CA2787896C - A method for measuring the water level of a body of water - Google Patents
A method for measuring the water level of a body of water Download PDFInfo
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- CA2787896C CA2787896C CA2787896A CA2787896A CA2787896C CA 2787896 C CA2787896 C CA 2787896C CA 2787896 A CA2787896 A CA 2787896A CA 2787896 A CA2787896 A CA 2787896A CA 2787896 C CA2787896 C CA 2787896C
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- reflector
- water
- radiation
- reflection
- reflection surfaces
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/12—Supports; Mounting means
- H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
- H01Q1/225—Supports; Mounting means by structural association with other equipment or articles used in level-measurement devices, e.g. for level gauge measurement
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
- G01F23/284—Electromagnetic waves
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/27—Adaptation for use in or on movable bodies
- H01Q1/28—Adaptation for use in or on aircraft, missiles, satellites, or balloons
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/27—Adaptation for use in or on movable bodies
- H01Q1/34—Adaptation for use in or on ships, submarines, buoys or torpedoes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/14—Reflecting surfaces; Equivalent structures
- H01Q15/18—Reflecting surfaces; Equivalent structures comprising plurality of mutually inclined plane surfaces, e.g. corner reflector
Abstract
The invention relates to a method for measuring the water level of a body of water.
This involves using a reflector (1, 101, 201, 301, 401, 501) comprising a number of reflection surfaces (1a, 1b) for reflecting electromagnetic radiation within a predetermined wavelength range and which is provided in or at the body of water such that a corner reflector is formed by the water surface (W) of the body of water and one or more reflection surfaces (1a, 1b) of the reflector (1, 101, 201, 301, 401, 501). As part of the method electromagnetic radiation within the predetermined wavelength range, emitted by a radiating device (3) arranged above the body of water, is incident upon the reflector (1, 101, 201, 301, 401, 501) such that the incident radiation is reflected back at the corner reflector based on a multiple reflection including the water surface (W). The distance between the radiating device (2) and the reflection centre of the corner reflector is measured via the delay time of the emitted and back-reflected radiation, and the water level (W) of the body of water is determined based on this measurement.
This involves using a reflector (1, 101, 201, 301, 401, 501) comprising a number of reflection surfaces (1a, 1b) for reflecting electromagnetic radiation within a predetermined wavelength range and which is provided in or at the body of water such that a corner reflector is formed by the water surface (W) of the body of water and one or more reflection surfaces (1a, 1b) of the reflector (1, 101, 201, 301, 401, 501). As part of the method electromagnetic radiation within the predetermined wavelength range, emitted by a radiating device (3) arranged above the body of water, is incident upon the reflector (1, 101, 201, 301, 401, 501) such that the incident radiation is reflected back at the corner reflector based on a multiple reflection including the water surface (W). The distance between the radiating device (2) and the reflection centre of the corner reflector is measured via the delay time of the emitted and back-reflected radiation, and the water level (W) of the body of water is determined based on this measurement.
Description
A METHOD FOR MEASURING THE WATER LEVEL OF A BODY OF
WATER
Description The invention relates to a method for measuring the water level of a body of water as well as to a corresponding measuring system.
Measuring the water level of artificial and natural waters such as rivers, likes and freshwater reservoirs is of great importance nowadays both for monitoring areas where there is a risk of flooding and areas with increasing water shortage.
As a rule water levels of bodies of water are read by human personnel at locally distributed gauge stations on the ground whereby the readings are transmitted electronically to central analysis centres. Such gauge stations comprise movable mechanisms or active electronics and are therefore prone to failing. In particular, in case of flooding gauge station are easily damaged or destroyed and therefore no longer usable for water level monitoring in particular in the case of flooding.
In documents [1] and [2], a method is described for interferometrically determining water levels over wide expanses in the Everglades (Florida) by means of SAR
radar (SAR = Synthetic Aperture Radar). The measuring of water levels described in these documents requires the presence of special water plants which protrude from the water surface and reflect radar waves. Such plants occur only rarely in the world.
Moreover, the method only supplies relative values and not an absolute water level.
Therefore, the need for a gauge station still exists.
It is therefore an object of the invention to provide an easy and reliable way of measuring the water level of a body of water without having to use gauge stations.
WATER
Description The invention relates to a method for measuring the water level of a body of water as well as to a corresponding measuring system.
Measuring the water level of artificial and natural waters such as rivers, likes and freshwater reservoirs is of great importance nowadays both for monitoring areas where there is a risk of flooding and areas with increasing water shortage.
As a rule water levels of bodies of water are read by human personnel at locally distributed gauge stations on the ground whereby the readings are transmitted electronically to central analysis centres. Such gauge stations comprise movable mechanisms or active electronics and are therefore prone to failing. In particular, in case of flooding gauge station are easily damaged or destroyed and therefore no longer usable for water level monitoring in particular in the case of flooding.
In documents [1] and [2], a method is described for interferometrically determining water levels over wide expanses in the Everglades (Florida) by means of SAR
radar (SAR = Synthetic Aperture Radar). The measuring of water levels described in these documents requires the presence of special water plants which protrude from the water surface and reflect radar waves. Such plants occur only rarely in the world.
Moreover, the method only supplies relative values and not an absolute water level.
Therefore, the need for a gauge station still exists.
It is therefore an object of the invention to provide an easy and reliable way of measuring the water level of a body of water without having to use gauge stations.
2 This object is solved by the method according to patent claim 1 and the measuring system according patent claim 14 and the use of a reflector according to patent claim 16 and the reflector according to patent claim 17. Embodiments of the invention are defined in the dependent claims.
In the measuring method according to the invention, a reflector is used which comprises a number (at least one) of reflecting surfaces for reflecting electromagnetic radiation within a predetermined wavelength range and which is provided in or at the body of water the water level of which is to be measured. The term 'body of water' is to be understood as covering a wide variety of waters such as any type of artificial or natural water, in particular rivers, lakes, wetlands, artificial lakes, maritime regions, water reservoirs and water basins. The reflector is arranged in or near the water (for example on the edge or on the shore of the water) such that a corner reflector is formed by the water surface of the body of water and one or more reflecting surfaces of the reflector. In other words, the reflecting surface or surfaces and the water surface which form the corner reflector, all extend substantially perpendicularly to each other.
In the method according to the invention, electromagnetic radiation within the predetermined wavelength range is emitted from a radiating device arranged above the water. This radiation is incident upon the reflector so as to be reflected back at the corner reflector formed by the reflecting surface or surfaces and the water surface based on a multiple reflection which includes the water surface. Back reflection, also called retro-reflection, is understood to mean that the incident radiation is reflected back essentially in the same direction in which it is incident upon the comer reflector. According to the invention therefore the incidence of radiation emitted by the radiating device and the comer reflector are oriented so as to make this retro-reflection happen.
In the measuring method according to the invention, a reflector is used which comprises a number (at least one) of reflecting surfaces for reflecting electromagnetic radiation within a predetermined wavelength range and which is provided in or at the body of water the water level of which is to be measured. The term 'body of water' is to be understood as covering a wide variety of waters such as any type of artificial or natural water, in particular rivers, lakes, wetlands, artificial lakes, maritime regions, water reservoirs and water basins. The reflector is arranged in or near the water (for example on the edge or on the shore of the water) such that a corner reflector is formed by the water surface of the body of water and one or more reflecting surfaces of the reflector. In other words, the reflecting surface or surfaces and the water surface which form the corner reflector, all extend substantially perpendicularly to each other.
