11. CONTROLLED-SOURCE AUDIO-FREQUENCY MAGNETOTELLURICS

Transcription

1 11. CONTROLLED-SOURCE AUDIO-FREQUENCY MAGNETOTELLURICS 11.1 INTRODUCTION FIXED FUNCTION KEYS CSAMT 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/CRES...13 SCREEN: MAG/PH...16 SCREEN: RHO/DPH...17 SCREEN: STACKS...18 JOB_INFO SUBMENU...19 SCOPE FUNCTION BOARD CALIBRATION SUBMENU GATHERING DATA PROGRAM START UP...26 DATA ACQUISITION...26 STOP ACQUISITION...27 ACQUISITION ERRORS VIEWING DATA A NOTE ON VARIABLE A-SPACING A NOTE ON PHASE A NOTE ON SCALING RESTRICTIONS NOTES ON FIELD CONFIGURATIONS MAGNETIC COIL CONNECTIONS GDP October 2014

2 GDP INSTRUCTION MANUAL FIELD CONFIGURATIONS RECONNAISSANCE CSAMT SETUP...38 CSAMT TRANSMITTER SETUP MAGNETIC SENSORS FIELD-CHECK October 2014 Section 11, Page 2 GDP-32 24

3 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS 11.1 INTRODUCTION Controlled Source Audio-frequency Magnetotellurics or CSAMT is an enhanced frequency domain EM program using synchronous stacking and averaging, and Fourier integral methods to improve the signal to noise ratio. Fundamental CSAMT frequencies range from (1/64) to 8192 Hz in binary steps. The data acquisition system uses stacking and averaging of Fourier transformed spectra of the 1 st, 3 rd, 5 th, 7 th and 9 th harmonics to obtain amplitude and phase measurements of the electric and magnetic fields. The highest harmonic frequency is 73,728 Hz (9 th harmonic of 8192 Hz), however frequencies above the Nyquist frequency of 16,384 Hz are invalid but are recorded. Harmonic data is always obtained with the GDP-32 24, so the separate GDP-32 II HACSAMT program is not required. Both electric (Ex, Ey, Ez) field measurements and magnetic (Hx, Hy, Hz) field measurements may be utilized with this method. A calibrate buffer is provided for the magnetic antenna calibrates, and is saved as XHAANT.CAL on the GDP C:\ drive. An older file format, HAANT.CAL, is also recognized if the new file is not found. The standard board calibrate buffer is saved as 24BOARD.CAL on the GDP C:\ drive. Board calibration data can be viewed in the Calibration submenu of the CSAMT program. If no calibrate files are found, empty files are created, and factors of 1.0 mag and 0.0 phase are assumed. SELECT UP SELECT DN Home End All selectable fields can be modified using and. 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 by use of these keys. Pressing moves the cursor around the various areas of interest for the main menu screen and some submenus in all programs. Go to Section 6 for information concerning calibration, synchronization and generic operation of all programs. Go to the end of this CSAMT Instruction Manual for suggestions on connecting the receiver for field measurements. Note: Some numeric or alphanumeric, values are not registered in the GDP memory until you PREV FIELD NEXT FIELD Pg Up Pg Dn Enter exit the parameter field by pressing,, or. The exceptions to this rule are the frequency and the powerline notch filters. Whenever the frequency is changed, the sample rate is automatically changed through the timing card. However, the anti-alias filter is not Enter changed until just prior to data acquisition. Pressing to acquire data, the receiver will automatically set the anti-alias filter as defined by internal look-up tables. GDP Section 11, Page 3 October 2014

4 GDP INSTRUCTION MANUAL 11.2 FIXED FUNCTION KEYS Six fixed function keys are located below the six soft function keys ( through ) at the bottom edge of the LCD. Enter the cache viewer. Data can be viewed as time-series or apparent resistivity plots vs. frequency. Exit the CSAMT program and return to the main menu for selection of other data acquisition programs. This key can also be used to exit submenus of the CSAMT program. Enter the calibrate and system checking submenu. See the Calibrate section of this manual as well as 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 11, Page 4 GDP-32 24

