|Wednesday, June 02|
Multi-scale analysis of evaporation from a boreal reservoir of eastern Canada
* Daniel Nadeau, Université Laval, Canada
Antoine Thiboult, Canada
Adrien Pierre, Canada
Habiba Kallel, Canada
Pierre-Erik Isabelle, Canada
Murray Mackay, Canada
Alain Rousseau, Canada
François Anctil, Canada
In Canada, there are more than two million water bodies spread over nearly 8% of the country's surface area. In addition to affecting the regional climate, lakes and reservoirs evaporate substantial quantities of water that are then ¬¬no longer available for local usages. Yet too few studies in the boreal environment have been conducted on this hydrological flux. This ambitious study presents an analysis of the evaporation from an 85 km2 hydroelectric reservoir with a mean depth of 42 m located in eastern Canada (50.7°N, 63.2°W), with the objective of better understanding the spatial and temporal variations of the flux, and thus enhancing available modeling tools. The field component of this work is based on direct observations of evaporation obtained using two flux towers deployed since June 2018, one on a floating platform and the other on the bank. Measurements using a new technique for estimating regional-scale evaporation, named microwave scintillometry, were also obtained for nearly two months in 2019. The modelling component of this study aims to evaluate the performance of the Canadian Small Lake Model (CSLM) in simulating the thermal regime of the water body and its exchanges with the atmosphere. Initial results indicate that evaporation is sustained in the fall until freeze-up of the reservoir in late December. When the ice breaks up at the end of May, the reservoir stores heat with little or no evaporation observed. In September, the surface temperature of the reservoir is constantly higher than the air temperature, leading to sustained evaporation day and night, and sensible heat fluxes peaking at night. Our analysis shows that the microwave scintillometry approach compares well with traditional flux measurements and underlines heterogeneous surface flux characteristics in the reservoir. For its part, the CSLM is well able to simulate the turbulent fluxes, but the modeled temperature profile seems to be particularly sensitive to windy events. Overall, this study sheds light on the dynamics of evaporation in northern water bodies and its relationship with the energy balance.
Improvements in Large Scale Particle Image Velocimetry: Hey Grayscale, Give the Other Colourspaces a Chance
* Cody Kupferschmidt, University of Guelph, Canada
Andrew Binns, Canada
"Surface image velocimetry (SIV) is a measurement technique that can be used to estimate the velocity of the free surface of a moving fluid. Typically, small objects known as tracers are added to a moving fluid in a process known as “seeding”, and the movement of these tracers are observed from video recordings. Through the tracking of tracers within a video recording, it is possible to recreate the paths travelled and to obtain vectors corresponding to the flow velocities at specific locations within the flow field. In comparison with other methods of velocity measurement, SIV has the advantage of being able to collect in-situ measurements without disturbing the flow field with a measurement device. SIV is often performed in laboratory settings where seeding, image illumination, and video recording can be closely controlled. Large-scale particle image velocimetry (LSPIV) is a subset of SIV that can be used for real-world applications where measurement regions can exceed tens of square meters, such as measuring water velocity in rivers and canals. LSPIV can include a seeding process, but often makes use of natural tracers such as ice, bubbles, debris, or reflectance on the water surface. To date, most implementations of LSPIV have used grayscale images for processing. However, the conversion of video data from colourspaces with multiple bands to a single grayscale band results in the loss of data. Recent studies in laboratory settings on particle image velocimetry (PIV) have demonstrated success in improving measurement repeatability through the use of multiple colour bands. For the current study we collected videos of the Speed River at three locations in Guelph, Ontario, Canada. We used the open-source software package OpenPIV (version 0.22.3) to perform LSPIV. We evaluated the ability of the algorithms to properly detect the correct global flow direction, and maximize inter-frame repeatability of local velocity measurements. Results for grayscale images were compared with the bands from other colourspaces including the red, green, and blue (RGB) colourspace, the hue, saturation, value (HSV) colourspace and the CIE LUV colourspace. Findings from this case study showed that while videos processed in the grayscale colourspace correctly identified the flow direction and produced repeatable local velocity measurements with low deviation, similar results could be achieved using other colour bands that contain measures of lightness or brightness, such as the red (RGB), green (RGB), blue (RGB), value (HSV), and luminance (LUV) bands. Imaging artifacts were present in all of the evaluated colourspaces, and produced localized regions within images with low inter-frame repeatability of local velocity measurements. Artifacts tended to be occur at different locations depending on the colourspace used, suggesting that combining outputs from multiple bands could be used as a technique to improve inter-frame velocity measurement repeatability. The findings of this research have potential applications for developing low cost post-processing techniques for improving the repeatability of LSPIV measurements, particularly under the varied illumination conditions typical of field measurements. "
