Design and Implementation of an Active Calibration System for Weather Radars

摘要

Pulsed weather radars can be used to depict meteorological conditions such as rainfall rate and wind velocity. These quantities are calculated from measurements of reflectivity, mean radial velocity and velocity spread using echo signal samples from weather targets. These radar measurements derive from modified radio frequency (RF) echo signal parameters, including amplitude, frequency and phase, returned to the radar from the weather target. RF scattering and propagation effects modily echo signal parameters. Bias and variance in the weather signal parameter estimates naturally influence the accuracy of all subsequent quantities produced. For meteorological products to be as accurate as possible, the amount of uncertainty in each estimated quantity must be minimized. If radar system parameters are not accurately known, the reflectivity estimate will be biased. A well-controlled calibration process is therefore critical to reduce the bias of the reflectivity estimate. This thesis presents the design and implementation of one such calibration system, specifically for use with the MWR-05XP (a Mobile Phased-Array Pulse-Doppler X- band Weather Radar first created at the Naval Postgraduate School in 2005), although the general results are applicable to all radars. The calibration system presented is an active, external calibrator intended to verily end- to- end radar system performance. Within this thesis, a background of the radar calibration problem along with the research objectives for this specific project and related works are introduced and discussed. The theory behind the operation of weather radar (how the three principle quantities are measured and related to signal parameters) is also presented and explained. The density function for precipitation, relation between signal correlation and velocity spread, and fundamentals of weather radar signal parameter estimation are given.