TOPOSOLNORM

Description

TOPOSOLNORM is a method to correct pre-classified radiometric values based on variable incidence angles.

Parameters

Name	Type	Length	Value range
Image Layer(s): Input channels	Raster port	0 - 1024
DEM Layer: Elevation channel or layer	Raster port	0 - 1
Classification layer: Input classification channel	Raster port	0 - 1
Input classes	Integer	0 - 1024
Solar azimuth	Float	0 - 1	0.0 - 360
Solar zenith	Float	0 - 1	0.0 - 90
Angles Layers: Solar angles file name	Raster port	0 -

Parameter descriptions

Image Layer(s): Input channels

Optionally specifies the list of channels in FILI that are to be topographically normalized. The default is to process all channels in FILI. In order to compute a shadow mask, the input file needs to include the blue and NIR bands.

DEM Layer: Elevation channel or layer

Specifies the elevation layer. The default is to take the first layer containing elevation data

Classification layer: Input classification channel

Specifies the classification layer. If not specified it will take first layer that is available.

Input classes

Specifies an array of input classes contained in the classification layer. The correction is applied separately to each class. If left blank all classes are used in the topographic normalization.

Solar azimuth

Optionally specifies the Solar Azimuth Angle. If this value is not provided, the values in the file metadata will be used.

Solar zenith

Optionally specifies the Solar Zenith Angle. If this value is not provided, the values in the file metadata will be used.

Angles Layers: Solar angles file name

Optionally specifies a file containing synthesized per-pixel solar zenith and azimuth angle layers. For Sentinal-2, Landsat-8 and pushbroom sensors, the FILEANG can be produced by running the SOLVIEWZAZ ppf prior to running TOPOSOLNORM. For Landsat-8 each band can have its own Solar zenith and Solar azimuth layer. TOPOSOLNORM will use the metadata contained within the FILEANG file to determine which channel contains the appropriate zenith and azimuth angles. If FILEANG is not defined and the input file does not contain metadata describing the angles, then the user needs to define the zenith and azimuth angles using the SAZANGL parameter.

Details

TOPOSOLNORM is a method to correct pre-classified radiometrically calibrated data based on variable incidence angles and bidirectional reflectance distribution function (BRDF) characteristic surfaces. This implementation of topographic normalization accounts for surfaces with different BRDF properties but is less sensitive to lower quality DEMs while accounting for various levels of skylight that is not eliminated during atmospheric correction.

TOPOSOLNORM requires a classification layer that isolates spectral classes with different BRDF characteristics that are homogeneous within a class except for variable solar incidence angles. In order for this process to be effective, a class needs to have sufficient pixels on both north and south facing slopes. A TOPOSOLNORM correction should only be applied to classes that are effected by topography. Do not apply a correction to classes such as cloud, water or shadow because this may lead to artifacts in the corrected imagery.