Differential‐frequency Doppler weather radar: Theory and experiment

Abstract

[1] To move toward spaceborne weather radars that can be deployed routinely as part of an instrument set consisting of passive and active sensors requires the development of smaller, lighter-weight radars. At the same time, the addition of a second frequency and an upgrade to Doppler capability are essential to retrieve information on the drop size distribution (DSD), vertical air motion, and storm dynamics. One approach to the problem is to use a single broadband transmitter-receiver and antenna where two narrowband frequencies are spaced apart by 7-10%. Use of Ka-band frequencies (26.5-40 GHz) provides adequate spatial resolution with a relatively small antenna. Moreover, the differential reflectivity and mean Doppler signals in this band are directly related to the median mass diameter of the snow and raindrop size distributions. We present in the paper theoretical calculations of the differential reflectivity and Doppler for several frequency pairs including those proposed for the Global Precipitation Mission (GPM) at 13.6 and 35 GHz. Measurements from a zenith-directed radar operated at 9.1 and 10 GHz are used to investigate the qualitative characteristics of the differential signals. Disdrometer data taken at the surface, just below the radar, show that the differential signals are related to characteristics of the raindrop size distribution. The stability of the DSD estimation procedure is tested using a simulation. The results indicate that reasonably stable estimates of the particle size distribution are feasible with a [31.5 GHz, 35 GHz] combination as long as a large number of independent samples are obtained.

Properties of light stratiform rain derived from 10‐ and 94‐GHz airborne Doppler radars measurements

“…Basic limitations of these methods are the errors incurred because of errors in deduced vertical winds and the effect of the turbulence. Meneghini et al [2003] has explored the possibility of using the difference of Doppler velocities at 13.6 and 35 GHz, which is not affected by the vertical air motion, to improve the RSD estimation.…”

A Feasibility Study for Simultaneous Estimates of Water Vapor and Precipitation Parameters Using a Three-Frequency Radar

“…Another difference between E 1 and E 1s is that an estimate for the latter quantity can be obtained from surface scattering measurements in regions of low pathintegrated water vapor. This is analogous to the "surface-reference technique," in which measurements of the surface return in rain-free areas are used to estimate path attenuation in the presence of rain (Tian et al 2002;Meneghini et al 2004). In particular, an estimate for the differential path attenuation from cloud and hydrometeors follows directly from (21), where the term P s ( f u , r s ) Ϫ P s ( f l , r s ) is approximated by surface returns measured in clear conditions.…”

“…To analyze errors in the estimate of differential water vapor given by (17) we construct a simple stratiform storm model derived from disdrometer-measured raindrop size distributions (Meneghini et al 2003). For each size distribution we compute the median mass diameter D 0 (mm) and number concentration N t (m Ϫ3 ).…”

Preface to special section: Remote Sensing of the Earth's Environment by Microwave Radiometers and Radar

“…Tanner and Riley [2003] describe the design of two new high-stability microwave water vapor radiometers along with a performance evaluation. Radar papers include a technique to measure rain from space in the paper by Meneghini et al [2003], and Zhang et al…”