Patent Description:
More specifically, the present invention relates to a non-invasive method and device with a microwave antenna that is flown over the river or open channel, or flowing water in an underground pipe or channel.

Non-invasive methods for measuring the flow velocity of water in a river or fluid in an open channel or sewer, i.e. methods wherein there is no contact between the measuring apparatus and the fluid, are becoming more and more popular. Among the techniques used to measure the fluid velocity in a non-invasive way we can find acoustic methods, optical methods, laser methods and microwave methods, the last one being the most popular.

Velocity profiling to measure the fluid velocity of a river or channel has been used for very long time. A first method consists of a velocity sensor attached to a wading rod which is moved through the cross section of a river or channel by an operator. When the water level and/or water velocity is too high to safely make the profiling by an operator, the velocity sensor can be attached to a cable crane system for rivers that is spanned across the river or channel. Those methods are very time consuming and very expensive. When the cable crane system for rivers is used, it is a stationary application that can only be used at one particular site, and can't be used when heavy floating debris are carried by the river.

More recently ADCP (Acoustic Doppler Current Profiler) have been used to measure the flow rate from rivers or open channels. ADPC's are placed on a small boat or floating device that is tethered by an operator from a bridge or by a cable crane system for rivers. Those methods have the drawbacks that they are time consuming and that they can't be used when the river or channel are carrying floating parts and devices and when the rivers and channels are flooded.

In order to overcome this problem recently non-invasive devices have been used, mainly microwave radar devices that are carried by an operator from a bridge, making a surface velocity profile. This method has the drawbacks of being time consuming and has the problem that bridge piers are creating flow disturbances both ways upstream and downstream especially when the piers are collecting floating debris carried by the river or channel.

Non-contact devices have been carried by cable crane system for rivers as well, but this method has the drawback that the stability of the cable crane system for rivers is not good enough for making accurate measurements. Additionally cable crane system for rivers remain very expensive and inflexible.

Hydrologists have been trying to use drones carrying non-contact velocity measuring devices without gathering perfect results as those velocity measuring devices were not specifically built to be carried by drones.

In this respect, the document <CIT> discloses an unmanned aerial vehicle for measuring a fluid parameter of a fluid flowing in a channel.

The document <CIT> discloses a system for gathering information useful to derive velocity of a free surface liquid flow wherein the system is incorporated in a helicopter.

The document <CIT> discloses a method for measuring velocity and depth of fluid flow in a channel including transmitting directed energy comprising a single energy beam slant-wise toward the surface of the fluid, the single beam allows to reduce the inaccuracies when computing the bulk flow.

The present invention aims to provide an improved non-invasive method and device to measure the flow rate of a river, open channel or fluid flowing in an underground pipe or channel when for the last one the access to the measuring site by an operator is difficult, impossible or dangerous, or simply that complicated confined space entry needs to be avoided.

A special non-invasive flow velocity device is mounted on a drone that is precisely flown over the fluid surface to be measured, gathering the velocity readings. The velocity information is associated with the shape and level measurement to calculate the wet area and by using the continuity equation Q = V * A the flow rate is calculated.

The preferred non-invasive velocity measuring device is the microwave Radar device, but it could be any other suitable non-invasive velocity measuring technology. Drones are handy to use but induce signals, noise and errors on the measurements.

The microwave measuring devices uses the Doppler shift frequency to measure the velocity of the water surface such as laser or non-contact acoustic devices. The vibrations induced by the flying drone induce frequency peaks that need to be eliminated using (an) on-board vibration sensor(s) to detect them. In order to reduce the overall vibrations induced by the flying drone which increase the overall noise level reducing the signal to noise ratio, an anti-vibration suspension device can be used. Pitch, roll and yaw of the drone influence the measurement as well, and need to be measured with an angle sensors for accurate velocity measurements. GPS and altitude measurements might be useful but are not mandatory as drones can be setup to fly precise routes with high accuracy. A wind measuring device, preferably a non-moving part <NUM> or <NUM> axis measuring device can be used to compensate for the wind influence, but those additional measurements are useful only when the water velocity is relatively slow.

More specifically, the present invention relates to a non-invasive microwave measuring device for calculating the flow rate of a fluid, the device comprising :.

According to preferred embodiments of the invention, the device is further limited by one of the following features or by a suitable combination thereof:.

