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University of Nebraska–Lincoln

Remote Sensing Glossary

Reference Information for Virtual Nebraska

Terms, Definitions and Concepts

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ice shelf

A thick mass of ice extending from a polar shore. The seaward edge is afloat and sometimes extends hundreds of miles into the sea.

IFOV

Instantaneous Field of View. See Multispectral Scanner for sample usage.

IGY

See International Geophysical Year.

image

Pictorial representation of data acquired by satellite systems, such as direct readout images from environmental satellites. An image is not a photograph. An image is composed of two-dimensional grids of individual picture elements (pixels). Each pixel has a numeric value that corresponds to the radiance or temperature of the specific ground area it depicts. See gray scale.

image resolution

The area represented by each pixel of a satellite image. The smaller the area represented by a pixel, the more accurate and detailed the image. For example, if a U.S. map and a world map are printed on identically sized sheets of paper, one square inch on the U.S. map will represent far less area and provide for more detail than one square inch on the world map. In this example the U.S. map has higher resolution. APT has a resolution of 4 km, HRPT has a resolution of 1.1 km and WEFAX resolution is 8 km.

imager

A satellite instrument that measures and maps the Earth and its atmosphere. Imager data are converted by computer into pictures.

inclination (aka i)

One of the six Keplerian elements, it indicates the angle of the orbit plane to the central body's equator. See Keplerian elements for diagram.

The elliptical path of a satellite orbit lies in a plane known as the orbital plane. The orbital plane always goes through the center of the Earth but may be tilted at any angle relative to the equator. Inclination is the angle between the equatorial plane and the orbital plane measured counter-clockwise at the ascending node.

A satellite in an orbit that exactly matches the equator has an inclination of 0 degree, whereas one whose orbit crosses the Earth's poles has an inclination of 90 degrees. Because the angle is measured in a counterclockwise direction, it is quite possible for a satellite to have an inclination of more than 90 degrees. An inclination of 180 degrees would mean the satellite is orbiting the equator, but in the opposite direction of the Earth's rotation. Some sun-synchronous satellites that maintain the same ground track throughout the year have inclinations of as much as 98 degrees. U.S. scientific satellites that study the sun are placed in orbits closer to the equator, frequently at 28 degrees inclination. Most weather satellites are placed in high-inclination orbits so they can oversee weather conditions worldwide. See orbital inclination.

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information system

All of the means and mechanisms for data receipt, processing, storage, retrieval, and analysis. Information Systems can be designed for storage and dissemination of a variety of data products--including primary data sets and both intermediate and final analyses--and for an interface providing connections to external computers, external data banks, and system users. To be effective, the design and operation of an information system must be carried out in close association with the primary producers of the data sets, as well as other groups producing integrated analyses or intermediate products.

infrared radiation (IR)

Infrared is electromagnetic radiation whose wavelength spans the region from about 0.7 to 1000 micrometers (longer than visible radiation, shorter than microwave radiation). Remote sensing instruments work by sensing radiation that is naturally emitted or reflected by the Earth's surface or from the atmosphere, or by sensing signals transmitted from a satellite and reflected back to it. In the visible and near-infrared regions, surface chemical composition, vegetation cover, and biological properties of surface matter can be measured. In the mid-infrared region, geological formations can be detected due to the absorption properties related to the structure of silicates. In the far infrared, emissions from the Earth's atmosphere and surface offer information about atmospheric and surface temperatures and water vapor and other trace constituents in the atmosphere. Since IR data are based on temperatures rather than visible radiation, the data may be obtained day or night.

INSAT

Indian National Satellite.

in situ

Latin for "in original place." Refers to measurements made at the actual location of the object or material measured. Compare remote sensing.

insolation

Solar radiation incident upon a unit horizontal surface on or above the Earth's surface.

instantaneous field of view (IFOV)

The field of view of a scanning detector system at a given instant. The range of angles scanned by the system is then called the field of view, or swath width.

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international date line

An imaginary line of longitude 180 degrees east or west of the prime meridian.

international designator

An internationally agreed-upon naming convention for satellites. The designator contains the last two digits of the launch year, the launch number of the year, and the part of the launch, i.e., RAS indicates payload, RBS the rocket booster, or second payload, etc.

International Geophysical Year (IGY)

(1957P58) The IGY was organized by the scientific community through the International Council of Scientific Unions (ICSU) . It was highlighted by international cooperation in the exploration of world-wide geophysical phenomena and by the inauguration of the space age through the launching of the first satellites (USSR's Sputnik I and US Explorer 1) to study the upper atmosphere and Earth's nearby environment.

International Space Year (ISY)

(1992) Designated the first international celebration of humanity's future in the space age. Themes included the global perspective of the space age, discovery, exploration, and scientific inquiry. An important ISY scientific focus was Mission to Planet Earth. A wide range of educational programs and public events emphasized ISY's global perspective.1992 also commemorated the 500th anniversary of Columbus' voyage to the New World and the 35th anniversary of the International Geophysical Year.

International System of Units (SI)

The International System of Units prescribes the symbols and prefixes shown in the table to form decimal multiples and submultiples of SI units.

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The following examples illustrate the use of these prefixes:

0.000,001 meters = 1 micrometer = 1µm
1000 meters = 1 kilometer = 1 km
1,000,000 cycles per second = 1,000,000 hertz = 1 megahertz =1 MHz

ion

Atom or molecule that has acquired an electric charge by the loss or gain of one or more electrons.

IPS

Inches per second.

IR

See infrared radiation.

isobars

Lines drawn on a weather map joining places of equal barometric pressure.

isothermal

Of or indicating equality of temperature.

isotherms

Lines connecting points of equal temperature on a weather map.

isthmus

Narrow strip of land located between two bodies of water, connecting two larger land areas.

ITOS (Improved TIROS Operational Satellite)

Second generation, polar-orbiting, environmental satellites utilized to augment NOAA's world-wide weather observation capabilities. ITOS were launched from 1970 - 1976, but eventually replaced by the third generation of polar-orbiting, environmental satellites TIROS-N (first launched in 1978). See TIROS.