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GNSS Reflectometry
GNSS reflectometry (or GNSS-R) involves making measurements from the reflections from the Earth of navigation signals from Global Navigation Satellite Systems such as GPS. The idea of using reflected GNSS signal for earth observation became more and more popular in the mid-1990s at NASA Langley Research Center and is also known as ''GPS reflectometry''. Research applications of GNSS-R are found in * Altimetry * Oceanography (Wave Height and Wind Speed) * Cryosphere monitoring * Soil moisture monitoring GNSS reflectometry is passive sensing that takes advantage of and relies on separate active sources - the satellites generating the navigation signals. For this, the GNSS receiver measures the signal delay from the satellite (the pseudorange measurement) and the rate of change of the range between satellite and observer (the Doppler measurement). The surface area of the reflected GNSS signal also provides the two parameters time delay and frequency change. As a result, the Delay ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
GNSS-R System Diagram
GNSS reflectometry (or GNSS-R) involves making measurements from the reflections from the Earth of navigation signals from Global Navigation Satellite Systems such as GPS. The idea of using reflected GNSS signal for earth observation became more and more popular in the mid-1990s at NASA Langley Research Center and is also known as ''GPS reflectometry''. Research applications of GNSS-R are found in * Altimetry * Oceanography (Wave Height and Wind Speed) * Cryosphere monitoring * Soil moisture monitoring GNSS reflectometry is passive sensing that takes advantage of and relies on separate active sources - the satellites generating the navigation signals. For this, the GNSS receiver measures the signal delay from the satellite (the pseudorange measurement) and the rate of change of the range between satellite and observer (the Doppler measurement). The surface area of the reflected GNSS signal also provides the two parameters time delay and frequency change. As a result, the Delay ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bistatic Radar
Bistatic radar is a radar system comprising a transmitter and receiver that are separated by a distance comparable to the expected target distance. Conversely, a conventional radar in which the transmitter and receiver are co-located is called a monostatic radar. A system containing multiple spatially diverse monostatic or bistatic radar components with a shared area of coverage is called ''multistatic radar''. Many long-range air-to-air and surface-to-air missile systems use semi-active radar homing, which is a form of bistatic radar. Types Pseudo-monostatic radars Some radar systems may have separate transmit and receive antennas, but if the angle subtended between transmitter, target and receiver (the bistatic angle) is close to zero, then they would still be regarded as monostatic or pseudo-monostatic. For example, some very long range HF radar systems may have a transmitter and receiver which are separated by a few tens of kilometres for electrical isolation, but as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyclone Global Navigation Satellite System (CYGNSS)
The Cyclone Global Navigation Satellite System (CYGNSS) is a space-based system developed by the University of Michigan and Southwest Research Institute with the aim of improving hurricane forecasting by better understanding the interactions between the sea and the air near the core of a storm. In June 2012, NASA sponsored the project for $152 million with the University of Michigan leading its development. Other participants in CYGNSS' development include the Southwest Research Institute, Sierra Nevada Corporation, and Surrey Satellite Technology. The plan was to build a constellation of eight micro-satellites to be launched simultaneously in a single launch vehicle into low Earth orbit, at 500 km altitude. The program was scheduled to launch December 12, 2016, and then observe two hurricane seasons. Problems with a pump on the launching aircraft prevented this first launch, but a second launch attempt took place successfully on December 15, 2016. Overview Forecasti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geophysical Research Letters
''Geophysical Research Letters'' is a biweekly peer-reviewed scientific journal of geoscience published by the American Geophysical Union that was established in 1974. The editor-in-chief is Harihar Rajaram. Aims and scope The journal aims for rapid publication of concise research reports on one or more of the disciplines covered by the American Geophysical Union, such as atmospheric sciences, solid Earth, space science, oceanography, hydrology, land surface processes, and the cryosphere. The journal also publishes invited reviews that cover advances achieved during the past two or three years. The target readership is the earth science community, the broader scientific community, and the general public. Abstracting and indexing This journal is abstracted and indexed in: According to the 2020 ''Journal Citation Reports'', the journal has a 2019 impact factor of 4.58. ''Geophysical Research Letters'' was also the 5th most cited publication on climate change between 1999 and 2 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Low Earth Orbit
A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never more than about one-third of the radius of Earth. The term ''LEO region'' is also used for the area of space below an altitude of (about one-third of Earth's radius). Objects in orbits that pass through this zone, even if they have an apogee further out or are sub-orbital, are carefully tracked since they present a collision risk to the many LEO satellites. All crewed space stations to date have been within LEO. From 1968 to 1972, the Apollo program's lunar missions sent humans beyond LEO. Since the end of the Apollo program, no human spaceflights have been beyond LEO. Defining characteristics A wide variety of sources define LEO in terms of altitude. The altitude of an object in an elliptic orbit can vary significantly along the orbit. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surrey Satellite Technology Ltd
