TOPOSOLNORM

Description

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

Parameters

Name	Type	Caption	Length	Value range
FILI *	String	Input file name	1 - 192
DBIC	Integer	Input channels	0 -
FILEDEM *	String	Elevation file name	1 - 192
DBEC	Integer	Elevation channel or layer	0 - 1
FILECLS *	String	Classification file name	1 - 192
DBCLSC	Integer	Input classification channel	0 - 1
CLSARR	Integer	Array of input classes	0 -
SAZANGL	Float	Solar zenith and azimuth angles (deg)	0 - 2	0.0 - 360
FILEANG	String	Solar angles file name	0 - 192
FILO *	String	Output file name for topographically corrected image.	1 - 192
MONITOR	String	Monitor mode	0 - 3	ON, OFF Default: ON

* Required parameter

Parameter descriptions

FILI

Specifies the name of the input file that contains the satellite image. The image should have sufficient metadata to derive the sensor name, product type and quantity (radiance, reflectance etc) of each band. If the image data are not corrected to reflectance, TOPOSOLNORM will convert the image values to reflectance on-the-fly.

DBIC

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.

FILEDEM

Specifies the file that contains the elevation (DEM) layer. The elevation file is mandatory. FILEDEM will be resampled if its projection or resolution differs from the input file.

DBEC

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

FILECLS

Specifies the file that contains the classification layer. The layer must have the same georeferencing information as the input file. The classification layer can be created by the SPECLASS or the SPECL PPFs; other classification layers can be provided. The classification file is mandatory.

DBCLSC

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

CLSARR

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.

SAZANGL

Optionally specifies the Solar Zenith and Azimuth Angle. If these values are not provided, the values in the file metadata will be used.

FILEANG

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.

FILO

Specifies the name of the output file to receive the topographically corrected scene. It will also store computed relative incidence angle layer and the flat area and topographic shadow masks.

The specified file must not already exist.

MONITOR

The program progress can be monitored by printing the percentage of processing completed. A system parameter, MONITOR, controls this activity.

Available options are:

• ON: Turns the monitor ON (default)
• OFF: Turns the monitor OFF (recommended if running in batch or background mode)

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.

Example

The following example shows how to use the topographic normolization for input Sentinel-2 image with provided DEM, classification file and per-pixel angles file created with SOLVIEWZAZ.

EASI>FILI    =   'S2A_MSIL1C_20170728T105621_N0205_R094_T33WWS_20170728T105621_10M.pix'  ! input file
EASI>DBIC    =
EASI>FILEDEM =   'DEM_REP.pix'   ! dem file
EASI>DBEC    =   1               ! dem channel
EASI>FILECLS =   'S2A_MSIL1C_20170728T105621_N0205_R094_T33WWS_20170728T105621_10M_classes.pix'  ! classes file
EASI>DBCLSC  =   1      !classes channel
EASI>CLSARR  =          !classes array (all)
EASI>SAZANGL =          !solar angles (default from metadata)
EASI>FILANG  =   'solviewzaz_10m.pix'    ! filang file
EASI>FILO    =   'toposolnorm.pix'       ! output file

EASI>run TOPOSOLNORM