RETRIEVAL OF OCEAN WAVE SPECTRA FROM SENTINEL-1 SAR IMAGE USING FAST FOURIER TRANSFORM

• Main Author: Amalia, Jessica
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/43367
• Institution: Institut Teknologi Bandung

The purpose of this study is to extract wave characteristics from Sentinel-1 Synthetic Aperture Radar (SAR) satellite imagery and visualize it into one wave map, validate the extracted wave characteristic to detect the limitations. Extraction of wavelength and wave direction is done in 1000 × 1000 pixel SAR image, which is 100 km2. The image is divided into 100 equal-sized tiles. Digital number of each pixel in the image data represents the ocean wave surface roughness. Two-dimensional Fast Fourier Transform (FFT) is applied to convert the data from spatial domain into frequency domain to be spectral image. Two-dimensional FFT generate the frequency domain information from digital number of Sentinel-1 SAR satellite imagery. The extracted ocean wave spectra is shown in polar plot of ocean wave spectra with an arrow that indicates wave direction. The polar plot contains the information of calculated wavelength and wave direction. The dominant frequency in spectral image is used to calculate wavelength and wave direction to produce 87 of 100 × 100 pixel tiles excluding data from land. The retrieved wave directions and wavelengths of 87 tiles are arranged into one wave map. Comparison of calculated wave characteristics and secondary data from European Centre for Medium-Range Weather Forecasts (ECMWF) produce insignificant result because there is no similarity neither relation of those data. The limitations of wave characteristics retrieval are satellite performance that affects data availability, natural condition of ocean surface waves determines the existence of distorted wave pattern, and technical term including the buildup process of extraction program and validation of calculated data.