MODIS LAI scale factor in AppEEARS

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mchl.mccrthy
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MODIS LAI scale factor in AppEEARS

by mchl.mccrthy » Mon May 09, 2022 10:40 am America/New_York

Hi there,

I'm downloading some MODIS LAI data (MCD15A2H-006) at the point scale using AppEEARS (which is a great tool, by the way!) The MODIS documentation says a scale factor of 0.1 needs to be accounted for upon download. But I can't find any documentation about whether that scale factor is accounted for in the AppEEARS workflow? Given the LAI values I get, I suspect it is, but it would be great if someone can confirm. Because the scale factor is only 10x different, it's not completely obvious. I'm sorry if that information is available and I missed it.

Thanks a lot,

Mike

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mchl.mccrthy
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Joined: Thu Oct 28, 2021 4:33 am America/New_York
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Re: MODIS LAI scale factor in AppEEARS

by mchl.mccrthy » Wed May 18, 2022 4:32 am America/New_York

The MODIS documentation is here: https://lpdaac.usgs.gov/products/mcd15a2hv006/

rapsodia86
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Re: MODIS LAI scale factor in AppEEARS

by rapsodia86 » Thu May 19, 2022 4:52 pm America/New_York

After the order is completed, open README file.
For point extraction it says:
"## 3. Point Sample Extraction Process
Datasets available in AppEEARS are served via OPeNDAP (Open-source Project for a Network Data Access Protocol) services. OPeNDAP services allow users to concisely pull pixel values from datasets via HTTPS requests. A middleware layer has been developed to interact with the OPeNDAP services. The middleware make it possible to extract scaled data values, with associated information, for pixels corresponding to a given coordinate and date range."
For area:
"## 3. Area Sample Extraction Process
When an area sample extraction request is successfully submitted, AppEEARS
implements a series of tools and services to extract the exact data the user is
interested in; or rather, extracts data from specific data layers that
intersect with the input vector file's features. AppEEARS first uploads the
input vector file and reprojects it to the source projection of the data layer
of interest. The PROJ.4 definitions for each data collection available through
AppEEARS are listed below. "

It means, points are scaled data values, while for area, downloaded images need the scale factor to be applied.

mchl.mccrthy
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Re: MODIS LAI scale factor in AppEEARS

by mchl.mccrthy » Fri May 27, 2022 8:50 am America/New_York

Hi there, thanks for pointing this out. LP DAAC just confirmed the same in an email: the point values are scaled in the csv files from AppEEARS. Cheers!

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