l2gen and gpt processing over mid-pacific

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gisjie
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l2gen and gpt processing over mid-pacific

by gisjie » Fri Mar 17, 2023 12:30 am America/New_York

I try to process data over the mid-pacific with geographical range across the 180E/180W line. For exapmple, north=22, south=12,east=-175, west=175. But the level2 product from l2gen gave extremly large x dimension. I guess l2gen thought that the longitude is from 175W to 175E. I tried to use 185 as east boudary instead, but seadas would not reconginze boundary values exceeds [-180,180]. How to handle this situation in l2gen and gpt processing?

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OB SeaDAS - xuanyang02
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Re: l2gen and gpt processing over mid-pacific

by OB SeaDAS - xuanyang02 » Fri Mar 17, 2023 10:43 am America/New_York

I tired l2gen on AQUA_MODIS.20230220T011000.L1B.hdf with north=22, south=12, east=-175, west=175..

I got the L2 file with the southwest point (176.85, 12.91) and northeast point (-175.47, 23.65). The x dimension is 0 to 682 pixels. I don't understand what you meant by "extremly large x dimension".
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gisjie
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Re: l2gen and gpt processing over mid-pacific

by gisjie » Sat Mar 18, 2023 9:27 pm America/New_York

Thanks! I tried l2gen the same Aqua image and got similar results from you. The issue should come from the GPT processing. Below is the graph xml file I used for mosaic, and the output array was 38500 x 1100.

<graph id="AQUA_MODIS">
<version>1.0</version>
<node id="MosaicNode">
<operator>Mosaic</operator>
<sources>
<sourceProducts>${sourceProducts}</sourceProducts>
</sources>
<parameters>
<variables>
<variable>
<name>chlor_a</name>
<expression>chlor_a</expression>
</variable>
<variable>
<name>Kd_490</name>
<expression>Kd_490</expression>
</variable>
</variables>
<crs>GEOGCS["WGS84(DD)", DATUM["WGS84", SPHEROID["WGS84", 6378137.0, 298.257223563]],PRIMEM["Greenwich", 0.0], UNIT["degree", 0.017453292519943295],AXIS["Geodetic longitude", EAST], AXIS["Geodetic latitude", NORTH]]</crs>
<resampling>Bicubic</resampling>
<westBound>175</westBound>
<northBound>22</northBound>
<eastBound>-175</eastBound>
<southBound>12</southBound>
<pixelSizeX>0.0090909</pixelSizeX>
<pixelSizeY>0.0090909</pixelSizeY>
</parameters>
</node>
</graph>

OB SeaDAS - xuanyang02
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Re: l2gen and gpt processing over mid-pacific

by OB SeaDAS - xuanyang02 » Mon Mar 20, 2023 4:00 pm America/New_York

Yes, gpt seems to have an issue with the geographic area that crosses the date line. The work around is to do mosaic twice, resulting in two files, one for the west and one for the east.

The 1st time for the region west of the date line --
<westBound>175</westBound>
<eastBound>179.9</eastBound>

The 2nd time for the east part --
<westBound>-179.9</westBound>
<eastBound>-175</eastBound>
Last edited by OB SeaDAS - xuanyang02 on Tue Mar 21, 2023 11:54 am America/New_York, edited 1 time in total.

gisjie
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Re: l2gen and gpt processing over mid-pacific

by gisjie » Mon Mar 20, 2023 8:34 pm America/New_York

Good idea. Thanks a lot!

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