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Home , Volumetric flow rate

An Innovative Image Processing Method for in Open Channels and

I.Hansen1, R. Warriar1, C. Satzger1, M. Sattler1, B. Luethi2, S. Peña-Haro2, R. Duester1 1SEBA Hydrometrie GmbH & Co. KG, Gewerbestr. 61A, 87600 Kaufbeuren, Germany 2Photrack AG, Ankerstr. 16a, 8004 Zurich, Switzerland Contact: Dr. Issa Hansen e-mail: [email protected] Phone: +49 (0) 834196480 Fax: +49 (0) 8341964848

ABSTRACT The DischargeKeeper is a completely new The parameter, also known as method for the continuous acquisition and the volumetric flow rate of a fluid, is storage of flow velocity profile, water level defined as the water passing over and flow rate of natural water , the cross-section per unit time. The irrigation and waste water channels. The discharge is one of the most important but DischargeKeeper consists of an IP- also the most demanding parameters camera, an infrared beamer, and a within the fields of hydrology and processing unit with remote data . There are many different transmission. The surface velocity profile systems available for measuring these is measured by means of an optical variables, however most of them are method for capturing the flow velocity. The intrusive (i.e. must be located within the water level detection is carried out ). There are some other systems simultaneously by an image processing that are non-intrusive, but they are technique. Subsequently, the discharge is constrained in their relative orientation with calculated directly on site. The equipment respect to the water surface (e.g. radar was tested at several sites and under systems). Image processing methods are different weather and light conditions. The a revolutionary measuring technique and validation of the DischargeKeeper was possess certain clear advantages since carried out by comparing the flow there is no need for expensive determined by the newly developed installations. Furthermore, they offer more gauge, against the flow measured by a flexibility than other non-intrusive reference gauge. The correlation between measurements systems. the measurements carried out by the camera-based system and by the SEBA Hydrometrie GmbH & Co. KG and reference gauge was highly satisfactory. Photrack AG have developed a new camera-based gauge for both water level and flow velocity detection, which is called Keywords: image processing, flow “DischargeKeeper”. measurement, water level, non-intrusive measurement, velocity measurement

1 INTRODUCTION the camera system of HydroPix The quantitative monitoring of water Monitoring, which is installed in a closed resources and hydraulic constructions sewer system having the advantage that includes the detection of basic hydraulic light conditions are stable without any day parameters, among other things. These and night time changes and that electrical are: the wet cross-section, the flow connection is available (Nguyen, velocity and the discharge. 2009). Further optical gauge system is the GaugeCam, which is designed for open The flow monitoring has an increasing channels and tested in the laboratory and importance in many areas of the world, at one site and proposes the usage of especially for risk management infrared light for night applications systems under the consideration of the (www.gaugecam.com). The GaugeKeeper, potential influence of climate change and a product of SEBA Hydrometrie GmbH & the reduction of natural meadows Co. KG, is further example for optical caused by human activities. “ have water level detection (Hasan et al, 2016) the greatest damage potential of all natural and (Hies et al., 2012). Other applications disasters worldwide and affect the greatest for both water level and velocity detection number of people” (unsidr, 2002). like RiverBoard (www.tenevia.com) use Therefore, an effective and timely server based image processing which monitoring of flow rates is a very crucial allow to connect different camera factor of quantitative hydrology and water technologies but require available and resources management. stable internet connections for real-time Monitoring of can be carried processing. Common optical systems for out by different methods. Rating curves, flow velocity detection require visible radar sensors and ultrasonic techniques objects (e.g. leaves or artificial tracers) on are some of the most applied methods the water surface for velocity detection. providing accurate and reliable data The aim of the present is to develop acquisition for discharge measurement or a new effective method for a continuous estimation. A disadvantage of these contactless water level, velocity and methods is the regular inspection of the discharge measurements by means of one site required due to environmental equipment. The developed non-intrusive changes, as most of them are intrusive equipment has to be in operation even systems. Optical methods for water level under critical conditions like floods and measurement have been investigated hydraulic jumps, under which other more widely in the recent years. A localized gauging methods could be significant example of water level temporal out of operation or not sufficiently detecting based on image processing is representative. Furthermore, the 2 developed method should be applicable The calibration of the DischargeKeeper independently of the presence of visible requires some input parameters. These particles on the water surface. The image are: the cross-section of the river/, processing and, as a result, the obtaining the positions of at least four reference of the discharge data should occur on site. points on the far shore of the river/channel and the position of the water line, METHODS which is equivalent to the initial water level SEBA Hydrometrie GmbH & Co. KG and (see figure 2). This position of the water Photrack AG have developed a new line and the reference points are only camera-based gauge for the continuous needed when setting up a site. acquisition and storage of flow velocity profiles, water levels and flow rates in The reference points can be placed rivers, water channels and waste water anywhere, as long as they are in the channels. The completely new method is camera field of vision. The x, y, z called “DischargeKeeper”, which consists coodinates of such reference points have of an IP-camera, an infrared beamer, and to be given to the DischargeKeeper. a measuring transducer with remote data The hydraulic input parameters (velocity transmission (see figure 1). The detection and water level) can be optically detected. algorithm is running in real-time on the Subsequently, the discharge is calculated device to provide on-site measurement 3 1 and evaluation. The measuring process directly on site ( Q=v · A m s ). including recording image streams takes about forty seconds. This enables very short measuring intervals (e.g. every minute). In addition to the digitized measured values, proof images are stored and can be transmitted to an FTP server via GPRS.

