Atmospheric Components Determination From Ground-Level Measurements During the Spectra Barax Campaigns (SPARC) Field Campaigns

The surface processes and ecosystem changes through response analysis (SPECTRA) Barrax campaigns were validation campaigns developed in the framework of the SPECTRA mission in order to verify that the geophysical data products provided by satellite imagery are consistent with the measurements made by independent means. Two campaigns took place in Barrax, Spain, during the summers of 2003 and 2004. This paper presents the results of the characterization of the atmospheric composition from solar radiation, radiosoundings, and lidar measurements. Several potentially interesting situations involving atmospheric layers with different types of aerosols and water content are discussed. The presence of a residual layer capping the mixing layer during some days of the 2003 campaign and the arrival of a dust-rich air mass from the Sahara on the last two days of the 2004 campaign provide some relevant aerosol vertical profiles to test atmospheric correction algorithms. The study of the effects of these atmospheric situations on radiative transfer calculations is required in the development and validation of advanced atmospheric correction codes for the new generation of Earth observation systems.     

Radiance Profile Enhancement for Solar Occultation Measurements

Distortions in received signals in solar occultation measurements made from space arise as a result of the systematic motion of the electro-optical sensor. In a wide range of cases, the motion-related signal distortions caused by the instrument's full modulation transfer function are as important as those from the optics. This paper demonstrates by simulation that existing techniques in the field of digital-image processing can be applied directly to solar occultation experiments to correct for these distortions. The resulting enhanced radiation profile is much closer to the true radiance profile than is the sampled output of the instrument. Use of this enhanced radiance profile in the inversion computation should improve the retrieved atmospheric profiles considerably. It also contains a study of the accuracy of such application from the point of view of instrument noise, uncertainties in the knowledge of the instrument function, and the nature of the power spectrum of the undistorted signal.     

Measurements of Earth-Space Attenuation at 230 GHz

Measurements of attenuation at 230 GHz through the total atmosphere due to the presence of oxygen and water vapor molecules, clouds, and rain are presented and discussed. The measurements were carried out using a specially designed superhetrodyne receiver mounted on a sun tracker. Simultaneons measurements were also carried out at 13 GHz. For a measuring site close to sea level at Holmdel, NJ, the "clear-sky" zenith attenuation was found to be given by A (dB) = 0.35 rho, where rho was the measured ground water vapor density in g/m/sup 3/. When the ground temperature was below about 7/spl deg/C, most cloud and overcast gave < 0.5 -dB attenuation whereas with a ground temperature greater than 13/spl deg/C, cloud attenuation was 8-10 times greater. Calculations of zenith attenuation in the 230-GHz atmospheric window were also made using the Gross analytic line shape, Schulze-Tolbert empirical line shape, and an empirically modified Gross line shape. These calculations were based on determinations of water vapor density and temperature made at the measurement site, and on radiosonde measurements made at a distance of 80 km away. Measured and calculated results are graphically compared. It is concluded that either the modified Gross line shape or the Schulze-Tolbert line shape gives conservative estimates of zenith attenuation at 230 GHz for clear days, while the Gross line shape gives fair agreement with measured results.     

Earth Rotation and Polar Motion: Measurements and Implications

Earth rotation and polar motion studies are embarking on a new era with the advent of highly accurate space geodetic techniques and the availability of global atmospheric angular momentum measurements. Space geodesy is opening new doors, answering old questions, and posing new ones. The angular momentum balance and the transfer of angular momentum between the solid Earth, atmosphere, and oceans are emerging as a problem of great scientific interest overlapping many areas, such as atmospheric science, oceanography, geodesy, and geodynamics. Here, the measurements of Earth rotation and polar motion (collectively referred to as Earth orientation) are described; the combination, smoothing, and intercomparison of these results from various techniques are presented. The calculation of atmospheric angular momentum (AAM) excitation functions are outlined; comparisons of the AAM excitation functions with variations in the length of day (LOD) and polar motion results are discussed. The associated geophysical implications (e.g., J2, 50-day oscillations) are stressed; anticipated advances and prospects for the future are high lighted.     

ARL-1 Raman激光雷达系统探测大气二氧化碳

介绍了中国科学院安徽光学精密机械研究所研制的测量对流层大气二氧化碳的ARI-I Raman激光雷达系统,以Nd:YAG三倍频作为发射光源,接收大气中氮气和二氧化碳的Raman后向散射信号,反演大气中的二氧化碳混合比分布.在ARL-1 Raman激光雷达系统中,设计了测量Raman激光雷达常数的标定装置,实验结果表明,定标光源LED的稳定度可达99.5%.利用该系统对边界层二氧化碳进行了初步定量测量和分析.     

Mechanical Measurements of the ALMA Prototype Antennas

The specifications of the Atacama large millimeter array (ALMA) have placed stringent requirements on the mechanical performance of its antennas. As part of the evaluation process of the VertexRSI and Alcatel EIE Consortium (AEC) ALMA prototype antennas, measurements of the path length, thermal, and azimuth bearing performance were made under a variety of weather conditions and observing modes. The results of mechanical measurements, reported here, were compared to the antenna specifications.     

