| As a typical extreme hydro-climatic disaster,drought has a profound impact on the industrial-agricultural production,social-economic activity,and survival of mankind.Therefore,the monitoring of drought is a core objective for the study of extreme weather,agricultural production,urban climate,and ecological environment.With the continuous developments of earth observation technology in recent years,drought monitoring has evolved from ground-based observation to space-air-ground integrated drought observation web.Faced with tremendous ground and satellite observation resources,it has been a key scientific question to construct highly efficient collaborative monitoring architecture in order to meet the timeliness,accuracy,and spatial-temporal coverage requirements in drought monitoring.At present.there are only some preliminary studies about multi-sensor collaboration in the remote sensing community.And limited collaborative monitoring methods based on multi-ground sensor or multi-satellite sensor have been proposed.With respect to the field of drought monitoring,researchers have continued to design new multivariate integrated drought indices.However,there is still no satisfying answer to the core scientific question that how to collaborate multi-sensor for the drought monitoring purpose.The current limitations include:The understanding of dynamic observation capability is unclear,and the cyber infrastructure of multi-sensor collaboration is lost;At the same time,the current multi-sensor research is limited to multi-data fusion or integration,without the collaboration during observation phase;Besides that,there is no approach to continuously monitor drought development process,let alone the quantitative measurement of accumulated drought impacts on the crop.Aiming at these scientific questions about multi-sensor collaboration for drought monitoring,this paper started from a systemic analysis on the observation capability,which is the main body of collaboration.And then this paper proposed several multi-ground,multi-satellite,and multi-ground-satellite based collaboration methods for the soil moisture monitoring,which is the core variable of drought.Based on that,this paper put forward a multi-sensor collaborated method for monitoring the development of drought,which is a direct solution for the complex drought event.After that,the process of drought has been integrated with the process of crop growing on the ground.By doing that,a new concept and model about accumulated drought index were proposed.The above research answered the question that how to collaborate multi-sensor for drought monitoring from multi-aspects,and also demonstrated the improvement of eff-iciency compared with singular sensor-based monitoring method.Specifically,this study includes the following five sections.(1)The capability foundation of multi-sensor collaboration for drought monitoring.The section conducted study on the capability foundation of multi-sensor collaboration.The dynamic observation capability was decomposed into five sub-capabilities,including spatial-temporal coverage capability,theme observation capability,spatial-temporal attribute capability,environment capability,and accuracy capability.The dynamic changes of observation capability was analyzed emphatically especially under different requirements of drought monitoring tasks.Finally,the model of dynamic observation capability index(DOCI)was proposed to quantify the observation capability during different drought montironig tasks.(2)One multi-satellite sensor collaboration method for soil moisture anomaly monitoring.Because of the lack of collaboration during monitoring process,this section put forward a multi-sensor collaboration method during the observation phase,named STMC,which is different from the current method after the observation phase.In this method,we first analyzed the important role played by regional soil moisture distribution and changes for soil moisture monitoring,which is one of the most critical variables in the drought monitoring.Then the fast detection algorithm for soil moisture anomaly was proposed.Finally,the STMC method collaborated high temporal resolution sensor and high spatial resolution sensor,to realize the fast detection and intensive observations for regional soil moisture anomaly.(3)One multi-ground sensor collaboration method for real time soil moisture monitoring and mapping.This section proposed a typical multi-ground sensor collaboration method based on the above new collaboration concept and open geospatial web services.The focus is on the cyber-physical information infrastructure based on multiple open geospatial web services for collaboration.It is consisted of three layers and two interaction models in the architecture.This method was applied in the multi-ground sensor collaboration experiment for real time soil moisture monitoring and mapping.It was suggested this infrastructure could be useful for realizing multi-sensor collaboration in a real case.(4)One multiple ground-satellite sensor collaboration method for soil moisture reconstruction.Based on the complementarity of ground soil moisture sensor and satellite sensor,this section proposed a new reconstruction method called SICR for regional soil moisture observation.The key is the quantitative relationship between the observation of ground and satellite sensor.SICR is consisted of four reconstruction rules,and realizes the regional soil moisture reconstruction under 100%cloud contamination.The performance of SICR method is better than satellite-based or in-situ sensor-based reconstruction method.(5)One multiple ground-satellite sensor collaboration method for agricultural drought process monitoring and impact assessing.Based on the evolving feature of agricultural drought development and different observation capabilities owned by satellite and ground sensor,this section proposed a multi-sensor collaboration method called EPMC for monitoring the process of agricultural drought.This method is capable to achieve the continuous monitoring of the anomaly sequence from precipitation to soil moisture and to vegetation condition.Then four different development phases during every agricultural drought event were extracted from EPMC.Based on that,a new agricultural drought index,called PADI was proposed.The model of PADI integrates both processes of agricultural drought and ground crop growth,which is the key to quantify the accumulated drought impacts on crop.The innovation of this study includes the following three aspects:(1)The dynamic changes of observation capability has been analyzed,and the dynamic observation capability index model was also proposed to realize quantantive calculation of observation capability under different tasks;(2)To meet the requirement of continuous soil moisture monitoring in drought situation from both spatial and temporal aspects,a satellite-ground sensor collaboration method was proposed to realize regional soil moisture reconstruction;(3)A drought evolution process-oriented satellite-ground sensor collaboration method and a new accumulated drought index model were proposed.Not only the whole development process of agricultural drought was obtained by sensor collaboration,but also the crop phenology information was further integrated to obtain the accumulated drought impacts on crop during its entire growing season. |
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