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Inland Water Remote Sensing Products
The National Water Research Institute’s Aquatic Optics and Remote Sensing Group, with the support of the Canadian Space Agency’s (CSA) Earth Observation Applications Development Program (EOADP) and Government Related Initiatives Program (GRIP), has been responsible for the development of Canadian inland water remote sensing products relevant to Environment Canada’s mandate to protect and conserve the resources of freshwater ecosystems. The group works towards the development, validation and application of models and algorithms to enable the extraction of inland water quality parameters from satellite observations of inland water colour.
Inland Water Quality Remote Sensing
Data from multispectral satellite sensors such as NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and the European Space Agency’s Medium Resolution Imaging Spectrometer (MERIS) have been used in extensive studies of Canadian inland waters. Time-series maps of spectral water-leaving radiance obtained from sensors such as these can be interpreted in terms of changes in water quality, illustrating seasonal and inter-annual variability of bright-water episodes such as intense phytoplankton blooms and the re-suspension of bottom sediments.
The technology and science are now in place within NWRI to acquire and process aquatic colour remote sensing data over Canadian inland waters in near-real-time, producing daily snapshots of inland water conditions on a routine, fully automated basis. Such products provide valuable synoptic coverage of Canada’s inland waters that has the potential to enhance the current capabilities of ground-based water quality monitoring networks. The group maintains an ongoing archive of imagery from the MODIS-Aqua sensor dating back to its launch in 2002. MODIS top-of-atmosphere data is acquired from NASA/Goddard Space Flight Center’s Ocean Colour Web facility in near-real time and processed at NWRI using a combination of NASA’s SeaDAS (SeaWiFS Data Analysis System) code and NWRI-developed programs to produce maps which include daily true colour composite images, water-leaving radiance and sea-surface temperature. Examples of these products can be seen below for the Great Lakes region. In due course these products will be available here, including access to the entire archive of images.
MODIS True Colour Composite
MODIS Water-leaving Radiance at 551 nm
MODIS Sea Surface Temperature
Click on images for enlarged views
Water-leaving radiance at 551 nm (MODIS band 12) describes the amount of light leaving the water column in the green portion of the visible spectrum, is affected by the degree to which dissolved and particulate matter present within the water column absorb and scatter the incident light, and can be treated as a general indicator of water clarity.
The MODIS Sea Surface Temperature product is derived using a long-wave SST algorithm making use of MODIS bands 31 and 32 at 11 and 12 μm respectively.
Aquatic Optics Research
Accurate interpretation of remotely sensed aquatic colour imagery relies upon a thorough understanding of the processes by which the material dissolved and suspended within the water column interacts with the incident light field. Field surveys are conducted using a suite of above- and in-water spectro-optical instruments in order to characterize the optical properties (specifically absorption and backscattering) of the water-colouring parameters, allowing the development of models to extract water quality products from in situ and remotely sensed aquatic colour.
Water Quality Products
Ongoing research continues to develop and validate techniques for the retrieval of specific water quality products including water clarity, suspended particulates, chlorophyll (as an indicator of algal biomass), which will be available here in the near future. These products, derived through a combination of empirical, inverse modelling and multivariate statistical methods, are being used in both long-term and event-driven monitoring applications to provide insight into areas of environmental research on scales unobtainable through conventional ground-based approaches.
For more information contact Caren Binding, 905-336-4721.
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