Refining electromagnetic bias estimation [sea surface height measurement]

Sea surface height measurements using remote sensing instruments have become increasingly accurate as satellite altimetry technology has matured. Early satellite missions had altimetry errors on the order of tens of centimetres. As these errors have been eliminated, the electromagnetic (EM) bias has become increasingly significant. The latest satellite missions, TOPEX/Poseidon and Jason-1, have EM bias error budgets of 4.2 cm and 2.5 cm, respectively. The purpose of our research has been to investigate methods to reduce the EM bias estimation errors to the sub-cm level. Most current EM bias models create estimates from geophysical properties that can be measured remotely. Typically these parameters are wind speed and significant wave height. The current operational model for the TOPEX/Poseidon and Jason-1 satellite missions is of this type. The operational model uses nonparametric methods to improve the accuracy of the estimates. In addition to improving the bias estimates, the latest operational model has shown a stronger agreement between satellite and tower EM bias models. Combining nonparametric techniques with the wind speed and significant wave height has created the most accurate empirical models to date. However, the amount of variance in the bias requires new methods to improve bias estimates. We made a preliminary study based on the angular dependence of the EM bias. Theoretical scattering models indicate that the bias is dependent on incidence angle, which may allow improved operational correction of the bias using a wide-swath altimeter.