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Giovanni-3 Operation Technical Summary: Along Track Swath Subsetter

Along Track Swath Subsetter

The Giovanni-3 Along Track Swath Subsetter finds and writes the subset of data that falls within the length of orbit that was selected for processing with the orbit picker.

The suite of datasets processed by A-Train Giovanni-3 do not naturally begin and end on the length of orbit selected for processing. Instead, all datasets of a given type (that span the processing interval in its entirety) are first collected and then trimmed to the spatial extent of the processing interval. The Giovanni-3 Along-Track Swath Subsetter performs this trimming service.

Input parameters

  • Data in Satellite Swath Format, stitched together along the CloudSat orbit track
     
  • Spatial extent of the orbit length selected with the orbit picker

Output Description
Data in Satellite Swath Format, trimmed to the length of orbit selected by the orbit picker.

Output Parameters
Same as input.

File Type
Input: HDF4
Output: HDF4

Sub-Definitions

  • Center Pixel: the middle pixel along the horizontal (across-track)
    dimension of the swath
  • Orbit Arc Length: the arc length of the orbit track selected
    for data processing in kilometers.
  • Orbit Picker: the orbit-based data selection tool for A-Train Giovanni-3
  • Orbit Track: the segment of orbit selected for data processing
  • Swath: 1- or 2-dimensional data structure, typically representing
    an array of measurements distributed along the center pixel of a
    satellite track.

Description of This Operation

  1. Determine the geolocation of the end points of the orbit track which was selected for processing with the orbit picker.
  2. Using the geolocation swaths, compute the arc distances between the end points of the orbit track and the center pixel of each scan line in the input subset.
  3. Determine which scan lines fall within one (orbit) arc length of BOTH orbit track end points.
  4. Write the subset, restricted to those scan lines computed in Step 3, 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.

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.

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Last updated: Nov 10, 2011 12:08 PM ET
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