Communications – electrical: acoustic wave systems and devices – Echo systems – Distance or direction finding
Utility Patent
1999-06-02
2001-01-02
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Echo systems
Distance or direction finding
C367S908000, C342S124000, C073S29000R
Utility Patent
active
06169706
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to echo ranging systems, and more particularly to the processing of return echo signals generated by such systems in order to identify wanted echo and determine its temporal location.
BACKGROUND OF THE INVENTION
Such systems typically depend on projecting towards a surface whose range is to be determined a short pulse of radiation having a wavelength which is very short compared to the range to be determined, and receiving a return signal including an echo reflected from the surface. The radiation may be acoustic radiation, typically in the range 10 to 50 kHz for general industrial applications, or electromagnetic (EM) radiation, typically microwave radiation in the range 5 to 10 GHz. Both exemplified forms of radiation have wavelengths of the same general order of magnitude, the wavelength in air of 10 kHz acoustic radiation and 10 GHz electromagnetic radiation being similar. Both are typically effectively reflected at an interface between material of substantially different densities although there are differences which may favour one or the other in particular applications. EM radiation is much less affected by the composition and temperature of an atmosphere in which it propagates, but its high speed of propagation has required different techniques to capture and display an echo profile. We have found, as described in U.S. Pat. No. 4,596,144 of which one of the present inventors was co-inventor and the content of which is hereby incorporated by reference, that successful echo processing in industrial applications is greatly facilitated by capturing and digitizing amplitude profiles of return signals over an extended period to generate a digital database the content of which may be processed to facilitate echo recognition. U.S. Pat. No. 4,890,266 issued Dec. 26, 1989, of which one of the present inventors was inventor, and the content of which is incorporated herein by reference, discloses further processing techniques applied to assist in recognizing a true or wanted echo. Both these patents describe the use of acoustic radiation.
In International Patent Application PCT/CA98/00117, which designates the United States, and the content of which is incorporated herein by reference, a microwave transducer head is described which, although using electromagnetic radiation, provides an output signal which is very similar in character to that return signal form of a typical acoustic transducer, and can be processed using similar techniques to those used for process return signals from acoustic transducers.
It is a particular characteristic of such a microwave transducer head that it produces a return signal that has, for a comparable range coverage, sufficiently similar characteristics and a duration of sufficiently comparable order of magnitude to that provided by an acoustic transducer that we have found that similar echo processing techniques can be used to those developed for processing acoustic return signals.
It is an object of the present invention to provide further improvements in echo processing techniques applicable to echo profile databases derived from either acoustic or microwave pulse-echo ranging systems, with a view to addressing two problems encountered in such systems.
A first problem is that, once a true or wanted echo has been identified, selection of the exact position to be assigned to that echo on the time axis for the purpose of range calculations still presents problems since echo shapes and characteristics can vary widely, and such variations will affect the results obtained using conventional techniques such as assuming a fixed relationship to the beginning or sill of the echo, or to the peak of the echo. The sill location will vary accordingly to the shape of the echo, and the peak may be difficult to determine for flat-topped or noisy echoes.
A second problem arises because transducers, whether acoustic or microwave, produce echo profiles in which echo signals are superimposed on a time varying background signal mainly caused by ringing of the transducer, whose characteristics vary from transducer to transducer, and with time, temperature and environment. It is usual practice to compare the echo profile with a time varying threshold (TVT) signal representing this background signal, but although numerous techniques for generating TVT signals are known, none are believed wholly satisfactory under all circumstances.
SUMMARY OF THE INVENTION
According to the invention, there is provided a method for processing an echo amplitude profile generated by an echo ranging system with reference to a temporal axis to identify return echoes comprised by the profile by identifying amplitude peaks in the profile above with respect to an amplitude axis, a threshold curve on the same temporal axis, wherein the threshold curve is generated by identifying rising edges of echoes in the profile, and generating curve segments extending on the temporal axis from points at or above said leading edges to intersections with descending edges of echoes in the profile, whereby to trace echo base lines delimiting access of the echoes.
According to a further feature of the invention, there is provided a method for processing an echo amplitude profile generated by an echo ranging system with reference to a temporal axis to identify return echoes comprised by the profile by identifying amplitude peaks in the profile above with respect to an amplitude axis, threshold curve on the same temporal axis, whereby to define echo base lines delimiting areas of the echoes, comprising identifying the position of at least a selected echo on the temporal axis by determining the temporal position of the centre of area of at least the selected one of the areas so delimited.
REFERENCES:
patent: 4315325 (1982-02-01), Blades
patent: 4837578 (1989-06-01), Gammell
patent: 4890266 (1989-12-01), Woodward
patent: 4992998 (1991-02-01), Woodward
patent: 5323361 (1994-06-01), Elle et al.
Bednarchuk Thomas Mike
Woodward Steven J.
Lobo Ian J.
Milltronics Ltd.
Ridout & Maybee
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