The present invention also relates to a non-invasive method for measuring velocity measurement and distribution of a fluid flowing through a pipe or channel or in a river or open channel, the method using a non-invasive microwave fluid velocity measuring device suspended to a drone and comprising at least one vibration sensor, said method comprising the steps of :.

According to preferred embodiments of the invention, the method is further limited by one of the following steps or by a suitable combination thereof:.

The invention relates to a non-invasive method and device for profiling the surface velocity of a river, open channel or underground conduit that is difficult, dangerous or impossible to access by an operator. The equipment (<NUM>) comprises a drone (<NUM>) carrying a non-invasive velocity measuring device, preferably a microwave Radar device (<NUM>). This device is suspended to the drone with a suspension system (<NUM>) that drastically reduces any vibrations generated by the drone (<NUM>). The drone is piloted by an operator from the riverbank or side of an open channel or from a bridge or from distance over Internet or Satellite control or in autopilot mode. The drone can be flown far enough from piers that can induce flow disturbances. To measure the flow rate of underground conduits (<NUM>), the drone can be piloted through an inspection manhole or other access to be flown over the fluid surface to be measured.

The drone is preferably flown at a specific constant distance over the fluid surface, so that it won't be hit by floating debris carried by the fluid. The distance can be anything from close to <NUM> to several meters depending on the application and the floating debris.

An additional distance measuring device (<NUM>) could be carried by the drone as well, but usually the accuracy of the GPS and altimeter from the drone is good enough to position the drone exactly over the fluid surface. The GPS coordinates and altitude could be gathered from the drone (<NUM>) by the measuring device (<NUM>) associated to the non-invasive velocity measuring device (<NUM>) over an appropriate communication link or could be generated by an optional GPS receiver and altimeter included in the measuring device (<NUM>) associated to the non-invasive velocity measuring device (<NUM>). Modern drones usually can fly accurately at predefined positions which can be repeated over time, avoiding handling the GPS and altimeter data. Over the appropriate communication link or over any suitable command, the device (<NUM>) can indicate to the drone (<NUM>) that the measurement of a defined spot of the fluid surface is terminated and that the drone (<NUM>) can fly to the next defined measuring spot.

Optionally a wind speed and direction device (<NUM>) can be used to validate the velocity data or correct them if necessary. Wind velocity information is usually interesting only when the water surface velocity is slow.

<FIG> shows the drone (<NUM>) with the velocity measuring device (<NUM>) with is attached to the drone using a special suspension device (<NUM>). The length of the suspension legs (<NUM>) can be of equal length as shown in <FIG> or can have different length as shown in <FIG> where the front legs are shorter than the back legs in order to automatically give an angle for the measuring device compared to the water surface and horizontal plane of the drone.

<FIG> shows a detailed view of the suspension system which is made out of lightweight rigid and robust tubed and rods. Usually carbon fibre tubes and rods are preferred. Three or more tubes (<NUM>) can be used. They are firmly attached using a mechanical structure made out of roads (<NUM>). Within the tubes (<NUM>) elastic ropes (<NUM>) are used in order to suspend the measuring device (<NUM>). The elastic ropes are fixed at the upper end to the suspension system which is attached to the drone (<NUM>). At the lower end the ropes (<NUM>) are free from the tubes (<NUM>) and slightly longer than the tubes. The measuring device will be attached to the elastic ropes. The elasticity of the ropes will be chosen so that the undesired vibrations are absorbed and that the vertical movements remain insignificant.

<FIG> shows a detailed view of an alternate suspension system using a lightweight rigid upper plate (<NUM>) which is attached to the drone and a lower lightweight rigid plate (<NUM>) which is attached to the non-invasive measuring device (<NUM>), both plates (<NUM>) and (<NUM>) are connected with silent block types dampers (<NUM>) having the requested elasticity and suspension characteristics for the application.

It is important that the measuring device used to be carried by drones has specific additional features allowing precise measurements. Among those features angle sensors and vibration sensors are required.

Despite the elastic suspension system, mechanical vibrations can be induced by the propellers of the drone (<NUM>). Those vibrations are usually at stable frequency which can be interpreted by the measuring system as a Doppler shift frequency representing a velocity measurement that should be discarded, as explained in more details below. The water velocity spectrum is based on the microwave signal returned by the flowing water with a Doppler frequency shift proportional to the water velocity. The microwave radar system can use a horn antenna or patch or patch array antenna.

