Browse Publications
2005 Reports
Note: Unless linked to the full text, reports are only available to NATO member nations from designated distribution centres.
Comparison between predictions made by the SUPREMO sonar performance model and measured data. SR-429. July 2005.
Infrared detection of marine mammals. SR-443. December 2005.Predictions of acoustic reverberation and target echo intensity, made by the SUPREMO sonar performance model, are compared with measured data gathered in the Malta Plateau region of the Mediterranean Sea. The model’s ability to predict these quantities is assessed and used as a measure of model performance. It is shown that the model, when given satisfactory input descriptions of the ocean environment, is capable of predicting reverberation intensity to modal errors of magnitude around -1dB with a spread of ±4dB around the modal values. Furthermore, the model is shown to be able to predict trends in signal-to-background intensity ratio as pulse centre frequency is varied between values of 1100Hz, and 1700Hz with bandwidths of 200Hz and 800Hz. The model-measured agreement observed indicates the suitability of the SUPREMO model for use within an environmentally adaptive, low-frequency, active sonar system.
An infrared (IR) binocular, designed for in-the-field military applications, was tested using in situ marine mammals during the Mar Ligure Joint Experiment 2003 (MLJX'03) that took place in August-September 2003 onboard the NRV Alliance. The test investigated the potential IR technology for marine mammal detection, in both day time and night time conditions. The effectiveness of this IR system in detecting marine mammals was strongly affected by weather conditions, ranging from excellent performance during clear and low sea-state conditions to poor performance during hazy conditions or higher sea-states. The IR system was tested during both day and night.
Effects of source and receiver positional offsets in multistatic range determination. SM-432. July 2005.
During the Adults’03 sea trial (a joint research project between NATO URC and TNO-FEL, The Netherlands) a number of experiments were conducted to investigate the effects of equipment offsets in multistatic range determination. The analysis presented in this report is based on data collected during experiment P02b where the two participant ships, both towing an LFAS source-receiver pair, were arranged into an in-line configuration and proceeded with same speed and heading. The direct blast arrivals are used to acoustically calculate the distance between sources and receivers. The comparison between the expected arrival times (according to the geometry) and the measured arrival times gives an indication on how equipment offsets, latencies, positional errors and unknown sound speed effect range determination.
Effects of the internal waves on the acoustic propagation. SM-433. July 2005.
A simple 2D model called SOFIA has been developed in order to predict sound-speed fluctuations in the water column due to linear internal waves. It is based on solving the equation governing the vertical particle velocity associated with the internal waves, using a modal decomposition of the internal wave field. The main feature of the model is the use of experimental data: the Brunt-Väisälä profile is calculated from the density profile registered by the CTD cast, the amplitudes of the normal modes are determined using ADCP data and the spectrum is deduced from the thermistor chain measurements. The effects of the linear internal waves on the acoustic propagation were studied through several numerical simulations using some sound-speed profiles predicted with the SOFIA model. The acoustic simulations were performed with the REVPA model, based on a wide-angle approximation of the parabolic equation (PE) method. Through these simulations, the possible relation between the influence of the internal waves and different values of the environmental parameters was assessed. The environmental parameters considered in this study were the source depth, the acoustic frequency and the sediment properties.
Experimental determination of seabed scattering law and environmental parameters from reverberation. SR-403. February 2005.
Simple theory shows that one can extract the scattering law angle dependence from ratio of reverberation to one-way propagation intensity measured on a vertical array (VLA). An experiment was carried out during BOUNDARY2003 and repeated during BOUNDARY2004 using an FM sweep as sound source first to measure vertical angle-dependent monostatic reverberation then to measure angle-dependent propagation loss as the ship mounted source moved away from the VLA. Both scattering and reflection properties are deduced in several ways without the need for modelling.
Manual of BORIS-SSA: Bottom Response from Inhomogeneities and Surface using the Small-Slope Approximation, Version 1.01. M-152. July 2005.
The description of a software tool capable of simulating, in the time domain, the acoustic time series resulting from scattering from various seafloor types and acoustic source/receiver geometries is presented in the form of a user manual. This package, named BORIS-SSA, is an upgrade, with various new features, of BORIS-3D. The parameters of the model characterize the sonar directivity and pulse shape, the geometrical configuration of the scattering problem and the geo-physical characteristics of the seafloor (but also sea surface or other surface). This surface can be generated to have various statistical behaviours or can be obtained from deterministic data based on the surface heights (profilometry, stereo-photogrammetry, bathymetry, etc). The package is platform independent and user friendly. This report is intended as a detailed description of the implementation on a source code level. A short introduction to the model underlying the package and a comprehensive demonstration program are also given.
Multistatic sensor placement with the complementary use of Doppler sensitive and insensitive waveforms. SR-427. July 2005.
Distributed multistatic active sonar systems have the potential to greatly improve surveillance capability against threat submarines. The geometric diversity of such systems provides an increased number of complementary detection opportunities to counter the underwater threat. The utilization of both Doppler sensitive and insensitive waveforms within such a multistatic network further improves the detection diversity and provides a more robust surveillance capability. This report describes the issues relevant to achieve this detection diversity, and shows the potential improvements of this approach. A simplified sonar signal excess model is described, which provides a capability to evaluate distributed sensor placements using both waveform types.
NATO Tactical Ocean Modelling System concept applicability. SR-411. October 2005.
