A METHOD FOR DETERMINING A POSITION DEVIATION, A POSITIONING SYSTEM AND AN UNDERWATER VEHICLE

Abstract

A method (1000) for determining a position deviation of a first node the method comprising obtaining (1110) input data, at a first and second position. Said input data comprises, an estimated position of the first node (p1) and a first velocity vector (v1) of the first node, obtaining (1120) the exact position (p.sub.2*) of the second node; obtaining (1125) the emitted frequency (f.sub.e) of an acoustic signal a source; (1130) receiving the acoustic signal (S) and measuring the observed frequency; calculating (1140) a second velocity vector (v12) which defines the velocity of the first node in relation to the second node; and calculating (1150), the angle () between the first velocity vector and the second velocity vector; determining (1160) based on the angle, the first velocity vector, and the estimated position of the first node, a line of direction (L) indicating the direction from the estimated position of the first node towards an estimated position of the second node, and determining (1300) based on a first and second line of direction an intersection point defining the estimated position of the second node (p.sub.2); determining (1400) a deviation vector (V.sub.d) corresponding to the difference between the estimated position of the second node and the exact position of the second node, and determining (1500) the position deviation of the first node which corresponds to the deviation vector. The disclosure further relates to a positioning system for determining a position deviation for a first node and an underwater vehicle.

Claims

1-9. (canceled)

10. A method (1000) for determining a position deviation of a first node (N.sub.1) between an estimated position (p1) and an actual position of the first node (p1*), wherein the first node (N.sub.1) is located in a mass of water, the method comprising: obtaining input data (1110), at a first position (P.sub.t1) of the first node at a first point in time (t.sub.1), and at a second position (P.sub.t2) of the first node at a second point in time (t.sub.2), wherein the second position of the first node (p1.sub.t2) is a different position than the first position of the first node (p1.sub.t1), and the second point in time (t.sub.2) follows the first point in time (t.sub.1), wherein said input data comprises: an estimated position of the first node (p1.sub.t1,p1.sub.t2), and a first velocity vector (v1.sub.t1, v1.sub.t2) of the first node (N.sub.1), obtaining (1120) the exact position of the second node (p.sub.2*); obtaining (1125) the emitted frequency (f.sub.e) of an acoustic signal a source; receiving (1130) the acoustic signal (S) from a second node (N.sub.2) and measuring the observed frequency (f.sub.o) of the received acoustic signal (S); calculating (1140) on basis of said observed frequency (f.sub.o) and said emitted frequency (f.sub.e), a second velocity vector (v12.sub.t1, v12.sub.t2) which defines the velocity of the first node in relation to the second node; calculating (1150), an angle (t.sub.1,t.sub.2), wherein the angle (t.sub.1,t.sub.2) is the angle between the first velocity vector (v1.sub.t1,v1.sub.t2) and the second velocity vector (v12.sub.t1, v12.sub.t2); and determining (1160), based on the angle (t.sub.1,t.sub.2), the first velocity vector (vl.sub.t1,v1.sub.t2), and the estimated position of the first node (p1.sub.t1,p1.sub.t2), a line of direction (Lt.sub.1, L.sub.t2), wherein the line of direction (Lt.sub.1,L.sub.t2) indicates the direction from the estimated position of the first node (p1,P.sub.t1,P.sub.t2) towards an estimated position of the second node (p.sub.2*); and based on the obtained measurements (1100) further: determining (1300), based on a first line of direction (L.sub.t1) and a second line of direction (L.sub.t2), an intersection point defining the estimated position of the second node (p.sub.2); determining (1400) a deviation vector (V.sub.d) which corresponds to the difference between the estimated position of the second node (p.sub.2) and the exact position of the second node (p.sub.2*), and determining (1500) the position deviation of the first node, wherein the position deviation of the first node corresponds to the deviation vector (V.sub.d).

11. The method (1000) according to claim 10, wherein the first node is an underwater vehicle.

12. The method (1000) according to claim 10, wherein the determining of the intersection point comprises use of a statistical model, which combines the lines of direction (L.sub.11, L.sub.t2) into an intersection point.

13. The method (1000) according to claim 10, wherein an acoustic signal (S), from the second node (N.sub.2) further comprises that the first node is the source of the acoustic signal (S), wherein the obtained acoustic signal (S) from the second node is a reflection of the acoustic signal (S) reflected by the second node.

14. The method (1000) according to claim 10, wherein the exact position of the second node (p.sub.2*) is obtained from the second node, or a third node, or from a database.

15. The method (1000) according to claim 10, wherein the position of the second node is fixed.

16. A positioning system (2000) for determining a position deviation for a first node (N.sub.1), wherein the positioning system (2000) comprises a positioning unit for estimating a position of the first node, means for receiving an acoustic signal and for measuring the frequency thereof, means for determining a first velocity vector of the first node, and processing means configured to execute the method according to claim 10.

