XXII ISPRS Congress 2012: Technical Commission VII

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Multivolume work

Persistent identifier:: 1663813779

Title:: XXII ISPRS Congress 2012

Sub title:: Melbourne, Australia, 25 August-1 September 2012

Year of publication:: 2013

Place of publication:: Red Hook, NY

Publisher of the original:: Curran Associates, Inc.

Identifier (digital):: 1663813779

Language:: English

Additional Notes:: Kongress-Thema: Imaging a sustainable future

Corporations:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Adapter:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Founder of work:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Other corporate:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Document type:: Multivolume work

Volume

Persistent identifier:: 1663821976

Title:: Technical Commission VII

Scope:: 546 Seiten

Year of publication:: 2013

Place of publication:: Red Hook, NY

Publisher of the original:: Curran Associates, Inc.

Identifier (digital):: 1663821976

Illustration:: Illustrationen, Diagramme

Signature of the source:: ZS 312(39,B7)

Language:: English

Additional Notes:: Erscheinungsdatum des Originals ist ermittelt.; Literaturangaben

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

Corporations:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Adapter:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Founder of work:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Other corporate:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2019

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: [VII/1: PHYSICAL MODELLING AND SIGNATURES IN REMOTE SENSING]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: REFLECTANCE CALIBRATION SCHEME FOR AIRBORNE FRAME CAMERA IMAGES U. Beisl

Document type:: Multivolume work

Structure type:: Chapter

International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012 XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia REFLECTANCE CALIBRATION SCHEME FOR AIRBORNE FRAME CAMERA IMAGES U. Beisl* * Leica Geosystems AG, 9435 Heerbrugg, Switzerland — Ulrich.Beisl@leica-geosystems.com Commission VII, WG VII/1 KEY WORDS: Atmosphere, Modelling, Radiometric, Calibration, Processing, Multispectral, Digital, Camera ABSTRACT: The image quality of photogrammetric images is influenced by various effects from outside the camera. One effect is the scattered light from the atmosphere that lowers contrast in the images and creates a colour shift towards the blue. Another is the changing illumination during the day which results in changing image brightness within an image block. In addition, there is the so-called bidirectional reflectance of the ground (BRDF effects) that is giving rise to a view and sun angle dependent brightness gradient in the image itself. To correct for the first two effects an atmospheric correction with reflectance calibration is chosen. The effects have been corrected successfully for ADS linescan sensor data by using a parametrization of the atmospheric quantities. Following Kaufman et al. the actual atmospheric condition is estimated by the brightness of a dark pixel taken from the image. The BRDF effects are corrected using a semi-empirical modelling of the brightness gradient. Both methods are now extended to frame cameras. Linescan sensors have a viewing geometry that is only dependent from the cross track view zenith angle. The difference for frame cameras now is to include the extra dimension of the view azimuth into the modelling. Since both the atmospheric correction and the BRDF correction require a model inversion with the help of image data, a different image sampling strategy is necessary which includes the azimuth angle dependence. For the atmospheric correction a sixth variable is added to the existing five variables visibility, view zenith angle, sun zenith angle, ground altitude, and flight altitude - thus multiplying the number of modelling input combinations for the offline-inversion. The parametrization has to reflect the view azimuth angle dependence. The BRDF model already contains the view azimuth dependence and is combined with a new sampling strategy. 1. INTRODUCTION Originally, photogrammetric camera systems were used for metric purposes in the geometric domain, i.e. for measuring distances, areas and angles. This was possible with the analog film cameras which provided sufficiently good contrast and sharpness. Attempts were made to use the wet film technology for radiometric measurements using densitometers, but the radiometric resolution was poor and the results were only stable within one film roll due to the influences of temperature and developer during film development. With large format digital sensors becoming affordable for photogrammetric users ten years ago, new application areas have developed quickly. Remote sensing applications which could be handled only with calibrated satellite images can now be solved with airborne images, too. In addition, a new mass market for cheap high resolution images for use in internet based mapping systems has emerged. In addition to a minimal geometric accuracy the new applications require a balanced radiometry and removal of atmospheric artefacts. When digital cameras appeared on the market the analog film data workflow had already turned digital by using film scanners. Therefore the geometric calibration algorithms could be easily transferred to the digital image data workflow. The radiometric processing of digital camera images had long been dominated by a mere relative calibration of the lens falloff. However, the large field of view (FOV) and the varying flying height of airborne cameras introduce strongly varying effects of atmospheric stray light, giving rise to a blue hue, increasing towards the borders of the images. Furthermore the effects of bidirectional ground reflectance (BRDF) cause varying brightness within the image, the most prominent ones being sunglint in the water and a hot-spot in the image at high sun elevation. To address these radiometric aspects an EUROSDR project was initiated (Honkavaara, 2011). In order to correct those environmental artefacts in airborne images, methods from satellite and hyperspectral airborne image workflows were adapted to the needs of high-resolution photogrammetric images. Those methods use physical models which require an absolute calibration of the airborne sensors. The Leica ADS40 camera was the first commercial photogrammetric camera that provided an absolute radiometric calibration (Beisl, 2006). This was the prerequisite for applying an automated atmospheric correction in the photogrammetric workflow, which was implemented together with a BRDF correction (Beisl et al, 2008). The atmospheric correction option for ADS image data has become the standard setting in the image workflow for XPro users (Downey et al., 2010). A validation of the reflectance calibration has been presented by (Markelin et al., 2010) and (Beisl et al., 2010). The Swiss Federal Office of Topography (swisstopo) is now using absolutely calibrated ADS images to produce two quality image products in an operational way (swissimage standard product and remote sensing basis product) (Schläpfer et al, 2012). This paper gives an outline, how to extend the ADS radiometric correction algorithms for use in frame sensors like DMC (Ryan et al. 2009) or RCD30 (Wagner, 2011), (Tempelmann, 2012).

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