DIGITAL ORTHORECTIFICATION OF SPACE-SHUTTLE COASTAL OCEAN PHOTOGRAPHS

Causes of geometric distortion in space shuttle imagery of targets on the Earth's surface are analysed. A mathematical model formulating the geometric distortion caused by the incidence angle and the local azim uth angle are derived, and the corresponding image processing scheme f or orthorectification is developed. The method is used for rectifying two sequential space shuttle photographs of continental shelf waters o ff the coast of south-west Africa taken by the space shuttle Atlantis during mission STS-36 in March 1990. The results indicate that mismatc hes between coastline images in unrectified photographs and a standard map have been almost eliminated in the rectified photographs, and the two photographs also match each other very well. Application of the s patial Fourier transform to oceanic internal wave packet signals at a selected test site yields directional wavenumber spectra, from which c omponents of the wave held, the dominant wavelength, and propagation d irections are determined. Comparisons between wavelengths and propagat ion directions derived from the spectra of the same site on the rectif ied and unrectified photographs show that the average rectification ra tio for wavelengths reaches 20 per cent, and for propagation direction s 10 per cent, including a 20 per cent rectification ratio for the cro ssing angle of the internal waves.