微射流强化混合对喷流红外辐射特性的影响

计算了微射流强化混合喷流在3~5μm波段的红外辐射特性,并与无微射流强化混合的喷流红外辐射特性进行了比较,分析了微射流强化混合对喷流红外辐射特性的影响.喷流的流场及温度场结果采用有限体积法求解N-S方程得到,采用Tam-Thies湍流模型模拟喷流.红外辐射特性的计算采用有限体积法求解吸收-发射性介质条件下的三维辐射传输方程得到.计算结果表明,在中等亚音速条件下,微射流可以达到较好的强化混合效果,射流流量占主流流量1%时,喷流的红外辐射强度比基准喷流的红外辐射强度降低15%左右,射流流量达到主流流量的3%时,喷流的红外辐射强度可以降低27%左右.     

脉冲射流强化混合对喷流红外辐射特性的影响

计算了脉冲射流强化混合喷流在3~5 μm波段的红外辐射特性,并与无脉冲激励喷流的红外辐射特性进行了比较,分析了脉冲射流强化混合对喷流红外隐身的效果.流场及温度场采用有限体积法和重整化群(RNG,Renormalization Group)k-ε湍流模型求解N-S方程得到.喷流的红外辐射强度采用有限体积法结合窄带模型求解吸收发射性介质辐射传输方程得到.计算结果显示,在亚音速条件下,少量的射流流量(占3%的主流流量)就可以使核心区长度缩减一半以上,在天顶角90°方向探测喷流的红外辐射强度,各个方位角上都有较大衰减,与激励源垂直的平面上的衰减效果相比,与之平行的平面上的更为强烈.      

巡航导弹红外辐射及大气衰减计算模型

对巡航导弹3个主要辐射源:蒙皮、尾喷管及羽流进行了深入分析,建立了巡航导弹红外辐射计算模型.此外,在红外辐射的大气传输理论基础上,综合考虑高度、倾斜及气象条件等各种因素,分析了大气衰减对红外辐射的影响,建立了大气透过率的理论模型与计算方法.最后,以某型号巡航导弹为例,利用此模型计算了3~5μm和8~12μm两个波段的红外辐射强度、大气光谱透过率和平均透过率,以及经过大气衰减后的红外辐射强度,并对计算结果进行了分析.结果表明,这是一种计算巡航导弹红外辐射的简单方法.      

材料粗糙度变化对卫星光谱红化效应的影响

在轨人造目标的地基观测光谱存在红化效应，影响对目标反射光谱的理解应用.目标在进入空间环境后外露材料表面粗糙度发生变化.本文结合材料的光谱散射特性、卫星轨道和观测条件，仿真分析了卫星表面材料粗糙度变化对红化效应的影响.基于文献中实验数据，设计不同粗糙度的卫星表面材料样本，模拟空间环境中材料表面粗糙度的变化.利用双向反射分布函数，建立不同粗糙度材料样本的光谱散射模型.理论模拟结果表明，材料表面粗糙度的变化会影响其光谱散射特性，散射光谱形态和散射分布取决于粗糙度及入射-反射几何关系.引入网格剖分和可见面片，利用材料双向反射分布函数，仿真计算卫星表面材料在不同粗糙度状态下，整个卫星在可见光波段的反射光谱信号.仿真结果表明，随着卫星表面材料粗糙度的增加，其反射光谱在600nm之后随波长增加而呈现上升趋势，这表明空间环境中外露材料表面粗糙度变化是卫星产生红化效应的原因之一.      

直流磁控溅射ZnO:Al薄膜的光电和红外发射特性

以锌、铝合金(ω(Al)=3%)为靶材,利用直流反应磁控溅射法制备了系列掺铝氧化锌ZnO:Al(ZAO)薄膜样品,通过X射线衍射(XRD)、扫描电子显微镜(SEM)、分光光度计、霍耳效应及红外发射率测量仪等测试仪器或方法表征了样品的结构、形貌、光学、电学及红外发射特性.测得样品最低电阻率达到1.8×10^-6(Ω·m),最大禁带宽度为3.47?eV,可见光区平均透过率达到90%,8~14?μm波段平均红外发射率在0.26~0.9之间.上述特性均随衬底温度和溅射功率的变化有着规律的变化.当方块电阻小于45?Ω时,薄膜在8~14?μm波段平均红外发射率与方块电阻遵循二阶函数变化规律.     

