CE-1卫星微波探测仪测温电路对地面定标精度的影响分析

简要介绍了基于微波连接网络硬件辐射传输模型的CE-1卫星微波探测仪定标试验,给出了试验结果,并对试验结果进行了分析和验证。在此基础上,重点分析了测温精度对地面定标结果的影响,分析结果表明,测温电路的测温精度达到0.5 K,测温电路的性能满足微波探测仪定标的要求,测温误差对地面定标精度的贡献小于0.1 K,在接收机工作温度和环境温度差别较大时,基于测温电路的微波连接网络硬件辐射传输模型校正使定标结果得到明显的改善。     

23.8GHz数字相关型全极化微波辐射计的定标及其影响分析

为实现全极化微波辐射计对海面风场的高精度测量,不但需要特殊的全极化定标基准,同时需要高稳定性的接收机系统。恒温控制是提高系统稳定性简单有效的途径之一。基于23.8GHz的数字相关型全极化微波辐射计,考虑温度对于定标的影响,采用特殊的温控方案,设计出一套恒温控制系统,使辐射计工作在一种稳定的状态下。实验结果表明:通过恒温控制可以使辐射计工作维持在一种稳定的状态,从而可以简化定标过程,延长定标周期,同时保证定标精度的要求。     

微波辐射计接收机的逆向辐射噪声对天线定标的影响仿真

基于有限积分算法,仿真计算了微波辐射计接收机的逆向辐射噪声温度对于接收天线口面的附加温度,并根据CST仿真软件计算结果,对照给定的简化理论模型,具体分析了微波辐射计逆向辐射噪声温度微波辐射计定标桶罩以及天线口面位置的影响。     

韩国科学技术卫星二号主载荷-双频微波辐射计

双频微波辐射计是韩国科学技术卫星二号的主载荷,目前已完成了正样研制并交付韩国。双频微波辐射计是全功率形式的微波辐射计,星上采用两点定标方式。由于受卫星平台的限制,天线不能做得很大并进行扫描,因此选择了接收机定标的方案,即定标支路和观测支路采用了不同的天线,通过多路开关与接收机连接。系统及验收测试表明,双频微波辐射计满足韩方的各项功能和性能指标要求。介绍了韩国科学技术卫星二号的基本情况以及双频微波辐射计的设计方案。给出了主要指标和系统试验结果。     

微波辐射计定标

对微波辐射计的两种定标方法进行了介绍,即分步定标法和整体定标法。分步定标法需要测量的中间参数较多,故误差来源多,定标精度低。整体定标一次完成,没有中间环节,因此定标精度较高,缺点是要求有一个提供给天线的准确、可靠的噪声环境,成本较高。本文在现有的实验条件下,分别对５．４ＧＨｚ和３７ＧＨｚ微波辐射计进行了整体定标和接收机定标,并对定标结果进行了对比。     

星载毫米波亚毫米波辐射计定标的初步研究

星载微波辐射计采用平方律检波,物体的辐射功率与接收机的输出电压成线性关系。因此星载微波辐射计采用高低温两点定标。其中高温定标源采用处在环境温度下的黑体,低温定标源为冷空背景辐射。由 Rayleigh-Jeans公式计算的物体的辐射功率与其物理温度成线性关系,但是随着物体频率的升高,Rayleigh-Jeans公式与Planck定律的近似误差越来越大,此时应根据Planck定律计算物体的辐射功率。从Planck定律出发,对毫米波、亚毫米波辐射计的定标方程进行了推导,并给出了高低温定标源的辐射功率在毫米波和亚毫米波段的表达式。     

X波段全极化微波辐射计的计算机仿真

全极化微波辐射计是未来星载遥感海面风场的重要微波遥感仪器,可为短期天气预报、气候学和海洋学研究提供重要的有价值信息,利用软件平台对全极化辐射计进行计算机仿真对于系统设计和全极化定标技术仿真验证具有重要的意义。对X波段相关型全极化微波辐射计进行了计算机仿真,基于ADS软件平台建立了相关型全极化微波辐射计系统仿真模型,对仿真模型有效性进行了验证,并在仿真模型基础上对全极化定标技术进行了仿真验证。结果表明仿真模型准确有效,可为系统设计和全极化定标仿真验证提供参考。     

