Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/002—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow wherein the flow is in an open channel
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
  • G01C11/00—Photogrammetry or videogrammetry, e.g. stereogrammetry; Photographic surveying
  • G01C11/04—Interpretation of pictures
  • G01C11/06—Interpretation of pictures by comparison of two or more pictures of the same area
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/704—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow using marked regions or existing inhomogeneities within the fluid stream, e.g. statistically occurring variations in a fluid parameter
  • G01F1/708—Measuring the time taken to traverse a fixed distance
  • G01F1/7086—Measuring the time taken to traverse a fixed distance using optical detecting arrangements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/704—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow using marked regions or existing inhomogeneities within the fluid stream, e.g. statistically occurring variations in a fluid parameter
  • G01F1/708—Measuring the time taken to traverse a fixed distance
  • G01F1/712—Measuring the time taken to traverse a fixed distance using auto-correlation or cross-correlation detection means

Definitions

• the present invention relates to a method for determining the flow rate of a watercourse by capturing and processing images. This determination or flow measurement is part of a stream monitoring. The invention applies more particularly to the monitoring of moving-bed rivers.
• Patent FR2993683 relates to a method for determining an observation parameter associated with a surface of water by imaging. This method requires the use of a visual medium, such as a water scale, at least partially immersed to determine the height of the water surface at a point in the watercourse. The height of water is determined by capturing and processing images of this visual medium.
• a visual medium such as a water scale
• An object of the invention is to provide a method for determining a flow rate of a stream that does not require any visual support or instrument immersed in the stream.
• An object of the invention is to provide a method for regularly and easily determining the flow rate of moving bed stream, particularly in flood.
• the bit rate is determined by capturing and processing images.
• the flow is calculated by evaluating the volume of water that flows in one second in one or more cross sections (or transects) of the watercourse. The calculated flow is based on flow velocity, stream bottom morphology, and water surface height at this cross-section.
• the invention relates to a method for determining the flow rate through at least one cross section of a watercourse, in particular with a moving bed, said at least one cross section being present in a so-called observation site of the stream, said flow rate determination being carried out by capturing images of the observation site by means of at least one camera, each point of said images having image coordinates in an image repository,
• said method comprising the following steps:
• the conversion model of each camera is generated by the following steps:
• Reference points are, for example, reflective targets distributed evenly over the observation site during the preliminary phase.
• the cartographic coordinates of the reference points are provided by a measurement tool having centimeter accuracy, such as a differential GPS receiver (or DGPS) or a tacheometer.
• a measurement tool having centimeter accuracy such as a differential GPS receiver (or DGPS) or a tacheometer.
• the georeferenced digital terrain model is generated by stereo-photogrammetry according to the following steps:
• the digital terrain model of the observation site is not generated from images captured by the cameras of the observation site.
• the digital terrain model (DTM) is generated by stereo-photogrammetry from images having a better resolution, for example from images (or photos) captured using a digital camera. by an operator.
• the georeferenced digital terrain model is generated by stereo- photogrammetry according to the following steps:
• a digital terrain model of the observation site by stereo- photogrammetry from images of the observation site captured by a capture device, such as a digital camera, said images from the capture device having a higher resolution than the images from the cameras of the observation site, said captured images further comprising reference points whose cartographic coordinates are predetermined, and
• the flow velocity in the water columns at said cross section is determined by a particle image velocimetry technique or PIV (for Particle Image Velocimetry in the Anglo-Saxon literature) applied to tracers, such as scum and / or wavelets present on the surface of the water to determine the surface flow velocity in the captured images and then determine the flow velocity in the water columns at said cross-section by applying a predetermined pattern to the surface flow rates.
• PIV for Particle Image Velocimetry in the Anglo-Saxon literature
• tracers such as scum and / or wavelets present on the surface of the water to determine the surface flow velocity in the captured images and then determine the flow velocity in the water columns at said cross-section by applying a predetermined pattern to the surface flow rates.
• This predetermined model is for example an empirical model configured with in situ measurements.
• the height of the water surface is determined by the following steps:
• the water zone is detected in the images by detection of the moving zones in the images.
• the method advantageously comprises an additional step of detecting the zones of vegetation in the images, said zones of vegetation being deduced from the moving zones to form the zone in water.
• the detected water zone is then more reliable.
• the water zone is detected in the images by calculating the variance and the average brightness of the pixels of the images, the water zone corresponding to the pixels whose average variance and brightness are greater than thresholds. predefined.
