Radiative properties of cirrus clouds observed during the European cloud radiation experiment '94 in Brittany by active and passive remote sensing observations

摘要

Abstract: The intensive field observation of EUCREX 94, (European cloud and radiation experiment) held in April 1994 in Brest, France, was a three-aircraft and ground-based experiment dedicated to the development and the validation of algorithms to derive relations between cirrus radiative properties and cirrus microstructure from remote sensing measurements. A multiangular visible radiometer with polarization capabilities called POLDER (polarization and directionality of Earth reflectances) was installed downward, on-board the instrumented German Falcon of the DLR. This aircraft was also equipped with upward and downward pyranometers and pyrgeometers and with PMS probe. The second instrumented aircraft was the ARAT (French Fokker 27 of INSU). It was equipped with the upward lidar LEANDRE (lambda equals 0.53 micrometer), with a photometer POLDER looking downward, and with upward and downward infrared radiometers $LB@lambda $ICTN (9.5 micrometer $MIN 11.5 micrometer)$RB and upward and downward pyranometers and pyrgeometers. During the upward and downward observations of the Fokker under cirrus, the Falcon performed optical measurements above and microphysical measurements inside clouds. A ground-based station with Lidar, infrared radiometric and sunphotometer measurements was also operating during the same time. The third aircraft was specially devoted to the low level clouds and was equipped with a Fast FSSP, upward and downward pyranometers and pyrgeometers and upward and downward infrared radiometers. During this intensive field of observations, four well documented cirrus cases were observed from aircraft and from the ground. Analysis of these observations is presented by comparison to radiative transfer calculations. These calculations are performed taking into account the optical properties of hexagonal ice crystals obtained by a ray-tracing method. All these observations allow us to determine a bulk property of cirrus clouds in particular a radiatively equivalent microstructure. !9