Features of ATCOR3 : mountainous terrain

The satellite scene has to be ortho-rectified to the selected 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 prior to ATCOR3.
The 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.

• SPECTRA module to determine the 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-4 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 the adjacency effect is included.
• Atmospheric database (look-up-tables of radiative transfer calculations with MODTRAN-4) covering a wide range of weather conditions and sun angles.
• Modules for image processing with constant atmospheric conditions or spatially varying conditions. The last option requires areas of known reflectance (dark vegetation, soil) in the scene. If a 1.6 or 2.2 micron channel exists these reference areas are masked automatically, otherwise interactively.
• Statistical haze removal: a fully automatic algorithm that masks haze and cloud regions and removes haze of land areas (low altitide haze).
• Cirrus cloud removal (requires a narrow 1.38 micron band).
• De-shadowing of cloud or building shadow areas.
• Retrieval of atmospheric water vapor column for sensors with water vapor bands (around 940/1130 nm). Example sensors: MOS-B, Hyperion.
• Quick topographic correction (without atmospheric correction)
• SKYVIEW: sky view factor calculation with a ray tracing program to determine the proportion of the sky hemisphere visible for each pixel of the terrain.
• SHADOW: cast shadow calculation depending on solar zenith and azimuth angle employing a ray tracing program.
• 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.
• Spectral polishing of reflectance cube (only hyperspectral imagery).
• Surface emissivity and surface (brightness) temperature maps for thermal band sensors.
• 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: net radiation, ground heat flux, latent heat, sensible heat flux.

Atmospheric Database

Input : Image file format must be BSQ (band sequential) with ENVI header

Output:

• Surface reflectance channels
• Surface (brightness) temperature, surface emissivity map
• Visibility index map (corresponds to total optical thickness at 550 nm) and aerosol optical thickness map
• 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.
  It can be applied after atmospheric correction.
• Value added channels: SAVI, LAI, FPAR, albedo, radiation and heat fluxes

Support : Support includes updates, bug fixes and e-mail / phone support for fully licensed users