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Logo: Institute of Photogrammetry and GeoInformation
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Logo: Institute of Photogrammetry and GeoInformation
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AnalySAR – Building detection in urban areas by fusion of optical and SAR imagery of very high resolution (2012)

Researcher:J. D. Wegner
Duration:since 2007

A growing number of optical sensors (IKONOS, Quickbird, Worldview) and radar sensors (TerraSAR-X, CosmoSkyMed), which acquire images using the “Synthetic Aperture Radar” technique (SAR), provide imagery of very high geometrical resolution. Due to the different spectral bands of both sensor principles, complementary object properties may be used for the detection of, for example, buildings.

Optical sensors acquire very high resolution imagery covering the entire visible spectrum. Optical images also correspond to human eye perception thus facilitating interpretation. However, since optical sensors acquire the sun light that is reflected at the earth's surface, they fail at night time and if clouds are covering the region of interest. SAR sensors are not subject to these restrictions because they actively emit a microwave signal, whose reflection at the earth's surface is recorded. Hence, it is possible to map objects regardless of sun illumination and dense cloud coverage. Nevertheless, one drawback is that SAR sensors do not capture colour information. Additionally, SAR specific effects occur due to the slant range geometry and the small angular resolution of the sensors. These effects complicate image interpretation particularly in urban areas (compare SAR image in Fig.1 and optical image in Fig. 2 ).

Fig.1: SAR image of airborne sensor Aes-1 overlaid with extracted lines, which occur due to multiple reflections of the radar signal at building walls and the ground

Fig. 2: Optical aerial image of the same area as in shown in the SAR image in Fig. 1, overlaid with the lines extracted from the SAR image


Fig. 3: Optical aerial image overlaid with building detection result based merely on building hints of the optical image

Fig. 4: Optical aerial image overlaid with building detection result based on building hints of both the optical image and the SAR image


In order to combine the advantages of both sensor types, new approaches for combined optical/SAR image analyses are developed. In a first step, building hints are extracted in the SAR image (red lines in Fig. 1) and in the optical image. Next, such hints are geometrically registered and used as input to a semi-supervised learning based probabilistic classification framework. We focus especially on the integration of context information into the probabilistic classification approach. A first building detection result using hints of both sensors is shown in Fig. 4. Future applications based on the developed algorithms could for example be automatically derived change maps that are needed after natural disasters like floods and land slides. 

This project is part of the bundle project "AnalySAR", which is carried out in cooperation with researchers at the TU Berlin and the TU Munich. It is funded by the German Science Foundation (DFG).


Wegner, J.D.; Soergel, U. (2008): Registration of SAR Optical Images Containing Bridges over Land: EARSel Workshop Remote Sensing - New Challenges of High Resolution. Bochum, 2008, 8 S., CD | file |

Wegner, J.D.; Soergel, U. (2008): Bridge height estimation from combined high-resolution optical and SAR imagery: IntArchPhRS. Band XXXVII, Teil B7-3. Peking, 2008, S. 1071-1076 | file |

Wegner, J.D.; Inglada,J.; Tison,C. (2008): Automatic Fusion of SAR and Optical Imagery based on Line Features: 7th European Conference on Synthetic Aperture Radar. Band 4. Friedrichshafen, 2008, S. 171-174 | file |

Wegner, J.D.; Auer, S.; Soergel, U. (2009): Analyse urbaner Gebiete mit optischen Bildern und SAR-Bildern sehr hoher Auflösung: DGPF Jahrestagung. Band 18. Jena, 2009, S. 387-398 | file |

Wegner, J.D.; Thiele, A.; Soergel, U. (2009): Building extraction in urban scenes from high-resolution InSAR data and optical imagery: 5th IEEE/GRSS/ISPRS Joint Urban Remote Sensing Event, Shanghai, 2009, 6 S., CD  | file |

Wegner, J.D.; Auer, S.; Soergel, U. (2009): Accuracy assessment of building height estimation from a high resolution optical image combined with a simulated SAR image: IntArchPhRS (38), Part 1-4-7/WS, Hannover, 6 S., CD | file |

Wegner, J.D.; Auer, S.; Thiele, A.; Soergel, U. (2009): Analysis of urban areas combining high-resolution optical and SAR imagery: 29th EARSeL Symposium - Imaging Europe, Chania, 2009, 8 S., CD | file |

Wegner, J.D.; Thiele, A.; Soergel, U.; 2009 (2009): Fusion of optical and InSAR features for building recognition in urban areas: IntArchPhRS, Vol. XXXVIII, Part 3/W4, pp.169-174 | file |

Wegner, J.D; Auer, S.; Soergel, U.; 2010 (2010): Extraction and Geometrical Accuracy of Double-bounce Lines in High Resolution SAR Images: Photogrammetric Engineering & Remote Sensing, vol. 76(9), pp. 1071-1080 more

Wegner, J.D.; Ok, A.O.; Thiele, A.; Rottensteiner, F.; Soergel, U. (2010): Urban building detection from optical and InSAR features exploiting context, In: Proceedings of Photogrammetric Computer Vision and Image Analysis Conference, IntArchPhRS vol. XXXVIII, part 3A, Paris, 2010, pp. 239-244 | file |

Wegner, J.D.; Hänsch, R.; Thiele, A.; Soergel, U. (2011): Building Detection From One Orthophoto and High-Resolution InSAR Data Using Conditional Random Fields: IEEE Journal of selected topics in applied Earth Observations and Remote Sensing, Vol. 4(1), pp. 83-91.  more

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