5 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS 11.3 CSAMT 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. 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 CSAMT 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 11, Page 5 October 2014

6 GDP INSTRUCTION MANUAL <1103a_24CSAMT_MainAreas> Full display screen showing defined areas. October 2014 Section 11, Page 6 GDP-32 24

7 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS <1103a_24CSAMT_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: 22 Block number. CSAMT174j Program name and version. BAT 12.7 Battery Level in Volts. Sats 0 Number of GPS satellites (when GPS sync option is available). 10 Jul 2014 Date. 23:17:37 Time (Hours, Minutes, Seconds). GDP Section 11, 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, acquisition progress steps, and requests operator confirmation or input. The third line contains labels for the soft function keys. These labels 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. LINE SETUP SELECT DN. These historical messages are cleared at 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 usually not changed after a survey has started, therefore they are located in the lower half of the screen. Though 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. TIME SERIES This setting determines if all the raw A-D readings should be written to the cache as a time series, Yes or No. Writing the time series to the cache significantly increases the size of the cache file. This option is set to No. for normal operation. It is set to Yes for enhanced Post Processing, for analyzing input signals or other diagnostic purposes. Note: The GDP always collects a continuous stream of A-D readings for all of the cycles, the time series, into a memory buffer for processing, regardless of this setting. A-SPACE E-field dipole size in meters or feet (a-spacing). Notice that entering a value in this field causes all the values in the Asp column of 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 Specifies units of length, Feet or Meters, for all length and space entries. LINE 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 Informative 2-character user defined identification. TX LOC Informative transmitter location, along line (X). The field for Tx designation is NNNNNNN with a floating decimal point. This field is not used for CSAMT calculations, but could be used as a location or survey designator LINE Y: Informative transmitter location, across line (Y). The field for Line designation is NNNNNNN with a floating decimal point. This field is not used for CSAMT calculations, but could be used as a location or survey designator RX LOC 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. End October 2014 Section 11, Page 8 GDP-32 24

9 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS Note: Zonge standard data processing programs sort first on station number, second on Rx and third on Tx. To ensure proper sorting in data processing the operator must make sure the station numbers are entered properly. ACQUISITION CONFIGURATION The Acquisition Configuration area of the screen contains the following fields: FREQ This selects the frequency to analyze. The selections increment in binary steps from to 8192 Hz. When the CYCL count is a binary value, adjusting the FREQ field up or down causes the cycles to automatically change by the same factor. When CYCL is set to a non-binary value it remains constant while the frequency is changed. CYCL This field specifies the number of cycles to average. All data points will be read in a continuous series without breaks. This value can be modified Home End directly to any value, or the and keys can be used to select values from 1 up 16,384 in binary steps. Note: While making selections to the FREQ, and CYCL, settings, the GDP will evaluate the memory and disk space required, based on those settings, and number of ON channels. If the selected or entered values would cause the collected data to exceed available memory, based on these settings the CYCL value will be reduced to a value that will allow maximum memory utilization. An audible warning will be given and the STATUS will indicate: Cycles Reduced, Not To Exceed Memory Limit. Note: This feature can be used to maximize the data collection capability of the GDP. The operator can enter a CYCL value of 99999, and it will be adjusted to the maximum cycles that can be collected in memory. STACKS The total number of time series records to be acquired and processed. Each STACK will be recorded in individual blocks in the cache file. Note: If the entered value would cause acquisition memory or 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 Selector for setting the method the GDP will use for setting gain. Options are ALWAYS ONCE DONE SPONLY MAN SELECT UP SELECT DN Automatic gaining with SP bucking, will occur before each stack. 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. SP bucking will be performed for all stacks. The gain values currently set in the Channel Table will not be altered. The gain and SP values currently set in the Channel Table will not be altered. GDP Section 11, Page 9 October 2014

