机载全极化微波辐射计系统设计及海面亮温的提取方法

机载全极化微波辐射计（Airborne full Polarization Microwave Radiometer,APMR）是国家重大科技基础设施航空遥感系统的主要载荷之一，用于获取来自地球表面和大气的微波辐射电场的极化信息，从而反演地球表面和大气的物理参数. APMR是一个5频点的被动微波遥感器，中心频点分别为10.7 GHz,18.7 GHz,23.8 GHz,37.0 GHz和90 GHz.其中，23.8 GHz和90 GHz采用水平和垂直极化接收方式；10.7 GHz,18.7 GHz和37.0 GHz采用全极化接收方式，同时接收观测场景辐射的4个Stokes参数亮温.该文在介绍我国第一台机载全极化微波辐射计APMR系统主要技术特点和基本性能指标的基础上，提出了由辐射计输出参数进行全极化定标、再进行海面亮温提取的二级数据处理方法，从而得到海面亮温的4个Stokes参数信息，其可用于海面风向、风速等参数的反演. APMR于2020年6月在东营进行了海上的搭载飞行试验，从实验结果中提取到的海面亮温与预期情况一致，这使仪器的工作性能以及海面亮温的提取方法得到验证，为未来机载平台获...     

一种热红外分裂窗辐射量线性组合的陆地温度遥感反演方法

分裂窗技术已成功应用于海温反演.但当其用于陆地温度反演时,通常产生较大误差.选用7类共51种标准地物,分析研究了各种分裂窗算法用于陆面温度反演所产生的误差及误差来源.提出了新的分裂窗算法,用分裂窗辐射量线性组合代替亮温线性组合.新的分裂窗反演算法受大气影响很小,使陆地温度反演精度优于3K,水体反演精度优于0.15K.     

基于微波高光谱技术的数据仿真及参数反演研究

发展高光谱微波辐射计对于提升大气参数反演精度具有重要意义。利用微波辐射传输模型mpm93以及BP 神经网络方法分别构建正演上行辐射亮温和反演大气温度廓线的模型,并研究了晴空条件下高光谱微波辐射计反演大气温度廓线的精度。54～58 GHz、64～68 GHz 在氧气吸收波段选取80 个通道作为高光谱通道,基于2015 年5～12 月昆明的探空资料进行正、反演仿真实验。选取微波成像仪/ 探测仪(SSMIS)的9 个温度探测通道进行对比实验,评估分析反演效果。实验结果表明:在大气3～10 km 高度范围内,高光谱通道的反演精度较SSMIS 提高了0.3 ～0.6 K;在0～3 km 高度范围内,反演精度提高了1 K。     

双通道微波辐射计反演大气剖面的改进算法

利用地基双通道微波辐射计(23.8和31.65GHz)所测量的大气辐射亮温以及地面的大气温度,湿度和压强测量值,给出了一种反演大气温度和水汽密度剖面的非线性回归算法,并利用郑州地区的历史探空资料进行仿真验证,结果表明非线性回归算法较线性回归算法具有更好的大气剖面反演精度.     

FY-3C微波湿温探测仪118 GHz和183 GHz通道辐射特性仿真分析

我国第二代极轨气象卫星的第三颗星——风云三号C星(FY-3C)已于2013年9月发射.为探讨微波湿温探测仪大气探测通道对大气参数的探测能力,采用威斯康星大学的非流体静力学中尺度模式系统(UW-NMS)模拟Katrina飓风的基础数据集,结合微波辐射传输模式,正演模拟分析了微波湿温探测仪118 GHz和183 GHz通道的辐射特性.仿真结果表明118 GHz和183 GHz通道作为星载亚毫米波大气探测通道,能够提供更加精细的大气温度和湿度廓线信息;冰态粒子的散射作用可使(118.75±5.0)GHz和(183.31±7.0)GHz通道亮温分别下降108 K和76 K,新增的探测频点和通道能提升对云雨大气的探测能力;118 GHz和183 GHz通道亮温对云中各种水凝物粒子响应的模拟分析结果证明了这两组通道在云中水凝物分布特性反演方面的潜在探测能力;大气中雨水含量的增加可以导致(118.75±5.0)GHz通道亮温下降4.5 K,118 GHz对液态粒子特有的响应能力,显示了其作为降水反演频点的优势;大气中雪粒子含量的增加会使(118.75±5.0)GHz通道亮温下降10 K,可利用该通道探测云中的雪晶含量.     

