Exercise_3 (1).docx

BIA4100: Location Analytics Exercise 3: MultiSpec Exercise Version: SP2021b Exercise Author: Erskine Exercise Editor: Johnson Credits: Original Lab Content Author Authored by Kurt Menke, GISP; Content Authored by Richard Smith, Ph.D., GISP Texas A&M University - Corpus Christi; The development of the original document was funded by the Department of Labor (DOL) Trade Adjustment Assistance Community College and Career Training (TAACCCT) Grant No. TC-22525-11-60-A-48; The National Information Security, Geospatial Technologies Consortium (NISGTC) is an entity of Collin College of Texas, Bellevue College of Washington, Bunker Hill Community College of Massachusetts, Del Mar College of Texas, Moraine Valley Community College of Illinois, Rio Salado College of Arizona, and Salt Lake Community College of Utah. Objective: Explore and Understand How to Display and Analyze Remotely Sensed Imagery Introduction In this exercise, you will learn how to display and inspect multi-band imagery in QGIS Desktop. They will use QGIS data processing tools to conduct an unsupervised classification of multi-spectral imagery. They will then use MultiSpec to perform a more advanced analysis. MultiSpec is a freeware multispectral image data analysis system created at the Purdue Research Foundation. MultiSpec provides the ability to analyze and classify imagery data, among other tasks. This lab has been adapted from four tutorial exercises provided by the MultiSpec team and introduces the software package. This exercise includes the following tasks: • Task 1 – Display and Inspection of Image Data • Task 2 – Supervised Classification Required and Recommended Tools QGIS, MultiSpec Objective: Learn the Basics of using QGIS Desktop and MultiSpec for Image Analysis

Image analysis is one of the largest uses of remote sensing imagery, especially with imagery that has recorded wavelengths beyond the visible spectrum. There are proprietary software packages designed specifically for remote sensing work such as ENVI and ERDAS Imagine. QGIS Desktop can now be used in combination with two additional FOSS4G software's, SAGA and GRASS, to also conduct image analysis. SAGA and GRASS are both standalone software packages that can be installed separately. However, the main analysis tools from both are now bundled with QGIS Desktop. This means that no additional installations are required in order to use GRASS and SAGA analysis tools via QGIS Desktop. However, some of this functionality is for more advanced users. For this reason, you will also learn how to use MultiSpec which is a very simple and intuitive, but powerful, freeware image analysis software package. This lab was adapted from the first four tutorials provided by the MultiSpec team. Task 1: Using data dictionaries and attribute selections There are many ways to view multi-band image data. Here you will explore some display options for a multi-band image in QGIS Desktop. 1. Open QGIS Desktop. 2. Click the Add Raster Layer button and navigate to the ex3data folder. Set the filter to All files (*)(*.*). 3. Select the file named ag020522_DPAC.img and click Open. This raster layer does not have a defined coordinate reference system (CRS). Therefore, QGIS opens the Coordinate Reference System Selector window. If this window does not open automatically, double-click the layer and click the Select CRS button under the General tab. This interface lets you define the CRS before the layer is added to the Layers panel. This raster is in UTM, zone 16, WGS84. 4. Type ‘zone 16’ into the Filter window. In the Coordinate reference systems of the world box you’ll see a list of all the CRSs with zone 16 in the name. Scroll through until you find WGS/84 UTM zone 16N (EPSG: 32616). Select it so that it appears in the Selected CRS box (see figure below) and click OK .

Coordinate Reference System Selector 5. The image will be added to QGIS (shown in figure below). This is an aerial photograph of a portion of the Davis Purdue Agriculture Center in Randolph County, Indiana.

Multi-band Image in QGIS Desktop 6. Save your QGIS Desktop project to your lab folder as ex3.qgs 7. Double click on the layer name in the Layers panel to open the Layer Properties. 8. Click on the Symbology tab. When an image has multiple color bands, QGIS defaults to a Multiband color rendering of that image. Colors on your computer monitor are created by combining three color channels: red, green and blue (RGB). By selecting three bands from a multiband image, and illuminating them with either red, green or blue light we create a color image. The multiband color renderer defaults to displaying Band 1 through the red channel, Band 2 through the green channel and Band 3 through the blue channel. However, we can change which bands are displayed through which channels. 9. Click the drop-down arrow for the Red band and change it to Band 3. Change the Blue band to Band 1 (see figure below).

Changing the band combination in QGIS 10. Click Apply and move the Layer Properties window so you can see the raster. Note : The difference between using Apply and using OK. Clicking OK saves the changes and closes the dialog window. Apply saves the changes and leaves the window open. If you want to change a setting, see the result and change another setting use Apply. 11. The image should now look like the figure below. This band combination creates what is known as a false color composite. Vegetation reflects a lot of near-infrared energy. You are now looking at the near-infrared through the red channel so vegetation shows up as red tones. The brighter the red, the more vigorous and healthier the vegetation. False Color Composite The Symbology tab also allows you to adjust Contrast enhancement. This setting gives you options to modify the appearance of the image when used in combination with the Load min/max values settings. Each band has values

from 0-255. By default, the renderer is set to use Cumulative count cut values from 2% to 98%. This setting eliminates the bottom and top 2% of the values. Many images have some outlying very low and high data values. These outlying data values can be eliminated by using the Cumulative count cut option. The Contrast enhancement is set by default to No enhancement. 12. The values currently being used for each band will appear in the Min/max boxes in the Band rendering area. 13. Change the Contrast Enhancement to Stretch to MinMax and click Apply. MinMax Stretch The Accuracy setting lets you either estimate the range of values from a sample or get the actual values. Obtaining actual values can take longer since QGIS has to look at all the values in the image, instead of a sample. 14. Now choose a Load min/max values setting of Mean +/- standard deviation to specify within 1 standard deviation and click Load. Click Apply to see the image change. 15. Change the Accuracy setting to Actual, and click the Load button to see the values change slightly. The raster gets a more saturated appearance (shown in figure below). These are the values within one standard deviation of the mean value. This is useful when you have one or two cells with abnormally high values in a raster grid that are having a negative impact on the rendering of the raster.

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