Simulation of Wind Gradient Errors in NROSS (Navy Remote Ocean Sensing System) Radar Scatterometer Data in a Simplified Geometry.
Final rept. May-Sep 86,
AIR/OCEAN REMOTE SENSING CO SAN DIEGO CA
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A set of simplified case studies is used to illuminate the effect of spatial gradients in normalized radar cross section NRCS on the accuracy of NRCS at NROSS Navy Remote Ocean Sensing System scatterometer NSCAT cell centroids, and at wind vector retrieval grid points displaced from the centroid. Values of linear and quadratic variables sx,y are estimated at the centroid and at a point displaced from the centroid of a parallelogram cell, using first the mean value S over the cell a nearest neighbor or binning approach and then a bilinear interpolation estimator Six,y. Isoparametric finite elements are used to take cell shape into account in the interpolation. At cell centroids with linear fields sx,y, errors are negligible using either S or Six,y. At cell centroids with nonlinear fields sx,y, errors using S and Six,y both approach 0.5 with interpolation errors being slightly less at spatial gradients of 0.1 dBkm. At displaced points with linear fields sx,y, errors using interpolation Six,y are negligible at all gradients, but error using cell means S exceeds 6 at gradients of 0.1 dBkm. At displaced points with nonlinear fields sx,y, error using interpolation Six,y approaches 2, while error using cell means S exceeds 7, near spatial gradients of 0.1 dBkm. The simulated errors associated with binning are large, and interpolation yields much better accuracy. Additional simulations using realistic wind fields and NSCAT Doppler cell patterns should be carried out to further quantify this component of the error budget.
- Active and Passive Radar Detection and Equipment