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 2. ATMOSPHERIC EFFECTS 2.1 Viewing Geometry The viewing geometry of line sensors simplifies radiometric corrections considerably since for a single flight line the view azimuth p is constant for every pixel, assuming the airplane movements are compensated by a stabilized platform. The area of a constant view zenith angle 6, is an image column (cf. Figure 1). Column average = mean reflectance for constant view zenith angle 6, and constant relative azimuth angle ¢ Figure 1. Viewing geometry for a line scan sensor. For frame sensors the area of constant view zenith angle is a circle and still has a varying view azimuth (cf. Figure 2). constant view / zenith angle 0, and / varying relative azimuth angle @ Figure 2. Viewing geometry for a frame sensor. 2.2 Reflectance Calibration of Aerial Images 2.2.1 Radiative Transfer Equation: For the physical description of the nadir looking passive Earth observation the radiative transfer theory of Chandrasekhar is used (Fraser et al., 1992). p ST, doy Lo L,=L, +2 (1) (1-sp) where Lm= measured at-sensor radiance Lo = path radiance for zero ground reflectance p = surface reflectance p = average surface reflectance of surrounding area S = mean solar spectral irradiance Town = total downward transmittance from top of the atmosphere (TOA) to the ground T, = total upward transmittance from ground to sensor s = spherical albedo of the atmosphere, i.e. the fraction of the upward radiance which is backscattered by the atmosphere For the case of atmospheric correction the surface reflectance p has to be calculated from the observed at sensor radiance L,, Solving eqn (1) for p gives: zl -L1,) = zu rl. ST.T (1- sg) wn up @) Suppose p is known then the quantities Lo, Taowns Tup> $, and S have to be calculated. The extraterrestrial irradiance S is given by a standard formula depending on the geographical latitude and the day of the year. 2.2.2 Model Inversion: Photogrammetric image processing has to deal with huge amounts of data, so a very efficient algorithm is needed to calculate Ly, Tyown, Typ, and s. Therefore the modified Song-Lu-Wesely method described in (Beisl et al., 2008) is used. The basic idea is the following: Standard atmospheric models calculate the at-sensor radiance, irradiance and transmittances based on a given ground reflectance, atmosphere and aerosol load. Since the ground reflectance is the unknown quantity, the model has to be inverted for a given at-sensor radiance. Unfortunately, none of the atmospheric parameters is known in case of aerial images. So standard values are assumed for all atmospheric and aerosol parameters except the horizontal visibility (which is related to the aerosol concentration) and, which has the biggest influence on the radiative transfer. A series of forward model runs is performed with all combinations of the input variables (ground elevation, flying height, sun zenith angle, view zenith angle, relative azimuth angle, and visibility), giving a multi-dimensional look-up table. The total transmittances are calculated indirectly from runs at three ground reflectances, because radiative transfer programs will typically only output the direct transmittance between sun and ground and between ground and sensor. The aim is to replace the non-observable quantity visibility by an observable quantity. The only available choice is the atmospheric reflectance à, in nadir view which is determined from the observed atmospheric reflectance à of a dark pixel viewed from a certain view zenith and azimuth angle. The atmospheric reflectance à is defined here as the difference of the observed top-of-atmosphere (TOA) reflectance a and the ground reflectance p of the dark pixel (eqn 3). The TOA reflectance is calculated from the at-sensor radiance L,, and the TOA irradiance S (eqn 4). ózo-p | (3) zl, S (4) For the dark pixel we assume an average reflectance p of 2 %. If the true reflectance spectrum of the dark pixel were known, a more accurate modelling would be possible. But if a wrong spectrum is taken then the whole image will be calibrated with this spectral error. Therefore a spectrally constant dark pixel reflectance is chosen.

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