Thursday, 13 February 2003: 3:15 PM
Wind fields derived from SAR during storm conditions
Our primary objective is verification of high-wind speed algorithms for RADARSAT SAR measurements. Our focus is the Hurricane Erin (2001). Surface wind data from Special Sensor Microwave/Imager (SSM/I) and QSCAT were used for the verification/ validation of SAR-derived winds. Particular attention was given to the maximum estimated winds. COAMPS winds from the operational US Navy outputs provided further verification data. These were not enhanced by the assimilation of observational data. Independent buoy data were also used. QSCAT and SSM/I data provide excellent data coverage, although their wind speeds have a maximum limit and cannot provide information about the extreme winds. In doing data comparison, there is a large scatter in the results for the remotely sensed winds and the model collocations. More analysis is needed in order to determine if this is due to the excessive time lag between the data samples. There seems to be an anomaly in the results of SAR-derived RADARSAT winds for the data from 13 September, when RADARSAT winds disagree with other data sets. More data are required in order to find if this is a systematic problem. Comparison with the in situ data showed agreement in wind speeds and directions.
A second objective is to demonstrate a methodology that can generate high-spatial resolution gridded vector wind fields, on synoptic time-scales. Using data from the Labrador Sea Deep Convection Experiments (LSDCE), this is accomplished using optimal interpolation (OI) to blend satellite wind data from ERS-2 and NSCAT scatterometers and TOPEX-Poseidon and ERS-2 altimeters with NWP (numerical weather prediction) model wind estimates. NWP model wind fields are produced on a 25-degree resolution grid. OI correlation functions and variances are derived from remotely sensed data. The resultant OI fields are used to validate SAR-derived vector winds from RADARSAT-1 images, collected LSDCE. Further validation of SAR-derived winds is also based on in situ ship-based winds.