Updated Recommendation: Adopting Equivalent Radar Cross Section (ERCS) as the Radiometric Measurement Quantity for SAR Images
This thread is hosted by the SAR Subgroup of the CEOS Working Group on Calibration and Validation.
It deals with an updated recommendation concerning the Adoption of ERCS as radiometric measurement quantity for SAR Images
Without touching the core idea of the ERCS concept we have drafted this updated proposal for a CEOS recommendation:
Manfred Zink started a proposal Wed 31 Aug 2016
Adopt ERCS (update) Closed Thu 8 Sep 2016
The pixel intensity in a SAR image results from the convolution of the complex target reflectivity function with the complex SAR system impulse response function.
Up to now, radiometric calibration was based on reference point targets whose radar cross section (RCS) was precisely known at boresight and at the SAR center frequency. The existing approach neglects two problems:
- Due to the convolution, the pixel intensity results from an “averaging” over frequency (range) and angle (azimuth).
- The pixel intensity does not only depend on amplitude (i.e., RCS), but also on the phase response of the target. Two targets with identical RCS may appear differently bright in a SAR image.
With modern high-resolution and high-accuracy SAR systems these problems become more severe and have to be considered during radiometric calibration. Instead of the reference target RCS, an “average” of the complex-valued (amplitude and phase) target response over the system bandwidth and angular range of the synthetic aperture has to be used. It is proposed to call this measurement quantity equivalent radar cross section (ERCS).
Calibration of SAR systems and annotation of SAR products shall use the equivalent radar cross section (ERCS).
|Agree - 3|
|Abstain - 3|
|Disagree - 3|
|Block - 3|
Wed 31 Aug 2016
This proposal sounds better than the previous attempt. However I worry about your statement about "averaging".
I propose to refer to an equivalent ideal isotropic point target and to take care of the deviation from ideal by convolution.
Björn Döring (DLR)
Thu 1 Sep 2016
The new proposal captures the core idea: Distinguish RCS from what we actually measure.
Wed 7 Sep 2016
To end this story in a positive way I will support your proposal with the recommendation to find a better word for the new quantity and let the world know about the proposed new SAR calibration algorithm. Piece of cake for DLR/ESA.