10 GDP INSTRUCTION MANUAL Note: On older versions of the Field Survey Program, the Automatic Gain algorithm does not apply an Attenuator setting. It assumes that the operator has set the transmitter to a level that will not require attenuation, relying instead on the increased dynamic range of the 24-bit analog converter. If the incoming signal does however require Attenuation, the MAN or SPONLY modes should be selected for GAIN. The SCOPE function can be used to inspect the incoming signal while making adjustments to the Transmitter Output. NOTCH OUT Powerline notch filter switch. There are several possible selections here, depending upon the hardware configuration of the receiver. 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: Powerline notch filters inject some noise into the system, and should only be used when absolutely necessary. More information on Notch Filter design can be found in Chapter 16. TXCR The Transmitter Current, in amperes. This value is the square-wave equivalent, or what is displayed on the transmitter current display. TIME MEM(mb) CHANNEL TABLE: Informational display of the total time required to collect, process and write to cache, all of the STACKS. Informational display of the memory required to collect all the cycles for one stack. The channel table refers to a separate section of the main menu where settings pertaining to a specific channel are made and results for that channel are displayed. The table is a distinct grouping of fields which can be accessed by pressing. There are four SCREEN: selections that configure the Channel Table. Pressing through: SETUP/CRES, MAG/PH, RHO/dPH, and STACKS. cycles October 2014 Section 11, Page 10 GDP-32 24

11 SOFT FUNCTION KEYS CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS The function keys through are considered soft function keys. They may perform different functions not only in different programs, but their functionality can also 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 start 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. GDP Section 11, 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 CSA, 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. <1103b_24CSAMT_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 24CSAMT.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 11, Page 12 GDP-32 24

13 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS SCREEN: CHANNEL TABLE DISPLAY SCREENS Cycle through the Channel Table screens by using. SCREEN: SETUP/CRES The SETUP screen is the initial Channel Table configuration displayed after starting the program. It can also be viewed by pressing and cycling through the screens. <1103c_24CSAMT_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 Cmp 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. 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, Ez Electric field designators GDP Section 11, Page 13 October 2014

14 GDP INSTRUCTION MANUAL Hx, Hy, Hz Magnetic field designators. (Antenna types are listed in Section 18.9 ANTENNA DESIGNATIONS ) Note: For computing the Cagniard resistivity from the E and H fields, the program matches orthogonal pairs of fields. For the example above, Channels 1 and 2 will be used to calculate RHOxy and channels 3 and 4 will be used to calculate RHOyx. Data for Hz are acquired and put into the data cache without any calculations being done on the value, other than removal of calibrates. Note: This field also indicates empty slots and cards not directly supported by the AMT program, such as NanoTEM cards. Sat S/Ant 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. Multi-usage field: 1) E-field designator: Identifies the station number for multiple E-field measurements. In the CSAVGW data processing software, for GDP Channel Number Meaning, E-field Channel, select Stn Number. <1103d_24CSAMT_Setup_Stn> 2) E-field designator: Identifies the station number offset to the RX LOC for multiple E-field measurements. The actual station location is equivalent to RX LOC plus S/ANT. In the CSAVGW data processing software, for GDP Channel Number Meaning, E-field Channel, select Stn # Offset. October 2014 Section 11, Page 14 GDP-32 24

15 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS <1103e_24CSAMT_Setup_Offset> Gain 3) 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 Designates an ANT/1 antenna (0), serial number Designates an MT antenna, serial number MT/AMT antenna, serial number Single channel TEM/3 (9), serial number 18. 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. 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. GDP Section 11, Page 15 October 2014