• the invention also relates to a method relating solely to determining the height of the water surface at a cross section (or transect) of the watercourse.
• the invention also relates to a method for determining the height of the water surface at at least one cross section of a watercourse, said cross section being present in a site called observation of the watercourse, said height determination being carried out by capturing images of the observation site by means of at least one camera, each point of said images having image coordinates in an image reference,
• a so-called conversion model for converting the image coordinates of points in the images provided by the camera into cartographic coordinates in a cartographic frame and, conversely, for converting the map coordinates of points into image coordinates in the image repository of the camera, • measurement of the topography of the observation site during the low water period, preferably when the watercourse is dry, so as to generate a georeferenced numerical land model of the observation site whose points are referenced in a cartographic landmark
• FIG. 1 is a schematic view of a cross section of a watercourse through which is measured the flow of the watercourse
• FIG. 2 is a flowchart showing the steps of the method of the invention, and FIGS. 3a and 3b illustrate the conversion model;
• the invention will be described in the context in determining the flow rate of a stream from images captured by cameras placed on the deck of a bridge spanning said stream.
• the cameras used are for example cameras usually used for surveillance applications.
• the flow rate is calculated by evaluating the volume of water that flows in one second in one or more transverse sections S of a stream C as shown in FIG. 1.
• the calculated flow is based on the flow velocity, the morphology of the watercourse bottom and the height of the water surface at this cross-section.
• Figure 2 is a diagram summarizing the steps of the method of the invention. It comprises five steps referenced E1 to E5. Steps E1 and E2 are carried out during a preliminary so-called georeferencing phase and steps E3 to E5 are carried out during a phase of observation (or monitoring) of the watercourse.
• the method comprises the following steps:
• step E1 determining a conversion model for each camera of the site
• step E2 measurement of the topography of the observation site during the low water period
• step E3 determination of the height of the water surface at each cross-section
• step E4 determination of the flow rate of water columns at each cross-section
• step E5 determination of the flow of water through each cross section.
• the calculations carried out in steps E3 to E5 are carried out in the image reference frames of the cameras installed on the observation site.
• Step El Determining a conversion model for each camera on the site
• the cartographic coordinates of the temporary reference points (provided by the geodesic measurement tool) and the image coordinates of these temporary reference points in the image repository of each of the images provided by the cameras are then available. According to the invention, it is then possible for each of the cameras to deduce a conversion model making it possible to convert the image coordinates of the image points in the image reference frame of the camera into cartographic coordinates in a cartographic reference frame. This model makes it possible to determine the footprint of each pixel of image.
• FIGS. 3a to 3b The conversion model generated is illustrated by FIGS. 3a to 3b.
• FIG. 3a is an image of the observation site displayed in the image frame of a camera and
• FIG. 3b represents the same image projected in a cartographic frame by application of the conversion model to the image of FIG. 3a.
• Step E2 measurement of the topography of the observation site during the low water period
• the topography of the observation site is measured during low-water periods, preferably when the watercourse is dry.
• This step aims to generate a digital terrain module or MN.
• This step is performed by stereo-photogrammetry. This technique is based on the principle of stereoscopic vision. Two images of the same object acquired from different points of view make it possible to reconstruct the three-dimensional geometry of this object. Images are correlated to search for peer points. The measurement of the offset between these homologous points makes it possible to calculate their position in three dimensions. The result obtained is then a cloud of points which is then interpolated to obtain a digital model of terrain.
• the images used for stereo-photogrammetry include reference points, temporary or otherwise, whose cartographic coordinates are known. These points are for example those already used for the generation of the conversion model. These are, for example, images captured by the cameras mounted on the deck of the bridge.
• a digital terrain model of the observation site is first generated by stereo-photogrammetry from images captured by the cameras of the bridge. Then, the generated DEM is georeferenced by relating the coordinates of the reference points in the relative coordinate system with the map coordinates of said reference points.
• the images used for this step are generated by a digital camera having a higher resolution than the cameras, for example of the order of at least 10 Megapixels.
• X photos (or images) every N meters are for example captured by an operator moving along the bridge. These X photos are preferably taken with different viewing angles (in the vertical plane) so as to cover an extended area upstream of the bridge.
• a DTM is initially calculated, in a relative reference, by stereo-photogrammetry from the images captured by the digital camera. This DTM is then georeferenced by relating the coordinates of the reference points in the relative coordinate system with the map coordinates of said reference points.
• Step E3 Measuring the height of the water surface This step can be performed, at least partially, in parallel with the step E4 for measuring the flow velocity.