17. An underwater vehicle comprising the positioning system (2000) according to claim 16.

18. The underwater vehicle according to claim 17, wherein the first node is an autonomous underwater vehicle.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0033] The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings.

[0034] FIGS. 1-2 schematically illustrates a first node in navigational communication with a second node according to some embodiments of the present disclosure.

[0035] FIG. 3 is a flowchart depicting embodiments of a method according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

[0036] The present disclosure will now be described with reference to the accompanying drawings, in which preferred example embodiments of the disclosure are shown. The disclosure may, however, be embodied in other forms and should not be construed as limited to the herein disclosed embodiments. The disclosed embodiments are provided to fully convey the scope of the disclosure to the skilled person.

[0037] The claimed method, and positioning system take place during a plurality of subsequent point in times t.sub.1, t.sub.2, t.sub.n later shown in FIG. 2. However, for ease of understanding the basics of the application, FIG. 1 aim to illustrate the basic concept of the method, and the positioning system and show what is happening during a first point in time t.sub.1.

[0038] FIG. 1 shows, for a first point in time t.sub.1, a first node N.sub.1 located in a first position p.sub.t1 during said first point in time t.sub.1. The first node N.sub.1 is having a first velocity vector v1.sub.t1 which represents the momentary rate of change of the distance travelled by said first node N.sub.1. The magnitude of the first velocity vector v1.sub.t1 gives the speed of the first node N.sub.1 while the vector direction gives the direction of the first node N.sub.1.

[0039] FIG. 1 also shows, for the same first point in time t.sub.1, a second node N.sub.2 located in a second position p.sub.2*, wherein the position of the second node p.sub.2* is the exact position of the second node N.sub.2, i.e., not an estimated position.

[0040] Shown is an acoustic signal S receivable by the first node N.sub.1, and based on said signal S and the use of Doppler shift (more about the use of Doppler shift in relation to FIG. 3, which discloses the method in detail), a second velocity vector v12.sub.t1 can be determined. The second velocity vector v12.sub.t1 defines the relative velocity of the first node N.sub.1 in relation to the second node N.sub.2.

[0041] On basis of the first velocity vector v1t.sub.1, and the second velocity vector v12.sub.t1, an angle .sub.t1 is calculated (i.e., the angle between the first velocity vector and the second velocity vector). Further, on basis on said an angle .sub.t1 and said first velocity vector v1.sub.t1 a line of direction Lt.sub.1, wherein the line of direction L.sub.t1 indicates the direction from the estimated position of the first node p.sub.t1 towards an estimated position of the second node p.sub.2.

[0042] In relation to FIGS. 2 and 3, it will be shown how the use of a plurality of lines of direction Lt.sub.1, Lt.sub.2, L.sub.tn is used to determine an intersection point which is used to determine the estimated position of the second node p.sub.2, and further to determine the position deviation between the estimated position of the second node (p.sub.2) and the exact position of the second node (p.sub.2*). Said position deviation, corresponds to the position deviation of the first node N.sub.1, i.e., the difference between the estimated position of the first node p.sub.t1 and the actual position of the first node p.sub.t1*.

[0043] FIG. 2 shows an extended view compared to the view shown in relation to FIG. 1. FIG. 2 further shows the first node N.sub.1 located at three different positions, p1.sub.t1 p1.sub.t2 p1.sub.tn, at three different point in times, t.sub.1, t.sub.2, t.sub.n, and the figure shows how each line of direction, Lt.sub.1, Lt.sub.2, Lin, together can indicate the estimated position of the second node.

[0044] As illustrated in relation to the figure, the lines of direction, Lt.sub.1, Lt.sub.2, L.sub.tn, constitute an intersection point defining the estimated position of the second node p.sub.2. On basis on said estimated position of the second node p.sub.2, a deviation vector V.sub.d (not shown) which corresponds to the difference between the estimated position of the second node p.sub.2, and the exact position of the second node p.sub.2* can be determined. Further, the deviation vector, V.sub.d also corresponds to the position deviation of the first node.

[0045] FIG. 2 shows an n'th position p.sub.tn of the first node in an n'th point in time t.sub.n. The n'th position of the first node aims to illustrate that the method is an ongoing procedure which for a plurality of point in times during the performing of said method.

[0046] Examples of embodiments of a method 1000 for determining a position deviation of a first node N.sub.1 between an estimated position p1 and an actual position of the first node p1*, will now be described with reference to the flowchart depicted in FIG. 3.

