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As Doppler lidars designed for environmental remote sensing move from ground-based platforms to airborne and space-based platforms, issues related to processing surface and near-surface returns are of increasing interest. In the case of Doppler wind lidars, the surface returns can be useful in calibrating the velocity estimates along the associated lines-of-sight, assuming the surface is not moving relative the Earth's frame of reference. This assumption may not hold for water surfaces and in that case, the Doppler signal might be useful in estimating surface currents (rivers and oceans). Whether the water returns are used for calibrating wind lidars or making water current measurements, the confounders of accurate observations include waves and the independent motions of overlying aerosols in the layer adjacent to the surface (LAS).
As part of a program to develop calibration/validation techniques for space-based Doppler wind lidars, a series of laboratory and airborne experiments are being executed. At NASA/MSFC a water slide has been constructed and used with a 2μm coherent lidar to study the signal from water surfaces having varying velocities, roughnesses and turbidities. The angle of the water slide to the lidar beam can also be varied to test the theoretical function of signal return vs. angle of incidence. Results of those experiments have provided input to the design and execution of a set of airborne 2μm coherent lidar experiments conducted in February and March 2002 out of Monterey, CA. The airborne system (funded by the US Navy and the Integrated Program Office of the NPOESS) collected data to be used to develop signal processing algorithms that can discriminate between the water surface motions and the velocity of the wind blown aerosols that are combined in the signal from just one range gate. This paper will report on both sets of experiments.
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