and the Jet Propulsion Laboratory. Throughout these years, we have collaborated with a large number of scientists, engineers, and students who helped in developing the basis for the material in this book. We sincerely thank them for creating a most pleasant atmosphere for work and scientific “enjoyment.” To name them all would lead to a very long list; however, we would like to acknowledge the numerous researchers at JPL who were kind enough to read and provide suggestions on how to improve the text for this and earlier editions – they include M. Abrams, M. Chahine, J. Curlander, D. Diner, M. Freilich, M. Gierach, R. Greene, A. Khazendar, Y. Lou, D. McCleese, P. Rosen, D. Vane, S. Vannan, J. Waters, and H. Nair – as well as our students and Postdocs at Caltech, who hopefully became interested enough in this field to carry the banner. We want also to acknowledge, as immigrant Americans, the golden opportunities that this great country provided us and fellow immigrants to follow their dreams.
We could not have completed this book without the dedicated assistants and artists who typed the text of the First Edition, improved the grammar, and did the artwork, in particular, Clara Sneed, Susan Salas, and Sylvia Munoz. Special thanks to Priscilla McLean for helping with this edition.
Charles Elachi and Jakob van Zyl
Pasadena, California, August 2020
1 Introduction
Remote sensing is defined as the acquisition of information about an object without being in physical contact with it. Information is acquired by detecting and measuring changes that the object imposes on the surrounding field, be it an electromagnetic, acoustic, or potential field. This could include an electromagnetic field emitted or reflected by the object, acoustic waves reflected or perturbed by the object, or perturbations of the surrounding gravity or magnetic potential field due to the presence of the object.
The term “remote sensing” is most commonly used in connection with electromagnetic techniques of information acquisition. These techniques cover the whole electromagnetic spectrum from the low‐frequency radio waves through the microwave, submillimeter, far infrared, near infrared, visible, ultraviolet, x‐ray, and gamma‐ray regions of the spectrum.
The advent of satellites is allowing the acquisition of global and synoptic detailed information about the planets (including the Earth) and their environments. Sensors on Earth‐orbiting satellites provide information about global patterns and dynamics of clouds, surface vegetation cover and its seasonal variations, surface morphologic structures, ocean surface temperature, and near‐surface wind. The rapid wide coverage capability of satellite platforms allows monitoring of rapidly changing phenomena, particularly in the atmosphere. The long duration and repetitive capability allows the observation of seasonal, annual, and longer term changes such as polar ice cover, desert expansion, solid surface motion, and subsidence and tropical deforestation. The wide‐scale synoptic coverage allows the observation and study of regional and continental scale features such as plate boundaries and mountain chains.
Sensors on planetary probes (orbiters, flybys, surface stations, and rovers) are providing similar information about the planets and objects in the solar system. By now all the planets in the solar system have been visited by one or more spacecraft. The comparative study of the properties of the planets is providing new insight into the formation and evolution of the solar system.
1.1 Types and Classes of Remote Sensing Data
The type of remote sensing data acquired is dependent on the type of information being sought, as well as on the size and dynamics of the object or phenomena being studied. The different types of remote sensing data and their characteristics are summarized in Table 1.1. The corresponding sensors and their role in acquiring different types of information are illustrated in Figure 1.1.
Two‐dimensional images are usually required when high‐resolution spatial information is needed, such as in the case of surface cover and structural mapping (Figs. 1.2 and 1.3), or when a global synoptic view is instantaneously required, such as in the case of meteorological and weather observations (Fig. 1.4). Two‐dimensional images can be acquired over wide regions of the electromagnetic spectrum (Fig. 1.5) and with a wide selection of spectral bandwidths. Imaging sensors are available in the microwave, infrared (IR), visible, and ultraviolet parts of the spectrum using electronic and photographic detectors. Images are acquired by using active illumination, such as radars or lasers; solar illumination, such as in the ultraviolet, visible, and near infrared; or emission from the surface, such as in thermal infrared, microwave emission (Fig. 1.6), and x‐ and gamma‐rays.
Table 1.1 Types of remote sensing data.
| Important type of information needed | Type of sensor | Examples of sensors |
|---|---|---|
| High spatial resolution and wide coverage | Imaging sensors, cameras | Large‐format camera (1984), Seasat imaging radar (1978), Magellan radar mapper (1989), Mars Global Surveyor Camera (1996), Mars Rover Camera (2004 and 2014), Cassini Camera (2006) |
| High spectral resolution over limited areas or along track lines | Spectrometers, spectroradiometers | Shuttle multispectral imaging radiometer (1981), Hyperion (2000) |
| Limited spectral resolution with high spatial resolution | Multispectral mappers | Landsat multispectral mapper and thematic mapper (1972–1999), SPOT (1986–2002), Galileo NIMS (1989) |
| High spectral and spatial resolution | Imaging spectrometer | Spaceborne imaging spectrometer (1991), ASTER (1999), Hyperion (2000) |
| High accuracy intensity measurement along line tracks or wide swath | Radiometers, scatterometers | Seasat (1978), ERS‐1/2 (1991, 1997), NSCAT (1996), QuikSCAT (1999), SeaWinds (2002) scatterometers |
| High accuracy intensity measurement with moderate imaging resolution and wide coverage | Imaging radiometers | Electronically scanned microwave radiometer (1975), SMOS (2007) |
| High accuracy measurement of location and profile | Altimeters, sounders | Seasat (1978), GEOSAT (1985), TOPEX/Poseidon (1992), and Jason (2001) altimeter, Pioneer Venus orbiter radar (1979), Mars orbiter altimeter (1990) |
| Three‐dimensional topographic mapping | Scanning altimeters and interferometers | Shuttle Radar Topography Mission (2000) |
| Surface displacement mapping | Radar interferometer | Sentinel (2012, 2016), SkyMed (2007), ALOS (2006), TANDEMX (2010), ALOS‐2 (2014) |
Spectrometers are used to detect, measure, and chart
