Simrad (Norway)

Sonar calibration using a standard point target is always crucial for sonar manufacturers and researchers. Traditionally a sphere with certain size and material is selected as the standard point target for a given frequency. As the sonar frequency increases, the required size of the sphere tends to decrease and its supporting structure may not be neglected. We discover that the thin wire is a better point target for high-frequency wideband sonars. This paper addresses how a stainless steel thin wire of a diameter of 0.356mm is successfully adopted to calibrate our newly developed high-frequency wideband multibeam sonar from 700kHz to 1.4MHz.

A prototype broadband echo sounder has been used for measuring zooplankton and fish in a new collaborative project between the Institute of Marine Research and Kongsberg Maritime-Simrad. The prototype system used is a Simrad broadband system which includes a transceiver operating from 10–500 kHz. We have mainly used the transceiver together with four separate Simrad ESXX-7CD standard pressure resistant transducers, the ES70-7CD, ES120-7CD, ES200-7CD, and ES333-7CD, covering the band from 50 to 450 kHz. The research has so far concentrated on data output formats, calibration methods, and measurements from single targets in ex situ and in situ situations. Examples of recorded reflected spectra for selected calibration and biological targets will be shown and the potential for improved aquatic ecosystem assessment discussed.

The new multi-beam sonar, MS70, is a horizontally observing sonar yielding very high spatial resolution when operating all 500 beams, covering the frequency band 75–112 kHz. The sonar has undergone sea trials from R/V G. O. Sars from December 2005. The presentation includes preliminary results obtained during this period. Topics covered will be sonar performance objectives, calibration methods, and preliminary results from calibration and school data acquisition. Examples of raw and processed 3-D and 4-D data from a stationary and surveying vessel on small sprat schools and large herring schools will be shown.

During the last few years autonomous underwater vehicle (AUV) technology has evolved from concept demonstrators towards commercial products. The driving forces are the move for energy exploitation towards deeper waters, naval applications and the Internet driven need for more intercontinental underwater communication cables. Other applications emerging for the future would be within environmental research and monitoring and deepwater exploration. Deepwater developments beyond the continental shelf would require the same level of survey data quality and intervention access as established for shallow water. The potential for cost savings is two folds. Firstly, there is a reduction in the survey cost it self and secondly there is a considerable cost saving by avoiding over design of subsea installations due to lack of sufficient documentation of the field. In this scenario, there is an increasing understanding that underwater robotics and in particular AUVs would play an important role in future survey and subsea engineering work. The AUV as a free swimming underwater survey sensor carrier has several advantages compared to cable controlled ROVs and deep towed systems. The paper focusses on the HUGIN AUV concept and field results from the North Sea and Gulf of Mexico.

Modern AUV designs must handle submerged autonomous operation for long periods of time. The state of the art solution embedded in the HUGIN AUVs is a Doppler velocity log (DVL) aided inertial navigation system (INS) that can integrate various forms of position measurement updates. In autonomous operations, position updates are only available in limited periods of time or space, thus the core velocity aided inertial navigation system must exhibit high accuracy. However, position uncertainty of a DVL aided inertial navigation system will eventually drift off, compromising either mission operation or requirements for accurate positioning of payload data. To meet the requirements for a range of military and civilian AUV applications, the HUGIN vehicles come with at flexible and powerful set of navigation techniques. Methods for position updates include GPS surface fix, DGPS-USBL, underwater transponder positioning (UTP) and bathymetric terrain navigation. Based on synthetic aperture sonar technology, a potentially revolutionary accurate velocity measurement is under development. HUGIN also comes with a navigation post-processing system (NavLab), which can be applied to increase navigational integrity and maximize position accuracy.

For pt. I see ibid., vol. 25, no. 1, p. 62-72 (2000). A receiver for coherent communication through underwater communication channels is analyzed. The receiver performance and stability versus delay spread, Doppler spread, and signal-to-noise ratio is quantified. The stability is governed by the ill-conditioning of a correlation matrix estimate and it sets the limit on how many taps should be used for a channel with a given number of degrees of freedom. The receiver is used extensively on both simulated and real data that are Doppler spread, and good performance in these channels is verified.

Scattering functions from several experiments demonstrate that acoustic underwater channels are doubly spread. Receivers used on these channels to date have difficulty with large Doppler spreads. A receiver to perform coherent communication over Doppler spread channels is presented in this first paper of two. The receiver contains a channel tracker and a linear decoder. The tracker operates by means of a modified recursive least squares algorithm which makes use of frequency-domain filters called Doppler lines. The decoder makes use of the channel tracker coefficients in order to perform minimum mean square error decoding. This first paper treats theoretical aspects whereas the second part presents implementation issues and results.

Hugin is an untethered underwater vehicle (UUV) intended for bathymetric seabed surveying. This paper presents a description of the vehicle with emphasis on the acoustic instrumentation. The authors specifically describe the integration of the different acoustic systems and how they affect each other. They also summarise the operational results and gives indications with regard to future plans.