisition will cause the Scope display to go away. <1303h_24AMT_Scope> The Scope display can be used to evaluate the input signal to a channel, as well as to evaluate the gain, attenuator and SP setting. The Scope's response time is faster than the analog panel displays, and will provide a better evaluation of the magnitude of higher frequency signals. While on the SETUP Screen, the operator can manually adjust the gain, attenuator and SP values, and evaluate their effect on the signal. If the trace of the signal reaches the top or bottom frame of the Scope, it will be saturating the A-D converter, and affecting measurements and interpretation of actual earth response. GDP Section 13, Page 19 October 2014

20 GDP INSTRUCTION MANUAL 13.4 BOARD CALIBRATION SUBMENU The calibration data for the AMT program are different than those for other GDP programs. The standard board calibrate buffer is saved in the GDP as C:\24BRDAMT.CAL. Board calibration data can be obtained and viewed in the Calibration submenu of the AMT program. AMT calibration data contains the magnitude and phase values for the 1 st, 6 th and 8 th harmonics. Calibration values for all the other programs contain the 1 st, 3 rd, 5 th, 7 th and 9 th harmonics. From the Main Menu press for the Calibration submenu. Only the channels that are On in the Channel Table are included for calibration and viewing in this submenu. Below is a sample of the calibration submenu display. <1303i_24AMT_CalAutoCal> The Channel Table for the calibration submenu contains the following fields: Board Gain Display the serial number of the analog board. They are in channel order, but because this display only includes channels that were On when the submenu was activated, the channel number cannot be assumed unless all channels are on. Calibration values are associated with board serial numbers, as opposed to channels, allowing operators place cards in different slots (channels) within the GDP case, without requiring recalibration. This also allows the GDP to detect if new cards have been added, which would require calibration. These settings can be made by the operator in order to obtain calibration sets at different gain and attenuation values. The gaining and attenuation circuitry on the analog boards can have a minor effect on the overall measurement of the incoming signal. If a high degree of accuracy is required, calibrations can be performed at specific gain settings. Calibration sets for different gain settings are all maintained within the same calibration file. Whenever readings are decalibrated, and a calibration for a specific gain setting is not available, the program uses the calibration values for the 00-0 gain. The AUTOCAL METHOD described below will not automatically cycle through all the possible gain setting October 2014 Section 13, Page 20 GDP-32 24

21 NATURAL SOURCE MAGNETOTELLURICS variations. The operator must perform an AUTOCAL calibration for each variation of gain setting. Thus, a calibration value for a gain of 11-0, cannot be obtained by performing calibrations for a 10-0 setting and a second calibration for a 01-0 setting. Board Cal Display the magnitude and phase values for the board calibration value just written to, or recalled from, the calibration file. The column label for the values displayed during either an AUTO_CK or 1SHOT_CK is changed to Cal File for clarity and comparison to the values obtained and displayed in the Check columns described below. System Cal Display the magnitude and phase of the raw values just obtained during a calibration. If no calibration was just performed, these display default values. These values are not recorded or maintained in memory. The system calibrate values represent the response of the system to the calibration signal input to the cards. Because the calibration signal is an ideal square wave, the FFT values of an ideal square wave are factored out of the readings in order to obtain a general board response, the Board Cal. The Board Cal values are those which are actually recorded in the cal file and used to decalibrate readings during data acquisition. Check Display board response values obtained during either the AUTO_CK or 1SHOT_CK procedures as described below. These provide the operator a visual confirmation of calibration and board quality made during the check procedures. These values are not maintained in a file or memory, and will display default values if a check reading has not just been performed. An indication of data quality is how closely these values match to those in the Cal File columns. The calibration and viewing parameters are set in the following fields: FREQ Hrm F CYCL S RATE The calibration frequency setting, from to 1024 Hz. The harmonic of the calibration frequency. The settings are F, 6 and 8. Next to this is the value for the harmonic. The setting for the number of cycles to acquire when measuring the calibration readings. The A-D sampling rate for the calibration set. NOTCH The Notch filter setting for the calibration set. This setting must be made manually and is not automatically changed during the AUTOCAL METHOD of calibration. HI PASS METHOD The High Pass filter setting for the calibration set. The operation method for the calibration. The selected calibration METHOD will be performed when the operator presses. The selections are: AUTOCAL Perform calibration starting at the selected FREQ, and automatically sequencing up to the highest frequency of This will also sequence through each of the harmonics (1st, 6th, and 8 th ), sample rates, and high pass filter settings for a full calibration set. Calibration set results are written to the calibration file. This automatic calibration does not cycle through the possible Enter GDP Section 13, Page 21 October 2014

22 GDP INSTRUCTION MANUAL NOTCH or gain values. Calibration sets for specific NOTCH and gain settings can be included in the calibration file, but calibrations must be made for each selection combination. Each set will contain the full range of harmonics, sample rate and filter settings. AUTO_CK Perform calibration in exactly the same manner as the AUTOCAL method described above, however rather than writing the results to the calibration file, it compares the resulting values to those already in the file. The automatic sequencing through the various frequencies progresses automatically up through the highest frequency, displaying the difference for each setting. If the difference between the resulting value and the value in the cache exceeds the delta phase percent limit set in the dθ% LIM field described below, the program will issue an audible alarm and pause for an operator response. The operator may press Escape to cancel the check, or any other key to continue. 1SHOTCAL Perform calibration for one FREQ setting. It will cycle through the harmonics, sample rates, and high pass filter settings for that frequency. The results are written to the calibration file. 1SHOT_CK Perform a calibration in exactly the same manner as the 1SHOTCAL method described above, however rather than writing the results to the calibration file, it compares the resulting values to those already in the file. If the difference between the resulting value and the value in the cache exceeds the delta phase percent limit set in the dθ% LIM field described below, the program will issue an audible alarm. SYS_CK This system check selection will cause a calibration signal to be enabled during data acquisition. The MODE selection, described below, will control how the signal is routed. The CAL V setting, described below, will set the reference voltage. Pressing Enter while this method is set will have no effect. To enable this method, the operator must press Escape to return to the Enter main menu, and then perform the system check readings by pressing. If the MODE is set to INTERNAL, the signal will only be routed to those channels that were On when the Calibration submenu was activated. For the EXTERNAL MODE, the operator must route the signals externally. No automatic checks are performed when the readings are made. The Main Menu will display a message below the date and time, indicating that the system check is enabled, as in the screen display below. October 2014 Section 13, Page 22 GDP-32 24

