MixModel

Mixture Model

The Mixture Model is a component that implements a raster decomposition using the mixture model strategy. The spatial resolution of remote sensing satellites, in general, allows that a single pixel contains more than a target (for example vegetation + shadow + soil). The mixture model algorithms allow to decompose the raster into fraction images, where the value of the resultant pixels indicate the fraction of each target inside the pixel.

The main information needed to execute a mixture model are:

One Raster file.

A map of pure endmembers, which are pixel values where the user knows the exact proportion of a component.

Sensor information for each band, if available

The available methods in TerraLib are:

Linear (Least Square Method): It is calculated by the following equation:

ri is the pixel value at band i,
aij is the known value of the component j at band i,
xj is the proportion of component j,
ei is the estimation error for band i.

Linear (Resticted Least Square Method (only 3 components, 4 bands): It is calculated by the same equation above but with a additional restriction over the fraction values.
Reference: Modelo Linear de Mistura Espectral Conceitos Teóricos, Algoritmos e Aplicações em Estudos na Amazônia Legal Linear Spectral Mixing Model, Theoretical Concepts, Algorithms and Applications in Studies in the Legal Amazon, Yosio Edemir Shimabukuro , Andeise Cerqueira Dutra e Egidio Arai.
Reference: Utilização de atributos derivados de proporções de classes dentro de um elemento de resolução de imagem pixel na classificação multiespectral de imagens de sensoriamento remoto, Ana Paula Dutra de Aguiar, Junho 1991.
PCA: The component matrix is transformed using Principal Component Analysis, and the fraction of each component is obtained by using the proper number of eigenvectors.

It is accessible through:

Raster Processing > Mixture Model... (list of all raster layers will be available)

This wizard consists of the following steps:

Wizard Page 1 - Selection of the layer with the desired raster (Layer Search)

On the List of Layers select the raster layer to apply the Mixture Model.
Optionally use Filter By Name field giving part of the layer name to help find the layer in the list.
Press Next to go to next step or Cancel to close the dialog.

Wizard Page 2 - Mixture Model interface

Type - Select the Type of mixture model to be used and set specific parameters (the parameters will vary depending on the selected contrast type).

Options

Create error images: indicate that output raster will include the error bands.
Decompose output image: indicate that output image will be decompose in separate bands.

Use tool to load components previously saved. over
Use tool to save components.

Raster Bands

Select the input Bands and the Sensor information for each band.

Use to create or edit spectral sensor information. (Select a Spectral Sensor)

Components - Components List contains a list the Names and the Values (one for each band) of the components acquired over the image (for example samples of soil, water and shadow). The number of components (samples) and bands must be the same.

Edit the name and select a color for new component. If the name already exists in list, this component will be selected for update, else will be creates a new. The component can also be selected by clicking on it in the list.

Use tool to delete selected component.

Use tool to and click over a "pure" sample over the image to acquire values to selected component.

Use tool to create a polygonal area to adquire values to selected component.

Use tool to create a rectangular area to adquire values to selected component.

Spectral Curves - This graph shows the relation of the values obtained from the selected bands to the wave length of the selected sensors.

Selected: shows only selected component.

All: shows all components of list.

Press Next to go to next step, Back to return to the previous wizard or Cancel to close the dialog.

Wizard Page 3 - Output information (Output Raster Information)

Raster Info - First press and inform the folder where the resulting file will be saved.
Name - inform the raster name.
Extra Parameters - if there are some, see the details on how to inform then here.
Press Finish to save the resulting raster or Back to go to the previous wizard page.

Hint: The Mixture Model result is added to the TerraView project as a new layer and the default style used is color composition. Use the Style Explorer to select just one band in monochromatic to check each component (soil, water, shadow).