CEOS SAR Workshop, Ulm, Germany, 27-28 May 2004

Summary: Geometry and Radiometry Session

Chairmen: M. Shimada (JAXA/EORC), C. Buck (ESA/ESTEC)

There were four presentations in this session.

D. Small of Univ. of Switzerland presented the paper “Geometric Calibration and Validation of ASAR Imagery”. By changing the sampling window start time (SWST) he achieved sub-pixel order geometric accuracy in the range direction. This might be a good calibration method.

S. Cote of CSA presented the paper “RADSARSAT-1 Radiometric Performance Maintained in Extended Mission” and showed that Radarsat-1 has been working properly over seven years and continues to provide consistently high accuracies in both radiometry and radiometry. The evaluation is being conducted using the Amazonian rainforest and active radar calibrators, the former of which is the reference calibration standard recommended from the 21st CEOS CAL/VAL plenary to the CEOS plenary and approved at the previous CEOS in Colorado Springs.

P. Meadows of BAE Systems in the UK presented the paper “ERS-2 SAR Performance: The 2004 Update” and showed that ERS-2 in single gyro mode achieves the significantly high performances of the radiometry of sub-decibels and a geometric precision of the order of 20 metres. The Amazonian rainforest is being used for antenna pattern characterization. Due to the one gyro operation, the Doppler frequency of the received signals deviate widely. Thus, the repeat pass interferometric application becomes less probable. Only the data which have less than one PRF range of Doppler is applicable for the user distribution.

I. Cummings of British Colombia University Canada presented the paper “Bi-static SAR Processing Using Non-linear Chirp Scaling”. In order to process the SAR data acquired in bi-static mode, which has different curvature and chirp rates in comparison to the original SAR data received in terms of pure backscatter, a non-linear chirp-scaling algorithm was developed. The image is formed successfully while the peak gain of the image is reduced by around one decibel. The image formation has some further improvement in reducing the peak power decrease.

Seed Questions

  1. What geometric accuracy should be achievable using only the information from recent satellites (Doppler, attitude data, position data, star tracker)?
  2. What radiometric accuracy should be achievable using only the information from recent satellites?

Discussion

To the question of what the best achievable geometric accuracy that current and future SARs might attain, it was assessed that existing systems can provide a geometric accuracy of better than 15 metres. The example of the X-SAR on board the Space Shuttle being the most accurate. Using the well-tuned beam characteristics of the X-SAR and calibrated attitude using the star tracker, an accuracy of a few metres was achieved. To the similar question of the achievable radiometric accuracy, the current SAR, Radarsat and ERS-2 achieved values are of the order of half a decibel. Use of the target in the Greenland is slightly problematic since the target has variation of the brightness (Radarsat experiments). The monitoring of the radiometry and geometry is very important to the user application. Thus, the reporting of the space agency as the annual activity was proposed.