Microwave Scatterometer Wind Retrieval Under High Sea State And Remote Sensing Of Ocean Responses To Tropical Cyclones

Spaceborne microwave scatterometers are the main tools to retrieve global sea surface wind.With the development of scatterometer wind retrieval methods over the last three decades,the accuracy of wind retrieval from scatterometer under regular conditions are high and the wind products have been successfully applied in various applications in oceanographic and atmospheric research.However,the quality of retrieved wind fields under extreme marine weather conditions is significantly degraded.This thesis aims to improve the scatterometer wind retrieval performance under extreme marine weather conditions,such as rain,wave breaking and high wind speed.The innovative results are summarized as followed:(1)the wind fields retrieved from HY-2A scatterometer were evaluated using the TAO array,NDBC array,ASCAT scatterometer wind measurements and NCEP model wind fields.The comparison results demonstrated the quality of wind fields from HY-2A scatterometer is good.(2)the effects of precipitation on HY-2A scatterometer Normalized Radar Backscatter Cross Section(NRCS)measurements and retrieved wind fields were studied and a model was proposed to correct the precipitation effects,which can improve the HY-2A scatterometer performance under rainy conditions.(3)the model proposed by Kudryavtsev(2003)was used to quantificationally investigate the effects of wave breaking on scatterometer NRCS.A new Geophysical Model Function(GMF)was constructed specially for HY-2A scatterometer.This GMF demonstrated a good performance even in extreme wind speed regime.(4)this thesis proposed a new wind retrieval method using combined HY-2A scatterometer and radiometer measurements,which extended the use of HY-2A scatterometer for high wind conditions.This thesis used the remote sensing data and Argo data to investigate the upper ocean physical and biological responses to the passing of the tropical cyclone,one of the most frequent extreme marine weather systems.The results demonstrated that the strong wind speed and wind curl would induce enhanced mixing and Ekman upwelling in the upper layer,which resulted decline of sea surface temperature,uplifting of thermocline,decline of sea surface height and increasing of sea surface Chlorophyll-a concentration.The appearance of Chlorophyll-a concentration maximum was usually several days lagged to the maximum of wind speed.The pre-existence of cold eddies in the track of tropical cyclones would enhance the upper ocean responses,resulting a more significant sea surface temperature drop and Chlorophyll-a concentration enhancement.The interaction of tropical cyclone with land in nearshore could enhance the concentration of suspended sediments and Colored Dissolved Organic Matter(CDOM),which resulted in a false Chlorophyll-a concentration enhancement.The work in this thesis could provide valuable information on the wind retrieval from Chinese HY-2A microwave scatterometer.The findings on upper ocean responses to the tropical cyclones could provide the reference to the application of remote sensing data in this field.