大气对星载被动微波影响分析研究

被动微波遥感具有全天候工作的能力,但是在不同的大气状态下被动微波遥感受大气的影响不同。为了研究大气对高级微波扫描辐射计AMSR-E (advanced microwave scanning radiometer-earth observing system)入瞳亮温的影响,分别采用晴空和典型层云大气数据作为微波辐射传输模型的输入,进行大气微波辐射信号的模拟工作并分析大气的影响。结果表明晴空下大气水汽是引起大气辐射的主要因素,晴空条件下大气对典型被动微波传感器低频的(<18.7 GHz)透过率大于0.98,在整个辐射传输过程中可以忽略不计。36.5和89 GHz的大气透过率在晴空下分别为0.896和0.756,在用微波高频通道进行陆表参数反演时需进行大气水汽影响的校正; 云覆盖条件或者阴天情况下云中液态水是引起大气辐射的主要因素,典型层云覆盖下大气的透过率在10.7,18.7和36.5 GHz分别为0.942,0.828和0.605。与晴空相比,由层云中液态水引起的大气下行辐射的增量在36.5 GHz最大达到75.365 K。表明在云覆盖时大气影响的校正过程中云层的影响是校正重点。最后利用大气探空数据计算了内蒙古海拉尔地区2013年夏季7月份的大气透过率,结果显示C、X波段的大气透过率接近1,89 GHz受水汽影响较大,其地球表层大气透过率不超过0.7。在内蒙古海拉尔地区,夏季大气透过率具有较为稳定的值,但是随着局部水汽的变化具有0.1左右的波动。     

The sky temperature in net radiant heat loss calculations from low-sloped roofs

The results of calculated and measured sky temperatures for a horizontal surface in clear night-time sky conditions are compared and discussed. In the case of large city areas (atmospheric pollution) the sky temperature may be about 10°C higher than the one calculated according to Swinbank's formula. The paper presents a quantitative analysis concerning the influence of the sky temperature values variations on net radiant heat loss and the heat balance of the low-sloped roofs.     

大气下行长波辐射快速实验测量方法研究

采用辐射传输模式模拟了特殊角度随气溶胶光学厚度及大气温湿度的变化情况,结果显示晴空下该角度不受气溶胶影响,受大气温度影响小,但受大气水汽含量影响显著,因此晴空下热红外光谱仪测量下行辐射时特殊天顶角可只根据大气水汽含量确定。西部荒漠地区下行辐射测量实验结果表明,据大气水汽含量确定的特殊角度值与实验结果一致,且该角度处辐射作为积分辐射符合精度要求。特殊角度值可用研究区大气水汽含量确定,该快速测量法可广泛用于野外实验,方便快捷测量准确瞬时下行辐射。     

针对测量仪器设计的天空亮度分析

天空亮度分布在大气光学领域有着重要的应用。利用Modtran计算了在各种大气、地表条件下的天空亮度分布,分析了大气模式、能见度、云对天空亮度分布的影响,给出了天空亮度的大致动态范围,为天空亮度测量仪器的研制,特别是探测器的选择提供了科学依据。     

AIRS与COSMIC反演大气温湿廓线比较

将福卫三号星系计划(COSMIC)气象、电离层及气候卫星探测系统、大气红外探测器(AIRS)反演的大气温度和湿度廓线与时间、空间匹配的欧洲中心中期天气预报(ECMWF)、美国环境预报中心(NCEP)分析值和无线电探空观测值进行比较, 结果表明, COSMIC具有垂直分辨率高、全天候的观测特点, 反演的大气温度和湿度廓线相对于AIRS而言与无线电探空观测值更接近, 能提供大气廓线的更精细结构, 但受掩星事件发生时所能探测最低高度的限制, 不能得到该高度以下的大气信息。AIRS在晴空时大气温湿廓线反演精度较高, 但受云天的限制, 在云层以下, 反演精度就大大降低。     