23 NATURAL SOURCE MAGNETOTELLURICS <1303j_24AMT_SysChk> MODE The selections are INTERNAL and EXTERNAL. INTERNAL will connect the calibration reference signal through internal circuits of the GDP, directly to the channel inputs for calibration. EXTERNAL will connect the calibration signal to the CAL+ and the CAL- terminal on the outside of the GDP case. The operator must then route the signal from these outputs through the desired channel components, and to the channel input terminals for calibration. Note: The calibration file does not maintain separate data sets for INTERNAL and EXTERNAL calibrations. The operator must decide which type of calibration is required and perform a full calibration for the desired MODE. CAL V Set the calibration signal voltage. Changes can only be made by the operator when the METHOD selection is SYS_CK for performing a system check. During the calibration and cal check METHODS, the value of the cal voltage is automatically adjusted when gain or attenuate settings are adjusted. The voltage is adjusted so that the signal to the A-D converter is 1.0 volts after being modified by the gain and attenuate circuits. All calibration values are based on a 1.0 volt signal being read by the A-D converters. dθ% LIM Set a stop limit while performing an AUTO_CK or 1SHOT_CK check of the calibration data in the calibration file and calibration readings made during the check. The delta phase percentage is calculated as the difference between the calibration phase just measured and the phase recorded in the file, divided by the phase recorded in the file, represented as a percent. dθ% = 100 (PhzMeasure PhzCal) PhzCal Note: The limit is normally set to 1% for running the AUTO_CK procedure, and can detect basic system or card errors. Generally the measured phase difference is well below this. Higher frequencies, which have calibrates with a greater number of cycles, can be expected to have GDP Section 13, Page 23 October 2014

24 GDP INSTRUCTION MANUAL phase differences of less than 0.05%. Lower frequencies, particularly the lowest frequency of a sample rate 0.016Hz, 0.063Hz, and 2Hz, can have higher differences around 0.2 %. When the NOTCH filter is IN, the differences near the harmonics of the NOTCH, can have significantly higher values, and may exceed the 1% limit. This does not indicate a hardware problem. There are two function keys that are active while in the Calibrate submenu, these are, labeled <PREV, and, labeled NEXT>. These give the operator the ability to scroll through all the calibration values within the calibration sets, incrementing and decrementing the frequency (FREQ), for a given harmonic, sample rate, and high pass filter selection. The operator can set the HRM, S RATE, and HI PASS, selection of interest, then by pressing or, the calibration values for all the frequencies with the selected settings will be displayed for the installed cards. October 2014 Section 13, Page 24 GDP-32 24

25 NATURAL SOURCE MAGNETOTELLURICS 13.5 GATHERING DATA PROGRAM START UP During start up, the AMT program will perform various system checks. It will search and identify all cards installed in the GDP. It will open up and index all calibration files. The input parameters from the last AMT session will be loaded into the display. When complete, the STATUS line will indicate Ready, and the message Press CONTINUE to take data will be displayed. If the GDP detects that the version of the board calibration file is incompatible with the version of the AMT program, the old calibrate file will be renamed to BOARDAMX.CAL and a new, empty, 24BRDAMT.CAL will be created. An audible warning will be made and the GDP will display a message to the operator that a new calibration must be performed. The GDP will wait for a key press in response before the startup process continues. If no calibrate files are found, the GDP will make an audible warning, inform the operator of the problem, and wait for a key press in response before the startup process continues. The required board calibration file is 24BRDAMT.CAL. The required antenna calibration file is XAMTANT.CAL, or the older AMTANT.CAL. If either of the files is not found, a new empty file will be created. The GDP will not inform the operator if the files do exist, but are empty. The No Cal Found symbol, '!', in the Channel Table will be the only indicator of missing calibrates. The GDP must perform the calibrates for the boards. The antenna calibration file must be provided by Zonge. DATA ACQUISITION When the STATUS is Ready, the operator can proceed to set the various parameters required for the data acquisition. After filling in the parameters for Job Information, Line Setup, Acquisition Configuration and setting up the Channel Table, the operator should confirm that calibrates are found, and that input signals are good. Use of the SCOPE can detect channel saturation, poor connections, and excessive power-line noise. Pressing sequence. Enter will start the data acquisition Enter Immediately after pressing, the GDP will set gains. When the selected gain method has completed, the GDP acquisition will synchronize with the timing card and indicate that it is taking data. At the high band, no other indication of collecting data will be observed, as the GDP is using its full resources to read the A-D cards and store the raw data into memory. For mid and lower bands, a progress bar will be displayed showing the time left for taking data. When data have been acquired, the results will be calculated and displayed. When acquiring a single stack of data at high or medium bands, the GDP will display the message Press ESCAPE to discard, CONTINUE to save Hit Key, make an audible signal, and then pause for the operator's response. The operator must then respond. The data will be written to the flash card or discarded, based on their review of the results. After responding, the GDP will write the data, make an audible signal, and be Ready for further acquisitions. GDP Section 13, Page 25 October 2014

