Parameter Setting in Py6s

[shahira ka]

Hi, 

I am trying to generate LUT using py6s. I was able to give user-defined geometry for various scenarios, like the following:

    s = SixS()

    s.geometry.solar_z = 30
    s.geometry.solar_a = 180
    s.geometry.view_z = 45
    s.geometry.view_a = 125

But I have seen in certain papers, (Improvements of 6S Look-Up-Table Based Surface Reflectance Employing Minimum Curvature Surface Method, and An estimation of surface reflectance for Advanced Himawari Imager (AHI) data using 6SV) people are using relative azimuth angle (i.e. sun azimuth angle - sensor azimuth angle) as an input parameter to the py6s code instead of giving them separately. This will eventually help in reducing the total run time required for generating LUTs. 

But I am unable to give relative azimuth as an input to the py6s. I could find a parameter named 'azimuthal_angle_difference' under the output variables. But I don't know how to give that as an input parameter. Please let me know how to do this. Any help regarding this matter will be highly appreciated. 

Kind Regards, 

[Robin Wilson]

Hi,

Unfortunately I don’t believe it is possible to specify a relative azimuth angle as input to the underlying 6S model, so therefore it isn’t possible using Py6S either. I can see from the 6S code that relative azimuth angles are used internally for some things, but the documentation doesn’t show a way of specifying this as an input parameter.

I don’t know how the people who wrote the other papers did it - I suspect they just ran for lots of solar azimuths and view azimuths, and then calculated the relative azimuth angle for each of them. It might be worth contacting them to see if they can give you more details on how they did it.

Best regards,

Robin

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