晴朗无云天空光谱辐射的近似计算模型

 利用大气光学质量和大气气溶胶光学厚度的经验公式,由HITRAN数据库获得大气分子谱线参数,基于辐射传输方程,给出了晴朗无云天空光谱辐射的近似计算模型。根据该近似计算模型对晴朗无云天空光谱辐射亮度进行的计算结果表明：天空光谱辐射亮度曲线上存在明显的O₂和H₂O吸收线;晴朗无云天空辐射的光谱分布偏蓝,天空亮度主要集中在短波段部分;太阳角小的天空光谱亮度出现“红移”现象;由于大气厚度变大,近地平的天空辐射亮度较大。     

一种半球形天空亮度测量仪器的研制

在大气光学领域中,天空亮度分布有着重要的应用.简要介绍了天空亮度的测量原理,在分析同类测量仪器的基础上,提出了一种用于白天的,可见及近红外波段天空亮度测量仪器的设计,介绍了系统的组成和探测器的选择.经过定标,仪器能够得到天空亮度的绝对值,其结果反映了真实天空亮度分布的变化.该仪器弥补了传统的天空亮度测量仪器住测量波段、实时性、便携性等方面的不足,更好地满足了实际的科研需求.     

空间目标的可见光散射与红外辐射

利用Lowtran7大气传输模型计算了0．4～0．8μm可见光波段的太阳辐射、大气自身的热辐射以及天地背景辐射。利用粗糙面光散射理论与双向反射分布函数计算了空中目标表面对太阳辐射、云层对阳光反射的散射。并利用传热学和背景辐射理论，根据能量守恒定律建立了空间目标表面温度的热平衡方程。以气球为例，计算了不同表面涂层材料的气球在不同地理位置、不同高度、不同时间、温度及辐射功率的变化。分析了空间目标红外辐射特性的一般规律和特征。     

Analytical study of the changes in the color of daylight due to sulfate droplets and soot grains in the atmosphere

Absorption of daylight by an atmospheric layer that comprises non-interacting water and sulfate droplets, interstitial soot grains, and composite sulfate-soot particles is determined by use of exact theories of Mie or extended-Mie scattering from all types of suspended particles. Interest is in the color of the sky, as observed from the ground underneath a light-absorbing atmospheric layer which has been synthesized as above. The end-result of the theory presented in this paper is the spectral radiant power distribution and the colorimetric features of daylight at ground level. The numerical application manifests that microlensing by sulfate droplets gives rise to enhanced absorption by soot grains, which results in attenuation and redshifts of daylight. An investigation is made of the changes in the color of the sky, as observed from the ground, due to pollution of the air by sulfuric acid and carbon.     

100 mK bolometers for the submillimetre common-user bolometer array (scuba) I. Design and construction

We describe the design and construction of bolometric detectors for SCUBA - the Submillimetre Common-User Bolometer Array for the James Clerk Maxwell Telescope in Hawaii. The instrument contains 131 individual detectors, in two arrays, optimized for the submillimetre atmospheric transmission windows. The detectors are cooled by dilution refrigeration to a temperature of 100 mK, so that the receiver performance will be limited by photon noise from the sky and telescope background in all wavebands. A future paper will describe the performance of the detectors with reference to typical data obtained during the laboratory commissioning period.     

Status and first results of the ANTARES neutrino telescope

The ANTARES detector is the most sensitive neutrino telescope observing the southern sky and the world’s first particle detector operating in the deep sea. It is installed in the Mediterranean Sea at a depth of 2475 m. As example for the first results, the determination of the atmospheric muon flux is discussed; a fair agreement with previous measurements is found. Furthermore, the results of a search for high-energy events in excess of the atmospheric neutrino flux are reported and significant limits are set on the diffuse cosmic neutrino flux in the multi-TeV to PeV energy range. Using data taken during the construction phase, a first analysis searching for point-like excesses in the neutrino sky distribution has been performed. The resulting sensitivity of ANTARES is reported and compared to measurements of other detectors.     

