GEM-2 User`s Manual
Contents
1. For a discussion of the theory and practical assumptions involved in these calculations see the article by Huang and Won 2001 entitled Conductivity and Susceptibility Mapping Using Broad band Electromagnetic Sensors published in the Journal of Environmental and Engineering Geo physics The article is available at the Geophex website How Do I Invert GEM 2 Multi Frequency Data to a Layered Earth A program for inverting the GEM 2 data to a Layered Earth Model can be downloaded from the About Geophex page of our web site This 1 D inversion program is provided for informational purposes only It should be considered as Beta version software We request users to work with our Geophex scientists to improve it There are several commercial software on the market that deal with the GEM type multi frequency data for 1 D 2 D and 3 D inversion What is the Depth of Exploration for GEM 2 This is a very complex question because the answer depends on many factors particularly on ground conductivity target volume and ambient electromagnetic noise Based on many analyses and field data we estimate the GEM 2 should be able to see about 20m in resistive areas gt 10000hm m and about 10m in conductive areas lt 1000hm m This figure assumes an ambi ent noise level of 5ppm The noise level is generally high in urban areas and low in rural areas For typical applications we do not recommend the GEM 2 for depths greater than 10m For2. Bar This area contains commands for setup operation and survey controls Power On side of iPaq field1 d 9 56 CD StripChart Command Buttons Status Bar Data Area Se 10 S615 SGO S625 5630 Control Bar Mark LnRes gt A se Page 1 Replacing and Charging the Battery To replace the battery unscrew the two battery door thumbscrews and remove the door Grasp the battery tab and pull the battery out of the compartment If the battery tab is missing stand the ski on end with the battery opening facing down place one hand to catch the battery then tap the ski gently on the ground to dis lodge the battery To install the battery simply plug it into the console label side up If it doesn t go all the way in it s upside down Simply remove the battery turn it over and try again When the battery is plugged in install the battery door and two thumb screws to hold it in place To charge the battery plug it into the external charger supplied with the system Follow the instructions provided with the charger Normal charging time is about 40 minutes WinceGEM Software Installation The iPaq supplied HP iPAQ 111 Classic Handheld is preloaded with the WinceGEM operating software with backup files in the SD card in the InstallGEM2 directory For a new re installation take the following steps in the directory InstallGEM2 tap the WinceGEM cef select Device as the location to install
3. GEM will automatically synchronize its internal clock to the GPS time The GPGGA EM noise level the Tx is off and can be useful for the Tx is on allows the user to strings are stored along with the EM data avoiding noisy frequencies If very noisy you may visualize the transmitted frequen 4 The Status Bar GPS indicator displays the presence of the GPS signal by displaying postpone the survey until off hours or weekend cies above the background noise when PPS is present along with the GPS quality number of satellites GEM 2 User s Manual Page 4 Female DB9 Connector The female DB9 connector provides RS232 communication to a computer A standard RS232 DB9 cable male female and RS232 to USB2 adapter is supplied for connecting to a PC The WinGEM software supplied with the system uses this connection to remotely control the GEM 2 The following communication parameters are used Baud rate 115 200 Parity None Data Bits 8 Handshaking None Stop Bits 1 Communication between Ski and Computer To transfer the communication of the ski from the iPaq s Bluetooth to computer RS232 click Setup then Ports and select Switch GEMPort to RS232 The password is 1234 To transfer the GEM2 ski communication back to the iPaq s Bluetooth connect your computer with a standard RS232 cable to the GEM 2 ski and use the GEMtoBT exe program supplied on the CD to re establish the communication with the iPaq s Bluetooth To force temporary RS232
