L3 PAR and HISOLZEN

[dem1]

Hi,

We would like to know if HISOLZEN pixels should be removed or kept for your L3 Photosynthetically Available Radiation (PAR) daily average product.
The PAR ATBD https://oceancolor.gsfc.nasa.gov/resources/atbd/par/ specifies that:
Level-3 Masking LAND,HISOLZEN,NAVFAIL,FILTER,HIGLINT
but I think that HISOLZEN is not applied on your L3 PAR, I checked on your L3 browser using the monthly climatology PAR vs RR443 (Aqua November monthly clim):

Is the PAR data less degraded on HISOLZEN than other ocean parameters like Rrs?
We tried to asses this using your SeaBASS in-situ validation tool which provides a configurable SZA threshold, but unfortunately we found no matchups with SZA>75°.
We also found this 2016 paper about PAR: "Extending the PAR products to Sun zenith angles larger than 75 degrees, a planned task, will
necessitate relaxing simplifying assumptions, e.g., the quasi single-scattering approximation, in the retrieval of the
cloud/surface albedo."
https://www.researchgate.net/profile/Jing-Tan-12/publication/303324080_Estimating_photosynthetically_available_radiation_at_the_ocean_surface_for_primary_production_3P_Project_modeling_evaluation_and_application_to_global_MERIS_imagery/links/5c5bc33992851c48a9bfdbc8/Estimating-photosynthetically-available-radiation-at-the-ocean-surface-for-primary-production-3P-Project-modeling-evaluation-and-application-to-global-MERIS-imagery.pdf

Thanks,
Julien

[dem1]

Hi,

Does anyone have any information on the topic?

Thanks a lot,
Julien
Copernicus Marine OCTAC Service

[OB.DAAC - SeanBailey]

Julian,

It is fine to use PAR as distribute. No, we do not exclude HISOLZEN for it as we do for the ocean color products because it doesn't' suffer from the same issues with atmospheric correction (it's uses a simple transmittance calculation, that is not as affected by the larger viewing angles as the aerosol determination in ocean color products).

BTW, the PI, Robert Frouin (and Jing Tang as well for the new PACE algorithm) approved the products we're distributing.

Regards,
Sean

[dem1]

Thanks a lot for your answer Sean.

A collegue who uses your monthly L3 PAR just found some strange patterns on high latitudes, example below (VIIRSN monthly PAR 2024-01).
Do you think these patterns are related to extreme Sun Zenith Angles?

Thanks,
Julien

https://oceandata.sci.gsfc.nasa.gov/showimages/VIIRS/IMAGES/PAR/L3/2024/0101/SNPP_VIIRS.20240101_20240131.L3m.MO.PAR.par.4km.nc.png

VIIRSN_MONTHLY_PAR_2024-01.png (165.41 KiB) Not viewed yet

[OB.DAAC - SeanBailey]

Julian,

No, but I do think there is a condition that should be flagged but isn't, allowing spurious high values in. If you drill down to the dailies, you can see what appears to be single scans with high values. It's in MODIS and VIIRS. We'll investigate.

Sean