This work examines, from a theoretical perspective, novel aspects of processing the frequency-modulated continuous wave (FMCW) radar returns from a fast quasicylindrical target moving along a relatively flat trajectory. There are various realworld scenarios in which such objects (as threats) approach victim vehicles. Pinpointing, in time and space, when a flattrajectory quasicylindrical object has penetrated a safety perimeter around an intended victim vehicle is important for activating just-in-time or pre-positioned countermeasures. With radar-enabled countermeasures, the resolution of the radar and its tracking algorithm are determinative of the power and indiscriminateness that the countermeasure needs to defeat a fast-flying threat in the vicinity of the “sacred” perimeter. A smaller location error and smaller timing error enable lowerpower, more precise, and less dangerous countermeasures to be deployed. In this work we examine a method that can potentially reduce the uncertainty in the target’s observed location to less than ten (and closer to five) centimeters at critical instants. With its conventional tracking having established an incoming missile’s flight path, a small FMCW radar can switch into a “lying-in-wait” mode for “end-zone” observation, in which a pre-designed resonant discrete-time filter can be shifted back and forth along the frequency spectrum to determine the instant at which the flying target has breached the safety perimeter. This paper discusses one way in which this can be accomplished, examines the theoretical underpinnings of the method, and makes a preliminary assessment of the uncertainty that can be expected. Simulation results are reported.
The objective is to identify the chemical composition of (isotropic and homogeneous) thin liquid and gel films on various surfaces by their infrared reflectance spectra. A bistatic optical sensing concept is proposed here in which a multi-wavelength laser source and a detector are physically displaced from each other. With the aid of the concept apparatus proposed, key optical variables can be measured in real time. The variables in question (substance thickness, refractive index, etc.) are those whose un-observability causes many types of monostatic sensor (in use today) to give ambiguous identifications. Knowledge of the aforementioned key optical variables would allow an adaptive signal-processing algorithm to make unambiguous identifications of the unknown chemicals by their infrared spectra, despite their variable presentations. The proposed bistatic sensor system consists of an optical transmitter and an optical receiver. The whole system can be mounted on a stable platform. Both the optical transmitter subsystem and the optical receiver subsystem contain auxiliary sensors to determine their relative spatial positions and orientations. For each subsystem, these auxiliary sensors include an orientation sensor, and rotational sensors for absolute angular position. A profilometer-and-machine-vision subsystem is also included. An important aspect of determining the necessary optical variables is an aperture that limits the interrogatory beams to a coherent pair, rejecting those resulting from successive multiple reflections. A set of equations is developed to characterize the propagation of a coherent pair of frequency-modulated thin beams through the system. It is also shown that frequency modulation can produce easily measurable beat frequencies for determination of sample thicknesses on the order of microns to millimeters. Also shown is how the apparatus’s polarization features allow it to measure the refractive index of any isotropic, homogeneous dielectric surface on which the unknown substance can sit. Concave, convex and flat supporting surfaces and menisci are discussed.
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