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Up Topic Products and Algorithms / Field Data - SeaBASS / in situ measurements (Rrs) (locked)
- By dogun Date 2016-10-12 02:18
Wondering if there are other sources (besides SeaBASS) for in situ Rrs data I can access for my work on validation of atmospheric correction methods over water surfaces. I could only managed to get VERY few from SeaBASS (MOBY site) that overlap with Landsat 8 overpass. Or anyone with suggestions on how to optimize data from SeaBASS for this type of work.

If anyone is willing to share/provide me with some data, I will acknowledge this and provide reference in my publication.

Thanks!
- By jasonlefler Date 2016-10-12 02:28
Landsat 8 has a very narrow swath width; ~115 miles vs. ~1500 miles for Aqua-MODIS.  It'll be difficult to get many coincident points at all, let alone ones that fit our quality criteria.  You could try cranking down the settings on our validation search.

That having been said, AERONET is another data source with reasonable coverage.

Jason
- By cwproctor Date 2016-10-12 13:12
It sounds like you are using the "Validation" data search results for different sensors, taking the in situ values from the results, and then using those to try to match with Landsat-8 files? That's not a bad approach, but it limits the number of possible results in some ways, since the validation search results from a given sensor are only displayed if there were successful match-ups (i.e., it is possible that match-ups that failed quality criteria for satellite sensor XYZ might work better for Landsat-8).  As Jason mentioned, if your interest is just obtaining the maximum number of in situ values possible from a validation search, you can try increasing the number of results by changing the "Exclusion Criteria" on the validation search page to include lower quality results.

Another idea is to start with the original in situ data that were submitted to SeaBASS, as you can find more in situ data points there than just backtracking from other validation searches. Use the "Bio-optical" search type. Change the search parameters to the Landsat-8 date range, and pick just the products you are interested in at the bottom of the page, where you should either write "Rrs" in the search bar (if you want only files that contain already calculated in situ Rrs) or else check the AOP box (those results plus others, including some where you might have to calculate Rrs from profiled measurements.) You can then look through the bundle of individual files to dig out data points of interest.

However, there are certain data sources used for SeaBASS validation that can't be found using the bio-optical search, for example, MOBY and AERONET-OC data. Those data aren't distributed in the bio-optical search because they weren't formally submitted to SeaBASS and it would be redundant to host them here when they are already in other databases. You can only find those in situ values in successful validation results, but otherwise you should consult their websites if you want to download more of their data.
- By cilori Date 2016-10-18 06:34
Thanks so much for your response. It's really a pain getting satellite matchups, but will keep searching the database.

Following your advice, if I wanted to use Rrs=LWn/F0. Wondering if I need to do any unit conversion, given Rrs is units of sr-1 and Lwn in another unit. Or I can simply use them (Thuiller's F0 and Lwn from AERONET OC or SeaBAS archive straight away)?

Thanks!
- By jpsco Date 2016-10-18 08:03
Hi, to answer your question about the units, the data in SeaBASS should have these units:
Lwn --> uW/cm^2/nm/sr
F0   --> uW/cm^2/nm

Therefore, you would be able to take the ratio of the two to get 1/sr. However, as a sanity check, it is good practice to verify that the /fields= and /units= headers in the SeaBASS data file(s) you are working with do in fact contain those units.

For more information on SeaBASS standard units, see:
http://seabass.gsfc.nasa.gov/wiki/article.cgi?article=stdfields
And for more information on SeaBASS headers and file metadata, see:
http://seabass.gsfc.nasa.gov/wiki/article.cgi?article=metadataheaders
- By cilori Date 2016-10-18 12:21
Thanks Jpsco!
Up Topic Products and Algorithms / Field Data - SeaBASS / in situ measurements (Rrs) (locked)

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