一种基于稀疏先验的综合孔径展源辐射成像统计反演方法

确定性的综合孔径辐射计反演方法没有考虑亮温分布先验信息的统计特性.针对亮温分布具有非连续特性的展源,本文提出了一种基于稀疏先验的综合孔径展源辐射成像统计反演方法.根据该方法,采用修正的差分算子提取亮温非连续分布展源中隐含的稀疏先验,建立稀疏先验概率分布的多层先验等效高斯模型,将图像反演等效为该模型超参数估计,并采用期望最大化算法估计该模型超参数.仿真和实验结果表明:与现有的综合孔径辐射计确定性反演方法相比,本文提出的反演方法不仅能有效提高反演图像的准确度,而且对综合孔径辐射计的各种误差鲁棒性更强.     

综合孔径辐射计亮温反演算法研究

综合孔径辐射计通过干涉测量技术反演目标辐射亮温图像,属于空域傅里叶变换范畴,其中相关运算中由各阵元之间传输延时造成的空间解相关效应,对亮温反演结果具有重要影响.文章从空域频率采样的角度分析了反演算法,同时探讨了G矩阵相关性以及空间解相关效应对亮温反演的影响.在传统的BG(Backus-Gilbert)算法基础上,提出了补偿空间解相关效应的方法,利用去相关矩阵对带宽、通道不一致性造成的误差进行了补偿.     

基于FY-3C/MWHTS资料的海洋晴空大气温湿廓线反演方法研究

针对搭载于风云三号C星(FY-3C)上的微波湿温探测仪(Microwave Humidity and Temperature Sounder, MWHTS), 建立了海洋晴空大气条件下温湿廓线同时反演的一维变分反演系统.通过对影响反演精度的各个因素进行分析, 确立了该系统的输入参数.对于FY-3C/MWHTS观测亮温与快速辐射传输(Radiative Transfer Model for TOVS, RTTOV)模型的模拟亮温之间的偏差和角度依赖性, 采用逐像元统计回归校正方法进行校正.选择西北太平洋海域晴空条件下的校正亮温数据进行温湿廓线的反演, 并利用欧洲中期天气预报中心再分析数据集对反演结果进行验证, 结果表明:反演的温度廓线和相对湿度廓线的最大平均偏差分别为1.09 K和5.4%, 最大均方根误差分别为1.48 K和22.69%, 与未校正亮温的反演结果相比, 温度廓线的均方根误差最大可减小1.56 K, 湿度廓线的均方根误差最大可减小14.71%.反演温湿廓线与背景廓线的精度对比表明:反演的温度廓线在10~70 hPa、300~350 hPa和700~850 hPa内的精度高于背景廓线的精度, 而反演湿度廓线的精度除了825~875 hPa, 其他范围均高于背景廓线的精度, 因此FY-3C/MWHTS观测亮温的反演结果可进一步提高预报廓线精度.     

综合孔径辐射计反演成像算法研究

高效的反演成像算法是综合孔径辐射计成像的关键技术之一。提出一种基于视场细分的改进反演成像算法,将视场细分成多个矩形子区域,利用反演亮温与可视度函数的傅里叶变换关系,得到每个子视场的反演亮温。通过理论证明和仿真计算表明:该算法可使系统中未消除的误差分量对亮温反演的影响最小,与常用的BG算法对比分析:表明了新算法的正确性和有效性,且计算速度快。     

微波辐射计

本文介绍了3厘米微波辐射计的部件性能、特点及测试结果.工作在9.375GHz下的反馈式零平衡辐射计,在0.2秒积分时间下,温度分辨率叶达0.6°K以下,其测量范围为100～300°K,辐射计带宽为120MHz.     

Microwave emission and reflection from the wind-roughened seasurface at 6.7 and 18.6 GHz

Microwave radiometric observations were made with specially designed microwave radiometers at 6.7 and 18.6 GHz, and the results were compared with those of other investigators, over the frequency range of 1-40 GHz. Dependences of sea surface emission and reflection on wind speed, frequency, incidence angle, and polarization type are discussed in detail, following discussions of the reflective processes of sky radiation and error estimation in the retrieval of mainlobe-averaged brightness temperature. The wind speed sensitivity of brightness temperature, emissivity, and reflectivity is formulated with respect to frequency and incidence angle in each polarization. The brightness temperature, emissivity and reflectivity at arbitrary wind speed are derived employing this formulation. Based on the results obtained it is suggested that the 10-19-GHz band may be optimal for satellite microwave radiometer observations of sea-surface wind     

Effects of foam on ocean surface microwave emission inferred from radiometric observations of reproducible breaking waves

