Effect Of Water Environment On The Spectral Reflectance Characteristics Of Submerged Plant

To reconstruct submersed aquatic vegetation has been recognized as a key measure for restoring eutrophicated lakes and rivers. Remote sensing technology can be used to monitor timely the distribution and growth situation of submersed vegetation on a large scale. However, suspended matters in waters may affect the spectral character of submersed vegetation, and therefore, affect the accuracy of monitoring and classification of the submersed vegetation using remote sensing images.The objective of this study is to investigate the effects of the water circumstance condition on the reflectance of the submersed vegetation, and quantitatively analyze the relation between the water circumstance condition and the reflectance of the submersed vegetation.In this study, we changed the concentrations of suspended matter, the concentrations of chlorophyll a and the depths of submerged vegetation in the water firstly. Then we measured the spectral reflectance of Hydrilla verticillata, a submersed plant using a ground FieldSpec Pro JR spectroradiometer above the water surface under the different water condition. The spectrum reflectance curves of the submersed vegetation formed a typical vegetation curve in the different water condition like the land vegetation, with a small peak at the green band, two peak at the near-infrared band and two low intensity absorption areas in the blue band and red band. The reflectance of the submersed vegetation at the 30 cm below the water surface in the visible spectrum was less than that beyond the 700 nm. When the depth of the submersed vegetation was decreased, the reflectance in the near-infrared would be higher than that in the visible spectrum.By analyzing the effect of water condition on the spectrum reflectance curves, we could find that the reflectance of the submersed vegetation would increased with the suspended matter concentrations, the chlorophyll a concentrations increasing, and the depth of the submersed vegetation decreasing. Due to an observed low signal-to-noise ratio at wavelength shorter than 400 nm and longer than 900 nm, only reflectance calculated between 400 and 900 nm was used. The correlation analysis result showed that the water condition affected the reflectance of the submersed vegetation at many bands. Based the 4 bands of the electromagnetic wave (the blue band: 430-470nm, the green band: 500-560nm, the red band: 620-760nm, the near infrared band: 760~900nm), we got the regression analysis between the suspendedmatter concentrations, the chlorophyll a concentrations, the depths of the submersed vegetation and their reflectance. The regression showed a clear linear relationship, which could correct the effect of the water condition on the reflectance spectrum of the submersed vegetation at some spectrum bands.After studying the correction of the single water condition effect on the reflectance of the submersed vegetation, we studied the effect of the two water condition on the reflectance of the submerged vegetation. We got the integrative formula to correct the effort of water suspended matter concentrations and the chlorophyll a concentrations on the reflectance of the submersed vegetation, which realized the integrative correction of the water conditions effort on the reflectance of the submersed vegetation.The result of this study could be applied to correct the affection of the water circumstance condition on the reflectance of the submersed vegetation, like the water suspended matter concentrations, the chlorophyll a concentrations and the depths of the submersed vegetation. The implications of this in terms of the ability of remote sensing to distinguish and monitor the distribution and dynamics of submersed vegetation on a large scale are discussed.