Front Remote Sensing Detection And Spatial And Time Change Analysis Of The Northeast Indian Ocean

The ocean front is one of an important mesoscale phenomenon,it's intensity and position always change with time.The frontal area is an important area for material exchange in the ocean.Its temporal and spatial changes are an important part of marine research.In this paper,by comparing several typical frontal detection methods,the ocean front remote sensing detection method suitable for the northeast Indian Ocean is developed.Based on this method,the multi-source satellite remote sensing data from 2002 to 2017 is used to carry out the analysis of the temporal and spatial changes of the northeast Indian Ocean frontal information,and discuss the respective trends of different fronts in detail,combined with wind and current data to carry out its correlation analysis with frontal intensity changes.The main work of this paper is as follows:(1)Comparing the adaptability of several typical frontal detection methods in the northeast Indian Ocean,the frontal automatic threshold detection method based on the combined Sobel and Canny operators is developed.Based on the SST,CHL and KD490 data from 2002 to 2017,this method is used to detect the front center line of each element in the northeast Indian Ocean.It is found that the temperature front and the ocean color front's change trend are roughly opposite,but the seasonal change of the temperature front is more obvious and detectable,the front areas are more.The seven temperature fronts detected are the Ganges-Brahmaputra Estuarine Front,the Irravadi Estuarine Front,the Palk Strait Front,the Sri Lankan Front,and the Malacca Strait Front,Java Island Front and 8°S Front.(2)The spatial distribution and seasonal variation analysis of the temperature front were carried out.It was found that the winter front occurred mostly in the northern part of the study area,with little change in the season.The summer front appeared mostly in the south,and the spring and autumn were in the transition period.The Ganges-Brahmaputra Estuarine Front and the Irravadi Estuarine Front mainly occurred during the prevailing northeast monsoon.The temperature difference across the front in winter has a large difference,and the shape and position are relatively stable.The average intensity of the Ganges-Brahmaputra Estuarine Front is relatively high;the average intensity of the Palk Strait Front is relative high,always occurs during the prevailing southwest monsoon,the intensity,the number of points and the temperature difference between the fronts changes are small,and the central position is relatively stable.The Sri Lankan Front and the Malacca Strait Front mainly exist in the southwest monsoon period,with low average intensity,points and temperature difference across the front.The average intensity of the Java Island Front is large,which exists in the prevailing period of the southwest monsoon,the interannual variation of the nearshore is small,and the westward extension is partially changed.Large;8°S Front was only detected during the prevailing southwest monsoon,with low intensity,large changes in points,cross-front temperature difference and center position.(3)Analyzed the correlation between wind,current and average intensity of the front,and found that the change of frontal intensity is consistent with the change of wind speed.The correlation between the Ganges-Brahmaputra Estuarine Front and the Irravadi Estuarine Front are highly correlated with the meridional wind speed.The southern Java Island and the 8°S front are more correlated with the zonal wind speed,and the correlation between winter and summer is different.The consistency between the average intensity of the front and the current is not high.The first four modal analysis of the EOF of the SLA are selected from the two typical front areas of the Ganges-Brahmaputra Estuarine Front and the Java Island Front.It is found that the SLA time coefficient of the Ganges-Brahmaputra Estuarine Front is basically consistent with the monsoon transition period.The SLA of the Java Island frontal zone is distributed along the southwest-northeast direction.