Infrared Radiator Camera Figure 2: Schematic overview of the geometrical input parameters required for the calibration of the DischargeKeeper

The surface velocity profile is measured by means of an optical method (based on the cross correlation technique) for capturing

Figure 1: Hardware components of the DischargeKeeper the flow velocity. The applied optical for a typical measuring site method for velocity measurements is

3 based on the well-established Particle Image Velocimetry (PIV) technique (Adrian, 1991), which is also known of being successfully applied to large scale free surface flows of or open channels, also known as Large Scale PIV (LSPIV).

The water level detection is carried out simultaneously by an image processing technique. For the estimation of the water level several optical methods are available.

A new approach (patent pending) for water level detection was developed to separate the moving water from the rest of the image using a sequence of images. The vertical velocity profile is obtained employing a roughness dependent mixing length model (Absi, 2006) (see figure 3).

The validation of the DischargeKeeper was carried out by comparing the flow determined by the newly developed gauge, against the flow measured by a moving boat ADCP-System (Acoustic Doppler Current Profiler) as well as the Figure 3: Overview of some measuring steps: optical detection of the surface velocity, mean velocity and discharge values, which are derived from model-based vertical velocity profile calculation a rating curve.

The developed method is also applicable RESULTS AND DISCUSSION using a mobile device App for Small Open- The developed optical gauge was tested Channel Flow Measurement (Lüthi et al., at several sites in Europe in the hydrology 2014 and Peña-Haro et al., 2015). and waste water sectors. The main validation process of the developed system was done based on the example of the site Thalhofen, which is located in Bavaria/Germany on the Wertach River (see figure 4). The green arrows on the 4 image are the optically detected velocity In addition, the DischargeKeepers’ vectors on the water surface and the red measurements were compared with rating line is corresponding with the optically curve values (see figures 6 and 7). The detected water level. discharge values derived from the rating curve are estimated according to the water level measurements by a floater. Therefore, some deviations were expected.

Discharge: Comparison DischargeKeeper vs Rating curve DK discharge [m³/s] wwa discharge [m³/s]

Figure 4: DischargeKeeper’s site on the Wertach River

The correlation between the Date measurements carried out by the camera- based system and by the reference gauge Figure 6: Comparison between the discharge values of was highly satisfactory. The deviation the DischargeKeeper and the rating curve between the DischargeKeeper and the ADCP measurements was less than 5% at The comparison between the rating curve 40% of the carried out measurements (in and the DischargeKeeper discharge data total 11 comparative measurements). A is made to roughly check the plausibility of deviation of less than 10% and less than the data collected by DischargeKeeper. 15% was achieved at 60% and 80% of the The behaviour of both curves was almost carried out measurements, respectively. similar. The difference was mostly between 0.01

3 3 m /s and 0.1 m /s (see figure 5). Water Level: Comparison DischargeKeeper vs Reference (floater) 2.00 DK water level 1.80 1.60 water level wwa Correlation camera-based system (DischargeKeeper) vs. ADCP 1.40 1.20 20 1.00 18 0.80 0.60 16 0.40 14 0.20 R² = 0.93 12 0.00 10 8 6 4 2 0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 Date ADCP Q [m3/s]

