EM31 ice thichness measuring device test from NASA, National Aeronautics and Space Administration

NASA EM31 Project diagram

North Pole Expedition 2003
Rhett Herman
This is a operational diagram of the NASA EM31 surface conductivity tester used for measuring ice thickness.   April 2003
  North Pole Expedition 2003
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This exhibit was posted on 5-29-2003

Please Note:  The background on this page is an aerial photo of the sea ice near the island of Svalbard, Norway

NASA EM-31 On the North Pole Page 2
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Rhett and Jim prepare the NASA EM-31 for initial use
Drawing by Daniel
This drawing was made by Daniel one of the students that was involved in the operation and testing of the EM-31.  At the right end of the EM-31 tube is a 9.8 Khz transmitter.  On the other end of the EM-31 Probe is a receiver also set for 9.8 Khz.  The receiver actually receives two signals, one which originates in the transmitter and travels down the tube (the reference signal) and another signal which travels out of the EM-31 transmitter, down through the ice and back to the receiver (The variable receiver input)  Here the phases of the two signals, the reference and the variable, are compared to give a result. 

The result, in it's own only shows the conductivity of the ice being tested, however, until actual, physical, holes have been drilled into the ice and a physical measurement is made, the conductivity reading is useless.  Once the physical holes are drilled and the measurements are made, these results are fed into the EM-31 as  calibration data.  Now the thickness of the ice can be actually measured with the EM-31 using the ice conductivity as a constant. 

The drawing above shows the EM-31 measuring an anomaly below the surface.  In the case of making measurements on the ice, the 9.8 Khz  signal gets reflected off of the bottom surface of the ice.  The interface of the Ice subsurface and the top of the salten sea is the anomaly that reflects the transmitters signal.    Therefore, measuring the phase difference between the reference signal and the received signal gives us the thickness of the ice. 

Click Here's a link to the actual  NASA Site for this project.







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