Review of Earth science research using terrestrial laser scanning

In this study we analyzed the relations between terrain characteristics and snow depth distribution in a small alpine catchment located in the central Spanish Pyrenees. Twelve field campaigns were conducted during 2012 and 2013, which were years characterized by very different cli- matic conditions. Snow depth was measured using a long range terrestrial laser scanner and analyses were performed at a spatial resolution of 5 m. Pearson's r correlation, mul- tiple linear regressions (MLRs) and binary regression trees (BRTs) were used to analyze the influence of topography on the snow depth distribution. The analyses were used to iden- tify the topographic variables that best explain the snow dis- tribution in this catchment, and to assess whether their contri- butions were variable over intra- and interannual timescales. The topographic position index (index that compares the rel- ative elevation of each cell in a digital elevation model to the mean elevation of a specified neighborhood around that cell with a specific shape and searching distance), which has rarely been used in these types of studies, most accurately explained the distribution of snow. The good capability of the topographic position index (TPI) to predict snow dis- tribution has been observed in both, MLRs and BRTs for all analyzed days. Other variables affecting the snow depth distribution included the maximum upwind slope, elevation and northing. The models developed to predict snow dis- tribution in the basin for each of the 12 survey days were similar in terms of the explanatory variables. However, the variance explained by the overall model and by each topo- graphic variable, especially those making a lesser contribu- tion, differed markedly between a year in which snow was abundant (2013) and a year when snow was scarce (2012), and also differed between surveys in which snow accumula- tion or melting conditions dominated in the preceding days. The total variance explained by the models clearly decreased for those days on which the snowpack was thinner and more patchily. Despite the differences in climatic conditions in the 2012 and 2013 snow seasons, similarities in snow distribu- tions patterns were observed which are directly related to ter- rain topographic characteristics.

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Topographic control of snowpack distribution in a small catchment in the central Spanish Pyrenees: intra- and inter-annual persistence

Modeling snow redistribution by wind and avalanches in hydrological studies in alpine catchments is important, as the spatial variability of the snow cover has an impact on timing and magnitude of the snowmelt runoff. Disregarding snow redistribution in models can lead to the formation of ‘snow towers,’ i.e., multi-year accumulation of snow at high elevations and an incorrect water balance. The reviewed approaches to deal with snow redistribution in hydrological models were first broadly grouped by the represented physical processes: (1) the correction of the precipitation input data to account mainly for preferential deposition, (2) the description of all wind-driven processes based on wind field data, (3) the description of gravitational transports and/or wind-driven processes based on topographic information, and (4) the statistical description of the variability of the snow water equivalent (SWE) to account for all types of snow redistribution. The review further assessed the implementation of these approaches in physically based and bucket-type hydrological models. Generally, snow redistribution consideration has improved the simulation of snow patterns and SWE and consequently the prediction of discharge in mountain catchments worldwide. Snow redistribution approaches still have some limitations and a large gap exists between the knowledge and processes in highly detailed physically based snow models and the widely used bucket-type hydrological models used for water resources and climate change studies. There is a real need to bridge this gap using the knowledge earned by snow redistribution modeling with established physically based models to develop more conceptual approaches for the application in bucket-type models.

Snow redistribution for the hydrological modeling of alpine catchments

. Erosion and deposition processes in badland areas are usually estimated using traditional observations of topographic changes, measured by erosion pins or profile metres (invasive techniques). In recent times, remote-sensing techniques (non-invasive) have been routinely applied in geomorphology studies, especially in erosion studies. These techniques provide the opportunity to build high-resolution topographic models at centimetre accuracy. By comparing different 3-D point clouds of the same area, obtained at different time intervals, the variations in the terrain and temporal dynamics can be analysed. The aim of this study is to assess and compare the functioning of terrestrial laser scanner (TLS, RIEGL LPM-321) and structure-from-motion photogrammetry (SfM) techniques (Camera FUJIFILM, Finepix x100 and software PhotoScan by AgiSoft) to evaluate erosion and deposition processes in two opposite slopes in a humid badlands area in the central Spanish Pyrenees. Results showed that TLS data sets and SfM photogrammetry techniques provide new opportunities in geomorphological erosion studies. The data we recorded over 1 year demonstrated that north-facing slopes experienced more intense and faster changing geomorphological dynamics than south-facing slopes as well as the highest erosion rates. Different seasonal processes were observed, with the highest topographic differences observed during winter periods and the high-intensity rainfalls in summer. While TLS provided the highest accuracy models, SfM photogrammetry was still a faster methodology in the field and precise at short distances. Both techniques present advantages and disadvantages, and do not require direct contact with the soil and thus prevent the usual surface disturbance of traditional and invasive methods.

