Effects of finite beam width and wind field divergence on Doppler radar measurements: Simulations

This paper describes the effects of wind field divergence on Doppler radar measurements. Incompressible fluids inherently have a horizontal divergence component in the presence of vertical gradients in the vertical motion. We present simulation studies which show that the radial velocity, measured from a vertically directed beam, can show a bias due to divergence created by the finite beam width effect. The bias can be of the order of a few centimeters per second, depending on beam width, divergence, and altitude. Furthermore, an indirect effect on the cross spectrum, which is typically used in multiple-receiver wind profiling algorithms, will be presented. Divergence causes a deformation of the isodops, thus distorting the Doppler sorting process implicit in the interferometric crossspectrum calculation.