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Hello François,

I processed one MODIS Aqua L1A data by Polymer using the default settings. Then I compared the MODIS Rrs412 images between the standard MODIS L2 data and the output from Polymer using the same color scheme and scale.

The two images look very different in terms of the magnitude and distribution of Rrs412. In addition, there are some white lines in the right image. As I do not have in situ data to validate the two images, I'd like to ask if you think the MODIS Rrs412 by Polymer is reasonable or not?

Thank you in advance.

Kind regards,
Mengmeng.

Hi Mengmeng,

Polymer does not provide remote sensing reflectancesin sr-1 but dimensionless water reflectance. Please make sure that you divide by pi to convert to Rrs.
Regarding the white lines, this may be due to some reprojection by your visualization software ? I guess your images are not displayed in the sensor geometry ?
Kind regards,
François

Hi François,

Thank you for your reply. No, I did not divide the output data by π.

I visualized the images with SeaDAS and reprojected the data using WGS1994 for both the MODIS L2 data and the output processed by polymer. Before I reprojected the data, the position of the latter data was opposite to the former data.

How to display the data in the sensor geometry?

Thank you in advance.

Kind regards,
Mengmeng.

Hello Mengmeng,
Sorry for the late reply.
Ah I see, the image may appear rotated compated to MODIS L2 because Polymer does not rotate the grid. In this case for visual comparison, you can rotate the SeaDAS display 180°.
Cheers,
François

Hello François,

Thank you very much for your reply. Do not worry, I know you were busy.

Yes, you're right. I also figured that out.

Kind regards,
Mengmeng.