<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">Dr. Helge Balk

UNIVERSITY OF OSLO   

DEPARTMENT OF PHYSICS

PB 1048 Blindern 0316 OSLO NORWAY

fax: +47 22 85 64 22 phone +47 22856489 mobile +47 97772401

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Misc

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Private

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Research

To day there is an increased interest in shallow water fish-stock assessment and improved monitoring techniques are essential.   Hydro-acoustic methods based on single beam, split beam, multi-beam and multi-frequency sonar seems promising. We are focusing on side-looking split-beam sonar. With the correct opening angle, one or a few horizontally mounted transducers can cover major part of a river cross-section. Horizontal beaming from a boat increases the sample volume from the upper part of the water column relative to down-looking applications.

There are, however, many pitfalls and problems connected to side-looking echo sounders in shallow water. High ping-to-ping and sample-to-sample intensity and phase variation in the echo signal from fish are one problem that makes detection difficult. Separating fish echoes from debris, bottom reflection and from erroneous echo detections of peaks in the background reverberation level are also difficult. Great care has to be taken with regard to selecting the site and to setting up the echo sounder’s recording parameters. Still the resulting sonar data might be difficult and tedious to analyse.  Automatic methods do not work when the signal to noise ratio becomes poor. The probability of detecting a fish by manual analysis becomes low.

Our research focuses on the understanding of the behaviour of sound in shallow water and on development of hardware and hardware and software to process and analyse data basically from single and split-beam transducers. Experiments on ice, field-works in rivers and modelling are important parts of our work. We measure the direct and reflected sound with hydrophones and echo sounders. Finite element method and ray tracing are applied in the modelling.   

Fish echoes in shallow water frequently take on multiple echo characteristics while fluctuations in the background takes on single fish characteristics. Hence, single echo detectors based on single fish echo criteria such as echo-intensity, length, shape and phase stability does not work well. To solve this we have developed an alternative single target detector working with the frequency spectra of the echo data. In addition to the single target detector, tracking and classification is important part of our fish counting model.

The sonar teem at the department of physics consist of Torfinn Lindem, my self and at the moment four Ms.Sci. students. 

(This paragraph was last updated 27.05.2002)

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Development of hydroacoustic methods for fish detection in shallow waters

Ref: Balk, H., 2001. Development of hydroacoustic methods for fish detection in shallow water, Faculty of Mathematics and Natural Science, University of Oslo 309 p. ISSN 1501-7710

Management of salmon stocks from various regions is of great importance.  Optimal management can only be achieved with knowledge of the size and the changes in the stocks. Hence, monitoring methods are important. In marine fisheries, split-beam echo sounders are frequently applied to monitor fish. In recent years this hydroacoustic fish detection method has been applied in many rivers. Aligning one or a few transducers horizontally provides a simple way to monitor major parts of a river's cross-section.

However, the horizontal shallow water application introduces new problems related to the acquisition, analysis, and interpretation of the sonar data. Fieldwork has been carried out in lakes and rivers, and a systematic analysis of these problems has been made. From the experience and the studies of the recorded material, new methods have been developed. Signal processing based on image analysis and classification theory is introduced, and promising results have been achieved. 

Read the thesis. (html)

PDF

 (Last updated 23.05.2002)
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Digitalisation of sonar (master thesis)
During the years 1994..1996 I wrote my master thesis  "Digitalisation of sonar". It describes the development of a hardware-software sonar system based on one to four transmitters / receivers connected in a chain and controlled by a laptop. High dynamic was gained by applying tuned passive circuits in the front end, and splitting the signal into three separate channels with different gain. A gain detector switched between the channels before sampling. To gain sufficient speed for real-time processing in an ordinary laptop running Win3.1 through the parallel port, a virtual device driver was written in assembly to replace the standard parallel port. Presenting echograms in real-time was also challenging and parts of the thesis was assigned to studies of data transport and screen updating in windows. The thesis consists of a total of 456 pages describing the hardware and software development and testing.

