In recent years, various types of floating algal blooms have been reported in oceans and lakes around the world. These include “green tides” of Ulva, “golden tides” of Sargassum, “red tides” of Noctiluca, and cyanobacterial blooms, among others. These floating algal blooms not only represent hazards to the marine and lake ecosystems, but also cause economic losses and human health problems. The launch of new satellite ocean color sensors can improve the monitoring capability of existing satellites for floating algal blooms.to evaluate the capacity of HY-1C/D CZI sensors (50 m resolution, 3-day revisit) in detecting and differentiating various types of floating algal blooms, and to analyze the spectral characteristics of blooms of several major floating algae using CZI data. Based on the types and distributions of major floating algal blooms in the global oceans and lakes, CZI data are obtained and analyzed for their spectral characteristics from the visually identified bloom features in the CZI false-color Red-Green-Blue images. The spectral characteristics are presented from the difference spectra between the identified image features and the surrounding waters, thus minimizing the impact of atmospheric signals and water signals on the spectra. All floating algal blooms show elevated reflectance in the near infrared wavelengths. In the visible wavelength range, the spectral shapes of Ulva prolifera, Sargassum horneri, and red Noctiluca scintillas are different and therefore can be differentiated from each other. Other blooms, for example Trichodesmium blooms or Microcystis blooms, can also be differentiated once some ancillary information is available.Based on the spectral features and combined with the environmental characteristics, the multi-band Hy-1C/D CZI images are found to be able to detect and differentiate different floating algal blooms. This capacity is important for monitoring floating algal blooms in the Yellow Sea and East China Sea where “multi-tide outbreaks” of Ulva, Sargassum, and Noctiluca may occur at the same time. Because of the high spatial and temporal resolutions, such a capacity is expected to make HY-1C/D CZI an important satellite sensor in near real-time monitoring as well as in quantitative analysis of floating algal blooms in the near future.

floating algae;HY-1C/D CZI;Ulva;Sargassum;Noctiluca;cyanobacteria