[0047] FIG. 3 is an illustrated example of steps or operations, which may be taken by the method 1000. The first aspect of this disclosure shows a method 1000 for determining a position deviation of a first node N.sub.1 between an estimated position p.sub.t1 and an actual position of the first node p.sub.t1*. The first node N.sub.1 is located in a mass of water. The method comprises the following operations:

[0048] Obtaining input data 1110, at a first position p.sub.t1 of the first node in a first point in time t.sub.1, and at a second position p.sub.t2 of the first node in a second point in time t.sub.2. The second position of the first node p1.sub.t2 is a different position than the first position of the first node p1.sub.t1, and the second point in time t2 follows the first point in time t.sub.1. The input data comprises, an estimated position of the first node p1.sub.t1, p1.sub.t2, and a first velocity vector v1.sub.t1, v1.sub.t2 of the first node N.sub.1,

[0049] Obtaining 1120 the exact position of the second node p.sub.2*. A preferred way of obtaining the exact position of the second node p.sub.2* is, from the second node N.sub.2, and by use of acoustic underwater communication. This communication is not illustrated in the figure.

[0050] Obtaining 1125 the emitted frequency fe of an acoustic signal. A preferred way of obtaining the emitted frequency fe of an acoustic signal is, from the second node N.sub.2, and by use of acoustic underwater communication. This communication is not illustrated in the figure.

[0051] Receiving 1130 an acoustic signal S, from a second node N.sub.2 and measuring the observed frequency fo of the received acoustic signal S.

[0052] Calculating 1140 on basis of on basis of said observed frequency f.sub.o and said emitted frequency f.sub.e, a second velocity vector v12.sub.t1, v12.sub.t2 which defines the velocity of the first node in relation to the second node. The calculation of second velocity vector v12.sub.t1, v12.sub.t2 is based the on relationship between observed frequency fo and the emitted frequency fe of the acoustic signal S. In other words, the calculation of the second velocity vector v12.sub.t1, v12.sub.t2 is based on Doppler shift, sometimes referred to as the Doppler effect. The observant reader would recognize that it takes a period of time, not merely a momentary point in time, to obtain the measurements of the Doppler shift, and thereby the second velocity vector v12. The explicit calculation of the second velocity vector v12 is not within the scope of this application. In this application, the second velocity vector v12 is determined at different point in times, t.sub.1, t.sub.2, t.sub.n, however the calculations and measurements in order determining the Doppler shift is performed over a period of time.

[0053] Calculating 1150, an angle .sub.t1, .sub.t2, wherein the angle .sub.t1, .sub.t2 is the angle between the first velocity vector v1 and the second velocity vector v12.

[0054] Determining 1160, based on the angle .sub.t1, .sub.t2, the first velocity vector v1.sub.t1, v1t.sub.2, and the estimated position of the first node p1.sub.t1, p1.sub.t2, a line of direction Lt.sub.1, Lt.sub.2, wherein the line of direction Lt.sub.1, L.sub.t2 indicates the direction from the estimated position of the first node p1,Pt.sub.1,P.sub.t2 towards an estimated position of the second node p.sub.2*.

[0055] Determining 1300, based on a first line of direction L.sub.t1 and a second line of direction Lt.sub.2, an intersection point defining the estimated position of the second node p.sub.2.

[0056] Determining 1400 a deviation vector V.sub.d which corresponds to the difference between the estimated position of the second node p.sub.2, and the exact position of the second node p.sub.2*.

[0057] Determining 1500 the position deviation of the first node, wherein the position deviation of the first node corresponds to the deviation vector V.sub.d.

[0058] In some embodiments, the determining of the intersection point comprises use of a statistical model, which combines the lines of direction Lt.sub.1, L.sub.t2 into an intersection point.

[0059] In some embodiments, an acoustic signal S, from the second node N.sub.2, further comprises that the first node is the source of the acoustic signal S, wherein the obtained acoustic signal S from the second node is a reflection of the acoustic signal S reflected by the second node.

[0060] In some embodiments, the exact position of the second node p.sub.2* is obtained from the second node, a third node, and/or from a database.

[0061] In some embodiments, the position of the second node is fixed.

[0062] The second aspect of this disclosure shows a positioning system configured to perform the first aspect (as disclosed hereinabove) for determining a position deviation for a first node N.sub.1, wherein the positioning system 2000 comprises a positioning unit for estimating the position of the first node, means for receiving an acoustic signal and for measuring the frequency thereof, means for determining a first velocity vector of the first node, and processing means, configured to execute the method according to any of the first aspect. The processing means is thus configured to obtain the data used in the method disclosed hereinabove, and to perform the calculations that are part of the method in order to determine the position deviation of the first node.

[0063] The third aspect of this disclosure shows an underwater vehicle, characterized in that it comprises a positioning system according to the second aspect as disclosed hereinabove.

[0064] In some embodiments, the first node is an autonomous underwater vehicle.

[0065] The person skilled in the art realizes that the present disclosure is not limited to the preferred embodiments described above. The person skilled in the art further realizes that modifications and variations are possible within the scope of the appended claims. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims.