The influence of clear sky and overcast conditions on the amount on the quality of optical data collected from drone in strong microtopography regions
Drones can quickly obtain optical data of target areas with high spatial resolution. Shadows have a negative impact on the quality of optical data, which further limits the accuracy of studies which based on these data. For strong microtopography regions, data is mainly collected under the clear sky and overcast condition. Shadows are more generated in strong microtopography regions because of the nature of itself. Direct sunlight under clear sky condition can generate a large area of shadow. Under overcast condition, light shadow produced by clouds will affect the entire study area. This study quantified and compared the differences under two sky conditions in the quality of the optical data collected by Parrot Sequoia sensor and the amount of shadow. The reflectance of the typical shadow regions is lower than that of the surface regions in all four multispectral bands for three pairs of image sets in April, June and August in Auchencorth Moss, and The amount of shadow pixels under overcast condition is much smaller than that under clear sky condition. Light shadows have almost no effect on reflectance, which can be drawn from the comparison in reflectance of the surface vegetation regions. These results indicate that data collected under overcast condition in strong microtopography regions will have better quality.