Welcome to the Earthdata User Forum! Here, subject matter experts from several NASA Distributed Active Archive Centers (DAAC) can discuss general questions, research needs and data applications. Users can query how to access, view and interpret the data.
by zhigang » Fri Jul 16, 2021 2:46 am America/New_York
I am processing some VIIRS data in SeaDAS with V2021.1 processor. The input data is L1A and GEO data downloaded from the ocean color portal. However, the result processed by l2gen missed some data, which should related to the bowtie effect. I have tried to map it using reproject and mosaic tool following the instructions in https://oceancolor.gsfc.nasa.gov/forum/ ... l?tid=5906, but the data still missed.
My examined data is V2020133054200.L1A_SNPP.nc, and command is like:
by gnwiii » Sat Jul 17, 2021 7:36 pm America/New_York
Can you explain what is meant by "remove bowtie"? Do you want to replace the pixels deleted in the scanline overlap areas at the edges of the scans for "improved" appearance? Do you have access to OCSSW Processing Software. e.g., linux (including WSL) or macOS?
by gnwiii » Tue Jul 20, 2021 7:47 am America/New_York
Supporting subset would complicate the area-weighting and interpolation at edges of the region, so maybe it should not be a big surprise that you get "unfilled" deletions in mapped images. Given that
mapping a single granual doesn't take long with modern hardware, it makes sense to produce mapped netcdf files of granuals and then apply a subset operation to the mapped image.
Are you using SeaDAS 8.1.0 and OCSSW tag=2021.2 software? There are several ways to make mapped images from a single level-2 granule: export the screen image in the GUI, l2mapgen, l2bin+l3mapgen+"some netcdf to image process". l2mapgen has changed from a python script that used l2bin+l3mapgen to a stand-alone program.
The SeaDAS "benchmark" script (which should be called "check that a fresh install is working properly" and is a download+install option in the OCSSW section of the GUI) produces an SMI image using l2bin+l3mapgen from a single MODIS Aqua granual at 1km resolution:
For older versions the SMI image has a Moire pattern of missing pixels near the pass edge, but the current version has filled in the missing pixels using the new area_weighting and interp=area options. The
previous benchmark script did use the subset option.
by gnwiii » Wed Jul 21, 2021 9:15 am America/New_York
You are very welcome. Hope you find a workflow that fits your use case. I should mention that the deletion artifacts (and Moire effects) are less of a problem at lower resolution. Also, ESA has their own binning tool in the Graph Processing Facility (GPF). It is mentioned in the SeaDAS 8 GUI Help GPF Operator Index, but not all ESA SNAP operators are available in SeaDAS 8.1.0 so you may have to use ESA SNAP.