Airborne optical air turbulence sensor for high-precision vector wind measurement: Scanning strategies

Under NASA sponsorship, Coherent Technologies, Inc. (CTI) has designed and built the transceiver, and is developing the scanner, for an airborne scanning optical wind sensor. A scanning, single-aperture architecture was chosen for the CTI/NASA Optical Air Data System. Techniques for vector wind estimation from LOS scalar velocity measurements, the choice of scan patterns and wind models for various applications, and various other considerations that led to this decision are discussed within. Estimating wind vectors requires taking multiple scalar velocity projections alone non-coplanar lines of sight. This can be done from several apertures to the same field point, or vice versa, and may involve either fixed or scanned beams. For a scanning, interpolative system, the choice of scan pattern and wind model are intimately related. Typically, more complicated models require more intricate scans to separate the fit parameters. Vector wind estimation error can arise from a variety of sources. Several effects can contribute to LOS velocity measurement noise, some of which stem from the scan itself. Inaccuracies in the scan deflection vector can also introduce error. Error can enter if the wind field model is not sufficiently sophisticated to account for small-scale turbulence. Finally, a surface-flux measurement technique is introduced, which promises to be less sensitive to noise and turbulence than wind vector estimation.