基于有限体积法和SNBCK模型的红外辐射特性计算

耦合求解流场、组分浓度场、基于SNBCK模型的气体辐射传输/能量方程以求准确模拟飞行器排气系统气动热力及红外特性.窄带模型参数由HITEMP逐线计算数据库计算得到.通过CO₂4.3μm波段吸收率计算,圆柱炉膛辐射换热特性计算两个算例验证了所采用程序求解辐射传输/能量方程的准确性.最后计算了两种二元喷管的红外特性,结果表明大宽高比二元喷管地面和空中状态红外辐射特性差异巨大.     

飞机红外辐射及大气透过率计算方法

研究了飞机目标的红外辐射特性,以及红外辐射在大气中的辐射衰减特性.根据现有的理论基础以及飞机自身结构特性,将飞机的红外辐射源分为蒙皮、尾喷口和羽流3部分,并提出了3个辐射源在不同波段、不同角度下的红外辐射特性计算方法.根据红外辐射的大气传输特性,采用了不同波长、不同弹目距离下的大气透过率简易计算方法,并将其与Lowtran7进行比较.计算了飞机在不同波段下,经大气衰减后,最终到达红外探测器的辐射强度.     

一种实现光学隐身的卫星构型设计

目前对地球同步轨道(GEO)空间目标的探测和识别,主要依赖光学监视系统接收其反射的太阳光线.鉴于可见光反射原理,和空间目标可见光反射特性计算模型,提出光学隐身卫星设计策略,分别对卫星平台构型、太阳能帆板、半球形遮光罩进行设计,对整星外形进行仿真分析,最后提出分布式卫星的构想.结果表明,该卫星构型光学横截面积峰值达到0.082 m~2,该构型设计具有较高的隐蔽性,不易被光学监视系统探测识别.     

Some aspects of temperature sounding of the atmosphere

Based on measurements with the interferometer spectrometer SI-1 on board of Meteor satellites the following problems are investigated: the systematic effect of the spectral response function in deriving effective radiation temperatures; the selection of ‘optimal’ spectral channels within the 15 μm region, and effects of additional molecular absorbers on the determination of the temperature profile. It can be shown that using broad-band window channels (half width ?20cm^?1) the derived surface temperature is significantly different from the surface temperature derived from narrow spectral band channels (e.g. for the HIRS window channel 8 this difference is about 1° C). Simulations of some combinations of spectral channels including one proposed as an optimal approach show no significant difference in the derived temperature profile. Neglecting the ozone absorption of the 14.1 μm band leads to a change in radiance of about 1.5 mW/m²sr cm^?1 and to a systematic error of the derived temperature of about ?2° C in the troposphere.     

FY-2卫星扫描辐射仪在轨定标方法

ＦＹ－ ２ 在轨定标是云图定量处理的关键。首先叙述了ＦＹ－ ２ 可见光、红外和水汽通道的定标方法;然后介绍了星上各通道的电定标及黑体定标的过程。结果表明红外通道在轨定标曲线与实验室定标非常接近。     

Satellite monitoring of surface temperatures in semi-desert: Differences between anthropogenically impacted terrain and protected natural vegetation