4. communications remove the console from the ski four corner screws turn the console on then momentarily push the RESET button on the bottom of the console Use WinGEM or GEMtoBT exe to set desired communications Then turn the console off and mount it back on the ski When power is turned back on communications will occur as chosen Software Included on the CD The CD included in the shipping contains the following Install iPaqPlus Installs iPaq software through Microsoft ActiveSync or SD memory chip Utils PC PC software for controlling the GEM and processing data Manuals GEM 2 Manual and WinGEMv4 Manual pdf format Readme rtf Listing of CD contents Technical Help For technical help please contact Geophex Ltd 605 Mercury St Raleigh NC 27603 USA Tel 919 839 8515 Fax 919 839 8528 Web www geophex com Or send emails to oren geophex com GEM 2 User s Manual How do I Learn More about the GEM Sensors The Geophex website www geophex com provides ample information about the GEM sensors design and operating principles survey tips manuals and downloadable software The site also carries many journal articles related to the GEM sensors which can be viewed or printed How Do I Convert the GEM 2 Data to Apparent Conductivity and Suscep tibility Using the EMInvertor Utility the GEM 2 ppm data can be converted to apparent conductivity and magnetic susceptibility at each frequency used for the survey
5. frequencies as factory default Modify the number of frequencies by selecting Cfg from the Control Bar and then Frequencies from the menu Reduce the num ber of frequencies to three for higher moments A maximum of five log spaced frequencies is recommended Adjust Base periods to average to control the number of 30 25 Hz base periods stacked before output occurs d 512 O Messe GD Contour z Transmit Receive Frequencies Count 5 Add Base periods to average Set GEM from file Save GEM to file Survey area Frequencies Regional settings Filtering Calibration AY 4 10 06 ok Line Length Line Spacing Area Width Bkg removal filter size sec L GPS survey Horizontal C Vertical Bi directional Uni directional Set GEM from file Save GEM to file Survey area Frequencies Regional settings Filtering Calibration Cancel Run Log View Cfg Setup Contour Select Survey area from the Cfg menu Insert survey area parameters select the corner to start the survey and direc tion If GPS is not selected the survey will be regarded as dead reckoning GEM 2 User s Manual Select one of the frequen cies then select one of the options and modify the fre quency as desired i536 ok a 1567 r 4 10 07 amp Adjust Sens Q_47010Hz Z _ Accumulate Bkg E From the Contour command bar select Sensi tivity Scheme in order to pick inph
6. is applied are logged for the specified 4804 d 02My 0f SDGemdata wise in UTM Battery status will display followed by a moving aver number of seconds each ci the GEM s battery infor age filter time the Logging button is Note the gbf file can be transferred to a PC and mation clicked This mode can be OO exported with the PC Export Utility Provided This useful for recording data at may be faster for large surveys discrete locations Advanced Features Male DB9 Connector 25 25 QD The male DB9 connector provides RS232 input from an external device such as a GPS re ceiver The following communication parameters are used RX Spectrum RX Spectrum Baud rate Selectable on the Router Port 9600 or 4800 Data Bits 8 Parity None Stop Bits 1 Handshaking None Connecting an external GPS When an external GPS is connected to the ski the following conditions apply 1 The GEM utilizes the PPS signal provided by the GPS at pin 8 of DB9 connector Serial communication is supported with GPS transmitted data at pin 2 and GPS received data at pin 3 Pin 5 is GND Pin 9 is 12V 500mA maximum supplied by the GEM Please confirm compatibility with your particular GPS before using the 12V supplied Environmental Passive Noise Spectrum is available The Environmental Active Noise 2 GPS unit must be set to send the GPGGA time of next PPS pulse once per second under the Run menu This shows the background Spectrum under the Run menu 3
