WHALES: an optimized retracker for satellite radar altimeter waveforms in sea state applications

The latest version of the European Space Agency's Sea State Climate Change Initiative database adopts a dedicated algorithm (retracker) 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 measurement physics, particularly the weighted analysis of residuals in the cost function. Moreover, the impact of WHALES on the sea state database is analyzed in terms of noise reduction and scatter index with in situ data, with a particular focus on the coastal zone, where WHALES primarily improves data quality and quantity compared to previous approaches. We found that valid data records increased by 30% at 5 km from the coast after applying the retracker discussed here.