WindSat, the first satellite polarimetric microwave radiometer, and the NPOESS Conical Microwave Imager/Sounder both have as a key objective the retrieval of the ocean surface wind vector from radiometric brightness temperatures. Available observations and models to date show that the wind direction signal is only 1-3 K peak-to-peak at 19 and 37 GHz, much smaller than the wind speed signal. In order to obtain sufficient accuracy for reliable wind direction retrieval, uncertainties in geophysical modeling of the sea surface emission on the order of 0.2 K need to be removed. The surface roughness spectrum has been addressed by many studies, but the azimuthal signature of the microwave emission from breaking waves and foam has not been adequately addressed. Recently, a number of experiments have been conducted to quantify the increase in sea surface microwave emission due to foam. Measurements from the Floating Instrumentation Platform indicated that the increase in ocean surface emission due to breaking waves may depend on the incidence and azimuth angles of observation. The need to quantify this dependence motivated systematic measurement of the microwave emission from reproducible breaking waves as a function of incidence and azimuth angles. A number of empirical parameterizations of whitecap coverage with wind speed were used to estimate the increase in brightness temperatures measured by a satellite microwave radiometer due to wave breaking in the field of view. These results provide the first empirically based parameterization with wind speed of the effect of breaking waves and foam on satellite brightness temperatures at 10.8, 19, and 37 GHz.     

Airborne imaging microwave radiometer. I. Radiometric analysis

The airborne imaging microwave radiometer (AIMR) was designed and built for regional scale sea ice mapping. It operates at 37 and 90 GHz (nominal), and collects radiance at two orthogonal polarizations from which one can compute horizontal and vertical polarizations. The sensitivity or precision (ΔT) of the radiometric data is on the order of 0.5-0.8 K for the 37 GHz channels and 0.8-1.5 for the 90 GHz channels. A detailed error analysis was conducted to assess the accuracy of the radiometric measurements. The error in the brightness temperatures of the original orthogonal polarizations channels was found to be on the order of 0.35-0.45 K for the 37 GHz channel and 0.55-0.65 K for the 90 GHz channel. The polarization conversion introduces additional errors and these are analyzed and computed for the LIMEX-89 data. The total error due to both calibration and polarization conversion for incidence angles greater than 20° is on the order of 0.65-0.70 K for 37 GHz and 0.75-0.85 K for 90 GHz. For incidence angles between 10° and 20° the error can be up to 1.5 K. As the incidence angle approaches zero the distinction between horizontal and vertical polarization breaks down and the error approaches infinity     

Classification of Baltic Sea ice types by airborne multifrequencymicrowave radiometer

An airborne multifrequency radiometer (24, 34, 48, and 94 GHz, vertical polarization) was used to investigate the behavior of the brightness temperature of different sea ice types in the Gulf of Bothnia (Baltic Sea). The measurements and the main results of the analysis are presented. The measurements were made in dry and wet conditions (air temperature above and below 0°C). The angle of incidence was 45° in all measurements. The following topics are evaluated: a) frequency dependency of the brightness temperature of different ice types, b) the capability of the multifrequency radiometer to classify ice types for winter navigation purposes, and c) the optimum measurement frequencies for mapping sea ice. The weather conditions had a significant impact on the radiometric signatures of some ice types (snow-covered compact pack ice and frost-covered new ice); the impact was the highest at 94 GHz. In all cases the overall classification accuracy was around 90% (the kappa coefficient was from 0.86 to 0.96) when the optimum channel combination (24/34 GHz and 94 GHz) was used     

The Dependence of Sea-Surface Microwave Emission on Wind Speed, Frequency, Incidence Angle, and Polarzation over the Frequency Range from 1 to 40 GHz

The dependence of sea-surface microwave emissive prop erties on wind speed, frequency, incidence angle, and polarization arn discussed in detail, in terms of wind-speed sensitivity of the brightnes temperature (defined as a change in brightness temperature with a un, change in wind speed) to the last three observational conditions, ovet the frequency range from 1 to 40 GHz, comparing our results at 6.7 and 18.6 GHz with many investigators' results at various levels from surface to satellite. This wind-speed sensitivity shows marked incidence angle and polarization dependencies. In vertical polarization, a wind-induced increase in the brightness temperature decreases with incidence angle. Then, the vertically polarized brightness temperature of the roughened sea surface is equal to that of the calm surface at an incidence angle between 50 ° and 600, and is higher below, and lower above, this angle; in other words, the above sensitivity is higher and takes a positive value at lower incidence angle and it is lower and takes negative value at higher incidence angle, with a wind-speed-insensitive angle existing between 500 and 600. A wind-induced change in the horizontally polarized brightness temperature shows no marked incidence angle dependence, but a uniform increase over the incidence angle. Both polarizations do not essentially change their characteristics in the above dependencies but gain wind-speed sensitivity with frequency; however, the horizontal polarization is much more sensitive to wind speed than the vertical one over the entire incidence and frequency ranges.     