Although the available ocean forecast schemes include a broad range of scales, they usually cannot account accurately for higher frequency ocean phenomena (sub-mesoscale to small scale) due to the uncertainty on the forcing fields and its initial phase. To overcome this uncertainty at present, extensive oceanographic data collection is required, which is very expensive and likely it will not be feasible to obtain on a sustained and substantial basis. To overcome these limitations at tactical level the NTOMS methodology is here proposed. It starts by running a model ensemble based on local available observations, builds robust statistics and introduces feature and high resolution modelling as a way to reduce uncertainty and increase systems performance. An implementation example during the trial MREA03 showed for surface drift related products that efficiency can increase by 20% and reliability can increase from 70 to 85%. Embedded feature modelling and the Mini-HOPS concepts are also outlined to locally improve the representation of the sub-mesoscale dynamics. It was concluded NTOMS approach to produce short term, locally more accurate oceanographic field estimation, accounting for the tactical modelling requirements.
NC3A-NURC joint trials of the SkyWAN Satcom TDMA system. SR-407. February 2005.
The report documents the trials conducted by NURC and NC3A in spring 2004. Trials were to assess the real time performance of a Satcom TDMA mechanism called SkyWAN in conjunction with end-to-end IP applications. That mechanism is currently used by NURC to support its operational communication links with its two NATO research vessels when at sea. In order not to disturb these operational links, NURC negotiated with Eutelsat additional Satcom bandwidth to support those experimental trials. The major points of interest reported in that note are the description of the NURC VSAT characteristics, the configuration architecture and setting related to the NURC-NC3A trials, the basic end to end performance and a preliminary conclusion on the use of the SkyWAN mechanism.
Near normal classification of the upper layer of the seabed. SM-421. July 2005.
Acoustic time series acquired at normal incidence from typical echosounders are highly dependent on the distance (also called "depth") between the transducer and the mean seabed level. As several classification systems use the seabed signal shape and energy, its depth dependence needs to be compensated for before processing. Without depth correction, a bias in the classification and inversion procedure is introduced. This paper describes the steps required to produce quasi depth-independent echoes for a given seabed type, that reduce the bias in the classification process. The proposed method is applied to data acquired in Nova Scotia on a geo-acoustically complicated area. Variability and reliability associated to this classification process is also investigated.
Performance modelling and validation for distributed multistatic tracking. SR-397. February 2005.
This report develops a distributed multi-sensor tracker performance model that accounts for the target fading effect that we observe in sea trial data. We study model-based performance as a function of key tracker parameters, the choice of tracker architecture, and the number of distributed sensors. We validate the fidelity of the model by comparing model-based performance with actual tracker performance based on simulated contact data.
Probabilistic modelling of sidescan sonar texture using pairwise pixel interactions. SR-424. June 2005.
Probability models used to describe sidescan sonar background pixels are usually represented using Rayleigh or K-distributions. While useful for many purposes, these distributions do not capture information which characterises non-independent pixel amplitudes which typify many textures found in modern high-resolution sidescan sonar data. Such models are necessary if we are to compute sensor and mission performance metrics such as probabilities of detection and classification. This report describes a flexible technique for describing sidescan sonar image textures using Markov Random Fields. Pairwise pixel interactions are expressed using gray level difference histograms and, due to the equivalence of Markov and Gibbs random fields, are used as sufficient statistics to a Gibbs probability distribution. The parameters of the Gibbs distribution are found using stochastic approximation and complex textures such as sand ripples and sea grass are successfully represented using this method. The Gibbs model is also shown to be capable of seabed segmentation based on texture, as well as capable of designing a simple constant-false-alarm-rate detector.
RADARSAT mapping of BORA winds in the Adriatic Sea. SR-422. March 2005.
We examine the meteorological phenomena associated with the BORA wind system over the Adriatic Sea using RADARSAT synthetic aperture radar (SAR) imagery. A Bora wind event spins off a number of related atmospheric phenomena which manifest in SAR imagery as: high- intensity jets in the Gulfs of Trieste and Kvarneric, low-intensity shadow regions and island wakes along the Croatian coasts, and high-intensity atmospheric barrier jet along the western Adriatic coast. A key element in this study is the high resolution wind mapping from SAR imagery using scatterometer inversion algorithms and characterizing the Bora morphology. The high-resolution imaging allows for identification of topographically-controlled features and diagnosis of regions of strong vorticity and 3D motion.
Seabed characterization by inversion of acoustic propagation and reverberation data received on a towed horizontal array. SR-417. February 2005.
Sonar performance prediction in shallow-water is highly dependent on the char-acteristics of the underwater environment. The bottom properties are critical input parameters to prediction tools and these parameters are probably the most dicult to estimate. Inversion of measured acoustic signals (direct propagation and diffuse reverberation) provides a technique to infer these bottom parameters. An ad-hoc approach using the sensors of the sonar system is proposed where the local geoacoustic properties are determined by inverting the data received on a horizontal array. The local geoacoustic properties are used as initial or guidance inputs to a reverberation model to estimate range-averaged geoacoustic and scattering properties from long-range reverberation data.
Side scan sonar image segmentation through multi-resolution texture features: a case study over the Luce Bay site during Northern Light 2003. SR-413. August 2005.
The segmentation of a side scan sonar (SSS) data set acquired in the Luce Bay site during the Northern Light '03 exercise by a Hugin autonomous underwater vehicle (AUV) equipped with an EdgeTech SSS, is presented and discussed. The segmentation was performed through the analysis of the image texture using a set of un-decimated wavelet transform features followed by classification using a supervised classifier based on the Mahalanobis distance in the feature space. The classifier was trained on four main sea floor classes, including low and high reflectivity sediments and sand ripples having two different ripple wavelengths, which are well discriminated in the feature space. A simple post-processing with geographic information system (GIS) tools was applied to smooth the data and convert pixels into polygons for a final output in AML/S57, the format adopted for data upload in Command and Control Information Systems (CCIS). The final thematic map showing the classification of the whole data set contains two distinct areas, the first in the inner leg (IL), showing no appreciable variations in the sea bed characteristics and the second, namely the outer leg (OL), having more variability.