<FIG> shows the microwave measuring device (<NUM>) suspended to the drone (<NUM>) sending a microwave signal (<NUM>) out to the water surface (<NUM>), said water surface reflecting a return signal (<NUM>).

Preferred steps for converting a velocity spectrum into a fluid surface velocity are described in the document <CIT>. They are the following. Each reflected pulse generates a measurement data. The number of reflected pulses in a sequence of measurements will generate a number of discrete data expressed in amplitude as a function of time. The spectrum of data expressed in the temporal domain is transformed into a frequency domain via a discrete Fourier transform (DFT), and preferably, a fast Fourier transform (FFT). Then a Gaussian curve is fitted on the spectrum of discrete data expressed in the frequency domain and the parameters of the Gaussian curve, namely the mean µ and the standard deviation σ respectively represent the measured velocity and the velocity distribution.

In <FIG>, the velocity spectrum with its fitted Gaussian curve (<NUM>) is illustrated, but the signal resulting from the vibration induced by the propellers (<NUM>) is also represented. The Doppler frequency analysis cannot differentiate the signal generated by the vibration and the signal generated by the flowing fluid, both are received as velocity signals and the microprocessor cannot decide which signal to take and will jump between both signals. If the measuring device is equipped with one or more vibration sensor(s) as in the present invention, a correction can be applied to the result. Indeed, vibration sensor is able to identify and eliminate false velocity readings induced by the drone (<NUM>) (linked to the vibration induced by the propellers). Such mechanical vibrations can be interpreted as velocity reading(s) (<NUM>) being more energetic than the real velocity measurement (<NUM>) as shown in <FIG>. This/those sensor(s) will only detect the mechanical vibrations and only the doted Gaussian curve will appear on the analyses from the vibration sensor(s). The same signal analysis approach is taken. Each sample generates a measurement data. The number of samples in a sequence of measurements will generate a number of discrete data expressed in amplitude as a function of time. The spectrum of data expressed in the temporal domain is transformed into a frequency domain via a discrete Fourier transform (DFT), and preferably, a fast Fourier transform (FFT). Then a Gaussian curve is fitted on the spectrum of discrete data expressed in the frequency domain and the parameters of the Gaussian curve, namely the mean µ and the standard deviation σ represent the measured vibration induced velocity and the vibration induced velocity distribution. Having the sole µ and σ from the vibration signal, it can easily mathematically be removed from the combined signal (named also "global signal" in the present invention), leaving the sole fluid velocity information (<NUM>).

The drone is an unmanned aerial vehicle that will have its Pitch, Roll and Yaw when moving or staying over the fluid surface as shown in <FIG>.

As shown in <FIG>, the Pitch will modify the elevation angle α from the microwave measuring device suspended, and this angle α has a direct influence on the resulting calculation of the horizontal fluid velocity as the measured velocity needs to be divided by the cosine of that angle α. It is very important that a microwave measuring device carried by a drone is equipped with an adequate measuring device for the Pitch angle as it changes with wind speed and direction. The Roll and Yaw are less important as the Roll doesn't directly influence the measuring result of the fluid velocity, but only slightly shifts the position of the illuminated section of the fluid surface. The Yaw influences directly the measured fluid velocity but the Yaw angle remains usually small and the correction remains small.

<FIG> shows the influence of the Yaw. When the microwave beam is not parallel with the Fluid Flow Direction FFD arrow but has an angle B, the measured velocity needs to be divided by the cosine of the Yaw angle B.

<FIG> shows an example of a river section that needs to be measured. The shape of the riverbed (<NUM>) has been measured and is stored in the measuring device. The water level combined to the riverbed shape allows to calculate the total width of the surface from the wetted section W, traverse distance from one riverbank to the other. This total width W is divided in a number n of sections having the same width wa, wb,. Each area is calculated for each section A, B, C. In the example shown in <FIG>, section A will be considered as a triangle, section B, C, E, & F will be considered as a trapeze, section D as a sum of two trapezes and section G as the sum of a trapeze and a triangle.

The device (<NUM>) (drone (<NUM>) and non-invasive microwave measuring device (<NUM>)) is piloted in the way that the microwave beam illuminates the centre part of each section A, B, C. N, driving the device at distance da, db, dc. dn from one riverbank.

An alternate method would be to determine sections A, B, C. N having the same area instead of the same width, and pilot the device (<NUM>) in the position to illuminate the centre part of each section of equal area with the microwave beam.

