Sea surface motion induced effects on high frequency underwater acoustic signals /

Güneş, Hasan
Acoustic signal scattering from the moving sea surface constitutes one of the most significant problems in underwater communication and sonar applications when dealing with signal processing especially at high frequencies. In this thesis, a realistic 3D linear sea surface wave model which solves governing equations is combined with a ray based computationally efficient acoustic model, BELLHOP, in order to simulate the effects of the time-evolving sea surface on acoustic waves. Rough sea surface realizations according to main environmental parameters (wind speed and fetch) are generated and imported into acoustic model to simulate temporal fluctuations in the acoustic signals. Doppler shifts in frequency of source signal are calculated by using the surface-normal velocities provided by sea surface wave model and acoustic rays provided by BELLHOP tool. Received timeseries are generated by convolution of source timeseries and time-varying impulse response of the underwater channel which is obtained from application of an existing interpolation scheme to arrival amplitude-delay pairs in order to simulate amplitude fluctuations as well. In addition, Monte Carlo based simulations are made to relate wind speed and acoustic signal fluctuations statistically.


Underwater channel modeling for sonar applications
Epçaçan, Erdal; Çiloğlu, Tolga; Department of Electrical and Electronics Engineering (2011)
Underwater acoustic channel models have been studied in the context of communication and sonar applications. Acoustic propagation channel in an underwater environment exhibits multipath, time-variability and Doppler e ects. In this thesis, multipath fading channel models, underwater physical properties and sound propagation characteristics are studied. An underwater channel model for sonar applications is proposed. In the proposed model, the physical characteristics of underwater environment are considered ...
Topology control vector based forwarding algorithm for underwater acoustic networks
Yazgı, İlkay; Baykal, Buyurman; Department of Electrical and Electronics Engineering (2015)
The communication range of underwater acoustic sensor networks (UASN) is limited by the underwater environment. Acoustic networks with huge number of sensors may have long communication range with appropriate protocols in literature. On the other hand, especially, the networks including small number of nodes have communication problems for long ranges. To challenge this problem, topology control in underwater acoustic networks is a promising solution. In this study, a novel approach, Topology Control Vector...
Seabed mapping using multibeam sonar and combining with former bathymetric data
Gürtürk, Fatih Furkan; Leblebicioğlu, Mehmet Kemal; Department of Electrical and Electronics Engineering (2015)
The most practical methods in underwater mapping are based on acoustic measurements. In this thesis, a simulation program was developed for mapping the sea depth with a multibeam echosounder. The factors affecting the mapping resolution and accuracy were shown on the simulation. The correction of the sound velocity profile, which affects the sonar’s performance, with the Ray Theory was explained. The error sources were explained for measured depth values on each beam and the position assigned for depth meas...
Wideband Channel Estimation With a Generative Adversarial Network
Balevi, Eren; Andrews, Jeffrey G. (2021-05-01)
Communication at high carrier frequencies such as millimeter wave (mmWave) and terahertz (THz) requires channel estimation for very large bandwidths at low SNR. Hence, allocating an orthogonal pilot tone for each coherence bandwidth leads to excessive number of pilots. We leverage generative adversarial networks (GANs) to accurately estimate frequency selective channels with few pilots at low SNR. The proposed estimator first learns to produce channel samples from the true but unknown channel distribution v...
Design of an FM-CW radar altimeter
Yetkil, Yaşar Barış; Demir, Şimşek; Department of Electrical and Electronics Engineering (2005)
Frequency modulated continuous wave (FM-CW) radar altimeters are used in civil and military applications. Proximity fuses, automatic cruise control systems of cars, radar altimeter of planes are examples to these applications. The goal of this thesis is to present a method for altitude determination using an FM-CW radar. For this purpose principles of radars and FM-CW systems are studied and related subjects are inspected. After this inspection, algorithms for altitude determination are evaluated. Consequen...
Citation Formats
H. Güneş, “Sea surface motion induced effects on high frequency underwater acoustic signals /,” M.S. - Master of Science, Middle East Technical University, 2014.