Advanced Classifiers 1

Introduction:

Unsupervised and supervised classification methods both sort pixels by the values they contain, but they only do this analysis on a pixel value. But not all features are larger than a pixel! Advanced classifiers sort pixels into different classes, while considering values at a sub-pixel level. The advanced classifiers used in this lab are 'Spectral Linear Unmixing' and 'Fuzzy Classifier'.

Methods:

In order to use Spectral Linear Unmixing (SLM), the spectral reflectance of the pure pixel values (end members) must be recorded before classification can be performed. First, the principal components of each band were calculated. Next, the principal components of bands one and two were plotted on a scatterplot graph. By circling the corners of the plotted pixels, it was possible to identify agricultural, bare earth, and water points. By plotting bands three and four, it was possible to identify the urban/built-up end member. Once all of the end members were collected, all of them were selected, and fractional images were created for each of the LULC classes.

Fuzzy classification sorts mixed value pixels into different classes by assessing how close the values are to one class or another. The first step of fuzzy classification was to collect 48 spectral signatures of both homogeneous and mixed land cover. Next, the spectral classes were used to classify each pixel into 5 different classes (or the 5 best potential classes). After the pixels were classified, a fuzzy convolution was performed to constrain the classifier to only the 5 specified classes.

Conclusion:

The results of the fuzzy classification were worse than both the Unsupervised and supervised classification schemes (Figure 1).

Figure 1: (From top left - clockwise) Unsupervised, Supervised,
Fuzzy classification with 48 signatures, and Fuzzy classification with 24 signatures.

It is likely that error in the fuzzy classifier was introduced during the collection of urban points, as it was difficult to find areas with homogeneous pixel values.