中国空间站微波链路引力红移检验仿真实验

利用高精度空载/星载原子钟进行引力红移检验是物理学领域的研究热点。随着原子钟精度的不断提高,利用高精度时频信号检验引力红移和测定重力位成为可能。中国空间站二号实验舱预计于2022年10月在轨运行,并搭载高精度原子钟组,为高精度引力红移实验奠定了基础。利用中国空间站的一组上行微波链路与下行微波链路进行双向时间/频率比对,从而实现引力红移检验。由于两条链路的频率及路径相同且极化方向相反,可以极大地消除误差干扰。结果表明,当空间站搭载的原子钟稳定度为$\mathrm{2}\times {\mathrm{10}}^{-\mathrm{15}}/\sqrt[]{\tau }$且长期稳定度约为10-18量级时,引力红移检验精度可达到10-7量级,比目前国际上最高的引力红移检验精度高1~2个量级。     

GPS卫星信号Doppler频移的计算与分析

在GPS导航定位系统中，多普勒频率偏移直接影响接收机性能。为了克服多普勒频率偏移的影响，提高接收机的GPS信号捕获速度，对多普勒频移估计算法进行研究。通过分析可视卫星的判定、Doppler频移计算方法，基于NewStar150GPS原理实验平台，使用C＋＋语言编程，开发Doppler频移计算程序。实验结果表明，Doppler频移的大小与a有关。当a〈90°时，多普勒频移为正，用户接收机收到的频率比卫星发射的频率要低。当a〉90°时，多普勒频移为负；当a=90°时，多普勒频移为0。     

高程对TDICCD相机像移补偿影响分析

高分辨率遥感卫星中常使用TDICCD(时间延迟积分CCD)相机,为获取高质量遥感影像,在相机成像过程中须采用像移补偿技术,而目前大部分像移补偿忽略了高程的影响。基于参考椭球面下成像矢量模型,建立考虑高程的成像矢量模型及解算方法流程,精确地计算相机成像时像点对应地面成像点的坐标及像移补偿参数。根据计算结果,分析高程对像移补偿参数的影响,在此基础上,综合考虑像移补偿参数精度对高程误差的要求、星上存储空间及高程查询速度,讨论星载数字高程模型(DEM)的生成,为星载DEM的使用及TDICCD相机高精度像移补偿提供理论基础和实验分析。     

基于动态阿伦方差的北斗星载原子钟特性分析

针对传统的阿伦方差等评价手段无法实现对星载原子钟进行动态性能评估的缺陷,将动态阿伦方差引入到BDS星载原子钟的监测和评估中。采用BDS多星定轨卫星钟差产品,基于动态阿伦方差算法对BDS原子钟在轨性能进行了研究,并利用BDS星地双向无线电时间比对钟差数据对其结果进行了对比和验证。实验结果表明,动态阿伦方差算法可以实现对BDS星载原子钟动态特性的有效评估,BDS原子钟的万秒稳定度的量级基本为在10-14,但是随着时间有一定的变化。     

导航卫星原子钟频率稳定度估计的小波方差方法

国内外学者对小波方差理论在原子钟性能分析方面的应用做了一些研究,但相关文献对小波方差的定义及其表征稳定度的特性描述却并不完全一致,这给应用研究造成不便。为此,首先根据时域方差定义的原理,相应地提出了小波方差、重叠小波方差和小波总方差的概念,然后经综合归纳,针对性地选择给出了应用于原子钟频率稳定度估计的"尺度域"小波方差的定义计算公式及等效自由度的计算方法。最后,通过一个算例与时域方差进行比较分析,总结明确了两者的关系及小波方差的特点,从而说明小波系列方差可以有效地进行原子钟频率稳定度的估计。     

下一代星载原子钟的新发展

高性能原子钟尤其是星载原子钟,在卫星导航定位系统中起着非常重要的作用。卫星导航定位系统的更新和发展要求更高精度、更小型化的新型星载原子钟。介绍了新物理原理和先进技术以及在新一代卫星导航定位系统和空间科学实验中有应用前景的新型原子钟的产生、发展以及它们目前的研究进展。     

数据融合模型选取对工业测量整体平差结果的影响分析

工业测量中,传统移站测量法的点位测量误差会随着移站次数的增加不断累积增加,导致最终的测量精度不可控。讨论了基于原始观测值和基于坐标观测值的两种整体平差数据融合方法,与传统移站测量法相比,这两种方法解算的点位精度较高且稳定。实验表明,即使融合的函数模型和随机模型等价,采用不同的融合方法,得到的融合结果并不完全等价。在实际应用中需根据具体情况选择不同的融合方法,从而得到解算精度可靠的待测点坐标。     

