# SAR Calibration Questions and a tool with snappy

Hello all!
I am an engineering student. Actually as my sophomore term project, I had to develop a tool for SAR Calibration. I used SNAP for this purpose. Then I discovered Snappy and so decided to write a script to automate the process. I wanted to know the correctness of the things I am doing for calibration. It would be great to get some inputs from you people.

I’m a super beginner at this so I am not sure of the correctness of my work. I read a lot of research papers for the methodology used for calibrating SAR. I used the ‘Calibration Constant’ value for calibration.
Can you kindly check if the method that I am following is correct or not? I’m using the steps as follows:

1. First I locate the corner reflector by giving the coordinates to the program.

2. Then I make a 128*128 subset around the point target for further calculations.

3)Then for background intensity correction, I take the mean of the background intensity by taking 4 subsets of the 128128 figure. I subtract the mean background intensity of the 128128 pixel square from it to get the value of Ip. (Ip is mean background corrected intensity)

1. Then I calculate Radar Cross Section given the length of corner reflector, and the frequency.

2. From Radar Cross Section (sigma) and other values like Ip, I calculate the calibration constant.

3. I have also added plots of intensity around corner reflectors in Python. I get a sharp peak at the location of corner reflector.

Is this good enough at a basic level? I plan to add more features like interpolation for better results. Based on the data which we were provided, I’m getting a reasonable value of Calibration Constant. Can you suggest me something that I might be missing?

Here’s a link to the GitHub repository for the project: https://github.com/WVik/sar-calibration-using-snappy

One paper which I read for Point Targets: http://aulavirtual.ig.conae.gov.ar/moodle/pluginfile.php/513/mod_page/content/28/MirkoPanozzoZenere.pdf

Hi WVik,

thanks for choosing SNAP and snappy for your implementation. Looks like interesting work, even though I have no knowledge about SAR data and how to work with it.

I’ve moved your post to the S1tbx category. I think it is better suited there, because your post does have only thematic questions and not real development questions.

Hi WVik,

Your attempt to finding a Calibration Constant is appreciable.

As you chosen 128*128 subset around a defined point., please be concern in the following…

1. The angular measures (provided to you as) values associated with Camera view point to Four corners of scene.
2. According to these values (calibration parameters) sigma, beeta, gamma can be computed.
3. For every subset of 128*128 these values may not apt for the execution.
I think, a formula which defines angular changes at four corners of each subset may solve it…
All the best