The thesis is available at the University library (Bibsys)

(Last updated 22.01.2002)

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Publications, proceedings and reports

Publications and presentations

2009    Balk, Helge; Lindem, Torfinn. Target detection in data from splitbeam echosounders and multi beam sonar systems. Invited talk  Evening seminar at the Norvegian society for image analysis and pattern recognition

 

2008    Tuser, Michael; Balk, Helge; Froutsova, Jaroslava; Kubecka, Jan; Muska, Milan. Suitability of DIDSON acoustic camera for quantitative fish stock assessment by mobile surveys. Symposium on the Echosystem Approach with Fisheries Acoustics and Complementary Technologies (SEAFACTS); 2008-06-15

 

2008    Rudstam, Lars G.; Knudsen, Frank R.; Balk, Helge; Gal, Gideon; Boscarino, Brent T.; Axenrot, Thomas. Acoustic characterization of Mysis relicta at multiple frequencies. Canadian Journal of Fisheries and Aquatic Sciences 2008 ;Volum 65.(12) s. 2769-2779

 

2008    Rakowitz, G; Herold, W; Fesl, C; Keckeis, H; Kubecka, J; Balk, Helge. Two methods to improve the accuracy of target-strength estimates for horizontal beaming. Fisheries Research 2008 ;Volum 93.(3) s. 324-331

 

2008    Rakowitz, G; Herold, W; Fesl, C; Keckeis, H; Kubecka, J; Balk, Helge. Two methods to improve the accuracy of target-strength estimates for horizontal beaming. Fisheries Research 2008 ;Volum 93.(3) s. 324-331

 

2008    Kubecka, Jan; Balk, Helge; Drastic, Vladislav; Frouzova, Jaroslava; Gassner, Hubert; Herzig, Alois; Jarolim, Oldoich; Juza, Tomas; Kratochvil, Michael; Vasek, Mojmir.  Large-scale acoustic surveys of an extremely shallow lake: Neusiedler See, Austria. Symposium on the Echosystem Approach with Fisheries Acoustics and Complementary Technologies (SEAFACTS); 2008-06-15 - 2008-06-21

 

2008    Jurvelius, Juha; Knudsen, Frank R.; Balk, Helge; Marjomäki, Timo J.; Peltonen, Heikki; Taskinen, Jouni; Tuomaala, Antti; Viljanen, Markku. Echo-sounding can discriminate between fish and macroinvertebrates in fresh water. Freshwater Biology 2008 ;Volum 53.

 

2008    Gjelland, Karl Øystein; Knudsen, Frank; Balk, Helge. Bias in swimming speed estimates from splitbeam acoustics should be corrected for with smoothing. Symposium on the Echosystem Approach with Fisheries Acoustics and Complementary Technologies (SEAFACTS); 2008-06-15

 

2008    Froutzova, Jaroslava; Kubecka, Jan; Balk, Helge. Fat echoes of oblique aspects : consequences for fish single echo detection. Symposium on the Echosystem Approach with Fisheries Acoustics and Complementary Technologies (SEAFACTS); 2008-06-15

 

2008    Drastik, Vladislav; Hohausova, Eva; Kubecka, Jan; Balk, Helge; Froutsova, Jaroslava. Classification of fish and plant echoes in acoustic surveys. Symposium on the Echosystem Approach with Fisheries Acoustics and Complementary Technologies (SEAFACTS); 2009-06-15

 

2008    Balk, Helge; Lindem, Torfinn; Kubecka, Jan. Split beam versus multi beam for monitoring migrating fish in rivers and shallow lakes. ICES Symposium on the Ecosystem Approach with Fisheries Acoustics and Complementary Technologies; 2008-06-15 - 2008-06-20

 

2008    Balk, Helge; Lindem, Torfinn. Analysis and visualization of data from DIDSON Acoustic camera. 31-th Scandinavian symposium on Physical Acoustics; 2008-01-27

 

2008      Hohausova, E; Kubecka, J; Frouzova, J; Husak, S; Balk, Helge. Experimental biomass assessment of three species of freshwater aquatic plants by horizontal acoustics. Journal of aquatic plant management 2008 ;Volum 46.