Impact of ice-supersaturated layers on atmospheric radiance

Evidence is presented that discrepancies reported between predicted and measured atmospheric downward-radiance under clear sky conditions could be due to the presence of ice haze layers. Such layers contribute significantly to the radiance in the thermal region while at the same time they contribute very little to the extinction in the visual region because of their low numbers and hence are not normally observed. The impact that ice haze layers could have on satellite-derived sea surface temperature calculations is also discussed.     

Validation of the community radiative transfer model

To validate the Community Radiative Transfer Model (CRTM) developed by the U.S. Joint Center for Satellite Data Assimilation (JCSDA), the discrete ordinate radiative transfer (DISORT) model and the line-by-line radiative transfer model (LBLRTM) are combined in order to provide a reference benchmark. Compared with the benchmark, the CRTM appears quite accurate for both clear sky and ice cloud radiance simulations with RMS errors below 0.2 K, except for clouds with small ice particles. In a computer CPU run time comparison, the CRTM is faster than DISORT by approximately two orders of magnitude. Using the operational MODIS cloud products and the European Center for Medium-range Weather Forecasting (ECMWF) atmospheric profiles as an input, the CRTM is employed to simulate the Atmospheric Infrared Sounder (AIRS) radiances. The CRTM simulations are shown to be in reasonably close agreement with the AIRS measurements (the discrepancies are within 2 K in terms of brightness temperature difference). Furthermore, the impact of uncertainties in the input cloud properties and atmospheric profiles on the CRTM simulations has been assessed. The CRTM-based brightness temperatures (BTs) at the top of the atmosphere (TOA), for both thin (τ<5) and thick (τ>30) clouds, are highly sensitive to uncertainties in atmospheric temperature and cloud top pressure. However, for an optically thick cloud, the CRTM-based BTs are not sensitive to the uncertainties of cloud optical thickness, effective particle size, and atmospheric humidity profiles. On the contrary, the uncertainties of the CRTM-based TOA BTs resulting from effective particle size and optical thickness are not negligible in an optically thin cloud.     

On the solar radiation field in a polluted atmosphere

Measurements of the fields of intensity and polarization of radiation from the sunlit sky, made in the heavily polluted atmosphere of Los Angeles, are compared with similar measurements obtained in Davis under particularly clear atmospheric conditions, and with computed fields for selected atmospheric models. Data for a thick stratus overcast are also included. The measurements are in six spectral intervals from the ultraviolet to the near infrared, the intervals being defined by interference type optical filters in combination with a photomultiplier tube having an S-20 response.     

实际大气湍流下弱光信标Shack-Hartmann波前传感器的波前斜率探测误差

 深入分析了Shack-Hartmann 波前传感器（S-H WFS）在实际大气湍流条件下弱光信标波前斜率的探测误差,导出了定量分析的数学模型。分析结果表明,当S-H WFS用于弱光信标（光子受限）湍流波前斜率的探测时,除了信标光起伏和探测器噪声外,大气强度闪烁、天空背景光等因素会增加探测误差,并且随着探测信标与天空背景光的对比度的下降,质心探测误差会随着孔径到达角起伏的增加而增加。     

Interpretation of NO2 absorption in twilight sky spectra

A multiple scattering model has been developed to calculate nitrogen dioxide (NO₂) absorption in the light from the zenith sky during twilight. Model studies show that this absorption is not very sensitive to the atmospheric temperature profile or to tropospheric NO₂.The model was used to interpret some ground-based measurements of NO₂ sky absorption. Values for the total stratospheric column amount vary from 2 to 12×10¹⁵moleccm^-2, and the mean altitude of the stratospheric concentration profile is around 35 km. These observations are in broad agreement with those of other workers.     

