Metocean Comparisons of Jason-2 and AltiKa-A Method to Develop a New Wind Speed Algorithm

• Published in: Marine geodesy 2015-09, Vol.38 (sup1), p.437-448
• Main Author: Quartly, G. D.
• Format: Article
• Language: English
• Subjects: Algorithms; AltiKa altimeter; Altimeters; band; Climate; Crossovers; Geodesy; histograms; Marine; Noise levels; Ocean waves; Roughness; sigma0; Statistics; Surface waves; Velocity; wave height; Wind; Wind speed
• ISSN: 0149-0419; 1521-060X
• DOI: 10.1080/01490419.2014.988834

As well as range, the AltiKa altimeter provides estimates of wave height, H s and normalized backscatter, σ 0 , that need to be assessed prior to statistics based on them being included in climate databases. An analysis of crossovers with the Jason-2 altimeter shows AltiKa H s values to be biased high by only ˜0.05m, with a standard deviation (s.d.) of ˜0.1m for seven-point averages. AltiKa's σ 0 values are 2.5-3 dB less than those from Jason-2, with a s.d. of ˜0.3 dB, with these relatively large mismatches to be expected as AltiKa measures a different part of the spectrum of sea surface roughness. A new wind speed algorithm is developed through matching a histogram of σ 0 values to that for Jason-2 wind speeds. The algorithm is robust to the use of short durations of data, with a consistency at roughly the 0.1 m/s level. Incorporation of H s as a secondary input reduces the assessed error at crossovers from 0.82 m/s to 0.71 m/s. A comparison across all altimeter frequencies used to date demonstrates that the lowest wind speeds preferentially develop the shortest scales of roughness.