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Handbook of Antenna Technologies – Chapter Radiometer Antennas

Peichl, Markus (2016) Handbook of Antenna Technologies – Chapter Radiometer Antennas. In: Handbook of Antenna Technologies Springer Reference. Springer Science+Business Media Singapore. pp. 2727-2794. ISBN 978-981-4560-43-6.

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Official URL: http://link.springer.com/book/10.1007%2F978-981-4560-44-3

Abstract

Microwave radiometry is concerned with purely passive sensing of naturally generated microwave radiation of thermal origin. Microwave radiometers are corresponding measuring devices typically designed and built as a very low-noise receiver followed by a signal recording unit. Usually, radiometers contain an antenna as the first reception component collecting the incoming radiation, and they measure radiation power expressed in an apparent temperature called brightness temperature. The observable brightness temperature of any object or surface depends on various chemical and physical quantities, whose concurrence is expressed by the objects’ emission (absorption), reflection, and transmission properties and its true temperature. Since the Earth has a temperature typically close to 300 K and the universe close to 3 K, a nearly arbitrary mixture of these two extreme temperatures can be expected. Consequently, our environment can show quite different brightness temperature values depending on the direction of actual observation. On the one hand, radiometer measurements are carried out stationary with respect to the antenna pointing direction in order to observe time-dependent variations of the brightness temperature. On the other hand, the brightness temperature of a whole scene is scanned in order to acquire locally changing one- or two-dimensional profiles, while the latter ones are assembled as a two-dimensional image comparable to a conventional photograph. Depending on the specific application, various antenna types are considered, where usually hard requirements with respect to beam width, side-lobe level, scan capability, and losses have to be addressed (▶Transmission Lines). Radiometric measurements are performed for Earth or planetary observation in space (▶Space Antennas including Terahertz Antennas), from aircraft platforms on the Earth’s surface and the atmosphere, or on the ground, either sensing the environment or sensing the universe, the latter being performed in radio astronomy (▶Antennas in Radio Telescope Systems). Usually, the brightness temperature is rarely used as the physical quantity of interest. More often, it is transferred via adequate physical models to other secondary or third quantities for more direct use in the case of Earth observation (e.g., soil moisture, ocean salinity, rain rate, snow cover, etc.), being performed already since the 1950s of the last century. However, in the last decades, microwave radiometry is as well used in many safety- and security-related applications, for which often only sufficient temperature contrast between an object and its surrounding is required besides spatial resolution for detection and recognition purposes. In this chapter relevant fundamentals of microwave radiometry are outlined for better understanding of antenna requirements, followed by an overview of typical types of radiometer antenna systems. Some existing antenna systems are discussed in order to illustrate the variability with respect to applications. A section on basic antenna quantities addresses key figures for practical design and verification and illustrates the results exemplarily for selected cases. Finally, a brief summary and an outlook on possible future implementations and other frequency ranges are given.

Item URL in elib:https://elib.dlr.de/110638/
Document Type:Book Section
Title:Handbook of Antenna Technologies – Chapter Radiometer Antennas
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Peichl, MarkusMarkus.Peichl (at) dlr.dehttps://orcid.org/0000-0003-0226-9786
Date:2016
Journal or Publication Title:Handbook of Antenna Technologies
Refereed publication:No
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
DOI :10.1007/978-981-4560-44-3
Page Range:pp. 2727-2794
Editors:
EditorsEmail
Chen, Z.N.UNSPECIFIED
Liu, D.UNSPECIFIED
Nakano, H.UNSPECIFIED
Qing, X.UNSPECIFIED
Zwick, T.UNSPECIFIED
Publisher:Springer Science+Business Media Singapore
Series Name:Springer Reference
ISBN:978-981-4560-43-6
Status:Published
Keywords:Microwave radiometry; Earth observation; Security; Antenna temperature; Antenna losses; Antenna reflection; Mechanical scanner; Focal plane array; Aperture synthesis; Frequency scanning; Digital beamforming; Sparse array; Spatial resolution; Sensitivity; Sampling
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Erdbeobachtung
DLR - Research theme (Project):R - Vorhaben Sicherheitsrelevante Erdbeobachtung
Location: Oberpfaffenhofen
Institutes and Institutions:Microwaves and Radar Institute > Reconnaissance and Security
Deposited By: Peichl, Dr.-Ing. Markus
Deposited On:12 Jan 2017 15:36
Last Modified:12 Jan 2017 15:36

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