An updated analysis of the ocean surface wind direction signal in passive microwave brightness temperatures

We analyze the wind direction signal for vertically (v) and horizontally (h) polarized microwave radiation at 37 GHz, 19 GHz, and 11 GHz; and an Earth incidence angle of 53/spl deg/. We use brightness temperatures from SSM/I and TMI and wind vectors from buoys and the QUIKSCAT scatterometer. The wind vectors are space and time collocated with the radiometer measurements. Water vapor, cloud water and sea surface temperature are obtained from independent measurements and are uncorrelated with the wind direction. We find a wind direction signal that is noticeably smaller at low and moderate wind speeds than a previous analysis had indicated. We attribute the discrepancy to errors in the atmospheric parameters that were present in the data set of the earlier study. We show that the polarization combination 2v-h is almost insensitive to atmospheric changes and agrees with the earlier results. The strength of our new signals agrees well with JPL aircraft radiometer measurements. It is significantly smaller than the prediction of the two-scale sea surface emission model for low and intermediate wind speeds.     

Variation of the Microwave Brightness Temperature of Sea Surfaces Covered with Mineral And Monomolecular Oil Films

Airborne microwave radiometer measurements over mineral and monomolecular oil films and adjacent clean sea surfaces are reported. An artificial crude-oil spill experiment in the New York Bight area showed a brightness temperature increase of the sea surface at 1.43 GHz as expected from a multilayered system with different dielectric constants. However, a monomolecular surface-film experiment with oleyl alcohol conducted in the North Sea during MARSEN in 1979 showed a strong brightness temperature depression at 1.43 GHz and no change in brightness temperature at 2.65 GHz. It is postulated that the monomolecular layer, because of its physical and chemical properties, polarized the underlying water molecules so strongly that the emissivity decreased from 0.31 to 0.016. It is estimated that the effective dielectric constant changed from 90 to 5.2 × 104. Because these phenomena occurred at 1.43 GHz it may be concluded that this frequency is very close to the center of a new anomalous dispersion region resulting from a restructuring of the water layer below the surface film.     

Radiometric observations of sea temperature at 2.65 GHz over the Chesapeake Bay

The present work describes the various corrections necessary in order to deduce ocean surface temperature fromS-band microwave radiometer measurements and applies these results to a series of data obtained with a high absolute accuracy radiometer. Measurements made with a 2.65 GHz radiometer from an aircraft flown over the Chesapeake Bay area are presented and compared in detail with accurately obtained sea truth data. For the calm sea, it was found that the observed brightness temperature agreed well with that calculated from the known sea surface and atmospheric properties over a fairly wide range of surface salinity values (0.2 per mille to 25 per mille). For cases where the surface wind speeds are of the order of 7 to 15 knots, an excess brightness temperature was observed which is attributable to surface roughness and microscale surface disturbances. The excess brightness temperature dependence on wind speed was found to correlate to a certain extent with the rms wave slope dependence on wind speed.     

Retrieving soil moisture from simulated brightness temperatures bya neural network

The authors present the retrievals of surface soil moisture (SM) from simulated brightness temperatures by a newly developed error propagation learning backpropagation (EPLBP) neural network. The frequencies of interest include 6.9 and 10.7 GHz of the advanced microwave scanning radiometer (AMSR) and 1.4 GHz (L-band) of the soil moisture and ocean salinity (SMOS) sensor. The land surface process/radiobrightness (LSP/R) model is used to provide time series of both SM and brightness temperatures at 6.9 and 10.7 GHz for AMSRs viewing angle of 55°, and at L-band for SMOS's multiple viewing angles of 0°, 10°, 20°, 30°, 40°, and 50° for prairie grassland with a column density of 3.7 km/m². These multiple frequencies and viewing angles allow the authors to design a variety of observation modes to examine their sensitivity to SM. For example, L-band brightness temperature at any single look angle is regarded as an L-band one-dimensional (1D) observation mode. Meanwhile, it can be combined with either the observation at the other angles to become an L-band two-dimensional (2D) or a multiple dimensional observation mode, or with the observation at 6.9 or 10.7 GHz to become a multiple frequency/dimensional observation mode. In this paper, it is shown that the sensitivity of radiobrightness at AMSR channels to SM is increased by incorporating L-band radiobrightness. In addition, the advantage of an L-band 2D or a multiple dimensional observation mode over an L-band 1D observation mode is demonstrated