A comparison of scatterometer-derived wind data over tropical cyclones as determined from ERS-2 and QuickSCAT data

Active microwave scatterometers have been available to the tropical forecaster for a number of years and have greatly enhanced the forecaster's ability to evaluate surface winds over tropical cyclones in the data poor regions of the tropical oceans. The latest new scatterometer, Sea Winds, was launched on board NASA's QuikSCAT satellite during the summer of 1999. This sensor was designed as a "quick" replacement to the NASA Scatterometer (NSCAT) that lost power in 1997 after only one year of operation. The Sea Winds scatterometer joins the European Space Agency (ESA) Earth Remote Sensing Satellite-2 (ERS-2) scatterometer which has been in operation since 1995 in supplying real time data to the tropical forecaster. The two scatterometers operate at slightly different frequencies and the surface wind data sets use different methods to determine the proper wind directions from the ambiguity solutions. In this paper comparisons are made between these different methods in order to determine any significant differences in the scatterometer-derived surface wind data over the tropical cyclones. In addition the sensitivity of each method to distinguish strong winds with high gradients within potentially heavy convective bands are examined.