Hemispherical Photogrammetry

Project title

Improving forest ecosystem diagnostics with special emphasis on radiation ecology issues in conjunction with digital hemispheric photogrammetry (DFG, completed).

Funding

German Research Foundation (DFG)

Motivation

Hemispheric photography is an established tool for assessing the radiation situation in forest stands. It has a clear advantage over the use of conventional radiation sensors because of the spatially resolved detection of the crown structure by a snapshot.

Objectives

The aim of the project was to derive geometric information about the canopy structure from hemispheric images for the determination of photosynthetically effective radiation values. This led to the following tasks:

Modeling the geometric projection for fisheye camera systems.
Development of a calibration method for cameras used for radiation determination.
Development of an automatic subpixel-accurate classification method for the determination of radiation-relevant areas in the images

Results

Geometric modeling

The functional relation between the object point and the corresponding image point was formulated for different fishey models and implemented in a bundle block adjustment. This allows the calibration of the fisheye camera systems with the help of a suitable calibration room. By determining individual distortion parameters for each channel of the hemispherical image, chromatic aberration effects can be corrected. A precise geometrical relation between the image of the fisheye camera and the reality can be established. The state of the sun, meteorological parameters and values from radiation models can now be transferred to the hemispherical crown images.

Kalibrierraum für Fischauge-Kamerasysteme — © IPF

Chromatische Aberration bei hemisphärischen Bildern — © IPF

Resultat der geometrischen Modellierung — © IPF

Classification of canopy images

An automatic method has been developed with which the radiation transmittance of individual pixels can be quantified subpixel-accurately. It is based on the gray value analysis along radial profiles in order to separate pure pixels from mixed pixels (1). The classification of the pure pixels takes place in two stages. A global rough classification (2) is followed by a local refinement (3). The classification of mixed pixel (4) is performed by scaling the gray value on the basis of local reference values of already classified pixels. The method is suitable for different weather conditions, different types of forest stands and is adapted to the special properties of hemispherical images.

Ablauf des Klassifikationsverfahrens — © IPF

Related Publications

1 bis 6 von 6 Einträgen

Schwalbe, E.; Maas, H.-G.; Kenter, M.; Wagner, S.: Hemispheric Image Modeling and Analysis Techniques for Solar Radiation Determination in Forest Ecosystems. In: Photogrammetric Engineering and Remote Sensing Vol. 75 (2009)

Schwalbe, E.; Maas, H.-G.; Kenter, M.; Wagner, S.: Profile based sub-pixel-classification of hemispherical image for solar radiation analysis in forest ecosystems. In: Proceedings of ISPRS Vommission VII Symposium (2006)

Schwalbe, E.; Maas, H.-G.: Ein Ansatz zur Elimination der chromatischen Aberration bei der Modellierung und Kalibrierung von Fisheye-Aufnahmesystemen. In: Photogrammetrie-Laserscanning-Optische 3D-Messtechnik, Beiträge Oldenburger 3D-Tage 2006 (2006)

Schwalbe, E.; Schneider, D.: Design and testing of mathematical models for a full-spherical camera on the basis of a rotating linear array sensor and a fisheye lens. In: Optical 3-D Measurement Techniques, Institute of Geodesy and Geophysics, TU Vienna Vol. 1 (2005), S. 245–254

Schwalbe, E.: Geometric modelling and calibration of fisheye lens camera systems. In: International archives of Photogrammetry, Remote Sensing and Spatioal Information Sciences (presented at 2nd Panoramic Photogrammetry Workshop) Vol. XXXVI, Part 5/W8 (2005)

Schwalbe, E.; Maas, H.-G.; Wagner, S.; Roscher, M.: Akquisition und Auswertung digitaler Hemisphärenbilder für waldökologische Untersuchungen. In: Publikationen der Deutschen Gesellschaft für Photogrammetrie, Fernerkundung und Geoinformation 13 (2004), S. 113–120

Diese Informationen werden vom Vorgängersystem FIS bereitgestellt.

Project Partners

The project was conducted in cooperation with the Institute of Silviculture and Forest Protection, Chair of Silviculture, Technische Universität Dresden.

Prof. Dr. habil. Sven Wagner
M.Sc.Forestry Manuela Kenter

Contact

Prof. Dr. habil. Hans-Gerd Maas (project management)
Dr.-Ing. Ellen Schwalbe (project work)