How to add land overlay map to POLYMER processed OLCI Image

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VPS
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How to add land overlay map to POLYMER processed OLCI Image

Post by VPS »

Hi Francois,

I processed my level 1 OLCI Image with POLYMER and then I tried to give a land overlay to this Image, but for some reason, the orientation of the POLYMER processed and land overlay map are not matching. See this figure download/file.php?mode=view&id=101

I tried the same after giving CRS projection, then also the result is the same. What is the reason for this? I did this in R not in SNAP.

It looked like the POLYMER processed image has much width compared to the land map. I don’t know if the image is corrupted, but I checked this with another image and the same result.

Then, I tried the same with the Weekly binned POLYMER composite image. This weekly binning was done using the GPT tool using the script. But here it looks like a good match between the weekly binned Chla and the Map overlay. See this figure download/file.php?mode=view&id=102

So the orientation problem is with the Level 2 POLYMER processed daily image. Can you guide me on what could be the problem with the Level 2 daily image?

Best, Vishnu
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fsteinmetz
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Re: How to add land overlay map to POLYMER processed OLCI Image

Post by fsteinmetz »

Hi Vishnu,

From your image, it seems you are assuming that Level2 products are provided on a regular grid in lat/lon, which is not the case. Please see the fields latitude and longitude, which are given per-pixel. After reprojection on a regular grid, it is indeed easier to overlay the coastlines.

Kind regards,
François
VPS
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Re: How to add land overlay map to POLYMER processed OLCI Image

Post by VPS »

Hi Francois,

Thank you very much for the reply.

Best, Vishnu
VPS
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Re: How to add land overlay map to POLYMER processed OLCI Image

Post by VPS »

Hello Francois,

As per your suggestion, I applied a CRS projection to the POLYMER processed image and again did the same thing, however, it did not work. I assume projection to a regular grid means giving a proper CRS projection to the image right? Or Is there something else I must do? If yes can you please guide me here?
Also, I am I have developed a model to calculate different phytoplankton groups from Sentinel 3 OLCI Rrs data. The input to this model is POLYMER processed Level 2 Rrs Image and the model final calculates phytoplankton groups from the image. I noticed this issue when I was validating the final phytoplankton retrieved from the satellite vs in-situ data, the in-situ location points are not correctly pointing in the final phytoplankton map. This phytoplankton spatial map is CRS projected as well. With this issue, I cannot even validate my product but this problem does not affect the binned image. I attached the final phytoplankton spatial map retrieved from POLYMER processed Image and as a reference, I showed the original in-situ location and when I enter the location in the map that point is lying far from the original point. Do you know why this is happening? This phytoplankton map is CRS projected as well.
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Re: How to add land overlay map to POLYMER processed OLCI Image

Post by fsteinmetz »

Hi Vishnu,
I you want to compare Polymer results with a binned image, you should also bin Polymer results, in order to compare the two images in the same grid.
A library such as https://pyresample.readthedocs.io/ may help.
Cheers,
François
VPS
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Re: How to add land overlay map to POLYMER processed OLCI Image

Post by VPS »

Hi Francois,

Actually, I don't want to compare. The problem is the in-situ location points are not correctly pointing in the image. The points are lying far away from the actual point. You can see the figure I attached in the last reply. I try to do this in R. The image is CRS projected as well. Even after CRS, I don't know why ins-situ points are lying far away from the actual location. I hope you understand my problem here.

Best, Vishnu
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Re: How to add land overlay map to POLYMER processed OLCI Image

Post by fsteinmetz »

Hi Vishnu,
The issue seems to relate to how you are locating your in-situ points in the image, and what you mean by applying CRS projection.
The easiest way to locate a point in the image should be to find the point with the closest lat/lon.
Cheers,
François
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