Abstract:
EMI (electromagnetic induction) records of ice thickness, utilized a Geonics EM-31 induction meter, were conducted with the meter suspended from the ship’s starboard A-frame, at heights varying from 2.5 to 4.0 meters. Conductance data (in millisiemens/meter) were acquired at 2 second intervals. Heights to the snow/ice surface were measured with a sonic ranger attached to the frame housing the
... EMI device. Data were recorded on a Campbell Scientific CX200 data logger (range measurements) and with Allegro Windows CX handheld computer (conductivity data) running Geonics EM31 acquisition software. Due to design constraints with the CX200 data logger, range measurements were only acquired at 60 second intervals. Range measurements were adjusted for speed of sound variation due to temperature. Geolocation of EMI/ranger data pairs was accomplished through simultaneous logging of the ships GPS track at a mean positional accuracy of < 3.0 meters. The data set includes EMI records of ice thickness along an outbound track from Palmer Station commenced 8 September at 18:49 GMT, at 64.48S 64.03W and terminated 9 September at 04:00 GMT at 64.53S 65.00W. However, due to uncertainties of conductivity measurements in predominately pancake ice conditions (< 100% ice concentration), ice thicknesses for this track will not be reported. The dataset also includes EMI records of ice thickness along an inbound track to Belgica Station commenced 25 September at 13:00 GMT, at 69.78S 90.02W and terminated 27 September at 3:41 GMT at the conclusion of way station 3 operations, due to high winds that persisted the remainder of the day. An estimated 90 kilometers of EMI data were collected along this inbound track. A frequency histogram of ice thickness measurements (n=957) along inbound track to Ice Station Belgica was constructed. During the journey out to the ice edge, the EM-31 was again deployed from the starboard A-frame to collect ice thickness data during transit. This transit began at approximately 69°55’S 93°45’W and extended to 68°50’S 90°12’W, a distance covered of 216 km. A digital surveillance camera was added to the instrumentation on the kayak to record images of the EM footprint (target ice) concurrent with the conductivity measurements. This video record was used in analyses to correct ice thickness determinations for varying ice concentration.
The Ice Thickness by Ship-borne Electromagnetic Induction (EMI) data provided plots of calibration values and fitted exponential models. Calibration of EMI conductance for instrument height was conducted using the open water method. Twenty two conductance measurements were acquired over open water (an ice lead at Palmer Station) at heights ranging from 4.2 to 0.6 meters, as acquired from an on-board distance ranger. All conductance values at heights over 1.4 meters (corresponding to the right flank of the theoretical curve) were fit to an exponential model. Y= 840.85e^(-.4947x), where y is conductance in millisiemens/meter, and x is instrument height (or distance to sea water). This equation was subsequently inverted to generate distance from seawater from conductivity measurements acquired in underway operations. A plot of calibration values and the fitted calibration curve can be found in the data set. 