The northern Sinai is a sandy semi-desert. Severe overgrazing and other anthropogenic pressures contribute to an extremely sparse vegetative cover. A 6×6 km area was fenced off in the summer of 1974, constituting an exclosure from the grazing herds and from harvesting of plants for firewood. The vegetation in this exclosure recovered rapidly. In this study, radiances and surface temperatures of the vegetated exclosure and of the surrounding anthropogenically impacted terrain were monitored for the period March–September 1981, using NOAA-6 satellite. This satellite carries the Advanced Very High Resolution Radiometer (AVHRR) that measures visible and solar infrared radiances and also radiation temperatures at 11 μm band. In the digital images, the exclosure forms an easily recognized square, darker in the visible and solar infrared AVHRR channels than the surroundings. We concentrated on the corner in which there was no anthropogenic activity. Based on the ratio of the radiance over the exclosure to that over the surrounding terrain, the protrusions parameter s (vertical projection of the protrusions per unit area) has been estimated. The average value of s for the various satellite passes is 0.20 as measured in the visible channel and 0.18 as measured in the solar infrared. The radiation temperatures of the exclosure and of the surrounding terrain were analyzed. The radiation temperatures of the vegetated exclosure (sand with protruding bushes) are higher (by up to 2.5°K) than those of the surrounding terrain (that can be approximately regarded as bare sand). It is concluded that in an arid climate, under the semi-dormant conditions of vegetation (which prevail at all times except for the desert-bloom period, after a rain) the evapotranspiration is low, so that its effect on the surface temperatures is very small. Under these conditions, the surface temperatures are controlled by the surface albedo and the air flow at the surface.     

Calibration of the VIS-channel of meteosat-2

The “VIS-channel” (the channel is sensitive between about .4 and 1.1 μm wavelength) of the European geostationary satellite Meteosat-2 is calibrated by the method of “vicarious calibration by means of calculated radiances”. The calibration constant, which connects the 6-bit-counts of the VIS-channel of the Meteosat-2 with the corresponding “effective radiances” is determined to be c_SAT = 2.3 W·m^?2·sr^?1/count with an accuracy of ± 10% (preliminary values). The calibration constant is valid for “gain 0” and the period until October 1981. The result means, that the VIS-channel of Meteosat-2 at the beginning of its lifetime is about 15% more sensitive than that of Meteosat-1 was at its end.     

FY-3A卫星与NOAA系列卫星高能带电粒子实测结果的比较

FY-3A卫星是运行于830 km高度的太阳同步轨道气象卫星, 其搭载的空间环境监测器可观测3~300 MeV的高能质子和0.15~5.70 MeV的高能电子. FY-3A卫星在轨工作期间, 太阳活动处于由谷年向峰年过渡期, 空间环境非常平静, 探测结果显示3~300 MeV的高能质子分布主要集中在南大西洋辐射带异常区, 0.15~5.70 MeV的高能电子分布区域除南大西洋异常区外, 还分布在南北两极高纬区域. FY-3A与NOAA卫星测量结果反映出带电粒子强度及分布区域随投掷角变化的空间各向异性特征. 本文在充分考虑了带电粒子时间、空间分布差异以及比对探测器之间自身设计差异的前提下, 经过归一化处理后, 首次对两颗卫星同期探测结果进行相关性分析, 验证了两颗卫星相同时空条件下高能带电粒子通量分布的一致性; 说明FY-3A空间环境监测器不仅具备空间带电粒子辐射监测能力, 且探测结果有效可靠, 可用作辐射带环境数据源的组成部分, 为发展新的模型, 深入研究辐射带高能粒子的分布、起源和传输等提供新的观测依据.      

利用青海湖对FY—1C、FY—2B气象卫星热红外通道进行在轨辐射定标

介绍利用青海湖辐射校正场对FY－1C、FY2B气象卫星热红外通道进行在轨辐射定标，先用CE312野外热红外辐射计在水面测量水表辐亮度，再经大气订正传递到卫星入瞳处，大气订正包括大气吸收削弱和大气产生热发射影响，这两部分对卫星信号的贡献通过辐射传输模式MODTRAN37计算出来，同时进行CE312与卫星通道光谱响应匹配，最终得到卫星入瞳处的表观辐亮度，这个辐亮度与卫星通道的计数值得到该通道绝对定标系数。我们对两颗卫星进行了多次定标，结果表明利用青海湖进行的在轨定标与星上定标系数相差5％左右，相当于3K的亮温差。     

Simultaneous measurements of sea surface temperature by GMS-1 and GMS-2

For accurate measurements of sea surface temperature in the 11 μm window region, it is necessary to eliminate the effect of atmospheric absorption. A technique using observations from different angles is one of the methods of eliminating this atmospheric effect. This technique is not possible at present, using a single satellite; but using two geosynchronous satellites, it is possible to observe a common area from two different elevation angles. To correct for atmospheric effects, therefore, we compared the infrared data obtained from observations at about the same time (less than a minute apart) on the equator using the GMS-1 and GMS-2 satellites which had about 20° longitudinal separation. It was found that if the infrared spectral wavelength channel of one geosynchronous satellite is selected to be different from that of the other, it is possible to improve the two-satellite observation technique of estimating water vapor content in a tropical atmosphere. This technique corresponds to split window measurements by the AVHRR radiometer on board the NOAA-7 satellite.     

