The Analysis Of Troposphere Microwave Radar Data, Middle And Upper Atmosphere Lidar Data And Their Retrieval Algorithms

For operational forecasting of river flow and flash floods,dense rain gage observations are desirable.But their installation has not been practical.Thus there has been considerable interest in utilizing weather radar,since it provides spatially and temporally continuous measurements that are immediately available.With the introduction of a weather radar onboard airplane or satellite,weather radar applications can be extended to a larger area,even to global scale.Airborne and spaceborne radar have a lot in common.Both instruments work at a rain-attenuating frequency,use a downward-looking,cross-track scanning geometry.Weather radars that operate at frequencies higher than 5GHz can be affected adversely by rain attenuation.However,for spacebome applications,where the size and mass of the antenna are limited,adequate spatial resolution can be obtained only by increasing the frequency.As demonstrated by Hitschfeld and Bordan(1954)in their classic study,estimates of rain rate from a single-attenuating wavelength radar are unstable when the path attenuation is large unless the radar constant and the drop size distribution are known to a high degree of accuracy.Because these conditions are seldom met,an alternative strategy is needed to complement the Hitschfeld-Bordan method for moderate and high rain rates.A way to overcome the problem is to use a constraint on the path-integrated attenuation(PIA)to bound the error.One of the proposed ways of estimating attenuation is the surface reference technique(SRT) developed over a number of years and extensively tested by airborne weather radar. kZS algorithm based on SRT is a stable rain rate retrieval algorithm for single beam and single frequency radar.It can work well for a quite large dynamic range of rain rate.It needs surface backscattering coefficient(σ⁰)and measured reflectivity factor at the surface(σ_m⁰)to get path-integrated attenuation(PIA)estimation.Estimation of attenuation coefficient k then can be easily caculated.And rain rate may future obtained by using a relevant k-R relation.In other words,if we set up aσ⁰ model, then we can easily retrieve rain rate using kZS.But the backscattering coefficient(σ⁰) varies with time and space and it isn't easy to use.We use TRMM/PR 2A21 data (from year 2002 to 2005),select three kinds of representative land surface(ocean, desert,rainforest)and investigate the their annual and seasonal changes ofσ⁰.Then we suggest an averageσ⁰ model.In order to find out whether the model can represent the realσ⁰ variation,we use kZS algorithm to test.And the rain retrieval result is pretty good over ocean and desert.Especially over ocean,the model can be used in a larger area.But in rainforest the result is not so good,and the model can only be used in a smaller area.For the data that are not suitable for kZS retrieval algorithm,the hybrid dual-beam/stereoradar algorithm is a good choice.In August 26 1998,NOAA/P3 plane made a flight at 1130UTC along the east coast of America,and the dual-beam airborne radar placed on it made a close observation on hurricane Bonnie.Almost the same time TRMM orbits fully observed the TC core.This made hurricane Bonnie to be a good comparing case.Before compared with TRMM,P3 radar data need to be processed.The measured reflectivity Z-field of P3 radar is corrected for path attenuation using the hybrid dual-beam/stereoradar algorithm.The rain pattern is also corrected for advection.Considering different cross-range resolution,we interpolate TRMM on the P3 grid.Because of the different sampling time of a hurricane by the airborne P3 radar and TRMM PR,the nearly instantaneous rain pattern observed by the PR may evolve,move during the airborne radar sampling.Such an effect is reduced by restricting the region for comparisons to a domain where the maximum time lag between the two samplings do not exceeding 600s.A serial of comparisons show the consistency between the results retrieved from the PR and P-3 data.It proves that the hybrid algorithm is a stable rain rate retrieval algorithm and suitable for airborne radar data. The middle and upper atmosphere is a region of complex photochemical and dynamic interaction and is perhaps the least understood region of the earth's atmosphere.Laser remote sensing(lidar)is one of the powerful remote-sensing techniques which offer the greatest promise of high temporal and spatial resolution observations of the atmosphere.A large number of dynamic processes in the earth's atmosphere and long-period changes of atmosphere parameters can be explored using lidar.The mesospheric Na layer is generally confined to the region between 80-110km and this layer is an excellent tracer of wave motion and now made important contribution to our understanding of the dynamic efforts of atmospheric tides and gravity near the mesopause.A Mie-Rayleigh-Sodium fluorescence lidar at the University of Science and Technology of China,Hefei(31.87°N,117.23°E),China,has been set up in December 2005,designed for measuring atmosphere parameters at altitudes between ground level to 110km.It is capable of detection of aerosol extinction(ground level to 30km), atmospheric density,temperature(25km-70km),and sodium density(80km-110km). After the lidar was set up,we have carried on routine observations.The characteristics of the shape,nocturnal and seasonal variations of the sodium layer at Hefei are given. The results show that the sodium abundance reaches a maximum of 6.014×10⁹cm^-2 in December and a minimum of 1.126×10⁹cm^-2in June.Monthly averaged Centroid height remain between 91.5～92.4km and has semi-annual variation.RMS width also illustrates semi-annual variation.