A Multipurpose Radar Simulation Package: QuickBeam

J. M. Haynes, R. T. Marchand, Z. Luo, A. Bodas-Salcedo, G. L. Stephens
2007 Bulletin of The American Meteorological Society - (BAMS)  
contrast, lower-frequency radars, such as those used in the NEXRAD system, operate closer to 3 GHz and are sensitive primarily to precipitation. Measurements of backscattered power are typically converted to the meteorological unit of radar refl ectivity, expressed in decibels (dBZ). Retrievals of quantities like cloud water content or precipitation rate then typically follow from these refl ectivity measurements. Since CloudSat observations provide detailed information on the structure of
more » ... e structure of cloud systems on a global scale, this information is especially valuable for evaluation of climate and weather prediction models. To compare modeled clouds to the new observations being made by CloudSat, it is useful to have a tool that converts modeled clouds to the equivalent radar refl ectivities measured by the CPR. QuickBeam is a user-friendly radar simulation package that performs this function and is freely available to the meteorological community. Th ough developed with CloudSat in mind, it simulates a wide range of meteorological radar systems, including both spaceborne and ground-based systems, operating at frequencies between L-band and W-band (1 to 110 MHz). THE SIMULATOR. Reflectivity simulations. To simulate a profi le of radar refl ectivities with Quick-Beam, the user specifi es a spectrum of mixing ratios of any number of hydrometeor species, including cloud and precipitation particles, as depicted in Fig. 1 . Th ese mixing ratios may be derived from sources such as numerical models or fi eld observations. Each species of hydrometeor can have its own distribution, phase, and mass-diameter relationship. Th e user matches each of these mixing ratios to one of the built-in distributions, including modifi ed gamma, exponential, power law, lognormal, and monodisperse. Th e user must also input a profi le of temperature and ambient relative humidity or use one of the built-in tropical or midlatitude profi les. Th is environmental sounding is used to calculate the scattering and absorption by atmospheric gases and thus the gaseous attenuation of the radar beam. S ince launch in April of 2006, CloudSat has provided the fi rst near-global view of the three-dimensional structure of clouds from space. CloudSat, part of NASA's aft ernoon A-TRAIN constellation of satellites, fl ies a 94-GHz cloud radar that takes near-nadir measurements of the vertical structure of both cloud and precipitation systems from a sunsynchronous orbit approximately 705 km above the Earth's surface. Observations of the variability of clouds over the surface of the Earth and through the depth of the atmosphere are creating a continually growing database that is useful for a broad range of meteorological applications, including evaluation of numerical prediction models and development of new and better convective parameterizations. Meteorological radar systems transmit a pulse of electromagnetic energy and measure the backscattered energy that is returned to the radar dish. Th e backscatter occurs as a result of interactions with cloud and precipitation particles, as well as intervening atmospheric gases like water vapor and oxygen. The way electromagnetic radiation interacts with these particles is dependent on the frequency of the radiation, and the type, size, orientation, and distribution of the particles. Th e CloudSat cloud profi ling radar (CPR) operates at 94 GHz and is therefore especially sensitive to cloud-sized particles. At this frequency, attenuation by water vapor is nonnegligible and attenuation by precipitation can be signifi cant. In
doi:10.1175/bams-88-11-1723 fatcat:jywzu7lqebal5dqknu7idqmpea