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GNSS Signals and Range Determination
Published in Basudeb Bhatta, Global Navigation Satellite Systems, 2021
The Doppler effect (or Doppler shift), is the change in frequency and wavelength of a wave for an observer moving relative to the source of the waves (Jones 1984). This phenomenon can be explained by a model provided by sound. An increase in the frequency of a sound is indicated by a rising pitch; a lower pitch is the result of a decrease in the frequency. A stationary observer listening to the blasting horn of a passing train will note that as the train gets closer, the pitch rises, and as the train travels away, the pitch falls. However, the change in the sound to the observer standing beside the track is not heard by the driver driving the train. He hears only one constant, steady pitch. The relative motion of the train with respect to the observer causes the apparent variation in the frequency of the horn.
Navigation
Published in R. Glenn Wright, Unmanned and Autonomous Ships, 2020
Radar – Radar supplements the human senses to help detect and avoid other vessels, to view ATON and land masses by using radio waves to detect objects and determine their range, angle, velocity and, in some cases, their characteristics. Analog signals requiring high levels of power traditionally used to implement this technology have been expanded to include digital signals that require far less power, which can be modified and adjusted to interrogate targets with different methods to extract additional information not possible using traditional analog techniques. Radar possesses the ability to produce velocity data regarding an object through use of the Doppler effect that senses changes in frequency as a result of movement in relation to the Radar transmitter. Automatic Radar Plotting Aid (ARPA) features can provide Radar contact object plotting to track course, speed, closest point of approach (CPA) and time of CPA as a means to determine the danger of collision with other ships, land masses or other objects.
Ultrasonography
Published in Jiří Jan, Medical Image Processing, Reconstruction and Analysis, 2019
In ultrasonography, the Doppler effect is used for measuring the blood velocity. Both mentioned partial phenomena are involved: the moving blood particles are insonified with a frequency modified due to particle movement in the ultrasonic field of the fixed transducer; consequently, due to scattering, every particle acts as a moving source of this modified frequency field, which is then detected by the transducer. Both effects are combined in synergy, obviously with u = v and α = β; as the blood velocity is much slower than the speed of ultrasound, Equation 7.16 may be simplified to fD=2f0vcosαc.
On the TSD deflection velocity measurements: a revision to the current state of the art and discussion over its applicability for concrete pavement assessment
Published in International Journal of Pavement Engineering, 2022
Martín Scavone, Samer W. Katicha, Gerardo W. Flintsch, Eugene Amarh
Consider a signal source emitting a wave signal (either light or sound) at a frequency fs. The Doppler effect (Albrecht 2003, Jendzurski and Paulter 2008, Zhang 2010) is the frequency shift (change in frequency) that occurs when the signal source is moving or when the signal is reflected off a moving surface (or both). In either case, the Doppler effect is the same, and therefore, it only depends on the relative movement of the source and the receiver or reflecting surface (Jendzurski and Paulter 2008, Zhang 2010). Therefore, when considering TSD Doppler velocimetry, instead of having the TSD moving in the x-direction and the pavement in the y-direction (deflecting), we can assume the TSD is fixed, and the pavement is moving in the x and y directions with velocities vx and vy. The relative velocity vector v is therefore given by: Where i and j are unit-length vectors representing the horizontal and vertical directions respectively. The velocity measured by the Doppler laser is equal to the dot product of the velocity v and the unit direction vector L of the Doppler laser (Albrecht 2003, Zhang 2010): Where θ is the angle of L the laser relative to the y-axis (vertical direction, Figure 1). See Appendix A for more details on how to remove the horizontal velocity component from the laser measurement to obtain the pavement deflection velocity (the vertical component).
The influences of Doppler shift on the wave dissipation and soil responses over the porous medium
Published in Coastal Engineering Journal, 2018
Jing-Hua Lin, Hung-Chu Hsu, Yang-Yih Chen
The Doppler shift (or called the Doppler effect) is the relative motion which is the change in the frequency of waves for an observer moving relative to the source. In the water wave, it represents the wave–current interaction. Nonuniform or uniform currents influence the characteristics of waves. The speed and wavelength are increased in waves encountering a favorable current and vice verse for the opposing current (Nielsen, 2012). The combined wave-current flow is generally existed in the ocean environment, such as the interaction between the ocean and the bayou, or the wave–tide current interaction in the open sea (Wolf and Prandle, 1999; Rusu, Bernardino, and Guedes Soares, 2011; Westhuysen, 2012; Dodet et al., 2013; Chen et al., 2013). Most existing papers studied the dynamic characteristics and neglected the interaction with the porous seabed in the wave–current interaction, such as Longuet-Higgins and Stewart (1960,1961), Jonsson et al.(1970; 1978), Jonsson (1977), Peregrine (1976), Thomas (1981,1990), Baddour and Song (1990), Groeneweg and Battjes (2003), Musumeci et al. (2006), Olabarrieta, Medina, and Castanedo (2010), Constantin and Strauss (2010) and Chen et al.(2013; 2014). Hence, the porous medium induced the energy dissipation is not discussed in these studies.
Requirements and challenges for infusion of SHM systems within Digital Twin platforms
Published in Structure and Infrastructure Engineering, 2023
Rolando Chacón, Joan R. Casas, Carlos Ramonell, Hector Posada, Irina Stipanovic, Sandra Škarić
Another technique is RADAR. The acronym reads Radio Detection and Ranging systems. By means of a transmitter, the radio produces an electromagnetic signal that is then propagated into the space by means of antenna. When this signal strikes an object, it gets reflected back. The reflected signal is known to be the echo signal. The receiver then processes the echoed signal. For finding the range of the object, the system uses the time taken by the signal to get reflected. For the target location, an angle is calculated from the direction of the echo signal to the direction where the antenna is pointing. For moving objects, the Doppler Effect is used to calculate the speed and range of such object.