ALOS Data Users Handbook

Section 7 Overview of Processing AlgorithmsMfW= N ⋅Equation 7.3-11PRFWhen it calculates in time domain, the reference function time length (N D ; the number of points) is as followsby Equation 7.3-8.NDfW= ⋅ PRFEquation 7.3-12FddThen output valid data (N out ) is represented as follows.N OUT =N – N D Equation 7.3-13d) 2-look and 4-look ProcessingIn 2-look processing, it multiplying the reference function after FFT of N points, and then processes theaperture length (less than M points) in two looks.In 4-look processing, it multiplying the reference function after FFT of N points, and then processes theaperture length (less than M points) in four looks.To process in two looks or four looks in frequency domain is equivalent to having synthetic aperture lengthdivided into two or four. The resolution in the azimuth direction is degraded twice or four times, but specklenoise is improved by 1 / 4 = 1/ 2 in case of 4-look processing.e) ImagingSince the data after multi-look processing is a complex number, it coverts the data into a real number in eachlook and superimposes the corresponding pixels from all looks for imaging.7-32