Workshop proceeding - final.pdf - Faculty of Information and ...

10]: The transitions of target locations (defined by range and apparent Doppler) are governed by the
ambiguity number, i.e., mode variable, while the ambiguity number transitions are state-dependent.
Exploiting the admissible transitions of target locations and ambiguity number, we have proposed a
dynamic programming (DP) based method for joint maximum a posteriori (MAP) estimation of
target’s trajectory in the ambiguous range-Doppler maps and the corresponding ambiguity number
sequence. The proposed method is investigated under both known and unknown nuisance parameters
(target power and noise variance). The detection and tracking performances of the proposed algorithm
are studied with respect to different system settings. Moreover, the effect of the prior uncertainty of
the nuisance parameters on the detection and tracking performance is also investigated.
2. Signal processing model for low PRF surveillance radars
The physical scenario considered here is shown in Fig.1. A low PRF surveillance radar is used for
monitoring a given area with an electronically scanned antenna. The surveillance area is divided into
small angular regions, visited by the antenna at a constant revisit intervalT R
. For many long range
targets, passing from one elevation beam to another during several scans happens infrequently due to
the geometric constraints; however, crossing azimuth beams happens much more frequently.
Therefore, each angular region is composed of a single elevation and N a azimuthal beam-pointing
positions. The azimuthal beamwidth is Δ
a
. The pulse repetition time is T p
and the number of train
pulses coherently processed is Nd
. At each visit, say, the kth
, the radar provides a multi-dimensional
data map (with four dimensions of range, azimuth, elevation and Doppler), each pixel is the reflected
power out of a signal processing unit, e.g., discrete Fourier transform(DFT), of a surveillance radar.
Fig.1. Radar surveillance zone illustration
The conventional signal processing method for surveillance radar first thresholds the data maps to
extract target plots (range, azimuth, elevation and Doppler locations), and then performs tracking
based on these plots. For targets of high SNR, this method works well, however, for targets of relative
low SNR, such as stealthy military aircraft and cruise missiles, thresholding throws away potentially
useful information, causing missing detections. Besides, since we are concerned with low PRF radar,
the Doppler plots are ambiguous; it’s hard to resolve the Doppler ambiguity under low SNR in the
framework of conventional methods. The TBD algorithms use several successive unthresholded data
maps to jointly determine the presence of a target and its trajectory (if present). TBD methods exploit
all the useful information among several scans and are especially preferred when encountering low
SNR targets. Besides, Doppler ambiguity is also implicitly resolved in the framework of TBD methods.
To simplify the exposition, we assume that the azimuth and elevation information are obtained
through antenna processing. The only relevant coordinates are range and Doppler. In an actual
implementation, one can choose to process azimuth-elevation and range-Doppler maps separately.
11