星载W波段毫米波辐射计研究

在863-2项目支持下,开展了W波段毫米波辐射计的研究。其工作中心频率为90.5 GHz,带宽为2 GHz,积分时间为200 ms时其系统灵敏度达到0.6 K,线性度优于0.999。这些技术指标基本达到了星载应用的要求。为配合扫描成像研制了两套天线系统,一套为Cassegrain天线,另外一套为二元光学天线,它是利用光学衍射原理制成的位相型Fresnel波带片。二元天线具有设计灵活、加工方便、体积小、重量轻、旁瓣电平低和安装方便等优点。W波段微波辐射计系统在实验室内进
行了扫描成像试验,取得了W波段微波辐射计扫描图像。     

车载多频率微波辐射计与观测数据应用

地基微波辐射计是被动微波遥感研究中进行地面实验的核心仪器。了解辐射计的观测原理以及实验方法对实验的设计和数据的分析具有重要意义。2007年遥感科学国家重点实验室购置了车载多频率微波辐射计,自仪器投入使用以来,获取了多种典型地表的微波辐射测量数据。基于车载多波段微波辐射计开展的地面观测实验为被动微波遥感地表参数反演算法的发展、辐射传输模型的验证等研究提供了重要的数据支持。详细介绍了车载多频率微波辐射计的配置、观测原理和定标方法,并结合地面实验,介绍了利用车载多频率微波辐射计进行实验的方法及数据的处理与应用。该研究对地基微波辐射计观测实验的设计与实施以及对辐射计数据的分析和使用有重要的参考价值。     

星载微波辐射计定标热源研究

介绍了应用频率在10-90GHz波段的星载微波辐射计定标热源的结构及其功能;论述了定标热源微波吸收材料选择、吸收体结构设计、热设计及温度测控等技术与方法;给出了定标热源吸收率和温度特性测试结果。地面和在轨运行均表明,该定标热源满足星载微波辐射计设计要求。     

Evaluation of the Oceansat‐1 Multi‐frequency Scanning Microwave Radiometer and its potential for soil moisture retrieval

The Multi‐frequency Scanning Microwave Radiometer (MSMR) aboard the Indian Space Research Organization—Oceansat‐1 platform measured land surface brightness temperature at a C‐band frequency and provided an opportunity for exploring large‐scale soil moisture retrieval during its two‐year period of operation. These data may provide a valuable extension to the Scanning Multichannel Microwave Radiometer (SMMR) and the Advanced Microwave Scanning Radiometer (AMSR) since they covered a portion of the time period between the two missions. This investigation was one of the first to utilize the MSMR data for a land application and, as a result, several data quality issues had to be addressed. These included geolocation accuracy, calibration (particularly over land), erroneous data, and the significance of anthropogenic radio‐frequency interference (RFI). Calibration of the low frequency channels was evaluated using inter‐comparisons between the Tropical Rainfall Measuring Mission/Microwave Imager (TRMM/TMI) and the MSMR brightness temperatures. Biases (TMI T _B>MSMR T _B) of 3.4 and 3.6 K were observed over land for the MSMR 10.65 GHz horizontal and vertical polarization channels, respectively. These results suggested that additional calibration of the MSMR data was required. Comparisons between the MSMR measured brightness temperature and ground measured volumetric soil moisture collected during the South Great Plain experiment (SGP99) indicated that the lower frequency and horizontal polarization observations had higher sensitivity to soil moisture. Using a previously developed soil emission model, multi‐temporal regional soil moisture distributions were retrieved for the continental United States. Comparisons between the MSMR based soil moisture and ground measured volumetric soil moisture indicated a standard error of estimate of 0.052 m³/m³.     

