This is not about the SNAP toolbox per se. Please help me out though. I am a novice in this area of SAR data processing. I need to understand the basics to implement a code. I am working on a project concerned with calculating the calibration constant(K). The metadata of a sentinel 1 product(dual-Pol) shows K to be 1.000000e+00. However the values that my code gives are way beyond this value.
- Is this the actual calibration constant as shown in metadata or not? If yes, how is this calculated in the first place? Can SNAP itself calculate the absolute calibration constant?
- I also have a quad-Pol RADARSAT-2 data but it does not contain K value in the metadata. How do I verify my code for such products.
It would be really helpful if someone could explain the process of finding K in SNAP or any other source(an existing software maybe) so that I can debug and test my code.
For Sentinel-1A, the absolution calibration constant (K) is indeed 1.0 as given in the product meta data. The calculate the radar cross-section of a distributed target or point target, please see the ESA document ‘Radiometric Calibration of S-1 Level-1 Products Generated
by the S-1 IPF’ available at https://sentinel.esa.int/documents/247904/685163/S1-Radiometric-Calibration-V1.0.pdf.
Thanks a lot! Is there a place where I could get the values of calibration constants of these SAR satellites like S1, RADARSAT-2, etc.
Hi, in general the best place to find calibration constants is in the product meta data (in case they vary with time period for example). This is the case for Sentinel1 A & B.
The calibration constant (K) is not sonething that you can compare from a a mission to another.
In general, K depedends on the imaging system (instrument + processor) configuration which is different for each mission.
In general, you should estimate the RCS over a point target for which the RCS is known. The calibration constant is the difference between the measured - expected value (in the average sense).
Once the calibration constant has been determined for a specific mission, you can calibrate the data to e.g. sigma nought which is intercomparable.