Figure 7: Comparison between the water level values of Figure 5: Correlation between the camera-based system the DischargeKeeper and the floater sensor (DischargeKeeper) the ADCP comparative measurements

5 The developed instrument is very suitable water levels and flow rates measurements for the application in the waste water and for providing a photographic evidence sector. The measurement by means of the of every measured value. This technology DischargeKeeper is often less demanding is applicable for on-site measurements of in the waste water sector, as the cross- the discharge in the hydrology and waste section there is usually more stable and water sectors, among other things. the water movement is highly visible (see Due to the optical image processing figures 8 and 9). method, the developed gauge system requires no contact with the measured medium. Therefore, silting or flotsam have no influence on the operation of the DischargeKeeper and it can work even in extreme events such as floods and hydraulic jumps. The distance can be up to 50 m between the camera and the far Figure 8: DischargeKeeper’s measuring site on the outflow of a waste water plant shore of the river or channel. This distance is for the default hard- and software specifications. Measuring at wider river or channels is possible after some respective adjustment and modification of the equipment’s configuration. The special lighting of the presented gauge system enables its operation under many different weather and light conditions. Figure 9: DischargeKeeper’s measuring site on the inflow of a waste water plant A special feature of this technology is that no flow tracers need to be added for flow

CONCLUSIONS AND OUTLOOK velocity detection. The DischargeKeeper operates on visible moving surface The presented optical gauge was structures. Nevertheless, naturally successfully verified and validated on occurring floating objects on the water several sites. The correlation between the surface (e.g. leaves) enhance the measurements carried out by the camera- measurement signal. based system and by the reference gauge Sufficient roughness on the water surface was highly satisfactory. The new and a visible river/channel shore developed gauge has proven to be a structures are beneficial conditions for reliable method for flow velocity profiles,

6 precise measurements. Sites with high http://interpraevent2016.ch/assets/editor/file s/IP16_CP_digital.pdf . ISBN 978-3- wind influence have to be avoided. 901164-24-8, Lucerne, Switzerland. The DischargeKeeper is maintenance- [4] Hies, T. Parasuraman, S.B., Wang, Y., free. The camera lenses and the glass of Duester, R., Eikaas, H.S, Tan, K.M. (2012): Enhanced Wa-ter-level Detection the illumination unit must be clean and by Image Processing. Proceedings 10th free of dirt. International Conference on Hydroin- formatics, HIC 2012, Hamburg, Germany The developed optical gauge will be tested [5] Lüthi, B., T. Philippe, and S. Peña-Haro. in the future under further weather and “Mobile Device App for Small Open- light conditions. A self-updating rating Channel Flow Measurement.” In Proceedings of the 7th International curve is being developed for a gapless Congress on Environmental Modelling and measurement even under critical light or Software, June 15-19, edited by D.P. Ames, N.W.T. Quinn, and A.E. Rizzoli. San Diego, flow conditions. California, USA., 2014.

[6] Nguyen, L. S., Schaeli, B., Sage, D., Kayal, S., Jeanbourquin, D., Barry, D. a, & Rossi, L. (2009). Vision-based system for the REFERENCES control and measurement of wastewater flow rate in sewer systems. Water science [1] Absi R. (2006). A roughness and time and technology, 60(9), 2281-9. dependent mixing length equation. Journal of Hydraulic, Coastal and Environmental [7] Peña-Haro, Salvador, Beat Lüthi, and , (Doboku Gakkai Ronbunshuu Thomas Philippe. “Smartphone for B), Japan Society of Civil Engineers, 62(4), Measuring River Discharge.,” Vol. Vol. 17, 437-446. EGU2015-1847, 2015. Vienna, Austria, 2015. [2] Adrian R.J. (1991). Particle-imaging techniques for experimental fluid [8] The United Nations office for disaster risk mechanics. Annual Review of Fluid reduction (2002). Mechanics 23, 261-304. http://www.unisdr.org/files/558_7639.pdf

[3] Hasan, I., M. Satzger, M. Sattler, R. [9] http://www.gaugecam.com Duester, T. Hies, E. Jose (2016). An [10] http://www.tenevia.com Effective Camera Based Water level recording Technology for Flood Monitoring [11] http://www.photrack.ch

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