Harmful algal blooms (HAB) is one of the most serious marine disasters, which not only reduce fishery production, deteriorates the marine environment, affects coastal tourist industry, but also cause human poison. The satellite remote sensing technology has the characteristics of large-scale, synchronized, low cost and rapid monitoring, it is become an important method for HAB observation. In this paper, we describe the HAB monitoring system based on remote sensing data which developed by the Second Institute of Oceanography, China. The system can achieve the whole procedure automatically from the satellite remote data acquirement and satellite image process, products generation, and it can automatically identify the HAB region using the spectral reflectance and inherent optical properties derived from remote sensing data. Currently, the National monitoring department has adopted this system for the operational monitoring of HAB in the East China Sea.
The coastal area of East China Sea (ECS) suffers from the harmful algal blooms (HAB) frequently every year in the
warm season. The most common causative phytoplankton algal species of HAB in the ECS in recent years are
Prorocentrum donghaiense (dinoflagellates), Karenia mikimotoi (dinoflagellates which could produce hemolytic and
ichthyotoxins) and Skeletonema costatum (diatom). The discrimination between the dinoflagellates and diatom HAB through ocean color remote sensing approach can add the knowledge of HAB events in ECS and help to the precaution. A series of in-situ measurement consisted of absorption coefficient, total scattering and particulate backscattering coefficient was conducted in the southern coast of Zhejiang Province in May 2009, and the estuary of Changjiang River in August 2009 and December 2010, which encountered two HAB events and a moderate bloom. The Inherent Optical
Properties (IOPs) of the bloom waters have significant difference between phytoplankton species in absorption and
backscattering properties. The chlorophyll a specific absorption coefficient (a*phy(λ)) for the bloom patches (chlorophyll a concentration >6mg m-3) differ greatly from the adjacent normal seawater, with the a*phy(λ) of bloom water lower than 0.03 m2 mg-1 while the a*phy(λ) of the adjacent normal seawater is much higher (even up to 0.06 m2 mg-1). Meanwhile, the backscattering coefficients at 6 wavebands (420, 442, 470, 510, 590 and 700nm) are also remarkably lower for bloom waters (<0.01 m-1) than the normal seawater (> 0.02 m-1). The backscattering coefficient ratio (Rbp(λ)) is much lower for diatom bloom waters than for dinoflagellates types (0.01079 vs. 0.01227). A discrimination model based on IOPs is
established, and several typical dinoflagellates and diatom bloom events including Prorocentrum donghaiense, Karenia mikimotoi and Skeletonema costatum in the ECS are picked out for testing with the MODIS-L2 and L3 ocean color remote sensing products from NASA website. The result proves that the satellite-derived inherent optical properties can be used to HAB detection and the discrimination of HAB species from dinoflagellates and the diatom types in the ECS.
The Changjiang River is the third largest river of the annual flux around the world, which has a great impact on the
ecosystem of the East China Sea and adjacent areas. Because of the shallow water, tide mixing and the runoff of the
Changjiang River and Qiantang River, the suspended particulate matter (SPM) concentration is extremely high in the
Changjiang Estuary, which is ever up to 2000mg/L. Due to the large water-leaving radiance at the near-infrared
wavelength, the operational atmospheric correction algorithm for the open ocean can not be applied to this region, and
the existing remote sensing algorithms for SPM may not be applicable for this extremely high turbidity waters. In this
paper, we firstly apply the blue wavelength atmospheric correction algorithm to MERIS Level-1 data to get the
reasonable spectral water-leaving radiances in the Changjiang Estuary. Based on the winter cruise data in 2007, a
regional SPM algorithm was developed using the bands ratio of the normalized water-leaving radiances between 779nm
and 560nm. This algorithm was validated by the summer cruise data in 2006, and the results show that the performance
of the algorithm was very well, and there was good agreement between the retrieved data and in-situ measured
concentrations of the SPM in the Changjiang Estuary, with the correlation coefficient of 0.98 in the logarithm form and
the averaged absolute relative error of 27.2%, and the standard deviation of 20.8mg/l in the linear form. Finally, the
seasonal variations of the SPM in the Changjiang Estuary were analyzed by the MERIS SPM maps retrieved by the
algorithms developed in this paper.
