This task performs Adaptive Coherence Estimator (ACE) target detection analysis, using the mean and covariance from subspace background statistics.

Example


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

  1. Open a spectral library.
  2. Open a hyperspectral image.
  3. Get the wavelength values and units from the image.
  4. Choose an individual spectrum from the spectral library.
  5. Resample the spectrum to the wavelengths of the image.
  6. Compute subspace background statistics.
  7. Run ACE target detection.
  8. 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 ACE task from the catalog of ENVITasks
ACETask = ENVITask('SpectralAdaptiveCoherenceEstimatorUsingSubspaceBackgroundStatistics')
 
; Define inputs
ACETask.INPUT_RASTER = raster
ACETask.SPECTRA = Task2.OUTPUT_SPECTRUM
ACETask.THRESHOLD = 0.6
 
; 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('SpectralAdaptiveCoherenceEstimatorUsingSubspaceBackgroundStatistics')

Input parameters (Set, Get): INPUT_RASTER, NAMES, OUTPUT_RASTER_URI, REGULARIZATION_METHOD, REGULARIZATION_TOLERANCE, SPECTRA, THRESHOLD

Output parameters (Get only): OUTPUT_RASTER

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

Input Parameters


INPUT_RASTER (required)

Specify a raster on which to perform the target detection.

NAMES (optional)

Specify an array of target names. The array size must be [number of targets].

OUTPUT_RASTER_URI (optional)

Specify a string with the fully qualified filename and path of the associated OUTPUT_RASTER.

  • If you do not specify this parameter, or set it to an exclamation symbol (!), ENVI creates a temporary file.
  • If you set it to the hash symbol (#), ENVI creates a file in the temporary directory, but this file will not be deleted when ENVI closes.

REGULARIZATION_METHOD (optional)

Specify a method for regularizing the covariance matrix:

  • Diagonal: Diagonal loading, increasing all singular values by the tolerance value.
  • Dominant: Dominant mode rejection, setting singular values less than the tolerance value to their mean.
  • None: No regularization is used.
  • Shrink: Shrinkage of singular values based on the tolerance value.
  • Threshold: Singular values less than the tolerance value are set to the tolerance value.
  • Truncate (default): Singular values less than the tolerance value are set to zero.

REGULARIZATION_TOLERANCE (optional)

Specify the tolerance value to use for matrix regularization. If not set, the following values will be used based on the regularization method

  • Diagonal: Ten times the smallest nonzero singular value.
  • Dominant: The value prescribed by Gavish & Donoho.
  • None: N/A
  • Shrink: The Oracle Approximating Shrinkage (OAS) estimator.
  • Threshold: The largest singular value times the machine precision.
  • Truncate (default): The largest singular value times the machine precision.

SPECTRA (required)

Specify a floating-point array with the target spectra. The array size is [number of bands, number of target spectra].

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).

Output Parameters


OUTPUT_RASTER

This is a reference to the output raster of filetype ENVI.

Methods


Execute

Parameter

ParameterNames

Properties


DESCRIPTION

DISPLAY_NAME

NAME

REVISION

TAGS

Version History


ENVI 5.2.1

Introduced

ENVI 6.2

Added the NAMES, REGULARIZATION_METHOD and REGULARIZATION_TOLERANCE parameters.

See Also


ENVITask, SpectralAdaptiveCoherenceEstimator Task, SpectralSubspaceBackgroundStatistics Task, Masking Support in ENVITasks