2B-LWC-RO (Cloud Liquid Water Content - Radar Only)

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Since the de-scoping of PABSI from CloudSat, the implementation plan has been modified to use an estimate of visible optical depth available in the 2B-TAU CloudSat product. This product is calculated using data from the CloudSat Profiling Radar and other sources, including radiance measurements from the MODIS instrument on the Aqua platform, with which CloudSat will orbit in close formation. In practice, 2B-LWC simply obtains visible optical depth from the 2B-TAU product; details of the workings of 2B-TAU are not relevant to the operation of 2B-LWC as long as 2B-TAU provides an estimate of visible optical depth and its uncertainty

A radar-only version of the retrieval has been implemented for use during the nighttime half of CloudSat's orbit when visible optical depth information will not be available. For continuity, the radar-only retrieval will also be run during the daytime half of the orbit.

The algorithm will use the 2B-CLDCLASS product to handle various cloud types. 2B-LWC results will be output for any cloud not classified as ``ice-only''; this will undoubtedly include many mixed-phase clouds and scenes where there are separate ice and liquid layers. At the present time, no CloudSat standard product explicitly handles these more complex cloud scenarios.

The 2B-LWC - Description and Interface Control Document document describes the algorithm that will be implemented operationally to estimate cloud liquid water content in clouds detected by CloudSat. For each radar profile, the algorithm will:

1.   Examine the 2B-GEOPROF product to determine if cloud

exists within the CloudSat data column,

2.   Examine the 2B-CLDCLASS product to determine what type the

clouds are and whether any portion of the detected cloud might be

in the liquid phase,

3.   For the entire orbit, use radar reflectivity factor (from

2B-GEOPROF) to obtain a radar-only estimate of cloud liquid water

content and cloud droplet effective radius,

4.   For the daytime portion of the orbit, use radar

reflectivity factor (from 2B-GEOPROF) and visible optical depth (from

2B-TAU) to estimate cloud liquid water content, cloud droplet

number density, and cloud droplet effective radius,

5.   For each of these estimates, calculate uncertainties and

covariance matrices, as well as ratios of the estimated values

derived using a priori data to values where no a priori data are

used.