Aerospace and Electronic Systems Magazine March 2018 - 26

Target Monitoring Using Small-Aperture Compact High-Frequency Surface Wave Radar

Figure 8.

Antenna arrangement of the three-channel and eight-channel HF radar.

Let Xk be the coordinate set of all targets at the k frame R-D
image:

{

T

X k = i, j 

}

(5)

where 1 ≤ i = r(k) ≤ M, 1 ≤ j = v(k) ≤ N, and 1 ≤ k ≤ K; here, k is
the frame number in each batch integration, detection, and tracking
process. Let Zk(i, j) be the echo intensity set of all targets at the k
frame R-D image:
 A + wk ( i, j ) when targets exist in the cell  ( i, j )
Z k ( i, j ) =  k
(6)
when no targets exist in the cell  ( i, j )
 wk ( i, j )

where Ak is the target echo intensity and wk (i, j) is the noise echo
intensity. The detailed process is as follows:
1. Track initialization-x1 = [i, j ]' ∈ X1, I ( x1 ) = z1 ( i, j ), and
Ψ1 ( x1 ) = 0. Here, I ( x k ) is the value function at the k frame.
Ψ k ( x k ) is the corresponding xk−1 when I ( x k −1 ) takes the maximum. Ψ k ( x k ) = 0 when k = 1.
2. Iteration process-When 2 ≤ k ≤ K, for all x k = i, j ' ∈ X'k,
I ( x k ) = max I ( x k −1 ) + zk ( i , j )

(7)

( xk ) = argxmax  I ( x k −1 )

(8)

x k −1

Ψk

k

where X kT is the searching scope in the dimension of range and velocity according to the motion state of the target. The target can
only locate within the several cells nearest the current position.
3. Track termination-{xˆ K } = {x K : I ( x K ) > VT }, where proper
threshold VT was selected to find all possible targets. For each xˆ k,
xˆ k = Ψ k +1 ( xˆ k +1 )

(9)

where k = k + 1. Then, the preliminary target tracking results can
be obtained, and these are the target traces set without azimuth in
the R-D coordinate {xˆ 1 , xˆ 2 ,, xˆ k }.

STEP 3: DOA ESTIMATION
When the target track is detected, only the radial velocity and range
can be obtained. The azimuth of each point in the track can be
estimated using the beam-forming method or the super-resolution
direction estimation method, based on its corresponding multiplechannel R-D data.
26

Figure 9.

Target trace without azimuth in the R-D-T coordinate.

METHOD VALIDATION WITH MEASUREMENT DATA
DESCRIPTION OF HF RADAR
The HFSWR system is located on the northern shore of Weihai,
China. The radar system can operate between 3 and 15 MHz. The
transmitting antenna adopts a log-periodic pattern. The receiving
antenna array of the radar system consists of eight elements. The
space between each element is 15 m. Data from only the first three
channels were chosen to simulate a compact HFSWR. Thus, the
aperture size of the three-channel array is 30 m, whereas that of
the full eight-channel array is 105 m. The antenna arrangements of
the three-channel and eight-channel arrays are shown in Figure 8.
The measured HF data used here were acquired on 31 October
2011. The working frequency was 4.7 MHz. The coherent integration time ΔT of the R-D image was 300 s. One hour of HF data
was selected for analysis, and synchronous AIS data were used
as in situ data to verify the detection result. Figure 9 shows the
target tracking result without azimuth at the stage of integration,
detection, and tracking in the R-D-T coordinates. Figure 10 shows
the final tracking result of the three-channel and eight-channel arrays in the latitude-longitude coordinate. The traces detected using
three channels are marked by red circles, and those using eight
channels are marked by blue circles.

VALIDATION WITH SYNCHRONOUS AIS
In the present study, AIS data were used to verify the validity of the
proposed method. AIS can provide location and motion information in real time for a cooperating vessel. AIS operates in the VHF

IEEE A&E SYSTEMS MAGAZINE

MARCH 2018



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