TERSETUP

Description

Automatically calculates the slope, aspect, and skyview rasters from an input DEM, in preparation for atmospheric correction over rugged terrain. TERSETUP outputs a PCIDSK file that holds the DEM, slope, aspect, and skyview channels required by the ATCOR algorithm.

Parameters

Name	Type	Length	Value range
InputDEM: Input elevation channel	Raster port	0 - 1	1 - Default: 1
OutputTerr: Output terrain derivatives channel *	Raster port	1 -
Background elevation value	Float	0 - 1
Elevation reference	String	0 - 1	MSL | ELLIPS
Elevation units	String	0 - 1	METER | FEET | US_FEET
Elevation scale	Float	0 - 1	Default: 1.0
Elevation offset	Float	0 - 1	Default: 0.0

* Required parameter

Parameter descriptions

InputDEM: Input elevation channel

Specifies the channel that contains the input digital elevation model (DEM).

OutputTerr: Output terrain derivatives channel

Specifies the output channel to receive the DEM, slope, aspect, and skyview.

Background elevation value

Optionally specifies the value that indicates which pixels are to be handled as No Data.

If this parameter is not specified, TERSETUP checks for a NO_DATA_VALUE metadata tag at the file level, then again at the channel level. If this value is not specified through the parameter or found in the metadata, all pixels of the DEM are assumed to be valid. All pixels with NO_DATA_VALUE in the input are assigned a NO_DATA_VALUE in the output.

Elevation reference

Optionally specifies the vertical reference for the elevation values.

If this parameter is not specified, the function searches for an ELEVATION_REF metadata tag at the file level, then again at the channel level. If this value is not specified through the parameter or found in the metadata, its value defaults to MSL.

Elevation units

Optionally specifies the units used to describe the elevation values of the input DEM file.

If this parameter is not specified, the function searches for an ELEVATION_UNITS metadata tag at the file level, then again at the channel level. If this value is not specified through the parameter or found in the metadata, its value defaults to METER.

Elevation scale

Optionally specifies the elevation scale used by the DEM.

If this parameter is not specified, the function searches for an ELEVATION_SCALE metadata tag at the file level, then again at the channel level. If this value is not specified through the parameter or found in the metadata, its value defaults to 1.0, indicating that the scale is 1:1.

Elevation offset

Optionally specifies the elevation offset used by the DEM.

If this parameter is not specified, the function searches for an ELEVATION_OFFSET metadata tag at the file level, then again at the channel level. If this value is not specified through the parameter or found in the metadata, the offset defaults to 0.0, indicating that there is no offset.

Details

TERSETUP is part of the atmospheric correction workflow, and is required when atmospherically correcting satellite imagery captured over rugged terrain. TERSETUP computes the terrain derivatives (slope, aspect, skyview). Running this function allows users to inspect topographic rasters prior to performing atmospheric correction.

TERSETUP first checks the parameter values; if these are not provided, the function then searches for the required metadata tags at the file level, then at the channel level. If the parameter values are not explicitly specified and are not found in the metadata tags, the function uses the default values.

TERSETUP defines the extents of the output terrain derivatives file (TERFILE), based on the DEM. If the elevation reference (ELEVREF) is MSL, the function copies the DEM values to the output file. If the DEM values refer to the ellipsoid, TERRSETUP performs an on-the fly conversion to MSL. Finally, the function computes the slope, aspect, and skyview values for each valid pixel in the DEM, at the specified DEM resolution.

The DEM is used to derive the slope and aspect rasters from which the skyview rasters can be derived. These terrain rasters are used throughout the atmospheric correction process, but most importantly, it is part of the calculation for computing the solar illumination map and cast shadow bitmap in ILLUMCAST.

The sky view map defines the fraction of sky not obstructed by surrounding terrain or features in the local hemisphere of a pixel. Furthermore, the contribution of reflected terrain radiation is calculated as the complement of the sky view.