Geophysics is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists, who usually study geophysics, physics, or one of the earth sciences at the graduate level, complete investigations across a wide range of scientific disciplines. The term geophysics classically refers to solid earth applications: Earth's shape; its gravitational, magnetic fields, and electromagnetic fields ; its internal structure and composition; its dynamics and their surface expression in plate tectonics, the generation of magmas, volcanism and rock formation. However, modern geophysics organizations and pure scientists use a broader definition that includes the water cycle including snow and ice; fluid dynamics of the oceans and the atmosphere; electricity and magnetism in the ionosphere and magnetosphere and solar-terrestrial physics; and analogous problems associated with the Moon and other planets.
Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1mm, which is shorter than the diameter of a grain of rice. At 30 Hz the corresponding wavelength is ~10,000 kilometers, which is longer than the radius of the Earth. Wavelength of a radio wave is inversely proportional to its frequency, because its velocity is constant. Like all electromagnetic waves, radio waves in a vacuum travel at the speed of light, and in the Earth's atmosphere at a slightly slower speed. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents. Naturally occurring radio waves are emitted by lightning and astronomical objects, and are part of the blackbody radiation emitted by all warm objects.
A microwave radiometer (MWR) is a radiometer that measures energy emitted at one millimeter-to-metre wavelengths (frequencies of 0.3–300 GHz) known as microwaves. Microwave radiometers are very sensitive receivers designed to measure thermally-emitted electromagnetic radiation. They are usually equipped with multiple receiving channels to derive the characteristic emission spectrum of planetary atmospheres, surfaces or extraterrestrial objects. Microwave radiometers are utilized in a variety of environmental and engineering applications, including remote sensing, weather forecasting, climate monitoring, radio astronomy and radio propagation studies.
Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Earth and other planets. Remote sensing is used in numerous fields, including geophysics, geography, land surveying and most Earth science disciplines ; it also has military, intelligence, commercial, economic, planning, and humanitarian applications, among others.
The International Union of Radio Science is one of 26 international scientific unions affiliated to the International Council for Science (ICSU).
The radio spectrum is the part of the electromagnetic spectrum with frequencies from 3 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particularly in telecommunication. To prevent interference between different users, the generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU).
Extremely high frequency (EHF) is the International Telecommunication Union (ITU) designation for the band of radio frequencies in the electromagnetic spectrum from 30 to 300 gigahertz (GHz). It lies between the super high frequency band and the far infrared band, the lower part of which is the terahertz band. Radio waves in this band have wavelengths from ten to one millimetre, so it is also called the millimetre band and radiation in this band is called millimetre waves, sometimes abbreviated MMW or mmWave. Millimetre-length electromagnetic waves were first investigated by Jagadish Chandra Bose, who generated waves of frequency up to 60 GHz during experiments in 1894–1896.
Ground-penetrating radar (GPR) is a geophysical method that uses radar pulses to image the subsurface. It is a non-intrusive method of surveying the sub-surface to investigate underground utilities such as concrete, asphalt, metals, pipes, cables or masonry. This nondestructive method uses electromagnetic radiation in the microwave band of the radio spectrum, and detects the reflected signals from subsurface structures. GPR can have applications in a variety of media, including rock, soil, ice, fresh water, pavements and structures. In the right conditions, practitioners can use GPR to detect subsurface objects, changes in material properties, and voids and cracks.
Geophysical survey is the systematic collection of geophysical data for spatial studies. Detection and analysis of the geophysical signals forms the core of Geophysical signal processing. The magnetic and gravitational fields emanating from the Earth's interior hold essential information concerning seismic activities and the internal structure. Hence, detection and analysis of the electric and Magnetic fields is very crucial. As the Electromagnetic and gravitational waves are multi-dimensional signals, all the 1-D transformation techniques can be extended for the analysis of these signals as well. Hence this article also discusses multi-dimensional signal processing techniques.
The IEEE Heinrich Hertz Medal was a science award presented by the IEEE for outstanding achievements in the field of electromagnetic waves. The medal was named in honour of German physicist Heinrich Hertz, and was first proposed in 1986 by IEEE Region 8 (Germany) as a centennial recognition of Hertz's work on electromagnetic radiation theory from 1886 to 1891. The medal was first awarded in 1988, and was presented annually until 2001. It was officially discontinued in November 2009.
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 3,000 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves, and received by another antenna connected to a radio receiver. Radio is widely used in modern technology, in radio communication, radar, radio navigation, remote control, remote sensing, and other applications.
James R. Wait was a Canadian electrical engineer and engineering physicist. In 1977, he was elected as a member of National Academy of Engineering in Electronics, Communication & Information Systems Engineering for his contributions to electromagnetic propagation engineering as it affects communication and geophysical exploration.
The Lviv Centre of Institute for Space Research, is a research institute at Lviv, Ukraine. It falls under the purview of the NASU and NSAU,.
Microwave engineering pertains to the study and design of microwave circuits, components, and systems. Fundamental principles are applied to analysis, design and measurement techniques in this field. The short wavelengths involved distinguish this discipline from electronic engineering. This is because there are different interactions with circuits, transmissions and propagation characteristics at microwave frequencies.
The following outline is provided as an overview of and topical guide to geophysics:
Henri Abraham (1868–1943) was a French physicist who made important contributions to the science of radio waves. He performed some of the first measurements of the propagation velocity of radio waves, helped develop France's first triode vacuum tube, and with Eugene Bloch invented the astable multivibrator. He was murdered at Auschwitz during the Holocaust.
Andrea Alù is an Italian American scientist and engineer, currently Einstein Professor of Physics at The City University of New York Graduate Center. He is known for his contributions to the fields of optics, photonics, plasmonics, and acoustics, most notably in the context of metamaterials and metasurfaces. He has co-authored over 650 journal papers and 35 book chapters, and he holds 11 U.S. patents.
One way of outlining the subject of radio science is listing the topics associated with it by authoritative bodies.
Kamal Sarabandi is an Iranian-American scientist and the Fawwaz T. Ulaby Distinguished University Professor of EECS and the Rufus S. Teesdale endowed Professor of Engineering at the University of Michigan, where he teaches and conducts research on the science and technology of microwave and millimeter wave radar remote sensing, wireless technology, electromagnetic wave propagation and scattering, metamaterials, antenna miniaturization, and nano antennas.
Mahta Moghaddam is an Iranian-American electrical and computer engineer and William M. Hogue Professor of Electrical Engineering in the Ming Hsieh Department of Electrical and Computer Engineering at the University of Southern California Viterbi School of Engineering. Moghaddam is also the president of the IEEE Antennas and Propagation Society and is known for developing sensor systems and algorithms for high-resolution characterization of the environment to quantify the effects of climate change. She also has developed innovative tools using microwave technology to visualize biological structures and target them in real-time with high-power focused microwave ablation.