基于机器学习算法的AMSR-2地表温度降尺度研究

MODIS日尺度的地表温度受到天气影响,有效像元信息严重缺失,这对数据稀缺区域尤为重要。以古尔班通古特沙漠为研究区,探索了采用AMSR-2的垂直极化亮度温度与植被指数对地表温度空间降尺度的方法,并用此方法填补了2018年MODIS的缺失像元。(1)通过十折交叉验证,对4种机器学习算法（Cubist、DBN、SVM、RF）、10个波段组合、2个空间尺度（5 km、10 km）下的训练模型进行了分析,表明RF算法精度明显高于其他3种算法,C09波段组合的验证精度高于其他波段组合。(2)构建了2个鲁棒性的随机森林算法地表温度降尺度模型（5 km|RF|09、10 km|RF|09）,将AMSR-2亮度温度降尺度到1km分辨率,表明5 km|RF|09模型反演结果更为合理,MODIS与站点验证的R2分别为0.971、0.930,RMSE分别为3.38 K、4.71 K,MAE分别为2.51 K、3.84 K。(3)降尺度结果填补MODIS地表温度缺失像元,将其应用到古尔班通古特沙漠长时间序列的陆表温度分析,可为数据稀缺区域数据获取提供科学参考。     

星载微波辐射计定标热源研究

介绍了应用频率在10~90 GHz波段的星载微波辐射计定标热源的结构及其功能;论述了定标热源微波吸收材料选择、吸收体结构设计、热设计及温度测控等技术与方法;给出了定标热源吸收率和温度特性测试结果。地面和在轨运行均表明,该定标热源满足星载微波辐射计设计要求。     

Comparing SMMR and AVHRR data for drought monitoring

Abstract

Coincident Scanning Microwave Multi-channel Radiometer 37 GHz and Advanced Very High Resolution Radiometer normalized difference vegetation index satellite data have been compared from drought-affected regions of sub-Saharan Africa and northeastern Brazil for the time period of 1980–1985. Although the two satellite data types can be highly correlated, differences between them were found for the Sahel zone in 1985 and for northeastern Brazil from 1984–1985. These findings suggest that scattering or surface roughness contributions may be greater than previously assumed for the 37 GHz microwave data. A programme of field measurements should be undertaken to increase our understanding of natural vegetation at 37 GHz and higher microwave frequencies.     

Further validation of a new methodology for surface moisture and vegetation optical depth retrieval

A series of validation studies for a recently developed soil moisture and optical depth retrieval algorithm is presented. The approach is largely theoretical, and uses a non-linear iterative optimization procedure to solve a simple radiative transfer equation for the two parameters from dual polarization satellite microwave brightness temperatures. The satellite retrievals were derived from night-time 6.6?GHz Nimbus Scanning Multichannel Microwave Radiometer (SMMR) observations, and were compared to soil moisture data sets from the USA, Mongolia, Turkmenistan and Russia. The surface temperature, which is also an unknown parameter in the model, is derived off-line from 37?GHz vertical polarized brightness temperatures. The new theoretical approach is independent of field observations of soil moisture or canopy biophysical measurements and can be used at any wavelength in the microwave region. The soil moisture retrievals compared well with the surface moisture observations from the various locations. The vegetation optical depth also compared well to time series of Normalized Difference Vegetation Index (NDVI) and showed similar seasonal patterns. From a global perspective, the satellite-derived surface soil moisture was consistent with expected spatial patterns, identifying both known dry areas such as deserts and semi-arid areas and moist agricultural areas very well. Spatial patterns of vegetation optical depth were found to be in agreement with NDVI. The methodology described in this study should be directly transferable to the Advanced Microwave Scanning Radiometer (AMSR) on the recently launched AQUA satellite.     

Monitoring global vegetation using Nimbus-7 37 GHz Data Some empirical relations

Abstract

The difference of the vertically and horizontally polarized brightness temperatures observed by the 37 GHz channel of the Scanning Multichannel Microwave Radiometer (SMMR) on board the Nimbus-7 satellite are correlated temporally with three indicators of vegetation density, namely the temporal variation of the atmospheric CO₂ concentration at Mauna Loa (Hawaii), rainfall over the Sahel and the normalized difference vegetation index derived from the Advanced Very High Resolution Radiometer (AVHRR) on board the NOAA-7 satellite. We find the SMMR 37GHz and AVHRR provide complementary data sets for monitoring global vegetation, the 37 GHz data being more suitable for arid and semi-arid regions as these data are more sensitive to changes in sparse vegetation. The 37 GHz data might be useful for understanding desertification and indexing CO₂ exchange between the biosphere and the atmosphere.     