 

2007    Rudstam, Lars G.; Gal, Gideon; Balk, Helge; Knudsen, Frank R.; Axenrot, Thomas; Boscarino, Brent. Multiple acoustic frequencies increase our ability to discriminate between fish, mysids and zooplankton. IAGLR 2007; 2007-05-28 - 2007-06-01

 

2007 J. Jurvelius, F.R. Knudsen, H. Balk, T.Mariomäki, H. Peltonen, J. Taskinen, A.Tuomaala, M.Viljanen.  Echo-sounding can discriminate between fish and macroinvertebrates in fresh water Freshwater Biology (2007) doi:10.1111/j.1365-2427.2007.01944.x

 

2007 Balk, Helge; Lindem, Torfinn; Kubecka, Jan; Frank, Knudsen. Recent advances in solving signal-to-noise problems in fisheries acoustics

Keynote talk at the FSAMPL07 conference, Ceske Budejovice, Czech Republic, September. 11-15,   2007.

 

2007 Balk Helge. Analysis of data from high frequency multi beam sonars. Scientific talk at the DIDSON workshop arranged by the University of Vienna 14..18 April 2007.

 

2006  Balk, Helge,  Introduction, presentation and theory for multi-frequency hydroacoustics. Invited to teach and partly lead the Multi frequency workshop at Cornell University; 26.08.2006 - 03.09.2006

 

2006 Balk, Helge. Sound waves and fish abundance. Talk at the University of Mildura (Au) Invited by CSIRO to assist establishing hydro-acoustic 29.05.2006 - 29.05.2006

 

2006 Balk, Helge; Lindem, Torfinn; Kubecka, Jan. Enhenced Crossfilter detector for target detection in data from echosounders.  29th SCANDINAVIAN SYMPOSIUM ON PHYSICAL ACOUSTICS; 29.01.2006 - 01.02.2006

 

2005 Balk,.H. 2005. Linear kretselekronikk. Unipub. 293p. Tutorial book in linear circuit analysis with focus on Fourier and Laplace transformations for the UiO course FYS3220.     

 

2005 Peltonen, H; Balk, Helge. The acoustic target strength of herring (Clupea harengus L.) in the northern Baltic Sea. ICES Journal of Marine Science 2005;62:803-808

 

2005 Frouzova, J; Kubecka, J; Balk, Helge; Frouz, J. Target strength of some European fish species and its dependence on fish body parameters. Fisheries Research 2005;75:86-96

 

2005 Balk, Helge. New methods for fish and bottom detection in data from split beam echosounders. Invited to talk and partly lead a seminar arrange by Ifremer, IRD and INRA ; 27.07.2005 - 29.07.2005

 

2005 Balk, Helge. A Ph. D. Class on Marine Bioacoustics. 29.05.2005 - 08.06.2005 Tjarnø (Se).  Invited teacher for the echo-sounder part of the class. Plenum lecturer, field work and laboratory classes.

 

 

2005 Balk, Helge; Lindem, Torfinn; Kubecka, Jan. New single echo detection methods for shallow water fisheries acoustics. [Scientific talk]. 135th Annual Meeting of American Society of Fisheries in Anchorage; 11.09.2005 - 15.09.2005

 

2005 Balk, Helge. New methods for fish and bottom detection in data from split beam echo-sounders. Seminar arrange by Ifremer, IRD and INRA at Ifremer in Brest; 27.07.2005 - 29.07.2005

 

2005  Balk, Helge; Lindem, Torfinn; Kubecka, Jan. New single echo detection methods for shallow water fishery acoustics [Vitenskapelig foredrag]. 149'th Meeting of the Acoustical Society of America; 15.05.2005 - 20.05.2005

 

 

2004 Balk, H. and T. Lindem, 2004. Sonar4 and Sonar5-Pro. Post processing system. Operator manual v5.9.4. Lindem Data Acquisition. 405 p.

