Roman Arbiol 
  
5 PRODUCT GENERATION 
The AeS-1 software runs on a network of standard PCs. The software is predominantly written in IDL and runs on Linux 
Operative System. 
5.1 SAR PROCESSING 
The hardware configuration at the ICC consists of 5 processing lines, each with two DLT drives and 13 slave PCs 
connected to the Ethernet. 
At each string the DLT containing a 130 km. long track is read, divided into segments of 0,5 GB with 25% longitudinal 
overlap and distributed among the slave PCs. Each segment takes up to 6.5 hours to process on a standard Pentium II 
450 MHz microprocessor with 256Mb RAM and 9 Gb disk. On average, a track is processed every 32.5 hours. The 
combined throughput of the 5 strings is a track every 6.5 hours. A central PC with a FoxPro DB dispatches jobs to every 
processing line and takes care of the archival and data management. 
The first step in processing consists of the reconstruction of the two complex images (intensity and phase) from the raw 
data signal of the two antennas. The aircraft motion is corrected at this stage. The two complex images are then co- 
registered for computing the interferogram on a pixel-to-pixel basis. The interferogram is then obtained by multiplying 
the first image with the complex conjugate of the second. The interferogram represents the phase difference due to the 
elevation of the terrain and is expressed (“wrapped”) modulo 2m. The “phase unwrapping” process computes the 
absolute phase difference by adding 2m if discontinuities of 2m are detected in the interferogram. The AeroSensing 
method for phase unwrapping is a hybrid least squares combined with region growing algorithm. 
All these processes are automatic and involve long computations in the Fourier space. The output is an image coded in 
slant range and an unwrapped phase interferogram. 
5,2 GEOCODING 
The phase unwrapping process can fail for several reasons. That is to say, there are discontinuities that are not well 
resolved, as in the case of the layovers and shadows, and terrain returning low signal (i.e. rivers). These errors must be 
removed by editing the phase manually. 
The elevations are then computed from the absolute phase after phase calibration. Two methods can be used: the first 
takes the elevation of a corner reflector and assigns it to the corresponding phase at this point (the phase becomes 
"calibrated"). The second method is iterative and is based on the interferograms of the contiguous tracks covering the 
same area from opposite sides. The process iterates until a solution that minimizes the differences in elevation is found. 
This method is very time-consuming but it does not require any ground control or operator interaction. 
Once the elevations are known, tracks are geocorrected and assembled together in a mosaicking process. As mentioned 
earlier, the SAR processing part runs in batch and can be managed by one operator. However, the geocoding requires 
manual intervention. A group of 12 operators with two supervisors and a project leader operate the configuration at the 
ICC. 
53 RADIOMETRIC CORRECTIONS 
Because the side looking geometry, the radar images are brighter at the nearest side and darker at the far range. A 
similar effect occurs with the relief: slopes oriented to the radar beam are brighter. Since a map sheet is formed by 
mosaicking consecutive opposite tracks, a radiometric compensation process is applied to equalize the radiometry 
(Fig.1). 
  
26 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000.