In the method according to the invention, electromagnetic radiation within the predetermined wavelength range is emitted from a radiating device arranged above the water. This radiation is incident upon the reflector so as to be reflected back at the corner reflector formed by the reflecting surface or surfaces and the water surface based on a multiple reflection which includes the water surface. Back reflection, also called retro-reflection, is understood to mean that the incident radiation is reflected back essentially in the same direction in which it is incident upon the comer reflector. According to the invention therefore the incidence of radiation emitted by the radiating device and the comer reflector are oriented so as to make this retro-reflection happen.
3 According to the invention, the water level of the body of water is determined. At first, the distance between the radiating device and the scatter or reflection centre of the corner reflector is determined. This reflection centre the location of which is linked proportionally to the water level is formed by the intersection or the intersecting edge between the reflecting surface or surfaces of the reflector and the water surface. The intersection or the intersecting edge may be an imaginary point or an imaginary edge which result as the intersection between extensions of the reflecting surface or surfaces of the reflector and the water surface. An imaginary intersection or an imaginary intersecting edge occurs, in particular, with embodiments, where the reflector is positioned on the edge or on the shore of the water. Distance measuring is performed by measuring the delay between the emission of the radiation being from the radiating device and its reception back at the location of the radiating device after retro-reflection at the corner reflector. By means of this delay time, it is easy to determine the distance between the radiating device and the corner reflector via the speed of light. Taking into account corresponding position data concerning the position of the radiating device and the reflector, the water level can be determined as will be explained by way of example in the detailed description with reference to Fig. 1.
The electromagnetic radiation emitted by the radiating device may comprise different wavelengths or lie in different wavelength ranges. Preferably, the radiation is generated by high-frequency radio waves with a frequency in the range between GHz and 30 GHz, in particular 10 GHz and higher. The angle of incidence of the radiation emitted by the radiating device may be in different angular ranges, in particular the radiation may be incident upon the corner reflector at an angle between 20 and 50 relative to the vertical.
The size of the reflecting surfaces of the reflector varies depending on the application or on the wavelength of the incident radiation. Preferably, the size of the reflector varies between 30 cm and 3 m, in particular between 30 cm and 2 m or 30 cm and cm. If the individual reflecting surfaces are shaped as squares, this size corresponds
The electromagnetic radiation emitted by the radiating device may comprise different wavelengths or lie in different wavelength ranges. Preferably, the radiation is generated by high-frequency radio waves with a frequency in the range between GHz and 30 GHz, in particular 10 GHz and higher. The angle of incidence of the radiation emitted by the radiating device may be in different angular ranges, in particular the radiation may be incident upon the corner reflector at an angle between 20 and 50 relative to the vertical.
The size of the reflecting surfaces of the reflector varies depending on the application or on the wavelength of the incident radiation. Preferably, the size of the reflector varies between 30 cm and 3 m, in particular between 30 cm and 2 m or 30 cm and cm. If the individual reflecting surfaces are shaped as squares, this size corresponds
4 to the length of an edge of the respective reflecting surfaces. In order to achieve a sufficient reflecting effect, the reflection surface or surfaces are preferably metallic, in particular made of aluminium and/or stainless steel.
In order to fix the reflector with respect to the water surface of the water, the reflector is mounted in or at the water in particular via suitable anchoring, for example it could be driven or concreted into the ground. All that is important here is that at least a part of the reflecting surfaces is arranged above the water surface and extends perpendicularly to the same.
In an especially preferred embodiment the distance is measured via radar and in particular via microwave radar, i.e. by means of radiation in the gigahertz range. The radiation incident upon the reflector is thus emitted by a radar sensor, in particular a SAR radar sensor well known in the state of the art such as the TerraSAR-X
which permits highly accurate measuring. Apart from emitting the radiation, the radar sensor also measures or detects the back-reflected radiation. This can be used for determining the delay time of the radiation, from which in turn the water level can be determined.
In an especially preferred embodiment, the radiation directed at the reflector or corner reflector is emitted by a radiating device arranged on a moving flying object, in particular a satellite or an aeroplane or a helicopter. When flying over a large area this will allow pointwise determination of water levels of large bodies of water at various locations via correspondingly provided reflectors.
The reflector used in the method according to the invention may be designed in various ways. In a particularly preferred embodiment, the reflector comprises at least one pair of two reflecting surfaces extending perpendicularly to each other and thus forming a right angle, wherein the water surface extends perpendicularly to each reflection surface of the at least one pair. In this variant therefore, the water surface and the reflector form one triple corner reflector, where retro-reflection is effected via a triple reflection on the corner reflector including the water surface.
As required, there is also the possibility for the reflector to comprise only one reflecting surface which is arranged in the water or in the vicinity of the water. In this case the reflecting surface and the water surface form a dual corner reflector, where retro-
In order to fix the reflector with respect to the water surface of the water, the reflector is mounted in or at the water in particular via suitable anchoring, for example it could be driven or concreted into the ground. All that is important here is that at least a part of the reflecting surfaces is arranged above the water surface and extends perpendicularly to the same.
In an especially preferred embodiment the distance is measured via radar and in particular via microwave radar, i.e. by means of radiation in the gigahertz range. The radiation incident upon the reflector is thus emitted by a radar sensor, in particular a SAR radar sensor well known in the state of the art such as the TerraSAR-X
which permits highly accurate measuring. Apart from emitting the radiation, the radar sensor also measures or detects the back-reflected radiation. This can be used for determining the delay time of the radiation, from which in turn the water level can be determined.
In an especially preferred embodiment, the radiation directed at the reflector or corner reflector is emitted by a radiating device arranged on a moving flying object, in particular a satellite or an aeroplane or a helicopter. When flying over a large area this will allow pointwise determination of water levels of large bodies of water at various locations via correspondingly provided reflectors.
The reflector used in the method according to the invention may be designed in various ways. In a particularly preferred embodiment, the reflector comprises at least one pair of two reflecting surfaces extending perpendicularly to each other and thus forming a right angle, wherein the water surface extends perpendicularly to each reflection surface of the at least one pair. In this variant therefore, the water surface and the reflector form one triple corner reflector, where retro-reflection is effected via a triple reflection on the corner reflector including the water surface.
As required, there is also the possibility for the reflector to comprise only one reflecting surface which is arranged in the water or in the vicinity of the water. In this case the reflecting surface and the water surface form a dual corner reflector, where retro-
5 reflection is effected by a reflection at the reflection surface and at the water surface.
When such a reflector is placed on the edge of the water, the radiation running between the reflection surface and the water surface during reflection bridges the shore area between the reflector and the edge of the water.
In a preferred embodiment of the above reflector, the reflector includes two pairs of reflection surfaces, wherein the reflection surfaces of a respective pair extend perpendicularly to each other and wherein the pairs are oriented in different directions so that measuring the water level can be effected from two directions or angular ranges of incident radiation. In one variant, the pairs of reflection surfaces may be offset against each other by for example 180 so that a respective reflection surface of the one pair is substantially perpendicular to one reflection surface of the other pair and extends in parallel to the other reflection surface of the other pair. In this variant further reflection surfaces are preferably formed by the rear sides of the respective reflection surfaces so that the corner reflector comprises four pairs of reflection surfaces offset by 90 in relation to each other. In this way water level measuring can be performed by means of the radiation incident from any given direction. In a further preferred embodiment, each pair of reflection surfaces is oriented towards an ascending or descending orbit of an earth-orbiting satellite, for example towards a polar or close-to-polar orbit of a satellite. In this variant, the radiation incident upon the corner reflector is generated by a radiating device on the satellite, wherein this radiating device preferably comprises a radar sensor.
In a further embodiment of the method according to the invention, a reflector is used which comprises an attenuation device for attenuating water waves of the body of water in the vicinity of the reflector. This allows the water level to be measured with a fair degree of accuracy even when there is a heavy swell. In a simple embodiment,
When such a reflector is placed on the edge of the water, the radiation running between the reflection surface and the water surface during reflection bridges the shore area between the reflector and the edge of the water.
