SpectralSubspaceBackgroundStatistics Task

This task computes background statistics by excluding anomalous pixels. When the true background is better characterized with a subspace background, spectral detection methods such as the SpectralAdaptiveCoherenceEstimator task achieve greater target-to-background separation. This can potentially improve detection results, particularly in scenes that contain a lot of clutter or man-made objects.

Alternatively, use the SpectralAdaptiveCoherenceEstimatorUsingSubspaceBackgroundStatistics task to run the ACE algorithm with subspace background statistics using just one task.

Example

ACE target detection involves multiple steps, as this code example demonstrates:

Open a spectral library.
Open a hyperspectral image.
Get the wavelength values and units from the image.
Choose an individual spectrum from the spectral library.
Resample the spectrum to the wavelengths of the image.
Compute subspace background statistics.
Run ACE target detection.
Display the resulting image. Brighter pixels represent a close match to the Dry Grass spectrum.

This example takes several minutes to complete. Copy and paste the following code into the IDL Editor:

; Launch the application

e = ENVI()

; Open a spectral library

specLibFile = FILEPATH('veg_2grn.sli', ROOT_DIR=e.ROOT_DIR, $

  SUBDIR=['resource', 'speclib', 'veg_lib'])

specLib = ENVISpectralLibrary(specLibFile)

; Open a hyperspectral image

file = FILEPATH('AVIRISReflectanceSubset.dat', $

  ROOT_DIR=e.ROOT_DIR, $

  SUBDIRECTORY = ['data', 'hyperspectral'])

raster = e.OpenRaster(file)

; Get wavelength values and units from raster

metadata = raster.METADATA

wavelengths = metadata['Wavelength']

wavelengthUnits = metadata['Wavelength Units']

; Get the selected spectrum from spectral library

Task1 = ENVITask('GetSpectrumFromLibrary')

Task1.INPUT_SPECTRAL_LIBRARY = specLib

Task1.SPECTRUM_NAME = 'Dry Grass'

Task1.Execute

; Get the resample spectrum task from the catalog of ENVITasks

Task2 = ENVITask('ResampleSpectrum')

; Define inputs

; Spectrum from library to be resampled

Task2.INPUT_SPECTRUM = Task1.SPECTRUM

; Wavelengths from spectral library

Task2.INPUT_WAVELENGTHS = Task1.WAVELENGTHS

; Wavelength units from spectral library

Task2.INPUT_WAVELENGTH_UNITS = Task1.WAVELENGTH_UNITS

; Wavelengths from raster

Task2.RESAMPLE_WAVELENGTHS = wavelengths

; Wavelength units from raster

Task2.RESAMPLE_WAVELENGTH_UNITS = wavelengthUnits

; Run the resample spectrum task

Task2.Execute

; Get the subspace background task

Task3 = ENVITask('SpectralSubspaceBackgroundStatistics')

; Define inputs

Task3.INPUT_RASTER = raster

Task3.THRESHOLD = 0.6

; Run the subspace background task

Task3.Execute

; Get the ACE task from the catalog of ENVITasks

ACETask = ENVITask('SpectralAdaptiveCoherenceEstimator')

; Define inputs

ACETask.INPUT_RASTER = raster

ACETask.SPECTRA = Task2.OUTPUT_SPECTRUM

ACETask.MEAN = Task3.MEAN

ACETask.COVARIANCE = Task3.COVARIANCE

; Run the task

ACETask.Execute

; Get the collection of data objects currently available in the Data Manager

DataColl = e.Data

; Add the output to the Data Manager

DataColl.Add, ACETask.OUTPUT_RASTER

; Display the result

View = e.GetView()

Layer = View.CreateLayer(ACETask.OUTPUT_RASTER)

Syntax

Result = ENVITask('SpectralSubspaceBackgroundStatistics')

Input properties (Set, Get): INPUT_RASTER, THRESHOLD

Output properties (Get only): COVARIANCE, EIGENVALUES, MEAN

Properties marked as "Set" are those that you can set to specific values. You can also retrieve their current values any time. Properties marked as "Get" are those whose values you can retrieve but not set.

Methods

This task inherits the following methods from ENVITask:

Properties

This task inherits the following properties from ENVITask:

COMMUTE_ON_DOWNSAMPLE

COVARIANCE (optional)

The covariance matrix of the subspace background, returned as a double-precision array [number of bands, number of bands].

EIGENVALUES (optional)

The eigenvalues of the subspace background.

INPUT_RASTER (required)

Specify the raster on which to compute the subspace background statistics.

MEAN (optional)

The mean of the subspace background, one for each band of the input raster.

THRESHOLD (optional)

Specify the fraction of the background to use for calculating the subspace background statistics. The data type is floating-point. The allowable range is 0.5 to 1.0 (the entire image).

Version History

ENVI 5.2. 1

Introduced

API Version

4.2