Developing Of A Model For Measuring And Extracting Ocean Surface Current Patterns From Radarsat-1 Sar And Altimeter Data

Remote sensing technology can be used to collect large scale data on ocean areas and provide precise information on ocean surface dynamics and atmospheric interactions. Many other ocean surface features can be detected by utilizing this technology. In this study, a robust model was developed based on Doppler frequency that utilizes RADARSAT-1 SAR imageries in measuring and extracting ocean surface current patterns such as velocity and direction. The SAR data used in the study were acquired during the period 20-31 March 2005 and supported with altimeter data of GEOSAT-2 and TOPEX/POSEIDON also collected at the same period. The study area is located between the longitudes 102°50'00'' to 103°40'00'' East and latitudes 5°25'00'' to 5°40'00'' North, at the east coast of Kuala Terengganu. The area was divided into four main parts comprising the onshore, fieldwork area, midshore, and offshore area witch is about 98 km. off the coast. The model was applied on the SAR image at three different modes (Wide- 3, High extended- 6 and Standard-2) with the objectives of 1) comparing between the modes and identifying the appropriate mode for coastal current modeling, 2) modeling the spectral intensity of the SAR data in the study area covering the onshore, midshore, offshore and the fieldwork area, 3) examining the impacts of tide and wind speed and direction on surface current movements on the coastal water of Kuala Terengganu, Malaysia and 4) investigating the impact of the Doppler frequency shift and incidence angle on the sea surface current detection. The results of the study were validated using TOPEX/POSEIDON satellite altimeter data for the same period and in situ data measurements taken with AWAC instrument during the fieldwork. The study did not only find that the incidence angle in SAR had an effect on the surface current patterns but also that, there is a strong relation between the image backscatter and Doppler frequency. It was again discovered that the velocity and direction of the current changed through the period of the study according to the changing of Doppler frequency shift used in the model to extract the sea surface current velocity and direction from the three SAR images. At the onshore area, the velocity of current extracted based on the Wide-3 mode varied between 0.22 m/s to 0.25 m/s with the average of 0.24 m/s, while based on the Standard-2 mode it varied between 0.52 m/s to 0.65 m/s with an average velocity of 0.56 m/s. The analysis of the spectral intensity of the SAR data in different modes showed variation among the four areas. The spectral intensity values were low in the onshore as against the high values recorded in the offshore. Regression analysis was used to establish the coefficient of determination between the velocities extracted from SAR data and the AWAC in situ measurements. The analysis showed a fairly high correlation between them of R² of 0.753 with the highest velocity under 0.27 m/s, R² of 0.726 with the highest velocity under 0.32 m/s and R² of 0.863 with the highest velocity under 0.75 m/s. These results were obtained from the regression between the AWAC data and the RADARSAT-1 SAR in Wide-3, Extended High-6 and Standard-2 modes respectively. It can be said that the investigation between different radar systems should be used as geomantic tool to investigate water current movement.

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