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ATCOR 4

Atmospheric & Topographic Correction
for wide FOV airborne optical scanner data

ATCOR 4: Top | Features | Methods | Results

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Summary

The airborne ATCOR (ATCOR-4) is applied to small and wide FOV sensors. For computational efficiency, there are separate modules for flat and rugged terrain imagery. A large "monochromatic" database of atmospheric correction functions comes with the ATCOR-4 model. The database was compiled with the Modtran^®-4 code (DISORT, 8 stream option). It comprises the altitudes 1 km to 10 km and 20 km (1 km increment, with occasional larger gaps). For a given sensor and range of operating altitudes the corresponding altitude files from the monochromatic database have to be resampled with the spectral filter functions of all channels.

The achievements of ATCOR-4 are:

• Implementation of an atmospheric/topographic correction algorithms for airborne scanner data for the solar (0.35-2.55 um) and thermal (8-14 um) spectral region
  • solar region: calculation of surface reflectance cube
  • thermal region: calculation of surface (brightness) temperature & emissivity
• Spatial visibility map (requires bands in the 1.6 or 2.2 micron region)
• Spatial water vapor map (requires bands in the 940/1130 nm region)
• Automatic visibility and aerosol type determination
• Haze removal (low altitude haze)
• Cirrus cloud removal
• Empirical BRDF correction (normalizing to nadir view)
• Quick topographic correction (without atmospheric correction)
• De-shadowing of cloud/building shadow areas
• Inflight sensor calibration using ground reference targets
• Algorithm for automatic classification of reflectance spectra
  (10-12 surface cover types, also used for emissivity maps)
• Calculation of value adding products :
  SAVI, LAI, FPAR, albedo, surface energy fluxes (radiation and heat fluxes)
• Correction of spectral "smile" effect supported (hyperspectral instruments)

Current Status of ATCOR 4

• Most recent release (March 2009): ATCOR 4 version 5.0,
• operational applicability with DAIS, AVIRIS, HyMap, CASI, AISA, Daedalus, and Hyspex imagery has been proven,
• full documentation (ATCOR 4 report available as PDF file) available.

Besides atmospheric correction, the surface reflectance cube retrieved from airborne data may be used to simulate top-of-atmosphere (TOA) radiance scenes with an ATCOR-4 add-on module. This is a convenient way to provide realistic data for a spaceborne version of an airborne instrument. Atmospheric parameters and the solar geometry can be varied and the resulting effect can be observed in the TOA radiance scene. After calculating the TOA radiance cube from hyperspectral imagery there is the possibility of synthesizing new hyper- or multi-spectral scenes with approriate spectral resampling.

Keywords

Atmospheric Topographic Correction, AVIRIS, DAIS, HyMap, Daedalus, CASI, Imaging Spectroscopy, Data Preprocessing, Inflight Calibration, surface reflectance, emissivity, temperature, airborne sensors, value adding products

Origin

This original stand alone IDL-application was developed by
Rudolf Richter, DLR - German Aerospace Center
D - 82234 Wessling (near Munich), Germany
e-mail: R.Richter@DLR.DE

Development and extensive testing was supported by DLR (German Aerospace Center) with DAIS, AVIRIS, HyMap, CASI, and Daedalus imagery. The software is licensed to ReSe Applications Schläpfer for commercial marketing. A synergetic use of the PARGE software for orthorectification is given through this partnership.

ATCOR 4: Top | Features | Methods | Results

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