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[McIDAS #QJI-536086]: Correction for MODIS bow-tie effect



Hi again Carolina,

After some more searching, I found that we still have a MODIS package on our
anonymous FTP server:

machine:   ftp.unidata.ucar.edu
user:      anonymous
pass:      address@hidden
directory: pub/mcidas/contrib
file:      modis_l1b.tar.gz

Here are the comments from a previous email about the code in this package:

 >I have been temporarily pulled away from the MODIS project to work on
 >another high priority project since May 2004. Even the latest version of
 >the MODIS remap software is more than one year old.  There were some
 >improvements being made to the software after I provided the decoders to
 >Dave.

 >We implemented the polar Stereographic projection remapping
 >program for the granules over the north polar region for the 1KM res L1B
 >(MOD021KM, and MYD021KM); and added the calibration block to the
 >remapped McIDAS multi-band AREA. For the 500m and 250m resolution L1B
 >data, the remap programs are pretty the same as before.  As I mentioned
 >to Dave, the software is still under development and at its testing
 >stage. Currently, there is no document for the software.  For a general
 >description on how the MODIS granules are re-projected and how the
 >bow-tie effect is corrected, please see my previous e-mail to Dave Santek.

 ...

 >I also include the
 >Makefile for the two remapping decoders. I used the HDF library with in
 >the McIDAS package.

 >Again, the code is not fully developed.  Because some settings are hard
 >coded, the software will need to be modified before it can be run on
 >other system.

 >Aiwu

The e-mail to Dave Santek that Aiwu is referring to is (note the date):

  >>Hi, Dave,
  >>
  >>I have put the MODIS L1B HDF decoders on our anonymous ftp server
  >>(ftp://gp16.www.noaa.gov) under directory /pub/modis. The tar file
  >>includes 3 decoders for L1B data at 1KM, HKM, and QKM resolution, some
  >>driver scripts for the our local remapping processing, as well as 3
  >>sample AREA files at different resolutions and GIF images. I have
  >>written a short compile script for compiling the 3 decoders using HDF
  >>library within McIDAS. We will keep at least 3 days on the server.
  >>
  >>Currently, we only remap/correct L1B data from SSEC MODIS realtime
  >>system. This is mainly because SSEC provides data in a more timely
  >>manner and the granules are generally longer than 5-minutes. Our
  >>customers ( Fire analysis, OSEI ) prefers SSEC's data. The remapped
  >>region is limited to CONUS (22N-53N, 125W-65W). The code can be easily
  >>modified to apply to global data. The output AREA file is in
  >>Rectilinear projection. Passes over the polar region are skipped.
  >>
  >>The 3 remappers/decoders are logically very similar. Since the bow-tie
  >>effect is caused by the over sampling of multi-scans between adjacent
  >>frames, to get ride of it, one possible is to remap the pass. What I am
  >>doing in the decoders is to use geolocation at 1km to interpolate into
  >>500m and 250m for HKM and QKM data, grid the raw data into an array by
  >>embedding each pixel using its lat/lon. Since resolution gets lower as
  >>it approaches the edges, patchy edge problem arises after the gridding.
  >>To fix the the problem, simple 1-D interpolation, extrapolation,
  >>nearest neighborhood filling are used to fill the holes.  As you could
  >>image, it is quite CPU consuming. Base on our user's interest, only
  >>selected bands are remapped: 8 bands( 1-4,6,22,31) at 1KM, 4 bands(1-4)
  >>at HKM, and 2 bands(1-2) at QKM.
  >>
  >>The software is still under development. Although it is
  >>semi-operational on our system, you may still see certain bugs in the
  >>code. For example, in the remapped images, there are some navigation
  >>problem( appears as boundary off 2 pixels near the edges). The PS
  >>remap/decoders for 1km and hkm are almost done. Since this project is
  >>still at its preliminary stage,we have no documents yet.  To make the
  >>code more readable, I have taken out some debug statements, added some
  >>comment lines in the program. Attached are 2 sample images( Chesapeake
  >>Bay, and Albemarle Sound)  generated from 250m raw data and remapped
  >>data.
  >>
  >>I don't mind at all that the software to be used by others. 

So, this code may or may not be helpful.

Best of luck!

Cheers,

Tom
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Ticket Details
===================
Ticket ID: QJI-536086
Department: Support McIDAS
Priority: Normal
Status: Closed


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