A Non-MLE Approach for Satellite Scatterometer Wind Vector Retrievals in Tropical Cyclones

Satellite microwave scatterometers are the principal source of global synoptic-scale ocean vector wind (OVW) measurements for a number of scientific and operational oceanic wind applications. However, for extreme wind events such as tropical cyclones, their performance is significantly degraded. This paper presents a novel OVW retrieval algorithm for tropical cyclones which improves the accuracy of scatterometer based ocean surface winds when compared to low-flying aircraft with in-situ and remotely sensed observations. Unlike the traditional maximum likelihood estimation (MLE) wind vector retrieval technique, this new approach sequentially estimates scalar wind directions and wind speeds. A detailed description of the algorithm is provided along with results for ten QuikSCAT hurricane overpasses (from 2003-2008) to evaluate the performance of the new algorithm. Results are compared with independent surface wind analyses from the National Oceanic and Atmospheric Administration (NOAA) Hurricane Research Division\u27s H*Wind surface analyses and with the corresponding SeaWinds Project\u27s L2B-12.5 km OVW products. They demonstrate that the proposed algorithm extends the SeaWinds capability to retrieve wind speeds beyond the current range of approximately 35 m/s (minimal hurricane category-1) with improved wind direction accuracy, making this new approach a potential candidate for current and future conically scanning scatterometer wind retrieval algorithms

High Quality Wind Retrievals For Hurricanes Isabel And Fabian Using The Seawinds Scatterometer

Hurricanes Isabel and Fabian offer an unprecedented look at tropical cyclones. With the availability of two identical instruments, temporal sampling was as frequent as 6-12 hours. Utilizing the SeaWinds Scatterometers\u27 ability to make simultaneous active and passive measurements, High quality wind and rain retrievals were performed for 8 storm passes. Passive rain estimates are used to quantify both the attenuating and scattering effects of precipitation, which can then be used to correct the active wind measurements. The high resolution of the retrievals allows for feature identification, while a binary rain mask removes pixels too contaminated for wind speed retrieval. Wind results compare well with surface models produced by the Hurricane Research Division of NOAA, and rain rates show great spatial similarity to SSM/I F13 and F15 data sets