China coastal sea is characteristic of the high concentration of suspended matter which has complex components of
mineral particles, organic detritus and phytoplankton, etc. The similarity of spectrum characters of mineral particles and
organic particles in backscattering coefficient, and the organic detritus and color dissolve organic matters (CDOM) in
absorption coefficient makes the information inverse of coastal ocean color become a very difficult work. In this paper,
based on the in situ data of optical investigation in East China Sea in the spring of 2003, including the absorption
coefficients of CDOM and de-pigment particles from laboratory spectrophotometer measurement, and the field
measurement with ac-9 (WET labs, Inc.), the optical properties of suspended particles were studied. And then, a
semi-analysis algorithm of particle attenuation coefficient (Cp) in ECS was developed. There are two key steps in this
algorithm, one is the estimation of the ratio of particle backscattering coefficient to the total scattering coefficient; and
the other is the retrieval of absorption coefficient of CDOM. With this inversion algorithm of Cp and the input of remote
sensing reflectance obtained from the underwater profiler radiometer (Satlantic. Inc.), the particle attenuation coefficient
was inversed, which was consistent well with the in situ data of Cp . In the high turbid water, the scattering signal is
dominant in the Cp values, so the modeled-Cp was less than the in situ data due to the underestimation of backscattering
coefficient in IOPs semi-analysis algorithms. The modeled -Cp at 660nm wavelength has the R2 of 0.84 and RMSE=0.22
compared with the attenuation coefficient at 650nm measured by the ac-9, in which the absorption coefficient of CDOM
is neglect. The semi-analysis algorithms of Cp developed in this paper showed a good potential to estimate the
biogeochemical parameters, like POC, but the further study should be focused on the distinguish of the sub-division
materials with more in situ data set.
The Colored Dissolved Organic Materials (CDOM) and the de-pigmented particles are the main components
affecting the ocean colors in China coastal waters (which are commonly considered as the Case II waters).
Understanding of their spectral characteristics is very important to develop the regional bio-optical algorithms for ocean
color remote sensing. The coastal water in East China Sea (ECS) is influenced by the terrestrial materials especially the
Yangtze River outflow, which has high dissolved organic and suspended materials concentration and complex particles
composition. In this paper, we analyze the in situ datasets collected in four seasons between 2006 and 2007 in ECS, and
get the spectral absorption models of CDOM and de-pigmented particles. The distributions of absorption coefficients of
CDOM ( ) and de-pigmented particles ( ) show a decreasing trend from coastal water to the off-shore waters,
which is influenced mainly by the Yangtze River outflow and coastal currents with remarkable seasonal variation in ESC.
The maxima of adp
CDOM a dp a
dp is very high and even up to 90 m-1 level in estuary waters that it will apparently influence the retrieval
of CDOM. The frequency of slops of the exponential spectrum of de-pigmented particles obeys the Gaussian distribution
and it has good relationships with the absorption coefficient especially in the near-shore areas. The optical characteristics
in ECS will give feasible reference to the further development of regional bio-optical algorithms.
A water wake detection method of airphotoes is proposed based on two-dimensional principal component analysis
(2DPCA) of the polar Fourier spectrum. This method improves the traditional Principal Components Analysis to obtain
the image direction from its Fourier power spectrum, transforms the Fourier spectrum to the polar coordinate based on
the image direction, so the polar Fourier spectrum is translation and rotation invariant. Compared to the previous method
of partitioning the Fourier spectrum to achieve texture features, the row 2DPCA, the column 2DPCA and the improved
2DPCA are used to analysis the polar Fourier spectrum. From experiment results of 40 images, it is proved that the
proposed algorithm can fetch the wake texture precisely.