Does ARCSI take into account surface orientation and elevation (respect to the ellipsoid) via DEM?

[lucia.m...@gmail.com]

Dear ARCSI developers and users,

I am using ARCSI with input DEM to retrieve bottom of atmosphere reflectance of LANDSAT 8 scenes.

If I understand well, DEM is considered in order to change image pixel elevation.

Is surface orientation (respect to the ellipsoid) considered in the correction scheme?

In which way?

Thank you in advance

Lucia

[Pete Bunting [pfb]]

Dear Lucia, 

ARCSI can use a DEM to build a look up table which includes elevation to perform a per-pixel correction to retrieve bottom of atmosphere reflectance. 

Surface orientation (i.e., topographic correction) and BRDF are currently not considered. We obviously plan to but we haven’t had time to extend ARCSI for that functionality. 

For the parameterisation of 6S the sensor angle is used as a single value for the whole image and there is an option to use a single global BRDF through 6S for the image but this has not been well tested and parameterised yet. To try that out use the following option  --grdrefl BRDFHapke

Many thanks, 

Pete

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[lucia.m...@gmail.com]

Dear Pete,

thank you for your reply. 

If I understand well, ax, bx, cx coefficient include elevation of target via DEM ingestion.

Does ARCSI take into account the local orientation of the surface to correct the apparent reflectance (TOA reflectance) 

to be used in the inversion with xa, xb amd xc coefficient?

In other words, assuming a uniform lambertian surface, the atmospherically corrected reflectance is estimate as

y=aX×(apparent reflectance)−bXsurface reflectance=y1.0+cX×y
where 

apparent reflectance = pi * measured_radiance / (cos_theta * solar_flux)

theta is the actual sun zenith angle (locally  defined via DEM).

Is it correct?

Thanl you in advance

Lucia

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