Coherent ladar imaging of the SEASAT satellite retro-reflector array using linear-FM chirp waveforms and pulse-compression

摘要

Coherent ladar imaging of satellite retro-reflector arrays is analyzed to determine some of the potential capabilities of coherent ladar systems for long range imaging. The satellites are at mega-meters of slant range and are basically angularly unresolved assuming a nominal one meter telescope used at a laser wavelength of 1.064 μm corresponding to a 281,625 GHz center-frequency. A coherent ladar may have a selectable waveform ranging from single nanosecond pulses through tone-pulses, but the imaging waveform considered here is the linear-FM chirp pulse-compression ladar waveform, which consists of a series of frequency chirps over a long period of time. The linear-FM chirp return is pulse compressed digitally using several possible approaches. Image reconstruction follows basic ISAR algorithms in forming a "range-resolved Doppler and intensity" (RRDI) image. A retro-reflector ring on the SEASAT satellite is used to illustrate the ladar's capability, although we spin the satellite faster than the true rotation rate to demonstrate waveform resolution. Several other useful algorithms as (multi-chirp) range-time-intensity (RTI matrix) range-bin summation and segmented-spectrum frequency-bin summation are also discussed. A covariance matrix calculation is applied to the RTI matrix and also to the segmented-spectrum matrix for the extraction of additional target information.