MODIS MOD09A1 Product negative reflectances

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nneckel
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MODIS MOD09A1 Product negative reflectances

by nneckel » Fri Feb 16, 2024 3:51 am America/New_York

Dear Sir or Madam,

I am working with the MOD09A1 v 6.1 product over the Arctic Ocean. I am particularly using bands 1, 2 and 3 of the product. Especially in band 2 I encountered many negative reflectance values over open water. The same pixels are however valid in the other bands. Is there any suggestion how to proceed with these negative reflectance values?

Kind Regards,

Niklas

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LP DAAC - lien
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Re: MODIS MOD09A1 Product negative reflectances

by LP DAAC - lien » Fri Feb 16, 2024 10:37 am America/New_York

Hi Niklas,
Sorry, but I don't think there is much that can be done about that, the MOD09 products are not recommended for water pixels.

The "anomalies" that you've identified, e.g. negative reflectance values,
are known issues in MODIS along with many other Surface Reflectance products such as Landsat surface reflectance.

The atmospheric correction and surface reflectance retrieval algorithms are not
ideal for water bodies due to the inherently low level of water leaving
radiances and consequently very low SNR. Quantitative remote sensing
retrievals of water column constituents requires different algorithms.
Similarly reflectance values greater than 1.0 can be encountered over
bright targets such as snow and playas. These are computational
artifacts. The surface reflectance QA bands and product user guides should
be consulted.
Please let me know if you have any questions.
Thanks,
Brett

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