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SHARAD
SHARAD (Mars SHAllow RADar sounder) is a subsurface sounding radar embarked on the '' Mars Reconnaissance Orbiter'' (MRO) probe. It complements the MARSIS radar on ''Mars Express'' orbiter, providing lower penetration capabilities (some hundred meters) but much finer resolution (15 metres - untapered - in free space). SHARAD was developed under the responsibility of the Italian Space Agency (ASI, Agenzia Spaziale Italiana), and provided to JPL for use on board NASA's '' Mars Reconnaissance Orbiter'' spacecraft in the frame of a NASA/ASI agreement which foresees exploitation of the data by a joint Italian/US team. The INFOCOM dept. of the University of Sapienza University of Rome is responsible for the instrument operations, while Thales Alenia Space Italia (formerly Alenia Spazio) designed and built the instruments. SHARAD operations are managed by INFOCOM from the SHARAD Operation Centre (SHOC), located within the Alcatel Alenia Space facilities in the suburbs of Rome. Scienc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antenna (radio)
In radio-frequency engineering, an antenna (American English) or aerial (British English) is an electronic device that converts an alternating current, alternating electric current into radio waves (transmitting), or radio waves into an electric current (receiving). It is the interface between radio waves Radio propagation, propagating through space and electric currents moving in metal Electrical conductor, conductors, used with a transmitter or receiver (radio), receiver. In transmission (telecommunications), transmission, a radio transmitter supplies an electric current to the antenna's Terminal (electronics), terminals, and the antenna radiates the energy from the current as electromagnetic radiation, electromagnetic waves (radio waves). In receiver (radio), reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplifier, amplified. Antennas are essential components ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carpinteria
Carpinteria (; , meaning "Carpentry") is a small seaside city in southeastern Santa Barbara County, California. Located on the Central Coast of California, it had a population of 13,264 at the 2020 census. Carpinteria is a popular surf destination; the city embraced the slogan "World's Safest Beach" in 1912, which it still uses today. History Carpinteria was home to a Chumash village during pre-colonial times, which was known as Šujtu. In 1769, the Spanish Portolá expedition came west along the beach from the previous night's encampment at Rincon. The explorers found a large native village on the point of land where Carpinteria Pier is today. The party camped nearby on August 17. Fray Juan Crespí, a Franciscan missionary travelling with the expedition, noted that "Not far from the town we saw some springs of pitch. The Indians have many canoes, and at the time were building one, for which reason the soldiers named this town La Carpinteria" (the carpentry shop). The Chu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
L'Aquila
L'Aquila ( ; ; ) is a city and ''comune'' in central Italy. It is the capital city of the Province of L'Aquila and the Abruzzo region in Italy. , it has a population of 69,902. Laid out within medieval walls on a hill in the wide valley of the Aterno-Pescara, Aterno river, it is surrounded by the Apennine Mountains, with the Gran Sasso d'Italia to the north-east. L'Aquila sits on a hillside in the middle of a narrow valley; the tall snow-capped mountains of the Gran Sasso massif flank the town. A maze of narrow streets, lined with Baroque and Renaissance buildings and churches, open onto elegant piazzas. Home to the University of L'Aquila, it is a lively college town and, as such, has many cultural institutions: a Repertory, repertory theatre, a symphony orchestra, a fine art academy, a state conservatory and a film institute. There are several ski resorts in the surrounding province (Campo Imperatore, Ovindoli, Pescasseroli, Roccaraso, Scanno, Abruzzo, Scanno). Geography Close ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Milan
Milan ( , , ; ) is a city in northern Italy, regional capital of Lombardy, the largest city in Italy by urban area and the List of cities in Italy, second-most-populous city proper in Italy after Rome. The city proper has a population of nearly 1.4 million, while its Metropolitan City of Milan, metropolitan city has 3.2 million residents. Within Europe, Milan is the fourth-most-populous List of urban areas in the European Union, urban area of the EU with 6.17 million inhabitants. According to national sources, the population within the wider Milan metropolitan area (also known as Greater Milan) is estimated between 7.5 million and 8.2 million, making it by far the List of metropolitan areas of Italy, largest metropolitan area in Italy and List of metropolitan areas in Europe, one of the largest in the EU.* * * * Milan is the economic capital of Italy, one of the economic capitals of Europe and a global centre for business, fashion and finance. Milan is reco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Signal Processor
A digital signal processor (DSP) is a specialized microprocessor chip, with its architecture optimized for the operational needs of digital signal processing. DSPs are fabricated on metal–oxide–semiconductor (MOS) integrated circuit chips. They are widely used in audio signal processing, telecommunications, digital image processing, radar, sonar and speech recognition systems, and in common consumer electronic devices such as mobile phones, disk drives and high-definition television (HDTV) products. The goal of a DSP is usually to measure, filter or compress continuous real-world analog signals. Most general-purpose microprocessors can also execute digital signal processing algorithms successfully, but may not be able to keep up with such processing continuously in real-time. Also, dedicated DSPs usually have better power efficiency, thus they are more suitable in portable devices such as mobile phones because of power consumption constraints. DSPs often use special m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Undersampling