 

2004 Balk, Helge. Reflection and diffraction of sound waves in shallow water and how this influences the sonar equations [Scientific talk]. Swedish acoustic meeting; 25.10.2004 - 26.10.2004

 

2004 Balk, Helge. Presentation of research results. Advanced analysis methods for fisheries acoustics. Detection methods for data characterized with low signal to noise ration [Scientific talk]. Workshop on hydro-acoustic methods; 31.03.2004 - 04.04.2004

 

2003 Balk, Helge; Lindem, Torfinn. Fish detection based on spectral differences in the echogram's range and temporal domain [Scientific talk]. ICES Fast meeting in Bergen; 18.07.2003 - 21.07.2003

 

2003 Balk, Helge; Lindem, Torfinn. Fish detection based on spectral differences in the echogram's range and temporal domain [Scientific talk]. ICES Fast meeting in Bergen; 18.07.2003 - 21.07.2003

 

2003  Balk, Helge; Lindem, Torfinn. A new method for single target detection [Poster]. 6th ICES Symposiom "Acoustics in fisheries and aquatic ecology" 2003. Published in: Book of Abstracts

 

2002 Lindem, T. and Balk, H. 2002. Measurements of acoustic sound fields in a shallow river.  Poster at ICES meeting in Montpelier Fr.

 

2002 Balk, H. and Lindem, T. 2002. Fish detection in rivers with split-beam sonars

Proc. 25’th  Scandinavian Symp. Phys Acoust., Vol. No. 2002-04.

 

 2002 Balk, H. and Lindem, T. 2002. A new method for single target detection in shallow water. Poster at ICES meeting in Montpelier Fr.

 

2002 Lindem, Torfinn; Balk, Helge; Vibeke, J.; Kjølerbakken, K. M.. Measurements of acoustic sound fields in a shallow river [Poster]. ICES Symposium on acoustics fisheries and aquatic echology 2002. Published in: Book of abstracts

 

 

2001 Balk, H., 2001. Development of hydro-acoustic methods for fish detection in shallow water. Oslo Dissertation for the degree of the Dr.Sci. 2001. Factulty of mathematics and natural sciences. University of Oslo ISSN 1501-7710 Nr. 137.  309 p. PDF

 

2001 Gjelland, Karl Øystein; Balk, Helge; Bøhn, Thomas. Laksetelling i Reisa med ekkolodd sommeren 2001 et prøveprosjekt. Tromsø: Norges Fiskerihøgskole, Universitetet i Tromsø 2002. 32 s.

 

2000 Balk, H. and Lindem, T. 2000.  A method for separating fish from noise in Sonar data characterized by low signal to noise ratio. Patent PCT/No00/00288

 

2000 Balk, H. and Lindem, T. 2000.  Improved fish detection in data from split beam transducers. Aquat. Living Resour. 13 (5), 2000, 297-303.

 

2000 Balk, Helge; Lindem, Torfinn. Improved fish detection in data from split-beam sonar. Aquatic Living Resources 2000;13:297-303

 

1999 Lindem, Torfinn; Balk, Helge; Knudsen, Frank R.. Sound propagation through shallow water can make unexpected modification to fish echoes recorded with a horizontally looking split beam system [Vitenskapelig foredrag]. 2nd International Shallow Water Fisheries Sonar Conference 1999

 

1999 Balk, H. and Lindem, T. 1999. Fish tracking in shallow water by applying image processing. Proc. 22’th Scandinavian Symp. Phys Acoust., 1999. Vol. No.  429904. pp 1-2.

 

1999 Lindem, Torfinn; Balk, Helge. Problems related to Time Varied Gain (TVG) and phase measurements with elliptic split beam transducers in shallow water, - some observations [Poster]. 22nd Scandinavian Symposium on Physical Acoustics 1999. Publisert i: NTNU Scientific/Technical Report No.429904

 

1998    Balk, H. and Lindem, T. 1998. Hydroacoustic fish counting in rivers and shallow waters, with focus on problems related to tracking in horizontal scanning sonar’s. Proc. 21’th  Scandinavian Symp. Phys Acoust., Vol. No. 1998-04 pp. 21-22.

 

1996       Balk, H. 1996. Digitalisation of Sonar, Department of Physics, University of Oslo 408p.

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 (This paragraph was last updated 01.06.2009)

 

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