Terrain Roughness Research Articles

Modelling uneven terrain for geo-location of mines detected via vehicular mounted sensors

When searching for landmines using vehicular-mounted sensors, it is important that the ground locations of the detected mines be accurately determined. This is useful for data association when one has multiple looks at a mine by a single sensor or if one uses multiple sensors. This knowledge is necessary for neutralizing the detected mines or at least marking them for avoidance. Factors that contribute to errors in geo-location include sensor error, inaccurate knowledge of the vehicle position and/or attitude, and incomplete knowledge about the terrain being searched. This paper addresses the problem of incomplete terrain knowledge and its effects on geo-location accuracy. It presents different techniques for modelling the terrain and reducing the geo-location errors. A variety of uneven surfaces have been simulated. Random noise has been added to the basic surfaces to simulate the terrain roughness. A terrain model is then derived based on measurements one could obtain from a coarse scan of the field of view using a ranging laser. Two types of sensors are considered for the landmine detection: Synthetic Aperture Forward-Looking Radar (SAFLR) and Camera Type Sensors such as Infrared (IR). Relationships between the terrain unevenness and resulting geo-location errors are presented. The geo-location errors are worse for the Camera Type Sensor, but they can be significant for SAFLR also. The results of this analysis demonstrate that there may be significant geo-location errors for situations where the terrain is not so smooth, e.g. off-road searches, and that the problem can be alleviated via better knowledge of the terrain. If the field of view is planar or almost planar, even coarse-range scanning can improve the geo-location accuracy. For more complex surfaces, finer scanning may be required (preliminary results on this topic were presented at the SPIE (International Society for Optical Engineering) Conference, Orlando, FL, April 2001 (G. Cook, S. Jakkidi, S. Kansal, C. Amazeen and K. Sherbondy, “Impact of uneven terrain on geo-locations errors for mines detected via vehicular mounted sensors”, in Proceedings of SPIE, 2001, pp. 594–605.)). The computed geo-location errors, and the conclusions drawn as to the effectiveness of the different models are presented in the paper.

Relief effects on aerial photos geometric correction

Aerial photos are the best support to detect changes in the landscape over the time, particularly when associated with GIS based analyses. Since all metrics calculated on a landscape (from area coverage by vegetation classes to patches shape and size) are sensible to geometric distortions, the geometric correction of aerial photos is due to allow a realistic multi-temporal study. In this paper the mostly used methods of rectification were applied to aerial photos of different terrain types, with respect to their roughness (a flat area, a hilly area and a volcanic area), aiming to test residuals in x and y axes, under different conditions of terrain roughness. Polynomial functions confirmed their power in rectification process only in case of flat areas, with an increase of the error with more rugged terrains; on the contrary, orthorectification assured great results for all terrain types.

Fire heterogeneity in Kakadu National Park, 1980 - 2000

Although it is generally acknowledged that fire-induced heterogeneity is important for maintaining diverse species assemblages in northern Australian savannas, scant relevant data are currently available to examine this proposition. The study takes advantage of a singular, detailed, bidecadal fire history assembled annually for Kakadu National Park to explore relationships between fire-induced heterogeneity and other terrain features. Three patch-based heterogeneity indices were calculated from assembled fire-history data for the central 1-ha cell of a 5 × 5 cell (25 ha) window; that is, at a spatial scale relevant to the home ranges of many small- to medium-sized native mammals. Two of these indices were first calculated separately for each year, employing different metrics based on the extent of burning occurring in the 5 × 5 cell array, and then averaged for each of four consecutive five-year periods and over all years. The third index was calculated as the sum of the coefficients of variation for four fire-regime variability parameters determined likewise for five- and 20-year periods. Assembled data illustrate that (1) fire-induced heterogeneity in Kakadu increased in each successive five-year period from 1981, and (2) when modelled with independent terrain coverages, significant relationships were obtained for all three heterogeneity indices with terrain roughness, distance to roads, and distance to drainage lines.

ドップラーソーダによる海岸と内陸部における平均風速と風速鉛直成分の乱れの強さの鉛直分布に関する研究

Authors' group has been conducting full-scale measurements of wind velocities by Doppler sodars. It is very important to accurately assess the profiles of mean wind speeds and turbulence intensities in relation to the terrain roughness. The profiles were evaluated for all data measured at seashore and two inshore sites. The profiles in strong winds can be approximately expressed by power laws at altitudes between 50m to 340m. The power exponents of mean wind speed profiles are approximately 0.07 for sea winds and 0.2〜0.3 for land winds. Those of turbulence intensity profiles of vertical velocity are approximately 0.0 and -0.2〜-0.4 respectively.

