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Titre : Recent Developments in Remote Sensing of Water Vapor using Microwave Radiometry from Ground-Based and Airborne Platforms
Nom du conférencier : Steve Reising
Son affiliation : Professeur, directeur du Microwave Systems Laboratory, Colorado State University, USA
Laboratoire organisateur : Labex IPSL
Date et heure : 05-03-2014 10h00
Lieu : UPMC - 4, place Jussieu - Paris 5e - IPSL - Tour 45-55, salle 219
Résumé :

Ce séminaire est organisé dans le cadre du Labex L-IPSL.

Precision satellite altimeters monitoring sea level on a global basis for more than two decades include nadir-viewing, co-located 18-37 GHz microwave radiometers to measure wet-tropospheric path delay. Due to the size of the surface fields of view at these frequencies, the accuracy of wet path retrievals is substantially degraded within 40 km of coastlines, and they are not available over land.  A viable approach to improve this capability is to add wide-band, high-frequency window channels in the 90-180 GHz band, thereby achieving finer spatial resolution for a limited antenna size. Colorado State University (CSU), in collaboration with the Caltech/NASA Jet Propulsion Laboratory (JPL), has designed, developed and produced a wide-band airborne radiometer, combining high-frequency millimeter-wave window channels at 90, 130 and 168 GHz, Jason-series microwave channels at 18.7, 23.8 and 34.0 GHz, and temperature- and water vapor-sounding channels for validation in the 118 GHz and 183 GHz bands, respectively.  This instrument will assess the spatial variability of wet-tropospheric path delay on 10-km and smaller spatial scales, and provide an airborne cal/val instrument for the SWOT and Jason-CS missions suitable for long-duration, high-altitude flight on the Global Hawk UAV. 

Ground-based microwave radiometers have been used for many years to measure total column water vapor and its profile.  An advantage of these instruments among other measurement techniques is their potential to track dynamic changes as well as gradients in water vapor profiles to aid in prediction of the timing and location of convective initiation. Over the past five years, ground-based studies using multi-frequency microwave profiling radiometers near 22 GHz have explored the trade-offs between accuracy and vertical resolution, choice of frequency channels in the microwave and millimeter wave based on information content, and the long-term deployment of coordinated networks of ground-based radiometers.  Recently, in 2011-2012, two-channel microwave radiometers at 23.8 and 30.0 GHz measurements were deployed in the equatorial Indian Ocean during the DYNAMO campaign. These measurements have been used to retrieve integrated water vapor and liquid water at zenith with very good accuracy. Using the cloudy sky ratio from elevation scans with the same radiometers have shown high sensitivity to slant water vapor, liquid water and precipitation index, even at elevation angles as low as 5°.

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