Acessing the Suomi/NPP VIIRS True Color Corrected Reflectance product

[AdeelH]

I am currently accessing Suomi/VIIRS imagery through the VNP09GA.v002 collection at https://cmr.earthdata.nasa.gov/stac/LPCLOUD/, but those images seem to have some visual artifacts that the images on Worldview do not. Example below.

On Worldview (Suomi/NPP VIIRS True Color Corrected Reflectance):

Same scene from VNP09GA.v002 (bands I3, M4, M3), notice the dust:

Most of the bands seem to have these artifacts.

My question is: how is the Suomi/NPP VIIRS True Color Corrected Reflectance layer generated and is it available for download in any STAC collection? If not, how would I go about generating it on my own?

[minniewong]

Here is a comparison of the two layers in Worldview: https://go.nasa.gov/3TK34m0 where you can see the same artifacts you outlined above.

Here is an explanation of what we did with MODIS, which VIIRS followed suit, and you might be able to use the tutorial at the bottom to create your own:

MODIS Corrected Reflectance vs. MODIS Surface Reflectance

The MODIS Corrected Reflectance algorithm utilizes MODIS Level 1B data (the calibrated, geolocated radiances). It is not a standard, science quality product. The purpose of this algorithm is to provide natural-looking images by removing gross atmospheric effects, such as Rayleigh scattering, from MODIS visible bands 1-7. The algorithm was developed by the original MODIS Rapid Response team to address the needs of the fire monitoring community who want to see smoke. Corrected Reflectance shows smoke more clearly than the standard Surface Reflectance product. In contrast, the MODIS Land Surface Reflectance product (MOD09) is a more complete atmospheric correction algorithm that includes aerosol correction, and is designed to derive land surface properties. In clear atmospheric conditions the Corrected Reflectance product is very similar to the MOD09 product, but they depart from each other in presence of aerosols. If you wish to perform a complete atmospheric correction, please do not use the Corrected Reflectance algorithm. An additional difference is that the Land Surface Reflectance product is only tuned for calculating the reflectance over land surfaces.

References: NASA Earthdata - Creating Reprojected True Color MODIS Images: A Tutorial https://www.earthdata.nasa.gov/s3fs-public/2022-02/MODIS_True_Color.pdf

Alternatively, if you don't want to generate your own, you can bring in the Corrected Reflectance imagery into your own GIS using the information in the GIBS API documentation: https://nasa-gibs.github.io/gibs-api-docs/

[AdeelH]

Thank you for the quick reply!

It seems like the corrected reflectances for neither MODIS nor VIIRS are available as STAC products. So my only options are to generate them myself or to use GIBS. And GIBS provides image files rather than georeferenced GeoTIFFs. Does that sound right?

Also, thanks for sharing the tutorial. Unfortunately, the links to tools in the tutorial seem broken. So:

• Is there a more up-to-date version of this tutorial?
• Do you know of any existing open source implementations of this algorithm? Perhaps the GIBS implementation?
• Is there a similar tutorial/documentation for VIIRS?

[minniewong]

Hello! You should be able to access the georeferenced GeoTIFFs through https://worldview.earthdata.nasa.gov (use the camera icon) or https://wvs.earthdata.nasa.gov to set up a request for GeoTIFFs.

[AdeelH]

The GIBS API approach is working well for me so far, so I consider my question answered. Thank you for all the help!