Assessing the performance of UAS-compatible multispectral and hyperspectral sensors for soil organic carbon prediction

Soil laboratory spectroscopy has proved its reliability for the estimation of soil organic carbon (SOC) by exploiting the relationship between electromagnetic radiation and key spectral features of organic matter located in the VIS-NIR-SWIR (350-2500 nm) region. It currently allows estimating soil variables at sampled points, however geo-statistical techniques have to be used to infer continuous spatial information on soil properties. In this regard, the use of proximal or remote sensing data could be very useful to provide detailed spectral sampling on soil spatial variability at the field or even regional scale. However, the factors affecting the quality of spectral acquisition in outdoor conditions need to be taken into account. In this perspective, we designed a study to investigate the capabilities of two portable hyperspectral sensors (STS-VIS and STS-NIR), and two multispectral cameras with narrow bands in the VIS-NIR region (Parrot Sequoia and Mini-MCA6), against a more sensitive reference hyper-spectral sensor (ASD Fieldspec-Pro 3) to provide data for SOC modelling from ground-based measurements. The aim of the comparison was to assess the performance of Partial Least Squares Regression (PLSR) models, when moving from laboratory to outdoor conditions, namely changing illumination, air conditions and sensor distance. Moreover, to verify the transferability of the prediction models between different measurement setups, we tested a methodology to align spectra acquired under different conditions (laboratory and outdoor) or by different instruments, by means of a calibration factor based on an internal soil standard. The results, in terms of Ratio of Performance to Deviation (RPD), showed that: i) the best performance for SOC modelling under outdoor conditions were obtained using the VIS-NIR range (RPD: 4.2), while the addition of the SWIR region resulted in a worsening of the prediction accuracy (RPD: 2.9); ii) modelling on the narrow bands of the two multispectral cameras (Parrot Sequoia and Tetracam Mini-MCA6) gave better performances (RPD: 4.2 and 3.4 respectively) than with the STS hyperspectral sensors (RPD: 2.6); iii) the STS employment in the outdoor benefitted from a laboratory model calibration adopting a spectral transfer using an internal soil standard, with the RPD increasing from 1.4 to 2.9 after the alignment. We therefore suggest that the employment of VIS-NIR-based portable instrument could be a strategy to obtain accurate and spatially distributed SOC data. Moreover, the perspective of their employment on UAS could represent a cost-effective solution for precision farming applications

AN ESTIMATE OF THE SEDIMENTS VOLUME ENTRAINABLE BY DEBRIS FLOW ALONG STROBEL AND SOUTH PEZOR\uccES CHANNELS AT FIAMES (DOLOMITES, ITALY)

The area of Fiames is located on a narrow and flat valley, 2 km north to Cortina d\u2019Ampezzo, and is bounded on the right side by the Pomagagnon and Pezor\ueces peaks. At the transition between rock vertical cliffs and talus, about twenty debris channels originate and affect the talus till the bottom of the valley. The Strobel and South Pezor\ueces channels were recently routed by debris flows in 2004 and 2006. Field surveys, topographical and geo-morphological measurements were carried out to recognize the sediments volume that the debris flow can entrain during triggering and routing phases. The estimate of the erodible sediment volume was obtained through the measurements of the geo-morphological and sediments features of source areas including their locations (channel bank or bottom). The resultant estimate can help in the design of the input debris flow hydrographs for dynamic modelling of debris flow and retain basins

Characteristics of debris flows just downstream the initiation area on Punta Nera cliffs, Venetian Dolomites

The Piees de ra Mognes fan at the base of the Punta Nera cliffs, in the Venetian Dolomites (Italy), has been subject to debris flow activity for decades. Until recently, these debris flows never reached the National Road 51 on the valley bottom. Debris flows usually initiated at the base of an incised rocky channel in the Punta Nera cliffs where runoff is delivered to loose scree deposits of the fan. The main debris flow channel is strongly incised at the apex of the fan and splits into several minor channels at lower elevations. During the autumn 2014 and May 2016, two cliff collapses produced large debris deposits. Since then, the frequency of debris flows increased considerably because of the availability of debris deposits at very steep slope that lowered the runoff discharge needed for the debris flow initiation. In a few cases, debris flows that initiated in the rocky channel reached and interrupted the National Road 51, about 2 km downstream the well-known touristic village of Cortina d\u2019Ampezzo. On July 2016, a monitoring station was placed at the beginning of the debris flow channel just downstream the base of the rocky channel. In the period between July and -September, the monitoring station recorded six debris flow events. Analysis of these data is used to describe the characteristics of debris flow initial routing. Moreover, we use video image analysis to investigate the velocity and depth of the surge from the 5 August 2016 event

Monitoraggio dei deflussi superficiali in un canale roccioso inciso sul campanile dimai a fiames (cortina d'ampezzo, BL): analisi preliminari