<FIG> shows the influence that a constant Roll angle would have on the device (<NUM>) position, (distance da, db, dc,. dn) to illuminate the centre part of each section with the microwave beam (constant Roll angle due to a constant wind speed and direction).

<FIG> shows the influence that a changing Roll angle would have on the device (<NUM>) position, (distance da, db, dc,. dn) to illuminate the centre part of each section with the microwave beam (changing Roll angle due to a changing wind speed and direction).

The flowrate for each section N can be calculated following the continuity equation QN = Vavg N * AN ; were QN is the flowrate from section N, Vavg N is the average velocity in the section N and AN is the area from section N. The average velocity of section N, Vavg N can be calculated from the measured surface velocity in the section N, Vmeas. N multiplied by the correction factor of section N, KN.

The correction factor KN from section N, is determined using the width wn of the section N, the average fluid depth in section N and a mathematical model computing those data to calculate the correction factor KN.

To total river flowrate is the sum of all individual flowrates in each section: QTOT = QA + QB + QC +.

An alternate method is described in <FIG> and consists in moving the device (<NUM>) (drone (<NUM>) with non-invasive microwave measuring system (<NUM>)) at constant speed over the hole width W of the river from one riverbank to the other. The speed of the device (<NUM>) in meter per second divided by the time taken for a full measurement sequence gives the distance d in meter. The area under this distance d (A, B, C,. N) can be calculated knowing the shape of the riverbed and the water level.

The flowrate for each section N can be calculated following the continuity equation QN = Vavg N * AN ; were QN is the flowrate from section N, Vavg N is the average velocity in the section N and AN is the area from section N.

The average velocity of section N, Vavg N can be calculated from the measured surface velocity in the section N, Vmeas. N multiplied by the correction factor of section N, KN.

The correction factor KN from section N, is determined using the width d of the section N, the average fluid depth in section N and a mathematical model computing those data to calculate the correction factor KN.

The total river flowrate is the sum of all individual flowrates in each section: QTOT = QA + QB + QC +.

<FIG> & <FIG> are showing the application when the device (<NUM>) (drone (<NUM>) & non-invasive microwave measuring device (<NUM>)) is used in underground channels or pipes (<NUM>). Depending on the hydraulic conditions and especially the water level, the device can be piloted to make several individual measurements in individual sections (A, B, C,. N) of equal width d or take one measurement in the centre of the conduit over a width D.

If the measurement is taken over individual sections, the flowrate for each section N can be calculated following the continuity equation QN = Vavg N * AN ; were QN is the flowrate from section N, Vavg N is the average velocity in the section N and AN is the area from section N.

To total flowrate in the channel is the sum of all individual flowrates in each section: QTOT = QA + QB + QC +.

If only one measurement is taken in the centre of the channel, the Vmeas over the distance D is taken and multiplied by a correction factor K to determine Vavg.

The correction factor K is determined using the shape and dimension of the channel, the water depth and the velocity distribution represented by σ. A mathematical model computes those data and calculates the correction factor K. * A, where Q is the flowrate, Vavg. is the average velocity in the wetted area and A is the surface from the wetted area.

In underground channels the drone (<NUM>) will be equipped with camera and light to facilitate the pilotage.

Claim 1:
A non-invasive microwave measuring device (<NUM>) for calculating the flow rate of a fluid, the device (<NUM>) comprising:
- a non-invasive microwave fluid velocity measuring device (<NUM>) comprising a patch antenna or horn antenna to generate a microwave signal (<NUM>) that is transmitted at a specific elevation angle α towards the fluid surface (<NUM>) and to receive the reflected microwave signal (<NUM>) from the fluid surface (<NUM>) with a doppler shift frequency, or any other non-invasive fluid velocity measuring device such as laser, optical, acoustic or other;
- a drone (<NUM>) to which is suspended the measuring device (<NUM>) characterized in that it is suspended via a suspension system (<NUM>),
said suspension system (<NUM>) eliminating vibration noise generated by the drone (<NUM>);
and in that the non-invasive microwave measuring device (<NUM>) further comprises:
- at least one vibration sensor to identify and eliminate false velocity readings induced by the drone (<NUM>);
- at least one angle sensor to compensate for Pitch, Roll and Yaw from the drone (<NUM>) that influence the fluid surface velocity measurement and determine the final angle from the measuring device (<NUM>) towards the fluid surface (<NUM>).