16 GDP INSTRUCTION MANUAL SCREEN: MAG/PH The MAG/PH screen can be reached by cycling. <1103f_24CSAMT_MagPh> The MAG/PH screen displays the columns MAG, θ(mr), and SEM. The column entry fields, Cmp, S/Ant, Gain, and the non-editing fields, Ch, Calibration Found, Saturated Reading, are described in the SETUP screen description above. MAG The decalibrated magnitude in volts for each E-field or kilogammas for each H-field component measured. SEM The decalibrated phase for each E- or H-field component measured. Standard error of the mean for phase values, in milliradians, calculated for each cycle for frequencies of 1 Hz and lower, or the average of 2 sec for frequencies of 2 Hz and above. October 2014 Section 11, Page 16 GDP-32 24

17 SCREEN: RHO/DPH CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS The RHO/dPH screen can be reached by cycling. <1103g_24CSAMT_RhoDPh> The RHO/dPH screen displays the columns: Rho, dθ(mr), and SEM. The column entry fields, Cmp, S/Ant, Gain, and the non-editing fields, Ch, Calibration Found, Saturated Reading, are described in the SETUP screen description above. Rho dθ(mr) Apparent resistivity in ohm-meters for each channel defined as an E-field channel (Ex, Ey) that has a matching orthogonal H-field channel (Hy, Hx). If the E- or H-field being measured on a particular channel does not have a corresponding orthogonal component (such as Hz, or Ex without a corresponding Hy), the value displayed will be the magnitude of the received signal in volts with the magnitude calibrates removed. For channels defined as H-field inputs, (Hx, Hy, Hz), the coil magnitude calibrates are also removed. Phase difference in milliradians for each channel defined as an E-field channel (Ex, Ey) that has a matching orthogonal H-field channel (Hy, Hx). If the E- or H-field being measured on a particular channel does not have a corresponding orthogonal component (such as Hz, or Ex without a corresponding Hy), the value displayed will be the phase of the received signal in milliradians with the phase calibrates removed. For channels defined as H-field inputs, (Hx, Hy, Hz), the coil phase calibrates are also removed. GDP Section 11, Page 17 October 2014

18 GDP INSTRUCTION MANUAL Note: The calibrations for both magnitude and phase are removed from the final displayed magnitudes and phases for all channels that are defined for H-field input, as long as a valid calibrate exists in the calibrate cache for the antenna defined in the S/Ant column. Therefore, you may notice large magnitude and phase differences between E-field and H-field channels when making system checks that use the same source for each channel. This difference in magnitude should also be kept in mind when observing received signal levels for field data. The magnitudes of the H-field channels have been normalized by the coil response. This means that the signal levels coming into the receiver are different than those being displayed in the data cache - the difference being the antenna calibration factor. SCREEN: STACKS The STACKS screen can be reached by cycling. This screen displays the selected results for the last 5 Stacks of data, as each stack is acquired. When this screen is displayed, the cursor is moved to the results selector field. The selections are: Mag, Ph, Rho, dph, SEM and RSEM. The Mag, Ph, Rho, dph and SEM values are identical to those displayed in the MAG/PH and RHO/dPH Screens. The RSEM value is accumulated over all the repeating stacks of an acquisition, where SEM represents the standard error for each individual stack. 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. <1103h_24CSAMT_Stacks> October 2014 Section 11, Page 18 GDP-32 24

19 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS 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 as well. <1103i_24CSAMT_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. GDP Section 11, Page 19 October 2014

20 SCOPE FUNCTION GDP INSTRUCTION MANUAL 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 clear the Scope display. <1103j_24CSAMT_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. Note: On older versions of the Field Survey Program, the Automatic Gain algorithm does not apply an Attenuator setting. It assumes that the operator has set the transmitter to a level that will not require attenuation, relying instead on the increased dynamic range of the 24-bit analog converter. If the incoming signal does however require Attenuation, the MAN or SPONLY modes should be selected for GAIN. The SCOPE function can be used to inspect the incoming signal while making adjustments to the Transmitter Output. October 2014 Section 11, Page 20 GDP-32 24