Le colate detritiche nella zona dolomitica sono innescate dai deflussi superficiali che discendono i canali incisi sulle pareti rocciose per movimentazione del materiale detritico giacente al piede di questi. Il monitoraggio dei deflussi superficiali \ue8 quindi di notevole importanza per lo studio di questi fenomeni di tipo impulsivo caratterizzati da un innesco difficilmente prevedibile in termini orari e spaziali. Il monitoraggio oltre a determinare le condizioni idrologiche associate alla generazione delle colate detritiche, permette la verifica e calibratura di modelli idrologici per la simulazione di fenomeni tipo flash floods. A partire dall'estate 2009, si \ue8 iniziato ad instrumentare l'area di Fiames, situata 2 km a nord di Cortina d\u2019Ampezzo lungo la SS 51, con pluviometri e nel Luglio 2010 si \ue8 installata al piede del Campanile Dimai una stazione dotata di telecamere e sensori di pressione per monitorare i deflussi e l'eventuale generazione delle colate detritiche. L'analisi dei dati dei sensori di pressione per ogni evento di deflusso superficiale ha permesso di caratterizzare la risposta idrologica di un versante roccioso. Nell' Agosto 2011 \ue8 stato installato, 50 m a monte della stazione, uno stramazzo in parete sottile in un canale roccioso largo 1.65 m. Si \ue8 verificato un evento di precipitazione di carattere impulsivo (16.6 mm in 10 minuti) ed i valori di portata misurati sono stati confrontati con quelli simulati mediante un modello idrologico per flash floods

Hydrologic response in the initiation area of the Dimai debris flow (Dolomites, Italian Alps)

Debris flows are fast moving landslides of mixed water and poorly sorted debris (IVERSON, 1997; CRUDEN AND VARNES, 1996). Because of the high flow velocity, impact forces, and long runout, debris flows are commonly regarded as one of the most hazardous landslide types (JAKOB, 2005). The Dolomites region (NE Italian Alps) has one of the most frequent return intervals for large debris flows on the world (PASUTO AND SOLDATI, 2004; SKERMER AND VANDINE, 2005). In the Dolomites the landscape is dominated by steep dolomite massifs rising up to 3300 m a.s.l. The rocky cliffs are connected to the bottom of alpine valleys by means of milder slopes where bedrock is covered by a thick debris talus, deposited in post-glacial climatic conditions. Debris flow channels are deeply incised in the talus slope and feeded by small headwater basins located on the cliffs (MARCHI AND TECCA, 1992; BERTI et alii, 199). These basins are typically very steep (45°-60° on the average) and mostly consist of exposed bedrock with no vegetation and almost absent soil cover. During high intensity short duration thunderstorms, rainfall water is collected by the rocky watersheds as overland flow and trunk streams incised in bedrock, and quickly delivered to the talus cones. Most of this water infiltrates into the channel bed debris and flows downstream as subsurface stormflow. However, when the infiltration capacity of the streambed is exceeded, surface flow appears in the channel and debris flows are triggered by the progressive erosion of the loose bed debris (BERTI AND SIMONI, 2005). Although this initiation mechanism has been widely recognized in the field (e.g. CANNON et alii, 2003), monitoring data describing the onset of channel runoff and the triggering process are still lacking. In this paper we describe the monitoring systems installed on a typical debris flow catchment of the Dolomites (Dimai basin, Cortina d’Ampezzo, Belluno), with the main aim of describing the hydrologic response in the initiation area

Runoff of small rocky headwater catchments: Field observations and hydrological modeling

In dolomitic headwater catchments, intense rainstorms of short duration produce runoff discharges that often trigger debris flows on the scree slopes at the base of rock cliffs. In order to measure these discharges, we placed a measuring facility at the outlet (elevation 1770 m a.s.l.) of a small, rocky headwater catchment (area 3c0.032 km2, average slope 3c320%) located in the Venetian Dolomites (North Eastern Italian Alps). The facility consists of an approximately rectangular basin, ending with a sharp-crested weir. Six runoff events were recorded in the period 2011\u20132014, providing a unique opportunity for characterizing the hydrological response of the catchment. The measured hydrographs display impulsive shapes, with an abrupt raise up to the peak, followed by a rapidly decreasing tail, until a nearly constant plateau is eventually reached. This behavior can be simulated by means of a distributed hydrological model if the excess rainfall is determined accurately. We show that using the Soil Conservation Service Curve-Number (SCS-CN) method and assuming a constant routing velocity invariably results in an underestimated peak flow and a delayed peak time. A satisfactory prediction of the impulsive hydrograph shape, including peak value and timing, is obtained only by combining the SCS-CN procedure with a simplified version of the Horton equation, and simulating runoff routing along the channel network through a matched diffusivity kinematic wave model. The robustness of the proposed methodology is tested through a comparison between simulated and observed timings of runoff or debris flow occurrence in two neighboring alpine basins