26 GDP INSTRUCTION MANUAL When acquiring data at a low band, the data is continuously written to the flash card while reading the data, so the operator will not be prompted to save or discard data. The GDP will make an audible signal and be ready immediately. STOP ACQUISITION If the operator wishes to cancel the acquisition of data at any time before normal completion of a Escape stack, or to terminate acquisition of a large number of stacks, pressing the key will stop the process. Depending on sample rate and the various stages of data acquisition, the GDP may stop immediately, or it may take a few moments to finish before it is ready. ACQUISITION ERRORS If there are any processing errors due to hardware or other acquisition issues, the GDP will make an audible signal, display a message to the operator, and wait for a response before going to the Ready state. If the AMT program is running a Time Schedule acquisition, the messages and audible signals will be issued, but the program will not pause for operator response, thus allowing the Schedule to continue. A history of error and warning messages is displayed below the Main Menu, in an area not normally visible on the smaller LCD screen. These messages can be useful to monitor the progress of a Time Schedule and to review any messages associated with an error VIEWING DATA After stacks of data have been acquired and saved to the cache file, the data can be reviewed by pressing. This will start the Cache Viewer. The initial display will display zero values in the table. The operator can make selections for BLOCK (stack), PLOT type, CH (channel), Enter and CYCLE. The operator must press to scan the cache and present the data. The display is not immediately updated upon making any of the selections in order not to scan the cache with each key press, thus slowing down response. The PLOT types for AMT are Rho_f, a Rho vs frequency plot; and TimeSr, a Voltage vs Time plot. When viewing the time series, each CYCLE can be selected. The cycle number selector wraps from 1 to the highest cycle when SELECT DN End is pressed. The operator can toggle between a GRAPH or TABLE view of the data by pressing. When in the TABLE view, the and keys scroll up or down the table, increasing or decreasing the cycle time for a TimeSr PLOT or frequency for a Rho_f PLOT. Pressing view. will shift the columns to other channels if there are more than 4 channels selected in the October 2014 Section 13, Page 26 GDP-32 24

27 NATURAL SOURCE MAGNETOTELLURICS When viewing the GRAPH of a TimeSr PLOT, the and keys increase or decrease the cycle count being displayed. The key will have no function. Below are some examples of the Rho vs frequency PLOT, with TABLE and GRAPH views of the data. <1306a_24AMT_CacView_Rho_Table_1> <1306b_24AMT_CacView_Rho_Graph_1> GDP Section 13, Page 27 October 2014

28 GDP INSTRUCTION MANUAL Below are some examples of the Time Series PLOT, with TABLE and GRAPH views of two cycles of the data. <1306c_24AMT_CacView_Time_Table_1> <1306d_24AMT_CacView_Time_Table_2> October 2014 Section 13, Page 28 GDP-32 24

29 NATURAL SOURCE MAGNETOTELLURICS <1306e_24AMT_CacView_Time_Graph_1> <1306f_24AMT_CacView_Time_Graph_2> GDP Section 13, Page 29 October 2014

30 GDP INSTRUCTION MANUAL 13.7 TIME SCHEDULE For AMT, the automatic time schedule submenu can be entered by pressing from the Main Menu. An example if the submenu is shown below. Note that End Time columns may be PREV FIELD SELECT UP Pg Up Home off-screen and require using to display, and to return. <1307a_24AMT_TimeSchedule> When running Time Schedules, the operation of the GDP is different than manual operation. Before each line, the GDP will wait for the START time. Then it will perform the requested gaining. It will then synchronize to the timing card and data acquisition will begin. Because of the variable ACQUIRE times for schedules, data will not be processed as it would be for normal processing. After acquisition, the data is written to the flash card. The cache file is then archived with a unique name which is encoded to identify the cache. Every line of the schedule is written to a unique cache file. After the cache has been archived, the GDP waits to start the next line of the schedule. Processing of the raw time series data contained in the archived cache will be done by post-processing programs. Each schedule line acquires one stack of data. Long, continuous acquisition periods are defined rather than multiple fragmented stacks of data. Schedules are written to the file 24AMTSCH.INI. This file can be copied to a PC and then copied to other GDPs in order for them to run the same schedule. It is possible to review this ASCII format schedule file, but it is advised to not edit the INI file. Doing so may alter the run times, which the GDP has calculated to ensure that running one schedule line will not cause the start of subsequent schedule lines to be missed. Because a specific copy of the Time Schedule file, always named 24AMTSCH.INI, may be running synchronously on several GDP receivers at any time, it is important to not accidentally alter a schedule, possibly altering synchronization between receivers. Therefore when entering October 2014 Section 13, Page 30 GDP-32 24

31 NATURAL SOURCE MAGNETOTELLURICS the time schedule submenu, the cursor is automatically moved to the MODE field, and it's value set to View. The cursor's movement will be restricted until the operator selects the MODE, EDIT, allowing the cursor to move to any of the editable fields. The number of individual time schedule entries is limited to 34. They are identified as numbers 1 through 9 and letters A through Y. This is to facilitate automatic archiving of the cache for each schedule line, with a unique file name, as described below. All entries are executed in the order shown in the menu. Only 10 lines of scheduled events will be shown in the screen. Once the user enters more than 10 lines, the GDP will display **MORE LINES** xxx above and to the right of the table, as shown in the example below. <1307b_24AMT_TimeSchedule_2> TIME SCHEDULE HEADER The fields displayed above the Schedule Table control several aspects of running a schedule, as well as providing some important information. The between the Header and Table. The Header fields are: key moves the cursor quickly ELAPSED DAY This sets the number of elapsed schedule days for the GDP time. This time determines which line of the schedule starts to run next. If a schedule is written such that the total time of a schedule would extend over several days, and the operator needs to have the GDP start on the second day, then the ELAPSED DAY should be set to 1. In the example above, the operator wishes the schedule to start on line 7, not on line 1, therefore the ELAPSED DAY is set to 1. Note: When ELAPSED DAY is set, the elapsed day displayed in the current time at the top of the screen also changes. GDP OFF AT END This field not only determines if the AMT program should exit when the schedule completes, it also determines if the schedule should repeat by rolling over to line 1. GDP Section 13, Page 31 October 2014

