(The following is an excerpt from the 1B-CPR Description and Interface Control Document. The entire document can be viewed from the CloudSat Standard Data Product Interface Control Document links page.)
The CPR measures the backscattered power as a function of distance from the radar. The backscattered power is sampled every 240 m; there are 125 range bins, for a total window of 30 km. The raw, Level 0 data are converted to calibrated Level 1B data using pre-launch and in-flight calibration measurements.
The CloudSat Cloud Profiling Radar (CPR) measures the backscattered power as a function of distance from the radar. The backscattered power is sampled every 240 m; there are 125 range bins, for a total window of 30 km. The raw, Level 0 data will be converted to calibrated Level 1B data using pre-launch and in-flight calibration measurements. The Level 1 B CPR Process Description and Interface Control Document presents the calibration theory and defines the Level 0 data contents, the Level 1B contents, and the conversion algorithm.
CloudSat Science and Engineering Data will be down-linked, from the CloudSat on-board data recorder, through the Air Force Satellite Communications Network (AFSCN) to the USAF RDT&E Support Center (RSC) in Albuquerque NM. There the data will be decommutated, checked for transmission errors (checksum), and stored on-line as a set of binary files. These raw data will be accessed by the DPC, via internet/ftp, for subsequent level 0 through level 2 processing.
Among the files, received from the RSC, are the Definitive Ephemeris and the Stored State of Health (SSOH) data. SSOH are available with each downlink, while the Definitive Ephemeris is produced once each day, for the previous day's orbit.
During normal processing, to produce the level 1B-CPR product, the Definitive Ephemeris is used after it arrives, to determine the Geolocation of each CloudSat profile. The Definitive Ephemeris contains the latitude, longitude and altitude of the satellite at 1-second intervals. One disadvantage of using the Definitive Ephemeris for Geolocation is that it is only available once per day at approximately 16 UTC. This file contains the orbital parameters for 0000 UTC through 2359 UTC on the previous Julian day. Thus the standard 1B-CPR data product will not be available until 16-40 hours after the data are actually measured.
In order to provide a "First Look" 1B-CPR product, the CloudSat DPC will process the GPS location data, that are contained in the SSOH data stream, to produce the 1B-CPR-FL. Since GPS data are available with each download of CPR science data, the DPC should be able to provide a 1B-CPR product, based on GPS location data, in less than 10 minutes of the time that data are received at the DPC.
The time lag, between the actual CPR measurement and the time the 1B-CPR-FL products is available at CIRA, is based on the combined lag times of the data downlink, transfer of data from the downlink site to the RSC, processing at the RSC, transfer of data to the DPC, and processing at the DPC. The total lag time is as follows:
a.
Minimum Data Latency = 45 minutes
b.
Maximum Data latency = 28.5 hours
c.
Expected Data Latency = 4.5 hours
The JPL document titled: "Level 1A Auxiliary Data Process Description and Interface Control Document" contains a description of the data processing that takes place at the DPC after the CPR Science Data, SSOH data, and Definitive Ephemeris data arrive. The following paragraphs provide a summary of the data processing with a description of the differences between the "Definitive Ephemeris" processing and the "First Look" (GPS) data processing.