In a preferred embodiment of the above reflector, the reflector includes two pairs of reflection surfaces, wherein the reflection surfaces of a respective pair extend perpendicularly to each other and wherein the pairs are oriented in different directions so that measuring the water level can be effected from two directions or angular ranges of incident radiation. In one variant, the pairs of reflection surfaces may be offset against each other by for example 180 so that a respective reflection surface of the one pair is substantially perpendicular to one reflection surface of the other pair and extends in parallel to the other reflection surface of the other pair. In this variant further reflection surfaces are preferably formed by the rear sides of the respective reflection surfaces so that the corner reflector comprises four pairs of reflection surfaces offset by 90 in relation to each other. In this way water level measuring can be performed by means of the radiation incident from any given direction. In a further preferred embodiment, each pair of reflection surfaces is oriented towards an ascending or descending orbit of an earth-orbiting satellite, for example towards a polar or close-to-polar orbit of a satellite. In this variant, the radiation incident upon the corner reflector is generated by a radiating device on the satellite, wherein this radiating device preferably comprises a radar sensor.
In a further embodiment of the method according to the invention, a reflector is used which comprises an attenuation device for attenuating water waves of the body of water in the vicinity of the reflector. This allows the water level to be measured with a fair degree of accuracy even when there is a heavy swell. In a simple embodiment,
6 the attenuation device comprises one or more screens which are transparent to electromagnetic radiation in the predetermined wavelength range, for example one or more Perspex panes. This provides a good screen for smoothing wave movements on the water surface in the area of the reflector.
As regards the above described embodiment of a reflector with at least one pair of reflection surfaces, a respective screen would extend between the reflection surfaces of a pair of reflections surfaces, in particular between those edges of reflection surfaces which are remote from the right angle formed between the reflection surfaces of the pair.
The attenuation device may also be formed so as to provide a cavity with at least one equalising opening or at least one equalising valve in the area of the reflection surfaces, wherein the at least one equalising opening or the at least one equalising valve is provided to allow air and/or water to flow through it. The cavity may therefore be either an air cavity above the water surface or a cavity filled with water from the body of water below the water surface. In both cases, attenuation of wave movements is achieved pneumatically or hydraulically by means of a corresponding opening or a valve. Preferably, the at least one equalising opening or the at least one equalising valve is provided in a lid closing off the at least one cavity which lid is preferably transparent to the electromagnetic radiation of the radiating device. In case of water from the body of water flowing through the opening or valve, the lid is arranged below the water surface, whilst in case of air flowing through opening or valve, the lid is arranged above the water surface. The variant just described of an attenuation device is preferably combined with the above-described embodiment of a transparent screen. With this arrangement, the cavity is formed by the at least one lid, one or more reflection surfaces of the reflector and at least one transparent screen.
In a preferred variant, in order to determine the water level from the measured distance between the radiating device and the corner reflector, a three-dimensional position of the radiating device and a two-dimensional position describing the
As regards the above described embodiment of a reflector with at least one pair of reflection surfaces, a respective screen would extend between the reflection surfaces of a pair of reflections surfaces, in particular between those edges of reflection surfaces which are remote from the right angle formed between the reflection surfaces of the pair.
The attenuation device may also be formed so as to provide a cavity with at least one equalising opening or at least one equalising valve in the area of the reflection surfaces, wherein the at least one equalising opening or the at least one equalising valve is provided to allow air and/or water to flow through it. The cavity may therefore be either an air cavity above the water surface or a cavity filled with water from the body of water below the water surface. In both cases, attenuation of wave movements is achieved pneumatically or hydraulically by means of a corresponding opening or a valve. Preferably, the at least one equalising opening or the at least one equalising valve is provided in a lid closing off the at least one cavity which lid is preferably transparent to the electromagnetic radiation of the radiating device. In case of water from the body of water flowing through the opening or valve, the lid is arranged below the water surface, whilst in case of air flowing through opening or valve, the lid is arranged above the water surface. The variant just described of an attenuation device is preferably combined with the above-described embodiment of a transparent screen. With this arrangement, the cavity is formed by the at least one lid, one or more reflection surfaces of the reflector and at least one transparent screen.
In a preferred variant, in order to determine the water level from the measured distance between the radiating device and the corner reflector, a three-dimensional position of the radiating device and a two-dimensional position describing the
7 position of the reflector in a top view on the earth surface are taken into account, whereby these positions are known or are determined as part of the method. The three-dimensional position and the two-dimensional position are determined in particular with respect of the same reference coordinate system. The position of the radiating device may be determined via GPS (GPS = Global Positioning System) or within the framework of the method. The two-dimensional position of the reflector can also be determined via GPS or may already be present in the form of GPS
coordinates.
In order to increase the measuring accuracy of the method, the water level of the body of water is determined in a further variant of the invention by providing a reference corner reflector the reflection surfaces of which do not comprise the water surface of the body of water, at a predetermined reference position in or at the body of water, wherein the distance between the reference radiating device and the reflection centre of the corner reflector is measured via the delay time of back-reflected radiation emitted by the radiating device. Since the actual distance is known due to the known reference position of the reference corner reflector, error compensation of the distance measurement may thus be carried out relative to the other reflector in or at the body of water using suitable processes.
Apart from the above-described measuring method, the invention also comprises a measuring system for measuring the water level of a body of water. This measuring system comprises a reflector which comprises a number (at least one) of reflection surfaces for reflecting electromagnetic radiation within a predetermined wavelength range and which is arranged in or at the body of water such that a corner reflector is formed by the water surface of the body of water and one or more reflection surfaces of the reflector. The measuring system further comprises a radiating device arranged above the body of water for emitting electromagnetic radiation within the predetermined wavelength range so that the emitted radiation is incident upon the reflector such that the incident radiation is reflected back at the corner reflector based on a multiple reflection which includes the water surface. The measuring system
coordinates.
In order to increase the measuring accuracy of the method, the water level of the body of water is determined in a further variant of the invention by providing a reference corner reflector the reflection surfaces of which do not comprise the water surface of the body of water, at a predetermined reference position in or at the body of water, wherein the distance between the reference radiating device and the reflection centre of the corner reflector is measured via the delay time of back-reflected radiation emitted by the radiating device. Since the actual distance is known due to the known reference position of the reference corner reflector, error compensation of the distance measurement may thus be carried out relative to the other reflector in or at the body of water using suitable processes.
Apart from the above-described measuring method, the invention also comprises a measuring system for measuring the water level of a body of water. This measuring system comprises a reflector which comprises a number (at least one) of reflection surfaces for reflecting electromagnetic radiation within a predetermined wavelength range and which is arranged in or at the body of water such that a corner reflector is formed by the water surface of the body of water and one or more reflection surfaces of the reflector. The measuring system further comprises a radiating device arranged above the body of water for emitting electromagnetic radiation within the predetermined wavelength range so that the emitted radiation is incident upon the reflector such that the incident radiation is reflected back at the corner reflector based on a multiple reflection which includes the water surface. The measuring system
8 further comprises a measuring device for measuring the distance between the radiating device and the reflection centre of the corner reflector via the delay time of the emitted and back-reflected radiation. In addition, an evaluation device for determining the water level of the body of water based on the measured distance is provided. In this measuring system, all concrete implementations described in relation to the above method may be realised. In particular, the reflector may be implemented as a reflector with at least one pair of reflection surfaces.
Furthermore, the reflector may comprise the above-described attenuation device. Measuring can be carried out, in particular, using a radar sensor, wherein in this case the radiating device and the measuring device are integrated in this radar sensor. The evaluation device may be arranged at any desired location. In particular, a central evaluation device may be provided to which the measured data captured by the measuring device is transmitted and where it may be evaluated for determining the water level.