21 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS 11.4 BOARD CALIBRATION SUBMENU The calibration data for the CSAMT program is shared with several other GDP programs: CR, TDIP, TEM SYSCHK a,d SYNC_CHK. The standard board calibrate buffer is saved in the GDP as C:\24BOARD.CAL. Board calibration data can be obtained and viewed in the Calibration submenu of the CSAMT program. CSAMT calibration data contain the 1 st, 3 rd, 5 th, 7 th and 9 th harmonic magnitude and phase values. 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. <1104a_24CSAMT_Call> 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. Calibration values are associated with board serial numbers, as opposed to channels, allowing operators to 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 variations. The operator must perform an AUTOCAL calibration for each variation of gain setting. Thus, a calibration GDP Section 11, Page 21 October 2014

22 GDP INSTRUCTION MANUAL 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 these values displayed during either a 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 CYCL NOTCH METHOD AUTOCAL The calibration frequency setting, from to 8192 Hz. The calibration values for the fundamental frequency from the calibrate file will be displayed as frequencies are selected. The setting for the number of cycles to acquire when measuring the calibration readings. 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. The operation method for the calibration. The selected calibration METHOD will be performed when the operator presses. The selections are: Perform calibration starting at the selected FREQ, and automatically sequencing up to the highest frequency of 8192 Hz. This will automatically select sample rates, and high pass filter settings for each frequency of the calibration set. Calibration sets include the magnitude and phase for the 1 st, 3 rd, 5 th, 7 th, and 9 th harmonics, which are written to the calibration file. This automatic calibration does not cycle through the possible 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. Enter October 2014 Section 11, Page 22 GDP-32 24

23 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS 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 the check, or any other key to continue. to cancel Note: One method of verifying both the calibration file and the operation of the CSAMT program is to perform calibration with the CSAMT program. Then exit CSAMT and start one of the other programs that share the 24BOARD.CAL file, CR, or TDIP. From the Calibrate submenu in that program, perform the AUTO_CK procedure. 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, Enter will set the reference voltage. Pressing while this method is set will have no effect. To enable this method, the operator must press Escape Escape to return to the main menu, and then perform the system check Enter 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. GDP Section 11, Page 23 October 2014

24 GDP INSTRUCTION MANUAL <1104b_24CSAMT_AutoSysChk> MODE ATO_SY_C System check selection: auto increment frequencies in addition to enabling the calibrate signal in the same manner as the SYS_CK method. The frequency will auto increment from the frequency set when initiated, up to 8192 Hz, collecting cycles and stacks as set for each frequency. See the section METHOD TO FIELD-CHECK MAGNETIC SENSORS for an example of how this feature can be used. 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 dθ% LIM Set the calibration signal voltage. Changes can only be made by the operator when the METHOD selection is SYS_CK or ATO_SY_C, 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. 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. October 2014 Section 11, Page 24 GDP-32 24

25 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS (PhzMeasure PhzCal) dθ% = 100 x 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 phase differences of less than 0.05%. Lower frequencies, particularly the lowest frequency of a sample rate 0.016, 0.063, 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. GDP Section 11, Page 25 October 2014

26 GDP INSTRUCTION MANUAL 11.5 GATHERING DATA PROGRAM START UP During start up, the CSAMT 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 CSAMT 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 CSAMT program, the old calibrate file will be renamed to BOARDCSX.CAL and a new, empty, 24BOARD.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, and 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 24BOARD.CAL. The required antenna calibration file is XHAANT.CAL, or the older HAANT.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 board calibrates. 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 calibrates are found, and that input signals are good. Use of the SCOPE can detect channel saturation, poor connections, and excessive powerline noise. Pressing acquisition sequence. Enter will start the data Enter Immediately after pressing, the GDP will set gains as requested. When the selected gain method has completed, the GDP acquisition will synchronize with the timing card and indicate that it is taking data. At frequencies of 2 Hz and above, 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 the computer memory. For 1 Hz and below, a progress bar will be displayed showing the time left for taking data. When data has been acquired, the results will be calculated and displayed. When taking a single stack of data, 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 acquisition. October 2014 Section 11, Page 26 GDP-32 24

