Smooth Terrain Research Articles

An Experimental Study on the Gait Patterns and Kinematics of Chinese Mitten Crabs

Despite the many studies on eight-legged animals and the importance of their mechanics of terrestrial locomotion, the mechanical energy of crabs in voluntary locomotion on uneven, unpredictable terrain surfaces has received little attention thus far. In this paper, motion video images of Chinese mitten crab (Eriocheir sinensis Milne-Edwards) locomotion on five types of terrains were recorded using a high-speed three-dimensional (3D) recording video system. The typical variables of locomotion such as gait patterns, duty factor, mechanical energy of the mass center, mass-specific rate of the total mechanical power of the mass center, and percentage recovery, were analyzed. Results show that the Chinese mitten crab uses random gaits instead of the alternating tetrapod gait with the increasing terrain roughness. The duty factors of the rows of the leading legs are greater for all terrains than those of the rows of the trailing legs. On smooth terrain, the duty factors of the rows of the trailing legs are greater than that on rough terrains. Kinematic measurements and calculations reveal that similar to mammals, birds, and arthropods, the Chinese mitten crab uses two fundamental gaits to save mechanical energy: the inverted pendulum gait and the bouncing gait. The bouncing gait is the main pattern of mechanical energy conservation. The low probability of injury and energy expenditure due to adaptations to various terrains induce the Chinese mitten crab to modify the mass-specific rate of the total mechanical power of the mass center. The statistical results of percentage recovery also reveal that the Chinese mitten crab has lower energy recovery efficiency over rough terrains compared with smooth terrains.

CO2 as the driving force of comet Hartley 2’s activity—An experimental study

In our experimental study we observed massive ice grain ejection driven by CO2, during several temperature ranges when the ice is warmed up. A'Hearn et al., 2011. Science 332, 1396–1400 and Meech et al., 2011. The Astrophysical Journal Letters 734, L1 among others, found that CO2 is the major driving force of the activity of Comet 103P/Hartley 2. In our experimental studies we found that CO2 is trapped in low temperature “cometary” amorphous water ice 3–4 orders of magnitude more efficiently than gases such as CO, CH4 and Ar. Thus, the ice grains which agglomerated to form the nuclei of comets where CO dominates CO2 in the coma seem to have formed in regions highly depleted in CO2. In the experiments we observed ice grains ranging from submicron to hundreds of microns, accompanied by jets of CO2. The experimentally observed cm size fragments, which were formed by cracking the overlying ice layer, could also be ejected under the cometary microgravity. These size ranges were also observed on Comet 103P/Hartley 2. The smooth terrain observed on Hartley 2’s “waist” is similar to the smooth terrain observed on comet Temple 1 and could have been formed by settling of ice grains ejected nearby, as observed in our experiments.

Proposal of a personal mobility vehicle capable of traversing rough terrain

Purpose: Personal mobility vehicles (PMVs) are now being actively developed. Most PMVs are wheel-driven, a mode of transport notable for its efficiency. However, such vehicles tend to have little mobility over rough terrain. We propose a new type of PMV, a vehicle that traverses relatively smooth terrain by wheel but is capable of negotiating rough terrain by using its wheel mechanisms as legs. Method: The PMV we propose is intended to provide its user with a degree of outdoor mobility in daily urban life, say when going to a neighbourhood shop or simply taking a stroll. We do not consider elevators and other infrastructural elements that should be barrier-free, but rather focus on unimproved terrains that act as barriers to transport; for example, the steps that often act as de facto boundaries around building entrances. Results: We developed a new type of PMV and implemented a new algorithm to realize the capability to move on rough terrain. We experimentally compared the capability of a commercially available PMV and the developed PMV. Conclusions: Through an experiment involving the traversing of a representative terrain and a comparative experiment using a stock PMV, we demonstrated the features of the proposed PMV.Implications for RehabilitationWe developed a single-seat personal mobility vehicle, the RT-Mover PType 3, which is capable of traversing steps and other unimproved terrain often found within an urban environment.RT-Mover PType 3 can handle oblique slopes and other terrain that can be quite difficult to negotiate with a conventional electric wheelchair, thus enabling individuals with impaired mobility to move freely about urban environments.The current vehicle is primarily intended for the active elderly and other individuals in fairly good health, although, through further research and development, we do hope to extend its usefulness to those with substantial mobility impairments.

