Proximal and remote sensing on the soil processes: from punctual to spatial approaches

Abstract

Soil layers and horizons have been described in the field by Pedologists who have enough knowledge about a given region. Although limited alternatives have been used to describe the soil by equipments under natural conditions. Therefore, we must expend efforts on applying the newest technologies on these studies. We have proposed to use Vis-NIR and X-Ray Fluorescence (portable) equipments to predict soil horizonation and its process. The main objectives were: i) Identify mineralogical differences between horizons, with inferences about translocations and geochemical alteration by proximal sensors; and ii) Expand the punctual information with RGB images and Digital Surface Model obtained by unmanned aerial vehicle. Seven soil profiles (Acrisol, Cambisol and five Ferralsols) were analyzed in a São Paulo, Brazil region. The data were vertically collected in the field with a Vis-NIR-SWIR (350 -2,500 nm) spectroradiometer and with a Portable X-ray Fluorescence (pXRF). Dried samples from each layer were analyzed by a Middle Infrared (MIR) (2,500 -20,000 nm). When with exposed soils, images were taken by UAV and Terrain derivatives were built by stereoscopy. Proximal sensors allowed to perform more robust hypothesis about soil formation processes. On-the-go proximal sensor allows to describe and better understand how soil bodies behave on the landscape. The clusterization with high density data from sensors allows to better describe soil profiles horizonation. The Vis-NIR-SWIR spectral range relationship together with soil color, provides better correspondence with traditional field observation. The combined use of Vis-NIR-SWIR, MIR and pXRF allows to identify the horizon boundaries more appropriately. There was a limit between the surface color of each profile and relief which took an important spatialization by UAV data. From profiles to spatial dimension, relief plus RGB of UAV indicated important delineation of soil units.