A typhoon (as well as a hurricane or tropical storm) is one of the largest air-sea interaction processes on the synoptic scale, which can greatly enhance the air-sea exchange of material and energy within a short time; meanwhile, a typhoon can significantly alter the water structure, seabed topography and geomorphology, and particle transport and deposition, as well as biogeochemical processes in the affected areas. Satellite remote sensing is the main approach to study the impact of typhoon on the sea surface temperature(SST) and the ocean color environment at present. The Taiwan Strait plays an important role in water and sediment exchange between the East China Sea and the South China Sea. This paper uses the data of the MODIS satellites to analyses the effects of Haitang(2005) on the SST, sea surface chlorophyll-a concentration(Chl-a) and total suspended matter(TSM) in the Taiwan Strait over different periods. During the typhoon-active period, the concentration of TSM significantly increased. The SST for the typhoon-active period was lower than that both the pre- and post- the typhoon periods. During the typhoon, Chl-a concentration increased. After the typhoon, the Chl-a concentration decreased, but still higher than before the typhoon. The Chl-a concentration near the Minjiang Estuary during the typhoon was slightly lower than that before the typhoon and after the typhoon. During the typhoon, the strong cyclonic wind-stress of the typhoon enhanced heat exchange between the water and the atmosphere, and a large amount of rainfall and run-off significantly decreased the SST. During the typhoon, the increased sediment discharged into the strait by rivers, and the re-suspension of seafloor sediment, increased the concentration of TSM in the coastal waters. Seawater with relatively high sediment concentration was transported to the middle of the strait after being carried by wind-induced flows. During the typhoon, in the waters near the typhoon’s path, Chl-a concentration increased. After the typhoon, Chl-a concentration near the Minjiang estuary dramatically increased than before the typhoon. Nutrient-rich bottom water stirred by the typhoon promoted an outbreak of aquatic organisms. The increase of Chl-a concentration has a certain delay because the growth of organisms takes time.
Red tide is an ecological anomaly that phytoplankton in seawater suddenly proliferation or aggregation under certain environmental conditions and within a period of time, resulting in seawater discoloration. Red tide not only endangers marine fisheries and aquaculture, deteriorates the marine environment, affects coastal tourist industry, but also causes human health problems. East China Sea (ECS) is a high incidence region of red tide disasters. Remote sensing is an effective means of monitoring red tides. In this paper, the high-incidence area of the red tide in the East China Sea is selected as the study area, MERIS L2 data is used as the data source to analyze and compare the normalized water radiation (nlw) spectral difference between the red tide water body and the non-red tide water body in the red tide event. Based on the spectral difference, this paper develops nlw560/nlw490>1.25 and nlw681-nlw665>0 algorithm to extract the red tide information of ECS. Applying the algorithm to ECS, the results show that the developed model can effectively determine the location of the red tide and correspond well with the results of the official bulletin. This indicates that the algorithm can effectively extract red tide information.
Red tide is an ecological anomaly that phytoplankton in seawater suddenly proliferate or aggregate under certain environmental conditions and within a period of time, resulting in seawater discoloration. Red tide not only harms marine fisheries and aquaculture, deteriorates the marine environment, affects coastal tourist industry, but also causes human health problems. East China Sea (ECS) is a region of high incidence of red tide disasters. Remote sensing has been proven an effective means of monitoring red tides. Phytoplankton-specific light absorption plays a fundamental role in the remote estimation of pigment biomass and red tide. This paper retrieves the phytoplankton absorption coefficient in decade based on MODIS data from July 2002 to June 2012 using quasi-analysis algorithm (QAA), analyzes and compares phytoplankton absorption coefficient spectral curves of red tide events with multiyear monthly averaged ones, as well as phytoplankton absorption coefficient spectral differences at the same location during red tide presence and absence. A new red tide monitoring algorithm based on the phytoplankton absorption coefficient is developed to extract red tide information of the ECS. With the application of the algorithm in the ECS, the results reveal that the developed model can effectively determine the location of red tides, with good correspondence to the results from an official bulletin. This demonstrates that the algorithm can effectively extract red tide information.
Concentration of suspended sediment directly affects the optical properties such as transparency and water color, and aquatic environment as well. This paper selects the Taiwan Strait as study area, establishes inversion mode of suspended sediment by coupling field data with remote sensing reflectance from MODIS data. Monthly-averaged concentrations and seasonal changes of suspended sediment from 2003 to 2012 were calculated and analyzed by the mode. The main results are as follows:(1) remote sensing reflectance at 555nm from MODIS data has high relativity with the field observed turbidity by regression equation of Y =0.8931e123.93x in which Y is TSM concentration, X is Rrs555 and R2 is 0.6836. (2)Suspended sediment in the Taiwan Strait has obviously spatial and temporal distribution characteristics, that higher concentration of suspended sediment is in coastal water and decreases from shore to sea, and highest concentration happens in winter.
Red tide not only destroys marine fishery production and deteriorates the marine environment, it also causes human health problems. In China, the East China Sea has a high incidence of red tide disasters. Remote sensing technology has been proven an effective means of monitoring red tides. Spectral information of red tide water is an important basis for establishing red tide remote sensing monitoring models. This paper analyzes and compares the differences between red tide event spectral curves and multiyear monthly averaged spectral curves of MODIS data from July 2002 to June 2012, and develops a red tide monitoring algorithm based on the background field, to extract red tide information of the East China Sea. With the application of the algorithm in the East China Sea, it reveals that it can effectively determine the location of red tide and extract red tide information.
Red tide not only destroys marine fishery production, deteriorates the marine environment, affects coastal tourist industry, but also causes human poison, even death by eating toxic seafood contaminated by red tide organisms. Remote sensing technology has the characteristics of large-scale, synchronized, rapid monitoring, so it is one of the most important and most effective means of red tide monitoring. This paper selects the high frequency red tides areas of the East China Sea as study area, MODIS/Aqua L2 data as the data source, analysis and compares the spectral differences in the red tide water bodies and non-red tide water bodies of many historical events. Based on the spectral differences, this paper develops the algorithm of Rrs555/Rrs488> 1.5 to extract the red tide information. Apply the algorithm on red tide event happened in the East China Sea on May 28, 2009 to extract the information of red tide, and found that the method can determine effectively the location of the occurrence of red tide; there is a good corresponding relationship between red tide extraction result and chlorophyll a concentration extracted by remote sensing, shows that these algorithm can determine effectively the location and extract the red tide information.
Concentration of suspended sediment directly affects the optical properties such as transparency and water color, and
aquatic environment as well. The paper selects the Minjiang Estuary, southeast coast of China as study area, and has
established inversion mode of suspended sediment by coupling field data with water-leaving radiation from MODIS data
in Minjiang Estuary. Monthly-averaged concentrations and seasonal changes of suspended sediment from 2002 to 2009
were calculated and analyzed by the mode. The main results are as follows: (1) Normalized water-leaving radiance
ratio(nLw667/nLw488) from MODIS data has high relativity with the field observed turbidity by regression equation of Y = 0.618X2 -5.720X + 18.94, in which Y is turbidity, X is nLW667/nLW488 and R2 is 0.716. (2)Suspended sediment in
the Minjiang Estuary has obviously spatial and temporal distribution characteristics, that higher concentration of
suspended sediment is in coastal water and decreases from shore to sea, and highest concentration happens in winter.
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