CoAuthors

Doug Vandemark (University of New Hampshire, USA); Ngan Tran (CLS/Space Oceanography Division, France); Desai Shailen (JPL, USA)

For radar altimeter missions, precise retrievals of geophysical parameters are often estimated by a so-called “retracking” scheme that fits an analytical model to the measured waveforms. Recently new TOPEX retracked datasets provided by JPL are available for evaluation, including a set of retracted products by (Maximum Likelihood Estimator) MLE3 that estimates three parameters(range, wave height, and return power) and MLE4 that estimates four parameters (the slope of the waveform trailing edge that is related to off nadir angle in addition to the three) (Thibaut et al., 2010).
New empirical sea state bias (SSB) models corrected for the range bias associated with ocean surface waves will be produced based on the new TOPEX retracked datasets. These sea state bias (SSB) models were developed in terms of the latest geophysical data record corrections (e.g. orbits, tides, wet/dry path delays, and so on) with the retracking revised range, wave height and wind speed data by several intensive retracking schemes, i.e. MLE3, MLE4 and etc.
The SSB model creation methods involve using a multi-year ensemble of yearly SSB correction models produced using direct sea level anomaly data coincident with altimeter wind speed and wave height (2D SSB), or wind speed, wave height and wave period (3D SSB). In the 3D case the wave period data are from global wave model hindcast data of an NCEP wind forced WAVEWATCH III model run in IFREMER. New SSB models based on retraced datasets will be derived for both TOPEX Side B and Side A and for both Ku and C band, and will be assessed against current TOPEX GDR SSB models in terms of a set of metrics, such as the tandem Jason/TOPEX orbit datasets, ascending vs. descending passes, 3DSSB vs. 2DSSB, and direct based SSB models vs. collinear difference based SSB, and others.