Pixel level fusion techniques for SAR and optical images: A review

Image Fusion is a process of combining two or more images into a single image which is more informative and hence more useful from an interpretation point of view. With the rapid development of different remote sensing satellites capturing information from the earth by sensing energy in different portions of the electromagnetic spectrum, complementary information about the area captured by different satellites is available. A fusion of these images is much more helpful in different remote sensing applications than that of single sensor image data. This paper discusses the necessity of fusing synthetic aperture radar (SAR) and optical imagery. A survey is presented for various pixel level approaches used for the fusion of SAR and optical images. Quality metrics used to evaluate the performance of a fusion algorithm, are briefly introduced and visual as well as quantitative evaluation of basic component substitution and wavelet-based fusion approaches is presented for the fusion of RISAT-1 SAR and Resourcesat-2 multispectral data. Finally, the review concludes that there is scope for further research of fusion of SAR and optical images due to various microwave and optical sensors with the improved resolution being launched regularly.