Planetary delay-Doppler radar and the long-code method

Delay-Doppler mapping continues to be the most widely used imaging technique in radar astronomy. Various methods have been devised to partition echoes in delay-Doppler space for different degrees of echo dispersion (as quantified by the overspreading factor F). These include the standard interpulse/intercode methods for underspread (F < 1) or slightly overspread (F > 1) echoes, intrapulse methods for grossly overspread echoes, and the long-code method for the intermediate case of moderate overspreading. Here the standard and long-code methods are compared, treating various aspects of experiment design, data analysis, and calibration. Recent and future applications of the long-code method are also reviewed.