We made a series of flights to study the spectral properties of the shadow cast by objects. The Parrot Bluegrass drone performed missions during cloudless skies at an altitude of 150 meters and was above the shadow zone during the entire flight. The area covered by the flight plan was partially in shadow.
When the drone flew over the shaded area, the sunshine sensor recorded the entire range of irradiance - direct, diffused, reflected. In contrast, the downward-facing sensor recorded mainly diffused and reflected irradiance.
I’m wondering how, over the shaded zone, did the camera perform self-calibrations? Is it possible to explain the calibration process over the shaded area? Is the surface reflectance obtained in the shaded zone valid?
Can someone explain to me?