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Projection offset with land MODIS image after export
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Projection offset with land MODIS image after export
projection modis level2 modis
10/2/14 9:47 AM
Hello,

I have been using BEAM VISAT 5.0 as part of a geospatial technology workshop for watershed managers in Uganda. We have been using the software to visualize and process MODIS data, both data from the ocean color team (level 2) and from the land team (MOD09GA). After viewing and processing data, we exported specific products as GeoTiffs for use in QGIS.

Before exporting the images, we reprojected each product to WGS84 using Processing --> Geometric Operations --> Reprojection. In the case of the ocean color imagery, the exported GeoTiff lined up well with the GIS data. However, in the case of the MOD09 data, the exported multiband image (a results of PCA analysis), the GeoTiff was offset from the GIS data by ~4km to the West.

Does anyone have an idea about why happened? What steps can I take to remedy this problem?

Thanks so much in advance for any suggestions.

Cheers,
Shane

Shane Bradt, PhD
University of New Hampshire
Dept. of Biological Sciences
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Attachment

Attachments: Reprojection_offset_modis_land.jpg (97.7k), Reprojection_offset_modis_ocean.jpg (25.5k)
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RE: Projection offset with land MODIS image after export
10/2/14 4:08 PM as a reply to Shane Bradt.
Hi Shane,

I've contacted the OceanColour group at NASA. Those guys who also build the SeaDAS application. They provide us with the reader for this kind of data. So let's see what they are saying.

Ocean Colour Forum

kind regards
Marco
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RE: Projection offset with land MODIS image after export
10/2/14 4:55 PM as a reply to Shane Bradt.
Shane,

Could you provide the filenames for the MOD09 and L2 files for which you noticed the problem?
Also, can you report the reader that was used for each file (load the files and use the Band Info tool, there will be an entry for the product reader class).

Thanks,
Sean
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RE: Projection offset with land MODIS image after export
10/6/14 10:44 AM as a reply to Sean Bailey.
Hi,

I'm working with Shane on this project. The file names were:

MOD09GA.A2014017.h21v08.005.2014019072612.hdf

and

A2014011114000.L2_LAC_OC.x.hdf

The reader is HDF-EOS products. I've attached a screenshot of the full band info for your information.

I've also include the shapefile used by Shane to show the mis-alignment. It is taken from NASA's SWBD dataset and has not been re-projected in any way.

(By the way, awesome software: blew everyone, including me, away!)

Cheers, Tom
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Attachments: LakeAlbert_SWBD.zip (141.5k), band info.jpg (164.4k)
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RE: Projection offset with land MODIS image after export
10/7/14 9:58 AM as a reply to Sean Bailey.
Sean,

sorry for bothering you. If it is the HDF-EOS reader, the issue is on us.

regards
Marco
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RE: Projection offset with land MODIS image after export
10/7/14 10:00 AM as a reply to Thomas John Ballatore.
Thomas, Shane,

we will have a look at this.

cheers
Marco
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RE: Projection offset with land MODIS image after export
10/7/14 3:38 PM as a reply to Marco Peters.
Dear Marco,

Thanks for following up on this!

I should also note that although Shane said the ocean color imagery lined up well (the A2014011114000.L2_LAC_OC.x.hdf file), I actually have some doubts about this...

I see that the Product Reader is different (SeaDAS-Supported Level 2 Products), so this might be a different issue, but if you look closely at the second screenshot he posted, you can see that ocean color image also has a slight shift such that some pixels in the southeast are actually overlapping land, and that there is a "buffer" in the northwest...i.e. the data appear to be shifted by perhaps 1/2 pixel to the lower right.

I trust the SWBD shapefile as it lines up with other independent data sources (Landsat, Open Street Map, and Google Earth images).

Thanks in advance,

Tom
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RE: Projection offset with land MODIS image after export
10/7/14 4:23 PM as a reply to Thomas John Ballatore.
Hi Thomas,

from the screenshot you send I see that you are still using the module beam-netcdf v5.0. There is a new one. You can find it in the module manager (), probably you should also update other modules.The module is listed as "NetCDF Product Reader and Writer"
With version 5.0.2 I'm getting a much better alignment with your shapefile. See screenshot.

regards
Marco
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Attachments: screen.png (267.7k)
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RE: Projection offset with land MODIS image after export
10/8/14 3:30 PM as a reply to Marco Peters.
Marco,

Thanks so much for that advice: I've tested it on my machine and indeed the land MODIS image lines up correctly! I'm new to BEAM and didn't know about the module manager...

Tom
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RE: Projection offset with land MODIS image after export
10/8/14 6:29 PM as a reply to Thomas John Ballatore.
Thomas,

The issues you see with the ocean product are not related to navigation, but rather masking that occurs during data processing.
When the data are processed, land pixels and pixels detected as cloud are excluded. The land mask used in the current processing is to blame for part of the apparent shift. (our upcoming processing will implement an improved landmask). Some of the pixels around the edge of the lake are flagged as cloud (likely erroneously), but as the cloud mask is a simple reflectance test on the NIR band (869nm), it is possible for elevated water reflectance in that channel can trip the cloud flag. The attached image show the land mask (brown) and cloud mask (red, but orange-ish under the shapefile layer) along with the imported shapefile.

Hope this clarifies some things for you emoticon

Regards,
Sean

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RE: Projection offset with land MODIS image after export
10/10/14 4:25 PM as a reply to Sean Bailey.
Sean,

That does indeed clarify the issue!

Thanks to all for help on these issues and cheers again to this great product. I'll be using it next week too with a different group of GIS/RS students.

Tom
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