ATCOR 4 Atmospheric Database
The database provided with ATCOR is compiled with the Modtran®-5 code using the scaled DISORT 8-stream option and the more accurate correlated-k algorithm in atmospheric absorption regions. The spectral sampling distance is 0.4 nm, equidistant over the range from 350 nm to 2550 nm. In the thermal region the spectral grid is 0.5 cm-1 (i.e. 5 nm at 10 micron).
This "monochromatic" spectral atmospheric database comprises the flight altitudes:
- 0 to 5 km above sea level, increment 1 km
- 10 km
- 20 km
- 99 km (for self-defined satellite systems)
Interpolated atmospheric look-up tables are generated for flight altitudes that do not match the 1 km grid.
The database supports the following aerosol types:
A discrete set of 6 water vapor columns is provided for each standard altitude and aerosol type. If water vapor bands are available for the retrieval of the water vapor map, these 6 files serve as grid points for the interpolation/extrapolation.
- 0.4 [g cm-2]
- 1.0 [g cm-2]
- 2.0 [g cm-2]
- 2.9 [g cm-2]
- 4.0 [g cm-2]
- 5.0 [g cm-2]
The low water vapor columns (wv=0.4-0.8 [g cm-2]) are typical for winter atmospheres, or dry conditions, the range 1.0 - 2.5 [g cm-2] comprises average summer conditions in moderate climates, values of 3.0 - 5.0 [g cm-2] can typically be expected in tropical summer climates. Values above the grid point 5.0 [g cm-2] will be extrapolated.
The database covers ground elevations from 0 to 2.5 km above sea level, extrapolation to higher elevations is performed automatically if required.
The database covers the solar zenith angle range 0 - 70 degrees.
When a new sensor is introduced the monochromatic database has to be resampled with the channel filter functions. This can conveniently be performed on a subset of the "monochromatic" files, i.e. only the required flight altitudes and desired aerosol types have to be selected. The resampled files are then stored in a sensor-specific atmospheric database for permanent use.