Abstract
Coloured dissolved organic matter (CDOM) is an important water property for lake management. Remote sensing using empirical algorithms has been used to estimate CDOM, with previous studies relying on coordinated field campaigns that coincided with satellite overpass. However, this requirement reduces the maximum possible sample size for model calibration. New satellites and advances in cloud computing platforms offer opportunities to revisit assumptions about methods used for empirical algorithm calibration. Here, we explore the opportunities and limits of using median values of Landsat 8 satellite images across southern Canada to estimate CDOM. We compare models created using an expansive view of satellite image availability with those emphasizing a tight timing between the date of field sampling and the date of satellite overpass. Models trained on median band values from across multiple summer seasons performed better (adjusted R2 = 0.70, N = 233) than models for which imagery was constrained to a 30-day time window (adjusted R2 = 0.45). Model fit improved rapidly when incorporating more images, producing a model at a national scale that performed comparably to others found in more limited spatial extents. This research indicated that dense satellite imagery holds new promise for understanding relationships between in situ CDOM and satellite reflectance data across large areas.
Highlights
Coloured dissolved organic matter (CDOM) is the optically measurable part of dissolved organic matter in water
Canada is a lake-rich country with a vast number of lakes distributed around its territory: it is estimated that there are over 900,000 lakes greater than 10 hectares that account for approximately 7% of the surface area of the country [20]
Based on the termed model as: results of the random forest using VSURF, we identified the best twotermed model as: ln(CDOM(a440 )) = a − b(ln(B3/B4)) − c(ln(B2)
Summary
Coloured dissolved organic matter (CDOM) is the optically measurable part of dissolved organic matter in water. It is optically characterized by its spectral absorption coefficient, aCDOM, at a reference wavelength (e.g., 440 nm). (3) the bioavailability and toxicity of contaminants in water by forming chemical complexes with metals [13,14], and (4) water quality for human use and consumption due to the high cost of purifying water with high CDOM concentrations [5,15,16]. Understanding CDOM levels is important for the monitoring and management of freshwater resources. There is limited in situ CDOM data collected relative to its importance, even though
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