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EM38_traitement.py
README.md
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README.md

EM38 sea-ice recording device

The repositery is use to perform recording of conductivimeter EM38-MK2 with a raspberry pi, GPS and RTC.

How to use it

  1. make sure everything is correctly connected :
    • USB hub connected to the raspi on the usb connector
    • USB key and serial adaptator to the USB hub
  2. Start the system by plug in a battery pack via the "power" usb connector
  3. the raspi takes around 1 minute to start recording
  4. start the EM38-MK2 and put it in the sled
  5. the raspi will record EM38 data at 6Hz and GPS at 1Hz
  6. The 7-segment display give an idea of the sea-ice thickness measure by the conductivimeter, based on the function implemented on the raspi (it can be false and needed adjustements)
  7. to stop the system, press 10 second on the red button on the side of the raspi (red LED flashing duriong 10 s) and release . The system will turn itself down after making copy of recording on the USB stick. If you don't shut down properly the system, the data will not be copy on the USB key. Please wait fews minutes before unplug the battery pack (the 7-segment display can still be on but the raspi will be off --> no more led on the raspi)

good to know

  • the EM38-MK2 can measure sea-ice thickness only because of the presence of salty water below sea-ice. It will not be able to measure anything if the water salinity is to low. For now, the conductivimeter is set to the estuary salinity (~28 PSU). If ice thickness is measure elsewhere, please adjust the conductivity/ice thickness function (fnt ice_thick l.78 in EM38_traitement.py)
  • The conductivity signal is affected by the temperature of the instrument. A good practice is to place the EM38-MK2 outside 10 to 15 min to stabilise in temperature.
  • data may require adjustements for sea-ice thickness, please perform few manual ice thickness measurements to verify the trasnfert function.
  • GPS signal is collected from the small orange case, with the raspberry pi.

data processing

datas are generated for each start of the system, named with timestamp of the datetime of the system start. It generate a EM38 file (.txt) and a GPS file(.nmea). to link both files, please follow the "em38_traitement.sh". Before perform the script, GPS file must be clean :

  • select only GGA sentence from the file (grep '$GPGGA' INFILE >> OUTFILE)
  • replace ":" by comma (sed -i -e "s/: /,/g" OUTFILE)

The script will perform merging of GPS and conductivity data, estimation of ice thickness through a function, plot some figures and generate a datafile.

Read the em38_traitement.py's header to get more informations

Contributing

  • Dany Dumont
  • Paul Nicot