32 GDP INSTRUCTION MANUAL When set to YES, the schedule only runs the lines once, at the times specified, and when complete, the AMT program ends, shuts the cards OFF, and exits to the Zonge Logo screen. When set to NO, the AMT program does not exit. Rather it repeats the schedule as if its line 1 starting time was adjusted to coincide with the end time of the last line. This means that the schedule can run continuously, and that the cache archive names are adjusted accordingly. This makes it appear as if the schedule is continuously edited and re-run immediately after it finished. It also allows several GDPs, such as a reference GDP and a roving GDP, to collect data in a synchronous fashion. Any GDP running the same schedule, can start at any time, and acquire data synchronously, with any other GDP which is also running the same schedule. See below for more information. CHANS This sets the maximum number of ON channels expected while actually running the schedule. The number of channels affects the time required to set gains and to write data, determining the total duration of each line, and when the next line starts. If several GDPs are expected to run synchronously, then the numbers of channels must be set to the maximum number of ON channels of all the receivers. Note: If the actual number of channels that are currently ON, exceeds the CHANS setting, two exclamation marks,!!, will be displayed after this value. If the schedule is run with these settings and actual ON channels, it is highly likely that each line will run longer than expected, thus missing the starting time of the next scheduled line. SPACE This field is informative and indicates the space needed for the cache file on the flash card. Note: If the estimated space exceeds the actual space currently available on the flash card, two exclamation marks,!!, will be displayed after this value. CACHE NAME This field is informative and indicates the name that will be given to the archived cache of the first schedule line. See below for more information about cache file naming. SCHEDULE START of the schedule. This field is informative and indicates the START of the first line SCHEDULE END This field is informative and indicates the expected time that the last line of the schedule will be completed. TIME SCHEDULE TABLE The Schedule Table displays the lines of the schedule and allows editing of schedule lines. moves the cursor quickly between the Header and Table. When the cursor is in the Table, the function keys are enabled to alter the number of lines in the schedule. removes all but the first line of the schedule. adds a line to the table by copying the line the cursor is currently on, and inserting it into the schedule as the next line, moving subsequent lines down one. deletes the line the cursor is on, moving subsequent lines up one. All schedule START times are recalculated after lines are added or deleted. October 2014 Section 13, Page 32 GDP-32 24

33 The Table columns are: NATURAL SOURCE MAGNETOTELLURICS START Sets the time when the line of the schedule will start. The START time fields are D HH:MM, representing the elapsed day, hour, and minute that the line will automatically start. The operator sets the SCHEDULE START time by setting the START of the first line of the schedule. START times for subsequent lines are automatically set equal to the end time of the previous line of the schedule. The START of any line can also be set manually. When setting the START time manually an L, indicating the time has been locked, will appear in the next column. Setting the time manually can give the operator additional time between schedule lines for various field requirements. The START time cannot be set to a time earlier than the End Time of the previous line. Common uses of this feature include: 1) operators who are collecting with both AMT and MT antennas, allowing the operator time to switch coils and change antenna serial numbers while keeping the same schedule and 2) operators wanting to collect very long time-series records who may wish to switch batteries during acquisition. Note: To edit coil numbers or any other field before the start of a schedule line, the schedule must be stopped, the fields edited, and then the schedule restarted. Lock BAND This field can be set manually or automatically, to lock, or unlock the START time. When locked, editing parameters of earlier schedule lines will not affect the START of this line, unless the START time would be before the End Time of the previous line. In this case, the lock is released and the START time reset to equal the previous End Time. When locked, the character L will be displayed. When unlocked, no character will be displayed. Selects the BAND for the acquisition of data for this line. This also sets the minimum ACQUIRE time allowed for the line, to acquire data for that band. The BAND selections are identical to the manual selections available on the Main Menu. GAIN TYPE Selects the type of gaining that is to be performed. The selections correspond to the selections available on the Main Menu, and operate in much the same manner. ALL(ways), and ONCE, will perform full autogaining. DONE and MAN(ual) will not affect the gain or SP settings, at the time the schedule is running, SPONLY will only adjust the SP, leaving the gains unchanged. MEMORY will recall the gain and SP values previously saved in memory for the selected BAND. MEM_SP will recall the gain values previously saved for the selected BAND, but will perform SP bucking prior to data acquisition. TIMESTAMP This informational field displays the time the actual data acquisition is expected to begin. Excessive gaining time or time overruns of previous lines of the schedule can affect this time. ACQUIRE Specify the length of time the data will be acquired, at the sample rate for the BAND specified. The time fields are D HH:MM:SS, representing the days, hours, minutes and seconds for acquisition. The minimum will be the acquisition, to the nearest second, that is required for manual acquisition of that BAND. Setting this field causes the remaining table fields for that schedule line, and all subsequent lines, to be adjusted. MEM mb This information field indicates the space required in megabytes, both in memory and on the flash card, to collect the data based on BAND, ACQUIRE time, and the GDP Section 13, Page 33 October 2014

