Use the Dimensionality Reduction and Band Selection panel to reduce the amount of spectral data to process in THOR. Hyperspectral data is largely redundant, with data from one band to the next generally changing very little. By reducing the redundant data, you can shorten processing times and improve target detection accuracy. THOR can reduce spectral data in two ways: dimensionality reduction and band selection.

Dimensionality reduction generally refers to applying a mathematical transformation to the input dataset to create a new dataset in which the output bands are a linear combination of every input band. The leading bands in the transformed data generally contain the unique content in the image, while the latter bands contain mostly noise and otherwise redundant information.

Band selection refers to selecting a discrete subset of input bands to continue processing with. You can select bands manually, or you can let ENVI automatically attempt to identify the most important bands for differentiating targets from background signatures.

In the Dimensionality Reduction and Band Selection panel, select a dimensionality reduction method from the Method drop-down list. The options are None (proceed with all bands of the input or atmospherically corrected image), Image Transform, Automated band selection, and Manual band selection. The area below the drop-down list will change to show the relevant parameters for the selected method.

Note: The Automated band selection method is only available if you selected background signatures using the Background Signature Selection panel.

If you imported an MRSL spectral libary in the Target Signature Selection panel, the option Diagnostic spectral features in metadata is available from the Method drop-down list. Select this option if you used the Spectral Library Builder to define diagnostic features for the target signatures, and you added the diagnostic metadata fields to your MRSL spectral library file. THOR will automatically detect the new fields and perform target detection using only those bands you defined for that signature.