Surface temperature estimation in Singhbhum Shear Zone of India using Landsat-7 ETM+ thermal infrared data

Land surface temperature (LST) is an important factor in global change studies, heat balance and as control for climate change. A comparative study of LST over parts of the Singhbhum Shear Zone in India was undertaken using various emissivity and temperature retrieval algorithms applied on visible and near infrared (VNIR), and thermal infrared (TIR) bands of high resolution Landsat-7 ETM+ imagery. LST results obtained from satellite data of October 26, 2001 and November 2, 2001 through various algorithms were validated with ground measurements collected during satellite overpass. In addition, LST products of MODIS and ASTER were compared with Landsat-7 ETM+ and ground truth data to explore the possibility of using multi-sensor approach in LST monitoring. An image-based dark object subtraction (DOS3) algorithm, which is yet to be tested for LST retrieval, was applied on VNIR bands to obtain atmospheric corrected surface reflectance images. Normalized difference vegetation index (NDVI) was estimated from VNIR reflectance image. Various surface emissivity retrieval algorithms based on NDVI and vegetation proportion were applied to ascertain emissivities of the various land cover categories in the study area in the spectral range of 10.4–12.5 μm. A minimum emissivity value of about 0.95 was observed over the reflective rock body with a maximum of about 0.99 over dense forest. A strong correlation was established between Landsat ETM+ reflectance band 3 and emissivity. Single channel based algorithms were adopted for surface radiance and brightness temperature. Finally, emissivity correction was applied on ‘brightness temperature’ to obtain LST. Estimated LST values obtained from various algorithms were compared with field ground measurements for different land cover categories. LST values obtained after using Valor’s emissivity and single channel equations were best correlated with ground truth temperature. Minimum LST is observed over dense forest as about 26 °C and maximum LST is observed over rock body of about 38 °C. The estimated LST showed that rock bodies, bare soils and built-up areas exhibit higher surface temperatures, while water bodies, agricultural croplands and dense vegetations have lower surface temperatures during the daytime. The accuracy of the estimated LST was within ±2 °C. LST comparison of ASTER and MODIS with Landsat has a maximum difference of 2 °C. Strong correlation was found between LST and spectral radiance of band 6 of Landsat-7 ETM+. Result corroborates the fact that surface temperatures over land use/land cover types are greatly influenced by the amount of vegetation present.     

Simulation of the land surface temperature from moon-based Earth observations

The land surface temperature (LST) is a key parameter for the Earth’s energy balance. As a natural satellite of the Earth, the orbital of the moon differs from that of current Earth observation satellites. It is a new way to measure the land surface temperature from the moon and has many advantages compared with artificial satellites. In this paper, we present a new method for simulating the LST measured by moon-based Earth observations. Firstly, a modified land-surface diurnal temperature cycle (DTC) method is applied to obtain the global LST at the same coordinated universal time (UTC) using the Moderate Resolution Imaging Spectroradiometer (MODIS) LST products. The lunar elevation angles calculated using the ephemeris data (DE405) from the Jet Propulsion Laboratory (JPL) were then applied to simulate the Earth coverage observed from the moon. At the same time, the modified DTC model was validated using in situ data, MODIS LST products, and the FengYun-2F (FY-2F) LST, respectively. The results show that the fitting accuracy (root-mean-square error, RMSE) of the modified DTC model is not greater than 0.72?°C for eight in situ stations with different land cover types, and the maximum fitting RMSE of the modified model is smaller than that of current DTC models. By the comparison of the simulated LST with MODIS and FY-2F LST products, the errors of the results were feasible and accredited, and the simulated global LST has a reasonable spatiotemporal distribution and change trend. The simulated LST data can therefore be used as base datasets to simulate the thermal infrared imagery from moon-based Earth observations in future research.