Abstract

A technique for remotely measuring atmospheric pressure was proposed in a previous paper¹. The technique is based on the fact that the difference between the optical pathlengths from a satellite to a ground target measured at two wavelengths is proportional to the atmospheric pressure at the target. The major error source is the differential pathlength measurement. The expected measurement accuracy is plotted in Figure 1 versus the satellite elevation angle. For a system operating at the fundamental (1.06 μm) and tripled (0.353 μm) YAG laser frequencies and with the laser pointing at nadir, the RMS pressure error (σ_p) is given by where σ_Td is the differential arrival time error. To obtain pressure accuracies at the millibar level, it is necessary to measure the differential arrival time with an accuracy of a few picoseconds or equivalently measure the differential pathlength with an accuracy of a few millimeters. If the ground target is a non-dispersive retroreflector and the laser pulse length is a few centimeters or less, millimeter level accuracy is feasible with current technology²,³. However, for the situation of greatest practical interest, the target is the ocean surface. Since the local surface height of the ocean can vary over a range of a few meters, the reflected pulse may be broadened to a few meters in length⁴. The problem is further complicated by the fact that the surface profile within the laser footprint is random and it is impossible to predict the mean return pulse shape in advance. As a consequence, it will be necessary to use less accurate suboptimal signal processing strategies to compute the differential pulse delay from the received signals.

© 1983 Optical Society of America