DESC:TECHNICAL FIELD

The present invention relates to the design of automatic track initiation procedure used in the multi-target tracking scheme developed for 2D/3D radar on static/moving platform.

BACKGROUND OF THE INVENTION

Modern surveillance radars equipped with state-of-the-art radar data processing unit is expected to aid the radar operator in decision making on potential air targets. Target tracks are initiated automatically, and the tracks are maintained with unique identity in modern radar data processing (RDP) system. To improve the delay from detection to track report generation the implementation of track while scan (TWS) tracker has been done on sector basis where a sector consists of one in n (user changeable) of the three sixty-degree search area. The plots received corresponding to each sector is stored in tracker data base. The data is stored in cyclic buffer.
Conventionally, radar tracking systems and particularly automatic track initiation schemes using measurements obtained from a stationary radar platform have been disclosed. In the conventional procedures, measurements which are not associated with existing tracks are used for track initiation. The computational complexity of the algorithms discussed in conventional systems and methods will be exponential in nature with number of measurement frames used.
For example, in US3699573 titled “System for automatic initiation of target tracking in track-while-scan radar” describes a technique which identifies the measurements not associated with any of the existing tracks and uses these data for initiating new tracks. Around each unassociated measurement a track initiation gate is formed. In the subsequent scan if unassociated measurement falls in this gate area and if it continues for a specific number of times, then a new track is initiated.
Further, in US4005415 titled “Automated radar data processing system” describes an automated radar data processing system that performs with three-dimensional data, optimizes the target video, automatically detects, classifies and tracks targets, and provides target data to the users. Operator efforts are then directed toward the monitoring and supervision of the automated operations of the radar. Any unassociated measurements are designated as tentative track. A tentative track is updated to confirmed track with subsequent updating.
Also, in US7508336 titled “Single scan track initiation for radars having rotating, electronically scanned antennas” describes single scan track initiation for radars having rotating electronically scanned antennas. The main outcome is an initial track having sufficient validity so that initiation process becomes fast. The possible number of false tracks generation is a drawback of fast initiation with single scan of measurement.
Further, in US3460137 titled “Track Initiation System” describes a technique wherein range information is used for initial identification and elevation information for finer identification.
Conventionally, multiple hypotheses tracking (MHT) based techniques for track initiation based on hypotheses generation using positional information have been disclosed. Further, various other techniques available for track initiation are multiple-tree based approach, single point and two-point difference method and Hough transform method. The conventional multiple tree algorithms are based on k-d tree approach and allows pruning redundant trees effectively. However, the technique gets affected with high density of measurement and computational advantage may not be possible to extract.
In another conventional single point initializing technique, tracks are initiated with velocity component as zero. Further, in a conventional two-point difference approach velocity is to be known. These conventional approaches do not consider the computation complexity. By using multiple frames of measurements, the approach becomes infeasible for practical applications. A conventional Hough transform (HT) based approach is restrictive to straight line targets and the modified HT based approach is efficient in clutter environment but performance degrades if target is maneuvering. The accuracy and reliability of all these approaches depends on number of scans used. The disadvantage of these techniques is the exponential complexity of computational needs.
In yet another conventional technique, track initiation using IMM-PDA and IPDA-IMM are disclosed. The IMM-PDA consists of parallel bank of PDA filters with IMM framework. One PDA filter for each trajectory model and PDA filter for no-target model. This approach is suitable for maneuvering target model. For non-maneuvering case IPDA approach is preferred one.
There is still a need for effective multi-target tracking technique for a static/moving platform.

