ATCOR 4 - Features
ATCOR 4 is a software for the atmospheric/topographic correction of airborne scanner data. This may be used in four different geometric situations, where the (optional) geo- rectification is to be done by PARGE or a compatible software:
- 1. flat terrain, no geocoding (raw geometry)
- 2. flat terrain, geocoded/rectified image on flat surfaces (one altitude)
- 3. rugged terrain, DEM and related layers required, ortho-rectified image
- 4. rugged terrain, geocoded (non resampled), DEM and related layers provided in raw geometry
- 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 : The radiometric calibration coefficients can be calculated where the atmospheric parameters and target surface reflectances are known. 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®-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).
- Retrieval of atmospheric water vapor column for sensors with water vapor bands (around 820/940/1130 nm). Example sensors: AVIRIS, HyMap, CASI.
- Statistical haze removal through use of a fully automatic algorithm that masks haze and cloud regions and removes haze of land areas.
- De-shadowing of cloud/building cast shadow areas using image-based shade detection routines.
- Cirrus cloud removal (requires a narrow 1.38 micron band).
- Empirical BRDF correction of irradiance effects.
- Optional quick topographic correction (without atmospheric correction).
- Automatic classification of spectral surface reflectance (program SPECL) using 12 surface cover templates. This is not a land use classification, but a reflectance-shape classification. Still, it may be useful as the classification algorithm is both fast and automatic.
- Surface emissivity and surface (brightness) temperature maps for thermal band sensors.
- Spectral polishing of reflectance cube (only hyperspectral imagery).
- The SPECTRA module is used to evaluate 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.
- Value added products in a separate file.
- Correction of spectral "smile" (across track variation of the spectral position of spectral bands for hyperspectral instruments,
- Adaption of solar reference spectrum,
- Diffuse and direct illumination components output,
- Works for hyperspectral, multispectral, and panchromatic imagery
- The atmospheric database (look-up-tables of radiative transfer calculations with Modtran®-5) covers a wide range of weather conditions and sun angles. (>>See further details)
All outputs are stored as band sequential binary data with standard ENVI header, i.e.:
- Surface reflectance cube
- Surface (brightness) temperature and emissivity (if multispectral thermal bands)
- Visibility index map (corresponds to total optical depth at 550 nm) and aerosol optical thickness map
- Water vapor map (if required water vapor channels are available, e.g. at 940 nm)
- Spectral reflectance / emissivity surface cover map (10-12 classes)
- Value added channels: SAVI, LAI, FPAR, albedo, radiation and heat fluxes
- Spectral direct and diffuse irradiance cubes
- Masks of haze/cloud/water, and saturated pixels
- AVIRIS, Hymap, Hyspex, Daedalus, CASI, AISA, Leica ADS, ...
Any user-specified sensor can easily be included by copying one of the existing "sensor*.dat" files and modifying it appropriately. Tools exist to generate the spectral channel filter functions for Gaussian or square wave response curves.
(Note: tilted sensors are not supported in the atmospheric database)Technical Conditions:
- Unix / Linux / Windows / MacOSX
- IDL Version 8.0 or higher or the free IDL Virtual Machine
- PARGE Version 3.x or compatible solution if orthorectified imagery is required.
- Large amount of RAM and a 64bit system are highly recommended in interactive mode (tiling capability to reduce memory requirements is available).
- maximum RAM requirements: 18*l*c [MB] (flat terrain) and 35*l*c [MB] (rugged terrain) allocated to IDL,
where l=lines, c=columns of image.
Example rugged terrain: l=3000, c=2000 requires 210 MB RAM
- 6 GB of disk space for atmospheric database
- ENVI license recommended, but not required
Example flat terrain: l=3000, c=2000 requires 108 MB RAM
- Support includes updates, bug fixes and e-mail / phone support for fully licensed users. Details about the software methodology can be found in the User Manual and in various published papers.