27 STOP ACQUISITION CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS 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 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 progress 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 to start the Cache Viewer. The initial display will display zero values in the table. The operator can make selections for SET (or BLOCK), PLOT type, CH (channel), and CYCLE. The SET value is a group of stacks, with various frequencies but the same channel station and antenna configurations. The FREQ field displays the frequency of a Set or Block. Enter 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 CSAMT are: Rho_f, Rho vs frequency for E-field channels in a Set. dph_f The phase difference in milliradians vs frequency for each channel in a Set, defined as an E-field channel (Ex, Ey) that has a matching orthogonal H-field channel (Hy, Hx), versus frequency. MagE_f The magnitude vs frequency for E-field channels in a Set. EPh_f The phase vs frequency for E-field channels in a Set. MagH_f The magnitude vs frequency for H-field channels in a Set. HPh_f The phase vs frequency for H-field channels in a Set. Stack The voltage vs time for stacked data, for any channel in a Block. TimeSr The voltage vs time for time series data, for any channel in a Block. If the optional TIME SERIES data was not recorded in the cache, the display will not update. 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. GDP Section 11, Page 27 October 2014

28 GDP INSTRUCTION MANUAL 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 Stack or TimeSr PLOT or frequency for the PLOT of a Set. Pressing will shift the columns to other channels if there are more than 4 channels selected in the view. 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. October 2014 Section 11, Page 28 GDP-32 24

29 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS Examples of the Rho vs frequency PLOT, with TABLE and GRAPH views of the data. <1105a_24CSAMT_CacView_Rho_Table> <1105b_24CSAMT_CacView_Rho_Graph> GDP Section 11, Page 29 October 2014

30 GDP INSTRUCTION MANUAL Examples of the Stack PLOT, with TABLE and GRAPH views. <1105c_24CSAMT_CacView_Stack_Table> <1105d_24CSAMT_CacView_Stack_Graph> October 2014 Section 11, Page 30 GDP-32 24

31 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS 11.7 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 the A-Spacing that is used is ALWAYS the value in the A-Spacing (ASP) column of the Channel Table. For example, if the operator sets the A-SPACE value to 50 m, then all of the numbers in the Channel Table are set to 50 m. If the operator then goes into the table and changes all of the values to 25 m for example, then the A-SPACE field will still be 50 m but the actual values used will be 25 m as shown in the ASP column of the Channel Table. The computer remembers the latest settings upon startup of the program A NOTE ON PHASE The CSAMT program is an absolute phase program - that is, the program measures the absolute phase shift between the transmitted signal and the received signal. For normal operations at low frequencies, the real-time phase shift should be around -100 to -200 milliradians for the E- fields, and around + /2 (1571 mr) for the H-fields. If the E-field phase is closer to radians (3142 mr) then you have some wires reversed. You can get rid of the radians of phase shift by either reversing the transmitter wires at the transmitter, or reversing the leads going into the receiver. For multi-channel receivers, it is easiest to make the change at the transmitter, and then maintain the same polarity throughout the survey. If the phase for the H-field channels is negative /2, you have a 180 degree phase shift. To correct this, just switch one of the connections at the receiver, or rotate the H-field sensor by 180 degrees, or reverse the antenna cable leads at the GDP A NOTE ON SCALING The following conventions are used for all measured and calculated parameters: E-field Voltage, (magnitude) displayed in volts. H-field Voltage, (magnitude) displayed in kilogammas when decalibrated with antenna cal. Current, displayed in amperes. Phase, displayed in milliradians. Apparent resistivity, displayed in ohm-meters. Dipole spacings, displayed in meters. Coil calibrate magnitudes, entered and displayed in millivolts per gamma. SP, displayed in millivolts SEM, displayed in milliradians 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 GDP Section 11, Page 31 October 2014

