Spectral Angle

Features:

Generates comparison between any two regions of interest interactively selected on the image using a spectral angle algorithm.

Steps:

1.       Load the file. Select Spectra Mathematics and select Spectral Angle from the dropdown menu.

2.       Click Select 1st spectrum. Draw a region of interest. A spectrum corresponding to the average spectrum of the selected region will appear in the SPECTRAL ANALYSIS panel.

3.       Click Select 2nd spectrum. Draw another region of interest. A spectrum corresponding to the average spectrum of the selected region will appear in the SPECTRAL ANALYSIS panel.

4.       Press Generate to measure the spectral angle between two objects.

A lower score corresponds to stronger spectral similarity. A score of 0 indicates perfect similarity. Usually, a score > 0.1 radians indicate no similarity.

5.       In the shown case where two objects were selected, the spectral angle is 0.05. For comparison, the spectral angle between the roof and the canopy is much higher 0.405 (not shown) indicating a low spectral correlation between the two subjects.

6.       Press Clear ROI/Spectra to start another spectral angle analysis or any other spectral tasks.

Additional Information:

The spectral angle algorithm determines the spectral similarity between two spectra by calculating the angle between the spectra. Smaller angles represent closer matches between the two selected areas.

References:

Kruse, F.A., A.B. Lefkoff, J.W. Boardman, K.B. Heidebrecht, A.T. Shapiro, P.J. Barloon, and A.F.H. Goetz. “The Spectral Image Processing System (SIPS)—Interactive Visualization and Analysis of Imaging Spectrometer Data.” Remote Sensing of Environment 44, no. 2–3 (May 1993): 145–63. https://doi.org/10.1016/0034-4257(93)90013-N.