Moreover, the invention refers to the use of a reflector comprising one or more reflection surfaces for reflecting electromagnetic radiation within a predetermined wavelength range in the above-described method according to the invention or the above-described measuring system according to the invention. The reflector may comprise each of the features described in relation to embodiments of the method according to the invention and relating to the reflector. In particular, the reflector may be implemented as a reflector with at least one pair of reflection surfaces and may comprise an attenuation device as required.
Moreover, the invention refers to a reflector especially suited for use in the method according to the invention or the measuring system according to the invention.
This reflector which comprises one or more reflection surfaces for reflecting electromagnetic radiation within a predetermined wavelength range, is characterised in that it further comprises an attenuation device for attenuating water waves of the body of water in the vicinity of the reflector and/or two pairs of reflection surfaces, wherein the reflection surfaces of a respective pair extend perpendicularly to each other and the pairs are oriented in different directions. Such a reflector may be used
Furthermore, the reflector may comprise the above-described attenuation device. Measuring can be carried out, in particular, using a radar sensor, wherein in this case the radiating device and the measuring device are integrated in this radar sensor. The evaluation device may be arranged at any desired location. In particular, a central evaluation device may be provided to which the measured data captured by the measuring device is transmitted and where it may be evaluated for determining the water level.
Moreover, the invention refers to the use of a reflector comprising one or more reflection surfaces for reflecting electromagnetic radiation within a predetermined wavelength range in the above-described method according to the invention or the above-described measuring system according to the invention. The reflector may comprise each of the features described in relation to embodiments of the method according to the invention and relating to the reflector. In particular, the reflector may be implemented as a reflector with at least one pair of reflection surfaces and may comprise an attenuation device as required.
Moreover, the invention refers to a reflector especially suited for use in the method according to the invention or the measuring system according to the invention.
This reflector which comprises one or more reflection surfaces for reflecting electromagnetic radiation within a predetermined wavelength range, is characterised in that it further comprises an attenuation device for attenuating water waves of the body of water in the vicinity of the reflector and/or two pairs of reflection surfaces, wherein the reflection surfaces of a respective pair extend perpendicularly to each other and the pairs are oriented in different directions. Such a reflector may be used
9 to measure the water level in cases where the swell is heavy or where electromagnetic radiation is incident from several radiation directions. This reflector may comprise all further previously described features regarding implementations of the reflector.
Embodiments of the invention will now be described in detail with reference to the enclosed figures, in which Fig. 1 is a schematic illustration of an embodiment of a measuring system according to the invention for measuring the water level of a body of water;
Fig. 2 shows a first embodiment of a reflector used in the method according to the invention;
Fig. 3 shows a second embodiment of a reflector used in the method according to the invention;
Fig. 4 shows a third embodiment of a reflector used in the method according to the invention;
Fig. 5 shows a fourth embodiment of a reflector used in the method according to the invention;
Fig. 6 shows a fifth embodiment of a reflector used in the method according to the invention;
Fig. 7 shows a sixth embodiment of a reflector used in the method according to the invention.
Fig. 1 shows a measuring arrangement for implementing an embodiment of the method according to the invention. The measuring arrangement is intended to determine the water level of a body of water, the water surface of which is indicated in Fig. 1 by a horizontal line W. The water level is measured with respect to a reference coordinate system the coordinate origin of which is designated with 0, and which comprises the horizontal coordinate axes x, y and the vertical coordinate axis 5 h. The illustration of Fig. 1 is simplified showing a planar earth surface geometry.
The calculation below is described based on this simplified geometry. However, the calculation may also be applied analogously to a curved geoid surface. In this case the calculation is somewhat more complicated but basically the same and being accurately performable. Transferring the calculation from a plane earth surface
Embodiments of the invention will now be described in detail with reference to the enclosed figures, in which Fig. 1 is a schematic illustration of an embodiment of a measuring system according to the invention for measuring the water level of a body of water;
Fig. 2 shows a first embodiment of a reflector used in the method according to the invention;
Fig. 3 shows a second embodiment of a reflector used in the method according to the invention;
Fig. 4 shows a third embodiment of a reflector used in the method according to the invention;
Fig. 5 shows a fourth embodiment of a reflector used in the method according to the invention;
Fig. 6 shows a fifth embodiment of a reflector used in the method according to the invention;
Fig. 7 shows a sixth embodiment of a reflector used in the method according to the invention.
Fig. 1 shows a measuring arrangement for implementing an embodiment of the method according to the invention. The measuring arrangement is intended to determine the water level of a body of water, the water surface of which is indicated in Fig. 1 by a horizontal line W. The water level is measured with respect to a reference coordinate system the coordinate origin of which is designated with 0, and which comprises the horizontal coordinate axes x, y and the vertical coordinate axis 5 h. The illustration of Fig. 1 is simplified showing a planar earth surface geometry.
The calculation below is described based on this simplified geometry. However, the calculation may also be applied analogously to a curved geoid surface. In this case the calculation is somewhat more complicated but basically the same and being accurately performable. Transferring the calculation from a plane earth surface
10 geometry to curved geometries lies within the experts' range of knowledge.
The height of water level Hw is measured according to Fig. 1 at a reflector 1 with reflection surfaces la and lb extending perpendicularly to each other, by utilising the retro-reflection of radar radiation emitted by a satellite. The satellite is schematically indicated in Fig. 1 and designated with reference numeral 2. Furthermore, Fig.
shows a schematically drawn radar sensor 3 located on the satellite (in particular a SAR radar), which emits the radar radiation in direction of water surface W.
The method according to the invention is realised in that the reflector 1 is mounted in the body of water such that the two reflection surfaces la and lb extend perpendicularly to the water surface W. Mounting of the reflector may be carried out by a suitable anchoring on the ground of the body of water, for example by concreting and driving it in. Furthermore, the reflector is oriented with respect to the known satellite orbit indicated by arrow P so as to ensure that the radar radiation of radar 3 is incident on the reflector such that a retro-reflection of the radiation by a multiple reflection at the two reflection surfaces 1 a and lb as well as at the water surface W takes place.
Hence, the reflector 1 and the water surface W form a triple comer reflector for reflecting the radar radiation.
The radar sensor 3 is used to measure the distance R between the satellite 2 and the reflector 1 by measuring the delay time of the radiation emitted from the radar sensor and back-reflected by reflector 1. This distance is dependent on the height Hw of the
The height of water level Hw is measured according to Fig. 1 at a reflector 1 with reflection surfaces la and lb extending perpendicularly to each other, by utilising the retro-reflection of radar radiation emitted by a satellite. The satellite is schematically indicated in Fig. 1 and designated with reference numeral 2. Furthermore, Fig.
shows a schematically drawn radar sensor 3 located on the satellite (in particular a SAR radar), which emits the radar radiation in direction of water surface W.
The method according to the invention is realised in that the reflector 1 is mounted in the body of water such that the two reflection surfaces la and lb extend perpendicularly to the water surface W. Mounting of the reflector may be carried out by a suitable anchoring on the ground of the body of water, for example by concreting and driving it in. Furthermore, the reflector is oriented with respect to the known satellite orbit indicated by arrow P so as to ensure that the radar radiation of radar 3 is incident on the reflector such that a retro-reflection of the radiation by a multiple reflection at the two reflection surfaces 1 a and lb as well as at the water surface W takes place.
Hence, the reflector 1 and the water surface W form a triple comer reflector for reflecting the radar radiation.
