嫦娥一号和二号卫星微波探测仪数据的交叉定标与一致性

嫦娥一号（CE-1）和嫦娥二号（CE-2）卫星分别于2007年和2010年发射,其上搭载着相同的微波探测仪（CELMS）.由于在轨定标和探测时间不同,两星的CELMS数据存在差异.为了提高数据的一致性,基于月球极区永久阴影区（PSR）,利用两步定标法对两星的CELMS数据进行交叉定标和时间校正.通过对不同纬度的亮温进行分析可知：两星的CELMS数据在3GHz,19.35GHz和37GHz通道的一致性良好;在中低纬度区域,CE-2卫星7.8GHz通道的亮温较CE-1卫星高,随着纬度的升高,差异逐渐变小并趋于一致.为避免经度跨度大对亮温的影响,选取云海盆地对交叉定标结果进行定量分析,结果表明两星在该区域的一致性良好,平均误差小于0.2K.由此可知,交叉定标和时间校正明显提高了两次观测数据的一致性,减小了由测量误差和时间变化引起的差异.     

蓝色国土的“守望者”——海洋二号卫星在轨运行三周年纪实

<正>截至2014年8月16日,海洋二号卫星在轨运行三周年,三年多的实践证明,该卫星观测精度达到国际先进水平;测定轨精度达到国际先进水平;我国星地激光高速数据传输达到国际先进水平,这些成果彰显了我国卫星关键核心部件自主研发能力,促进了我国卫星研制生产信息化水平的提升——     

了解全球海洋表面盐度国际“宝瓶座”卫星升空

2011年6月10日,美国德尔它-2火箭成功发射了价值2.78亿美元的"宝瓶座"/科学应用卫星-D,它是美国和阿根廷宝的合作项目,美国称它为"宝瓶座",阿根廷称它为科学应用卫星-D,下面简称"宝瓶座"卫星。它载有美国、阿根廷、巴西、加拿大、法国和意大利等国家的多种科学探测仪     

卫星重力测量中加速度计在轨参数校准方法研究

文章介绍了静电悬浮加速度计的基本工作原理,概述了目前卫星重力测量中加速度计参数的在轨外部校准方法,讨论了利用推进器推力、卫星旋转产生的离心力、引力开展加速度计标度因数在轨实时标定的可行性。     

HY-2卫星定标检验场多波段微波辐射计系统设计

Oceanic Multiband Microwave Radiometer（OMMR）是针对中国HY-2卫星扫描微波辐射计的定标和检验而设计的五频段十通道微波辐射计. 由于工作环境恶劣以及仪器长期稳定连续360°观测的需求,使其研制具有较大挑战. 本文重点介绍该微波辐射计的系统构成、技术指标设计与实现,阐述了系统指标测试和定标过程. 测试结果表明其满足设计要求.     

Performance assessment of real-time orbit determination for the Haiyang-2D using onboard BDS-3/GPS observations

The Global Navigation Satellite System (GNSS) receivers equipped on the Haiyang-2D (HY-2D) satellite is capable of tracking the signals of both the third generation of BeiDou satellite navigation System (BDS-3) and the Global Positioning System (GPS), which make it feasible to assess the performance of real-time orbit determination (RTOD) for the HY-2D using onboard GNSS observations. In this study, the achievable accuracy and convergence time of RTOD for the HY-2D using onboard BDS-3 and GPS observations are analyzed. Benefiting from the binary-offset-carrier (BOC) modulation, the BDS-3 C1X signal includes less noise than the GPS C1C signal, which has the same signal frequency and chipping rate. The root mean squares (RMS) of the noises of C1X and C1C code measurements are 0.579 m and 1.636 m, respectively. Thanks to a ten-times higher chipping rate, the code measurements of BDS-3 C5P, GPS C1W and C2W are less noisy. The RMS of code noises of BDS-3 C5P, GPS C1W, and C2W are 0.044 m, 0.386 m, and 0.272 m, respectively. For the HY-2D orbit, the three-dimensional (3D) and radial accuracies can reach 31.8 cm and 7.5 cm with only BDS-3 observations, around 50 % better than the corresponding accuracies with GPS. Better performance of the BDS-3 in RTOD for the HY-2D is attributed to the high quality of its broadcast ephemeris. When random parameters are used to absorb ephemeris errors, substantial improvement is seen in the accuracy of HY-2D orbit with either BDS-3 or GPS. The 3D RMS of HY-2D orbit errors with BDS-3 and GPS are enhanced to 23.1 cm and 33.6 cm, and the RMS of the radial components are improved to 6.1 cm and 13.3 cm, respectively. The convergence time is 41.6 and 75.5 min for the RTOD with BDS-3 and GPS, while it is reduced to 39.2 and 27.4 min after the broadcast ephemeris errors are absorbed by random parameters. Overall, the achievable accuracy of RTOD with BDS-3 reaches decimeter level, which is even better than that with GPS, making real-time navigation using onboard BDS-3 observations a feasible choice for future remote sensing missions.     

