Showing papers by "Guifu Zhang published in 2000"
24 Jul 2000
TL;DR: In this paper, a method for retrieving DSD parameters and using them to calculate rain rate and the characteristic size was proposed, where the Gamma DSD with three parameters is capable of describing a broader variation in raindrop size distribution than an exponential distribution.
Abstract: Since the idea of differential reflectivity was first proposed the polarimetric radar technique has attracted great attention. Polarization radar measurements such as radar reflectivity (Z/sub HH/), differential reflectivity (Z/sub DR/) specific differential phase shift (K/sub DP/), and linear de-polarization ratio (LDR) have been successfully measured. These polarimetric measurements provide more information about precipitation and allow better characterization of hydrometeors. Z/sub DR/ and K/sub DP/ contain drop size information. Rain rate estimation from radar measurements is based on empirical models such as the Z-R relation, R(Z,Z/sub Dr/) and R(K/sub DP/). The empirical relations cannot give accurate results of estimation for various types of rain and drop size distribution (DSD). Accurate rain rate estimation requires detailed knowledge of rain DSD. In the past, rain DSD was commonly assumed to be an exponential distribution. Some observations, however, indicate that natural rain DSD contains fewer of both very large and very small drops than exponential distribution. The Gamma DSD with three parameters is capable of describing a broader variation in raindrop size distribution than an exponential distribution. The problem is how to retrieve the three parameters from limited radar measurements. The authors propose a method for retrieving DSD parameters and use them to calculate rain rate and the characteristic size.
3 citations
24 Jul 2000
TL;DR: In this article, a combination of detailed numerical simulations with radar and radiometer data demonstrated the feasibility of a dual-wavelength system for derivation of range-gated LWC along the beam path under a variety of realistic atmospheric conditions and suggested a technique for determining the presence of Mie scatterers.
Abstract: Transmitted radiation at W or K/sub a/-band is measurably attenuated by liquid water whereas at X-band is not; the range-differentiated difference between the returned signal is proportional to the amount of liquid present. The liquid water retrieval is confounded by the presence of hydrometeors, either ice or liquid, in the Mie-scattering size range (where the particle diameter is comparable to the radar wavelength). A dual-wavelength system consisting of Xand K/sub a/-bands is best suited for ground-based remote sensing of mixed-phase clouds. Factors such as Mie scattering, shallow clouds, and sensitivity of the X-band radar limited the LWC retrieval. A combination of detailed numerical simulations with radar and radiometer data demonstrated the feasibility of a dual-wavelength system for derivation of range-gated LWC along the beam path under a variety of realistic atmospheric conditions and suggested a technique for determining the presence of Mie scatterers. In this study, tri-frequency radar (X, K/sub a/, W-band) measurements collected during MWISP (Mount Washington Icing Sensors Project) were analyzed. Three different data sets exhibit distinct scattering characteristics: (a) Rayleigh scattering, (b) Mie scattering at W-band, and (c) Mie scattering at both W and K/sub a/-bands. The liquid water path estimates along the radar beam are compared with collocated microwave radiometer measurements. In addition, spatial and temporal variations in LWC and droplet size are retrieved.
1 citations