7. more discussion on this subject consult the Skin depth Nomogram in GEM 2 Principle of Operation on our web site Depth of exploration for a given earth medium is determined by the operating frequency There fore measuring the earth response at multiple frequencies is equivalent to measuring the earth response from multiple depths Hence such data can be used to image a 3 D distribution of sub surface objects Results from several environmental sites indicate that the multi frequency data from GEM 2 is far superior in characterizing buried metallic and non metallic targets to data from conventional single frequency sensors For handheld sensors the transmitter receiver coil sepa ration is inherently small and has little to do with the depth of exploration For comprehensive discussions and examples please read an article by Huang Depth of investi gation for small broadband electromagnetic sensors published in 2005 in Geophysics v 70 n 6 pp G135 G142 also available at the Geophex website One conclusion is that small co located sensors like the GEM 2 and GEM 3 the depth of exploration is proportional to the square root of the skin depth expressed in meters Page 5
8. 232 on the ski to another computer GEM 2 User s Manual Getting the GEM 2 Up and Running Power the GEM ski and the iPaq Tap the Geophex icon on the screen and wait for the program to establish communication with the ski Select type of display Stripchart displays the data for a selected frequency or other parame ters such as Q sum for the last 20 seconds using the PDA time unless GPS is used Contour displays realtime 2D painting of the selected data Spectrum displays instantaneous Q re sponse over all frequencies d o6 ok StripChart d 238 D Contour 56 10 56 15 5620 56 25 56 230 E Run Log View Contour Run Log View Oa RE P CE ok Zone 17 North Q E Router Port from the Setup Ports menu allows the selection of the GPS baud rate The GPS must be set to send the GPGGA string only Regional Settings select 50Hz or 60Hz powerline frequency The GEM data will contain a column show ing the powerline amplitude in milliGauss at the selected frequency As a default iPaq communi cates with GEM via Bluetooth The outbound port of the Blue tooth must be set as the GEM Port in the Setup Ports menu baud 115 200 The Ports menu allows the user to switch to RS232 if the user wants to control the GEM from a separate computer If GPS is used also select the zone of the survey area and the desired GPS output Page 2 Check Change Frequencies The GEM transmits four
9. GEM 2 User s Manual What is the GEM 2 This is the 2008 model of the GEM 2 While it has several new features the basic sensor function remains the same it meas ures apparent electrical conductivities at multiple user selected frequencies and magnetic susceptibility at the lowest selected frequency The GEM 2 consists of the ski that contains all sensing ele ments an electronics enclosure that plugs onto the ski a de tachable iPaq for display and a shoulder strap GEM 2 Features e Attached electronics enclosure permits easy field battery pack replacement e Simplified electronics extends battery life and eliminates cooling fans e PDA IPaq as the user interface with full WinceGEM function 97 3 ality External GPS connector with 12V power available Dead reckoning survey option Frequency range up to 90 kHz Lightweight 8 lbs or 3 6 kg Bluetooth communication to the PDA and RS232 serial ports to any other external devices Real time painting of the survey area for quick data look No need to download data after each survey data are stored in the internal memory as well as on the SD card in separate gbf files for each survey e The gbf files may be converted to csv format after the survey on either the PDA or another computer e On demand the PDA displays the environmental noise spectrum i e transmitter off and stores it on the SD card for later analysis Note This manual assumes that you are familia
10. and tap Install on the bottom left of the screen Once the installation is com pleted tap OK on the top right corner and repeat the same procedures for the EMExport cef To set up the Geophex logo as a shortcut tap Start select Settings in the Personal tab select the Today icon in the Items tab uncheck all items leaving just the WinceGemPlus selected Set Bluetooth as the default to communicate with the ski ski power ON Tap the Bluetooth icon to go to the Bluetooth Manager under the Setting General tab turn Bluetooth on and select Default Tap the Accessibility tab and check Allow other devices to connect select All devices and check Other devices can discover me also check Use PocketPC device name for Bluetooth On Services tab select Serial Port check Enable services click the Advanced command button and verify that the Inbound COM port is 5 and Outbound is 6 Tap OK on the top right corner and click Manager button select Active Connection tab select New scroll down and select Explore a Bluetooth Device select Next and wait for the iPaq to find the ski Bluetooth and set it as the default COM port Note During a survey we strongly recommend that the iPaq be left attached to the top of the ski console its removal may cause a slight offset in the background data For remote applications the iPaq can be removed up to 10m from the ski Note The user may opt to disable the Bluetooth and instead use a PC connected by hardwire to an RS
