Remote Sensing in an

Transcription

1 Chapter 9: Information about your downloaded Landsat Data Remote Sensing in an ArcMap Environment Remote Sensing Analysis in an ArcMap Environment Tammy E. Parece Image source: landsat.usgs.gov Tammy Parece James Campbell John McGee NSF DUE ; This workbook is available online as text (.pdf s) and short video tutorials via:

2 The project described in this publication was supported by Grant Number G14AP00002 from the Department of the Interior, United States Geological Survey to AmericaView. Its contents are solely the responsibility of the authors; the views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U.S. Government. Mention of trade names or commercial products does not constitute their endorsement by the U.S. Government.

3 The instructional materials contained within these documents are copyrighted property of VirginiaView, its partners and other participating AmericaView consortium members. These materials may be reproduced and used by educators for instructional purposes. No permission is granted to use the materials for paid consulting or instruction where a fee is collected. Reproduction or translation of any part of this document beyond that permitted in Section 107 or 108 of the 1976 United States Copyright Act without the permission of the copyright owner(s) is unlawful. Introduction: Landsat images are frequently used for land remote sensing analyses. The first Landsat Satellite was launched in The Landsat mission continues to this date with the most recent Landsat Data Continuity Mission satellite (now Landsat 8) launched in February, For more information and specific details on Landsat satellites, sensors, and potential analyses using Landsat images go to: Landsat images are free and downloadable from the internet from or You have already downloaded at least one scene from the USGS and this tutorial provides you with information to understand basics of your scene. Decisions on exactly which specific images you need for your specific analyses cannot be answered from this tutorial. Jpeg of the Landsat scene you ordered from previous tutorials 79 P age

4 In the process of ordering and downloading your Landsat scene, you had access to the following information. This gave you a screen shot of a natural color preview and some of the metadata. The metadata gives you information about your Landsat Scene. We will not review each line as much of it is self-explanatory. The metadata provides the scene identification number. The scene identification number includes the Julian date the image was acquired. For this image, it was acquired in 2011, Julian day 072 which in 2011 is March 13. You can use the Landsat Scene Identification Number if you need to reorder the exact same scene at a later date. This will also be the name of each one of the image files 80 P age

5 that we downloaded. Remember, we ordered Landsat 4-5, this data tells us, the scene is actually from Landsat 5. The ground station was Gatineau, Canada. Landsat 5 imagery is always taken during the day. It provides the path and row numbers; this information will allow you to request the same scene but using different dates. The sensor had no anomalies while active for this particular scene. The metadata continues here. Remember the scene we requested was for less than 10% cloud cover. This is the average cloud cover for the entire scene. For this particular one, the average was only 6% but as you can see over the next 4 lines, the cloud cover did vary across the scene. The metadata also provide us with the sun s elevation and azimuth, which will assist us if we want to include shadowing or solar insolation in our analyses. Many of the rows on this portion of the metadata relate to latitudes and longitudes of different areas of the scene. 81 P age

6 When we unzipped our bulk download, we ended up with the 12 files listed above. The first 7 have the scene identification number and also the band number. Landsat 5 had 7 bands, thus we have one image for each of the seven bands. Each band represents a different region of the electromagnetic spectrum. For Landsat 5 these are as follows: Size of the pixel for the band ( With the exception of the Thermal Channel (Band 6), the resolution (pixel size) is 30 meters by 30 meters. For Landsat 5, the Thermal Channel s pixel size is 120 meters by 120 meters. 82 P age

7 This file is a text file that provides information on the resultant residual error from the ground control points (when the scene was geo-referenced to the ground). Yes, you do not have to geo-reference the scene as this step has already been completed by the USGS. Sometimes it is easier to read the.txt files if you import them into a spreadsheet. For instance for this specific file, opening.txt looks like: Importing the data into a spreadsheet looks like: Much easier to read and understand. 83 P age

8 Here is another text file. It is metadata. Yes, again. But this file actually has additional data that was not listed when you explored the metadata from the link. This metadata also provides: sensor name thematic mapper (TM), radiance information, DATUM = "WGS84", ELLIPSOID = "WGS84", UTM_ZONE = 17, the number of ground control points and related RMSE, and other information. You should always review the metadata on any file prior to conducting analyses. These two files refer to the ground control points (GCP). One is a jpeg of the GCPs and their visual location on the Landsat scene. If you open this file, note that the GCPs are different colors. The.txt file gives you the residuals for each GCP and also ranks them by the color coding. 84 P age

9 The final file is and is actually a file that has much of the information that we have just reiterated in this tutorial. To open this file, first open a notepad or another word processing program and then open the file within the program. Do not try to open the file by double clicking on it, as that will take you to an internet window asking which program you want to use to open it. If you have never worked with a Landsat image, we highly recommend that you read this document and the other.txt files. Is any other pre-processing needed before you start using your Landsat Scene? Scenes downloaded from EarthExplorer and requesting the Landsat Surface Reflectance Data, the USGS has already preprocessed it for surface reflectance. If you are working with any other scene downloaded, you need to consider preprocessing for surface reflectance (see Masek, J.G., et al., A Landsat surface reflectance data set for North America, Geoscience and Remote Sensing Letters, : p ) For more information about the level and type of USGS processing of Landsat scenes, go to Landsat data. Now you are ready to proceed to the next tutorial which prepares you to analyze your 85 P age

10 Notes: 86 P age