34 GDP INSTRUCTION MANUAL CHANS (number of on channels). If the space exceeds the memory of the computer, an exclamation mark,!, will be displayed after this field. If this space, accumulated for all the schedule lines, exceeds the available flash card space, the SPACE field in the header will indicate!!. WRITE MMM This represents the time in minutes, allowed to write data to the disk before the next schedule line is set to begin. The minimum amount of time is estimated whenever the CHANS, BAND or ACQUIRE fields are modified. This value can be modified upward to accommodate different flash cards. Large capacity flash cards can be slow to write to. Writing time also appears to increase as the flash card fills to capacity. End Time This informational field is displayed in an area not usually visible by the LCD Pg Up screen, unless the screen display is shifted by pressing. It indicates when each line of the schedule is estimated to be finished. It also represents the minimum start time for the next line of the schedule. The End Time of the last schedule line is also the START of a repeating schedule. ARCHIVE FILE NAMING Data for every line of a schedule is archived in its own uniquely named cache file, within the limits of the DOS 8.3 file name structure. The encoding allows the cache files of multiple GDPs, and multiple runs or schedules, to be gathered into a single folder on a PC, with little concern about overwriting files and loss of data. The GDP ID, the schedule start time, and schedule line, are encoded into the name. The actual date and time of a file can be quickly identified by looking at the DOS or Windows timestamp. Understanding this encoding can help to identify which GDP and which schedule line generated a particular cache file. The encoding of the Time Schedule Cache name is limited by the DOS 8.3 naming constraint. The format is: SSSMDHML.CAC SSS represents the serial number of the GDP, decimal number. M Represents the month the schedule was started, base 36 D The day of the month the schedule was started, base 36 Note: this starting date represents the actual day the operator pressed "GO", without the addition of the elapsed days the given line started. H Represents the hour the acquisition started, base 36, 24-hr clock. M Because there are 60 minutes in an hour, this represents the minutes / 2, in a base 36 number. Thus an 'A' would represent 20 or 21 minutes after the hour. L This represents the line number of the schedule, as displayed on the schedule screen, base 36 For example: 328BEH01.CAC decodes as: 328 Front panel GDP SN 328 B 11 (November) E 14 day of month H 17 hours or 5 PM 0 0 minutes 1 Line 1 PREV FIELD October 2014 Section 13, Page 34 GDP-32 24

35 NATURAL SOURCE MAGNETOTELLURICS Base 36 code, values 0 through 35. Code M,D,H,& Line Minutes A B C D E F G H <1307c_24AMT_ScheduleArchiveNaming.txt> Code M,D,H,& Line Minutes I J K L M N O P Q R S T U 30 V 31 W 32 X 33 Y 34 Z 35 STARTING A NON-REPEATING TIME SCHEDULE A non-repeating Time Schedule is configured when the GDP OFF AT END field is set to YES. When it runs, the START times are fixed, and when the schedule ends, the AMT program shuts down the cards, and exits to the Zonge logo screen. Below is an example of a schedule which is configured to be non-repeating. <1307d_24AMT_TimeSchedule_3> GDP Section 13, Page 35 October 2014

36 GDP INSTRUCTION MANUAL Normally, the operator would start the schedule at some time prior to the starting time of the first line of the schedule, which in this example is 16:00, 4 PM. To start the schedule, press from the Main Menu. Assuming no editing of the schedule needs to be done, ensure that the GDP OFF AT END is set to YES. This field can be edited while in MODE: View. From the Time Schedule submenu, the operator can press without initializing running of the schedule. to return to the Main Menu To run the schedule, from the Time Schedule submenu, in either Edit or View MODE, press Enter. The program will exit the submenu, and return to the Main Menu and initialize the schedule. The GDP STATUS should be Ready. The help line will display a message similar to: TS(1) DEFINED: CONT starts TS acq. F6 reviews TS This indicates that a valid time schedule has been defined, and that the operator should press Escape Enter to start data acquisition, or press to return to the Time Schedule submenu. The operator can also press Escape to abandon running the schedule. At this point, prior to pressing Enter, the operator can make some minor channel adjustments. Enter Pressing will cause the schedule to run. It will wait for the next upcoming line to START. For example, if the current GDP time is 0 12:56:49 (0 elapsed days, the GDP would start a three hour count down timer, roughly similar to the example below. <1307e_24AMT_TimeScheduleRun_1> The schedule will then begin running line 1 at 16:00:00. October 2014 Section 13, Page 36 GDP-32 24

37 NATURAL SOURCE MAGNETOTELLURICS If, for example, the operator missed the start time of the first line, the GDP would automatically wait to start the second line. If the GDP would start any of the lines after their specified START time, data acquisition of that line of the schedule would probably extend past the START of the next line, possibly missing all further START times. Below is an example of the schedule having started after the line 1 START time. <1307f_24AMT_TimeScheduleRun_2> For this example, the operator needs to start running the schedule on line 4. This line would normally start on the second day of a schedule, but perhaps the GDP was recently shut down and its elapsed day counter reset to 0. In this case the operator would press to start the submenu, then move the cursor to the ELAPSED DAY field, and set its value to 1. This will cause the GDP time display to be set to 1, forcing the current time to indicate that it has elapsed one day since the start of the schedule. Pressing Enter will cause a return to the Main Menu, and to Enter initialize the run. Pressing again will start the run. Now, even though it is near 1 PM, which is before the START of line 1, the GDP will now be waiting to start line 4, as in the display below. GDP Section 13, Page 37 October 2014

38 GDP INSTRUCTION MANUAL <1307g_24AMT_TimeScheduleRun_3> In all of the above cases, the GDP would normally continue running until line 6, finishes on the second day of the schedule. At this time the AMT program would exit. To cancel a schedule at any time, the operator should press currently in memory will be written to the cache. Escape. At this point, all the data STARTING A REPEATING TIME SCHEDULE A repeating Time Schedule is configured when the GDP OFF AT END field is set to NO. When it runs, the START times of the schedule file itself are fixed. When the schedule run starts however, the GDP will calculate when to start, assuming that the schedule continuously repeats, rather than shutting down the end of a single run. Note: It is advised that a schedule which is intended to run as a repeating schedule, not have a total duration of more than one day. Rather it should probably be able to repeat several times in a single day. Below is an example of a schedule set to repeat. October 2014 Section 13, Page 38 GDP-32 24