Charting the growth of the Turkish‐Iranian plateau

Stretching from the Persian Gulf up through Turkey, the northwest‐southeast running Zagros fold‐and‐thrust belt is a region of extensive crustal deformation and seismic activity. Near the Zagros Mountains the structure of the Middle Eastern region is the result of the intersection of three tectonic plates, with the Eurasian plate being squished on both sides by the Arabian and Indian plates. Convergence of the plates is driving the formation of the Turkish‐Iranian plateau, a high‐elevation expanse of relatively smooth terrain reaching in some places more than 2 kilometers into the sky and lying northeast of the Zagros belt.

Thermal inertia and surface roughness of Comet 9P/Tempel 1

Re-calibrated near-infrared spectroscopy of the resolved nucleus of Comet 9P/Tempel 1 acquired by the Deep Impact spacecraft has been analyzed by utilizing the post-Stardust-NExT nucleus shape model and spin pole solution, as well as a novel thermophysical model that explicitly accounts for small-scale surface roughness and thermal inertia. We find that the thermal inertia varies measurably across the surface, and that thermal emission from certain regions only can be reproduced satisfactory if surface roughness is accounted for. Particularly, a scarped/pitted terrain that experienced morning sunrise during the flyby is measurably rough (Hapke mean slope angle ∼45°) and has a thermal inertia of at most 50Jm−2K−1s−1/2, but probably much lower. However, thick layered terrain and thin layered terrain experiencing local noon during the flyby have a substantially larger thermal inertia, reaching 150Jm−2K−1s−1/2 if the surface is as rough as the scarped/pitted terrain, but 200Jm−2K−1s−1/2 if the terrain is considered locally flat. Furthermore, the reddening of the nucleus near-infrared 1.5–2.2μm spectrum varies between morphological units, being reddest for thick layered terrain (median value 3.4%kÅ−1) and most neutral for the smooth terrain known to contain surface water ice (median value 3.1%kÅ−1). Thus, Comet 9P/Tempel 1 is heterogeneous in terms of both thermophysical and optical properties, due to formation conditions and/or post-formation processing.

Landform‐oriented flow‐routing algorithm for the dual‐structure loess terrain based on digital elevation models

AbstractThe loess landform in the Loess Plateau of China is with typical dual structure, namely, the upper smooth positive terrain and the lower cliffy negative terrain (P–N terrain for short). Obvious differences in their morphological feature, geomorphological mechanism, and hydrological process could be found in the both areas. Based on the differences, a flow‐routing algorithm that separately addresses the dual‐structure terrain would be necessary to encompass this spatial variation in their hydrological behaviour. This paper proposes a mixed flow‐routing algorithm to address aforementioned problems. First, the loess landform surface is divided into P–N terrains based on digital elevation models. Then, specific catchment area is calculated with the new algorithm to simulate the water flows in both positive and negative terrain areas. The mixed algorithm consists of the multiple flow‐routing algorithm (multiple‐flow direction) for positive areas and the D8 algorithm for negative areas, respectively. The approach is validated in two typical geomorphologic areas with low hills and dense gullies in the northern Shaanxi Loess Plateau. Four indices are used to examine the results, which show that the new algorithm is more suitable for loess terrain in simulating the spatial distribution of water accumulation, as well as in modeling the flow characteristics of the true surface by considering the morphological structures of the terrain. Copyright © 2013 John Wiley & Sons, Ltd.

A Two-Stage Quality Control Method for 2-m Temperature Observations Using Biweight Means and a Progressive EOF Analysis

Abstract The relatively smooth terrain embedded in the numerical model creates an elevation difference against the actual terrain, which in turn makes the quality control of 2-m temperature difficult when forecast or analysis fields are utilized in the process. In this paper, a two-stage quality control method is proposed to address the quality control of 2-m temperature, using biweight means and a progressive EOF analysis. The study is made to improve the quality control of the observed 2-m temperature collected by China and its neighboring areas, based on the 6-h T639 analysis from December 2009 to February 2010. Results show that the proposed two-stage quality control method can secure the needed quality control better, compared with a regular EOF quality control process. The new method is, in particular, able to remove the data that are dotted with consecutive errors but showing small fluctuations. Meanwhile, compared with the lapse rate of temperature method, the biweight mean method is able to remove the systematic bias generated by the model. It turns out that such methods make the distributions of observation increments (the difference between observation and background) more Gaussian-like, which ensures the data quality after the quality control.

