Exploring the Potential of Hyperspectral Remote Sensing for Assessing Nitrate Distributions in Surface Water: In-Situ Experiments
Abstract
Nitrate is a key aquatic nitrogen species and an important indicator of anthropogenic impacts on water quality. Regulatory agencies through the world mandate nitrate monitoring in freshwater and coastal marine settings over large spatial scales. While remote sensing techniques are clearly advantageous in this context, and have proven useful in monitoring other water quality properties (e.g., chlorophyll, organic matter, suspended solids), researchers have thus far been unable to extend this approach to smaller molecules, such as nitrate . Here, we undertook a controlled tank experiment indoors (using artificial light) and outdoors (natural light) to characterize and compare the relationship between nitrate concentrations and reflectance of shallow waters. Nitrate standards ranging from 0 to 100 ppm (as NO3) were tested in a matrix of de-ionized water. Reflectances were recorded using a spectroradiometer (ASD FieldSpec), and tank bottom and depth effect were characterized and parameterized using Remote Cosine Receptor (RCR). Resulting reflectance spectra, specifically in and around a small peak at roughly 404 nm, correlated well with the lower range of nitrate concentrations (1-30 ppm, R2 = 0.84), but poorly at greater concentrations. The reason for this inconsistent behavior is not yet clear and the subject of further investigations. The hyperspectral reflectance study is currently being pilot-tested on the Lower Merced River in Central California, an agricultural watershed where nitrate levels vary seasonally from roughly 0.5 to 10 ppm. Synoptic surveys using in-situ UV-visible spectroscopy are providing longitudinal nitrate maps for comparison with hyperspectral reflectance spectra collected along the river. The hyperspectral system will be tested on several reaches of the river during low flow conditions in Fall 2011. Currently, the system is undergoing further testing with nitrate, dissolved organic matter, chlorophyll-a and turbidity standards in preparation for the field tests.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B13A0533Z
- Keywords:
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- 0400 BIOGEOSCIENCES;
- 0480 BIOGEOSCIENCES / Remote sensing;
- 0496 BIOGEOSCIENCES / Water quality