WHALES: An enhanced retracker for satellite radar altimeter delay-only waveforms in sea state applications

The European Space Agency’s Sea State Climate Change Initiative adopted a physical retracking algorithm to reprocess two decades of satellite altimetry measurements and provide long time series of significant wave height in the global ocean. This paper describes the main characteristics of this algorithm, called WHALES, and analyzes the impact of algorithm choices on the estimates of significant wave height, particularly the statistically weighted analysis of residuals in the cost function. Moreover, the performance of WHALES is analyzed in terms of noise level and error statistics using buoy data as reference, with a particular focus on the coastal zone. We found that valid data records increased by 30% at 5 km from the coast when switching from the standard MLE retracker to WHALES. • The WHALES algorithm estimates wave height from radar altimetry signals. • The impact of algorithm choices on measurement physics is analyzed. • Validation shows noise reduction and improved data quality in coastal zones.