CMRT09

Stilla, Uwe

Bibliographic data

Monograph

Persistent identifier:: 856955019

Author:: Stilla, Uwe

Title:: CMRT09

Sub title:: object extraction for 3D city models, road databases, and traffic monitoring ; concepts, algorithms and evaluation ; Paris, France, September 3 - 4, 2009 ; [joint conference of ISPRS working groups III/4 and III/5]

Scope:: X, 234 Seiten

Year of publication:: 2009

Place of publication:: Lemmer

Publisher of the original:: GITC

Identifier (digital):: 856955019

Illustration:: Illustrationen, Diagramme, Karten

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: RAY TRACING AND SAR-TOMOGRAPHY FOR 3D ANALYSIS OF MICROWAVE SCATTERING AT MAN-MADE OBJECTS S. Auer, X. Zhu, S. Hinz, R. Bamler

Document type:: Monograph

Structure type:: Chapter

In: Stilla U, Rottensteiner F, Paparoditis N (Eds) CMRT09. IAPRS, Vol. XXXVIII, Part 3/W4 — Paris, France, 3-4 September, 2009 159 Eventually, the simulation process provides the following output data for each reflection contribution detected in the 3D object scene: • coordinates in azimuth, slant range, and elevation [units: meter] • intensity data [dimensionless value between 0 and 1] • bounce level information for every reflection contribution [1 for single bounce, 2 for double bounce, etc.] • flags marking specular reflection effects [value 0 or 1] Figure 2: left: Simulation using box model having a size of 20 m x 20 m x 20 m, line of sight indicated by arrow; right: simulated reflectivity map simulated (slant- range indicated by arrow) Figure 3: simulation using step model (left), line of sight indicated by arrow; simulated reflectivity map (right), slant-range indicated by arrow 2.3 Reflectivity maps in azimuth and slant range Firstly, all reflection contributions are mapped into the azimuth - slant range plane. Afterwards, a regular grid is imposed onto the plane and intensity contributions are summed up for each image pixel. Figure 2 shows the resulting reflectivity map for a cube (dimensions: 20 m x 20 m x 20 m) which has been illuminated by the virtual SAR sensor using an incidence angle of 45 degrees. The size of one resolution cell has been fixed to cover 0.5 m x 0.5 m in azimuth and slant range. Surface parameters are chosen in a way that box surfaces can be clearly distinguished from ground parts, i.e. in the current example box surfaces show stronger diffuse backscattering than the surrounding ground. Following top-down in ground range direction, diffuse single bounce contributions of the ground are visible followed by a layover area of ground, wall of the box and top of the box. At the end of the layover area, a strong double bounce line is visible which is caused by the interaction between the front wall and the ground in front of the box. For this type of scene geometry, a 2D simulation and analysis is usually sufficient. The next section will however illustrate examples that underline the necessity of including the elevation direction as third dimension into the simulation. Figure 4: selection of pixel for elevation analysis (left); definition of three slices (right) in slant-range (1), azimuth (2), and elevation direction (3) 2.4 3D analysis of scattering effects Figure 3 shows a reflectivity map simulated by illuminating a step model (width: 10 m, length 20 m, height 20 m). For providing the map, the same imaging geometry has been chosen as for the box example, i.e. the step was oriented in direction to the sensor and the incidence angle was fixed to 45 degrees in order to obtain specific overlay effects for single and double bounce contributions which are explained in the following. Compared to the reflectivity map containing the box model (Figure 2), the reflectivity map of the step shows similar characteristics. Both the layover area of single bounce contributions and the location of focused double bounce contributions are identical. Only the size of the shadow zone indicates a height difference between the illuminated objects. In the case of the step model, separation of dihedrals - two right angles at the steps - is impossible in the reflectivity map since all double bounce effects are condensed in one single line. Hence, separation of scattering effects in elevation direction may be helpful since it enables to resolve layover effects for the purpose of distinguishing several scatterers within one resolution cell. To this end, an interactive click-tool has been included into the simulator for defining two-dimensional slices to be analyzed. In the case of the given reflectivity map for the step model, one pixel is selected, e.g. located in the double bounce area as shown in Figure 4. Based on the coordinates of the pixel center, three slices are defined: • slice no. 1 for displaying elevation data in slant-range direction • slice no. 2 for displaying elevation data in azimuth direction

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