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The application of terrestrial laser scanner and SfM photogrammetry in measuring erosion and deposition processes in two opposite slopes in a humid badlands area (central Spanish Pyrenees)

We review the effects of climate variability and land use / land cover changes in the Central Spanish Pyrenees at different spatial and temporal scales. Paleoclimatic studies based upon multi-proxy analyses of lacustrine, glacial and speleothematic deposits, among others, have demonstrated the occurrence of intense climatic fluctuations not only during the Late Upper Pleistocene associated to deglaciation, but also during the Holocene, affecting plant cover distribution, runoff generation, flood frequency, and the spatial organization of human activities, particularly during the 8.2 event, the Bronze Age, the Medieval Climatic Anomaly and the Little Ice Age. The study of the impact of human activity on landscape dynamics during the last 150 years has revealed dramatic changes in plant cover structure and distribution, in both the montane and the sub-alpine belts and, consequently, changes in runoff generation, soil erosion intensity, and sediment sources, whatever the spatial scale used. In general, the maximum human pressure on the territory was reached during the middle of the 19th century, with the cultivation of most of the south-facing slopes up to approximately 1650 m a.s.l., and the frequent use of fire to control shrub colonization, resulting in intense soil erosion and degradation processes, as well as the development of braided rivers with a high torrentiality. Farmland abandonment since the beginning of the 20th century (and, particularly, since the 1960s) and the declining livestock pressure have favoured plant recolonization, with the expansion of shrubs and forests in the old cultivated and grazing areas, the human-induced reforestation of large hillslopes, and the treeline upward in the subalpine belt, in this latter case with the contribution of climate warming. The most outstanding consequences of such an evolution have been: (i) the sustained decline of discharge in the Pyrenean rivers since the 1970s because of increasing actual evapotranspiration; (ii) the spatial shrinkage of sediment source areas; (iii) the increasing uncoupled geomorphic dynamics between hillslopes and channels; (iv) the decreasing importance of snow accumulation and snowmelt processes in the fluvial regime of the Pyrenean rivers, with earlier onset of the high spring discharges; (v) the changes in reservoir hydrological dynamics and the need for new management policies; and (vi) the increasing scouring processes that affect most of the Pyrenean rivers. The studies carried out on Global Change and its consequences in the Central Pyrenees confirm the extreme complexity of interactions occurring in the natural systems, and the quick response of plant cover, runoff generation and soil erosion as a consequence of climatic and land use changes.

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Los efectos geoecológicos del cambio global en el Pirineo Central español: una revisión a distintas escalas espaciales y temporales

This paper presents the methodology used to develop snow depth distribution maps for a small catchment in the Central Spanish Pyrenees covering 55 ha in a 1:10,000 scale. The Main Map was obtained using LiDAR (light detection and ranging) technology from a long-range Terrestrial Laser Scanner (TLS) in six field surveys undertaken during the 2012 winter–spring period. This technique enabled the acquisition of information at a very high resolution concerning the spatial variability of snow cover, providing snow depth information for remote areas where data acquisition is complex and hazardous. We describe the methodological steps and the quality assessment applied in developing the maps. Comparison with manual measurements confirmed the reliability of the snow depth maps, including areas located at large distances from the scanner (800 m). This method provides a promising tool for future investigations of snow dynamics in mountainous environments.

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Mapping the annual evolution of snow depth in a small catchment in the Pyrenees using the long-range terrestrial laser scanning

This paper presents the application of a long range terrestrial laser scanner for monitoring snow accumulation and evolution of glaciers in the Pyrenees. With this study we are showing the great potential of the methodology presented for studies in mountain environments, particularly in research related to the cryosphere monitoring in relation to climate variability and the complex topography typical of mountain environments. We present a comprehensive

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Utilización de técnicas de láser escáner terrestre en la monitorización de procesos geomorfológicos dinámicos: el manto de nieve y heleros en áreas de montaña

This paper presents the application of a long range terrestrial laser scanner for monitoring snow accumulation and evolution of glaciers in the Pyrenees. With this study we are showing the great potential of the methodology presented for studies in mountain environments, particularly in research related to the cryosphere monitoring in relation to climate variability and the complex topography typical of mountain environments. We present a comprehensive protocol for the acquisition and processing of point clouds measured by a laser scanner (RIEGL LPM-321) for the generation of digital terrain models, in order to compare the models obtained at different times. Thus it is possible to obtain snow thickness and changes of ice thickness. As case studies, results from two small ice masses located in the massif of Monte Perdido and snow accumulation on a small basin located in the Tena Valley are presented.

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Application of terrestrial laser scanner techniques for monitoring dynamic geomorphological processes: snow accumulation and ice masses in mountain areas

G. Arguedas

Papers

Mapping the annual evolution of snow depth in a small catchment in the Pyrenees using the long-range terrestrial laser scanning

Utilización de técnicas de láser escáner terrestre en la monitorización de procesos geomorfológicos dinámicos: el manto de nieve y heleros en áreas de montaña

Application of terrestrial laser scanner techniques for monitoring dynamic geomorphological processes: snow accumulation and ice masses in mountain areas