在片校准标准件基底边界条件影响

通过分析国内外校准标准件物理边界条件,研究不同校准基底的物理边界条件对共面波导(CPW)传输线特性和校准准确度的影响。研制了W波段砷化镓衬底的多线TRL在片校准标准件,将在片校准标准件分别放置在金属卡盘、玻璃片、吸波材料三种校准基底上。用三种不同校准基底的校准标准件对试验装置校准后,分别提取了CPW传输线的衰减常数、相对介电常数和特征阻抗,并对商用校准标准件104-783A的短路标准和传输线标准进行了测试,验证了结果的合理性。     

地-月L2点中继星月球近旁转移轨道设计

位于地月L2点周期轨道的中继星将首次为"嫦娥4号"月球背面着陆探测任务提供通信中继服务。中继星转移轨道设计是中继任务实施的关键环节。针对中继星转移轨道存在转移时间、近月点高度和halo轨道振幅等约束条件,系统研究了基于月球近旁的地月L2点转移轨道设计方法。首先基于限制性三体模型,分析了halo轨道族与着陆点可见性关系;然后将月球近旁转移轨道分为地月直接转移段和地月动平衡点附近周期轨道拟流形入轨转移段,采用带有状态约束的微分修正算法对这两段轨道进行拼接,得到了从地球附近至目标轨道族的月球近旁转移轨道;最后,针对南族halo轨道分析了halo轨道振幅和月球飞越高度对转移轨道设计的影响,以及转移轨道的入轨相位分布。仿真结果表明:月球近旁转移轨道设计方案具备工程上的可行性与优越性。该方案可以为实际工程任务和应用提供参考。     

A comparison of ionosonde measured foF2 and IRI-2016 predictions over China

A comparison of the ionospheric F-region critical frequency (foF2) between ionosonde measurements and IRI-2016 predictions is studied over China during the period from January 2008 to October 2016. Four stations are selected, and the latitude coverage starts at 49.4°N and ends at 23.2°N with a sequential latitude interval of about 10°, the corresponding geomagnetic latitudes are from 39.5°N to 13.2°N. The results show that the variability of the observed foF2 versus latitudes, seasons, local time and levels of solar activity could be well reproduced by IRI-2016. However, the daily lowest value of foF2 from the IRI-2016 prediction occurs earlier than that from the ionosonde. Around the sunrise, the IRI-2016 prediction shows a very sharp rise and grows much faster than the observed foF2 in every month. The foF2 difference between the two options (URSI and CCIR) in IRI-2016 increases as the F10.7 index decreases. During 2008–2009, the annual average deviations of URSI and CCIR range from ?5% to ?10% and from 5% to ?5%, respectively. Generally, the CCIR performs better than URSI during postsunset under low solar activity or in Equatorial Ionization Anomaly (EIA) region over China, while it shows no large difference in performance with URSI in other locations or for other time.     

N_2O单组元微推进系统贮箱自增压特性

建立了氧化亚氮(N₂O)贮箱自增压地面试验系统,针对亚牛级氧化亚氮单组元微推进系统的推进剂自增压供给过程开展了初步测试试验.基于三区域集总参数物理模型建立了氧化亚氮单组元微推进系统贮箱自增压数学模型,针对相同试验条件下的贮箱自增压过程开展了数值模拟,模拟结果与试验数据吻合较好,验证了仿真模型的准确性.仿真及试验结果均表明,为了确保推力器工作全过程中推进剂供应稳定,在亚牛级氧化亚氮单组元微推进系统的自增压过程中需要对氧化亚氮贮箱进行热量补偿来保证贮箱压力的稳定性,而贮箱压力下降速度分别随着贮箱初始充填率的减少、贮箱容积的减小及氧化亚氮质量流率的增加而增大.     

An optimal selection of probability distribution functions for unsupervised land cover classification of PALSAR-2 data

Different types of classification techniques are available in the literature for the classification of Synthetic Aperture Radar (SAR) data into various land cover classes. Various SAR images are available for land cover classification such as ALOS PALSAR (PALSAR-1, PALSAR-2), RADARSAT and ENVISAT. In this paper, we have attempted to explore probability distribution function (pdf) based land cover classification using PALSAR-2 data. Over 20 different statistical distribution functions are analyzed for different classes based on statistical parameters. Probability distribution functions are selected based on Chi-squared goodness of fit test for each individual class. A decision tree based classifier is developed for classification based on the selected pdf functions and its statistical parameters. The proposed classification approach has an accuracy of 83.93%.     

Antioxidant capacity reduced in scallions grown under elevated CO2 independent of assayed light intensity

Long-duration manned space missions mandate the development of a sustainable life support system and effective countermeasures against damaging space radiation. To mitigate the risk of inevitable exposure to space radiation, cultivation of fresh fruits and vegetables rich in antioxidants is an attractive alternative to pharmacological agents. However it has yet to be established whether antioxidant properties of crops can be preserved or enhanced in a space environment where environmental conditions differ from that which plants have acclimated to on earth. Scallion (Allium fistulosum) rich in antioxidant vitamins C and A, and flavonoids was used as a model plant to study the impact of a range of CO₂ concentrations and light intensities that are likely encountered in a space habitat on food quality traits. Scallions were hydroponically grown in controlled environmental chambers under a combination of 3 CO₂ concentrations of 400, 1200 and 4000 μmol mol⁻¹ and 3 light intensity levels of 150, 300, 450 μmol m⁻² s⁻¹. Total antioxidant activity (TAA) of scallion extracts was determined using a radical cation scavenging assay. Both elevated CO₂ and increasing light intensity enhanced biomass accumulation, but effects on TAA (based on dry weight) differed. TAA was reduced for plants grown under elevated CO₂, but remained unchanged with increases in light intensity. Elevated CO₂ stimulated greater biomass production than antioxidants, while an increase in photosynthetic photo flux promoted the synthesis of antioxidant compounds at a rate similar to that of biomass. Consequently light is a more effective stimulus than CO₂ for antioxidant production.