Atmospheric Correction

ac_thumbAtmospheric correction is the process of removing atmospheric contributions from remotely-sensed imagery. Satellite imagery of the Earth’s surface inherently contains contamination due to absorption and scattering of light by atmospheric gases and aerosols. Correcting for the atmosphere allows for cleaner imagery, more accurate spectral signatures, and more accurate feature discrimination and identification.

Atmospheric Correction Tool (ACT)

ACT is a software tool created by CPI for the removal of atmospheric effects in remotely-sensed imagery. The current version of ACT is based on pre-calculated look-up tables (LUTs) that have been created using outputs from the four-dimensional radiative transfer model AETHER™. The LUTs are based on multiple AETHER™ simulations of the complete atmospheric radiative environment under different atmospheric conditions and viewing geometries. ACT performs atmospheric correction on an image by choosing the appropriate LUT data for the image date, location and viewing geometry, and then calculates surface reflectance. Currently ACT has been implemented for Landsat 7 and Landsat 8 imagery, although development is underway to expand ACT to include the DigitalGlobe Worldview-2 and Blackbridge RapidEye sensors. ACT is currently implemented as a stand-alone Windows application.

ACT v1.0 Results

The left panel shows a raw Landsat 7 RGB image. The right panel shows the same scene with ACT correction. The corrected image is much cleaner and it is much easier to discern surface features and colors.

ACT also incorporates an optional topographic correction that takes into account the slope and aspect of the terrain surface for the entire image to calculate changes in the incident solar irradiance. The topographic correction simulates the image as being illuminated from directly above, resulting in a reduction in shadowing due to terrain features. The topographic correction improves results for applications such as land cover classification and vegetation analysis.

ACT v1.1 Results

The left panel shows an ACT corrected Landsat 7 image without topographic correction, while the right panel shows the same scene with topographic correction. The correction greatly reduces shadows.

Haze and cloud removal capabilities are currently in development and will be implemented in ACT v2.0. Preliminary results are shown below.

Preliminary ACT v2.0 Results

The left panel shows Band 1 of a Landsat 7 image with extensive cloud-cover, seen as white areas. The right panel shows the same scene after undergoing the prototype haze/cloud correction algorithm. The cloudiness is greatly reduced and several surface features are now visible below the clouds.

ACT Development to Date:

Development of ACT is ongoing. For further information or a demonstration of capabilities please contact CPI.