32 GDP INSTRUCTION MANUAL RESTRICTIONS The only restrictions on setting up the channels and using this program are to make sure the E- field channels always precede the corresponding 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. Following are some examples for connecting and defining the channels: 1. Reconnaissance Scalar CSAMT measurements on 7 separate stations: <1110a_24CSAMT_ReconScalar> This example of scalar CSAMT, measures E-fields at 7 different stations, with the H-field antenna placed near the center of the array. This type of array is normally used for reconnaissance surveys. The numbers 1 through 7 in the Sta/Ant field are used as station identifiers for data processing using a data processing station file, and are not actual station locations. The same is true for Tx and Rx identifiers. The RX LOC value is commonly used to indicate the location of the GDP. These numbers can be any value from 0 to The number 2156 on the Channel 8 Hy line indicates that the calibrates for ANT/6 Serial Number 215 are to be used. This exact number must identify the calibrates in the XHAANT.CAL antenna calibrate file. October 2014 Section 11, Page 32 GDP-32 24

33 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS 2. Four station scalar measurements, stations 1, 2, 3, and 4: <1110b_24CSAMT_StationScalar> This example of multiple station scalar measurements further defines the use of the station identifier for the E-fields in the Sta/Ant field. Cagniard resistivity is calculated using Ex (channel 3) and the Hy from the next nearest channel (channel 4). Likewise for the phase difference calculations, the phase for Ex (channel 3) and Hy (channel 4) are used to form the difference. For this example we are using four single-channel ANT/6's for the H-field measurements. GDP Section 11, Page 33 October 2014

34 GDP INSTRUCTION MANUAL 3. Two station vector measurements: <1110c_24CSAMT_2StationVector> This example is just a rearrangement of the setup in Example 2 above to provide vector measurements, x and y components, at each of two stations. For this example we are using four single-channel ANT/6's for the H-field measurements. October 2014 Section 11, Page 34 GDP-32 24

35 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS 4. Single station tensor measurements: <1110d_24CSAMT_SingleStationTensor_1> <1110e_24CSAMT_SingleStationTensor_2> Remember, for full tensor measurements we need to make identical measurements from two orthogonally oriented transmitters. Hence the identical channel notation for the two transmitters. We identify the two different sources by using the Tx field as shown, and generating separate files with our data processing programs. GDP Section 11, Page 35 October 2014

36 GDP INSTRUCTION MANUAL For this example, ANT/6 single axis magnetic antennas are used for Hz. All other notation is as above in the previous examples. These data were acquired using an RC network and a constant current laboratory transmitter. The RC network is as follows: 50 K 1 uf 50 K October 2014 Section 11, Page 36 GDP-32 24

37 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS 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 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. The following figures provide examples of receiver connections using the REFERENCE ELECTRODE or REFERENCE POT connected to both analog ground (COM) and case ground (CASE GND). 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 MAGNETIC COIL CONNECTIONS If the magnetic coil being used has a differential (3-wire) output, connect the two signal wires to the red and black input terminals, and the ground wire to COM on the Analog I/O side-panel. If the magnetic coil has a single-ended (2 wire) output, connect the signal wire to the red input and connect the ground wire (or shield, if it is a coaxial cable) to the black input. GDP Section 11, Page 37 October 2014

38 GDP INSTRUCTION MANUAL FIELD CONFIGURATIONS RECONNAISSANCE CSAMT SETUP October 2014 Section 11, Page 38 GDP-32 24

39 CONTROLLED-SOURCE AUDIO FREQUENCY MAGNETOTELLURICS CSAMT TRANSMITTER SETUP GDP Section 11, Page 39 October 2014