Broadband matched-field processing of transient signals in shallow water

Full Field Inversion Methods in Ocean and Seismo-Acoustics

1995

Self Cite

This paper presents some of the preliminary work aimed at estimating the ocean bottom morphological structure in coastal waters using a towed array. In order to obtain an idea of the expected performance of the system and draw some conclusions on its operation this study presents the sensitivity of three processors to variations of: array length, source and receiver positions, sensor noise, source frequency and frequency band. Conclusions tend to demonstrate that cost function sensitivity to sound speed variations is higher on the bottom top layers and it increases with array length. An increased sensitivity is generally acompanied by a cost function non-monotonic behavior creating local minima and making it more difficult to reach the global minimum. Attenuations have in general small influence on the acoustic field structure and are therefore difficult to estimate. Increasing the signal frequency band by incoherent module averaging has no significant influence on sensitivity. A cost function relaying on the conventional matched filter has shown low sensitivity to sensor noise and is being extended to matching directional data from bottom arrivals at several frequencies. Mismatch cases, mainly those related to array/source relative position, will be also presented.

Section: Simulation Resultssupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

A Sensitivity Study for Full-Field Inversion of Geo-Acoustic Data with a Towed Array in Shallow Water

Full Field Inversion Methods in Ocean and Seismo-Acoustics

1995

Self Cite

“…Generally the searched parameters aims to solve three classes of problems: passive source localization, matched field inversion for geoacoustic parameters and ocean acoustic tomography to perform estimation of water column sound speed profile (or the closely related ocean temperature field). Important benchmarking in MFP are found in (Bucker, 1976;Tolstoy et al, 1991;Jesus, 1993;Baggeroer et al, 1993).…”

Section: Environmental Focusingmentioning

confidence: 99%

Time-variant Adaptive Passive Time Reversal Equaliser and a Perspective for Environmental Focusing Method

Maia

Silva

Proceedings of the 4th International Conference on Sensor Networks

2015

High digital data throughput in Underwater Acoustic Communications (UAComm) is a challenging subject, specially in shallow water where the channel is a wave-guide causing multipath propagation and where Doppler effect usually occurs due to relative source-receiver motion jointly to ocean dynamics. The source and receiver sensors can be used for telemetry in point-to-point underwater communications or as nodes of an underwater acoustic network within the scope of oceanic research observatory or offshore activities. However, channel tracking is required for reliable digital underwater communications between the sensors, which is a hard task due to the complicated propagation of acoustic waves in the ocean. Equalisation is often required to perform a compensation method aiming to overcome the inter-symbol interference (ISI) caused by multipath propagation. The motivation of this work is to propose a compensation method deploying the adaptive passive time-reversal (ApTR) equaliser, aiming to perform ISI mitigation jointly to Doppler compensation in time-variant channels. The benefit given by ApTR processing would be the performance improvement in underwater communications between an active sensor and a vertical line array of receiver sensors, relying in well-succeed time-variant channel impulse response estimation. Furthermore, this position paper discusses the perspective of use an environmental focusing method for channel estimation within the ApTR equaliser, based on the idea that a set of oceanic acoustic physical parameters-which are generally estimated in low-frequency matched field processing problems like geoacoustic assessment, ocean tomography and source localizationcould be conveniently used for channel compensation in high frequency underwater communications using a carefully chosen search space of replicas. The results are two fold: in one hand the equalisation shall improve the UAComm system, and in the other hand, the best match of channel parameters consequently yields a refined local environmental assessment.

“…Experimental results have shown that increasing the number of frequencies results in more consistent source localization estimates. 9,10,16,17 In order to test that possibility, the LFM sweeps emitted in the same time slots as the MT were processed. A number of 30 frequencies ranging from 820 to 1500 Hz with a spacing of 23.4 Hz were selected.…”

Section: The 10 Km Trackmentioning

confidence: 99%

Source localization in a time-varying ocean waveguide

Soares

Siderius

The Journal of the Acoustical Society of America

2002

One of the most stringent impairments in matched-field processing is the impact of missing or erroneous environmental information on the final source location estimate. This problem is known in the literature as model mismatch and is strongly frequency dependent. Another unavoidable factor that contributes to model mismatch is the natural time and spatial variability of the ocean waveguide. As a consequence, most of the experimental results obtained to date focus on short source-receiver ranges (usually <5 km), stationary sources, reduced time windows and frequencies generally below 600 Hz. This paper shows that MFP source localization can be made robust to time-space environmental mismatch if the parameters responsible for the mismatch are clearly identified, properly modeled and (time-)adaptively estimated by a focalization procedure prior to MFP source localization. The data acquired during the ADVENT'99 sea trial at 2, 5, and 10 km source-receiver ranges and in two frequency bands, below and above 600 Hz, provided an excellent opportunity to test the proposed techniques. The results indicate that an adequate parametrization of the waveguide is effective up to 10 km range in both frequency bands achieving a precise localization during the whole recording of the 5 km track, and most of the 10 km track. It is shown that the increasing MFP dependence on erroneous environmental information in the higher frequency and at longer ranges can only be accounted for by including a time dependent modeling of the water column sound speed profile.