Pulse Compressed RADAR (Level 1)

 

Level 1 data includes the pulse-compressed radar data which includes both low-gain (3 μs) and high-gain (10 μs) pulses.

The data are hosted in the following directory:

/AGAP/DataLevel_1/RADAR/PulseCompressed

This folder is divided into a number of subfolders according to survey lines.  The survey lines have the following naming convention:

L###  –   “Long lines”.  These are north-south lines spaced at 5km

T#####  –  “Tie lines”.  These are east-west lines spaced at 33km

F#####  –  “Fuji lines”.  These are the continuation of selected tie lines to the west (Dome Fuji) side of the main grid.

V#####  –  “Vostok lines”.  These are the continuation of selected tie lines to the east (Lake Vostok) side of the main grid

Each subfolder contains a number of radar files in matlab format.  The naming convention is best illustrated by an example:

F13b_L290-209_HGe4.mat

In this case, “13b” is the flight number (typically, two survey lines were flown in each flight), “L290” is the survey line number, and “209” is the file number (each file represents ~3.5km of along-track distance).  The file number is always the 3 digits following the only dash in the file name.  The suffix “HG” indicates that this is a high gain (10 μs) pulse, and “e4” indicates that this is the 4th channel.

To facilitate locating files of interest, each survey line is displayed as a .jpg image with file numbers displayed at the top of the echogram.  The browse images are located in:

/AGAP/DataLevel_1/RADAR/DecimatedSAR_images

These files contain the following variables:

BedPixel Sample index representing the bed return. Data were picked on horizontally decimated (10x) migrated data and then interpolated back onto the present data, which have full horizontal resolution. Size: 1×2500
ComputerTime Timestamp, in seconds. This is close to GMT and GPS time but differs slightly from both. Size: 1×2500
FlightElev Aircraft elevation, relative to WGS84. Size: 1×2500
HG/LG Complex data matrix. Size: 9000×2500 (HG) or 8160×2500 (LG)
Icethick Ice thickness of the bed return, in meters. Data were picked on horizontally decimated (10x) migrated data and then interpolated back onto the present data, which has full horizontal resolution. Value differs from VertScale(BedPixel) because “Icethick” was defined using a variable surface given by “SurfElev”, while “VertScale” uses the mean surface within each file. Size: 1×2500
Lat Latitude, in decimal degrees. Size: 1×2500
Lon Longitude, in decimal degrees. Size:1×2500
SurfElev Elevation of the ice surface. Value is derived from interpolation of the Bamber DEM. Size: 1×2500
TWT Two-Way Time, in seconds. Size: 9000×1 (HG) or 8160×1 (LG)
VertScale A vertical scale (in m) for the radar matrix, computed using “c_air”, “c_ice”, “surfind”, and no firn correction. Size: 9000×1 (HG) or 8160×1 (LG)
X Easting in km, in a Lambert Conic Conformal projection (parallels: 77S, 83S, origin: 80S, 80E, false easting: 2000km, false northing: 2000km). Size: 1×2500
Y Northing in km, in the same projection. Size: 1×2500
breakind Index of the sample representing the direct arrival. “TWT” is measured relative to this sample. No correction was made for delay-time of direct arrival. Value used was 1280 (HG) or 440 (LG).
c_air Velocity of radio waves in air, in m/s. Value used was 3×108.
c_ice Velocity of radio waves in ice, in m/s. Value used was 1.68×108.
dy_air Vertical pixel size in air (m), computed using “c_air” and “samp_int”.
dy_ice Vertical pixel size in ice (m), computed using “c_ice” and “samp_int”.
f Center frequency of the radar system. Value was 150 MHz.
samp_int Sample interval of the radar system (s). Value used was 8.333×10-9.
surfind Index representing the mean location of the surface return, as determined from “SurfElev”, “FlightElev”, and “c_air”.

Known Issues:

  1.  Most of the data were processed with an older version of the gps processing scripts which linearized the timestamps and occasionally failed to properly fix 24hr offsets.  The final version of the data will use a newer version of the gps processing scripts in which these problems have been fixed.  A minority of the present release was processed with the newer scripts; these are listed in the accompanying spreadsheet.  Horizontal offsets in position data between the new and old scripts are typically on the order of 8m.

Unknown Issues:

If you discover any other problems in this dataset, do not hesitate to contact us.