Development of Water Correction Algorithm for Underwater Vegetation Signals

Author(s): Cho, H. ;  Lu, D.;  Washington, M.

The unique spectral characteristics of green vegetation, low reflectance in red and high reflectance in Near-Infrared (NIR), have been used to develop vegetation indices, such as Normalized Difference Vegetation Index (NDVI). Our preliminary studies suggest that NDVI was not a useful indicator for submerged aquatic vegetation (SAV), even in clear water, due to energy absorption by water in the NIR region. In order to improve the use of the vegetation indices, we modeled the depth-induced water absorption and scattering through a controlled indoor experiment. We used a GER 1500 spectroradiometer to collect spectral data over an experimental water tank (70cm tall, 50cm wide) that was deployed with a black panel or a white panel at a time; the panels were cut to fit the bottom of the tank. Our assumptions were: (1) the black bottom panel absorbs 100% incoming light; (2) the white bottom panel reflects 100% incoming light; and (3) the water volume scattering and absorption remains the same for the two conditions (black and white bottoms) at a given depth. The measured upwelling radiance was converted to % reflectance. We developed correctional algorithms for water scattering and absorption using the reflectance data. After finding the contribution of these features, we were able to remove the water effects from the measured data. The SAV reflectance that was corrected using the algorithm produced a spectral signature more closely resembling those of terrestrial vegetation. The application of the algorithm significantly improved the vegetation signals, especially in the NIR region. Our results suggest the conventional NDVI: (1) is not a good indicator for submerged plants even at shallow waters (0.3 m); and (2) the index values can significantly improve once the water effects are modeled and removed.


Technical Presentations

  • Delta Water Quality
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  • Sediments
  • Non-Point
  • Management and Sustainability
  • Wood Treatment
  • Modeling
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Responsible Site Design: Implementing Innovative Stormwater Management Strategies

The primary goal of the workshop is to create a dynamic learning experience that examines the role of stormwater management in the built environment. The workshop will focus on integrating ecologically sound water management approaches into site design. After the workshop, attendees will be familiar with the following concepts and technical issues:

  • Knowledge of the stormwater treatment chain
  • Knowledge of the impact of land use codes on stormwater management
  • Application of a design process that mitigates the effects of stormwater on-site
  • Knowledge of the relationship between land use codes and design for innovative stormwater management


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