Glint correction activation in Polymer

Post Reply
dmantsis
Posts: 8
Joined: Mon Dec 13, 2021 9:53 am
company / institution: Centre for Research and Technology Hellas
Location: Thessaloniki

Glint correction activation in Polymer

Post by dmantsis »

Hi everyone
I am running Polymer at the moment on a linux machine. I am not using anything in my settings except that I call ERA5 ancillary data. I was wondering if Polymer automatically removes the glint and the adjacency effect, or these have to be activated manually in the settings. If the answer is yes, does anyone know how to call these in my "run_atm_corr" function?

Thank you
User avatar
fsteinmetz
Site Admin
Posts: 252
Joined: Fri Sep 07, 2018 1:34 pm
company / institution: Hygeos
Location: Lille, France
Contact:

Re: Glint correction activation in Polymer

Post by fsteinmetz »

Hi Damianos,
Yes, Polymer does correct for glint and adjacency effects. It does burk correction, so it can not be disactivated.
Cheers,
François
dmantsis
Posts: 8
Joined: Mon Dec 13, 2021 9:53 am
company / institution: Centre for Research and Technology Hellas
Location: Thessaloniki

Re: Glint correction activation in Polymer

Post by dmantsis »

Hi
One more thing. I am studying a small dam lake at a 300 m altitude. I am using ERA5 for ancillary. Given that the resolution of the ERA5 is on the order of tenths of kilometers it is impossible for the algorithm to estimate the exact depth of the overlying atmosphere. This is compromised even more by the intense topography in the surrounding area. If my lake is at 300m altitude, the algorithm might think that it is at a 600m altitude simply because the 25Km topographic data of ERA5 is not sufficient for such a small scale study. Is there something that I can do to fix this, and let Polymer know the exact altitude? How can this be specified in the run_atm_corr function, and is there something else that needs to be deactivated?

Thank you
User avatar
fsteinmetz
Site Admin
Posts: 252
Joined: Fri Sep 07, 2018 1:34 pm
company / institution: Hygeos
Location: Lille, France
Contact:

Re: Glint correction activation in Polymer

Post by fsteinmetz »

Hi,
Yes you can specify a fixed altitude for the whole image, by passing the keyword altitude to the level1 object.
eg: Level1_...(..., altitude=300)

However, I see that there can be an inconsistency issue regarding the use of the altitude keyword. The atmospheric pressure is supposed to be the sea level pressure, and the altitude model is used to calculate the surface pressure. This is the case for the OLCI Level1 ancillary data, the NASA ancillary data, but not ERA5 which provides already surface pressure. Thus, providing an non-zero altitude (altitude is zero by default, thus no altitude correction) would result in an incorrect surface pressure correction. I will fix this inconsistency in the next polymer version. In the meantime I advise to use NASA ancillary data if you want to provide an altitude.

Kind regards,
François
Post Reply