An extended range sonar in which a projected carrier sound frequency is modulated by second and third lower sound frequencies and a train of alternate pulses of the second and third frequency modulated carrier frequency are projected at a fourth frequency switching rate. The echo signal is extracted from the total received signal by first abstracting the second and third frequency components of the envelope of the received signal; abstracting the fourth frequency component of the envelope of each of the second and third frequencies and combining the separate fourth frequencies components of the second and third frequencies to secure an echo signal indicating the presence of a discrete target.
A method of marking a pipeline location eliminates ambiguity in case there are leaks near the location of a marker. It employs a marker that emits two separate frequencies that are modulated by a third frequency lower than either of the other two. Detection of the marker on a pipeline pig is done by separating the two frequencies and demodulating the third. Then by determining the coincidence of all three for a predetermined number of consecutive cycles of the third frequency, the marker location will be positively identified.
A matched-phase noise filter includes an analog to digital converter (ADC) for receiving an analog composite, noise-dominated signal containing a signal of interest and producing a digital composite signal, an input/output port receiving the digital composite signal and providing a matched-phase signal, and a processor receiving the digital composite signal via the I/O port and generating the matched-phase signal. According to one aspect of the invention, the signal to noise ratio between the signal of interest and a noise component within the digital composite signal is increased by approximately an order of magnitude, based on an actual spectrum of the digital composite signal and an estimated spectrum of the noise component, and independent of the particular form of the signal of interest. A method of matched-phase noise filtering for improving the SNR of a noise dominated signal independent of the form of the signal is also described.
A dual frequency, synthetic aperture, sonar system includes a transmitter r projecting insonifying pings alternatively at first and second frequencies and a linear receiving array carried by a vehicle so as to receive returns from said pings. The first and second frequency returns are separated and subjected to processing in parallel channels where they are resolved into in-phase and quadrature components for subsequent phase-error correction, coherent addition, and synthetic aperture beamforming.
Apparatus and method of processing in an ultrasonic alarm system to detect the doppler-shifted components which indicate the presence of an intruder. A master control applies to each of the transmitter transducers a signal which alternates between two frequencies at a modulation frequency. The output signal from the receiving transducer is synchronously detected and low pass filtered. The filtered signal is applied to electronics which respond to the presence of modulation frequency components in the filter output signal. A first embodiment utilizes a high-Q bandpass filter having a resonance frequency equal to the modulation frequency. In a second embodiment, the modulation frequency is used to effectively perform a correlation between the received signal and the modulation frequency.
A sonar system comprises a transmitter adapted to provide pulse sequences, wherein each of the pulse sequences includes pulses that reflect off an object, a receiver adapted to receive the reflected pulses, and a processor. The processor is configured to transmit a first pulse sequence via the transmitter to obtain a first distance to the object in a first distance range and to transmit a second pulse sequence via the transmitter to obtain a second distance to the object in a second distance range. The processor is configured to transmit the second pulse sequence in response to being unable to obtain the first distance to the object in the first distance range.