In signal processing, undersampling or bandpass sampling is a technique where one samples a bandpass-filtered signal at a sample rate below its Nyquist rate (twice the upper cutoff frequency), but is still able to reconstruct the signal. When one undersamples a bandpass signal, the samples are indistinguishable from the samples of a low-frequency alias of the high-frequency signal. Such sampling is also known as bandpass sampling, harmonic sampling, IF sampling, and direct IF-to-digital conversion. Description The Fourier transforms of real-valued functions are symmetrical around the 0 Hz axis. After sampling, only a periodic summation of the Fourier transform (called discrete-time Fourier transform) is still available. The individual frequency-shifted copies of the original transform are called ''aliases''. The frequency offset between adjacent aliases is the sampling-rate, denoted by ''fs''. When the aliases are mutually exclusive (spectrally), the original transf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Matching Network
In electrical engineering, impedance matching is the practice of designing or adjusting the input impedance or output impedance of an electrical device for a desired value. Often, the desired value is selected to maximize power transfer or minimize signal reflection. For example, impedance matching typically is used to improve power transfer from a radio transmitter via the interconnecting transmission line to the antenna. Signals on a transmission line will be transmitted without reflections if the transmission line is terminated with a matching impedance. Techniques of impedance matching include transformers, adjustable networks of lumped resistance, capacitance and inductance, or properly proportioned transmission lines. Practical impedance-matching devices will generally provide best results over a specified frequency band. The concept of impedance matching is widespread in electrical engineering, but is relevant in other applications in which a form of energy, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carrier Wave
In telecommunications, a carrier wave, carrier signal, or just carrier, is a periodic waveform (usually sinusoidal) that conveys information through a process called ''modulation''. One or more of the wave's properties, such as amplitude or frequency, are modified by an information bearing signal, called the ''message signal'' or ''modulation signal''. The carrier frequency is usually much higher than the message signal frequency; this is because it is usually impractical to transmit signals with low frequencies over long distances (due to attenuation). The purpose of the carrier is usually either to transmit the information through space as an electromagnetic wave (as in radio communication), or to allow several carriers at different frequencies to share a common physical transmission medium by frequency division multiplexing (as in a cable television system). The term originated in radio communication, where the carrier wave creates the waves which carry the information (mod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Signal Processing
Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing ''signals'', such as audio signal processing, sound, image processing, images, Scalar potential, potential fields, Seismic tomography, seismic signals, Altimeter, altimetry processing, and scientific measurements. Signal processing techniques are used to optimize transmissions, Data storage, digital storage efficiency, correcting distorted signals, improve subjective video quality, and to detect or pinpoint components of interest in a measured signal. History According to Alan V. Oppenheim and Ronald W. Schafer, the principles of signal processing can be found in the classical numerical analysis techniques of the 17th century. They further state that the digital refinement of these techniques can be found in the digital control systems of the 1940s and 1950s. In 1948, Claude Shannon wrote the influential paper "A Mathematical Theory of Communication" which was publis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pulse Repetition Frequency
The pulse-repetition frequency (PRF) is the number of pulses of a repeating signal in a specific time unit. The term is used within a number of technical disciplines, notably radar. In radar, a radio signal of a particular carrier frequency is turned on and off; the term "frequency" refers to the carrier, while the PRF refers to the number of switches. Both are measured in terms of cycle per second, or hertz. The PRF is normally much lower than the frequency. For instance, a typical World War II radar like the Type 7 GCI radar had a basic carrier frequency of 209 MHz (209 million cycles per second) and a PRF of 300 or 500 pulses per second. A related measure is the pulse width, the amount of time the transmitter is turned on during each pulse. After producing a brief pulse of radio signal, the transmitter is turned off in order for the receiver units to detect the reflections of that signal off distant targets. Since the radio signal has to travel out to the target and back ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aerobraking
Aerobraking is a spaceflight maneuver that reduces the high point of an elliptical orbit (apoapsis) by flying the vehicle through the atmosphere at the low point of the orbit (periapsis). The resulting drag slows the spacecraft. Aerobraking is used when a spacecraft requires a low orbit after arriving at a body with an atmosphere, as it requires less fuel than using propulsion to slow down. Method When an interplanetary vehicle arrives at its destination, it must reduce its velocity to achieve orbit or to land. To reach a low, near-circular orbit around a body with substantial gravity (as is required for many scientific studies), the required velocity changes can be on the order of kilometers per second. Using propulsion, the rocket equation dictates that a large fraction of the spacecraft mass must consist of fuel. This reduces the science payload and/or requires a large and expensive rocket. Provided the target body has an atmosphere, aerobraking can be used to reduce fuel re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
