Sun angles from Sequioa+ and Ebee / correcting reflectance for sloping terrain.

Could someone please give me some further  details of the angles in the PROJECT_sun_angles.csv file that is generated when using Pix4d and the sequioa in an ebee. I am assuming that the sunsensor_nadir_angle_degree is the angle of a normal through the sunsensor to the vertical? What is the sunsensor_sun_angle_degree relative to? There seems to be a lot of variability in the recorded angles during one flight (~40 degrees for sun angle; 20 degrees for nadir angle). 

I have a site with quite sloping topography. I’m wondering about the potential of correcting the reflectance values based on angle of sun to slope; for which I’d want the sun angle relative to horizontal.

If anyone had existing workflows for correcting reflectance for terrain slope I would be interested to hear of them.



| Iain |

Hi Iain,

  1. sunsensor_sun_angle_degree is the angle between the normal of the sunshine sensor and the sun ray.

  2. sunsensor_nadir_angle_degree is the angle between the normal of the sunshine sensor and the true-up vector.

  3. We assume that the field is flat and horizontal in the Mapper. The radiometric correction allows to correct for the slope, but we need to interface it with the result from the calibration to get the terrain data, so, for now, we hard-code the angle to nadir.

Let me know if that answers your question.

Can you elaborate on point #3? I have data that needs to be corrected for slope using terrain data - where do I start? Is there a tutorial? I don’t see any such options under the radiometric correction.
Thank you!