39 NATURAL SOURCE MAGNETOTELLURICS <1307h_24AMT_TimeSchedule_4> For a non-repeating, schedule, the operator would make sure that the GDP was started just before the starting time of the schedule. For a repeating schedule, the operator can start at any time that is convenient for field operations. For example, the schedule above, is set to start at 16:00, however, the operator initiates it at 15:23:31. The repeating schedule is waiting to start line 1, at 15:24:00, on the first elapsed day of the schedule, as shown below. <1307i_24AMT_TimeScheduleRun_4> A repeating schedule calculates actual start times to be repeats of the basic schedule, during a 24- hour period starting from the start time of line 1 of the schedule, in this case 16:00. This schedule starts at 16:00, then repeats continuously through midnight, and into the next day, ending just before 16:00. Before 16:00, of the second day, this set of repeating cycles of the schedule ends, and a new repeating set of cycles starts again at exactly 16:00. GDP Section 13, Page 39 October 2014

40 GDP INSTRUCTION MANUAL A second GDP could run this exact same schedule, initiating its run at 17:14:30, for example, and wait for a starting time of 17:15:00. Rather than starting on line 1, this start time is closest to the start of line 5 of a repeat of the basic schedule. <1307j_24AMT_TimeScheduleRun_5> The table below, based on the examples above, shows how two GDPs could run this schedule. The GDP with a front panel serial# 328, is set up to take unattended reference recordings, starting at 15:23:31. A second GDP with a front panel serial# 275, acts as a roving recorder, first initiating a run at 15:40:00, first collecting data for line 4 at 15:41. The rover then proceeds to acquire data for each of the lines of the schedule. It then relocates and initiates another run at 17:40:30, again staying long enough to acquire data for each line of the schedule. October 2014 Section 13, Page 40 GDP-32 24

41 NATURAL SOURCE MAGNETOTELLURICS Reference Roving Time Line Cache File Cache File 1 15: FC1.CAC 1 15: FC2.CAC 1 15: FC3.CAC 1 15: FC4.CAC FC4.CAC 1 15: FC5.CAC FC5.CAC 1 15: FC6.CAC FC6.CAC 1 15: FP1.CAC FP1.CAC 0 16: G01.CAC G01.CAC 0 16: G02.CAC G02.CAC 0 16: G03.CAC G03.CAC 0 16: G04.CAC 0 16: G05.CAC 0 16: G06.CAC 0 16: GD1.CAC 0 16: GD2.CAC 0 16: GD3.CAC 0 16: GD4.CAC 0 16: GD5.CAC 0 16: GD6.CAC 0 16: GR1.CAC 0 17: GR2.CAC 0 17: GR3.CAC 0 17: GR4.CAC 0 17: GR5.CAC GR5.CAC 0 17: GR6.CAC GR6.CAC 0 17: HA1.CAC HA1.CAC 0 17: HA2.CAC HA2.CAC 0 17: HA3.CAC HA3.CAC 0 17: HA4.CAC HA4.CAC 0 17: HA5.CAC 0 17: HA6.CAC <1307k_24AMT_SchdRunTbl_1.txt> Note: The repeating schedule does not exactly fit a 24-hour period, so the last repeat of the schedule starting at 15:51 only records data for line 1 of the schedule before starting a new series of repeats at the basic schedule start time of 16:00. GDP Section 13, Page 41 October 2014

42 GDP INSTRUCTION MANUAL 13.8 CACHE FILE The AMT data cache is much like that of other GDP programs. It contains binary data blocks with ASCII metadata descriptors. See Chapter 7, DATA, FILE AND PROGRAM TRANSFER for more detailed information. Note: Though the cache file can be viewed and partially read with simple text editing programs, doing so can irrevocably destroy the navigation pointers within the file, or the data itself, resulting in total loss of data. The AMT cache contains the following records for every stack recorded: Header Cal The ASCII header record contains survey data including: job descriptors, locations, channel component types, GPS timing, and other data required for post processing. This is the only portion of the cache which can be edited with the CACEDIT program. This record contains the calibration factors for all the channels, in ASCII format. Time Series A binary data record containing all the raw A-D data readings for all the channels. Calc Data A binary data record containing real and Imaginary pairs from cascade decimation. Summary Quality A binary data record containing the Rho vs Frequency data. An ASCII record of the GDP's internal temperature, humidity and battery voltage at the end of acquisition. Note: Long time series data collected through use of the Time Schedule features does not contain Calc Data or Summary records. The following is an example of the Header metadata for an AMT cache. HEADER.TYPE,Survey DATA.VERSION,1.01 DATA.BLOCK,1 DATA.SKIP,0 DATA.STACKCTDN,3 GDP.DATE,07/02/2014 GDP.TIME,06:03: SURVEY.TYPE,AMT SURVEY.ACQMETHOD,timeseries LINE.NAME,AJO ROAD LINE.NUMBER, LINE.DIRECTION,N LINE.SPREAD,1A JOB.NAME,Quality Assurance JOB.FOR,Customer JOB.BY,Engineering JOB.NUMBER, JOB GDP.OPERATOR,Zonge Field Crew GDP.TYPE,GDP32-24 GDP.PROGVER,AMT2.24j GDP.SIGSOURCE,Field GDP.CALVOLTS, GDP.SYNC,Manual October 2014 Section 13, Page 42 GDP-32 24

