Oct 15, 2003
Product ID Site - Flight Line Length (km) Bandwidth (C,L,P) Mhz
ts1598 Fraser90-1 40 40-40-20
 
URL to backscatter image: http://blacks.jpl.nasa.gov/PRECISION/ts1598.jpg
 
The standard AIRSAR data files are included on the CD-ROM/DVD along with browse GIF image files.  Please note that due to large file sizes, CD-ROM’s may be too small to hold all the data, and the data might be spread across multiple discs.  For more information about what these files are and the format, please visit the http://airsar.jpl.nasa.gov web page.

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.

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.

This data was acquired in a mixed bandwidth mode. However, we have processed the imagery so that the data will be co-registered. The resolution and swath are dependent on the bandwidth, so the smaller bandwidth data has a worse resolution than the higher bandwidth data, and we have not processed some of the swath from the smaller bandwidth data.
Tie-pointing information
5 Ground control points (GCPs) for the ts1598 product were obtained from the SRTM DEM 1 arcsecond scale maps, which have approx 5 m contour intervals. We made our best effort to find GCP's that span the cross-track dimension of the imagery. The offset between the datum of the maps and the WGS84 ellipsoid for this product was 0.00000 meters. This offset was applied when calculating the absolute height of the AIRSAR DEM. Therefore, the height values of the AIRSAR DEM will differ from the height values of the topographic maps by this amount.

During tie-pointing, we applied the offset between the datum of the maps and the WGS84 datum that AIRSAR uses, and compared these heights with the heights read off the AIRSAR DEM.

We then calculated the height offset/tilt that produces a DEM in best agreement with the map values. At this stage, the geo-location of the GCP's is not considered.

The c-band height offset applied was 25.9236 m, and the phase correction corresponding to the tilt correction was 7.81009 cycles.The l-band height offset applied was 13.7785 m, and the phase correction corresponding to the tilt correction was 0.982732 cycles.

The mean and standard deviation of the height difference between the map values and the image values is -0.829053 m and stdev =2.19026 m at c-band.The mean and standard deviation of the height difference between the map values and the image values is 0.293213 m and stdev =7.40537 m at l-band.

We corrected the horizontal position of the imagery by approximately AVG_DISTANCE: 19.226750 m based on a comparison with map coordinates

You may want to apply additional GCPs as part of your analysis.

Additional Comments

Due to a byte slip by the digital subsystem during acquisition, and the resulting misalignment between interferometric channels, we were not able to process imagery after line 5300.
There was substantial vertical motion by the DC-8 platform during this datatake, which may introduce errors in the DEM (up to 10 m on average). However, the calibration of the data should be good.
If you have any questions, please contact Bruce Chapman at:
Tel: 818-354-3603
Fax: 818-393-5285
E-mail: bruce.chapman@jpl.nasa.gov