北斗卫星钟稳定性分析及噪声识别

通过对频率稳定性分析和噪声识别理论的研究,运用重叠Hadamard方差计算了北斗卫星钟的频率稳定度;并结合自相关函数理论,使用Lag1自相关函数分析了影响北斗卫星钟的主要噪声类型。实验结果表明,所分析的4颗卫星原子钟的天稳定度都达到了10-13水平;影响其稳定性的主要噪声为调频白噪声、调频闪变噪声和调频随机游走噪声。     

两点后方交会在工业检测中的应用研究

用全站仪检测工业设备时经常需要移站测量,本文根据移站前后两个公共点利用后方交会求取移站后测站点坐标,通过解平面三角形求取测站点平面坐标,采用距离进行加权平均求取高程值,通过实验验证了该方法的可行性。     

等频大地水准面的概念及应用

阐述了等频大地水准面的概念及其理论基础，讨论了等频大地水准面与经典大地水准面的关系，提出了测定位差和高程差的新方法──引力或重力频移法，探讨了利用频移观测法解边值问题求定地球外部重力位的途径。     

光流特征聚类的车载全景序列影像匹配方法

提出一种光流特征聚类的车载全景序列影像匹配方法.采用非参数化的均值漂移特征聚类思想,以SIFT多尺度特征匹配点的位置量和光流矢量,构建了影像特征空间的空域和值域;利用特征空间中对应的显著图像光流特征为聚类条件,实现了全景序列影像的匹配;最后以全景极线几何约束为条件进行粗差的剔除.通过相同、不同内点率以及不同数据的试验对比分析,本文方法在匹配正确点数和正确率方面要优于经典的Ransac法和金字塔Lucas-Kanade光流法,尤其在场景复杂造成的低内点率情况下,算法表现较为稳定,并可较好地剔除由重复纹理、运动物体、尺度变化等产生的匹配点粗差.     

大气遥感双视场米散射激光雷达信号拼接

介绍了一种双视场米散射激光雷达信号拼接方法。主要思想是寻找近场和远场信号都具有高信噪比的最佳拼接区域,求解该区域两种信号之间的函数关系,自动实现激光雷达近场信号与远场信号的有效拼接和反演。拼接结果兼具近场信号探测盲区低和远场信号探测高度高的优点。反演结果表明,该方法能够准确有效地实现双视场信号拼接,并能反演得到高精度的气溶胶光学特性。     

Retrieval of chlorophyll from the sea-leaving radiance in the Arabian sea

Error estimates in chlorophyll retrieval in the sea from satellite data have always been higher compared to the errors in retrieval of sea surface temperature or wind speed from satellite data. This is due to the higher percentage of noise in optical signals compared to infrared or microwave signals reaching the satellite. The noise is introduced both at the sea surface itself and also while signal passes passage through atmosphere. In the present work, we have attempted to investigate the noise introduced at the sea surface. During the validation experiment of the optical sensor MOS-B onboard Indian Remote Sensing Satellite IRS-P3, simultaneous measurements of chlorophyll concentration and sea leaving radiance have been made along the satellite passes in the Arabian sea. The algorithms used in the present studies are not found to give satisfactory values of chlorophyll in about 30% of cases. The possible sources of errors in retrieving chlorophyll concentration have been discussed.     

光学与微波植被指数协同反演农作物叶面积指数的可行性分析

光学遥感是目前反演植被叶面积指数LAI（Leaf Area Index）的主要手段,但是当叶面积指数较大时存在光学遥感信息饱和、反演精度显著降低的问题。叶面积指数和平均叶倾角对光学、微波波段范围内反射和散射特性都有重要影响,主要表现在植被结构参数的变化可以引起冠层孔隙率和消光截面大小的改变。本文以典型农作物玉米为例,通过构建统一的PROSAIL和MIMICS模型输入参数,生成一套玉米全生长期光学二向反射率和全极化微波后向散射系数模拟库和冠层参数库。通过对模拟数据与LAI敏感性和相关性分析得出：（1）光学植被指数MNDVI_{(800 nm,2000 nm)},在LAI为0—3时敏感,基于MNDVI与LAI的回归模型可以估算LAI变化 0.4的情况,RMSE是0.33,R²是0.958。（2）微波植被指数SAR_{SRVI(1.4 GHz HH,9.6 GHz HV)},在LAI为3—6时敏感,基于SAR_SRVI与LAI的回归模型可以估算LAI变化1的情况,RMSE为0.22,R²是0.9839。研究表明,采用分段敏感的植被指数,协同光学和微波遥感反演玉米全生长期叶面积指数是可行的。     

Estimating the Leaf Area Index,height and biomass of maize using HJ-1 and RADARSAT-2

New optical and microwave integrated vegetation indices (VIs) were designed based on observations from both field experiments and satellite (HJ-1 and RADARSAT-2) data. It was found that these VIs perform better in estimating the structure parameters of maize, such as Leaf Area Index (LAI), height and biomass, than the original ones. This investigation focused on the difference of interaction between the multispectral reflectance and microwave backscattering signatures with the maize growth variables. Because the maize was near the heading stage with large vegetation coverage in the experiment, the reflectance of the near-infrared band of HJ-1 was much less sensitive to the structure variables than that of the visible-light band. Thus, the optical VIs formulated using those bands were saturated to estimate the structure parameters. With respect to the RADARSAT-2 data, there was a relatively strong relationship between the HV cross-polarization and the volume scattering of the maize, which was mostly determined by the crown structure. The modified VIs were designed using both the VIs of HJ-1 and the HV cross-polarization of RADARSAT-2 to overcome the saturation limitation. The validation showed that this integrated method of determining VIs is a good alternative to that using only the optical or microwave observation.     