Assessment of Atmospheric Limitations on the Determination of the Solar Spectral Constant from Ground-Based Spectroradiometer Measurements

Ground-based solar radiometer measurements have long been used to investigate various properties of both the Earth's atmosphere and the sun. This paper addresses the problem of attempting to measure the solar spectral irradiance with heretofore unachieved levels of accuracy and precision (~0.5 and ~0.1 percent, respectively) via spectroradiometer measurements made at high-altitude ground stations. Instrumentation and calibration approaches are discussed, but attention is primarily directed toward assessing limitations imposed by the atmosphere. Assessments of factors such as diffuse light contributions, uncertainty in airmass determination, variability in atmospheric optical depth, spectroradiometer bandwidth, and data analysis methods are included in the paper.     

A Low-Level Atmospheric Vertical Velocity Comparison between a High-Resolution Acoustic Sounder and a Turbulence Probe

Power spectra of vertical wind velocity, obtained using a 6.5-kHz monostatic atmospheric acoustic sounder, are presented which clearly show the inertial subrange. The spectra are compared with directly measured spectra, all measurements being made at a height of 8 m. Very good agreement is found under convective conditions although some spectral loss in the sounder measurements is experienced 2 in stable conditions. The wind structure parameter Cv2 is also estimated from the spectral density of the vertical component of the wind speed and compared with direct measurements. Time series comparisons of vertical wind velocity and Cv2, are also presented.     

Ground-Based Detection of Aircraft Icing Conditions Using Microwave Radiometers

The potential role of ground-based remote sensors in the detection of atmospheric conditions conducive to aircraft icing is evaluated. Zenith measurements of liquid water and profiles of atmospheric temperature were made by microwave radiometers located at Stapleton International Airport, Denver, Colorado. Radiometer data and sky cover observations for a two-year period were correlated with icing occurrences reported by aircraft pilots in the area. Data limitations in this study include the following: 1) the radiometer observations were made at one location and in the zenith direction only, whereas icing conditions may be highly variable in space; 2) because pilot reports vary greatly with time of day, aircraft route, etc., the reports do not systematically verify the presence of icing conditions in all situations. Given these limitations, it is concluded that the liquid measurement makes a critical contribution to the detection of icing conditions. This measurement is not generally available (e. g., from radiosondes), except from sensors like the radiometer.     

Loss Measurements of the Beam Waveguide

The diffraction loss of a new low-loss waveguide for millimeter and shorter wavelength, called the beam waveguide, was measured. The loss measurements were made using a resonator technique. The beam waveguide resonator derived from the beam waveguide consists of confocal paraboloids and is itself a very useful millimeter and sub-millimeter wave circuit component having already found application in some optical masers. Measurements made to determine the reflection loss of the resonator end plates also resulted in information on the loss of 90/spl deg/ bends in the beam waveguide. The results of the loss measurements made on the beam waveguide, in the frequency range near 9 Gc, are in good agreement with theoretical values given by Goubau.     

大气吸收闪烁测量

大孔径闪烁仪(1arge aperture scintillometer,LAS)的使用,提供了大气近地面层区域平均热通量测量的手段,但区域平均水汽通量的测量还是一个没有解决的重要问题.用LAS测量到的闪烁低频频谱和大气水汽起伏有关,和Nieveen的测量结果不同,在频谱的低端还测量到一个和吸收介质外尺度对应的拐角频率...     

Multifrequency Microwave Radiometer Measurements of Soil Moisture

Ground-based microwave radiometer experiments were performed to investigate the effects of moisture, temperature, and roughness on microwave emission from bare soils. Measurements were made at frequencies of 0.6-0.9, 1.4, and 10.7 GHz using van-mounted radiometers to observe prepared soil sites in Kern County, CA. The sites were instrumented for monitoring soil characteristics and surface meteorological conditions. Brightness temperature variations of approximately 15 K at 1.4 GHz and 25 K at 10.7 GHz were observed as a result of diurnal changes in the soil temperature. Increasing the soil moisture content from 2 to 15 percent by volume resulted in brightness temperature decreases of approximately 70 K at 0.775 and 1.4 GHz, and 40 K at 10.7 GHz, depending, to a lesser extent, on polarization and viewing angle. The results show the significance of soil temperature in deriving soil moisture from microwave radiometer measurements. Comparisons of the microwave measurements with theoretical predictions using a smooth surface model show reasonable agreement and support previous results of this nature obtained with other soil types. Approximately equal sensitivity to soil moisture was observed at 0.775 and 1.4 GHz, although the sampling depth is greater at the lower frequency.     

