Comparison of Airborne and Spaceborne 95-GHz Radar Reflectivities and Evaluation of Multiple Scattering Effects in Spaceborne Measurements

Abstract

This paper provides an evaluation of the level 1 (reflectivity) CloudSat products by making use of coincident measurements collected by an airborne 95-GHz radar during the African Monsoon Multidisciplinary Analysis (AMMA) experiment that took place in summer 2006 over West Africa. In a first step the airborne radar calibration is assessed. Collocated measurements of the spaceborne and airborne radars within the ice anvil of a mesoscale convective system are then compared. Several aspects are interesting in this comparison: First, both instruments exhibit attenuation within the ice part of the convective system, which suggests either the presence of a significant amount of supercooled liquid water above the melting layer or the presence of wet and very dense ice. Second, from the differences in the observed reflectivity values, a multiple scattering enhancement of at least 2.5 dB in the CloudSat reflectivities at flight altitude is estimated. The main conclusion of this paper is that in such thick anvils of mesoscale convective systems the CloudSat measurements have to be corrected for this effect, if one wants to derive accurate level 2 products such as the ice water content from radar reflectivity. This effect is expected to be much smaller in nonprecipitating clouds though.

Potential of microwave observations for the evaluation of rainfall and convection in a regional climate model in the frame of HyMeX and MED-CORDEX

“…In this study, we also use measurements from an airborne 95 GHz Doppler cloud radar named RASTA (Protat et al, 2004;Bouniol et al, 2008;Protat et al, 2009;Delanoë et al, 2013). During the HyMeX SOP-1, RASTA was installed on-board an aircraft which carried out 18 flights (about 50 flight hours) .…”

Differential absorption radar techniques: surface pressure

“…This model has been used in the external calibration of CloudSat (Tanelli et al, 2008) and the Radar Aéroporté et Sol de Télédétection des Propriétés Nuageuses (RASTA) (Bouniol et al, 2008). Mean-square surface slopes were taken from the empirical relationship described by Wu (1990), using the microwave dielectric constants for seawater modeled by Klein and Swift (1977).…”

On the observation of unusual high concentration of small chain-like aggregate ice crystals and large ice water contents near the top of a deep convective cloud during the CIRCLE-2 experiment

“…This instrument (described in details by Protat et al, 2004) is the airborne combination of two instruments: a multi-beam (three antennas pointing downward in three non-collinear directions, including one near-nadir pointing angle) 95-GHz Doppler cloud radar named RASTA (Radar SysTem Airborne, see Bouniol et al, 2008 andProtat et al, 2009 for further details) and a triple-wavelength (355, 532, and 1064 nm) and dual-polarization (532 nm) backscatter lidar. Unfortunately, during the 26 May flight the lidar was not operational, so in this study only the Doppler cloud radar observations are used.…”

“…The vertical and horizontal resolutions of the data are 60 m and 150 m, respectively. The blind distance is 180 m. The RASTA radar has been calibrated using ocean surface backscatter at 95 GHz (Bouniol et al, 2008). The sensitivity of the airborne cloud radar during CIRCLE-2 was −31.5 dBZ at 1 km range.…”