The radar sensor 3 is used to measure the distance R between the satellite 2 and the reflector 1 by measuring the delay time of the radiation emitted from the radar sensor and back-reflected by reflector 1. This distance is dependent on the height Hw of the
11 water line, since the water surface is part of the reflection surfaces during retro-reflection resulting in the measured distance R increasing the more the water level decreases. In other words, retro-reflection is used to measure the distance R
between the corner formed by water surface W and reflector 1, and the radar sensor, wherein the position of this corner depends on the height of the water line.
Further, in the measuring arrangement of Fig. 1, the position of satellite 2 above the earth surface is known in the reference coordinate system. For reasons of simplicity it is assumed that satellite 2 is located just above the x-axis of the coordinate system at position XS. Moreover, the fixed mounting position of reflector 1 with respect to the earth surface is known, wherein this position, in the scenario of Fig. 1, for reasons of simplicity, also lies along the x-axis of the reference coordinate system and is given by the coordinate xR. Also known is the height Hsat of the satellite with respect to the reference plane given by the x-axis and the y-axis of the reference coordinate system. The water level Hw with respect to the position of the x-axis of the reference coordinate system can then be determined in a simple way from the measured distance R, the difference Ax = XR - xs1 and the height Hat of the satellite as follows:
Hw= Hat ¨ ¨ Ax2 To determine the water level, the current position of the satellite is thus required, and this can be determined from the known satellite orbit. The (two-dimensional) position of the reflector is also known and, for example, is given in GPS
coordinates.
The measuring accuracy of the measured water level depends on the error of the satellite orbit determination and the delay time-based determination of the distance R
as well as the angle of incidence of the radar radiation hitting the reflector 1, wherein this angle of incidence is designated 0 in Fig. 1. With modern satellite systems, the absolute error achievable for a 45 angle of incidence of radar radiation is currently approx. 6 cm. In a variant of the method according to the invention the accuracy of the water level measurement may be improved by positioning a second conventional
between the corner formed by water surface W and reflector 1, and the radar sensor, wherein the position of this corner depends on the height of the water line.
Further, in the measuring arrangement of Fig. 1, the position of satellite 2 above the earth surface is known in the reference coordinate system. For reasons of simplicity it is assumed that satellite 2 is located just above the x-axis of the coordinate system at position XS. Moreover, the fixed mounting position of reflector 1 with respect to the earth surface is known, wherein this position, in the scenario of Fig. 1, for reasons of simplicity, also lies along the x-axis of the reference coordinate system and is given by the coordinate xR. Also known is the height Hsat of the satellite with respect to the reference plane given by the x-axis and the y-axis of the reference coordinate system. The water level Hw with respect to the position of the x-axis of the reference coordinate system can then be determined in a simple way from the measured distance R, the difference Ax = XR - xs1 and the height Hat of the satellite as follows:
Hw= Hat ¨ ¨ Ax2 To determine the water level, the current position of the satellite is thus required, and this can be determined from the known satellite orbit. The (two-dimensional) position of the reflector is also known and, for example, is given in GPS
coordinates.
The measuring accuracy of the measured water level depends on the error of the satellite orbit determination and the delay time-based determination of the distance R
as well as the angle of incidence of the radar radiation hitting the reflector 1, wherein this angle of incidence is designated 0 in Fig. 1. With modern satellite systems, the absolute error achievable for a 45 angle of incidence of radar radiation is currently approx. 6 cm. In a variant of the method according to the invention the accuracy of the water level measurement may be improved by positioning a second conventional
12 corner reflector (not shown) with three accurately measured axes in the vicinity of the body of water whose level is to be measured, for example on its shore. The three-dimensional position of this corner reflector which comprises three reflection surfaces extending perpendicularly to each other is well known. This reflector also reflects the radar radiation back to radar sensor 3. This means that also on the basis of the radiation reflected from this second comer reflector, the distance between this reflector and sensor 3 can be measured by a delay time measurement and used as a comparative value. The error in measuring the distance R can thus be substantially reduced, and it is even possible to achieve water level readings which are accurate down to less than one centimetre.
The measuring method described with reference to Fig. 1 is used to determine water levels of any bodies of water such as large areas of wetland or remote expanses of water. It is also suitable for monitoring the levels of artificial lakes and rivers.
Generally speaking, the method described with reference to Fig. 1 can be used for measuring both artificial and natural waters as well as artificially created water basins. The description of the embodiment of the method according to the invention with reference to Fig. 1 is to be regarded as merely an example and suitable variations for determining the water level of a body of water are feasible. In particular, the radar sensor used for distance measurement may be replaced by a sensor, which determines the delay time based on electromagnetic radiation in a wavelength range other than radar radiation. In addition, the sensor need not be provided on a satellite but it may be arranged on an aeroplane which flies over the body of water to be measured. In this case, the position of the aeroplane must be known when performing measurements, wherein this position may be determined via GPS, for example. It is also possible to perform measurements in a stationary manner in that the sensor is arranged at a fixed accurately predetermined position above the water surface.
The principle of the invention has been described with reference to Fig. 1 based on a reflector 1, which comprises two reflection surfaces 1a and 1 b, wherein, if the
The measuring method described with reference to Fig. 1 is used to determine water levels of any bodies of water such as large areas of wetland or remote expanses of water. It is also suitable for monitoring the levels of artificial lakes and rivers.
Generally speaking, the method described with reference to Fig. 1 can be used for measuring both artificial and natural waters as well as artificially created water basins. The description of the embodiment of the method according to the invention with reference to Fig. 1 is to be regarded as merely an example and suitable variations for determining the water level of a body of water are feasible. In particular, the radar sensor used for distance measurement may be replaced by a sensor, which determines the delay time based on electromagnetic radiation in a wavelength range other than radar radiation. In addition, the sensor need not be provided on a satellite but it may be arranged on an aeroplane which flies over the body of water to be measured. In this case, the position of the aeroplane must be known when performing measurements, wherein this position may be determined via GPS, for example. It is also possible to perform measurements in a stationary manner in that the sensor is arranged at a fixed accurately predetermined position above the water surface.
The principle of the invention has been described with reference to Fig. 1 based on a reflector 1, which comprises two reflection surfaces 1a and 1 b, wherein, if the
13 reflector is arranged in the water, a triple corner reflector is formed by including the water surface as a reflection surface. However, it may also be possible, if required, that the reflector forms a single reflecting wall which is arranged in the body of water or on the shore of the body of water such that the reflecting wall and the water surface form a dual comer reflector which back-reflects suitable incident radiation by a reflection on the wall and the water surface in the same direction as the incident radiation.
In the following, especially preferred embodiments of reflectors are described which may be used in the measuring method according to the invention. Fig. 2 shows a first embodiment of a reflector 1, which corresponds to the reflector in the measuring arrangement of Fig. 1. In Fig. 2 and also in Figs. 3 to 7, the reflector is shown at the position in the water used for the measuring procedure, wherein the water surface W
is indicated in a perspective view as a dotted surface. The part of the reflector lying beneath the water surface is drawn as a broken line. In Fig. 2 one can recognise, in particular, the right-angle arrangement of the two reflection surfaces la and lb and the water surface W, which is represented by the three 90 angles. This means that the water surface W and the two portions of reflection surfaces la and lb protruding from the water surface form a corner reflector. Reflector 1 does not comprise any moving parts and reflects, in conjunction with the water surface, a relatively wide angle range allowing it to be observed from various positions in space and in the air.
In order to ensure that a reflector used in the method according to the invention can be observed from several directions, the reflector may be of double-sided construction, wherein such a double-sided construction is shown in the embodiment of Fig. 3. The corner reflector 101 shown there comprises, apart from the rectangular reflection surfaces la and lb which correspond to the reflection surfaces of the reflector in Fig. 2, two further reflection surfaces 1 c and 1 d of which only the rear side is visible in Fig. 3. Reflection surface lc is an elongation of reflection surface lb and is perpendicular to reflection surface la. Reflection surface Id represents an elongation of reflection surface la and is perpendicular to reflection surface lb.