STARTER: a statistical GIS-based model for the prediction of snow avalanche susceptibility using terrain features—application to Alta Val Badia, Italian Dolomites

This article describes a methodology to localise areas with high potential towards natural snowpack instability under particular meteorological conditions, at the scale of an Alpine valley. Localisation is based on statistically relating known release areas of past avalanche events to maps of: (1) slope inclination, (2) slope orientation (aspect), (3) elevation, (4) distance from crest lines, (5) terrain roughness and (6) concavities/convexities. The maps have been built using two different GIS softwares while the statistical analyses have been performed with a specific software handling also Fuzzy Set theory algorithms. The results of the statistical analyses have been verified on test release—areas which have not been used as input data for the statistical analyses. Verification allowed to quantify how reliably the susceptibility values were calculated, to compare the values obtained using different combinations of terrain features and to finally decide on the most efficient combination. The susceptibility maps were calculated and verified for three different meteorological scenarios (given by three classes of snow depth). Verification has shown that the accuracy of the susceptibility maps was between 67% and 82%. The three susceptibility maps show a remarkable difference in the spatial pattern of the highest susceptibility pixels suggesting that for different meteorological scenarios different classes of terrain features need to be considered. The possibility to make combinations of terrain features and to assess and verify their statistical relationship with release areas of past avalanche events is the major original step made by STARTER. Linking those release areas to meteorological scenarios is an attempt to include in the analysis the combined influence of terrain features and meteorological conditions towards snowpack instability.

Rule-Based Traversability Indices for Multi-Scale Terrain Assessment

This paper presents novel measures of terrain traversability at three different scales of resolution; namely Local, Regional, and Global Traversability Indices. The Local Traversability Index is related by a set of linguistic rules to local obstacles and surface softness, measured by on-board sensors mounted on the robot. The rule-based Regional Traversability Index is computed from the terrain roughness and slope that are extracted from video images obtained by on-board cameras. The Global Traversability Index is obtained from the terrain topographic map, and is based on the natural or man-made surface features such as mountains and craters. Each traversability index is represented by four fuzzy sets with the linguistic labels {POOR, LOW, MODERATE, HIGH}, corresponding to surfaces that are unsafe, moderately-unsafe, moderately-safe, or safe for traversal, respectively 1.

Azimuthal anisotropy of longwave and infrared window radiances from the Clouds and the Earth's Radiant Energy System on the Tropical Rainfall Measuring Mission and Terra satellites

Shadowing by vegetation, landforms, or clouds can reduce the surface temperature relative to unshadowed portions of the same land area. This shading effect can cause azimuthal variation of the outgoing infrared radiance that is currently not taken into account in remote sensing and Earth radiation budget analyses. In this paper, multiangle longwave (LW) (5–200 μm) and window (WN) (8–12 μm) radiances taken by the Clouds and the Earth's Radiant Energy System (CERES) rotating azimuth plane scanner on the Tropical Rainfall Measuring Mission (TRMM) and Terra satellites are used to determine the azimuthal anisotropy of LW and WN fields over all solar zenith angles and surface types in clear and cloudy conditions. The azimuthal component of the anisotropy is isolated by constructing limb‐darkening models for each category of surface type and topography in each solar zenith angle (SZA) bin. The viewing zenith angle dependence of WN and LW radiances in clear scenes depends on the SZA, possibly because of changes in the boundary layer temperature structure during the day. The observed mean radiances, in general, are greater when viewing the sunlit hemisphere (backscattering) than when viewing the shaded (forward scattering) hemisphere. This forward‐back contrast increases with increasing terrain roughness and is stronger for surfaces with open vegetation such as shrubs and grass than for contiguous vegetation like forests. The anisotropy is less well defined for barren deserts. Maximum anisotropy occurs for SZAs between 48° and 70°. This paper provides the first evidence that clouds also induce longwave azimuthal anisotropy. Strong forward‐back radiance contrast is evident for partly, mostly, and overcast scenes for SZA < 48°. The contrast disappears for overcast scenes and decreases for partly and mostly cloudy scenes at higher SZAs. The TRMM sampling is limited and causes some biases at particular angle sets but overall provides a reasonable depiction of the anisotropy at all SZAs. Terra yields a more accurate anisotropy characterization but only for SZAs between 48° and 70°. A simple model constructed from the TRMM results for clear scenes reduces clear‐sky temperature prediction RMS errors by 38% or more while minimizing the biases associated with azimuthal anisotropy. The model should yield similar or better reductions in the errors associated with retrievals of skin temperature or LW fluxes, especially those from geostationary satellites. In addition, future analyses of combined TRMM, Terra, and Aqua CERES data will likely provide more accurate correction models that could further reduce errors in surface skin temperature and radiative flux for both clear and cloudy scenes.

Sensitivity of a physically based method for terrain interpolation to initial conditions and its conditioning on stream location

AbstractProduction of digital elevation maps often requires interpolation of observations at particular locations. For hydrologic applications the resulting surface should have well defined drainage directions, should reproduce the roughness of natural terrain and should ideally preserve distributions of elevations, slopes and curvatures. The work of J. Niemann et al. (Water Resources Research, 2003, vol. 39, pp. 1017–1032) proposes a physically based interpolation method that is an improvement over commonly used linear or fractal interpolators. The methodology does have difficulty dealing with very sparse initial elevation and boundary flux information. This work suggests that using the commonly available horizontal location of main channels (‘blue lines’) improves the physical interpolation significantly. The results are illustrated on two river basins. Copyright © 2004 John Wiley & Sons, Ltd.

Exploration of Factors Limiting Biomass Estimation by Polarimetric Radar in Tropical Forests

Direct inversion of radar return signals for forest biomass estimation is limited by signal saturation at medium biomass levels (roughly 150 ton/ha for P-band). Disturbing factors such as forest structural differences - and, notably, at low biomass levels, terrain roughness, and soil moisture variation - cause further complications. A new and indirect inversion approach is proposed that may circumvent such problems. Using multifrequency polarimetric radar the forest structure can be assessed accurately. Ecological relationships link these structures with biomass levels, even for high biomass levels. The LIFEFORM model is introduced as a new approach to transform field observations of the complex tropical forest into input files for the theoretical UTARTCAN polarimetric backscatter model. The validity of UTARTCAN for a wide range of forest structures is shown. Backscatter simulations for a wide range of forest structures, terrain roughness, and soil moisture clearly show the limitations of the direct approach and the validity of the proposed indirect approach up to very high levels of biomass.

A wind map of Bangladesh

Utilization of wind energy in Bangladesh has been slow mainly due to lack of quality wind data. Recent measurements in some places have shown significant wind energy potentials in Bangladesh. In this paper, a wind map is presented which incorporates several microscale features, such as terrain roughness, elevation etc. with a mesoscale model. Several meso-maps were obtained from global databases and a suitable model was chosen and modified for a 30-m elevation. Ground data from various sources were collected and modified for height and land condition adjustments based on local knowledge and GIS information. It was found that, the generated wind map and the modified ground data resemble. Annual average wind speed at 30 m height along the coastal belt is above 5 m/s. Wind speed in northeastern parts is above 4.5 m/s while inland wind speed is around 3.5 m/s for most part of Bangladesh. Small-scale wind turbines could be installed and tested in locations such as St. Martins Island, Cox’s Bazar, Patenga, Bhola, Barguna, Dinajpur, Thakurgaon and Panchagar.

The nucleus of Comet Borrelly: a study of morphology and surface brightness

Stereo images obtained during the DS1 flyby were analyzed to derive a topographic model for the nucleus of Comet 19P/Borrelly for morphologic and photometric studies. The elongated nucleus has an overall concave shape, resembling a peanut, with the lower end tilted towards the camera. The bimodal character of surface-slopes and curvatures support the idea that the nucleus is a gravitational aggregate, consisting of two fragments in contact. Our photometric modeling suggests that topographic shading effects on Borrelly's surface are very minor (<10%) at the given resolution of the terrain model. Instead, albedo effects are thought to dominate Borrelly's large variations in surface brightness. With 90% of the visible surface having single scattering albedos between 0.008 and 0.024, Borrelly is confirmed to be among the darkest of the known Solar System objects. Photometrically corrected images emphasize that the nucleus has distinct, contiguous terrains covered with either bright or dark, smooth or mottled materials. Also, mapping of the changes in surface brightness with phase angle suggests that terrain roughness at subpixel scale is not uniform over the nucleus. High surface roughness is noted in particular near the transition between the upper and lower end of the nucleus, as well as near the presumed source region of Borrelly's main jets. Borrelly's surface is complex and characterized by distinct types of materials that have different compositional and/or physical properties.

