Uncertainty in the optical remote estimation of the biomass of Ulva prolifera macroalgae using MODIS imagery in the Yellow Sea.

A laboratory experiment was conducted to obtain a floating algae index (FAI) of the floating macroalgae (Ulva prolifera), corresponding to various values of biomass per unit area (BPA). A piecewise empirical model was used to fit the statistical relationships between BPA and FAI, corresponding to FAI <= 0.2 (BPA <= 1.81kg/m(2)) and FAI. 0.2 (BPA. 1.81 kg/m(2)). Spectral mixing derived results show that a linear relationship between FAI and BPA is maintained when the BPA of endmembers is less than 1.81 kg/m2. However, when the BPA of the endmembers exceeds 1.81 kg/m(2), there is substantial uncertainty in the optical remote estimation of biomass. Although the MODIS-derived FAI of Ulva prolifera is often less than 0.2, it is very difficult to determine whether the FAI results from low BPA (<= 1.81kg/m(2)) of the endmembers, or from a low area ratio including high BPA (> 1.81 kg/m(2)), due to pixel mixing. If it is assumed that the unit biomass distribution of pure endmembers is a standard Gaussian distribution, then the uncertainty in the biomass estimation of Ulva prolifera from MODIS data can be expressed. This results in the uncertainty of similar to 36% in total biomass estimation, similar to 43% of which was contributed by a few pixels (10% of total pixels) with high FAI (> 0.05). The uncertainty in BPA caused by high FAI (> 0.05) pixels is about 7.2 times that for low FAI (<= 0.05) pixels. In future research, the spatial distribution characteristics of the FAI of pure endmembers need to be considered in order to improve the accuracy of optical remote estimation of floating Ulva prolifera. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement