GIS Applications for Water, Wastewater, and Stormwater Systems - Chapter 3

CHAPTER 3 Remote Sensing Applications Can a satellite 400 miles above the ground surface help you locate a leaking pipe? Read this chapter to find out. The Landsat 7 Enhanced Thematic Mapper (ETM+) scene of the lower Chesapeake Bay region acquired on July 5, 1999 (Image courtesy of USGS). Copyright © 2005 by Taylor & Francis LEARNING OBJECTIVE The learning objective of this chapter is to comprehend the applications of remote sensing technology in the water industry. MAJOR TOPICS · Remote sensing satellites · Applications of satellite imagery · Types of remote sensing data · Digital orthophotos · Using remote sensing for land-use classification · Image processing software · Anticipated future trends LIST OF CHAPTER ACRONYMS DEM Digital Elevation Model DOP Digital Orthophoto DOQ Digital Orthophoto Quadrangle DOQQ Digital Orthophoto Quarter Quadrangle LIDAR Laser Imaging Detection and Ranging LULC Land Use/Land Cover TM Thematic Mapper (onboard Landsat satellite) USGS United States Geological Survey ALBANY COUNTY’S REMOTE SENSING APPLICATION Public-domain digital aerial photography data, such as USGS digital orthophoto quadrangles (DOQs) and digital orthophoto quarter quadrangles (DOQQs), usually become outdated in rapidly developing areas. For such areas, high-resolution satellite imagery may be a cost-effective source of more recent overhead images. Albany County, located in southeastern Wyoming, covers 4,400 mi2, has a stu-dent-based population of 30,000, and has 1,600 mi of roads. For rural communities such as Albany County, building a GIS from scratch can be an expensive endeavor due to lack of resources. The County’s day-to-day mapping functions required a data layer of imagery for the entire county. Various data options were reviewed, including aerial flights, existing DOQs, and satellite imagery. New aerial imagery was elimi-nated because it was too expensive. Existing DOQs were not suitable because they were 7 years old and did not reflect recent county growth trends. In addition, costs associated with updating the County’s existing digital aerial photography exceeded $100,000. High-resolution satellite imagery, on the other hand, allowed the County to have high-resolution up-to-date views of the entire county for $32,000. For 85 mi2 of populated areas, the County selected 1-m pan-sharpened IKONOS satellite imagery (described later in this chapter). For the rest of the county, 90 quads of Copyright © 2005 by Taylor & Francis CARTERRA DOQ 5-m black and white (B&W) imagery was selected. Both products were produced by Space Imaging (Thornton, Colorado). Thanks to this geographic-imaging approach, planning tasks previously requiring months to complete took only days after the County implemented this project (Frank, 2001). In the Albany County of Wyoming, addition of high-resolution up-to-date imagery to GIS data reduced the completion of typical planning tasks from months to a few days. INTRODUCTION The technologies that are commonly used in conjunction with GIS are commonly referred to as GIS-related technologies. Examples include remote sensing, global positioning system (GPS) surveying, the Internet, and wireless technologies. This chapter will focus on remote sensing, one of the most successful GIS-related-technologies. Other related technologies are described elsewhere in the book. Remote sensing allows obtaining data of a process from a location far away from the user. Remote sensing can, therefore, be defined as a data collection method that does not require direct observation by people. Remote sensing is the process of detection, identification, and analysis of objects through the use of sensors located remotely from the object. Three types of remote sensing systems are useful in the water industry: 1. Aerial photographs 2. Satellite imagery 3. Radar imagery The data from these systems are commonly referred to as remote sensing or remotely sensed data. Sometimes, remote sensing data are incorrectly confused with supervisory control and data acquisition (SCADA) data used to operate water and wastewater treatment plants. Remote sensing data collected using airplanes are called aerial photographs or aerial photos. Digital remote sensing data collected from satellites are called satellite imagery or images. Digital pictures of the Earth are taken by satellites from 400 to 500 mi above the ground compared with aerial photographs that are taken by aircraft from 1 mi above the ground (for low-altitude photography) to 7 to 8 mi above the ground (for high-altitude photography). The chart in Figure 3.1 shows the altitude difference between the aircraft- and satellite-type remote sensing systems. Radar imagery or images are another type of remote sensing data but their usage is not widespread in the water industry. Although the definition of remote sensing includes aerial photos and radar data, remote sensing is often considered synonymous with satellite imagery. The American Society for Photogrammetry and Remote Sensing (ASPRS) values the U.S. remote sensing industry at about $1.3 billion (as of 2001) and forecasts 13% annual growth, giving values of $3.4 billion by 2005 and $6 billion by 2010. The industry currently consists of about 220 core companies employing about 200,000 employees in the areas of remote sensing, photogrammetry, and GIS imaging. A 2001 Copyright © 2005 by Taylor & Francis 1000 400–500 mi 100 10 7–8 mi 1 1 mi Low Altitude High Altitude Satellite Remote Sensing System Type Figure 3.1 Altitude difference in aerial photography and satellite imagery. ASPRS study concludes that utilities are one of the greatest untapped potential markets and that a shortage of trained workers is one of the greatest challenges to the growth of the remote sensing industry (Barnes, 2001a). Although vector GIS data are still an important and vital tool for many water industry applications, the newer raster GIS applications of satellite imagery are beginning to make a major move into the GIS and mapping market. The benefits of satellite imagery are (Schultz, 1988): 1. They enable aerial measurements in place of point measurements. 2. They offer high spatial and/or temporal resolution. 3. All information is collected and stored at one place. 4. Data are available in digital form. 5. Data acquisition does not interfere with data observation. 6. Data can be gathered for remote areas that are otherwise inaccessible. 7. Once the remote sensing networks are installed, data measurement is relatively inexpensive. Satellite imagery is stored in a pixel (raster) format that makes it ideally suited for incorporation into a GIS (Engman, 1993). Thus, satellite imagery can be treated as raster-type GIS data. Image processing equipment and methods can be used to Copyright © 2005 by Taylor & Francis extract useful information from hard copy and digital images and combine it with other data layers in a GIS. Image data sources including scanned paper maps, aerial photographs, and satellite imagery can be used in a GIS when reprojected as image maps. Projected images can be used as a background or as a base map upon which other vector layers are overlaid. Casual GIS users can easily import remote sensing imagery into their GIS projects as an image theme (or layer). However, advanced remote sensing applica-tions and image analyses require formal remote sensing training and digital image processing skills. The incorporation of remote sensing data in a GIS requires a digital image processing software such as ERDAS IMAGINE, Geomatica, ER Mapper, or ENVI, or a raster GIS software with image processing capability, such as ArcGRID or IDRISI. Such programs are described later in this chapter. These are exciting times both for the GIS and the remote sensing industries, thanks to dramatic price and performance breakthroughs in GIS hardware and software. The increasing use of GIS is contributing to a renewed interest in satellite imagery by nongeographers, such as civil and environmental engineers. Although GIS technology is promoting the use of satellite imagery, satellite imagery is also in turn advancing the use of GIS. Although non-GIS stand-alone image processing software can be used for exploring satellite imagery, those with GIS capabilities are more suitable because they can combine imagery with additional information, such as demographic and topographic data (Corbley, 2000). REMOTE SENSING APPLICATIONS Satellite imagery is not restricted to the visible (0.4 to 0.7 µm wavelength) part of the electromagnetic spectrum. Satellite sensors can record Earth images at wave-lengths not visible to the human eye, such as near-infrared and thermal-infrared bands. Different satellite bands provide information about different objects and conditions of the Earth. For example, thermal-infrared band (10.4 to 12.5 µm wave-length) data are useful for soil–moisture discrimination. These bands of satellite data can be used as different data layers in a GIS for further analysis. Remote sensing applications in the water industry are as diverse and numerous as the GIS applications themselves. Typical examples are listed below: 1. Satellite remote sensing has contributed to water resources applications and research for three decades (Jackson, 2000). Remote sensing data are especially useful in watershed hydrologic modeling. Satellite imagery can be used to estimate input parameters for both the lumped-parameter and distributed-type hydrologic models. 2. Satellite imagery can be used for delineating watersheds and streams. For example, SPOT satellite’s stereographic capability can generate topographic data. Terra satellite can provide digital elevation models (DEMs) from stereo images. (These and other satellites are discussed later in this chapter.) Topographic and DEM data collected by satellites can be processed in GIS for automatic delineation of water-shed boundaries and streams. 3. Remote sensing data are used for land-use classification. GIS can help to refine or verify the imagery-based land-use classes. Copyright © 2005 by Taylor & Francis ... - tailieumienphi.vn