In the following, especially preferred embodiments of reflectors are described which may be used in the measuring method according to the invention. Fig. 2 shows a first embodiment of a reflector 1, which corresponds to the reflector in the measuring arrangement of Fig. 1. In Fig. 2 and also in Figs. 3 to 7, the reflector is shown at the position in the water used for the measuring procedure, wherein the water surface W
is indicated in a perspective view as a dotted surface. The part of the reflector lying beneath the water surface is drawn as a broken line. In Fig. 2 one can recognise, in particular, the right-angle arrangement of the two reflection surfaces la and lb and the water surface W, which is represented by the three 90 angles. This means that the water surface W and the two portions of reflection surfaces la and lb protruding from the water surface form a corner reflector. Reflector 1 does not comprise any moving parts and reflects, in conjunction with the water surface, a relatively wide angle range allowing it to be observed from various positions in space and in the air.
In order to ensure that a reflector used in the method according to the invention can be observed from several directions, the reflector may be of double-sided construction, wherein such a double-sided construction is shown in the embodiment of Fig. 3. The corner reflector 101 shown there comprises, apart from the rectangular reflection surfaces la and lb which correspond to the reflection surfaces of the reflector in Fig. 2, two further reflection surfaces 1 c and 1 d of which only the rear side is visible in Fig. 3. Reflection surface lc is an elongation of reflection surface lb and is perpendicular to reflection surface la. Reflection surface Id represents an elongation of reflection surface la and is perpendicular to reflection surface lb.
14 When performing the measurement according to the invention, this reflector is again arranged in the body of water so as to ensure that all reflection surfaces la to id are perpendicular to the water surface W. With the aid of reflector 101, a retro-reflection is thus achieved from two angular ranges, i.e. from one angular range directed towards the reflection surfaces la and lb, and from one angular range directed towards reflection surfaces lc and ld. Since the reflector of Fig. 2 is suitable for capturing radiation from two sides, this embodiment is particularly suited to the evaluation of radar signals of ascending and descending orbits of polar earth exploration satellites. There is also the possibility, if required, for the rear sides of the respective reflection surfaces la to Id to also be reflective thus forming further reflection surfaces. In this way a reflector is created with four pairs of reflection surfaces which reflects back radiation from substantially all directions.
Fig. 4 shows a further embodiment of a reflector according to the invention which is designated by reference numeral 201. This reflector permits attenuation of horizontal wave movements in the area of reflection surfaces la and lb, said wave movements making it difficult to measure retro-reflected radiation. Attenuation is achieved with the aid of a dielectric water wave screen 4 which is transparent to incident radiation and which is arranged in the shown reflector between edges K of reflection surfaces la and lb. Analogously to reflection surfaces la and lb, the part of the water wave screen 4 lying below the water surface is indicated by broken lines. In a preferred variant, the water screen or wave shield may be formed by a Perspex pane.
Fig. 5 shows a modified embodiment of the reflector of Fig. 4. This wave reflector is designated by reference numeral 301 and substantially corresponds to the construction of the reflector of Fig. 4. However, in the embodiment of Fig. 5, the attenuation of water pressure waves also includes attenuation of water pressure waves which penetrate from below via the opening formed by reflection surfaces la and lb and screen 4. These pressure waves may map themselves on the water surface in the area of reflection surfaces la and lb and may falsify the measuring result.
Attenuation of the pressure waves penetrating from below is achieved, according to Fig. 5, via a lid 5 provided on the top of the reflector with a corresponding opening 6 realised by an opening pipe, whereby an air cavity is formed which allows air to pass slowly only through opening 6. This has the effect of equalising a pressure wave penetrating into the cavity. An undisturbed mean water level is thus created in the 5 reflector which is insensitive against short-term fluctuations of the water line.
Fig. 6 shows a modification of the embodiment of Fig. 5. This reflector designated by reference numeral 401 also permits attenuation of water wave movements in the cavity formed by reflection surfaces la and lb and screen 4. In contrast to the 10 embodiment of Fig. 5, this is achieved here by providing a lid 7 arranged below the water surface with an opening 8 realised via an opening pipe. Due to the small amount of water flowing through opening 8, this reflector also is insensitive against pressure waves penetrating from below resulting in a mean constant water level being formed in the space formed by reflection surfaces la and lb and screen 4.
Some of the previously described different embodiments may be combined in various ways. Fig. 7 shows an exemplary embodiment of a reflector 501 which analogously to the reflector of Fig. 3 comprises four reflection surfaces la to Id extending perpendicularly to each other. Analogously to the embodiment of Fig.
4, the front edges of reflection surfaces la and lb have a transparent screen 4 arranged between them. Furthermore, a lid 5 with opening 6 on the top of the reflector is provided analogously to the embodiment of Fig. 5, and a lid 7 below the water surface with opening 8 is provided analogously to the embodiment in Fig. 6.
Using the embodiment shown in Pig. 7, a particularly good attenuation of wave movements is achieved for the corner reflector formed by reflection surfaces la and lb.
If required, the rear corner reflector formed by reflection surfaces 1 c and 1 d may be formed analogously to the front corner reflector, i.e. it may also comprise a screen 4 and corresponding lids 5 and 7 with openings 6 and 8.
The measuring method described above comprises a number of advantages. In particular, it allows water levels of difficult-to-access bodies of water to be measured without having to provide gauge stations which have to be read locally, whether by humans or electronically. All that is needed is to mount a corresponding reflector in a known position in or at the body of water, and the water level can then be determined via retro-reflection of radiation on the reflector. This can be achieved by radar sensors already in use, in particular satellite-carried radar sensors, with which, given corresponding calibrations, very high distance accuracies can be achieved within a range of just a few centimetres. And a further improvement of accuracy is possible by using a reference corner reflector with accurately measured position. The radar rays which are reflected back by the reflector in or at the water, appear as a bright pixel in the radar image. From the position of this pixel, it is possible to calculate the slant distance between the radar sensor and the angle corner between the reflection surfaces of the reflector and the water surface. The water level can then be derived with great accuracy from the slant distance via the (known) horizontal position of the reflector.
Bibliography [1] Sang-Hoon Hong, Shimon Wdowinski, Sang-Wan Kim: "Small Temporal Baseline Subset (STBAS): A New INSAR Technique for Multi-Temporal Monitoring Wetland's Water Level Changes", IEEE International Geoscience & Remote Sensing Symposium 2008 [2] Hong, S.-H.; Wdowinski, S.; Kim, S.W.: "Evaluation of TerraSAR-X
Observations for Wetland InSAR Application", Geoscience and Remote Sensing, IEEE Transactions on: Accepted for future publication
Fig. 4 shows a further embodiment of a reflector according to the invention which is designated by reference numeral 201. This reflector permits attenuation of horizontal wave movements in the area of reflection surfaces la and lb, said wave movements making it difficult to measure retro-reflected radiation. Attenuation is achieved with the aid of a dielectric water wave screen 4 which is transparent to incident radiation and which is arranged in the shown reflector between edges K of reflection surfaces la and lb. Analogously to reflection surfaces la and lb, the part of the water wave screen 4 lying below the water surface is indicated by broken lines. In a preferred variant, the water screen or wave shield may be formed by a Perspex pane.
Fig. 5 shows a modified embodiment of the reflector of Fig. 4. This wave reflector is designated by reference numeral 301 and substantially corresponds to the construction of the reflector of Fig. 4. However, in the embodiment of Fig. 5, the attenuation of water pressure waves also includes attenuation of water pressure waves which penetrate from below via the opening formed by reflection surfaces la and lb and screen 4. These pressure waves may map themselves on the water surface in the area of reflection surfaces la and lb and may falsify the measuring result.
