Abstract

Space-based lidar systems are being designed^1–3 to measure accurately atmospheric wind profiles. Space-based lidar systems use an orbiting spacecraft with a pulsed laser source and measure the Doppler shift between the transmitted and received frequencies to estimate the atmospheric wind velocities. If a significant return from the ground (sea) is possible, the spacecraft speed and height are estimated from it and these results and the Doppler shift are then used to estimate the wind velocities in the atmosphere. It is expected that at the proposed wavelengths, there will be enough backscatter from the aerosols⁴ but there may not be significant return from the ground. So a coherent (heterodyne) detection system is being proposed for signal processing because it can make best use of low ground returns. However for a heterodyne detection scheme to provide best results, it is important that the receiving aperture must be aligned properly and for the proposed wind sounder, this amounts to only a few microradians tolerance in alignment. It is suspected⁵ that the satellite motion relative to the ground may introduce errors in the order of a few microradians in the spherical coordinate angles of the direction of returning radiation because of special relativity. We are interested in addressing this issue and developing analytical expressions for the location and direction for the return radiation, Doppler shift in frequency and the amount of tip for the receiver aperture. Also we are interested in the diffuse scattering direction at the ground, which does not require any tipping of the receiver aperture. All the three cases of retro-reflection, specular reflection and diffuse scattering by the ground should be treated though retro-reflection and diffuse scattering are more important.

© 1995 Optical Society of America