Research And Design Of Microwave Limb Sounder

Atmospheric limb sounding is a new observation method, with high spatial coverage of the nadir observation as well as high vertical resolution of the occultation method。It can effectivly monitor the global distribution of ozone, aerosols and trace gases(such as: NO₂ , BrO, OClO, and SO₂ ) which play important roles in ozone dissipating process through tropospheric to stratospheric。So far, in our country,various types of satellites in orbit are not yet capable of providing data and information on atmospheric composition。Fortunately, observing atmospheric composition from sky has been started。This article summarizes and elaborates the development of modern microwave limb sounding techniques。It provides a comprehensive understanding of principles and methods used in the limb sounders which has been developed.I design a millimeter-wave limb sounder used for higher troposphere / lower stratosphere atmospheric measurement, which aims to provide a reference for the application system。I simulate the antenna performance at 118Ghz and design an auto-correlation spectrometer based on FPGA technology。With respect to fundamental theories, the paper summarizes and describes the general theory of atmospheric radiative transfer and molecular spectroscopy, introducing the general procedure of frequency selection for optimum measurement。This paper gives details on limb observation geometry,vertical resolution,the upper and lower observation height limits and sensitivity。It also compare the performance of current foreign atmospheric limb sounders。There are many contemporary radio frequency device technology widely used for astronomical observation, including the quasi-optical theory, the frequency selective surface and polarization gate。It also analyzes the structure of a Cassegrain antenna with the feed design requirements,superconducting mixer technology often used in conjunction with the refrigerator and development and also the development of radio frequency spectrum analyzers。This paper designs MLS–UTLS which is used to detect the absorption of atmospheric radiation brightness temperature from the top of troposphere and the bottom of stratosphere ,retrievie temperature, pressure, humidity and trace and trace gas composition changes in the density and distribution。It proposes system specifications including measurement frequencies used for detecting expected components , system sensitivity,vertical resolution , frequency resolution and others。A given antenna performance parameters available, including geographic structure and scanning methods。I uses Grasp 9 conduct experimental analysis of the dual offset Cassegrain antenna system at 118GHz。The detailed radiometer system block diagram and frequency conversion unit are presented。Quasi-optical devices using polarization grid, the frequency selective surface separate front frequensies。Folding Fabry - Perot ring resonator cmbine radiation signal with the local oscillator signal and fed them to the Schottky diode mixer。Second IF conversion module consisit of an IF signal frequency band separation module, two local oscillator signal generator module and the second down converter, dowmconvert the 1st IF's to a common 2nd IF frequency centered at 900MHz.The backend spectrum analyzer combines filter bank and digital auto-correlaor spectrometer to achieve large bandwidth and high spectral resolution。It also gives a number of practical considerations to the comand and data handing subsysytem as well as the calibration。Finally, this paper introduces the principle of using digital auto-correlation to detect spectrum, and adopt FPGA technology to design an auto-correlation spectrum analyzer with analysis bandwidth of 12.5MHz and spectral resolution of 0.15MHz。Autocorrelation spectrum analyzer is composed of ADC device, the core control unit, ping-pong RAM data buffer, the accumulator module, FFT module and the mode module。Use pipelines technology and ping-pong RAM memory to write and read data, can continuously buffer the A / D data and effectively reduce the system computation time. It also gives the subsystem structure diagram and implementation。The functional performance of each module in the ISE simulation environment are also presented。...