An FPGA-based method for non-linear LADAR image scanning correction and enhancement

Abstract

Upon acquisition of a non-corrected LADAR image, a noticeable sinusoidal spatial distortion is present in the image. Resonant horizontal scanners must oscillate at high frequencies (in the kilohertz), and therefore they must scan in a sinusoidal pattern. As a result, the laser beam scans slower at the left and right edges of the object and scans the fastest at the center of the object. When the pixels are sampled at a constant rate with respect to time, as it is most commonly done, the resulting image will be noticeably compressed at the center and expanded at the left and right side. The design and testing of an FPGA-based embedded method for correction of this non-linear distortion upon acquisition is the focus of this paper. A working prototype has been currently obtained. This method incorporates dynamic adjustment of the sampling rate upon acquisition. Instead of sampling at a constant rate with respect to time, it is the goal of this system to sample at a constant rate with respect to position (of the deflected laser beam). The sampling rate with respect to time must therefore vary in a non-linear fashion. This is easiest if it is done within an FPGA that controls the acquisition of the data through the ADC (Analog to Digital Conversion), as we show in this work.