Atmospheric & Topographic Correction (ATCOR)
ATCOR is a method used to reduce atmospheric and illumination effects on satellite image data to retrieve physical parameters of the earth's surface such as atmospheric conditions (emissivity, temperature), thermal and atmospheric radiance and transmittance functions to simulate the simplified properties of a 3D atmosphere.
The method is restricted to high resolution satellite imagery. The algorithm can be applied to multispectral and panchromatic imagery. The objective of this method is important for analysis in order to:
- Remove or reduce the influence of atmospheric and solar illumination
- Be able to compare multi-temporal satellite images with different times of acquisition. After time atmospheric correction, changes observed are due to different features on the earth's surface rather than differences of the atmospheric condition
- Improve the results of change detection and classification algorithms
- Be able to compare multi-sensor images with similar spectral bands
- To compare ground reflectance data retrieved from satellite imagery to the ground reflectance from measurements in the field
Left: Scene without ATCOR; Right: Scene with ATCOR
ATCOR method is used for various applications such as:
- Multi-temporal and multi-sensoral land cover classification
- Forest damage monitoring
- Surface temperature mapping
- Harvest estimations
- Erosion monitoring
ATCOR 2 - Correction of Flat Terrain
Processing of bands consists of the total signal at the sensor by path radiance, reflected radiation from the viewed pixel and radiation from the neighborhood (topological space). The atmospheric condition such as water vapor content, aerosol type and visibility for a scene can be estimated with the SPECTRA module, followed by surface reflectance spectrum of the primary area in the scene which can be viewed as a function of the selected atmospheric parameters.
Schematic sketch of radiation components for a flat terrain
Processing of bands by path radiance emitted by the atmosphere between ground and sensor, emitted ground radiance (temperature and Emissivity) and reflected downwelling thermal atmosphere flux. Scattered radiation from the neighborhood is usually neglected in the thermal region due to the scattering efficiency of atmosphere decreases strongly with wavelength.
ATCOR 3 - Mountainous Terrain
ATCOR3 is atmospheric correction and haze removal software used to correct changes in the spectral reflectance of materials on the earth's surface. ATCOR3 includes all of the capabilities of ATCOR2 and can be integrated with a DEM for atmospheric correction of images depicting rugged terrain.
Schematic sketch of radiation components for rugged terrain
- Produce sharp and brilliant satellite imagery
- Reduce the shadow effect in mountainous terrain
- Obtain better classification results by using real reflectance values
- Compare multi-temporal and multi-sensoral values
- Calculate value added products such as sky view factor and cast shadow calculation
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