Identify Vegetation and Non-Vegetation Spectra

This example shows you how to:

• Use 2-D spectral data as a hypercube for the hyperspectral functions.

• Separate vegetation and non-vegetation spectra by using ndvi function.

This example requires the Image Processing Toolbox™ Hyperspectral Imaging Library. You can install the Image Processing Toolbox Hyperspectral Imaging Library from Add-On Explorer. For more information about installing add-ons, see Get and Manage Add-Ons. The Image Processing Toolbox Hyperspectral Imaging Library requires desktop MATLAB®, as MATLAB® Online™ and MATLAB® Mobile™ do not support the library.

Load 2-D Spectral Data

Load 2-D spectral data containing 20 endmembers of the Indian Pines data set into the workspace.

load("indian_pines_endmembers_20.mat")

Load the wavelength values for each band of the Indian Pines data set into the workspace.

load("indian_pines_wavelength.mat")

Prepare Test Data to Use for Hyperspectral Functions

Reshape the 2-D spectral data into a 3-D volume data using the reshape function.

[numSpectra,spectralDim] = size(endmembers);
dataCube = reshape(endmembers,[numSpectra 1 spectralDim]);

Create a 3-D hypercube object, with a singleton dimension, by specifying the 3-D volume data dataCube and wavelength information wavelength to the hypercube function.

hCube = hypercube(dataCube,wavelength);

Compute NDVI to Separate Vegetation and Non-Vegetation Spectra

Compute the NDVI value for each spectrum in the hypercube object.

ndviVal = ndvi(hCube);

Vegetation spectra typically have NDVI values greater than zero and non-vegetation spectra typically have NDVI values less than zero. Perform thresholding to separate the vegetation and non-vegetation spectra.

index = ndviVal > 0;

Plot the vegetation and non-vegetation endmembers.

subplot(2,1,1)
plot(endmembers(index,:)')
title("Vegetation endmembers")
xlabel("Bands")
ylabel("Reflectance Values")
axis tight
subplot(2,1,2)
plot(endmembers(~index,:)')
title("Non-Vegetation endmembers")
xlabel("Bands")
ylabel("Reflectance Values")
axis tight