Intelligence, Surveillance, and Reconnaissance - Spawar

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INTELLIGENCE, SURVEILLANCE, AND RECONNAISSANCE
split-aperture adaptive beamforming process. The objective is to generate
signal clusters in bearing and frequency space. Tracking is accomplished
by association of clusters, in bearing and frequency space (narrowband)
or bearing only (broadband), over time (Figure 4). An – tracker is used
to associate the acoustic clusters to the magnetic track to form a contact
track [5].
Contact Classification
Contact tracks, generated by the acoustic and magnetic track association
process, include contact data structures that are the input to the classification
process. These data structures consist of the magnetic and acoustic
feature sets listed below.
1. Magnetic (MA): defines specific magnetic features such as magnetic
moment, depth, and magnetic score. Membership functions are used
to provide the scoring criteria.
2. Number of Blade Harmonics (NBH): defines a blade harmonic
structure and provides membership functions for evaluating the
number of blade harmonics.
3. Blade Harmonic Power (BHP): provides a membership function
for evaluating the range normalized average power in each blade
harmonic.
4. Non-Blade Power (NBP): provides a membership function for
evaluating the range normalized average power in each non-blade
narrow-band signal.
5. Contact Bearing Rate (CBR): provides a membership function for
evaluating the contact bearing rate.
6. Number of Signal Events (NSE): provides a membership function
for evaluating the number of associated signal events in each contact
track.
A discriminant score for each contact is calculated using these features
and associated membership functions [6]. The membership functions provide
estimates of the probability of existence of each of the features. The
contact discriminant scoring function is shown below in Eq. (2)
DS = DSMA + DSNBH + DSBHP + DSNBP + DSCBR + DSNSE (2)
where DS is the discriminant score (ranges from –1 to +1), DSMA is the
magnetic discriminant score, DSNBH is the number of blade harmonics
discriminant score, DSBHP is the blade harmonics power discriminant
score, DSNBP is the non-blade harmonics power discriminant score,
DSCBR is the contact bearing rate discriminant score, and DSNSE is the
number of signal events discriminant score.
Contact Scoring
The decision to transmit a contact report to the command center is based
on the contact score. The contact score is calculated and updated from
one processing interval to the next by using a discriminant function classifier.
The algorithm used by the classifier is given below in Eq. (3).
TS(i) = TS(i–1) + K[DS(i) –TS(i–1)] (3)
where TS is the target score (ranges from –1 to +1), K is the smoothing
constant (ranges from 0.2 to 0.8), and DS is the discriminant score (ranges
from –1 to +1). The target score is computed with a first-order recursion.
TIME
BEARING
FIGURE 4. Association of acoustic (blue)
and magnetic track (red) in time and
bearing.