Surrey Satellite Technology Ltd, or SSTL, is a company involved in the manufacture and operation of small satellites. A spin-off company of the University of Surrey, it is presently wholly owned by Airbus Defence and Space. The company began out of research efforts centred upon amateur radio satellites, known by the UoSAT (University of Surrey Satellite) name or by an OSCAR (Orbital Satellite Carrying Amateur Radio) designation. SSTL was founded in 1985, following successful trials on the use of commercial off-the-shelf (COTS) components on satellites, cumulating in the ''UoSat-1'' test satellite. It funds research projects with the university's Surrey Space Centre, which does research into satellite and space topics. In April 2008, the University of Surrey agreed to sell its majority share in the company to European multinational conglomerate EADS Astrium. In August 2008, SSTL opened a US subsidiary, which included both offices and a production site in Denver, Colorado; [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disaster Monitoring Constellation
The Disaster Monitoring Constellation for International Imaging (DMCii) or just Disaster Monitoring Constellation (DMC) consists of a number of remote sensing satellites constructed by Surrey Satellite Technology Ltd (SSTL) and operated for the Algerian, Nigerian, Turkish, British and Chinese governments by DMC International Imaging. The DMC provides emergency Earth imaging for disaster relief under the International Charter for Space and Major Disasters, which the DMC formally joined in November 2005. Other DMC Earth imagery is used for a variety of civil applications by a variety of governments. Spare available imaging capacity is sold under contract. The DMC provides far larger areas of imagery than, but at comparable resolution to, established government imaging satellites such as Landsat. DMC imagery was deliberately designed to be comparable to Landsat imagery, in order to leverage the expertise and software of the large established remote sensing community used to working ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multistatic Radar
A multistatic radar system contains multiple spatially diverse monostatic radar or bistatic radar components with a shared area of coverage. An important distinction of systems based on these individual radar geometries is the added requirement for some level of data fusion to take place between component parts. The spatial diversity afforded by multistatic systems allows different aspects of a target to be viewed simultaneously. The potential for information gain can give rise to a number of advantages over conventional systems. Multistatic radar is often referred to as "multisite" or "netted" radar and is comparable with the idea of macrodiversity in communications. A further subset of multistatic radar with roots in communications is that of MIMO radar. Characteristics Since multistatic radar may contain both monostatic and bistatic components, the advantages and disadvantages of each radar arrangement will also apply to multistatic systems. A system with N transmitters and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surface Roughness
Surface roughness, often shortened to roughness, is a component of surface finish (surface texture). It is quantified by the deviations in the direction of the normal vector of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small, the surface is smooth. In surface metrology, roughness is typically considered to be the high-frequency, short-wavelength component of a measured surface. However, in practice it is often necessary to know both the amplitude and frequency to ensure that a surface is fit for a purpose. Roughness plays an important role in determining how a real object will interact with its environment. In tribology, rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces. Roughness is often a good predictor of the performance of a mechanical component, since irregularities on the surface may form nucleation sites for cracks or corrosion. On the other hand, roughness may pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
GNSS
A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows satellite navigation devices to determine their location (longitude, latitude, and altitude/elevation) to high precision (within a few centimetres to metres) using time signals transmitted along a line of sight by radio from satellites. The system can be used for providing position, navigation or for tracking the position of something fitted with a receiver (satellite tracking). The signals also allow the electronic receiver to calculate the current local time to a high precision, which allows time synchronisation. These uses are collectively known as Positioning, Navigation and Timing (PNT). One set of critical vulnerabilities in satellite communications are the signals that govern positioning, navigation and timing (PNT). Failure to properly secure these transmissions could not only disrupt satellite networks but wreak havoc on a host of dependent sy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dielectric
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor, because they have no loosely bound, or free, electrons that may drift through the material, but instead they shift, only slightly, from their average equilibrium positions, causing dielectric polarisation. Because of dielectric polarisation, positive charges are displaced in the direction of the field and negative charges shift in the direction opposite to the field (for example, if the field is moving parallel to the positive ''x'' axis, the negative charges will shift in the negative ''x'' direction). This creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polaris ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
