Analysis Of The Evolution Process Of NPP In The Pacific Region Based On SeaWiFS And MODIS Data

Ocean net primary production is an important parameter in the marine ecosystem,and at the same time an indicator of the photosynthesis capacity of phytoplankton in the ocean.In recent years,a large number of studies have analyzed the response relationship of marine environmental elements in ENSO events,such as ocean surface temperature,ocean wind field,etc.However,for the abnormal change process objects of NPP and the four types of ENSO events,the occurrence,development and extinction The research and analysis of the relationship between them are relatively small,and they cannot show the evolution process of the merger and division of the abnormal change process object in the ENSO event and the evolution mode of the ENSO event.Based on this,this thesis relies on the Chinese Academy of Sciences' strategic type A pilot project-the global ocean anomalous change process remote sensing monitoring system and the national key research and development plan project-ocean anomalous behavior mining,focusing on the analysis of the evolution process of the abnormal changes in the primary productivity of the Pacific Ocean.Through the DcSTCA algorithm,the ocean spatiotemporal process expression method,the Pacific Ocean is selected as the research area,and the long-term series of Sea Wi FS and MODIS data are used to calculate the spatiotemporal evolution characteristics of the NPP abnormal change process object,and analyze the correlation between the NPP abnormal change process object and the four types of ENSO events Relations,further extract the core evolution structure of the abnormal change process object,and finally establish the evolution mode of the abnormal change process object of the NPP during the ENSO event,which provides a theoretical basis for future ENSO event identification.The specific results are as follows:1)To establish a marine primary productivity raster dataset,this paper uses Sea Wi FS(Sea-Viewing Wide Field-of-View Sensor)R2014 version NPP data from January 1998 to December 2002 and the data from January 2003 to December 2019 MODIS(Moderate Resolution Imaging Spectroradiometer)R2018 version of NPP data.Through the standardized monthly average anomaly algorithm—Z-score,the fluctuation component caused by the season is eliminated,and the NPP standardized anomaly data set in the Pacific Ocean is obtained(1998-2019).2)Using the DcSTCA algorithm,the ocean spatiotemporal process expression method,the positive anomaly change process objects and the negative anomaly change process objects of the ocean net primary productivity in the Pacific area were extracted for 22 years,and the time and space of the NPP positive anomaly change process objects and the negative anomaly change process objects in the Pacific area were counted.Statistical characteristics,and analyze the temporal and spatial distribution characteristics and evolution behavior distribution characteristics of the NPP abnormal change process objects in ENSO events from three aspects:time distribution,space distribution and evolution behavior distribution.3)Analyzing the process of splitting and merging objects in the process of abnormal NPP changes in ENSO events and the correlation between the changes of their areas and the ENSO characterization index MEI,and then using the idea of Minimum Spanning Tree(MST)to identify the core evolution structure of objects in the process of abnormal NPP changes to get four main evolution structures,and finally establishing four evolution models of the NPP abnormal change process objects in the Pacific Ocean during the ENSO event.