43 NATURAL SOURCE MAGNETOTELLURICS GDP.GAINMETHOD,Manual GDP.GAINMODE, Noisy GDP.FPSN,328 GDP.SN,3252 GDP.TCARDSN,336 GDP.NUMCARD,8 GDP.ADCARDSN,C83C,C87E,C8DA,C880,C83D,C8FF,C875,E8D2 GDP.ADCARDSND,60,126,218,128,61,255,117,210 GDP.CARDTYPE,ANA24CARD,ANA24CARD,ANA24CARD,ANA24CARD,ANA24CARD,ANA24CAR D,ANA24CARD,ANA24CARD GDP.ADCARDVER,09,8B,0B,89,09,0B,0B,09 GDP.ADCARDFEAT,05,07,07,07,05,07,07,07 GDP.BAT, GDP.TEMP, GDP.HUMID, GPS.WEEK,1799 GPS.SEC, GPS.LOCALTIMEOFFSET,-07:00 GPS.LEAPSECOND,16 GPS.LAT, GPS.LON, GPS.ALT, GPS.PDOP, GPS.NUMSAT,0 GPS.TCDAC, GPS.STATUS,0 GPS.SN,0 GPS.FW,0 GPS.SW,0 TS.ADFREQ,1024 TS.NCYCLE,256 TS.NWAVEFORM,32 TS.DECFAC,1 TS.NPNT,8192 RX.STN,100 RX.AZIMUTH,360 RX.ASPACE,25 UNIT.LENGTH,m CH.NUMON,3 CH.ADCARDSN,C83C,C87E,C8DA CH.GDPSLOT,1,2,3 CH.FACTOR, e-007, e-007, e-007 CH.GAINFACTOR,1,1,1 CH.GAIN,00-0,00-0,00-0 CH.NUMBER,1,2,2156 CH.CRES,0,0,0,0,0,0,0,0 CH.CMP,ex,ex,hy CH.SP,0,0,0 CH.LENGTH,25,25,25 CH.EXTGAIN,1,1,1 CH.NOTCH,NONE,NONE,NONE CH.HIGHPASS,NONE,NONE,NONE CH.LOWPASS,283,283,283 <1308a_24AMT_CacHeader.txt> GDP Section 13, Page 43 October 2014

44 GDP INSTRUCTION MANUAL 13.9 A NOTE ON VARIABLE A-SPACING When using variable A-Spacings, the key to getting the correct A-Spacing entered and used, is to remember that: 1) the A-Spacing that is used is ALWAYS the value in the Channel Table, and 2) the A-SPACE field outside of the Channel Table will RESET the values in the Channel Table. For example, if the operator sets the A-SPACE field value in the header to 50 m, then all of the numbers in the Variable Asp channel table are set to 50 m. If the operator then goes into the Channel Table column and changes one of the values to, say, 25 m, then the A-Spacing value shown in the Channel Table will be used for GDP calculations and in post-processing A NOTE ON PHASE For scalar operations the phase difference between Ex and Hy should be between and milliradians. In the presence of 2- and 3-D features, or when measuring fields in an anisotropic environment, the phase values can approach radians ( mr). For vector operations, keep the phase differences negative for ExHy and positive for EyHx by Ex positive east, Hy positive north, and Ey positive north, Hx positive east. This method uses the Z- positive UP right-hand rule. For tensor measurements orient Ex positive east, Hy positive north and then Ey positive is oriented north and Hx positive east. For this configuration the phase difference will be negative for Ex Hy and positive for Hx Ey, which is the standard tensor setup for Z positive UP. For a Z positive DOWN tensor measurement orient Ex positive north, Hy positive east and then Ey positive is oriented east and Hx positive north. If the phase differences are negative when they should be positive (and vice versa), this means that you have either the E-field or H-field orientations wrong. To correct this, just switch one of the connections at the receiver, or rotate the H-field sensor by 180 degrees A NOTE ON SCALING The following convention is used for all measured and calculated parameters: Voltage (magnitudes), displayed in volts. Phase, displayed in milliradians. Apparent resistivity, displayed in ohm-meters. Dipole spacings, displayed in meters or feet as selected next to the A-SPACE field. Coil calibrate magnitudes, entered and displayed in millivolts per gamma. SP, displayed in millivolts CC, displayed in units from 0.00 to 1.00 E-field (magnitudes), displayed in volts. H-field(magnitudes), displayed in kilo-gammas If scaling is necessary, the following labels are appended to the end of the number string: M - Mega units K - Kilo units m - milli units u - micro units October 2014 Section 13, Page 44 GDP-32 24

45 NATURAL SOURCE MAGNETOTELLURICS CASCADE DECIMATION OVERVIEW For the upper three frequency bands (very high, high and medium bands), data are gathered in time series records of 4141 points each ( extra points used in the decimation filter). The data are then processed in 32 point records, for all of the data points for that level. Decimation Total Points Data points Level Bursts per burst processed The low frequency band acquires data on a continuous basis, and filters, decimates and transforms the data real time. The length of the time series record depends upon the level of decimation chosen. If the full 13 levels are selected, the number of points processed range from 256 at Hz to 2.12 million at 8 Hz. Decimation levels and base frequencies for the five frequency bands are: Low Frequency Band Sample Rate = 32 Hz Decimation Base Frequency Frequencies Levels Frequency Interval Obtained 2.5 Hz Hz 1.5, 2, 3, 4, 8 Hz , 1. + above ,.5 + above ,.25 + above , above , above , above , above , above , above , above , above For the Low Band, three levels of decimation are available: Decimation Frequency Levels Interval Hz Hz Hz GDP Section 13, Page 45 October 2014