瑞利-拉曼散射激光雷达探测大气温度分布

介绍一台用于夜晚探测大气温度分布的L625瑞利-拉曼(Rayleigh-Raman)散射激光雷达。采用Nd：YAG激光器三倍频输出355nm作为发射激光，利用弱光子计数技术检测大气中分子的瑞利散射和N2分子振动拉曼散射回波，分析得到了平流层和对流层中上部大气温度的垂直分布廓线。其观测结果分别与HALOE／UARS卫星和无线电气象探空仪结果进行了对比分析。其中，激光雷达观测的平流层温度与HALOE卫星的结果对比表明，它们在高度25～65km内显示出较好的一致性，20个夜晚的平均温度差别基本上小于2K。激光雷达与无线电气象探空仪探测的对流层温度在高度为5～18km内反映了较为一致的分布趋势，15个夜晚的平均温度差别在6～16．5km高度内小于3K。这些结果表明，L625瑞利-拉曼散射激光雷达观测数据可靠，可用于大气温度分布的常规观测和分析研究。     

基于FTIR的目标背景辐射测量方法研究

介绍了用FTIR光谱仪进行目标背景辐射测量的方法,通过黑体对系统的光谱响应进行标定,得出系统的仪器响应函数IRF。分析背景辐射和大气的衰减作用对目标红外辐射的影响。应用MODTRAN大气辐射传输软件计算大气辐射等相关参数,给出了大气透过率谱以及测量得到的大气背景辐射谱。     

Computer-Aided Microwave Impedance Measurements

The use of a general purpose digital computer to convert data obtained from a network analyzer system to parameters useful to the circuit or device engineer is discussed. Measurement errors resulting from system imperfections such as coupler directivity and reflections from small discontinuities are removed by matrix manipulation while the data are being processed. The computer program was written to allow any three known impedances to be used as references. The use of arbitrary reference impedances instead of ideal short circuits, ideal open circuits, or perfectly matched terminations allows greater flexibility and in most cases permits the system to be calibrated with only three measurements at each frequency. Quantitative results are presented which show the large reduction of the error vector obtained when measurements are corrected using the method described. The corrected results are compared with the manufacturer's calibration data for some loads. All measurements are compared with measurements made on a recently marketed automatic network analyzer system. The computer program was written to allow the use of a time-sharing remote-access computer for fast turn-around time for small amounts of data. A second program was written for use with batch-process computers when large amounts of data are needed.     

Field-Strength Measurements of Microwave-Oven Leakage at 915 MHz

Measurements of electric field strength of microwave emissions from microwave ovens in the 915-MHz industrial-scientificmedical (ISM) band are reported. Field strengths were determined at 10 and 1000 ft under laboratory conditions and in the vicinity of two large condominium buildings, containing 385 ovens, in Ft. Lauderdale, Florida. Monitoring equipment consisted of dipole and log-periodic antennas feeding the input of a spectrum analyzer which was interfaced to a minicomputer system for automatic data acquisition and analysis. Under controlled conditions, the tested oven produced maximum field strengths of 123.5 dBuV/m and 81.0 dB,uV/m at distances of 10 and 1000 ft, respectively. Fields as high as 79.0 dBuVm were observed at the Florida location, approximately 500 ft from the buildings. Additional measurements were made of band occupancy and the effects of load placement in the oven, orientation of the oven, and polarization of the emerging fields.     

基于实测的大气参数计算厦门海域大气层顶大气散射辐射的角度分布

本文由在地面实测的气溶胶光学厚度与海面反射率计算出厦门海域大气层顶0.55μm波段大气散射辐射的空间分布与0.3-3.0μm地面总辐射，计算的地面总辐射与辐射总表的测量值有较好的一致性。     

大气气溶胶光学特性激光雷达探测

本文叙述了大气气溶胶探测激光雷达方程解和数据处理方法，给出了我们自行研制的L625和L300两台激光雷达系统的结构和主要技术参数，对平流层和对流层大气气溶胶光学特性的激光雷达探测结果进行了分析和讨论。     

Measurements of Atmospheric Water Vapor Above Mauna Kea Using an Infrared Radiometer

This paper presents the first results from a prototype infrared radiometer which has been developed to measure variations in atmospheric water vapor column abundance from high altitude sites. The performance of the infrared radiometer is compared and contrasted with that of a water vapor monitor operating at radio frequencies. Analysis shows that the infrared radiometer can measure variations at the level of ～ 1 μm precipitable water vapor (pwv) in an integration time of 1 s when the total column abundance is ～0.5 mm pwv. Since variations in atmospheric water vapor are the dominant source of phase noise in (sub)millimeter astronomical interferometry, an instrument capable of rapid and high sensitivity water vapor measurements has the potential to provide the necessary phase correction information for interferometric arrays.     

纯转动拉曼激光雷达反演低层大气折射率廓线

大气折射率是影响光电探测领域测量精度的重要因素.为了提高光电测量精度,提出利用纯转动拉曼激光雷达信号反演低层大气折射率廓线的方法.通过接收N2和O2的纯转动拉曼回波信号,由双光栅单色仪分光后获得高低量子信号.根据高低量子信号的比值反演得出大气温度和大气压强廓线,从而获得大气折射指数垂直分布.通过与折射指数理论模型相比较,表明纯转动拉曼激光雷达反演对流层折射指数有较高的精度.给出了多组折射指数廓线的反演结果,得出多天夜晚不同时刻折射指数的特性.结果表明一天中不同时刻折射指数变化较小,7.5 km内最大相对误差约为0.4%;不同月份之间折射指数波动较为明显,4.5 km内相对误差可达3.5%左右.