ReSe Applications Schläpfer provides atmospheric correction software for remote sensing images.

Features of ATCOR2 and ATCOR3

 
Basics | Features | Sensor Support | Methods | ATCOR-2 Results | ATCOR-3 Results
 

Overview of features common to both programs:

Technical Requirements - see below

  • Atmospheric database (look-up-tables of radiative transfer calculations with Modtran®-5) covering a wide range of weather conditions and sun angles.
  • Image processing with constant atmospheric conditions or spatially varying aerosol conditions (the latter is retrieved from image if near- or short wave infrared bands are available).
  • Included module to determine atmospheric parameters (aerosol type, visibility, water vapor). This can be done by comparing retrieved scene reflectance spectra of various surface covers with library spectra as a function of the selected atmospheric parameter.
  • The atmospheric database includes a wide range of pre-calculated radiative transfer runs for different weather conditions and sun angles employing the Modtran®-5 code (DISORT 8-stream option for multiple scattering).
  • Capability for inflight radiometric calibration: for known atmospheric parameters and known target surface reflectances the radiometric calibration coefficients can be calculated. This corresponds to the improved method of empirical line fit because it includes the adjacency effect.
  • Visibility estimate prior to scene processing (interactive mode)
  • Aerosol type estimate prior to scene processing (interactive mode)
  • Retrieval of atmospheric water vapor column for sensors with water vapor bands (around 940/1130 nm). Example sensors: MOS-B, Hyperion.
  • Statistical haze removal: a fully automatic algorithm that masks haze and cloud regions and removes haze of land areas (low altitude haze).
  • Cirrus cloud removal (requires a narrow 1.38 micron band).
  • De-shadowing of cloud or building shadow areas, using image-based shadow detection routines.
  • Automatic classification of spectral surface reflectance (program SPECL2) using 10 surface cover templates. This is not a land use classification, but a reflectance-shape classification. Still, it may be useful as it is a fast automatic classification algorithm.
  • Surface emissivity and surface (brightness) temperature outputs for thermal band sensors.
  • Spectral polishing of reflectance cube (only hyperspectral imagery).
  • Value added products in a separate file (16 bit integer) : vegetation index SAVI, LAI, FPAR, wavelength-integrated albedo, absorbed solar radiation flux. In addition, surface energy fluxes for thermal band sensors can be calculated: net radiation, ground heat flux, latent heat, sensible heat flux.
  • Correction of spectral "smile" supported (hyperspectral instruments).
  • Correction of observation BRDF effects using the BREFCOR method. The method is applicable to satellite imagery if a number of images is acquired under varying observation angles in order to improve mosaicking results.
Inputs:
  • Calibrated Image file in BSQ (band sequential) ENVI format.
  • DEM and DEM derived layers for topographic correction (ATCOR3 only).
Outputs:
  • Surface reflectance channels
  • Surface (brightness) temperature and surface emissivity map
  • Visibility index map (corresponds to total optical depth at 550 nm)
  • Water vapor map (if required water vapor channels are available, e.g. at 940 nm)
  • Surface cover map derived from template surface reflectance spectra (10 classes) : a fast automatic spectral classification.
    This can be applied after atmospheric correction.
  • Value adding channels: SAVI, LAI, FPAR, albedo, radiation and heat fluxes
  • Diffuse and direct irradiance spectra.

All output image files are stored as BSQ (band sequential) binary with ENVI header.

Features available in ATCOR 3 only

The satellite scene has to be ortho-rectified to a DEM (digital elevation model) before the ATCOR3 processing starts. DEM slope and aspect files have to be calculated as well. The ray tracing programs SKYVIEW and SHADOW are optional, but should be completed prior to the main ATCOR3 processing.
This processing eliminates the atmospheric/topographic effects and generates surface data (reflectance, temperature) corresponding to a flat terrain. Problems can arise in regions where the spatial resolution of the DEM is not adequate.

For topographic processing with ATCOR 3, the following features are available:
  • Sky view factor calculation with a ray tracing program to determine the proportion of the sky hemisphere visible for each pixel of the terrain.
  • Cast shadow calculation depending on solar zenith and azimuth angle employing a ray tracing program.
  • Optional quick topographic correction (without atmospheric correction).
  • Terrain-dependent calculation of both the diffuse and the direct proportion of the irradiance and its correction for any exposition.
  • Terrain-dependent correction of the atmospheric transmission.
  • Empirical correction of incidence BRDF effects in sloped terrain.
  • Optional terrain-dependent diffuse and direct irradiance cubes.

Technical Requirements

  • IDL Version 8.4 or higher or free IDL Virtual Machine 8.4 or higher
  • Operating systems: Windows / Unix / Linux / Mac OSX
  • 64bit Installation of OS and IDL
  • ATCOR 2 (flat terrain) RAM: 18*l*c [MB] allocated to IDL,
    where l=lines, c=columns of image.
    Example: l=3000, c=1000 requires 54 MB RAM
  • ATCOR 3 (mountainous terrain) RAM: 35*l*c [MB] allocated to IDL,
    where l=lines, c=columns of image.
    Example: l=3000, c=1000 requires 105 MB RAM
  • If the required RAM exceeds the available memory for a large scene the tiling option can be applied which splits the image into a number of smaller sub-images ("tiles"), processes all tiles, finally merges the tiles, and automatically deletes the temporary sub-images.
  • An ENVI license is recommended, but not required