This study uses the MODIS-Aqua satellite data provided by the National Aeronautics and Space Administration (NASA) and matches with the time and location of the chlorophyll-a concentration data measured by SeaBASS to select the satellite data time and observation area. The number of matched data is 924. Firstly, remote sensing reflectance (Rrs) is used to classify satellite remote sensing data into different water bodies, and then the best chlorophyll-a concentration algorithm is established. The results show that the mean percentage difference (MPD) in Case 2 water is 131.2% through comparing the percentage of chlorophyll-a provided by MODIS with the in-situ observations. In addition, the chlorophyll-a concentration of the new algorithm compared with the in-situ chlorophyll-a concentration are also calculated. The mean percentage difference in Case 2 water is 26.6%, and the average chlorophyll-a is 6.16 mg/m3 , which is much closer to the in-situ value,7.22 mg/m3 than the average chlorophyll-a of MODIS, 13.7 mg/m3. The chlorophyll-a concentration deduced by the new algorithm of this study is consistent with the in-situ values in Case 2 water, and it is much more convergent than the data of MODIS. Obviously, the new algorithm established in this study can be used to improve the chlorophyll-a concentration estimation results in Case 2 water. When the new algorithm is applied to calculate the chlorophyll-a concentration of the marginal Northwestern Pacific, the value is still higher than the offshore waters. Additionally, the chlorophyll-a concentration calculated by this new algorithm is lower than the value provided by MODIS, but the difference between them in the offshore waters is small. However, the algorithm of this study can improve the overestimation of the original MODIS value.
Tide gauge data provided by the University of Hawaii Sea Level Center and daily sea surface temperature (SST) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) product are used in this study to analyze the influence of tide on the SST in the seas of Northwestern Pacific. In the marginal region, the climatology SST is lower in the northwestern area than that in the southeastern area. In the coastal region, the SST at spring tide is higher than that at neap tide in winter, but it is lower in other seasons. In the adjacent waters of East China Sea and Yellow Sea, the SST at spring tide is higher than that at neap tide in winter and summer but it is lower in spring and autumn. In the open ocean region, the SST at spring tide is higher than that at neap tide in winter, but it is lower in other seasons. In conclusion, not only the river discharge and topography, but also tides could influence the SST variations, especially in the open ocean region.
Changes of oceanic salinity are highly related to the variations of evaporation and precipitation. To understand the influence of rainfall on the sea surface salinity (SSS) in the waters adjacent to Taiwan, satellite remote sensing data from the year of 2012 to 2014 are employed in this study. The daily rain rate data obtained from Special Sensor Microwave Imager (SSM/I), Tropical Rainfall Measuring Mission’s Microwave Imager (TRMM/TMI), Advanced Microwave Scanning Radiometer (AMSR), and WindSat Polarimetric Radiometer. The SSS data was derived from the measurements of radiometer instruments onboard the Aquarius satellite. The results show the average values of SSS in east of Taiwan, east of Luzon and South China Sea are 33.83 psu, 34.05 psu, and 32.84 psu, respectively, in the condition of daily rain rate higher than 1 mm/hr. In contrast to the rainfall condition, the average values of SSS are 34.07 psu, 34.26 psu, and 33.09 psu in the three areas, respectively at no rain condition (rain rate less than 1 mm/hr). During the cases of heavy rainfall caused by spiral rain bands of typhoon, the SSS is diluted with an average value of -0.78 psu when the average rain rate is higher than 4 mm/hr. However, the SSS was increased after temporarily decreased during the typhoon cases. A possible reason to explain this phenomenon is that the heavy rainfall caused by the spiral rain bands of typhoon may dilute the sea surface water, but the strong winds can uplift the higher salinity of subsurface water to the sea surface.