A Multi-Spectral Polarimeter for Measurements of Direct Solar and Diffused Sky Radiation: Calibration and Measurements

A multi-spectral polarimeter (FPR1000) is designed to measure the radiance and degree of polarization of the sky radiation as well as the extinction of solar irradiance using the same optical system. This enables us to make consistent measurements of the direct solar and diffused sky radiation. Measurements are made at the same wavelength regions as Polarization and Directionality of the Earth’s Reflectances (POLDER) and Ocean Color and Temperature Scanner (OCTS) onboard Advanced Earth Observing Satellite (ADEOS). Based on measurements for the Langley plot calibration made at Mauna Loa Observatory, the calibration constants are obtained by considering the effect of absorption by water vapor and uniformly mixed gas. Preliminary analyses of the measurements of sky radiation and direct solar irradiance carried out in the western part of the Pacific Ocean are presented. Combined measurements of the extinction of solar irradiance, and the radiance and degree of polarization of sky radiation could be useful in improving retrieval of optical characteristics of aerosol and for atmospheric correction.     

Millimetric flux densities as a test of atmospheric turbulence

In this paper it is shown how submillimetre and millimetre flux density measurements of sky fluctuations can be used to infer the characteristics of atmospheric turbulence.Two different approaches have been followed: first, by considering the observed process as due to the atmospheric turbulence, we used the r.m.s. sky fluctuations to derive some physical parametres characterizing the phenomenon; second, by investigating the power spectrum and the autocorrelation function, we derive an empirical model (the AR model) to try to deduce the physical process. In this case, the fitted power spectrum agrees strikingly with that predicted by the theory of a stationary turbulent flow for the atmosphere in the sampled frequency range. This kind of modeling can help to disentangle the atmospheric fluctuations from the extraterrestrial signal in ground-based astrophysical measurements.Measurements of the water vapour content and atmospheric transmission at the Italian Base in Antarctica, where the data have been taken, at the wavelengths of 350 μm, 1 and 2mm are also reported.     

Effect of the reflection of underlying surface on sky radiance distribution

Sky radiance might be influenced by the multiple reflectance between the earth's albedo surface and the atmosphere. Based on the Lambert's law and the radiative transfer equation (RTE), a model is developed to calculate the additional sky radiance at wavelengths of 0.4-3 μm due to the reflectance contribution of the underlying surface. The iterative method is used to calculate sky radiance without the reflectance from underlying surface. The hybrid modified delta-Eddington approximation is used to compute the atmospheric reflection of the radiation from the earth's surface. An interaction factor is introduced to deal with the multiple reflectance between the atmosphere and the underlying surface. The sky radiance increment is evaluated for some different albedos of the earth's surface. The results show that the sky radiance increment rises rapidly while viewing zenith angle is near to 90°, and the larger the albedo of the earth's surface is, the more obvious this effect appears.     

低太阳高度角条件下的天空偏振模式模拟及大气折射影响研究

为模拟低太阳高度角条件下的天空偏振模式,自主开发了考虑大气球形几何及大气折射效应的辐射传输模式VSPART,并将其运用于漫射光偏振特性仿真.在模式中,基于射线追踪法实现了光线传播轨迹的追踪和入射光偏振态及透过率的计算,基于矩阵算法实现了辐射传输方程的求解.将VSPART模拟结果与基准值、SPDISORT模拟值进行了比较,验证了模型的准确性.在瑞利散射大气和含气溶胶大气条件下,模拟并分析了漫射光偏振度及偏振方向的分布特征,讨论了大气球形几何及折射效应对天空偏振度的影响.结果表明,低太阳高度角条件下,随着波长增加,瑞利散射大气对应的偏振度整体随之增强,中性点向大天顶角方向移动;气溶胶的存在并不改变天空偏振度分布特征,但对偏振方向影响显著,随着光学厚度的增加,天空偏振度值迅速降低;中性点的偏移可能与低阶散射过程紧密相关;大气球形几何和折射效应的主要影响区域为地平线区域、两中性点附近及天顶区域;瑞利散射大气条件下,随着波长增加,大气球形几何及折射效应的影响逐步减弱,特别在中性点附近及天顶区域,其影响逐步消失;随着气溶胶光学厚度的增加,其影响随之增强.