Estimating snow cover from publicly available images

In this paper we study the problem of estimating snow cover in mountainous regions, that is, the spatial extent of the earth surface covered by snow. We argue that publicly available visual content, in the form of user generated photographs and image feeds from outdoor webcams, can both be leveraged as additional measurement sources, complementing existing ground, satellite and airborne sensor data. To this end, we describe two content acquisition and processing pipelines that are tailored to such sources, addressing the specific challenges posed by each of them, e.g., identifying the mountain peaks, filtering out images taken in bad weather conditions, handling varying illumination conditions. The final outcome is summarized in a snow cover index, which indicates for a specific mountain and day of the year, the fraction of visible area covered by snow, possibly at different elevations. We created a manually labelled dataset to assess the accuracy of the image snow covered area estimation, achieving 90.0% precision at 91.1% recall. In addition, we show that seasonal trends related to air temperature are captured by the snow cover index.Comment: submitted to IEEE Transactions on Multimedi

Suitability of ground-based SfM-MVS for monitoring glacial and periglacial processes

Photo-based surface reconstruction is rapidly emerging as an alternative survey technique to lidar (light detection and ranging) in many fields of geoscience fostered by the recent development of computer vision algorithms such as structure from motion (SfM) and dense image matching such as multi-view stereo (MVS). The objectives of this work are to test the suitability of the ground-based SfM-MVS approach for calculating the geodetic mass balance of a 2.1km2 glacier and for detecting the surface displacement of a neighbouring active rock glacier located in the eastern Italian Alps. The photos were acquired in 2013 and 2014 using a digital consumer-grade camera during single-day field surveys. Airborne laser scanning (ALS, otherwise known as airborne lidar) data were used as benchmarks to estimate the accuracy of the photogrammetric digital elevation models (DEMs) and the reliability of the method. The SfM-MVS approach enabled the reconstruction of high-quality DEMs, which provided estimates of glacial and periglacial processes similar to those achievable using ALS. In stable bedrock areas outside the glacier, the mean and the standard deviation of the elevation difference between the SfM-MVS DEM and the ALS DEM was-0.42 \ub1 1.72 and 0.03 \ub1 0.74 m in 2013 and 2014, respectively. The overall pattern of elevation loss and gain on the glacier were similar with both methods, ranging between-5.53 and + 3.48 m. In the rock glacier area, the elevation difference between the SfM-MVS DEM and the ALS DEM was 0.02 \ub1 0.17 m. The SfM-MVS was able to reproduce the patterns and the magnitudes of displacement of the rock glacier observed by the ALS, ranging between 0.00 and 0.48 m per year. The use of natural targets as ground control points, the occurrence of shadowed and low-contrast areas, and in particular the suboptimal camera network geometry imposed by the morphology of the study area were the main factors affecting the accuracy of photogrammetric DEMs negatively. Technical improvements such as using an aerial platform and/or placing artificial targets could significantly improve the results but run the risk of being more demanding in terms of costs and logistics

Estimating site occupancy for four threatened mammals in southeastern Laos

textThe tropical forests of Indochina harbor a suite of globally threatened tropical mammal species. These species are difficult to detect, and subsequently understudied. Noninvasive camera trapping was used to survey terrestrial mammals from a protected area in southeastern Lao PDR (Xe Sap National Protected Area). The presence-absence of four mammals (mainland serow Capricornis milneedwardsii, muntjac Muntiacus spp., macaque Macaca spp., and wild pig Sus scrofa) was modeled in an occupancy framework thereby accounting for detection probabilities. Our goals were to establish baseline occupancy data to assist with biological monitoring and to better understand the factors influencing the distribution of the target species. Naïve occupancy, or the proportion of sites at which the target species was detected, was 0.58 for muntjac, 0.55 for macaque, 0.38 for wild pig, and 0.30 for serow. True occupancy estimates (Ψ ± SE) from top-ranked models was 0.79 ± 0.21 for macaque, 0.74 ± 0.13 for muntjac, 0.51 ± 0.13 for wild pig, and 0.48 ± 0.18 for serow. The results underscore the importance of accounting for imperfect detection rates when studying rare or elusive species. I included two site covariates (forest type and distance to nearest village) in the occupancy models. Estimating occupancy as a function of site covariates improved model performance and provided insight into landscape-level factors that affect species occurrence. In the top-ranked models, serow occupancy was higher in hill evergreen forest (HEGF) than semi-evergreen forest (SEGF). Muntjac occupancy was higher in areas further from villages. Macaque occupancy was higher in areas closer to villages. Wild pig occupancy was higher in areas further from villages and in HEGF. I recommend using an occupancy framework to analyze occurrence data for difficult-to-study tropical mammal species. The results highlight the importance of Xe Sap NPA for large mammal conservation in the region.Ecology, Evolution and Behavio