Biomechanics and energetics of walking on uneven terrain

Walking on uneven terrain is more energetically costly than walking on smooth ground, but the biomechanical factors that contribute to this increase are unknown. To identify possible factors, we constructed an uneven terrain treadmill that allowed us to record biomechanical, electromyographic and metabolic energetics data from human subjects. We hypothesized that walking on uneven terrain would increase step width and length variability, joint mechanical work and muscle co-activation compared with walking on smooth terrain. We tested healthy subjects (N=11) walking at 1.0 m s(-1), and found that, when walking on uneven terrain with up to 2.5 cm variation, subjects decreased their step length by 4% and did not significantly change their step width, while both step length and width variability increased significantly (22 and 36%, respectively; P<0.05). Uneven terrain walking caused a 28 and 62% increase in positive knee and hip work, respectively, and a 26% greater magnitude of negative knee work (0.0106, 0.1078 and 0.0425 J kg(-1), respectively; P<0.05). Mean muscle activity increased in seven muscles in the lower leg and thigh (P<0.05). These changes caused overall net metabolic energy expenditure to increase by 0.73 W kg(-1) (28%; P<0.0001). Much of that increase could be explained by the increased mechanical work observed at the knee and hip. Greater muscle co-activation could also contribute to increased energetic cost but to unknown degree. The findings provide insight into how lower limb muscles are used differently for natural terrain compared with laboratory conditions.

Surface geomorphology of Jupiter Family Comets: A geologic process perspective

Recent spacecraft encounters with Jupiter Family Comets have revealed markedly diverse surface morphologies: Wild 2 is dominated by steep-walled and flat-floored depressions, Tempel 1 is relatively smooth and exhibits evidence for flows and layering, while Hartley 2 is bi-lobed with knobby terrain at its ends and a much smoother terrain in its middle. This diversity of surface morphologies has been interpreted as an evolutionary sequence (Belton, M.J.S. [2010]. Icarus 210, 881–897) where Jupiter Family Comets evolve from Wild 2 morphology, then to Tempel 1 morphology, and finally to Hartley 2 morphology. We propose instead that the diversity of surface morphology reflects geologic processing with diverse outcomes. In addition to impact cratering, we consider surface modification driven by the cometary activity which is responsible for gas and dust production. We consider eolian erosion that may be driven by the outflow of cometary vapor, making use of information from wind tunnel experiments and in situ studies of eolian erosion on Mars. We adopt the model of van der Waals cohesion recently proposed by Scheeres et al. (Scheeres, D., Hartzell, C., Sanchez, P., Swift, M. [2010]. Icarus 210, 968–984) and find that the average CO2 vapor outflow flux at Hartley 2 of 0.95×1017cm−2s−1 implies wind speeds sufficient to mobilize particles of 10cm size even close to the icy reservoirs where the vapor is evolved, below the surface. We suggest that particles are mobilized and entrained in flows within sub-surface outflow channels, emerging to be readily lifted into the coma, and fragmenting in the process. Although water production from Hartley 2 is greater, most of it is evolved in the coma from icy particles and does not contribute to eolian erosion of the nucleus. On the other hand, the much lower vapor outflow flux at Tempel 1 of 4×1014cm−2s−1 is insufficient, in the present model, to mobilize particles but is consistent with generating repeated fluidization episodes. The Wild 2 case is intermediate, with average outflow flux 7×1016cm−2s−1 which would be, in our model, sufficient to support eolian erosion. The steep-walled, flat-floor depressions on Wild 2 may have originated as impact features but have been subsequently modified by eolian erosion causing slope recession. We do not have definitive evidence to discriminate between an evolutionary sequence and diverse geologic outcomes, but we suggest future in situ observations at comets that may do so.

Assessment of a Photogrammetric Approach for Urban DSM Extraction from Tri‐Stereoscopic Satellite Imagery

AbstractBuilt‐up environments are extremely complex for 3D surface modelling purposes. The main distortions that hamper 3D reconstruction from 2D imagery are image dissimilarities, concealed areas, shadows, height discontinuities and discrepancies between smooth terrain and man‐made features. A methodology is proposed to improve automatic photogrammetric extraction of an urban surface model from high resolution satellite imagery with the emphasis on strategies to reduce the effects of the cited distortions and to make image matching more robust. Instead of a “standard” stereoscopic approach, a digital surface model is derived from tri‐stereoscopic satellite imagery. This is based on an extensive multi‐image matching strategy that fully benefits from the geometric and radiometric information contained in the three images. The bundled triplet consists of an IKONOS along‐track pair and an additional near‐nadir IKONOS image. For the tri‐stereoscopic study a densely built‐up area, extending from the centre of Istanbul to the urban fringe, is selected. The accuracy of the model extracted from the IKONOS triplet, as well as the model extracted from only the along‐track stereopair, are assessed by comparison with 3D check points and 3D building vector data.

Impact reduction mobile robot and the design of the compliant legs

In most mobile robots, the ability to move from point to point in various types of terrain was the most crucial part to the design. Being able to survive through impact conditions is also essential for robots under hazardous circumstances such as rescue robots or military robots. In this paper, we designed and developed a robot with impact reduction mechanism which is based on the compliant design of its legs. The stiffness of the legs was designed to not only to serve walking purposes but also to help reduce the impact while dropping. An experiment was set to investigate how the radius of curvature of the connecting plate and the compliant leg of the robot play a role in impact absorption. The radius of curvature is one of the key factors which vary the stiffness of the compliant parts. With this design, the robot will gradually press the ground during landing using springlike legs. The compliant legs with nonlinear spring constant help absorb impact energy while the robot hits the ground. During drop-landing motion, the robot also transforms itself from a spherical shape into a legged robot while landing. The legs are extended into a walking mechanism on uneven terrain and retracted to create a ball shaped robot for rolling motion over smooth terrain. The transformation between the spherical shaped robot and the legged robot increase its motion capabilities under various conditions including falling, rolling and walking.

Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO 263I-I and EU Directive 2002/44/EC

Operators of load-haul-dump (LHD) vehicles are commonly exposed to whole-body-vibration (WBV) levels above ISO 2631–1 and EU Directive 2002/44/EC guidelines. WBV was measured at the floor and seat while the same operator drove two LHDs on a controlled test track while driving speed, bucket load, ride control, terrain type, driving task, and seat optimization were varied. Frequency-weighted RMS acceleration was calculated and A(8) values were modeled for six driving scenarios. Vibration exposure was lowest when the LHD was driven at the lowest speed, forward, over smooth terrain, with ride control on and the bucket loaded (0.20 m/s2). The A(8) decreased from 0.84 m/s2when driving with ride control off, over mixed terrain using all gears, to 0.53 m/s2when driving with ride control on and an optimized seat. The estimated daily exposure decreased but remained just above the ISO 2631–1 and EU Directive 2002/44/EC guidelines.

Earthquake‐generated landslides: An important control of riverbed erosion

River erosion is a powerful shaper of topography, cutting through bedrock and over time converting smooth terrain to rolling hills or jagged cliffs. The rate of bedrock incision is influenced by the stream's slope and width, the water's flow rate, and the presence of sediment, among other factors. Researchers know sediment can play two conflicting roles: If the river's sediment load is low, it acts like sandpaper, increasing the rate of riverbed erosion. If there is plentiful sediment in the river, it forms a protective barrier along the riverbed, limiting erosion. What remains uncertain, however, is the influence of large, periodic inputs of sediment that enter rivers because of landslides or other extreme events.

Mountain snow distribution governed by an altitudinal gradient and terrain roughness

[1] The heterogeneous mountain snow cover is challenging the eye and the analytical mind of the observer. The snow distribution affects water resources, natural hazards such as avalanches and ecology. While a lot of recent research has helped to better understand this snow distribution and the processes that cause the heterogeneity, it has not yet been possible to predict snow distribution satisfactorily on the basis of terrain parameters alone. We present a model of the mean snow depth in topographic control units as a function of two terrain parameters: the conventional elevation plus a fractal roughness parameter. For this we used a unique data set of high resolution measurements of snow depth from an airborne laser scanner. The model captures the heterogeneous snow distribution by merely analysing the terrain and the mean precipitation. This unusually simple relationship holds for clusters of the snow depths of small topographical units. By applying fractal analysis, we describe the roughness of the terrain and use this parameter for the prediction of snow deposition. Rougher terrain holds less snow than smoother terrain. This finding is important not only for avalanche warning or eco-hydrological applications, but also for reliably predicting how snow water storage may change in the light of the pronounced climate change already ongoing in mountain regions.

Assessments of FY-3A Microwave Humidity Sounder measurements using NOAA-18 Microwave Humidity Sounder

[1] The measurements from FY-3 MicroWave Humidity Sounder (MWHS) are compared with the data from NOAA-18 Microwave Humidity Sounder (MHS) under various atmospheric and surface conditions. A quality control (QC) procedure is applied to allow the comparison be conducted separately for outliers and nonoutliers. The QC algorithm includes a gross error check, instrument noise spikes through noise equivalent differential temperature, and an O-B biweighting check, where O represents satellite observations and B is model-simulated brightness temperature by Radiative Transfer for TIROS-N Operational Vertical Sounder based on the 6 h forecast fields of the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS). It is found that (1) the global bias and standard deviation of O-B from MWHS brightness temperatures are comparable in magnitudes to those of MHS measurements, (2) positive O-B outliers prevail in channel 3 for both MWHS and MHS instruments, and (3) biases of channels 4 and 5 are predominantly negative over land for both MWHS and MHS. A series of sensitivity experiments are carried out to demonstrate that the large positive O-B biases could be due to the errors in the atmospheric water vapor profiles from the model forecast fields being too wet, and that the negative biases over land arise mostly from errors in surface emissivity, but smooth model terrain also contributes to negative biases over land.

Spatially explicit modeling of conflict zones between wildlife and snow sports: prioritizing areas for winter refuges

Outdoor winter recreation exerts an increasing pressure upon mountain ecosystems, with unpredictable, free-ranging activities (e.g., ski mountaineering, snowboarding, and snowshoeing) representing a major source of stress for wildlife. Mitigating anthropogenic disturbance requires the spatially explicit prediction of the interference between the activities of humans and wildlife. We applied spatial modeling to localize conflict zones between wintering Black Grouse (Tetrao tetrix), a declining species of Alpine timberline ecosystems, and two free-ranging winter sports (off-piste skiing [including snow-boarding] and snowshoeing). Track data (snow-sports and birds' traces) obtained from aerial photographs taken over a 585-km transect running along the timberline, implemented within a maximum entropy model, were used to predict the occurrence of snow sports and Black Grouse as a function of landscape characteristics. By modeling Black Grouse presence in the theoretical absence of free-ranging activities and ski infrastructure, we first estimated the amount of habitat reduction caused by these two factors. The models were then extrapolated to the altitudinal range occupied by Black Grouse, while the spatial extent and intensity of potential conflict were assessed by calculating the probability of human-wildlife co-occurrence. The two snow-sports showed different distribution patterns. Skiers' occurrence was mainly determined by ski-lift presence and a smooth terrain, while snowshoers' occurrence was linked to hiking or skiing routes and moderate slopes. Wintering Black Grouse avoided ski lifts and areas frequented by free-ranging snow sports. According to the models, Black Grouse have faced a substantial reduction of suitable wintering habitat along the timberline transect: 12% due to ski infrastructure and another 16% when adding free-ranging activities. Extrapolating the models over the whole study area results in an overall habitat loss due to ski infrastructure of 10%, while there was a > 10% probability of human-wildlife encounters on 67% of the remaining area of suitable wintering habitat. Only 23% of the wintering habitat was thus free of anthropogenic disturbance. By identifying zones of potential conflict, while rating its relative intensity, our model provides a powerful tool to delineate and prioritize areas where wildlife winter refuges and visitor steering measures should be implemented.

Variability and stability analysis of walking of transfemoral amputees

Variability and stability of walking of eight transfemoral amputees and eight healthy controls was studied under four conditions: walking inside on a smooth terrain, walking while performing a dual-task and walking outside on (ir)regular surfaces. Trunk accelerations were recorded with a tri-axial accelerometer. Walking speed, mean and coefficient of variation of stride times (ST) and the root mean squares (RMS) of trunk accelerations was calculated. Gait variability and stability were quantified using measures derived from the theory of stochastic dynamics. Regularity was indexed using the sample entropy (SEn) and the scaling exponent α derived form Detrended Fluctuations Analysis. Local stability (LSE) quantified gait stability. Walking speed was lower, but ST variability was not different for amputees than controls. RMS of medio-lateral accelerations was higher for amputees; SEn was higher, implying less predictable accelerations, and LSE higher, indicating decreased stability. The largest condition effect was present for walking outside: trunk RMS increased and LSE decreased. Differences in walking between amputees and healthy controls and their responses to perturbations revealed themselves in the magnitude, variability and stability measures of trunk accelerations. These results imply that quantifying the dynamical structure of trunk accelerations can differentiate between groups with different walking abilities and between conditions of increasing difficulty and may therefore provide a useful diagnostic tool.

SMOOTHING IMPRECISE 1.5D TERRAINS

We study optimization problems for polyhedral terrains in the presence of data imprecision. An imprecise terrain is given by a triangulated point set where the height component of the vertices is specified by an interval of possible values. We restrict ourselves to terrains with a one-dimensional projection, usually referred to as 1.5-dimensional terrains, where an imprecise terrain is given by an x-monotone polyline, and the y-coordinate of each vertex is not fixed but only constrained to a given interval. Motivated mainly by applications in terrain analysis, in this paper we study five different optimization measures related to obtaining smooth terrains, for the 1.5-dimensional case. In particular, we present exact algorithms to minimize and maximize the total turning angle, as well as to minimize the maximum slope change. Furthermore, we also give approximation algorithms to minimize the largest turning angle and to maximize the smallest turning angle.

Techniques for averting and correcting errors in 3D terrain topology measurements

The emergence of high-fidelity vehicle and tyre models has raised the requirements for 3D terrain measurement capabilities. Inaccuracies that were once tolerable for measurement of general terrain roughness are no longer acceptable for these new applications. The data inaccuracies that arise from small inertial errors are compounded by difficulties in managing massive file sizes. These faults are most apparent when combining multiple lanes of data in the post-processing phase. This work develops two correction techniques: a general method for any terrain type and a more computationally efficient method for smooth terrain. The general terrain correction method uses overlapping points in the horizontal plane to build a discontinuity vector and applies that vector to correct adjacent lanes. While this method effectively eliminates lane-to-lane discontinuities, it is computationally inefficient for terrain that lacks localized disturbances. For simulations using smooth terrain surfaces, such as racetracks or highways, data can be down-sampled through a mean interpolation method to smooth the artefacts of inertial errors. This work provides the vehicle test engineer with guidelines to minimize inertial errors during the data collection phase as well as a post-processing tool to combine multiple lanes of high-fidelity 3D terrain surfaces.

The influence of DEM resolution on simulated solar radiation‐induced glacier melt

AbstractThe influence of digital elevation model (DEM) resolution to modelled glacier melt during peak melt production was evaluated by performing a clear sky GIS radiation simulation over the Peyto Glacier in the Canadian Rockies. DEMs were generated at eight resolutions ranging from 1 m to 1000 m grid spacing from airborne lidar data. When applied to the planar area (PA) of the terrain, it was found that total melt increased with DEM resolution (r2 = 0·63) by 4% over 3 orders of magnitude. This systematic scaling‐effect was mitigated at the basin scale, however, when the DEM slope variant area (SVA) was used to account for the increased divergence from PA as resolution increases. However, even after the inclusion of SVA in glacier surface melt simulations, localized melt variations with scale were still evident in the ablation and accumulation zone observations. In the ablation zone, there was a systematic increase in simulated melt (∼4%) as resolution decreased from 1 m to 1000 m (r2 = 0·89), with the opposite effect in the accumulation zone (r2 = 0·81). DEM resolution also affected the diurnal melt cycle, such that for the entire glacier there was a tendency for a morning over‐estimation and afternoon underestimation of melt rate with decreasing resolution. For the accumulation zone, there was an increased melt rate at low resolutions occurring in the afternoon, while in the ablation zone there was a tendency for increasing melt rates with decreasing resolution throughout the day. These localized spatio‐temporal variations in simulated melt are largely due to the lowering of ridges and raising of valley floors that occur as resolution decreases. This scale dependence in the representation of terrain morphology directly controls the pattern and relative proportion of direct beam shadowing over actively melting surfaces and thereby has a systematic influence on the grid cell‐level hydrological balance. It is recommended that GIS‐based glacier melt modelling routines take into account the slope area of grid cells, while noting that the choice of DEM scale can have a discernible and systematic influence on modelled runoff magnitude. It is important to note that while higher grid resolutions mitigate the effect of terrain smoothing on spatio‐temporal melt patterns, lower resolutions actually mitigate the systematic error associated with assuming all surface areas are planar. Copyright © 2010 John Wiley &amp; Sons, Ltd and Her Majesty the Queen in right of Canada.