Prediction of chlorophyll a concentration using HJ-1 satellite imagery for Xiangxi Bay in Three Gorges Reservoir

Since the impoundment of the Three Gorges Reservoir in 2003, algal blooms have frequently been observed in it. The chlorophyll a concentration is an important parameter for evaluating algal blooms. In this study, the chlorophyll a concentration in Xiangxi Bay, in the Three Gorges Reservoir, was predicted using HJ-1 satellite imagery. Several models were established based on a correlation analysis between in situ measurements of the chlorophyll a concentration and the values obtained from satellite images of the study area from January 2010 to December 2011. Chlorophyll a concentrations in Xiangxi Bay were predicted based on the established models. The results show that the maximum correlation is between the reflectance of the band combination of B4/（B2＋B3） and in situ measurements of chlorophyll a concentration. The root mean square errors of the predicted values using the linear and quadratic models are 18.49 mg/m3 and 18.52 mg/m3, respectively, and the average relative errors are 37.79% and 36.79%, respectively. The results provide a reference for water bloom prediction in typical tributaries of the Three Gorges Reservoir and contribute to large-scale remote sensing monitoring and water quality management.

Inversion and verification of chlorophyll a concentration in the Bohai Bay

Chlorophyll a concentration is to characterize the amount of phytoplankton.In this paper,the chlorophyll a concentration is retrieved using the OC3M and OC2algorithms based on the MODIS remote sensing data,and using the band ratio,OC3G and YOC algorithms based on the GOCI remote sensing data.Based on the chlorophyll a measured data in the Bohai Bay in spring,2012,the spatial distribution trends of retrieval results are consistent with the measured results.By the inversion precision analysis,the accuracy of retrieval results of band ratio method based on GOCI is similar to that of OC3M method based on the MODIS.The precision retrieval results of YOC method based on GOCI are higher than the other methods.

Declined trends of chlorophyll a in the South China Sea over 2005–2019 from remote sensing reconstruction

Chlorophyll a concentration(CHL)is an important proxy of the marine ecological environment and phytoplankton production.Long-term trends in CHL of the South China Sea(SCS)reflect the changes in the ecosystem’s productivity and functionality in the regional carbon cycle.In this study,we applied a previously reconstructed 15-a(2005–2019)CHL product,which has a complete coverage at 4 km and daily resolutions,to analyze the long-term trends of CHL in the SCS.Quantile regression was used to elaborate on the long-term trends of high,median,and low CHL values,as an extended method of conventional linear regression.The results showed downward trends of the SCS CHL for the 75th,50th,and 25th quantile in the past 15 a,which were−0.0040 mg/(m^(3)·a)(−1.62%per year),−0.0023 mg/(m^(3)·a)(−1.10%per year),and−0.0019 mg/(m^(3)·a)(−1.01%per year).The negative trends in winter(November to March)were more prominent than those in summer(May to September).In terms of spatial distribution,the downward trend was more significant in regions with higher CHL.These led to a reduced standard deviation of CHL over time and space.We further explored the influence of various dynamic factors on CHL trends for the entire SCS and two typical systems(winter Luzon Strait(LZ)and summer Vietnam Upwelling System(SV))with single-variate linear regression and multivariate Random Forest analysis.The multivariate analysis suggested the CHL trend pattern can be best explained by the trends of wind speed and mixed-layer depth.The divergent importance of controlling factors for LZ and SV can explain the different CHL trends for the two systems.This study expanded our understanding of the long-term changes of CHL in the SCS and provided a reference for investigating changes in the marine ecosystem.

Response of Chlorophyll a, SPAD Values and Chlorophyll Fluorescence Parameters in Leaves of Apricot Affected Some Abiotic Factors

Experimental trail conducted in Jasenica, Bosnia and Herzegovina have showed apricot （Prunus persica L） leaf injures especially on the edges in the middle of the season. Leaf edges show chlorosis starting from the tip due to lack of Chlorophyll. Affected leaves start falling and renew leaves masse as respond to stress conditions which also delay fruits maturation. Technological development in detecting the stress of high plants trough the leaf fluorescence and Chlorophyll concentration have led to the introduction of instruments which utilize fluorescence as a basis for determining stress level. The paper was aimed to show whether the productivity values calculated from Chlorophyll fluorescence Fv/Fm were comparable to those produced by spectrophotometric method in detecting Chlorophyll a concentration and SPAD values detected by Chlorophyll meter （SPAD-502）. Measurements of nitrogen content were also provided in order to obtain accuracy of SPAD meter since Chlorophyll molecules contain nitrogen in their structure. To test the relationship between these three technique regression relationship was obtained. Regression coefficient between Fv/Fm values and Chlorophyll a concentration mg g-t was high. Also, strong regression coefficient was observed between Chlorophyll a and SPAD values indicating a good accuracy of this device which was also confirmed by good regression between nitrogen content and SPAD values. Fluorometer measurements on injured leaves samples of apricot have also reviled the Fv/Fm values below 0.83 which is in according with numerous authors who considered a line for indicating stress factors.

Seasonal variation of the shape and location of the Luzon cold eddy

Using observational data from multiple satellites,we studied seasonal variations of the shape and location of the Luzon cold eddy(LCE)northwest of Luzon Island.The shape and location of the LCE have obvious seasonal variations.The LCE occurs,develops,and disappears from December to April of the next year.During this period,the shape of the LCE changed from a flat ellipse to a circular ellipse,and the change in shape can be reflected by the increase of the ellipticity of the LCE from 0.16 to 0.82.The latitude of center location of the LCE changes from 17.4°N to 19°N,and the change in latitude can reach 1.6°.Further study showed that seasonal variation of the northeast monsoon intensity leads to the change in the shape and location of the LCE.The seasonal variation of the LCE shape can significantly alter the spatial distribution of the thermal front and chlorophyll a northwest of the Luzon Island by geostrophic advection.