The testing and implementation of Image Velocimetry techniques for flow measurements in Canadian rivers
* James Bomhof, Environment and Climate Change Canada, Canada
Elizabeth Jamieson, Canada
Alain Goulet, Canada
Zac Bishop, Canada
Malyssa Maurier, Canada
"Image Velocimetry is a technique in which computer algorithms are applied to a series of images to extract velocities of objects and textures within the images. In recent years, Image Velocimetry been adapted to large scales for estimating water surface velocities and discharge in rivers. Advancements in image processing techniques and software, the increasing availability of station cameras, and better cell phone networks enabling higher data transmission rates have made Image Velocimetry a feasible and attractive non-contact discharge estimation method. Image Velocimetry is particularly useful for remote locations or sites with rapidly varying conditions, where acquiring timely discharge data with instruments in the water can be challenging and expensive. The Water Survey of Canada (WSC) is investigating the use and implementation Image Velocimetry as a standard method for discharge estimation at some sites or under certain conditions in the near future. Over the past year, the WSC has made significant progress in the investigation and testing of Image Velocimetry for discharge monitoring in an operational context. This presentation will 1) provide an overview of Image Velocimetry methods, 2) discuss the potential applications for this technique, 3) compare the velocity and discharge results with those from conventional measurement methods, and 4) discuss lessons learned from the practical application of these methods. "
Validation of monitoring and mapping soil moisture content over the agricultural lands by the synergistic use of passive and active microwave remote sensing measurements
* Farzane Mohseni, Faculty of Geodesy and Geomatics Engineering, K. N. TOOSI University of Technology, Iran (Islamic Republic of)
Mehdi Mokhtarzade, Iran (Islamic Republic of)
Saeid Homayouni, Canada
Soil moisture plays a vital role in many studies such as biomass estimation, the climate change effects, drought monitoring, and flood prediction. So far, many research works have been carried out to estimate soil moisture using remote sensing techniques. SMAP/Sentinel-1 soil moisture product is recently developed to monitor and map soil moisture with global coverage from 180°W to 180°E, and from approximately 60°N and 60°S, at the spatial resolution 3km. in this study, we attempted to evaluate the performance of this soil moisture product over the agricultural lands of REMEDHUS site.
Lake monitoring in Nunavik - The advantage of community based monitoring and winter fieldwork
* Véronique Dubos, INRS, Canada
André St-Hilaire, Canada
Normand Bergeron, Canada
"Access to fieldwork in Nunavik (northern Quebec Inuit territory) implies heavy logistic and costs due to the scarcity of roads outside the communities. Adding to these difficulties, researchers are often confronted to the short period of summer to do fieldwork in such a cold region. Through an example of lake monitoring during winter by local fishers, the presented work highlights the advantages and challenges of doing community based monitoring during winter. The project consists in characterizing and modeling Arctic char (Salvelinus alpinus) winter habitat. Arctic char has a circumpolar distribution and is the northernmost freshwater fish species. They use lakes to overwinter. The objective was to assess fish preference for some specific habitats and determine the characteristics of these sites. The fieldwork consisted in measuring thermal and physico-chemical characteristics of the water column of sites used for overwintering. Punctual detailed measurements were conducted with fishers to have the fish habitat location. In addition, lakes were instrumented with thermographs by Inuit fishers while they were going fishing. They also took notes of GPS location, water depth, ice and snow depth, presence of fish and they did underwater videos. Ice cover thickness varied between 0.46 m and 0.97 m and water temperatures were between -0.10°C and 1.26°C. This monitoring strategy allowed to characterize several lakes and also to get habitat variables several times during winter for some sites. Winter monitoring was an easy way to access different sites. Frozen lakes and rivers and snowpack made transportation easier than during summer condition. Nonetheless, cold weather was challenging for the equipment. Availability of multiple instruments for the same measurements can be helpful and access to a warm shelter is a must to recharge batteries and allow for melting ice around the instruments. Community-led monitoring can be profitable as Inuit harvesters are going regularly on the land and are knowledgeable of the sites usually used by the fish. Use of community based monitoring is a valuable method where the sampled territory is regularly used by local communities. A short training was useful to improve the level of detail and facilitate the communication of data collected. "