Summary of the Invention

An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below.
Accordingly, in one aspect of the present invention relates to a method for automatic multi-target track initiation from moving platform 400 using backward sequential technique, the method comprising: selecting measurements falling inside an auto track initiation zone and having acceptable attributes as seed measurements 410, associating to a branch of a potential track, measurements from previous scan falling inside acceptance region and having attributes matching to that of seed measurement 420, splitting branch of the potential track in case of more than one measurement inside acceptance region having attributes matching to that of seed measurement 430, deleting branch of the potential track having number of associated measurements less than threshold n_t which is computed under assumption that number of target detection across scans is binomially distributed with P_D probability of detection 440, selecting one branch of the potential track per seed measurement based on least residual of first order polynomial fit 450 and validating the potential track by testing speed and acceleration calculated using the first order polynomial fit against acceptable speed and acceleration interval for track initiation 460.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.
Brief description of the drawings
The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:
Figure 1 illustrates a moving radar platform scenario according to the implementation of proposed multi-track initiation technique method of the present disclosure.
Figure 2 illustrates an acceptance region for a seed measurement according to the implementation of the proposed multi-track initiation technique method of the present disclosure.
Figure 3 illustrates generation of potential tracks scheme for a given seed measurement according to the implementation of the proposed multi-track initiation technique method of the present disclosure.
Figure 4 illustrates a method for automatic multi-target track initiation from moving platform using backward sequential technique according to the implementation of the proposed multi-track initiation technique method of the present disclosure.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.
Detailed description of the invention
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.
By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic is intended to provide.
Figs. 1 through 4, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way that would limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged communications system. The terms used to describe various embodiments are exemplary. It should be understood that these are provided to merely aid the understanding of the description, and that their use and definitions, in no way limit the scope of the invention. Terms first, second, and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise. A set is defined as a non-empty set including at least one element.
In the present invention, a method for multi-track initiation using backward sequential technique which involves the processing of sequence of measurements received during consecutive radar scans in backward direction, is disclosed.
A track initiation scheme for multi target tracking considering scenarios having clutter, false alarms with less than unity probability of detection is disclosed. In the embodiment, other target related attributes like range spread, azimuth spread, Doppler etc. may be used. The method disclosed includes radar platform motion compensation for track initiation which is compulsory in case of radar on moving platform.
The object of the present invention is to provide an automatic track initiation scheme for 2D/3D radar on static/moving platform having less than unity probability of detection. The modern radar measurement includes spatial location in term of range, azimuth and elevation along with attributes like range spread, azimuth spread, Doppler etc. In an embodiment, a track initiation method which also use target attribute. The method includes the radar platform motion compensation for radar on moving platform for example ship borne radar. The number of potential tracks generated in the disclosed method does not increase exponentially by eliminating potential tracks having number of associated measurements less than a threshold calculated based probability of target detection in a scan and total number of scans processed till that instant.
In an exemplary embodiment, the multi-track initiation method uses the backward sequential technique. According to step 1, the method includes letting a current measurement frame that to be processed for track initiation as a measurement frame.
This is denoted as . Then, measurements from the measurement frame falling inside an auto initiation zone to be selected. These measurements have attributes like range spread, azimuth spread and Doppler (if available) in acceptable interval. Then the said measurements may be considered as a seed measurement. In the step 1, let be a set of seed measurement
In an exemplary embodiment, according to step 2, for every seed measurement with a time stamp from measurement frame – an acceptance set of measurements with a time stamp from measurement frame is set up as follows.
Let and be denoted as radar platform location at time and at time . Now, and is to be subtracted from and respectively to bring both measurement to common co-ordinate system. Then acceptance set of measurements for seed measurement is given by,


(1)
where,
is change in radar platform location at time with respect to that at time .
If, and has similar attribute, i.e. variation in attributes are within in acceptable interval, otherwise .
In an exemplary embodiment, according to step 2, region obtained accounts for minimum and maximum motion of the target, characterized by a minimum and a maximum speed, denoted and respectively and similarity in attribute like range spread, azimuth spread and Doppler (if available).
In an exemplary embodiment, according to step 2, for every measurement from falling into region obtained a branch of the potential track is set up. If no measurement from second scan is found in the acceptance region of seed measurement , then the seed measurement may be dropped.
In an exemplary embodiment, according to step 3, for every branch of the potential track in , consisting of at least two measurements – an acceptance set of measurement with time stamp from measurement frame is set up.
Let with time stamp be seed measurement and with time stamp be latest associated measurements of the potential track.
Using a straight-line extrapolation (first order polynomial) to the time , distance vector may be defined.

(2)
where
(3)
is extrapolated measurement at time . Substituting , we get

(4)

is change in radar platform location at time with respect to that at and is change in radar platform location at time with respect to that at .
Assuming the measurement errors to be independent, normal and zero-mean, the acceptance set for measurements is given by,
(5)
, and are measurement error co-variance matrix of , and .
. If measurement and has similar attribute, i.e. variation in attributes are within in acceptable interval, otherwise .
The threshold for given “gate probability” is such that