Pyroclastic flow hazard assessment at Vesuvius (Italy) by using numerical modeling. I. Large-scale dynamics

The thermofluid dynamics of pyroclastic flows down the slopes of Vesuvius (Italy) were investigated using physical modeling of the magma ascent and pyroclastic dispersal processes. The expected properties and conditions of the magma, such as its anhydrous composition, water content, and temperature, were based on the present knowledge of the magmatic system and were used as input data for the magma ascent model. The predicted vent conditions were used to define the boundary conditions for the simulation of pyroclastic flow dispersal along selected two-dimensional axisymmetric profiles, representative of the southern and northern slopes of Vesuvius. The model employed describes the temporal evolution of a three-phase mixture composed of a continuous gas phase and two solid phases representative of fine and coarse particles. The specific terrain roughness of the slopes of Vesuvius, caused by the presence of pine woods and urban settlements, was also estimated and accounted for by the model. Several simulations were carried out by assuming different magmatic compositions (in terms of water content and temperature), eruption intensities, topographic profiles, and flow duration. Pyroclastic flow dynamics appear to be strongly influenced by the fountain and atmospheric dynamics showing complex, unsteady, and, in some cases, non-intuitive behaviors. The mass flow-rate per unit angle of propagation of the flow proves to be the most critical parameter controlling the run-out and, therefore, the hazard on the slopes of Vesuvius. The two-dimensional topographic profiles employed also appear to significantly affect the flow propagation. Simulation outputs allow the quantification of the spatial and temporal evolution of several flow variables that are critical in hazard mitigation studies. The analysis of these variables is extensively described in a companion paper (Esposti Ongaro et al. 2002, this volume).

Characteristics of wind and rainfall induced by typhoons from the viewpoint of building damage

Meteorological data during typhoons, measured at 46 JMA meteorological observatories in Japan from 1975 to 1997, are analyzed from the viewpoint of building damage. The number of typhoons used for the present analysis ranges from 29 at Sapporo to 110 at Okinawa. Special attention is paid to the gust factor and the intensity and amount of precipitation at and after the occurrence of the maximum peak gust. Based on the results, a simple model of the gust factor is provided, in which the effect of terrain roughness is considered. Furthermore a stochastic model is proposed for the amount of precipitation as a function of the shortest distance between the typhoon center and the observation site. These models can be incorporated into a prediction model of typhoon-induced building damage, which the authors are now developing.

Heterogeneous Traffic Induced Effects on Vertical Dispersion Parameter in the Near Field of Roadways - a Wind Tunnel Study

The varying traffic parameters such as traffic volume, speed, shape and size, and terrain roughness conditions play a vital role on dispersion of pollutants in the near field of roadways. Simulation experiments were carried out in the Environmental Wind Tunnel (EWT) to evaluate the traffic induced effects on vertical dispersion parameter (σ z ) for heterogeneous traffic conditions in the near field of roadways for evaluating the effect of variations in traffic volume, terrain roughness condition and approaching wind direction. The model vehicle movement system was fabricated and made operational in the EWT, which allowed the variation in traffic volume, speed and wind road inclination. Sixty-six hydrocarbon tracer experiments were performed to evaluate σ z in the near field of roadways for variable traffic volume, three terrain roughness conditions and two approaching wind directions (i.e., 90° and 60°). The values of σ z for heterogeneous traffic conditions were found to be higher for low roughness conditions in comparison to other two higher roughness conditions for various traffic volumes and approaching wind directions.

Simultaneous wind measurements over two sites using Doppler sodars

In wind-resistant design of buildings and structures, it is very important to accurately assess the design wind speed at a particular site, considering the variation in wind speed with terrain roughness. In this study, the authors attempt to find a reasonable method for estimating design wind speed for a given terrain roughness, through simultaneous observations of atmospheric boundary layer wind speeds over two sites with different roughnesses using Doppler sodars. The mean wind speed profiles at the two sites during the same storms were compared to study the variation in mean wind speed as this is affected by inland terrain roughness.

The roughness of natural terrain: A planetary and remote sensing perspective

We examine the various methods and parameters in common use for quantifying and reporting surface topographic “roughness.” It is shown that scale‐dependent roughness parameters are almost always required, though not widely used. We suggest a method of standardizing the parameters that are computed and reported so that topographic data gathered by different workers using different field techniques can be directly and easily intercompared. We illustrate the proposed method by analyzing topographic data from 60 different surfaces gathered by five different groups and examine the information for common features. We briefly discuss the implications of our analysis for studies of planetary surface roughness, lander safety, and radar remote sensing modeling and analysis.

