WO1996034297A1

WO1996034297A1 - A method for the installation calibration of a passive acoustic listening system

Info

Publication number: WO1996034297A1
Application number: PCT/NO1996/000061
Authority: WO
Inventors: Arve Gustavsen; Ragnvald Otterlei; Tore Endresen
Original assignee: Arve Gustavsen; Ragnvald Otterlei; Tore Endresen
Priority date: 1995-04-27
Filing date: 1996-03-20
Publication date: 1996-10-31
Also published as: NO308813B1; AU5704896A; NO951597D0; NO951597L

Abstract

The installation of a listening system is achieved without measuring the distances or the directions between the listening stations. These parameters are automatically calculated by utilising a method for automatic installation calibration. Approximate values for the relative positioning and direction can also be entered to support the calibration calculations. The invention is a method for the correct calibration of a passive acoustic listening system when such a listening system is used for the determination of the direction to or the positioning of the origin of sound signals. The calibration can be utilised for listening systems working in 2 or 3 geographical dimensions. The method is valid for the installation of a listening system consisting of at least 2 listening stations, together including at least 4 microphones. The relative distance between the listening stations and the relative direction to each listening station is calculated. The clock synchronising of each listening station is also determined. The complete calibration is performed by the repositioning of a sound generator to a series of geographical positions, unknown to the listening system. In each position, the sound generator transmits a characteristic sound.

Description

A method for the installation calibration of a passive acoustic listening system.

The present invention relates to systems installed for listening purpose, consisting of listening stations with microphones, capable of presenting correct direction to and/or the positioning of any distinct sound received from a 3 dimensional geographical field of vision.

The present invention presents an automatic method to determine the relative position of the listening stations, the relative direction between them and the synchronising of die clocks in each individual listening station.

The capabilities of measuring the relative distance and direction is especially valuable when the physical conditions for manual measuring is difficult or will give approximate results. The synchronising of the clocks for each listening station is important and necessary for the accuracy of the measurements of the listening system. The quality of the relative time measurement between the individual listening stations are decisive for the quality in the direction- and position-finding of distinct sound originated within any area of interest.

No methods have been found, describing the present invention.

One method for calibrating acoustic system has been discussed and described in G01

Sl/72:

" Method for the calibration of an underwater transponder system, and means to apply the method" .

The referred invention describes the method of calculating the relative distance between a set of minimum three transponders, located close to the seabed, and based upon the intercommunication of signals between the transponders and a sound generator. The method described in G01 Sl/72 deviates significantly from the present invention which describes that the listening stations through an intercommunication identifies the relative inter distances based upon signals received from one single sound generator, and that the position of this sound generator is unknown and do not receive any signals from the listening stations. The method described in G01 Sl/72 do not mention any synchronising of clocks. The present invention deviates also from the G01 Sl/72 while the unknown parameters, relative distance between listening stations, relative direction of the listening stations and the clock adjustments are all defined by the positioning of the sound generator in a number of positions within the acoustic reach of the listening stations. The method is general in its nature, and is not demanding any knowledge about the actual positioning of the listening stations, requiring only line of sight to the sound generator and that the sound intensity is acceptable for the selected microphones. This is achieved by methods as described in the following claims.

The listening system, prepared for automatic installation calibration, needs a minimum amount of equipment to facilitate the calibration. At least 4 microphones must be installed, and distributed to at least 2 listening stations.

These microphones shall be capable of relaying signals, relevant for all available acoustics within the frequency range of the microphones for a further calculation in the listening system.

When the listening stations have been mounted in unknown positions, the calibration is made by moving a sound generator from one unknown geographical position to another. In each position, the sound generator produces a number of calibration measuring series. These calibration measuring series are adapted to the features in the listening system. It is a precondition that the listening system is utilising time measurements, phase measurements or both of the said measurements in the position- and direction-finding of the origin of the sound. It is furthermore a precondition that the listening system can be entered into an installation mode in which it is prepared to receive signals from the above defined calibration measuring series.

According to the present invention, the unknown values for relative distance between the listening stations, and the relative direction of these stations as well as the clock synchronising can be calculated as long the number of mathematical equations are sufficiently greater than the number of unknown values. This is achieved by moving the sound generator to a sufficient number of positions.

Correspondingly, the number of microphones involved, as well as the distribution of these microphones to listening stations are decisive parameters in the requirements for surplus mathematical equations. The minimum solution of 4 microphones gives a calibration in 2 geographical dimensions with a sufficient accuracy. In order to extend the calibration to an installation of a listening system in space, one more microphone is required.

The final calculation and solution of the mathematical equations can be performed within the listening system, or externally in a separate computer system.

The calculated values are fundamental for the accurate position- and direction-finding of a listening system, and substitutes the tedious manual measuring of the same values.

Another feature of the present invention is that approximate values for the relative distance and direction between the listening stations can be entered, and that these approximate values are included in the calculations when utilising the mobile sound generator.

Claims

1. A method for the calibration of the geographical position and the clock synchronising for the main elements in a passive acoustic listening system, consisting of a number of interconnected listening stations, each equipped with one or more microphones, including processing means for analysis of sound signals received from the said microphones, for the main purpose of calculating direction to the origin of acoustic sound, position of acoustic sound origins or both, and that the said listening system consists of at least 2 listening stations with a minimum of 4 microphones for the purpose of installation calibration, in order to calculate the relative distance between said listening station, in order to calculate the relative angle between the said listening stations, and in order to perform clock synchronising of said listening stations, by utilising special correction signals received from a sound generator, producing said signals from a number of geographical positions, initially unknown to the listening system, and that the said microphones are located within line of sight of the position of the said sound generator, providing the correction signals, characterised in that the same acoustic correction signals are received by all listening stations, produced by a sound generator positioned within line of sight of each microphones included in the calibration procedure, and that the sound generator is moved to a limited number of such geographical positions, and that the characteristics for the said signal is measured in each listening station for each said position from which the sound generator transmits said signals.

2. A method according to claim 1 , characterised in that the capability to calculate the relative distance between the listening stations, the relative angle to each listening station, or the combination thereof, and that the clock synchronising is calculated, defined by the surplus of mathematical equations.

3. A method according to claim 2, characterised in that the capability to implement approximate values for the relative distance between the listening station, the relative direction of the listening station or combinations of such approximate values.