Chair: Jose M.F. Moura, Carnegie Mellon University (USA)
Arthur B. Baggeroer, Massachusetts Institute of Technology (USA)
Henrik Schmidt, Massachusetts Institute of Technology (USA)
Matched field and ocean acoustic tomography concern the estimation of parameters for models of ocean environments using acoustics. Both require full field representations for the observed signals since waveguide effects are important. We present Cramer-Rao lower bounds for the attainable accuracy of both methods. These bounds are expressed in terms of the Green's function for the propagation between source and receivers.
Theodore G. Birdsall, University of Michigan (USA)
Systems for bistatic monitoring of ocean processes differ radically from monostatic systems searching for targets. This paper discusses basic principles, showing how these effect signal design, signal processing goals and signal processing techniques. In addition, computer advances have a strong influence in changing signal processing choices, sometimes rendering yesterday's optimums today's curiosities, and perhaps converting today's impossibilities into tomorrow's challenges.
Jeffrey L. Krolik, Duke University (USA)
Sunil Narasimhan, Duke University (USA)
The ability to measure climate-related mean changes in ocean temperature is fundamentally limited by the presence of mesoscale variability. In this paper, the Cramer-Rao Lower Bound on the estimation of the mean depth-dependent temperature profile is evaluated to determine the highest accuracy which could be achieved by acoustic thermometry of ocean climate. Evaluation of the bound is performed using a model of sound-speed variability derived from real Pacific Ocean environmental data. Results indicate that a low-order Chebyshev polynomial may be a good choice for climate signal representation. The general behavior of the bound is determined by a subtle interaction between the climate signal basis, a priori mesoscale noise statistics, and observation-time-bandwidth-signal-to-noise ratio product.
Jose M. F. Moura, Carnegie Mellon University (USA)
M. Joao Rendas, Universite de Nice
Georges Bienvenu, Thomson-Sintra (ASM) (FRANCE)
Extension of the operational range of underwater location techniques has been related to the incorporation of reliable acoustic propagation models, that closely predict oceans' behaviour. In this paper, the performance of ocean tomography and passive localization of underwater acoustic sources is studied, by analyzing the coupling of performance degradations imposed by modeling mismatches on the ability to estimate the position of acoustic sources.
C. Noel et C. Viala, Societe SEMANTICS
F. Evennouet Y Stephan, Hydrographique et Oceanographique de la Marine
F.R. Martin- Lauzer, Groupe d'Etudes Sous-Marines de l'Atlantique (FRANCE)
An acoustic tomography experiment, supported by European MAST contracts, has been carried out in the all occidental Mediterranean sea. During 10 months in 1994, acoustic phase shift keying signals have been emitted at a pulse rate of 1 per 4 hours and received by seven sources-receivers localized in the all basin and spaced by several hundred kilometers. In addition, signals from two of these sources localized near Corse and Sardinia were received on a vertical array moored at 800m depth near Nice. So, it means a joint assessment of arrival angles and times of acoustic signals and a useful improvement in general problem of identification of acoustic paths. Signals received on 16 hydrophones of this 40 meters long array were recorded and processed to extract propagation time and arrival angle of each ray path. This paper reports the results of the analysis of these last data records and discuss observation of wave fronts at each hydrophone depth, tractability, and study of arrival peaks as a function of time and angle.
Paul W. Fieguth, Massachusetts Institute of Technology (USA)
William C. Karl, Massachusetts Institute of Technology (USA)
Alan S. Willsky, Massachusetts Institute of Technology (USA)
A recent significant problem in oceanographic remote sensing is the dense gridding or smoothing of sparsely sampled altimetric data. The smoothing of altimetric measurements has an application much broader than just the regular production of elevation maps for oceanographers, however. In particular, the ability to estimate ocean circulation patterns from altimetric data can serve as an important measure for the verification of ocean acoustic tomographic results. In this paper we present a multiscale technique capable of extremely efficient interpolation of altimetric data: about 256,000 estimates and estimation error variances are computed in one minute on a Sun Sparc-10. We also demonstrate how similar techniques may be used to directly estimate the surface gradient and biases in the geoid-model error.
Toshio M. Chin, National Center for Atmospheric Research
Arthur J. Mariano, University of Miami (USA)
Large-scale extended Kalman filters for atmospheric and oceanic circulation models can readily be approximated using a wavelet transform or a Markov random field model. For a filtering problem where the unknown field of the state variables is highly correlated and the observations are relatively sparse, the wavelet-approximated filter seems more appropriate. For a problem in which the covariance matrix is non-singular and a relatively large quantity of independent observations are processed, the MRF-approximated filter seems more appropriate.
Amir Asif, Carnegie Mellon University (USA)
Jose M. F. Moura, Carnegie Mellon University (USA)
The paper discusses a scheme based on Kalman-Bucy filters for the assimilation of satellite data in equatorial beta plane ocean circulation models. The state equation of the Kalman-Bucy filter is obtained by decoupling the non-linearities from the Navier-Stokes equations by assuming an inviscid isentropic shallow water motion. Direct application of the Kalman-Bucy filter leads to a computationally intensive algorithm which precludes its application to meaningful sized domains. By imposing a Gauss Markov random field (GMRF) structure on the error covariance matrix, we obtain an efficient recursive algorithm capable of estimating the velocity fields and the sea surface height.
Jules S. Jaffe, Scripps Institute of Oceanography (USA)
Girish Chandran, Scripps Institute of Oceanography (USA)
Edward Reuss, Scripps Institute of Oceanography (USA)
The use of acoustical techniques in oceanography is well known. Traditional application include Anti Submarine Warfare (ASW) and have concentrated on long range, low frequency propagation. More recently, consideration of the possibilities for creating high frequency, real time, multi-dimensional imaging systems (2 and 3-D) has emerged. Unfortunately, due to a lack of experimental investigation, the propagation issues related to such instruments are relatively unknown. Our group has been taking high frequency acoustic pictures in the ocean for almost a decade. Recently we have been developing a 3-dimensional multibeam imaging system for tracking small animals in the sea. As part of this effort we are looking at both the spatial and temporal correlation scales for the propagation of high frequency sound. In this talk, the theory of operation of these types of systems will be discussed along with the specific environmental acoustical issues such as variability which provides challenges to all working in this area.