Landsliding and sediment dynamics following the 2008 Wenchuan Earthquake in the Beichuan area of China

Extensive and widespread landsliding is a common feature in a post-earthquake mountainous environment. The intense seismic shaking of an earthquake leaves the ground destabilised and thus very susceptible to slope failure. In addition to co-seismic landsliding, many slopes retain the high potential to fail for a significant amount of time beyond seismic activity. Therefore there is a need to further develop our understanding of sediment dynamics of steep mountain environments once the shaking has stopped. The 2008 Wenchuan Earthquake in China resulted in widespread landsliding, generating large volumes of loose rock and soil. Examples from other recent large earthquakes warn of the potential secondary hazards associated with such loose material: up to 30m of river-bed aggradation was seen following the 1999 Chi-Chi Earthquake, Taiwan and it is thought that Sichuan may experience hazards of a similar magnitude. Preliminary reports and oblique photographs have displayed significant levels of sediment aggradation in certain areas and summer monsoonal rains continue to trigger further landslide failures. In addition to the associated hazards, this event has provided the opportunity to investigate sediment dynamics following a large earthquake (Mw = 7.9) in a unique area of heterogeneous lithology and wide ranging geophysical variables, which has been impacted upon by both seismic and post-seismic (rainfall) activity. This study uses a combination of desk-based and field-based research in order to examine the distribution and evolution of post-seismic landslide failures. Volume-area scaling laws are developed in order to allow erosion rates to be calculated and finally an innovative oblique photography technique is used to constrain the depth of sediment aggradation. The results demonstrate that as a source of material, the occurrence of landslides in this region is controlled by a combination of topographic, geologic and seismological factors. Resulting volume estimations and subsequent erosion rates indicate that the Wenchuan earthquake has potentially destroyed more material through erosion than it has built through surface uplift. To conclude the movement of sediment through a mountain catchment, levels of sediment aggradation show that a significant proportion of material from the hillslope is transported down into the valley bottom; this is seen to coincide with periods of intense rainfall. Overall, this research derives a unique assessment of sediment mobilisation in Sichuan in order to understand the controls on sediment remobilisation and secondary hazards. By constraining the extent of sediment sources and transfer, this research has the potential to aid the prediction of future post-earthquake hazards and landscape response in Sichuan, providing insight into the role of earthquakes in landscape evolution

Tree squirrels and fishers in Northern California: The effects of masting hardwoods on stand use

In western North America, tree squirrels such as western gray (Sciurus griseus) and Douglas squirrels (Tamiasciurus douglasii) are potentially important prey for fishers (Pekania pennanti). Western gray squirrels in particular may be highly ranked due to their large body size. Masting trees including black oak (Quercus kelloggii) and tanoak (Notholithocarpus densiflorus) produce an important food source for tree squirrels; therefore, forest stands containing these trees may be useful to foraging fishers. I hypothesized that; 1) the abundance of western gray and Douglas squirrels in a stand is influenced by the mast production capacity of that stand, and 2) fisher stand use is influenced by the tree squirrel abundance in a stand. I deployed remote cameras for 44 weeks in 2017 in 85 forest stands dominated by compositions of conifer, or co-dominant with conifers and tanoak or black oak in the northern Sierra Nevada Mountains of California. I predicted that; 1) forest stands with the greatest capacity for mast production would have the highest probability of occupancy and detection of tree squirrels; 2) stands with the highest occupancy and detection of tree squirrels would have the highest probability of fisher occupancy and detection, and 3) fisher stand use and detection would be conditional on the western gray squirrel occupancy status of that stand. I tested the effects of stand type and other covariates on tree squirrel and fisher occupancy and detection using single-species occupancy models, and tested the effect of gray squirrel presence on fisher occupancy and detection probability using two-species co-occurrence models. Douglas squirrels occupied most sites (psi = 0.96-1.0) irrespective of stand type. Gray squirrels and fishers had highest rates of occupancy (psi = 0.86, Ψ = 0.93) and detection (p = 0.28, p = 0.13) in tanoak co-dominant stands. Fisher stand use patterns suggested both conditional and unconditional occupancy with western gray squirrels, and model-averaged occupancy estimates were highest in tanoak co-dominant stands regardless of whether gray squirrels were present (psi = 0.95) or absent (psi = 0.97). The results of this study indicate that habitats containing masting trees such tanoak may support greater numbers of western gray squirrels than other habitats, and retention of these trees across the landscape may improve foraging habitat for fishers

