Classification Results of Six Images
The classification results from each of the six images generated from the image fusion techniques using the panchromatic data are:
-
HPF Technique. Compared to the signatures generated based on the band-overlay classification, the signatures from the HPF classification are quite different. The HPF technique has resulted in changes to the spectral characteristics of the transformed data set, which are exemplified in both the classified image and the spectral response curves (Figures 1 and 2).
- IHS Technique. In order to investigate the effect that stretching the panchromatic band to match intensity component has on classification, both the non-stretched and stretched fusion images were classified. The results obtained from classifying the IHS image with panchromatic band stretched to match the intensity component is quite similar to the band overlay image with the panchromatic data and is a considerable improvement over the results of that used the non-stretched panchromatic data (Figures 3 and 4).
Stretching the panchromatic band to match the intensity component prior to converting the IHS components back to RGB space has a positive impact in terms of classification. Because the descriptive statistics of the stretched IHS-transformed data are more similar to the original data than the non-stretched data, the classification results are very similar to the results using the original non-enhanced data and are therefore considered to be more accurate compared to the non-stretch results.
Since the spectral data are used to generate the signatures are so similar to the band-overlay image and it is this information on which classification is based, the signatures for each land-cover class are very similar in shape to the band-overlay signatures. The mean brightness values are slightly lower than band overlay (Figures 5 and 6).
- PCA Transformation Technique. The classification results based on the image generated using PCA transformation technique is very dissimilar to the classified image based on the band overlay fusion technique (Figures 7 and 8).
Evaluation
The classification based on the IHS image (with the panchromatic stretch) was very similar to the band overlay image. Because the results from the two techniques are so similar, there is no advantage to use this technique over the simpler band-overlay technique.
Evaluation of the RADARSAT-1 data revealed them to be complementary in terms of separating the villages from the land cover class. Apart from the village area, the rest of the images were classified well using band overlay. A ‘sequential masking’ classification procedure introduced by Ehrlich and others (1994) was selected to classify the whole area. The sequential masking approach to classification is based on photo interpretation technique whereby the most distinct image features are classified first. This sequence continues until the entire image is classified.