Integration of LiDAR and optical remote sensing for the study of fluvial and anthropogenic landforms in the Brenta-Bacchiglione alluvial plain (NE Italy)

The geomorphological study of alluvial plains takes great advantage from the integration of detailed altimetry with high resolution images, especially in the lower relief sectors, like those in the distal plain of the Brenta and Bacchiglione rivers near the city of Padua (mean slope 0.4‰).The LiDAR data which were specifically acquired for this research (Riegl LMS-Q560; mean density 7 points/m 1101 2 , over 123 km 2 ), were classified and interpolated in order to map fluvial and anthropogenic landforms. The DEM (z accuracy <5-10 cm) was processed and analyzed in integration with high resolution oblique and vertical (VIS+IR) aerial images, acquired in specific seasonal time windows, to maximize the vegetation response (cropmarks) to soils, deposits, and palaeohydrographic features. A detailed field survey (hand augerings, soil profile description, deep borehole stratigraphy) was conducted to validate the remote sensing interpretations. The detailed topography allows to individuate low rise interfluves and scarps (<1-2 m), paleochannels, scroll bars and crevasse splays. The reconstruction of the precise “ground” surface has allowed a better definition of the geometry of the multi-stratified archeological mound in the historical center of Padua. Cropmarks result the most appropriate to complete the mapping of the numerous fluvial forms, that have no topographic relevance being smaller (i.e. minor crevasse channels and splays) and/or flatted by anthropic activity (mainly ploughing). LiDAR intensity permits a precise individuation of LGM deposits that have shown peculiar reflectivity related to specific soil characteristics (i.e., presence of calcic and argillic horizons). At this scale (cell size <0.5-1 m) the real complexity of this highly anthropized low plain environment fully emerges. The results bring advances in the comprehension of the Holocene evolution of the Brenta-Bacchiglione plain, also in close relation to ancient settlements.