3.5
CloudSat Cloud Detection and Cloud Masking
Roger Marchand, PNNL, Richland, WA; and G. G. Mace and Q. Zhang
Scheduled for launch in April 2004, CloudSat is an experimental satellite that will use millimeter-wave radar to measure the vertical structure of clouds and cloud properties from space. CloudSat will fly in orbital formation as part of a constellation of satellites including AQUA, CALIPSO, PARASOL, and AURA. The radar uses 3.3 ms pulses providing cloud and precipitation information with a 500-m vertical range resolution, but the measurements will be sampled at 250 m in range and 0.16 s along the nadir track giving an effective FOV of approximately 1.4 × 1.6 km. When the data is average to 0.32s, the minimum detectable signal of the CloudSat radar is expected to be between -28 and -29 dBZ and will remain above -26 dBZ for the life of the mission. Further details on the radar and CloudSat science objects can be found in the recent BAMS article by Stephens et al. [2002].
Existing algorithms to distinguish clouds and other hydrometeors from radar noise, which have long been used by ground-based radars, have been modified for use with CloudSat. While the CloudSat algorithm is similar to that of Clothiaux et al. [1995, 1999, 2000], there are a number of significant changes including a variable time-integration scheme, which looks for targets too weak to be detected at the full 0.16 s sampling but can be detected if longer time-integrations are considered, and an actual significance mask which gives the likelihood that any point considered a cloud might be a false detection. In this presentation, examples of the CloudSat algorithm applied to downward-looking measurements from aircraft taken during the recent CRYSTAL-FACE and several other experiments will be shown. These examples will highlight the effect of the significance mask and time-integration scheme. The presentation will also show how the 500 m resolution and associated oversampling effect the cloud detection and computation of the relative occurrence of cloud with altitude.
Clothiaux EE, Miller MA, Albrecht BA, Ackerman TP, Verlinde J, Babb BM, Peters RM, and Syrett WJ, 1995 “An evaluation of a 94 GHz radar for remote sensing of cloud properties,” J.Atmos.Oceanic Technol., 12, 201 –229.
Clothiaux EE ,and Coauthors, 1999 “The Atmospheric Radiation Measurement program cloud radars: Operational modes.,” J.Atmos.Oceanic Technol., 16, 819 –827.
Clothiaux EE, T.P.Ackerman, G.G.Mace, K.P.Moran, R.T. Marchand, M.A.Miller, and B.E.Martner, 2000 “Objective determination of cloud heights and radar reflectivities using a combination of active remote sensors at the ARM CART sites,” J.Appl.Meteor., 39, 645 –665.
STEPHENS GL, VANE DB, BOAIN RJ, MACE GG, SASSEN K, WANG Z, ILLINGWORTH AJ, O’CONNOR EJ, ROSSOW WB, DURDEN SL, MILLER SD, AUSTIN RT, BENEDETTI A, MITRESCU C, AND THE CLOUDSAT SCIENCE TEAM, 2000 “THE CLOUDSAT MISSION AND THE A-TRAIN: A New Dimension of Space-Based Observations of Clouds and Precipitation,” BAMS, Dec. 2002, p. 1771-90.
Session 3, MM-wave radar observations on cloud and climate - I
Thursday, 7 August 2003, 8:00 AM-10:00 AM
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