2B-IWC-RO (Cloud Ice Water Content - Radar Only)

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The ice cloud algorithm and the liquid cloud algorithm are conceptually very similar. They utilize the same input data and produce similar output data. The main difference resides in the forward model which will be described in section \ref{forward}.

The CloudSat 2B-IWC Algorithm is a retrieval of cloud ice water content, effective radius, and related quantities that is planned to be run on all CloudSat Profiling Radar (CPR) profiles of reflectivity deemed to contain ice or mixed phase clouds. The retrieval is designed to use radar reflectivity and visible optical depth if both these data streams are available.
The source for the visible optical depth will be the MODIS instrument on the Aqua platform, with which CloudSat will orbit in close formation. In practice, 2B-IWC obtains visible optical depth from the 2B-TAU product; details of the workings of 2B-TAU are not relevant to the operation of 2B-IWC 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-IWC results will be output for any cloud not classified as ``water--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-IWC - Description and Interface Control Document document describes the algorithm that will be implemented operationally to estimate cloud ice 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 ice phase.

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

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

content and cloud particle effective radius,

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

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

2B-TAU) to estimate cloud ice water content, cloud

number concentration, and cloud particle 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.