Attenuation of the pressure waves penetrating from below is achieved, according to Fig. 5, via a lid 5 provided on the top of the reflector with a corresponding opening 6 realised by an opening pipe, whereby an air cavity is formed which allows air to pass slowly only through opening 6. This has the effect of equalising a pressure wave penetrating into the cavity. An undisturbed mean water level is thus created in the 5 reflector which is insensitive against short-term fluctuations of the water line.
Fig. 6 shows a modification of the embodiment of Fig. 5. This reflector designated by reference numeral 401 also permits attenuation of water wave movements in the cavity formed by reflection surfaces la and lb and screen 4. In contrast to the 10 embodiment of Fig. 5, this is achieved here by providing a lid 7 arranged below the water surface with an opening 8 realised via an opening pipe. Due to the small amount of water flowing through opening 8, this reflector also is insensitive against pressure waves penetrating from below resulting in a mean constant water level being formed in the space formed by reflection surfaces la and lb and screen 4.
Some of the previously described different embodiments may be combined in various ways. Fig. 7 shows an exemplary embodiment of a reflector 501 which analogously to the reflector of Fig. 3 comprises four reflection surfaces la to Id extending perpendicularly to each other. Analogously to the embodiment of Fig.
4, the front edges of reflection surfaces la and lb have a transparent screen 4 arranged between them. Furthermore, a lid 5 with opening 6 on the top of the reflector is provided analogously to the embodiment of Fig. 5, and a lid 7 below the water surface with opening 8 is provided analogously to the embodiment in Fig. 6.
Using the embodiment shown in Pig. 7, a particularly good attenuation of wave movements is achieved for the corner reflector formed by reflection surfaces la and lb.
If required, the rear corner reflector formed by reflection surfaces 1 c and 1 d may be formed analogously to the front corner reflector, i.e. it may also comprise a screen 4 and corresponding lids 5 and 7 with openings 6 and 8.
The measuring method described above comprises a number of advantages. In particular, it allows water levels of difficult-to-access bodies of water to be measured without having to provide gauge stations which have to be read locally, whether by humans or electronically. All that is needed is to mount a corresponding reflector in a known position in or at the body of water, and the water level can then be determined via retro-reflection of radiation on the reflector. This can be achieved by radar sensors already in use, in particular satellite-carried radar sensors, with which, given corresponding calibrations, very high distance accuracies can be achieved within a range of just a few centimetres. And a further improvement of accuracy is possible by using a reference corner reflector with accurately measured position. The radar rays which are reflected back by the reflector in or at the water, appear as a bright pixel in the radar image. From the position of this pixel, it is possible to calculate the slant distance between the radar sensor and the angle corner between the reflection surfaces of the reflector and the water surface. The water level can then be derived with great accuracy from the slant distance via the (known) horizontal position of the reflector.
Bibliography [1] Sang-Hoon Hong, Shimon Wdowinski, Sang-Wan Kim: "Small Temporal Baseline Subset (STBAS): A New INSAR Technique for Multi-Temporal Monitoring Wetland's Water Level Changes", IEEE International Geoscience & Remote Sensing Symposium 2008 [2] Hong, S.-H.; Wdowinski, S.; Kim, S.W.: "Evaluation of TerraSAR-X
Observations for Wetland InSAR Application", Geoscience and Remote Sensing, IEEE Transactions on: Accepted for future publication
Claims (19)
1 A method for measuring the water level of a body of water with the aid of a reflector (1, 101, 201, 301, 401, 501) comprising a number of reflection surfaces (1a, 1b) for reflecting electromagnetic radiation within a predetermined wavelength range and which is positioned in or at the body of water such that a corner reflector is formed by the water surface (W) of the body of water and at least one reflection surface (1a, 1b) of the reflector (1, 101, 201, 301, 401, 501), wherein - electromagnetic radiation within the predetermined wavelength range, which is emitted by a radiating device (3) arranged above the body of water, is incident upon the reflector (1, 101, 201, 301, 401, 501) such that the incident radiation is reflected back at the corner reflector based on multiple reflections including the water surface (W);
- a distance between the radiating device (3) and a reflection centre of the corner reflector is measured via the delay time of the emitted and back-reflected radiation, and the water level (W) of the body of water is determined based on this measurement, wherein, when determining the water level of the body of water (W), a three-dimensional position of the radiating device (3) and a two-dimensional position describing the position of the reflector (1) in a top view on the earth surface is taken into consideration.
- a distance between the radiating device (3) and a reflection centre of the corner reflector is measured via the delay time of the emitted and back-reflected radiation, and the water level (W) of the body of water is determined based on this measurement, wherein, when determining the water level of the body of water (W), a three-dimensional position of the radiating device (3) and a two-dimensional position describing the position of the reflector (1) in a top view on the earth surface is taken into consideration.
2. The method according to claim 1, characterised in that the radiation incident upon the reflector (1, 101, 201, 301, 401, 501) is emitted by a radiating device (3) in the form of a radar sensor, and the back-reflected radiation is captured with this radar sensor.
3 the method according to claim 2, characterized in that the radiation incident upon the reflector (1, 101, 201, 301, 401, 501) is emitted by a SAR radar sensor.
4. The method according to any one of claims 1 to 3 characterised in that the radiation is emitted by a radiating device (3) on a moving flying object (2).
5. The method according to claim 4, characterized in that the radiation is emitted by a satellite (2) or an aeroplane or a helicopter.
6. The method according to any one of claims 1 to 5 characterised in that the reflector (1, 101, 201, 301, 401, 501) comprises at least one pair of two reflection surfaces (1a, 1b) forming a right angle, wherein the water surface (W) extends perpendicularly to each reflection surface (1a, 1b) of the at least one pair.
7. The method according to claim 6, characterised in that the reflector (101, 501) provided comprises two pairs of reflection surfaces (1a, 1b, 1c, 1d), wherein the reflection surfaces (1a, 1b, 1c, 1d) of a respective pair extend perpendicularly to each other and the pairs are oriented in different directions.
8. The method according to any one of claims 1 to 7 characterised in that the reflector (201, 301, 401, 501) provided comprises an attenuation device (4, 5, 6, 7, 8) for attenuating water waves of the body of water in the vicinity of the reflector (201, 301, 401, 501).
9. The method according to claim 8, characterised in that the attenuation device (4, 5, 6, 7, 8) comprises one or more screens (4) which are transparent to the electromagnetic radiation in the predetermined wavelength range.
10. The method according to claim 9, as dependent from one of claims 4 and 5, characterised in that a respective screen (4) extends between the reflection surfaces (1a, 1b) of a pair of reflection surfaces.
11. The method according to claim 10 characterised in that the respective screen (4) extends between reflection surface edges (K) which are remote from the right angle formed between the reflection surfaces (1a, 1b) of the pair.
12. The method according to one of claims 8 to 11, characterised in that the attenuation device (4, 5, 6, 7, 8) comprises a cavity with at least one equalising opening (6, 8) or at least one equalising valve, wherein the at least one equalising opening (6, 8) or the at least one equalising valve is provided for the through-flow of air and/or water.
13. The method according to claim 12, characterised in that the at least one equalising opening (6, 8) or the at least one equalising valve is provided in at least one lid (5, 7) closing the cavity.
14. The method according to claim 13, as dependent from any one of claims 7, 8 and 9, characterised in that the cavity is formed by the at least one lid (5, 6), one or more reflection surfaces (1a, 1b) of the reflector (301, 401, 501) and at least one transparent screen (4).
