I.11 Remote Sensing and Geographic Information Systems
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I.11 Remote Sensing and Geographic Information Systems Catherine H. Graham and Scott J. Goetz OUTLINE 1. Basic concepts of remote sensing and geographic information systems 2. Applications of RS and GIS in ecology Remote sensing (RS) and geographic information systems (GIS) provide data and tools that are used extensively across ecology, evolution, biogeography, and conservation biology. Some fields in particular, such as landscape ecology and biogeography, have relied heavily and increasingly on sophisticated analyses afforded by these data and tools. GLOSSARY electromagnetic energy. Energy or radiation in a wave in space with an electrical field that varies in magnitude in a direction perpendicular to the direction in which the radiation is traveling and a magnetic field oriented at right angles to the electrical field. geospatial. The distribution of information in a geographic sense such that entities can be located by some coordinate of a reference system (i.e., latitude and longitude), which places these entities at some point on the globe. global positioning system (GPS). This system is a set of 24 satellites that orbit the Earth and communicate their position to a ground receiving device providing the geographic location of that receiver. 1. BASIC CONCEPTS OF REMOTE SENSING AND GEOGRAPHIC INFORMATION SYSTEMS Broadly, RS is the gathering and processing of data about the physical world by a device detecting electromagnetic energy that is not in contact with the object , area, or phenomenon under investigation. For example, the images in Google Earth (http://earth .google.com) are products of RS that provide information about vegetation and human uses of the land, such as agriculture, roads, and buildings. As such, RS is generally used to generate data that are often then imported into a GIS. A GIS is a collection of tools that provide the ability to capture, display, manage, and analyze most forms of spatial data that are geographically referenced to the Earth’s surface (i.e., identified according to location). An important feature in GIS is the ability to relate different types of information, such as remotely sensed vegetation images and maps of human population density , in a geospatial context to explore associations and relationships among these various types of information . Together, RS and GIS, along with other relatively recent tools, such as geographic positioning systems (GPS) and sophisticated spatial statistics, provide a powerful platform to advance our understanding of the natural world. In this chapter, we first describe RS and GIS in greater detail, and we then provide some examples of how they are used in ecology. Remote Sensing RS data provide real-time information about what is happening on our planet and can be used in a wide range of ecological studies. For example, it is now relatively easy to quantify deforestation rates across different ecosystems or even detect a fire in a remote area. RS uses theory developed in physics to measure electromagnetic energy emitted or reflected from distant objects. Electromagnetic radiation/energy can be described in terms of a stream of photons, which are massless particles, each traveling in a wavelike pattern and moving at the speed of light. This radiation varies across a spectrum of different amounts of energy in photons and size and frequency of waves. RS applications typically use wavelengths that include the visible wavelengths (blue through red), the infrared, and microwave regions of the electromagnetic spectrum (figure 1). Different types of objects (such as grassland and forest canopies) reflect, absorb, or scatter electromagnetic energy differently and, as a result, emit electromagnetic waves at different magnitudes in different portions of the electromagnetic spectrum. The principle behind RS is to detect and identify these characteristic waves (i.e., varying energy levels) for different materials, which are often referred to as spectral signatures. This is done by documenting the reflectance across a range of electromagnetic wavelengths for one or more objects or vegetation types. This information is often displayed as a spectral reflectance curve (figure 2; for an interactive tool, visit http://geospatial.amnh.org/ remote_sensing/widgets/spectral_curve/index.html). One of the first and still widely used sources of RS data is imagery from the Land Satellite (Landsat) series of sensors, first launched in 1973. The most recent Landsat images have seven different bands that cover a spectrum of 0.450 mm to 2.35 mm. Information about the reflectances in each of these bands can be used to classify different regions of an image (generally referred to as picture elements or pixels) as a certain...