Techniques for real-time compression of RS-170 high resolution radar images

The article reviews and summarizes the results of a Norden study to evaluate real-time JPEG and wavelet compression of the RS-170 images taken from the display of the APG-76 high resolution SAR multimode radar system and transmitted to the ground. The significant advantages of this compression are twofold: the ability to retain large quantities of flight test images at better compression rates than that provided by the lossless GIF format; and the ability to transmit the images in near-real time from the ground station to a home base over standard telephone lines or even over a cellular phone. We have investigated several techniques, considered in the literature to be at or near the state of the art, for lossy compression of APG-76 radar images captured on the ground. We have achieved up to 15:1 in JPEG compression rates without significant picture degradation, if the images are first de-noised. If the pictures are not de-noised, then an 8:1 compression rate can be achieved with little degradation, but at 15:1, JPEG does degrade the images. Although in 1995 we could find no wavelet technique that bettered JPEG, we recently acquired a wavelet implementation that, at 15:1 compression, measured nearly 30 dB in peak signal to noise ratio (PSNR), and was 1.6 dB better than JPEG. This represents a long step towards the 3 dB PSNR improvement required to achieve 2:1 compression improvement over JPEG.