We applied a P-band filter to reduce the impact of interference in the P-band imagery. However, there may be a small amount of p-band interference still present in the data. In addition, in some cases, the P-band filter is not effective. Because the P-band filter may adversely impact the calibration of the data, we provide both the filtered and unfiltered files.

This data was acquired in ping-pong mode, which means that the XTI antennas were alternately used to transmit and receive this effectively doubles the baseline (potentially increasing the height accuracy), but decreases the SNR. Either the normal or the doubled baseline can be used in processing the data. Usually, we use the long baseline, but if there are problems, we use the normal baseline. The long baseline was used in processing this data. This data was collected in the XTI1 mode, which means that C-band data was collected using two C-band Vertically polarized antennas separated vertically on the airplane. We interfere the imagery from these two antennas to estimate the ground surface topography. We also measured the CVV radar backscatter (sigma0), and projected this to the estimated ground surface topography (making corrections to the radiometry (antenna pattern and pixel size), based on the local incidence angle. If L-band and P-band data were sampled at the same rate, we also project the compressed stokes matrix data from these bands to the ground surface topography, and make radiometric adjustments to the antenna pattern and pixel size based on the local incidence angle. If they are not sampled at the same rate, then they are left in the slant range projection.

The AIRSAR DEM product is in meters and represents the elevation of the terrain above a spherical approximation to the WGS-84 ellipsoid. The radius of this approximating sphere is calculated using a so-called "peg point".

Common errors in the imagery:

It is not unusual for the processed DEM to suffer from multi-path effects that we currently cannot correct. These artifacts manifest themselves as vertical along track banding (of a few meters) in the topography.

In areas of low correlation (sometimes associated with uncompensated motion, but usually in areas that are shadowed or subject to layover), we sometimes have difficulty unwapping the phase, which results in holes in the imagery.

Uncompensated motion can effect the calibration of the imagery (looks like cross track streaks). Usually this occurs if the flight was very turbulent, or if the motion data was not properly tracking the motion of the DC-8.

If we have sufficient tie points, we may be able to detect errors in the geolocation of the data relative to the map data. In that case, we will update the location of the imagery, but we will note in this letter if the correction was necessary. It will be noted below under Tie-pointing information.