Improvement of altimeter re-tracking performance utilizing the AGC-derived thermal noise level

This paper tries to establish a relationship between the AGC (Automated Gain Control) value and thermal noise level in satellite altimetry. The motivation is that: in the non-ocean situation, the noise floor level may be too high to be reasonable, especially in C-Band as we would see. This may occur from the ground surface echoes which enter the noise gate. In the re-tracking procedure if the improper noise level was adopted, some errors may be introduced. In these situations the noise level can be derived from the AGC value.