On the optimum radar beam angle to minimize statistical estimation error of momentum flux using conjugate beam technique

Abstract

Multi beam experiments were conducted using MST radar at Gadanki (13.5°N, 79.2°E) to examine the dependence of statistical estimation error of momentum flux of wind fluctuations on radar beam angle. We find that an optimum angle between 9°-12° with sufficient integration minimizes the error at a value nearly equal to the irreducible error in the troposphere. The balance between the angle dependence of horizontal velocity measurement precision and spatial stationarity seems to decide the optimal beam separation. We also show that the radial velocities obtained by Doppler beam-swinging method must be appropriately corrected for anisotropy of VHF radio wave scatterers, particularly for lower beam angles, which are found to get affected substantially. Momentum flux of wind fluctuations estimated using low radar beam angles need a longer time of integration to reduce statistical error to its minimum value.