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\f1\b \cf0 These data are double precision numerical arrays that contain geolocated, unprocessed, 1GHz multi-polarization ground penetrating radar amplitudes as a function of travel-time. 
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File names use the following convention: SNEX20_BSU_GPR_Raw_pE_GPR_DDMMYYYY_XX.nc \
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Data files contain the trace header (metadata) and the raw, multiplexed GPR traces. The following applies to all files:\
Coordinate Projection: UTM Zone 12 N \
Elevation: m above sea level (EGM96) \
Uncertainty in horizontal position is roughly 70 cm. This follows from adding the DGPS HDOP (50 cm) and uncertainty in the sled location (50 cm) in quadrature. \
The standard deviation of surface elevation within this 70 cm radius is roughly 1 cm. \
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\f1\b The initial 20 rows of this array are the trace header. Each row is described below:
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1. The Trace Number: 1:n traces \
2. The Channel Number: 1) HH polarization; 2) HV polarization\
3. The Nominal Frequency of the GPR Antennas [MHz] \
4. The Time Sample Interval in nanoseconds [10^-9s]: This information, along with row 5, can be used to configure the travel-time axis (e.g. [0:row4:(row5-1).*row4 = TWT axis) \
5. Number of Samples per Trace: This information can be used to configure the travel-time axis \
6. GPR array midpoint geometry for position dead reckoning [m] (Reltaive to Tx1) \
7. The Horizontal Antenna Separation (offset) of the GPR channel \
8. Time of day in UTC seconds \
9. X coordinate of shot gather bin center [m] \
10. Y coordinate of shot gather bin center [m] \
11. Z coordinate of shot gather bin center [m] \
12. Distance along transect of shot gather bin center [m] \
13. Speed of the Radar Array [m/s] \
14. Heading of the shot gather bin center [degrees] \
15. Slope of Snow surface [degrees] \
16. X coordinate of GPR antenna midpoint [m] \
17. Y coordinate of GPR antenna midpoint [m] \
18. Z coordinate of GPR antenna midpoint [m] \
19. Distance along traverse route of GPR antenna midpoint [m] \
20. Heading of GPR antenna midpoint [degrees]\
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The unprocessed, multiplexed GPR traces are appended beneath row 20 of the trace header. The data matrix is typically 300 rows. \
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\f1\b Data Collection:\
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\f0\b0 \cf0 Radar imagery was acquired using the Sensors & Software pulseEKKO PRO 1 GHz ground penetrating radar with a multi-channel adapter. One transmitting antenna (horizontal polarization) and two receiving antennas (horizontal and vertical polarization) were configured using the multi-channel adapter. The two-channels have the same antenna separation but differ in polarization; channel 1 is HH, channel 2 is HV, the antenna separation is 25 cm. The radar was towed behind a snowmobile and acquired data continuously. The spatial sample interval of the radar imagery is a function of the snowmobile speed. GPS positions were acquired concurrently with the radar acquisition using the Juniper Systems Geode antenna. Information derived from the GPS positions (speed, heading, slope) is included in the trace header. \
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\f1\b \cf0 Data Processing:\
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\f0\b0 \cf0 Radar amplitudes are unprocessed in a multiplexed format. The individual radar images of each channel must be called from the data array by the channel number. Because the GPR was operated continuously, GPS positions and GPR traces acquired while the snowmobile was stationary have been removed. GPS positions recorded at 1 Hz were then interpolated to the radar traces (acquired at ~60 Hz) using piecewise cubic hermite interpolating polynomials and a process of dead reckoning was applied to relocate the GPS positions to the reflection midpoints of the multi-polarization GPR antennas. }