High altitude aircraft remote sensing during the 1988 Yellowstone national park wildfires

Abstract

The advancement of satellite remote sensing has offered greater potential for mapping volcanic deposits. Although the development of weather‐independent microwave remote sensing has made the frequent detection over large area detection of deposits using SAR intensity image is sometimes hindered by ambiguities and noise. The ambiguities occur in volcanic deposit areas covered by young vegetation and that give either high or low backscatter depending upon their orientation. For this reason coherent images were integrated with SAR intensity images to extract more reliable information about volcanic deposited area. Besides, the layover areas due to the viewing geometry of SAR make difficulties to map the volcanic deposits on every side of the mountain. To avoid the influence of layover effects fusion techniques of ascending and descending pass SAR intensity and coherent images were developed. Using the fused images with an optical image, a color composite was developed to identify the areas affected by an eruption. In this color composite, especially vegetation damages can be easily identified.     

实时定标微波辐射计的仿真研究

实时定标微波辐射计是一种新体制的微波辐射计,它能有效地消除系统增益波动和有效本机噪声波动的影响,适合星载应用。对以全功率微波辐射计为基础的实时定标微波辐射计进行了仿真研究,建立了系统各环节的仿真模型。在仿真试验中,采用了快速离散傅里叶变换处理信号,分析并缓解了由于频程跨度大带来的频率分辨率与采样点数之间的矛盾。仿真结果为优化设计提供了重要参考,并证明所建模型准确、有效,也为进一步实现星载环境仿真调试奠定了基础。     

微波通信网站建设中的测量保障方法

结合微波通信控制网站建设与改造工程,总结探讨了微波通信网站建设中测绘保障的内容、要求和主要方法,对GPS、GIS在工程建设中的应用作了初步探讨,指出了工程中测绘保障的重点和注意点。     

多角度遥感估算稀疏团粒分布型土壤表面粗糙度方法初探

表面粗糙度是影响土壤在微波波段发射和散射辐射的主要因素之一,也是微波遥感研究与应用的重要参量。由于微波后向散射还受介电特性、穿透深度等因素的影响,在微波遥感应用中往往难以单独考虑介质表面粗糙度,给参数估算与反演带来了一定困难。在可见光、近红外波段,粗糙度作为土壤表面重要的结构参数之一,直接影响着土壤的二向反射分布特征。因此,本文尝试利用光学多角度观测信息,反演土壤表面粗糙度。基于地表二向反射几何光学模型,假设裸土像元由随机分布于平坦表面的土壤团粒组成,将团粒近似为半椭球体,建立裸露土壤表面二向反射模型,模拟不同粗糙度条件下土壤表面像元的二向反射分布特征。进一步尝试采用多角度观测数据反演模型,估算土壤团粒的几何结构参数,进而计算土壤表面均方根高度,作为表面粗糙度的衡量指标。地面实测多角度数据的初步验证结果表明,多角度光学遥感估算土壤表面粗糙度的方法是可行的。     

Prediction of L-band signal attenuation in forests using 3D vegetation structure from airborne LiDAR

In this study, we propose a novel method to predict microwave attenuation in forested areas by using airborne Light Detection and Ranging (LiDAR). While propagating through a vegetative medium, microwave signals suffer from reflection, absorption, and scattering within vegetation, which cause signal attenuation and, consequently, deteriorate signal reception and information interpretation. A Fresnel zone enveloping the radio frequency line-of-sight is applied to segment vegetation structure occluding signal propagation. Return parameters and the spatial distribution of vegetation from the airborne LiDAR inside Fresnel zones are used to weight the laser points to estimate directional vegetation structure. A Directional Vegetation Density (DVD) model is developed through regression that links the vegetation structure to the signal attenuation at the L-band using GPS observations in a mixed forest in North Central Florida. The DVD model is compared with currently-used empirical models and obtained better R² values of 0.54 than the slab-based models. Finally, the model is evaluated by comparing with GPS observations of signal attenuation. An overall root mean square error of 3.51 dB and a maximum absolute error of 9.38 dB are found. Sophisticated classification algorithms and full-waveform LiDAR systems may significantly improve the estimation of signal attenuation.