Laboratory #5: Supervised Classification

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Laboratory #5: Supervised Classification. Objective. This laboratory serves as an introduction to supervised and unsupervised image classification, the DIRS ...
Laboratory #5: Supervised Classification

Objective This laboratory serves as an introduction to supervised and unsupervised image classification, the DIRS Modular Imaging Spectrometer Instrument (MISI), and the spectral signatures of materials. Image classification is discussed in (Schott, ”Remote Sensing: The Image Chain Approach,” pg. 255-280). You will be using ENVI to classify a MISI scene of the RIT campus. The prelab had you perform an unsupervised, k-means classification of the scene. For this lab, you will be using the class map you created in the prelab as a training data set for the supervised classification. The background & theory of your report should include a discussion of confusion matrices, spectral signatures of the classified materials, MISI, GML supervised classification, and k-means unsupervised classification. Make sure to present and discuss the results you obtained during the prelab in the discussion section of your report.

Data You will be using the same data as you did in the prelab. All image data you will need is located in /cis/www/cis/htdocs/class/simg762/Lab5 or http://www.cis.rit.edu/class/simg762/Lab5/. Specifically, the files you will need are: • MISI_28jun02 (image file) • MISI_28jun02.hdr (header file) The MISI image was acquired on June 28, 2002 flown at an altitude of 3000feet above ground level. This yields pixels of 6 feet. The imagery was collected as a initial test flight for collection season 2002. MISI is a research platform and is under constant modification and calibration. Information about MISI can be found at: http://www.cis.rit.edu/research/dirs/research/misi.html Additional MISI preview imagery may be located at: http://www.cis.rit.edu/research/dirs/research/IMAGEcol/index.html#2001 This is a MISI level 1 image - no geometric correction has been applied.

Procedure Supervised classification using K-means class map 1. There is an option in ENVI to generate ROIs via band threshold. We are going to utilize this tool to create ROIs from the class map created from the k-means classification. For each class, input the class number as both the max and min values (i.e. the thresholding will only include the class you indicate). Since you will be generating a lot of ROIs be sure to keep straight which were generated for what. It may be helpful when labeling the ROIs that you specify that these are ROIs from the k-means class map (i.e. k grass, k road). These ROIs will be used as a training data set for supervised classification. This is where your list of what number corresponds to what class comes in handy.

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Figure 1: Table of evaluation techniques 2. Perform a gaussian maximum likelihood supervised classification (GML) using the k-means based ROIs as the training data. Report the single precision value used. Set the rule images to output to memory and output the result image to a file.

Evaluation of the k-means based supervised classification 1. Use the ENVI post classification tools to construct a confusion matrix against the k-means based GML output and the input k-means based ROIs. 2. Additionally, construct a confusion matrix using the k-means based GML output and the truth ROIs you used in the prelab. 3. Another post processing analysis technique is class statistics. Run ”class statistics” on the k-means based GML class map. The first input image is the GML output and the second is the original hyperspectral, MISI image which is spectrally subset to the first three bands (RGB). Select all classes. Do not run a min/max stdev graph, but instead include the histogram statistics. 4. Report the means and standard deviations of each class in the 3 bands. 5. Reconstruct the histograms so that all of the classes are shown in a single plot for each band. You can do this by first selecting Options->New Window: Blank to create a new plot. Then right-click on the class histograms to show the legend. Drag the appropriate legends titles into the new plot window to create the new histograms. You should end up with three plots (one for each band, RGB) that contain K histograms each (the number of classes).

Supervised classification using truth ROIs 1. In the prelab you constructed ROIs that simulated ground truth for the image by selecting areas where you were sure of the content. Repeat the above GML classification and evaluation using these truth ROIs as the training data for the classification. 2. The chart shown in Figure 1 should clarify what evaluation techniques will need to be run for which classification images and against which ROIs.

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