REMOTE SENSING IN EARTH & SPACE SCIENCE WHAT IS REMOTE SENSING? Remote sensing is a method of measuring the composition, temperature, and other properties of an object by means of electromagnetic radiation emitted, absorbed, or reflected by the object. Electromagnetic radiation includes not only visible light, but also infrared, microwave, and radio radiation of longer wavelength and lower energy than visible light, and ultraviolet, x-ray, and gamma-ray radiation of shorter wavelength and higher energy. Two primary methods of remote sensing are imaging and spectroscopy. Recently, advances in electronic imaging technology have produced a combination of both of these, known as imaging spectroscopy. They have also extended the wavelength ranges accessible, to include a much broader range of the electromagnetic spectrum (ranging from X-rays to the far infrared).

REMOTE SENSING IN EARTH & SPACE SCIENCE Satellites in Earth orbit can provide complete global coverage, at regularly repeating intervals, and over long periods of time. Earth observing satellites utilize a wide range of orbital altitudes and inclinations, depending on the types of observations and time periods of interest. Satellite sensors can observe in wavelength ranges of electromagnetic radiation that are not transmitted through the lower atmosphere, such as ultraviolet and some types of infrared radiation, to make measurements of the upper layers of the atmosphere (such as the ionosphere and the ozone layer of the stratosphere). Satellites can also make highly accurate, long-term measurements of the Sun’s output of radiation, in nearly all ranges of the electromagnetic spectrum, for comparison with direct atmospheric measurements and predictions of global climate change.

REMOTE SENSING IN EARTH & SPACE SCIENCE EXAMPLES OF SPACE-BASED REMOTE SENSING IN EARTH SCIENCE Weather Satellites are the best known, and one of the first and most important, space-based remote sensing applications. Earth Resources Satellites, such as Landsat, are similar to weather satellites but focus on land and ocean areas and include techniques for measuring composition, temperature, and other properties of the objects observed. Satellites such as the Upper Atmosphere Research Satellite (UARS) and the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) make observations and measurements of the upper atmosphere (stratosphere and above) to determine composition, temperature, and other properties; and also make observations of solar radiation for comparison. The most recently launched set of three satellites, constituting NASA’s Earth Observing System (EOS), are Terra, Aqua, and Aura (which are focused on land, water, and atmospheric measurements, respectively).

Earth Observing Satellites Two major types of Earth observing satellites are those in near-polar orbits, at relatively low altitudes (a few hundred km), and ones in equatorial orbits at an altitude of about 35,800 km. The latter type satellite orbits, known as geosynchronous orbits, have a period of revolution of 24 hours, the same as the period of Earth’s rotation on its axis; hence nearly an entire hemisphere of Earth can be maintained in continuous (day and night) view.

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Landsat Thematic Mapper Image of the Washington, DC Area

ASTER / Terra Image of Washington, DC Area Advanced Spaceborne Thermal Emission and Reflection Radiometer (June 1, 2000)

Mt. St. Helens Volcano, 1980

LandSat View of Mt. St. Helens, Post-Eruption

Hurricane Viewed from a Space Shuttle

Sequence of 3 Images of Hurricane Andrew (1992) Viewed from Geosynchronous Orbit

View of Earth from Geosynchronous Orbit

Reduction in Antarctic Ozone Due to Chlorine Pollution of the Stratosphere

Polar Aurora as Viewed from Space Shuttle

Extreme-UV Images of Earth’s Plasmasphere Obtained by the IMAGE Satellite