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The Impact of Microrelief Forms on Mobility of Terrain Vehicles

When deploying off-road vehicles in military and rescue operations, it is necessary to analyse the characteristics of the terrain, its segmentation and obstacles, that can significantly eliminate the movement of this technique. The mobility of off-road vehicles depends on many factors such as terrain relief, soil, vegetation, water, road network, settlement unit structure, meteorological conditions, etc. The goal of this paper is to identify the critical micro-relief forms in the selected test area, which can be important for the transportation analyses and cartographic visualization, especially for the military and rescue operations management during the crisis situations and natural disasters such as floods, fires, storms, military operations, etc. Both of the relief parameters and technical vehicles parameters were considered for the cross-country movement analysis to predict the GO, SLOW GO and NO GO areas as a part of crisis management support.


Introduction
Geographical support and cartographic visualization is very important and indispensable element in solution of prediction system and resolution of elimination of a crisis situation impact. In the case when we are not able to use some segments on the roads (damaged or destroyed objects, traffic jam, etc.) we must to provide the complete cross-country mobility analyses to solve the transportation problems.
The main terrain elements, which determine the cross-country movement, are relief slopes and microrelief forms. Both of the relief parameters and technical vehicles parameters are important for the cross-country pass ability analyses. These analyses are often concentrated on predicting the obstacles to support the safe movement of terrain vehicles. There is a large body of literature describing the general methodologies of the cross-country movement evaluation using terrain data .
Microrelief forms are very important for the movement of off-road vehicles. Often, they cannot be detected from digital terrain models if the density of elevation points is 10 m or more.
The essential forms and parameters to the assessment of microrelief forms impact to cross-country mobility are as follows (see      We can describe terrain segments using the relief profiles, which may be continuously, randomly rough, may consist solely of a single discrete obstacle, uniformly spaced obstacles of a specific height or may be anything in between. The other possibility is to divide a terrain area into partial areas and to describe each of them by an assignment of value characterizing it (longitudinal and transversal gradient -, , coefficient of rolling resistance -(f) and coefficient of static friction -(). The less these areas will be, the more accurate calculations from the point of view of vehicle movement can be made, see figure 4.  If we will ponder the general orientation of plane in fixed grid system, then the longitudinal gradient in direction of vehicle route determined from the nearest utmost points of matrix model will be according to figure 5.
at the calculation of transversal inclination by use of the slant range of vehicle route in terrain and the truncation of terrain relief roughness between points B and C.
The transversal inclination will be according to figure 4: at the calculation of transversal inclination by use of slant range between points A and B.

Data and Methods
Different geographical data sources can be used to carry out terrain analyses and identify the terrain obstacles and microrelief forms as well. One method, which can be used during operation for terrain analyses, is using a topographic map. This type of maps is intended for assessment of landscape in relation to planning, commanding and controlling the military or rescue operations, for orientation and navigation in the terrain or for study of military-geographical characteristics of territory in generally.
Members of the Army of the Czech Republic (ACR) can use the most detailed map product -the Topographic Map in a scale 1: 25000 (TM 25), see figure 6, for the purpose of terrain analyses on the tactical level. The terrain relief is represented on this map by contour lines, elevation points and other objects that represent microrelief forms. The content of the map is subject of the cartographic generalization and this data source is not suitable for a detailed terrain analysis such as the identification of microrelief objects. Nowadays, it is more efficient to use modern information technologies for a terrain analysis, process digital geographic data and creating the thematic map products. The source digital database for creating the topographic maps in ACR is Digital Landscape Model 25 (DMU 25), see figure 7. This data creates a cartographic model at a scale of 1: 25000. For this reason, this data is already generalizedthe position of microrelief objects on the map may differ in the actual position or some microrelief objects are not displayed in the map.  Information about relief and local elevation conditions can be obtained from the digital elevation models. In the Czech Republic, there is an elevation model -Digital Terrain Model of the Czech Republic of the 5th generation (DMR 5), which by its declared total mean height error 0.18 meters can capture effectively the detailed diversity of terrain relief.
To evaluate the terrain relief features and identify microrelief objects can be used DMR 5 because this model cover whole territory of the Czech Republic and it is the most accurate from available elevation models. Based on the previous study [24], the DMR 5 was converted from the heights of discrete points format to a raster format of pixel size 0.5 meter. SW ArcGIS and its tools for spatial analyses Arc Toolbox Spatial Analysis were used to identify microrelief terrain obstacles. The Slope tool calculates the first derivative value of the input surface on a cell-by-cell basis (see figure 8 and figure 9). The Curvature tool calculates the second derivative value of the input surface on a cell-by-cell basis. For the microrelief objects identification was used profile curvature (horizontal curvature), see figure 10 and figure 11. For the verification of above-mentioned method, the part of military training area was chosen (1.46 square kilometre), where natural and artificial microrelief objects occur.  In the figure 8, it is possible to identify the terrain forms in places of rapid change of slope value. Figure 9 shows that not all microrelief object are included in DMU 25.  In the figure 10, it is possible to identify the terrain forms in places, where profile curvature reaches the local minima (convex curvature) and maxima (concave curvature). Figure 11 shows that not all microrelief objects are included in DMU 25 as well as in figure 9.
Another task of the analysis is to express influence of microrelief objects on their overcoming by military vehicles. The parameters of terrain shapes were compared with technical parameters of two selected wheeled vehicle types (table 2)rate of climbing ability versus terrain inclination value and wheelbase and ground clearance versus profile curvature, see [5].     Figure 15. Classified terrain profile curvature for Tatra 815 8x8impassable (red), probably impassable (orange) and passable terrain (green).

Results
Using the above-mentioned methodology, ARC GIS SW and digital relief model DMR 5, we created the relief slope coverage of the cross-country mobility map 1:25 000 -CCM 25, see figure 16. In the next phase of the research, we searched for such microrelief objects, which can cause by their profile curvature and slope characteristics the vehicle to get stuck, see figure 17 and figure 18.  We found that DMR 5 captures microrelief shapes more accurately than topographic maps, see figure  19 and figure 20.  impassable (red), probably impassable (orange) and passable terrain (green). Blue polygons represent areas of microrelief objects that DMU 25 does not include.

Conclusion
The cross-country mobility research as a part of the terrain analyses is very important, especially during natural disasters and crises situations, when some road segments and objects can be damaged, destroyed or crowded. In these cases, we must use the special rescue vehicles and know which terrain areas are passable and which not to ensure the rescue personnel, vehicles and optimize the rescue procedure. The cross-country mobility methodology is possible to exploit for terrain rescue vehicle navigation adapting the procedure for each type of vehicle knowing its technical parameters. For the future research approach it will be necessary to create more accurate databases, especially elevation databases with the precision corresponding with the dimensions and other vehicle technical parameterssee also [23]. Another problem is effectively to link up the cross-country movement digital map with the GPS navigation vehicle system and to train the vehicle crews to effectively use these systems.