Old COASTZ processing flag

semaj545 · by **semaj545** » Tue Jan 02, 2018 4:51 pm America/New_York

I'm working with the SNPP VIIRS chlorophyll concnetration product and i've heard tell of the old processing flag, COASTZ, that warns if the pixel occurred in waters <30 m. Does anyone know if this information is still available? I'm wondering if it's posibble to mask out shallow water for these data in the Canadian Arctic.

OB.DAACx - SeanBailey · by **OB.DAACx - SeanBailey** » Wed Jan 03, 2018 3:24 pm America/New_York

The COASTZ flag is still populated in the l2_flag array for L2 files....so, yes, you can still use it to mask out data that were deemed to be shallower than 30m by the bathymetry data set.
It's the 7th bit (or 2^6....or 64 in decimal)
Regards,
Sean

semaj545 · by **semaj545** » Wed Jan 03, 2018 7:16 pm America/New_York

Oh ok. So not with the L3 data then? I've been working with the L3 product but it wasnt marked in either the L2 or L3 default mask at https://oceancolor.gsfc.nasa.gov/atbd/ocl2flags/. Thanks.

OB.DAACx - SeanBailey · by **OB.DAACx - SeanBailey** » Wed Jan 03, 2018 7:29 pm America/New_York

No, there are a set of flags applied as masks when binning the L2 data to create the L3 data. The L3 do not have a corresponding set of flags. COASTZ is not masked in L3 generation, however a lot of coastal data are excluded as being masked as straylight contaminated....but that's not the same thing as a bathymetry mask :wink:
To apply such at L3, you would need to do so yourself using an appropriate bathymetric data set. SeaDAS can do this for you. We even have a video tutorial on the subject. :grin:

Sean

semaj545 · by **semaj545** » Thu Jan 04, 2018 9:18 pm America/New_York

Yes. I see that SeaDAS can do this but i'm trying to circumnavigate the factthat i'm on a windows machine and can't install the ocprocessing. I will get my hands on the bathymetry data and mask it myself outside of SeaDAS. Thanks!

OB.DAACx - SeanBailey · by **OB.DAACx - SeanBailey** » Fri Jan 05, 2018 9:31 am America/New_York

For what I described, you do not need the OCSSW processors. It is all done within the Java GUI application and can be done under Windows.

Below is a 4km resolution image of a monthly Chlorophyll product from VIIRS cropped to the Great White North using the Crop tool with a blue
mask set to 30m and shallower generated using the Bathymetry tool.

Note, the inland water bodies are not masked. This is because the depth is based on mean sea level and the local elevation is likely above that.
BTW, the bathymetry tool uses the ETOPO1 data set.

Sean

semaj545 · by **semaj545** » Fri Jan 05, 2018 10:31 am America/New_York

Ok. Thanks!

semaj545 · by **semaj545** » Fri Jan 05, 2018 10:41 am America/New_York

The trouble I had when trying to run a bathymetry mask in SeaDAS is that it asks me if i want to install the ETOPO1_ocssw.nc file and when i click OK it says the installation failed and the mask isn't generated. I thought this was because i needed to install the ocprocessing package?

OB.DAACx - SeanBailey · by **OB.DAACx - SeanBailey** » Fri Jan 05, 2018 11:04 am America/New_York

No, the OCSSW processing isn't required. The GUI should grab the ETOPO data set from our server and put it in your SeaDAS install root. If the automatic installation failed, you can do it manually.

Sean

semaj545 · by **semaj545** » Fri Jan 05, 2018 11:19 am America/New_York

Ok i'll give that a go. Thanks Sean.