Spaceborne L-band InSAR Example: PALSAR Data
PALSAR InSAR Processing
Two coherent acquisitions of PALSAR data were acquired over the Los Angeles area of southern California. These data were from consecutive orbital cycles (46 days) and represent a coherent pair which can be used to do SAR interferometry (InSAR). Details of this data are shown below:
| Site | Los Angeles, California |
| Source | ALOS / PALSAR |
| Acquisition Time | 06:20 GMT (22:20 local -1 day) |
| Acquisition Dates | 30 June 2006 and 15 August 2006 (GMT) |
| Radar Mode | L-HH, single polarization |
| Center Incidence Angle | 38.7 degrees (nominal) |
| Range to Center (approx) | 870 km |
| Ground Pixel Spacing | 7.5 m, 3.3 m (range, azimuth) |
| Ground Resolution | 10.3 m, 6.5 m (range, azimuth) |
| Perpendicular Baseline | approximately 3 km |
The three images to the left provide an overview of the results. The first image displays one of the data collections as a SAR image. Of note in these data are some significant radio interference, (which has not been filtered out) and some obvious aspect effects. The aspect effect (also known as the "Burbank effect" after observations in early SEASAT data) is an enhanced backscatter for urban regions that happen to align with the radar flight. The enhancement is due to the increased number of dihedral and trihedral scattering centers properly aligned with the radar.
Using only the two SAR images, one can detect non-coherent changes between the images. The data can be combined in many ways to make the changes more visually obvious. An example of a 2-color change detection image from this PALSAR data is shown here.
The second image to the left is the interferometric coherence. Due to the longer wavelength (than C-band) and the relatively high bandwidth (28MHz), good coherence is obtained in urban regions even with a perpendicular baseline of over 3 km and a repeat period of 46 days. The third image shows the differential phase between the two passes, where we have used an elevation model to remove phase signals due to topography. No obvious ground motion is evident in this result, however, upon close observations, one can observe residual phase associated with large man-made structures not captured in the elevation model used. These are particularly obvious in the downtown LA area, as well as along Wilshire Boulevard and in Century City. (These details may not be obvious in these low resolution versions of the images, however, this animated GIF illustrates the residual phase associated with uncaptured urban structures within the DEM.)
For more information, contact David Cohen