3D diachronic survey of riparian vegetation dynamics by photogrammetric methods: application of UAV and small airplane photographs
The three dimensional surveys of vegetation dynamics and fluvial landform adjustments at the decadal scale is needed to better understand feedbacks between morphodynamics and vegetation establishment and succession within fluvial corridors. Here, we tested the photogrammetry approach using aerial photographs of a wooded point bar in the lower Allier river, France, taken in summer 2014 at two resolutions. First, aerial photographs were taken from a small airplane, at an altitude of 500 m. Second, photographs were taken from an unmanned aerial vehicle (UAV), at an altitude of 80 m. The resolution of the photographs is 10 cm/pixel and 25 mm/pixel, respectively. We used these aerial photographs to produce canopy height models (CHM) of the wooded point bar. The accuracy of both CHMs was then analyzed by comparison with vegetation height measurements collected during a field campaign. There is high concordance between the two models and we consider the two approaches complementary. The former is adequate to map riparian vegetation dynamics at the corridor scale but with a low frequency of aerial missions (once or twice a year) because of cost and complexities associated with campaign organization. Conversely, the latter approach is suitable for a high resolution mapping at finer scales (e.g. point bar) with a lower logistical workload and higher campaign frequency adjusted to events such as floods. In addition, past dynamics of the studied point bar were analyzed by successfully producing CHMs from pre-existing aerial photographs.