Jean-Paul Vinson

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...

A New Shipborne Microwave Refractometer for Estimating the Evaporation Flux at the Sea Surface

Abstract After a brief description of humidity measurement and a short presentation of methods of microwave refractometry for evaporation flux, a new X-band refractometer system is presented. Based on a new design and a new material for the microwave cavity, it does not need calibration for refractive index variations because of its reduced thermal time constant. The new device has been combined with a sonic anemometer and traditional mean meteorological measurements on a 12-m shipborne mast. It has been found to be very efficient for obtaining humidity fluctuations and fluxes in the CATCH 97 (Couplage avec l’ATmosphere en Conditions Hivernales) and FETCH 98 (Flux, Etat de la mer et Teledetection en condition de fetCH variable) experiments under various wind and stability conditions. The inertial subrange is of very high quality. To first order, the evaporation flux and refractive index flux are very similar. In extreme meteorological conditions, such as those encountered during CATCH, the sensible heat f...

BASTA: A 95-GHz FMCW Doppler Radar for Cloud and Fog Studies

Doppler cloud radars are amazing tools to characterize cloud and fog properties and to improve their representation in models. However commercially-available cloud radars (35 and 95 GHz) are still very expensive, which hinders their widespread deployment. In this study we present the development of a lower-cost semi-operational 95 GHz Doppler cloud radar called BASTA for Bistatic rAdar SysTem for Atmospheric studies. In order to drastically reduce the cost of the instrument a different approach is used compared to traditional pulsed radars: instead of transmitting a large amount of energy for a very short time period (as a pulse), a lower amount of energy is transmitted continuously. In the paper we show that using specific signal processing technique the radar can challenge expensive radars and provide high-quality measurements of cloud and fog. The latest version of the instrument has a sensitivity of about -50 dBZ at 1 km for 3 s integration and a vertical resolution of 25 m. BASTA radar currently uses four successive modes for specific applications: the 12.5 m vertical resolution mode is dedicated to fog and low clouds, the 25 m mode is for liquid and ice mid-tropospheric clouds and the 100 m and 200 m are ideal for optically-thin high-level ice clouds. We also highlight the advantage of such a radar for calibration procedures and field operations. The radar comes with a set of products dedicated to cloud and fog studies. For instance, cloud mask, corrected Doppler velocity and multi mode products combining high sensitivity mode and high resolution modes are provided.