15. The method according to any one of claims 1 to 14 characterised in that a reference corner reflector the reflection surfaces of which do not comprise the water surface (W) of the body of water, is provided at a predetermined reference position in or at the body of water for determining the water level of the body or water, wherein the distance between the radiating device (3) and the reflection centre of the reference corner reflector is measured via the delay time of the radiation emitted by the radiating device (2) and reflected back on the reference corner reflector.
16. A measuring system for measuring the water level of a body of water, comprising:
- a reflector (1, 101, 201, 301, 401, 501) comprising a number of reflection surfaces (1a, 1b) for reflecting electromagnetic radiation within a predetermined wavelength range and arranged in or at the body of water such that a corner reflector is formed by the water surface (W) of the body of water and the one or more reflection surfaces (1a, 1b) of the reflector;
- a radiating device (3) arranged above the body of water for emitting electromagnetic radiation within the predetermined wavelength range such that the emitted radiation is incident upon the reflector (1, 101, 201, 301, 401, 501) whereby the incident radiation is reflected back at the corner reflector based on a multiple reflection including the water surface (W);
- a measuring device for measuring the distance between the radiating device (3) and the reflection centre of the corner reflector via the delay time of the emitted and back-reflected radiation;
- an evaluating device for determining the water level (W) based on the measured distance taking into consideration a three-dimensional position of the radiating device (3) and a two-dimensional position describing the position of the reflector (12) in a top view on the earth surface.
- a reflector (1, 101, 201, 301, 401, 501) comprising a number of reflection surfaces (1a, 1b) for reflecting electromagnetic radiation within a predetermined wavelength range and arranged in or at the body of water such that a corner reflector is formed by the water surface (W) of the body of water and the one or more reflection surfaces (1a, 1b) of the reflector;
- a radiating device (3) arranged above the body of water for emitting electromagnetic radiation within the predetermined wavelength range such that the emitted radiation is incident upon the reflector (1, 101, 201, 301, 401, 501) whereby the incident radiation is reflected back at the corner reflector based on a multiple reflection including the water surface (W);
- a measuring device for measuring the distance between the radiating device (3) and the reflection centre of the corner reflector via the delay time of the emitted and back-reflected radiation;
- an evaluating device for determining the water level (W) based on the measured distance taking into consideration a three-dimensional position of the radiating device (3) and a two-dimensional position describing the position of the reflector (12) in a top view on the earth surface.
17. The measuring system according to claim 16, which is implemented such that using the measuring system a method according to one of claims 2 to 15 can be performed.
18. Use of a reflector comprising one or more reflection surfaces (1a, 1b) for reflecting electromagnetic radiation within a predetermined wavelength range in a method according to one of claims 1 to 15 or in a measuring system according to claim 16 or 17.
19. A reflector for use in a method according to one of claims 1 to 15, comprising one or more reflection surfaces (1a, 1b) for reflecting electromagnetic radiation within a predetermined wavelength range characterised in that the reflector (1) includes at least one of:
an attenuation device (4, 5, 6, 7, 8) for attenuating water waves of the body of water in the vicinity of the reflector (201, 301, 401, 501) and two pairs of reflection surfaces (1a, 1b, 1c, 1d), wherein the reflection surfaces (1a, 1b, 1c, 1d) of each respective pair extend perpendicularly to one another and the pairs are oriented in different directions.
an attenuation device (4, 5, 6, 7, 8) for attenuating water waves of the body of water in the vicinity of the reflector (201, 301, 401, 501) and two pairs of reflection surfaces (1a, 1b, 1c, 1d), wherein the reflection surfaces (1a, 1b, 1c, 1d) of each respective pair extend perpendicularly to one another and the pairs are oriented in different directions.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE201010001440 DE102010001440B4 (en) | 2010-02-01 | 2010-02-01 | Method and measuring system for measuring the water level of a water body |
| DE102010001440.0 | 2010-02-01 | ||
| PCT/EP2011/050372 WO2011092056A2 (en) | 2010-02-01 | 2011-01-13 | Method for measuring the water level of a body of water |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2787896A1 CA2787896A1 (en) | 2011-08-04 |
| CA2787896C true CA2787896C (en) | 2015-07-21 |
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Family Applications (1)
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|---|---|---|---|
| CA2787896A Expired - Fee Related CA2787896C (en) | 2010-02-01 | 2011-01-13 | A method for measuring the water level of a body of water |
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| EP (1) | EP2531822A2 (en) |
| CA (1) | CA2787896C (en) |
| DE (1) | DE102010001440B4 (en) |
| WO (1) | WO2011092056A2 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1401469B1 (en) * | 2010-06-28 | 2013-07-26 | Tele Rilevamento Europa T R E S R L | SYSTEM FOR MEASURING THE MOVEMENT OF SOIL WITH IMAGES USING AT LEAST A REFLECTOR OF ELECTROMAGNETIC WAVES |
| CN105136073B (en) * | 2015-08-14 | 2017-09-12 | 昆明理工大学 | A kind of meteorological calibration model in deformation of slope monitoring |
| CN105182339A (en) * | 2015-09-25 | 2015-12-23 | 昆明理工大学 | Method for correcting environmental influences at slope deformation monitoring on the basis of corner reflector |
| EP3748313A1 (en) | 2019-06-05 | 2020-12-09 | Rosemount Tank Radar AB | Radar level gauging using corner reflector formed by product surface and tank wall |
| CN111983609B (en) * | 2020-07-30 | 2022-02-08 | 中国科学院空天信息创新研究院 | Wet reed extraction method based on radar remote sensing image |
| CN113567981B (en) * | 2021-06-28 | 2023-08-08 | 中国电建集团华东勘测设计研究院有限公司 | Automatic extraction method for flood risk area based on SAR image |
Family Cites Families (10)
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|---|---|---|---|---|
| US3258737A (en) * | 1966-06-28 | Ciavaglia silent underwater beacon | ||
| US2823365A (en) * | 1945-07-18 | 1958-02-11 | Rines Robert Harvey | Electro-acoustic system and method |
| NL91659C (en) * | 1950-05-13 | |||
| AU497632B2 (en) * | 1974-01-03 | 1978-12-21 | Commonwealth Of Australia, The | Ground plane corner reflectors |
| US4184155A (en) * | 1978-09-22 | 1980-01-15 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Radar target for remotely sensing hydrological phenomena |
| US4914734A (en) * | 1989-07-21 | 1990-04-03 | The United States Of America As Represented By The Secretary Of The Air Force | Intensity area correlation addition to terrain radiometric area correlation |
| JP4167784B2 (en) * | 1999-12-20 | 2008-10-22 | トーテックス株式会社 | Corner reflector for radio wave reflection |
| CA2636235C (en) * | 2006-01-03 | 2014-11-25 | Altamira Information, S.L. | Active device for the reception and the emission of electromagnetic waves |
| WO2009144754A1 (en) * | 2008-05-29 | 2009-12-03 | Telespazio S.P.A. | Target detection in a sar-imaged sea area |
| DE102008029771A1 (en) * | 2008-06-25 | 2009-12-31 | Endress + Hauser Gmbh + Co. Kg | Arrangement for level measurement |
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2010
- 2010-02-01 DE DE201010001440 patent/DE102010001440B4/en not_active Expired - Fee Related
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2011
- 2011-01-13 CA CA2787896A patent/CA2787896C/en not_active Expired - Fee Related
- 2011-01-13 WO PCT/EP2011/050372 patent/WO2011092056A2/en active Application Filing
- 2011-01-13 EP EP11701634A patent/EP2531822A2/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| DE102010001440B4 (en) | 2014-01-16 |
| WO2011092056A2 (en) | 2011-08-04 |
| EP2531822A2 (en) | 2012-12-12 |
| CA2787896A1 (en) | 2011-08-04 |
| WO2011092056A3 (en) | 2011-10-13 |
| DE102010001440A1 (en) | 2011-08-04 |
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