• the height of the water surface is substantially the same along the cross section.
• the height of the water surface is defined as the value of the coordinate z in an orthonormal frame ( ⁇ , ⁇ , ⁇ , ⁇ ).
• the height of water is determined as follows: - extraction of the water zone in the images captured by the cameras;
• the water surface height at the cross-section then corresponds to the highest point of the image DTM for this section.
• the extraction of the zone in water can be carried out in different ways.
• the water zone corresponds to the moving zones in the filmed image sequence.
• This moving area is determined by calculating the PIV velocity field for the images captured by the cameras as described below for step E4 for measuring the velocity of flow.
• This moving area corresponds to the image points whose velocity vector is non-zero.
• the vegetation zones are excluded from the water zone.
• the vegetation zones are detected on the basis of radiometric criteria, and in particular their color (green).
• the detection of the water zone can be calculated by calculating the variance of the value of the pixels and their average brightness over several consecutive images. These two parameters, combined together, form an index of presence of water. The higher these parameters are, the higher the probability of water presence. Subsequently, an automatic thresholding technique is used to generate a bit mask. This mask is processed again to remove isolated points and noise.
• the water zone is detected in the images, it is superimposed on the image DEM. Only the portion of the DTM corresponding to the water zone is conserved and, as indicated above, the height of the water surface of the river then corresponds, for a given cross section of the DTM, to the highest point of this section. of the DTM.
• Step E4 Measuring the flow rate
• This step is performed on the same images as those for which the water height was calculated.
• the flow velocity of the water columns at the cross-section is calculated in two stages: firstly, the velocity of the surface water is calculated at the cross-sectional level, then, in a second step, the flow rate of the entire water column is calculated.
• the PIV method is an optical method for measuring the instantaneous velocity of a fluid. This method is usually used in the laboratory.
• the fluid whose speed is measured is seeded with particles passives called tracers that follow the dynamics of the flow.
• the fluid as well as the particles are illuminated by a laser so that the particles are visible. Since the stream is imaged at high frequency, it is possible, thanks to correlation algorithms, to follow a particle on two consecutive images. It is therefore the movement of the particles that makes it possible to calculate the velocity field of the studied flow. In this case, it is proposed to use the spray, scum or wavelets present on the surface of the water as tracers.
• the PIV software looks for similar image portions (or correlation windows) in an image portion called the search window (more extensive than the correlation window).
• the similarity criterion is defined statistically.
• the shift between the two correlation windows of two successive images is in fact the measure of the spatial shift that has occurred between the two images. Knowing the time interval between the two images (1/25 second), we get a speed. This process is performed for each plotter of the image (a correlation window is defined around each point of the image) and allows to reconstruct the speed field.
• This method applied to the images of the observation site makes it possible to obtain a velocity vector field for all the tracers and, by interpolation, for all the points of each of the images.
• the vector field which is expressed in pixels per second (pixels / s)
• the passage in a cartographic reference frame using the conversion model defined in step E1 makes it possible to obtain velocity vectors expressed in meters per second (m / s) and makes it possible to correct the distortions generated by the inclination of the camera.
• the speed measured by the PIV method is a speed of the surface flow.
• step E3 The water height calculated in step E3 is also provided to the model to calculate velocities over the entire water column between the bottom (zero velocity) and the surface (highest velocity).
• Step E5 Flow calculation
• the flow of water through one or more cross section (s) of the river is calculated from: the flow velocity in the water columns present along the cross-section, - the height of the water surface at this cross-section, and
• the flow is calculated on 3 cross sections of the river and the flow rate is the average flow so as to reduce the uncertainties on the measurements.
• the invention also relates to the method for determining the water surface height as such as defined in step E3.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Image Processing (AREA)
• Instructional Devices (AREA)
• Measuring Volume Flow (AREA)

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• 2016
  • 2016-05-27 FR FR1654777A patent/FR3051901A1/fr active Pending
  • 2016-07-01 FR FR1656289A patent/FR3051902B1/fr not_active Expired - Fee Related
• 2017
  • 2017-05-24 WO PCT/FR2017/051298 patent/WO2017203179A1/fr unknown
  • 2017-05-24 EP EP17732506.5A patent/EP3465100A1/de not_active Withdrawn
  • 2017-05-24 CA CA3025944A patent/CA3025944A1/fr not_active Abandoned
  • 2017-05-24 CN CN201780045543.7A patent/CN109564118A/zh active Pending
  • 2017-05-24 JP JP2018562199A patent/JP2019522185A/ja active Pending

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