46 GDP INSTRUCTION MANUAL Medium Frequency Band Sample Rate = 1024 Hz Decimation Base Frequency Frequencies Levels Frequency Interval Obtained Hz Hz 192, 256 Hz 96, , 64 24, 32 12, 16 6, 8 3, 4 High Frequency Band Sample Rate = Hz Decimation Base Frequency Frequencies Levels Frequency Interval Obtained Hz Hz 6144, 8192 Hz 3072, , , , , 256 A 5-point digital, low-pass filter is used on the time series for each level of decimation. The coefficients for this filter are as follows: a 0 = a 4 = 1.0 a 1 = a 3 = a 2 = (From Wight, D.E. and Bostick, F.X., 1980 Proceedings IEEE International Conference on Acoustic Speech and Signal Processing, April 9-11, 1980, Denver CO. pp October 2014 Section 13, Page 46 GDP-32 24

47 13.13 RESTRICTIONS NATURAL SOURCE MAGNETOTELLURICS The main restriction on setting up the channels and using this program is to make sure the E- field channels always precede the corresponding orthogonal H-field channels. In calculating Cagniard resistivities, the program first looks for an E-field channel, and then matches it up with the first orthogonal H-field channel that it finds when going down the channel list. AMT should always have Hx and Hy channels even if there are only E-field components because the orientation of the source field is unknown. Processing solves linear equations Ex = Zxx*Hx + Zxy*Hy for Zxx and Zxy, and Ey = Zyx*Hx + Zyy*Hy for Zyx and Zyy. Following is an example for connecting and defining the channels for scalar measurements on 7 separate stations: <1313a_24AMT_Restrictions_1> This example is similar to scalar CSAMT, measuring E-fields at 7 different stations, with the H- field antenna placed near the center of the array. This array is normally used for reconnaissance or E-Map applications. In this example, the Stn/Ant and the RX LOC values are actual electrode locations along the line. An alternative method is to use sequential numbers which index into station files which provide the actual values for the post processing programs. The RX LOC value is used to indicate the location of the GDP. These numbers can be any value from 0 to The numbers 2356 and 2156 on the CH 7 and 8 lines, indicate that the calibrates for AMT antennas Serial Number 2356 and 2156 are to be used. These exact numbers must identify the calibrates in the AMT antenna calibrate cache. If antenna calibration records are not found in the antenna cache the AMT program will display a large exclamation point (!) next to the channel number in the channel table. Data acquisition can be completed without the proper coil calibration record loaded into the cache, but the data displayed on the GDP screen will not include the coil calibration and thus will not accurately represent the actual earth response. GDP Section 13, Page 47 October 2014

48 GDP INSTRUCTION MANUAL NOTES ON FIELD CONFIGURATIONS When running multiple channel receiver systems, you must be very careful to avoid common mode problems. Common mode effects are caused by lack of a reference voltage or level (floating ground), or a reference level that exceeds common mode limits of the input amplifiers. Common mode levels for the standard configuration of the GDP are 10 volts. With external isolation amplifiers, this level can be extended to several thousand volts, but in exchange you have to contend with higher noise and a lower overall frequency response. The best configuration that we have found is to install a REFERENCE ELECTRODE (standard copper/copper-sulfate electrode or equivalent), connected to analog ground (COM on the analog side-panel) and the case ground (CASE GND on the side panel), positioned next to the receiver and at least one meter distant from the nearest receiving electrode. Another consideration is protection from static discharge and nearby lightning strokes. This protection is maximized by connecting the case ground to the REFERENCE ELECTRODE as well. Additional protection in lightning-prone areas can be afforded by using a galvanized iron plate (or equivalent) as a REFERENCE ELECTRODE. This plate should be buried close to the receiver in a hole that has been well watered and the soil mixed to make good mud contact with the plate. Typical size for the plate would be 30 by 30 cm. We have found that for most environments, the best noise rejection is obtained by connecting the analog ground (COM) to the case ground (CASE GND) on the analog I/O side panel. October 2014 Section 13, Page 48 GDP-32 24

49 13.16 FIELD CONFIGURATIONS NATURAL SOURCE MAGNETOTELLURICS 1316a_SingleStationMT GDP Section 13, Page 49 October 2014

50 GDP INSTRUCTION MANUAL LOCAL REMOTE REFERENCE MT 1316b_LocalRemoteRefMT October 2014 Section 13, Page 50 GDP-32 24

51 NATURAL SOURCE MAGNETOTELLURICS LOCAL REMOTE REFERENCE MT 1316c_SetupMT_Tensor_2stns GDP Section 13, Page 51 October 2014

52 GDP INSTRUCTION MANUAL 1316d_SetupMT_StnClusters October 2014 Section 13, Page 52 GDP-32 24

53 NATURAL SOURCE MAGNETOTELLURICS METHOD TO FIELD-CHECK MAGNETIC SENSORS It is possible to field check the operation of an antenna by using the GDP calibrator as a signal source as follows: 1. Connect a 1 Kohm resistor between the Black and Red input terminals for channel Take a piece of wire or test lead and make a single turn around the antenna case as shown on the diagram. Connect one end of the wire to the Negative CALIBRATE output and the other end to the Negative (black) input terminal for Channel Connect a test lead from the Red CALIBRATE output to the Red Input for Channel Connect the coil output cable to the Channel 2 inputs as shown on the diagram. 5. Turn on the receiver and enter the CSAMT program. Set Channel 1 to Ex and Channel 2 to Hy with the antenna number set to Set the frequency to the lowest value you want to check - for instance Hz. 7. Turn on the antenna. 8. Enter the calibrate program by pressing the key. Move the cursor down to the METHOD field and select ATO_SY_CK. Then for MODE, select Escape EXTERNAL. Press to finish setting up the external calibrate system, and to begin taking data. 9. Press to archive any existing cache data and clear the current cache. Enter 10. Press to start taking data. The program will automatically acquire data for each frequency, for example Hz through 8192 Hz. 11. Enter the data mode by pressing. GDP Section 13, Page 53 October 2014