Dears,
I'm looking for a daily PAR dataset for Uganda mainland (from January 2017 till present times (the most recent, the best).
I already investigated few sources unsuccessfully:
ECMWF - Era Interim:
http://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc/
==> fits more or less our requirements but the data seems to be corrupted:
https://software.ecmwf.int/wiki/display/CKB/ERA-Interim%3A+surface+photosynthetically+active+radiation+%28surface+PAR%29+values+are+too+low
NASA - MODIS:
https://giovanni.gsfc.nasa.gov/giovanni/#service=TmAvMp&starttime=&endtime=&dataKeyword=par
==> unfortunately, I only find data covering ocean and nothing for continents
Thank you for your help and consideration,
C.
Open the link that is attached and see if you can find something useful out of the 33 matching collections.
https://search.earthdata.nasa.gov/search?m=-2.25!22.0078125!3!1!0!0%2C2&qt=2017-01-01T00%3A00%3A00.000Z%2C2017-10-27T23%3A59%3A59.000Z&q=+Photosynthetically+Active+Radiation&ok=+Photosynthetically+Active+Radiation&sb=28.265625%2C-1.7578125%2C35.5078125%2C5.1328125
Howdy Christophe,
The best approach is to use Global Radiation (GLR) as a proxy for PAR since GLR is a standard daily measurement in meteorology and hence much more available globally.
But pay attention, measurements for one year in Tsukuba, Japan (36.05°N, 140.13°E). PAR / GRL increased with water vapor pressure (e) from 0.40 to 0.47 and increased with decreasing clearness index, it did not strongly depend on solar zenith angle (θ) however (about 3%). So the PAR / GLR ratio is not really constant.
Many researchers use a PAR / GLR ratio of 0.48 as a rule of thumb, but as you have noticed one needs atmospheric humidity and atmospheric visibility as well to get more accurate PAR estimates from GLR. So best is to look for GLR measurements and convert these into PAR, using humidity and visibility as well in an accurate model. A model example is found at:
http://www.biblioteca.uma.es/bbldoc/articulos/16695732.pdf
Good Luck,
Frank
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