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Influence of cloud cover and light intensity on the quality of photographic material obtained during nadir photogrammetric flights

Kozuba Jarosław, Marcisz Marek, Maliszewski Łukasz

Transport Problems

2025

T. 20, z. 1

39--49

The current research aimed to compare RGB images taken during nadir photogrammetric flights made in different seasons of the year and different times of the day, which resulted in the collection of material taken in different light intensities and during different levels of cloud cover (in conditions without precipitation). The flight was carried out in an area with a varied land cover, which was reflected in the accuracy of the details visible in the photos (land, buildings, vegetation, vehicles, reservoirs, watercourses, etc.). The flights were carried out at an altitude of 120 m AGL, with the size of the ground pixel being no larger than 0.04 m and the overlap at the level of 85%. An unmanned aerial vehicle (DJI Matrice 210 v2 with a DJI Zenmuse X5S camera and an Olympus M.Zuiko 12 mm lens) was used. The obtained material was processed in the Pix4D Mapper program, which allowed us to compare photos taken at different light intensities (at different degrees of cloudiness); in this way, they were assessed in terms of clarity of detail. The same flight parameters (including setting the AutoFocus option) made it possible to indicate how the lighting intensity affects the quality and quantity of recognized details, with the distinction of the type of buildings, land, vegetation, vehicles, and water objects. It was found that the details visible in orthophotomosaics created from photos taken in low light intensity are characterized by a less visible raster texture, which causes difficulties in assessing the material of which the object is made. With low light intensity, however, the geometry of cubature objects is better exposed, making it easier to determine the type of architecture and the development boundaries. Orthophotomosaics created from photos obtained at high light intensity are characterized by much greater contrast, which is an important parameter in recognizing soil and vegetation. The issue of the size of an object that can be considered in terms of clarity has not been fully resolved. The dimensions of many point and linear objects are usually below the resolving power of orthophotomosaics. However, the variety of shapes and similar colors and shades sometimes limit the recognition and differentiation of objects from the soil and vegetation category in orthophotomosaics. The minimum degree of sky coverage with clouds, expressed as a percentage, was determined: low light intensity appears from 62% cloud cover, medium intensity from 37%, and high intensity from 19%. A SWOT analysis showed the low costs of UAV operations and the relatively short time of data acquisition, as well as the rapidly growing UAV market.