is chi-square distribution with (dimension of measurement vector) degrees of freedom.
In an exemplary embodiment, according to step 3, if more than one measurement is found in the acceptance region for a branch of the potential track, then this branch of the potential track is split.
In an exemplary embodiment, according to step 4, assume that target detection is independent across radar scan with probability of detection in each scan. This implies the number of target detection across radar scan is binomial distributed with probability of success in each scan.
In an exemplary embodiment, according to step 4, For given confidence threshold , probability of detection and = number of scans processed, smallest is to be calculated such that,
(6)
is the cumulative distribution function of binomial distribution.
According to the step 4, drop the potential track in if number of associated measurements is (7)
In an exemplary embodiment, according to the method the step 3 and step 4 described are to be repeated for .
In an exemplary embodiment, according to step 5, if there are more than one branch of the potential track with same seed measurement, then one having least residual for the first order polynomial fit may be selected.
In an exemplary embodiment, according to step 6, the final track selection is done by testing calculated speed and acceleration using the first order polynomial fit against acceptable speed and acceleration interval for track initiation.
Figure 1 illustrates the moving radar platform scenario according to the implementation of the proposed multi-track initiation technique method.
In one embodiment, depicted in Figure 1, 104 is measurement vector in Cartesian co-ordinate system of a target 103 with respect to radar platform location 101 having radar coverage area 102 as origin of co-ordinate system at time instant . 108 is measurement vector in Cartesian co-ordinate system of the same target 7 with respect to radar platform location 105 having radar coverage area 106 as origin of co-ordinate system at time instant . 109 indicate is change in radar platform location at time with respect to radar platform location at time .
Figure 2 illustrates acceptance region for seed according to the implementation of the proposed multi-track initiation technique method.
In one embodiment, depicted in Figure 2, an acceptance region of seed measurement 201 is area outside minimum motion region 202 which accounts for minimum target speed and inside maximum motion region 203 which accounts for maximum target speed .
Figure 3 illustrates generation of branches of the potential track scheme for a given seed measurement according to the implementation of the proposed multi-track initiation technique method.
In one embodiment, depicted in Figure 3, for a given seed measurement 301 from the measurement frame 302, there is one measurement fall inside acceptance region 303 from the measurement frame 304. Using seed measurement and measurement from acceptance region 305 is set at first order extrapolated location in measurement frame 306. Since there are two measurement fall inside acceptance region 305, this branch of the potential track gets spilt into two for each measurement. Again, using seed measurement and latest appended measurement from acceptance region 307, 308 for both branches of the potential track are set at first order extrapolated location in measurement frame 309. There is one measurement fall inside acceptance region 307, lower branch of the potential track gets appended with this measurement. Since there is no measurement inside acceptance region 308, upper branch of the potential track gets deleted in step 4 of disclosed scheme. Using seed measurement and latest appended measurement from acceptance region 310 for only surviving branch of the potential track is set at first order extrapolated location in measurement frame 311. This again gets appended with a measurement falling inside acceptance region 310.

Figure 4 illustrates a method for automatic multi-target track initiation from moving platform using backward sequential technique according to the implementation of the proposed multi-track initiation technique method of the present disclosure.
The figure illustrates a method for automatic multi-target track initiation from moving platform using backward sequential technique. In one embodiment, the present invention relates to a method for automatic multi-target track initiation from moving platform 400 using backward sequential technique, the method comprising: selecting measurements falling inside an auto track initiation zone and having acceptable attributes as seed measurements 410, associating to a branch of a potential track, measurements from previous scan falling inside acceptance region and having attributes matching to that of seed measurement 420, splitting branch of the potential track in case of more than one measurement falling inside acceptance region having attributes matching to that of seed measurement 430, deleting branch of the potential track having number of associated measurements less than threshold n_t which is computed under assumption that number of target detection across scans is binomially distributed with P_D probability of detection 440, selecting one branch of the potential track per seed measurement based on least residual of first order polynomial fit 450 and validating the potential track by testing speed and acceleration calculated using the first order polynomial fit against acceptable speed and acceleration interval for track initiation.
In one embodiment, the method further comprises associating to the seed measurement, measurements from immediate previous scan falling inside acceptance region which accounts for minimum and maximum motion of the target and having attributes matching to that of seed measurement.
In another embodiment, the method further comprises associating to the potential track, measurements from further previous scan falling inside acceptance region centered at straight line extrapolated (first order polynomial fit) location calculated using seed and latest associated measurement of a potential track and having attributes matching to that of seed measurement.
In an exemplary embodiment, wherein if no measurement from immediate previous scan is found in the acceptance region around the seed measurement, then the seed measurement is dropped. The attributes of the targets may be range spread, azimuth spread, Doppler, etc. The change in the radar platform location is compensated for radar on moving platform using precise platform location provided by GPS and/or heading and speed of platform provided by gyroscope.
In an exemplary embodiment, the allowed variation in range spread for measurement attribute similarity can be fixed by a user tunable parameter. Further, allowed variation in range spread for measurement attribute similarity may be varied depending on measured target range and calculated target speed.
In an exemplary embodiment, the allowed variation in azimuth spread for measurement attribute similarity can be fixed by a user tunable parameter. Further, the allowed variation in azimuth spread for measurement attribute similarity may be varied depending on measured target range and calculated target heading.
In an exemplary embodiment, the allowed variation in Doppler for measurement attribute similarity can be fixed by a user tunable parameter. Further, the allowed variation in Doppler for measurement attribute similarity may be varied depending on calculated target radial speed.
In an exemplary embodiment, the multi-track initiation technique is capable to set the minimum and maximum velocity of target track initiation.
In an exemplary embodiment, the multi-track initiation technique is capable to set the minimum and maximum acceleration of target track initiation. The minimum and maximum velocity and acceleration for target track initiation is user tunable parameter.
In an exemplary embodiment, the multi-track initiation technique is capable to set number scans to be processed for target track initiation. The number scans to be processed for target track initiation is a user tunable parameter.
In an exemplary embodiment, the gate size for measurement association can be controlled by setting gate probability .
In an exemplary embodiment, the minimum number of detections for target track initiation can be fixed by a user tunable parameter. Further, the minimum number of detections for target track initiation can be varying depending on user specified probability of detection and confidence threshold .
In an exemplary embodiment, the invention describes an automatic multi-track initiation for 2D/3D radar on static/moving platform. In various embodiment herein, the design of unique technique in which number of potential tracks generated in the disclosed scheme does not increase exponentially. Further, it also uses target attributes like range spread, azimuth spread, Doppler etc. In various embodiment disclosed herein, the method includes the radar platform motion compensation for radar on moving platform.
Those skilled in this technology can make various alterations and modifications without departing from the scope and spirit of the invention. Therefore, the scope of the invention shall be defined and protected by the following claims and their equivalents.
FIGS. 1-4 are merely representational and are not drawn to scale. Certain portions thereof may be exaggerated, while others may be minimized. FIGS. 1-4 illustrate various embodiments of the invention that can be understood and appropriately carried out by those of ordinary skill in the art.
In the foregoing detailed description of embodiments of the invention, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description of embodiments of the invention, with each claim standing on its own as a separate embodiment.
It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively.
,CLAIMS:

1. A method for automatic multi-target track initiation from moving platform 400 using backward sequential technique, the method comprising:
selecting measurements falling inside an auto track initiation zone and having acceptable attributes as seed measurements 410;
associating to a branch of a potential track, measurements from previous scan falling inside acceptance region and having attributes matching to that of seed measurement 420;
splitting branch of the potential track in case of more than one measurement inside acceptance region having attributes matching to that of seed measurement 430;
deleting branch of the potential track having number of associated measurements less than threshold n_t which is computed under assumption that number of target detection across scans is binomially distributed with P_D probability of detection 440;
selecting one branch of the potential track per seed measurement based on least residual of first order polynomial fit 450; and
validating the potential track by testing speed and acceleration calculated using the first order polynomial fit against acceptable speed and acceleration interval for track initiation 460.

2. The method as claimed in claim 1, comprises associating to the seed measurement, measurements from immediate previous scan falling inside acceptance region which accounts for minimum and maximum motion of the target and having attributes matching to that of seed measurement.
3. The method as claimed in claim 1, further comprises associating to the potential track, measurements from further previous scan falling inside acceptance region centered at straight line extrapolated (first order polynomial fit) location calculated using seed and latest associated measurement of a potential track and having attributes matching to that of seed measurement.

4. The method as claimed in claim 1, wherein if no measurement from immediate previous scan is found in the acceptance region around the seed measurement, then the seed measurement is dropped.

5. The method as claimed in claim 1, wherein the attributes of the targets may be range spread, azimuth spread, Doppler, etc.

6. The method as claimed in claim 1, wherein the change in the radar platform location is compensated for radar on moving platform using precise platform location provided by GPS and/or heading and speed of platform provided by gyroscope.

7. The method as claimed in claim 1, wherein an allowed variation in range spread for measurement attribute similarity is fixed or varied depending on measured target range and calculated target speed.

8. The method as claimed in claim 1, wherein the allowed variation in azimuth spread for measurement attribute similarity is fixed or varied depending on measured target range and calculated target heading.

9. The method as claimed in claim 1, wherein the allowed variation in Doppler for measurement attribute similarity is fixed or varied depending on calculated target radial speed.

10. The method as claimed in claim 1, wherein the minimum and maximum velocity and acceleration for target track initiation is user tunable parameter.

11. The method as claimed in claim 1, wherein the number scans to be processed for target track initiation is user tunable parameter.

12. The method as claimed in claim 1, wherein the gate size for measurement association is controlled by setting gate probability P_G.

13. The method as claimed in claim 1, wherein the minimum number of detections for target track initiation is fixed or varied depending on probability of detection P_D and confidence threshold C_t.