The impact of resolution on the accuracy of hydrologic data derived from DEMs

Hydrologic data derived from digital elevation models (DEM) has been regarded as an effective method in the spatial analysis of geographical information systems (GIS). However, both DEM resolution and terrain complexity has impacts on the accuracy of hydrologie derivatives. In this study, a multi-resolution and multi-relief comparative approach was used as a major methodology to investigate the accuracy of hydrologie data derived from DEMs. The experiment reveals that DEM terrain representation error affects the accuracy of DEM hydrological derivatives (drainage networks and watershed etc.). Coarser DEM resolutions can usually cause worse results. However, uncertain result commonly exists in this calculation. The derivative errors can be found closely related with DEM vertical resolution and terrain roughness. DEM vertical resolution can be found closely related with the accuracy of DEM hydrological derivatives, especially in the smooth plain area. If the mean slope is less than 4 degrees, the derived hydrologie data are usually unreliable. This result may be helpful in estimating the accuracy of the hydrologie derivatives and determining the DEM resolution that is appropriate to the accuracy requirement of a particular user. By applying a threshold value to subset the cells of a higher accumulation flow, a stream network of a specific network density can be extracted. Some very important geomorphologie characteristics, e.g., shallow and deep gullies, can be separately extracted by means of adjusting the threshold value. However, such a flow accumulationbased processing method can not correctly derive those streams that pass through the working area because it is hard to accumulate enough flow direction values to express the stream channels at the stream’s entrance area. Consequently, errors will definitely occur at the stream’s entrance area. In addition, erroneous derivatives can also be found in deriving some particular rivers, e.g., perched (hanging up) rivers, anastomosing rivers and braided rivers. Therefore, more work should be done to develop and perfect the algorithms.

Dynamic Damping and Stiffness Characteristics of the Rolling Tire

Abstract A variable parameter model to study dynamic tire responses is presented. A modified device to measure terrain roughness is used to measure dynamic damping and stiffness characteristics of rolling tires. The device was used to examine the dynamic behavior of a tire in the speed range from 0 to 10 km/h. The inflation pressure during the tests was adjusted to 160, 240, and 320 kPa. The vertical load was 5.2 kN. The results indicate that the damping and stiffness decrease with velocity. Regression formulas for the non-linear experimental damping and stiffness are obtained. These results can be used as input parameters for vehicle simulation to evaluate the vehicle's driving and comfort performance in the medium-low frequency range (0–100 Hz). This way it can be important for tire design and the forecasting of the dynamic behavior of tires.

Evaluation on the accuracy of digital elevation models

There is a growing interest in investigating the accuracy of digital elevation model (DEM). However people usually have an unbalanced view on DEM errors. They emphasize DEM sampling errors, but ignore the impact of DEM resolution and terrian roughness on the accuracy of terrain representation. This research puts forward the concept of DEM terrain representation error (Et) and then investigates the generation, factors, measurement and simulation of DEM terrain representation errors. A multi-resolution and multi-relief comparative approach is used as the major methodology in this research. The experiment reveals a quantitative relationship between the error and the variation of resolution and terrain roughness at a global level. Root mean square error (RMS Et) is regressed against surface profile curvature (V) and DEM resolution (R) at 10 resolution levels. It is found that the RMS Et may be expressed asRMS Et=(0.0061·V+0.0052)·V+0.2415. This result may be very useful in forecasting DEM accuracy, as well as in determining the DEM resolution related to the accuracy requirement of particular application.

3-D modelling of wind field adjustment using finite differences in a terrain conformal coordinate system

A mass consistent model is developed in order to obtain a wind field which adjusts to an initial one. For the construction of the initial field, horizontal interpolation is considered at the level of the measure stations over the terrain. From these values, vertical wind profiles are built according to atmospheric stability conditions, terrain roughness, geostrophic wind, atmospheric stratification. The problem is formulated in terms of an incompressible fluid with no-flow-through conditions on the terrain. The adjustment is carried out by minimizing a least-square function. Lagrange multipliers technique leads to an elliptic problem, which is discretized using finite-differences schemes after applying a proposed system of terrain conformal coordinate. This change not only simplifies the mesh generation, but leads to simpler boundary conditions and allows the definition of the vertical spacing with more resolution near the terrain without affecting the efficiency. Finally, the numerical model is applied to realistic data corresponding to the Island of La Palma (Canary Islands).