Principles of Modern Radar - Volume 2 1891121537

712 CHAPTER 16 Human Detection With Radar: Dismount DetectionFIGURE 16-1Illustration oftransmitted pulsedDoppler chirp signaland key parameterdefinitions.FrequencyBandwidth = γτf 0τ TimeAmplitudeτT 2T 3T ttˆ tˆ tˆhuman targets the principle of superposition is valid. Moreover, work by Van Dorp [51] hasshown that by (1) dividing the human body into just 12 parts, (2) modeling each part as apoint target, and (3) summing the responses, a mathematical model for the human responsethat matches remarkably well with measured spectrogram data can be produced. Thus, amathematical approximation to the human radar return may be written from (16.1) asK∑( ) ˆt − t d,is h (n,t) = a t,i rect e j[−2π f ct d,i +πγ(ˆt−t d,i ) 2 ](16.3)τi=1where K is the total number of parts into which the body is divided, and i is an indexreferring to each body part (1 ≤ i ≤ K ). Embedded within this equation are two factorsthat are directly impacted by human modeling: the time-varying range R i of each bodypart to the radar (in t d,i = 2R i /c), and RCS of each component (i.e., the factor σ in a t,i ).16.2.2 Human Kinematic ModelsResearchers have pursued a variety of approaches in modeling human kinematics, mostof which revolve around decomposing the human body into a finite number of parts andcomputing the time-varying range for each part using kinematic models. An alternativeapproach has been taken by R. G. Raj, who has pointed out that in many cases humanactivity occurs in real-time unconstrained environments, where the type of activity ormodel parameters are not known a priori, leading to a mismatch between the true activityand motion model used. Thus, Raj proposed directly modeling and classifying the timefrequencymotion curves using a Gaussian g-snake model [62, 63].Nevertheless, kinematic models have provided valuable insight and utility in the detectionand identification of dismounts and remain the most widely explored approachtoday. For example, He [64] recently proposed a modified version of the linear-rigidmodel developed by Zhang [65] in which the head and torso were modeled as a singlepoint scatterer, the arms as independent cylinders, and the legs as two interconnectedcylinders. The periodic arm motion was modeled as being that of a pendulum, while theleg motion was modeled by a combination of vibrations and rotations.