Spectrum Management for Science in the 21st Century (2010) / Chapter Skim
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1 Introduction
1 Introduction
Pages 6-17
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From page 6... ...
This global view was only made possible by the development of advanced sensors that were able to take advantage of the new perspective offered by satellites. Chief among the new classes of sensors used in the nearly five decades since TIROS has been the passive microwave radiometer, which holds the unique advantage over optical and infrared systems of being able to probe through clouds.
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From page 7... ...
The popular use of microwae within the passive remote sensing community may have arisen in an attempt to distinguish microwave observations from visible and infrared remote sensing observations in which the Rayleigh-Jeans approximation is not applicable, and radiance power is expressed as an equivalent brightness temperature. The EESS passive microwave measurements are referenced to absolute temperature.
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From page 8... ...
1.1 THE PASSIVE RADIO SPECTRUM Radio astronomy and passive Earth remote sensing both rely on detecting, recording, and interpreting weak natural radio frequency emissions. These emis sions are radiated by all absorptive bodies: for example, forests, clouds, the Sun, and galaxies.
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From page 9... ...
merge with infrared radiation, and some studies require continuous measurements from the radio into the infrared bands, and even on to optical bands or beyond. Natural radio emissions are generated by a variety of mechanisms.
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In radio astronomy, a proper interpretation of line radiation provides information on the composition, density, and temperature of the material under study. Radio astronomers are interested in frequency bands where an interesting atomic or molecular transition occurs and where Earth's atmosphere is particularly transparent.
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From page 11... ...
Optimal frequencies for measuring continuum radiation are between the major transition frequencies for oxygen and water vapor (see Figures 1.2 and 1.3)
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From page 12... ...
The ability of passive microwave Earth remote sensing to study water in various phases, at both continuum and spectral line frequencies, means that these instruments will be increasingly used to pro vide key information. Whether obtained for use in day-to-day weather forecasting operations or for long-term climate studies, passive microwave measurements of Earth represent one of the most important scientific uses of the radio spectrum.
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From page 13... ...
There are two fundamentally different categories of spectrum users. One cat egory consists of active users -- those who transmit radio signals to achieve their ends, which may be voice or data communications, radar surveillance, or even Earth remote sensing using radars or other transmitters.
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From page 14... ...
activities are extremely sensitive, as they must respond to very weak natural radiations. Follow ing is a list of characteristics of EESS and RAS measurements that must be taken into account in considering radio frequency interference (RFI)
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From page 15... ...
Finding: Owing to their receive-only nature, the passive Earth Exploration-Satellite Service and Radio Astronomy Service, operating from 10 MHz to 3 THz, are inca pable of interfering with other services. 1.4 INTERFERENCE MITIGATION Users of the RAS and EESS go to considerable effort to mitigate the effects of RFI.
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From page 16... ...
Since these are personal devices, the total emission level is generally proportional to the population and level of development in any given area. • Radio telescopes gain a great deal of protection from RFI by locating in remote areas -- for example, in the National Radio Quiet Zone in West Virginia, behind high moun tains, or in remote desert areas.
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From page 17... ...
introduction well as methods for mitigating the impact of interference. Finally, Chapter 5 pro vides the committee's recommendations for continuing to enable passive scientific uses of the radio spectrum.
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