Skip to content. | Skip to navigation

Personal tools
You are here: GES DISC Home Giovanni - Interactive Visualization and Analysis Giovanni-3 Operation Technical Summary: A-Train Across Track Subset

Giovanni-3 Operation Technical Summary: A-Train Across Track Subset

A-Train Across Track Subset


The Giovanni A-Train Across (CloudSat) Track operation performs an analysis of science parameters along the CloudSat orbit track. Only CloudSat science parameters can be supplied directly to Giovanni along the CloudSat orbit track. Giovanni-3 requires data from all platforms other than CloudSat to be pre-subsetted along the CloudSat orbit track or undergo subsetting during Giovanni-3 processing. The Across-Track Swath Subsetter performs this service on those datasets which have not already been subsetted along the CloudSat orbit track.

Input parameters

  • Data in Satellite Swath Format, stitched together along  the orbit track
  • CloudSat orbital elements

Output Description
Data in Satellite Swath Format, subsetted along the CloudSat orbit track.

Output Parameters
Same as input.

File Type
Input: HDF4
Output: HDF4

Sub-Definitions

  • Frame: individual data element along the scan line. 
  • Swath: 1- or 2-dimensional data structure, typically representing
    an array of measurements distributed along the center pixel of a
    satellite track. 
  • Scan Line: horizontal (across-track) dimension of swath. 
  • TLE (Two-Line Elements): orbital elements of the platform along
    which the across-track subset is to be performed.

Description of This Operation

  1. Use the CloudSat TLE to compute the geolocations of the CloudSat orbit
    track that spans the swath being processed.
  2. Estimate when CloudSat passes closest to the central scan line of the
    swath to be subsetted.
  3. Perform an exhaustive search along this scan line for the frame whose
    geolocation lies closest to the CloudSat orbit track.
  4. For each remaining scan line, identify the frame that lies closest
    to the CloudSat orbit track. Narrow the search using the previous
    collocation solution.
  5. Complete the process by subsetting each science parameter along the
    CloudSat orbit track. Extract a pre-determined number of frames
    surrounding the collocation frame within each scan line found in the
    swath being subsetted. If the data consists of profile data, the
    profile about each colloaction frame is extracted. The swath width
    of the subset is roughly 200km.
  6. Write the subset in Satellite Swath Format.

Algorithm Details
 IDL is used because array-based operations may be performed
 easily in that language.

Caveats/Warnings
-  The vertical and horizontal dimensions for swaths described here are the transpose of the arrangement used in HDF4 files.

- Only Aqua AIRS science parameters undergo the across-track subsetting process, because the data from all other platforms currently processed by the A-Train Giovanni instance have already been subsetted along the CloudSat orbit track.

Origin/Software
Implemented in IDL.

Other Information
 This document currently describes only the mathematical approach used
 in the computation.

 

This Technical Summary page is a draft version -- for information on this operation while
the document is being prepared, please send a message to GES DISC Help.

Document Actions
NASA Logo - nasa.gov
NASA Privacy Policy and Important Notices
Last updated: Nov 10, 2011 12:08 PM ET
Top