Optical waveguides – Miscellaneous
Reexamination Certificate
1999-06-15
2001-08-14
Bovernick, Rodney (Department: 2874)
Optical waveguides
Miscellaneous
C250S254000, C250S255000, C250S256000
Reexamination Certificate
active
06275645
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a subsurface exploration method and apparatus which allows a concentration of at least one substance to be determined at a below-ground region. More particularly, the invention relates to a method of subsurface exploration in which a substance normally present at a particular below-ground region is monitored or has its concentration detected and to an apparatus for this purpose.
BACKGROUND OF THE INVENTION
Subsurface exploration can be desirable for a large number of reasons and can serve for a wide variety of purposes. For example, one may wish to detect the presence, concentration, change of concentration or the like of a substance which is naturally present at a particular below-ground region, or a substance which may appear at such a region because of leeching or migration from another location, as in the case of monitoring waste disposal sites, or one may wish to determine the concentration of a marker substance introduced into the region as an indication of migration of materials through the region. For this purpose, it is customary to provide a well or bore hole and a monitoring unit in the cell or bore holes.
One process for subsurface exploration in which at one location in the ground at least one marker substance is introduced, has been described by M. Schöttler in: “Entwicklung eines Einbohrlock-Verfahrens zur Messung horizontaler Grundwasserströmungen” lines 19, 20 of page 1, (Development of a Single Borehole Process for Measurement of Horizontal Ground Water Flows).
In this article, a borehole probe is described for carrying out the process. The borehole probe operates with a measurement cell which contains two light sources, a lens system and a special video camera. A marker substance (tracer) of a material capable of fluorescence is liberated centrally over an observation region on which the system is focussed with a focal length of several millimeters. This region lies axially centrally of the measurement cross section and is freely traversable by the flow to be measured. Light emitted from the light sources are re-emitted light of shifted wavelength from the marker are registered by the video camera as bright image points. A contrasting image point is found on an image plane captured by video techniques.
This borehole probe and the process by which it is used and is effective can be provided in standard 10 cm (4 inch) wide boreholes.
Another borehole probe from GSF Munich, Germany, can detect the movement of radio-active marker substances. For this purpose, however, it is necessary to make use of a short-lived isotope which must be produced in a nuclear reactor. This process is relatively expensive. In addition, because the marker substance has a relatively short life, it is sensitive to storage time and it is difficult to keep available quantities of the marker in stock.
The University of California has developed a bore hole probe in which a sample is pumped from the subterranean region of an above-ground location. This system does not permit in situ measurement.
The Technical University of Freiburg, Germany has also developed a bore hole probe. This system operates with heat pulses and has been found to be suitable only for the determination of high ground water speeds.
OBJECTS OF THE INVENTION
It is, therefore, the principal object of the present invention to provide a simple, versatile, reliable and economical process for subsurface exploration which will avoid the drawbacks of earlier systems.
Another object of this invention is to provide an improved apparatus for determining the concentration, in situ of a substance in a below-ground region.
Still another object of this invention is to provide a method of and an apparatus for subsurface exploration which can be used to monitor or determine a wide range of ground water velocities than has been possible heretofore, which does not require generation of a radio-active isotope, and which is free from the need for specialized video cameras or the like.
Still another object of this invention is to provide a subsurface exploration probe which can be of low cost.
SUMMARY OF THE INVENTION
These object and others which will become apparent hereinafter are attained, in accordance with the invention, in a system in which at least at one below-ground region, at least one substance is so excited by electromagnetic radiation to which that substances is subjected that it will, in turn, emit electromagnetic radiation. Either that re-emitted radiation or the originally introduced radiation is conducted via a waveguide at least in part between the below-ground region and the region at which the electromagnetic energy is generated and/or analyzed.
According to the invention, the process is so carried out that a coupling in and/or the coupling out of the electromagnetic energy with respect to the below-ground region is effected via a light-conducting or optical fiber.
Advantageously, the electromagnetic radiation includes a light beam which can have an emission wavelength between 200 nm and 950 nm. The substance which is detected in this manner is a substance which can be excited by the light radiation, preferably so as to be luminescent. In this case, an energy absorption takes place via atoms, molecules or condensed material, whereas the emission can be either a phosphorescence or a fluorescence which is detected by the out-coupling of the re-emitted light to the measurement location. While the re-emitted light is evaluated externally of the borehole, the fact that the light is transmitted out of the region for evaluation does not change the fact that the measurement is in situ at the region and is carried out with a high time resolution.
According to a feature of the invention, a bore hole probe can be provided to measure concentration of a substance in the ground and has at least one means for coupling the electromagnetic radiation to the region and/or coupling electromagnetic radiation out of the region, such means including a light-conductive fiber. Especially small dimensions of the probe can be obtained when the light-conducting fiber serves both as the means for coupling the electromagnetic energy into and out of the system.
For detecting flow velocity of nonfluorescent substances it is advantageous to introduce into the region a marker substance, preferably from an upper location in the bore hole. A homogeneous distribution of the substance to be measured can be obtained by providing a mixing device as part of the bore hole probe in the bore hole.
The light beam can be generated by a laser. It has been found to be advantageous to provide the laser above ground, although it can be provided in the bore hole. In this case a relatively bulky laser can be used which has particularly desirable emission characteristics, allowing it to cover both UV and visible ranges.
It is possible, in accordance with the invention, to utilize a very compact laser. With a highly compact semiconductor laser, in the form, for example, of a pn laser diode in which the pn transition serves as a pump for the laser, the active (amplifying) material is formed by a semiconductor with a direct band gap. The active region of the laser diode is a thin laser in the direct vicinity of the space charge region of the pa transition. The laser diode emits coherent radiation with the line widths of the order of magnitude of 0.1 nm and with sharp directionality.
A further suitable light source for incorporation in the bore hole probe is a luminescence diode (LED, light emitting diode). The luminescence diode contains a semiconductive material with a p-doped region and an n-doped region. Excess charge carriers provided in these regions diffuse respectively in each other region and recombine there as its charge carriers. The result is an incoherent electromagnetic radiation with a duplicate line width of the order of magnitude of several 10 nm. The band width depends upon the selection of the semiconductive material and its doping.
For the best possible separation between emitted light and re-emitted l
Höltkemeier Jürgen
Vereecken Harry
Bovernick Rodney
Dubno Herbert
Forschungszentrum Julich GmbH
Pak Sung
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