GIS and Remote Sensing

GE110 Fall 2008 Week 4 October 18, 2010 GIS and Remote Sensing Lab 2 LANDSAT 7 and ASTER In this lab, you will: 1. Process the LANDSAT 7 ETM+ image to emphasize the useful information a. Transformations (Optional) I. Band ratios II. Decorrelation Stretch III. PCA b. Pan-sharp image (Optional) 2. Process the ASTER image in ENVI a. Apply the georeference to L1A image b. Image stacking c. Transformaiton analysis 3. Way to save your image to Arcmap a. From Display window b. From Main Menu For LANDSAT: Band transformations: o Band transformation can reduce the effect of environment and highlight the spectral variations of minerals or your study target. The command band transformations are band ratios, Decorrelation Stretch, PCA transformation, MNF transformation etc. o The index and band ratio result can be saved as a separate file, so that you can later overlay it on top of your GIS layer. Please refer to the last section about saving your image. a. Band ratio o Click Transform/Band Ratios in the MAIN MENU to begin the band ratio function. You can process several band ratios at the same time. o The common used band ratios are listed in the handout on Monday. Please note: 1. Images (bands) need to have the same resolution before the band transformation. For example, Band 6 and band 8 cannot process with the other bands unless you resample them to the same resolution. 2. When you make the RGB image from the band ratios result and normal bands, you may

want to put the band ratio result in the RED color. It will stand out the target. b. Vegetation indices (optional) Click Spectral/vegetation analysis in the MAIN MENU to find the function you want to use. Please note: 1. You can also compute the vegetation index by yourself by using the Band Math function under the Basic Tools. Here are some basic vegetation indexes that you can use: NIR Red = RVI Ratio vegetation index Tucker 1979 (NIR - Red) (NIR + Red) = NDVI Normalized difference vegetation index Tucker 1979 c. PCA (Source: http://academic.emporia.edu/aberjame/remote/landsat/landsat_proc.htm) Click Transform/ Principal component to begin with. Click forward PC rotation -> compute new statistics and rotate. Select 6/6 Bands subset (Band 1-5 and 7). You can use different components to compose a RGB image. (ex: R/G/B = PC1/PC2/PC4) Please note: PCA is a good way to find the different rock/mineral on ground because this analysis can easily separate different surface materials/ different terrains from the image. However, these results (components) do not carry out material information directly. You need to have local information to tell what each component is related to. Pan Sharpening For the Landsat-7 image (as many other satellite image), you can use the pan-sharpening function to increase its color image resolution from 30 m to 15 m (as ASTER s resolution). If you do it, you need to decide the band combinations first. 1. To compute the Pan-Sharpening image, click the Image Sharpening under Transform in main menu, and either HSV or Color Normalized method 2. Select Input of color band from Available Bands list 3. Choose the Band Combination that you want to use in RGB band. 4. For the High resolution Input file, choose the Landsat-7 Band 8. 5. Change the resampling method to Bilinear and click the choose to define the output file path and file name. 6. Open the pan-sharpening image in the New Display 7. The image sharpening result might show different color with your original image. To match the color, we can use the Histogram matching under the Enhance function in your display toolbar. NOTE: This function will match the histogram between two

display, so you need to have at least two display images to use this function. For ASTER: 1. ASTER image has more band selection than LANDSAT image. However, the processing step is different than LANDSAT image. 2. If you need to order the ASTER image for your research propose, it might be a better choice to order L1B image since the processing is easier than L1A image. However, some software may ask L1A image as the input file format, so ask expert before ordering the image. 3. To open the ASTER data, open.hdf file in your computer. Apply the georeference to L1A image 1. It is not easy to directly read L1A image into ArcMap because its geometry haven t apply to the image itself. (You can directly read L1B image into ArcMap, but it is not easy to process the image under the ArcMap, and its location may away from the location it should be) 2. To apply the georeference to L1A image, click Basic Tools / Preprocessing / Data- Specific Utilities/ ASTER / Georeference Data 3. Because ASTER has three different resolutions, so we need to do it separately to process whole bands in a single image. First, we chose the VINR bands (the first one, 3/3 Bands) as input file. 4. Keep the projection as the UTM, and change the Datum to WGS 84 (you can also use

North America 1983), click ok. 5. Define the output filename in Registration Parameters window, and click ok to start the processing. 6. Repeat these steps for SWIR (the third one, 6/6 Bands) and TIR bands (The last one, 5/5 Bands). 7. After these processes, you should see three new files in the available bands list. Comparing with the original L1A data, These files has the geo information with in the image. If you want to do the band transformations, you need to stack these three file together! Otherwise you can stop here and display/save your image. Please note: you cannot orthorectify your image after georeference it. So if you want to orthorectify your data, do orthorectify instead of georeference. Image stacking 1. The propose of stack image is to resample these image to the same resolutions, also it will put all of the image under the same file, so it will be easier to do furthermore analyses such as band transformations. 2. To stack these layers together, click Basic Tools / Layer Stacking 3. Click import file to add these georeferenced files (3 files) into the list. Change the Pixel Size to 15m, and define the output file name, click Okay to start processing. 4. After processing, you should get a file in your band list that contains the entire bands from your original ASTER L1A image. Now you can start to do band combinations, band transformations Transformaiton analysis The transformation process is almost the same as LANDSAT image. Here are some common used band ratios and band combinations for ASTER image. (Source: ASTER mineral index Processing Manual, complied by Aleks Kalinowski and Simon Oliver, Geoscience Australia) You can download the PDF manual on the internet: www.ga.gov.au/image_cache/ga7833.pdf

Way to save your image to ArcMap 1. There are two ways to save your image to the ArcMap for your project. You can either save it from the Display window, or from the Main Menu. 2. Tiff/Geotiff is a common format that you can use to import the image to ArcMap. 3. If you save your band combinations from display windows, you will preserve the image histogram but may lost the original data information 4. If you save your band combinations from Main Menu, you will need to adjust image color again in ArcMap, but you will preserve the original data information. 5. There is no best way to do it but depends on your need. If you want to do image profiling in ArcMap, you will need to original image information. If you need to display the color of image, it may be a good idea to save the adjusted image histogram.