Avaliação metrológica de modelos digitais de elevação obtidos por veículo aéreo não tripulado, aplicados a estudos de processos erosivos do solo

Abstract

The use of aero photogrammetry surveys using unmanned aerial vehicle (UAV) and Structure From Motion (SfM) techniques has been presented as a major advance for studies of the dynamics of soil erosive processes by comparing multitemporal series of digital elevation model (DEM) and orthophoto mosaics. The estimation of erosion and deposition volumes by comparison of DEMs can be done by means of altimetric changes detection, called Goemorphic Change Detection. In this case, knowledge of the uncertai nties associated with each digital elevation model (DEM), as well as the propagation of errors for its proper use, is of paramount importance. This study aim was to assess the spatial resolution and the altimetric accuracy of digital elevation models obtai ned from different aerial photogrammetric survey configurations with UAV and validated by topography and geodesy techniques, and comparisons between replicates of DEMs obtained before and after the execution of controlled excavations. We performed flights of 15 m up to 100 m and obtained DEMs of Ground Sample Distance (GSD) from 1 cm to 8 cm and an altimetric error of the order of 1 cm to 14 cm. The results of the comparison between replicates of the DEMs, before and after the excavation, presented volumetric discrepancies of 0.1 m3 to 8 m³, called "inclusion errors" and percentages of 64% to 100% of omission in the detection of the controlled excavations. The second part of this study aimed to evaluate a series of four DEMs obtained over a year to monitor erosive processes in an area of gully and gully and its correlation with rainfall accumulated during the study period. Therefore, it were obtained DEMs of GSD of 10 cm with centimetric order accuracy were obtained; it was also possible to detect erosion and deposition events of the order of 2 m³ in furrows and gullies in the initial stage and events of the order of 100 m³ in gullies at an advanced stage. It were obtained DEMs of GSD of 10 and altimetric accuracy of centimeter order; it was also possible to detect erosion and deposition events of the order of 2 m³ in furrows and gullies in the initial stage and events of the order of 100 m³ in gullies at an advanced stage.