Satellite observed seasonal and inter-annual variation of vegetation over the Kalahari,The Great Victoria Desert,and The Great Sandy Desert: 1979–1984

We present time-series observations by two spaceborne sensors over three desert regions, the Kalahari (in southern Africa), and the Great Victoria Desert and the Great Sandy Desert (in western Australia). The observations are by the Advanced Very High Resolution Radiometer on board the NOAA-7 satellite from April 1982 to December 1984, and by the Scanning Multichannel Microwave Radiometer on board the Nimbus-7 satellite from January 1979 to February 1985. The objective was to compare and contrast seasonal and interannual variation of vegetation over these three deserts using the normalized difference vegetation index and the 37 GHz brightness temperature. The seasonal variation from both sensors was found to be most pronounced over the Kalahari, followed by the Great Sandy Desert and the Great Victoria Desert. The normalized difference vegetation index was roughly identical over the two Australian deserts and was significantly higher for the Kalahari. Additionally, there was no consistent change from both sensors over the two Australian deserts, but a consistent decrease from 1979 to 1984 over the Kalahari was found in the 37 GHz microwave data.     

Observation of hydrological features with Nimbus-7 37 GHz data,applied to South America

Abstract

The microwave polarization difference temperature (MPDT) prepared from 37 GHz Scanning Multifrequency Microwave Radiometer (SMMR) data from the Nimbus-7 satellite allows a unique vision of hydrological features, especially of humid areas. From the series of monthly images from 1979 to 1985 the major hydrological features of four major river basins of South America are briefly examined. These include rivers of the Amazon, La Plata, Orinoco and Sao Francisco basins, wetlands in the La Plata and Amazon basins and floods in the La Plata basin. Many hydrological features appear much as they do on conventional maps. An interesting perspective can be derived from the ways in which they differ from conventional maps.     

Observed and modelled effects of ice lens formation on passive microwave brightness temperatures over snow covered tundra

Immediately before an April 2007 snow survey and passive microwave radiometer field campaign in the Northwest Territories, Canada, a rain-on-snow event deposited a thin (~ 3 mm) continuous layer of ice on the surface of the snowpack. At eight sites the brightness temperature (T_b) of the undisturbed snow pack was measured with a multi-frequency dual polarization (6.9, 19, 37, and 89 GHz) ground based radiometer system. The ice lens was then carefully removed and the T_bs were measured again. The individual V-pol channels and the 37 V − 19 V difference were largely unaffected by the presence of the ice lens, exhibiting a systematic shift of about 3 K. In comparison, the ice lens had a considerable effect on the H-pol T_b at all frequencies, with a mean difference (ice lens present − ice lens removed) of − 9 K (± 5.3 K) at 6.9 GHz, − 40 K (± 11.3 K) at 19 GHz, − 33 K (± 7.6 K) at 37 GHz, and − 19 K (± 8.0 K) at 89 GHz. The effect of the ice lens on H-pol measurements was also observed with spaceborne data from the Advanced Microwave Scanning Radiometer (AMSR-E) satellite data.Simulations of T_b were produced for each site using a new two layer formulation of the Helsinki University of Technology (HUT) snow emission model. The ice lens was used as the top layer and the underlying snowpack considered as a homogenous second layer. The agreement between observations and simulations was variable, with agreement strongest at 19 GHz. A comparison with simulations produced using the Microwave Emission Model of Layered Snowpacks (MEMLS) suggests HUT model uncertainty is related not to the ice lens, but to difficulties in simulating emission from deep snow. Overall, the observations and simulations suggest H-pol measurements are capable of detecting new ice layers across the tundra snowpack, while V-pol measurements are more appropriate for snow water equivalent (SWE) retrievals due to their relative insensitivity to ice layers.