Similarities and differences of SAR derived wind fields using two different methods: the local gradient and the continuous wavelet transform methods
Stefano Zecchetto(3), Di Tomaso Simona(4), Nirchio Francesco(1) and De Biasio Francesco(2)
(1) Agenzia Spaziale Italiana, Loc. Terlecchia, 75100, Matera, Italy
(2) Istituzione Segnalazione e Previsione Maree, Palazzo Cavalli, San Marco 4090, Venezia, Italy
(3) Consiglio Nazionale delle Ricerche, Corso Stati Uniti 4, 35127, Italy
(4) Simona Di Tomaso
Consorzio Innova, Recinto II Fiorentini,10, 75100 Matera, Italy
We present a discussion about the performances of two different methods to derive the wind field from SAR images without a-priori information on wind direction. These are the method based on the Continuous Wavelet Transform (CWT2) (Zecchetto and De Biasio, 2002) and a method based on the estimation of the local gradient (Kock, 2004).
The input data are full resolution ERS images, they are averaged several times until the space resolution is reduced up to 200 m or so, to filter out unwanted oceanographic features like wind waves or swell.
The CWT2 method extracts the backscatter signatures in the SAR image likely related to the structure of the marine atmospheric boundary layer; it derives the aliased wind direction from direction of the major axis of the cells-like detected structures and then resolves the ambiguity looking at the backscatter distribution inside them.
The local gradient method divides the image into sub images depending on the space grid over which the wind is requested; then it defines four image operators which are applied on the imagery to produce a map of valid points on which the local gradient directions are computed. The local wind direction is orthogonal to the more frequent gradient direction. The wind intensity is computed applying the CMOD4. The results are compared for validation with satellite scatterometer winds. A preliminary use of wind data in oil spill detection activity is also presented.
The results presented are relevant to ERS images taken over the Mediterranean Sea.
Kock, W., Directional Analysis of SAR Images Aiming at Wind Direction, IEEE Transaction on Geoscience and Remote Sensing, vol. 42 No. 4 , 2004
Zecchetto, S. and F. De Biasio, On shape, orientation and structure of atmospheric cells inside wind rolls in two SAR images , IEEE Trans. of Geoscience and Remote Sensing, vol. 40, n. 10, 2257-2262, 2002
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,