Methodology for Aligning and Comparing Spaceborne Radar and Ground-Based Radar Observations

Abstract

Direct intercomparisons between space- and ground-based radar measurements can be a challenging task. Differences in viewing aspects between space and earth observations, propagation paths, frequencies, resolution volume size, and time synchronization mismatch between space- and ground-based observations can contribute to direct point-by-point intercomparison errors. This problem is further complicated by geometric distortions induced upon the space-based observations caused by the movements and attitude perturbations of the spacecraft itself. A method to align measurements between these two systems is presented. The method makes use of variable resolution volume matching between the two systems and presents a technique to minimize the effects of potential geometric distortion in space radar observations relative to ground measurements. Applications of the method are shown that make a comparison between the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) reflectivity measurements and ground radar. A method has been developed that aligns space radar (SR) data with ground radar (GR) observations for the purpose of cross validation of the two systems. Accurate and precise alignment of observations requires meticulous attention to detail that is important in minimizing measurement uncertainties between the two systems so that quantitative analysis of bias, attenuation, and characterization of the microphysical properties of the atmospheric medium can be made along space radar beams via ground-based measurements. Reconciliation of the difference in resolution volumes between the two systems, due to size and orientation, and the need to align ground and space radar points have been previously investigated: Bolen and Chandrasekar (1999, 2000a) used a correlation-shift procedure and a momentbased technique, respectively, for final alignment of points. The work of Bolen and Chandrasekar was motivated by the need to evaluate attenuation correction in space radar echo returns. An independent procedure, motivated by the need to match reflectivity, was presented by Anagnastou et al. (2001), who provided a comprehensive study comparing space radar with ground radar reflectivity measurements. The method presented in this paper uses a variable volume matching scheme with a polynomial technique for alignment of SR and GR points. A theoretical modeling of potential