ENVISAT radar altimeter tracker bias

In the past, errors in the determination of the orbit were dominant in radar altimeter missions, but technical advances have improved the orbit accuracy and hence, other sources of error have become more important. Sea-state bias is now the main source of error and can be divided into three sea-state dependent errors: skewness, electromagnetic bias, and tracker bias. We estimated the magnitude of the third term, by retracking ocean waveforms from ENVISAT RA-2. The retracking algorithm used is based on Maximum Likelihood Estimation. Tracker bias shows a seasonal and geographical dependence related to the distribution of significant wave height (SWH) and time origin differences.We estimated amean value of 0.13±0.07%SWH. Temporal and regional dependent errors are introduced when using a linear retracker processing approach.