Apparatus and methods are disclosed for detecting anomalies in microwave penetrable material that may be used for locating plastic mines or pipes underneath the ground. A transmitter is positioned at a plurality of different positions above the ground. A microwave signal is transmitted that is stepped over a plurality of frequencies. At each position, a plurality of reflections are received corresponding to each of the plurality of frequencies that were transmitted. A complex target vector may be produced at each position that contains complex values corresponding to magnitude, phase, and time delay for each of the plurality of reflections received at that location. A complex reference data vector may be produced, either based on predetermined values or based on data from the received plurality of reflections. A comparison is made between the complex target vector and the complex reference data vector to produce a channel vector. In one embodiment, an operator may be applied to the channel vector such as a complex filter matrix or to add a complex conjugate. A response signal is produced and anomalies are detected by variations in the response signal with respect to the plurality of positions.
A microwave-enhanced infrared thermography technique for detecting buried objects exploits varying phase shifts experienced by different-frequency microwave signals reflected from objects back toward the surface, the phase shifts resulting in different interference patterns and therefore different temperature distribution patterns near the surface. Respective infrared images of an area are captured prior to microwave heating, after a first heating with a first frequency, and after heating with a second frequency different from the first. Pairs of the images are subtracted to form temperature rise images showing patterns of temperature rise in the two cycles, and the temperature rise images are subtracted to form a difference image which is analyzed to identify characteristics indicating the presence of buried objects.
A method determines a complex reflection impulse response of a fiber Bragg grating. The method includes providing a measured amplitude of a complex reflection spectrum of the fiber Bragg grating. The method further includes providing an estimated phase term of the complex reflection spectrum. The method further includes multiplying the measured amplitude and the estimated phase term to generate an estimated complex reflection spectrum. The method further includes calculating an inverse Fourier transform of the estimated complex reflection spectrum, wherein the inverse Fourier transform is a function of time. The method further includes calculating an estimated complex reflection impulse response by applying at least one constraint to the inverse Fourier transform of the estimated complex reflection spectrum.
A threshold level is set in advance that has varied signal level values of reflected waves for which an object detection signal is to be generated, where the values vary in response to a distance to the object. In regard to discriminating a phase difference of respective waves reflected from an object and the signal level of the waves reflected from that object, and obtaining two distances to an object due to fold-over error when using only the phase difference, the present invention uses the signal level of the reflected waves to judge which distance is the correct distance.
An apparatus characterizes at least one fiber Bragg grating. The apparatus includes a laser pulse source, an optical spectrum analyzer, and multiple optical paths. A first optical path includes a pulse stretcher and an attenuator. A second optical path optically coupled to the first optical path includes a mirror. A third optical path optically coupled to the first optical path includes a first fiber Bragg grating. A fourth optical path is optically coupled to the second optical path, the third optical path, and the optical spectrum analyzer. A fifth optical path optically coupled to the laser pulse source and the optical spectrum analyzer includes a delay line.
An acoustic measurement installation including acoustic measurement instrumentation, in particular an acoustic measurement antenna fitted with at least one microphone; a positioning system for positioning the antenna by ultrasound and including at least one ultrasound emitter mounted on the antenna at a known distance relative to the microphone and an ultrasound receiver base for receiving the signals emitted by each emitter and adapted to determine the position of each emitter; and a control unit for controlling the positioning system for positioning the antenna and the acoustic measurement instrumentation. The control system is adapted during a first stage to cause each emitter to emit in succession in order to determine the position of the antenna, and during a second stage to cause the microphones to perform acquisition in order to implement acoustic measurement using the measurement instrumentation.