Mammalian habitat use along a residential development gradient in northern Colorado

2013 Summer.Includes bibliographical references."Exurban" development occupies nearly five times more land in the United States than urban and suburban development combined. Understanding the effects of exurban development on biodiversity thus has important and wide-ranging implications for the planning, construction and stewardship of sustainable communities and surrounding rural lands. To assess the impact of exurban development on mammalian habitat use, wildlife cameras were placed along a unique development gradient designed to capture landscape permeability in a rapidly growing rural region of Colorado. Multiple-season species occupancy and relative activity (frequency of detections) were measured in summer and winter seasons and these data were analyzed in conjunction with a novel, acoustic-based approach to assessing human activity. Impacts of exurban housing varied by mammal species, with some species, such as bobcats, elk, and coyotes, showing decreased activity and occupancy levels at higher housing densities, whereas others, including red foxes and Abert's squirrels, occurred more frequently in these areas. Human-sourced activities associated with development and non-natural sound levels emerged as top models for most species. Relative activity rates corroborated occupancy results, indicating that some species not only use habitat in high density areas, they use it more frequently. In addition, some species, including black bears, preferentially used embedded greenbelts in high-density exurban subdivisions, suggesting that greenbelts may be important for structural and functional connectivity. This study demonstrates that the impacts of exurban development are species-dependent. However, incorporating well-designed and naturally vegetated open spaces into development projects and minimizing human disturbance may be critical to mitigating development impacts to most wildlife in regions undergoing continued exurban expansion

Monitoring Populations and Movement of Bobcats (Lynx rufus) on the Eastern Slope of the Sierra Nevada Mountains of California

Monitoring the spatial ecology and population densities of carnivores is critical for effective management and conservation of these populations and the ecosystems in which they exist. However, effective monitoring of carnivore populations through estimates of space use, habitat selection and densities can be difficult due to their relatively low densities and wide ranging, elusive behaviors. Bobcats (Lynx rufus) are medium sized, top-level predators which are widely distributed across North America. Quantifying space use, habitat selection and developing effective population monitoring strategies for this species will have important implications for wildlife management. My first objective was to use telemetry data to evaluate space use parameters such as home range and core area estimates, seasonal movement patters and relative habitat selection of bobcats on the eastern slope of the Sierra Nevada Mountains of California, USA. Using GPS collars, I collected data on 38 bobcats (male n = 25, female n = 13) from 2015-2018. Using kernel density home range analysis, I was successfully able to estimate home range and core area sizes for male and female bobcats and examine differences in size between sexes and between seasons. Furthermore, I developed resource selection functions (RSF) to explore relative habitat selection of male and female bobcats in the study area. My second objective was to evaluate accurate, non-invasive monitoring strategies for bobcats. Using camera trap data, I compared closed capture mark-recapture (CMR) and spatially explicit capture-recapture (SECR) methods for estimating densities of bobcats. Data was collected over a 6-week survey period in April-May of 2018. The different methods yielded very different estimates of density and spatial scale parameters. These differences likely stem from a low positive identification rate of bobcats based on pelage patterns. My findings suggest that in sparsely vegetated, open, homogenous desert ecosystems that photographic mark recapture may not be appropriate due to low identification rate of individuals. To my knowledge, my study provides the first evaluation of space use and habitat selection by bobcats on the eastern slope of the Sierra Nevada Mountains of California. Furthermore, very little research has been conducted evaluating bobcat density and monitoring strategies in this area. The findings from this study will facilitate management and monitoring of bobcats in the eastern Sierra Nevada as well as providing important insights into the spatial ecology of bobcats in this area