Study On The Retrieval Theory And Method Of Sea Surface Pressure Basing On Passive Microwave Observations

Sea surface pressure is an important meteorological parameter,which has very important applications in the fields of numerical weather prediction,climatology studies and tropical cyclone(TC)analysis and prediction.The proposed surface pressure remote sensing methods have problems of low spatial and temporal resolutions,incapability to work all-weather and poor detection accuracy during strong winds.To solve these problems,a new method of retrieving sea surface pressure using passive microwave observations at oxygen absorption band was proposed in this dissertation.Retrieval models were established using the observations of spaceborne microwave radiometer.Retrieval results were validated againest analysis data and in situ observations.The purpose of this dissertation is to provide sea surface pressure data with high accuracy,high spatial and temporal resolution for meteorological applications and atmospheric science research.Based on the atmospheric radiation transfer equation,the theoretical basis of retrieving sea surface pressure using passive microwave observations was established.Sea surface pressure sounding is achieved by microwave radiometers due to their capability to measure the total columnar oxygen absorption.The direct relationship between brightness temperatures(TBs)observed by spaceborne microwave radiometers and sea surface pressure was deduced and verified by simulation.Sensitivity analysis experiments have been carried out which show that the observed TBs in the wing of oxygen absorption band are sensitive to the variation of sea surface pressure and are suitable for the estimation of sea surface pressure.This provides a basis for the selection of sensing frequency of sea surface pressure.A retrieval algorithm to estimate sea surface pressure in mid-to-low sea state conditions was proposed.Using the measured TBs of Advanced Technology Microwave Sounder(ATMS)onboard the Suomi-National Polar-Orbiting Operational Environmental Satellite System Preparatory Project(SNPP)satellite and the Microwave Humidity and Temperature Sounder(MWHTS)onboard the Fengyun-3C(FY-3C)satellite,the retrieval of sea surface pressure in mid-to-low(40°S-40°N)latitudes was performed.The retrievals were compared with analysis data and in situ data.Results show that the proposed retrieval algorithm can estimate sea surface pressure over mid-to-low latitude areas with the root mean square errors of less than2.0 hPa,3.0 hPa,and 3.5 hPa for clear-sky,cloudy,and rainy conditions,respectively.Several TC retrieval experiments show that the proposed retrieval algorithm behaves well under mid-to-low sea state conditions and has strong capability to identify tropical cyclones.However,the retrieval performance during very strong winds(1-minute sustained winds>26 m/s)is not satisfactory due to the abnormal temperature and humidity structures near intense TCs'centers.Considering the influence of abnormal temperature and humidity structures on the retrieval of sea surface pressure,a retrieval algorithm for TC conditions was proposed.The TC algorithm is applied after the abnormal low pressure areas are captured by the mid-to-low sea state algorithm.The TC algorithm uses brightness temperatures(TBs)and TB anomalies together to accurately estimate TC surface pressure field.TB warm anomalies are measurements of TC upper-tropospheric temperature anomaly which relates to the pressure anomaly near TC centers.The addition of TB anomalies improves the estimation accuracy during strong winds.In addition,retrieval experiments for TCs with different intensities were completed not only using the observations from the SNPP/ATMS but also the FY-3C/MWHTS.The retrievals were compared with analysis data and in situ data.Results show that the proposed method can estimate the surface pressure fields of a TC's core area(within a 2°circular radius from the center)with an accuracy of better than 4.0hPa,5.0 hPa,and 8.0 hPa for tropical depressions or tropical storms,typhoons or hurricanes,and severe typhoons or major hurricanes,respectively.In addition,the accuracy of the retrieved central pressure is better than 6.0 hPa,8.0 hPa,and 10.0 hPa for tropical depressions or tropical storms,typhoons or hurricanes,and severe typhoons or major hurricanes,respectively.To compare the detection capability of sea surface pressure in 50-60 GHz and 118GHz,the TB data measured by ATMS and MWHTS were used to obtain surface pressure in mid-to-low sea state and TC conditions.In situ data and analysis data were used to validate the retrievals.Results show that the detection capability of sea surface pressure in 50-60 GHz and 118 GHz are all encouraging.Their detection capability are similar in mid-to-low sea state conditions.For TC conditions,the detection capability of 50-60 GHz is a little better than 118 GHz.This provides a reference for high spatial resolution surface pressure observations in low orbit satellites and high temporal resolution observation through geostationary orbit in the future.