11. ase or Q quadrature of a frequency or Qsum to be dis played painted on the survey area Start Tx and wait until the Log button becomes avail able Building Waveform Please wait 05 0 O00 000S 00 0 00 15 O02 Run Log View Cfg Setup Eg d 2 51 ok Contour v Run Log View Contour E When the survey is com pleted stop Tx The contour color scale may be adjusted by selecting Sensitivity from the Contour menu Clicking Log will start the survey at this point the oper ating system will open a dedi cated file to store the data in the internal iPaq memory and a backup in the SDC By the end of the line press Log again Run Log View Contour ex ME 2 52 Contour Pra a t Smoothing map 55 Rendering Abort Run Log View Contour From the Contour control bar select Smooth Image Move to the next line and press Log again the line number in the status bar will increment by one d 242 ok Contour z Run Log View Contour EA 62 52 ok Contour v 7 EOE Run Log View Contour This is an example of a basic contour map of a survey area Page 3 Export the Survey Data sacs Other Advanced Features di 149 ok 5 RE Template survey E type Output oy D D ex ME 5 21 From Run control bar select Close L GPs egrees _ All export Dead Reckoning Survey Bidirectional O Unidirectional Horizontal C Vertical Survey and then select E
12. r with the basics of operating the iPaq and Win dows CE The Getting Started Guide that comes with the iPaq supplies most of the necessary details Note The iPaq included in the package contains the original manufacturer s warranty Should you need repair service contact them directly For updated information on this and other Geophex Some abbreviations used in this manual products please visit www geophex com send email to sales geophex com or write to SD card Secure Digital Card Tx Transmitter Geophex Ltd 605 Mercury Street Cfg Configurations Raleigh NC 27603 USA I Inphase Q Quadrature GEM is a Registered Trade Mark of Geophex GEM 2 User s Manual iPag Layout The iPaq screen is divided into the following four areas Command Bar The left and right hand command buttons correspond to the left and right hand push buttons along the bottom of the iPaq All four command buttons become green when active Only active commands are visible Status bar BAT Shows the battery health the 1 warning is at 15 the BAT bar background changes to red along with a continuous beep at 10 the transmitter will stop at 5 GPS Represents PPS and quality satellite number STA A D overload turns RED when analog inputs are overloaded LINE Displays the line number starting from 0 during the dead reckoning survey Data Area This area displays survey data in StripChart Contour or Spectrum mode Control
13. xport Survey Tap on the file to be lo cated and exported to the SDC directory SDgemdata If a GPS survey was conducted an xg gem csv will be created for dead reckoning an xr gem csv iy EMExport Er q 1 22 Open re Ln Length Ln Spacing lami 110 000 5 000 Starting point coord X Y Freeze Time series spectra Show GPS Folder All Folders Ej nn EER Type Geophex Files gbf v Select survey parameters for dead reckoning enter the line length and spacing then the X Y of the starting point and Export A csv file with the Run Log View Cfg Setup Contour m s GGemdata 01 d O1My 2 4 01 d 01My 2 SDGemdata 5 1 6 4 same name will be created on the SDC If SDC is Show GPS will pop up a From Cfg menu select Log menu allows selection of 02 d 01My 0 GGemdata 5 1 7 0 unavailable the file will be saved in the iPaq window showing the exter Filtering the processor data logging mode If you 4 02 d 01My 0 SDGemdata 5 1 7 0 memory If the survey was done with a GPS then nal GPS received string performs smoothing of the enter a non zero value for amp 03 d 01My 0 GGemdata 5 1 9 0 Sa ae i 3803 d 01My 0 SDGemdata 5 1 9 0 click the GPS box If Degrees is selected the See below for details and Q data in time A mov the Time period samples 04 d O2My Of GGemdata 5 2 2 2 data will be exported in lat long degrees other ing median filter
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