NSF COLDEX Delay Doppler Radar Profiles of Southern Dome A, Antarctica

<div>
<p>Underway coherent radar data, transformed from the along track space domain to the wavenumber domain to reveal the Doppler response of signals, indicates the direction of returning echoes. This delay-Doppler processing can be used to constrain the degree of scattering or specularity of the target surfaces (<a href="https://doi.org/10.1029/92JE00742">Tyler et al. 1992</a>, <a href="https://doi.org/10.1016/j.icarus.2019.02.037">Michaelides and Schroeder, 2019</a>).</p>

<p>These MARFA 60 MHz radar data have been processed using a delay-Doppler approach to obtain three views of the echo data: one pointing 11° ahead of the aircraft, one pointing 11° behind the aircraft, and one directly below the aircraft. The data is organized with individual transects as separate netCDF4 files. Delay Doppler processing operated on a 1 m sampled version of the <a href="https://doi.org/10.15784/601768">raw data</a>, using a 1000 m aperture. The fast time sampling of the product is 0.2 µsec, and the along track sampling is 500 m. </p>

<p>The maximum value in each delay doppler bin was found. The channels were scaled using the noise floor. The data are processed using only the right aircraft wing high gain channel (MARFA channel 6) to widen the across track beam pattern and reduce the effect of aircraft roll.</p>

<p> X and Y GPS locations of the aircraft in EPSG 3031 (Antarctic Polar Stereographic) coordinates are included. </p>

<p>Browse images in PNG format (*_specularity.gmt) show the following:</p>
<ol>
<li>An RGB version with the nadir view loaded into blue, and the sum of the fore and aft views loaded into the red and green channels, with the tracked surface and the bottom of the stratigraphic unit traced.</li>
<li>A grayscale view of the sum of the fore and aft views.</li>
<li>A grayscale view of the nadir view.</li>
</ol>

<p>A tab delimited ASCII table (*_specularity.gmt) is included for each transect with the following columns:
<ol>
<li>x: easting coordinate in EPSG 3031 projection [meters] </li>
<li>y: northing coordinate in EPSG 3031 projection [meters] </li>
<li>surface[s]: time delay to the surface [microseconds] </li>
<li>base_specular[s]: time delay to base of the specular englacial unit [microseconds] </li>
<li>deep_scattering_zone[s]: time delay to 1 microsecond into scattering basal unit in [microseconds] </li>
<li>slope: slope of the transition the base of the specular englacial unit </li>
<li>slope: srf_spec: signal to noise ratio of the detected surface return [dB]. Note for the high gain channel this will be usually saturated</li>
<li>dsz_power: signal to noise ratio of the echos in the basal unit [dB]</li>
</ol></p>

The netCDF4 files are structured as follows:

<pre><code>netcdf TRANSECTNAME_dd_analysis.nc {
group: channels {
dimensions:
fast_time = 320;
direction = 3;
aperture = UNLIMITED;
variables:
double fast_time(fast_time=XXX);

double direction(direction=3);

float normalized_max_in_bin(aperture=XXX, fast_time=320, direction=3);
:_ChunkSizes = 1U, 320U, 3U; // uint

double X(aperture=XXX);
:units = "m";
:_ChunkSizes = XXXU; // uint

double Y(aperture=XXX);
:units = "m";
:_ChunkSizes = XXXU; // uint

}

// global attributes:
:increment = 500L; // long
:aperture = 1000L; // long
:transect = "TRANSECTNAME";
:processor = "denoise1";
:channel = 6L; // long
}</code></pre>
</div>