人机合作的免疫算法及其在布局设计中的应用

提出一种人机合作的免疫算法（HCCIA）。它将设计者提供的初始人工个体和混沌初始化生成的初始算法个体合并组成初始群体,然后经自适应交叉、变异和免疫选择等算子操作,进化寻优。同时,还适时和适量地将设计者给出的新人工个体加入到算法群体,替换掉其中较差的个体。如此循环,直至达到结束准则。该算法有利于充分发挥人机各自特长,为更好地解决复杂工程设计问题提供了方便。文中以卫星舱布局设计为背景的算例验证了此算法的可行性和有效性。     

Satellite-Based Energy Balance for Mapping Evapotranspiration with Internalized Calibration (METRIC)—Model

Mapping evapotranspiration at high resolution with internalized calibration (METRIC) is a satellite-based image-processing model for calculating evapotranspiration (ET) as a residual of the surface energy balance. METRIC uses as its foundation the pioneering SEBAL energy balance process developed in The Netherlands by Bastiaanssen, where the near-surface temperature gradients are an indexed function of radiometric surface temperature, thereby eliminating the need for absolutely accurate surface temperature and the need for air-temperature measurements. The surface energy balance is internally calibrated using ground-based reference ET to reduce computational biases inherent to remote sensing-based energy balance and to provide congruency with traditional methods for ET. Slope and aspect functions and temperature lapsing are used in applications in mountainous terrain. METRIC algorithms are designed for relatively routine application by trained engineers and other technical professionals who possess a familiarity with energy balance and basic radiation physics. The primary inputs for the model are short-wave and long-wave (thermal) images from a satellite (e.g., Landsat and MODIS), a digital elevation model and ground-based weather data measured within or near the area of interest. ET “maps” (i.e., images) via METRIC provide the means to quantify ET on a field-by-field basis in terms of both the rate and spatial distribution. METRIC has some significant advantages over many traditional applications of satellite-based energy balance in that its calibration is made using reference ET, rather than the evaporative fraction. The use of reference ET for the extrapolation of instantaneous ET from periods of 24?h and longer compensates for regional advection effects by not tying the evaporative fraction to net radiation, since ET can exceed daily net radiation in many arid or semi-arid locations. METRIC has some significant advantages over conventional methods of estimating ET from crop coefficient curves in that neither the crop development stages, nor the specific crop type need to be known with METRIC. In addition, energy balance can detect reduced ET caused by water shortage.     

Urban Damage Estimation Using Statistical Processing of Satellite Images

Remotely sensed satellite imagery of an earthquake-affected region can significantly assist in estimating the severity of infrastructure damage. Modern high-resolution satellite systems have been launched to provide users optical imagery with submeter accuracy, which enable the possibility of sensing damage for individual structures by means of pre- and postevent imagery. Recognizing these advancements, herein, we focus our study on the region of Bam, Iran, which was devastated by a moment magnitude Mw = 6.6 earthquake on December 26, 2003, causing approximately 43,200 lives lost. The recognition of urban structures within the Bam region is obtained by performing morphological filtering and intensity thresholding, which is further optimized through a statistical procedure. By overlaying the recognized structures with the pre- and postevent images, three object-based change detection methods are presented. The performance of change indices resulting from the three change detection methods is evaluated by means of a histogram-based classification approach. Damage estimation results are presented using easily interpretable maps, wherein individual structures are rendered with colors representing the severity of damage.     

Residential Water Savings Associated with Satellite-Based ET Irrigation Controllers

A mixed landscape irrigation study was conducted on 27 residential sites in Las Vegas to quantify water savings associated with satellite irrigation controllers. Seventeen sites were equipped with evapotranspiration-based (ET) satellite irrigation controllers and ten sites were designated as control sites and retrofitted with nonET-based irrigation controllers. Results showed that 13 of 16 ET-based controller sites saved water compared to four of ten of the nonET-based control sites. When all control sites were grouped together, a statistical difference occurred between the control and ET-based groups (ET-based controller=+20% savings) (p<0.05). Results from this study indicated that water savings were not because of deficit irrigations at the expense of the landscape plant material. Eighty-one percent of the variation in the total outdoor water use could be described by the total turfgrass area at each site. Such results would suggest that turfgrass limitations have merit, if the grass being restricted is tall fescue growing in an arid environment.     

1588v2在电信网应用的标准化进程

文章介绍了1588v2在电信网领域应用的背景、需求和主要标准组织ITU-T的相关工作进展,包括频率同步应用和时间同步应用。通过分析目前1588v2电信应用规范中的热点问题,如影响1588v2频率恢复性能的网络分组延时变化(PDV)指标、1588v2端到端频率传送的应用场景和协议规范,提出1588v2在电信网络部署的可靠性、可管理维护等特点和基本思路,并对未来标准化需要解决的问题进行总结。     

Modeling the Hinge Moment of Skew-Mounted Tape Spring Folds

Tape springs, defined as thin metallic strips with an initially curved cross section, are an attractive structural solution and hinge mechanism for small satellite deployable structures due to their low mass, low cost, and general simplicity. When mounted at skewed angles to the hinge line, the tapes can be subjected to complex folds involving both bending and twisting of the tape. These folds have been experimentally investigated and theories have been developed to model the resulting opening moment. However, the opening moments of these theories are not equivalent to the opening moment about the hinge line, which is the parameter required in satellite deployment applications. This paper derives a method to determine the hinge moment from the previous theories and compares the theoretical predictions with experimental and finite element results. It uses this model to investigate the predicted hinge moment trends for full deployments of 180°. The model is then applied to a practical spacecraft hinge application.     

Active Magnetic Control Methods for Small Satellite

A small satellite is likely to tumble as the result of separating from the rocket. It is therefore very important to capture it promptly with finite magnetic torque. Magnetic torque is orthogonal to the external magnetic field; therefore, it is impossible to generate precisely the control torque that would be required according to simple control theories. However, it is possible to define the desirable torque first and then derive from this the actual control torque. A criteria is presented for this derivation and two control algorithms are formulated, based on nonlinear design theories. One is the energy method that takes the Lyapunov function as a control criteria and uses a divided districts control algorithm to determine the desirable torque. The other one uses the variable structure control method to define the desirable torque. The results of computer simulation indicated that these algorithms have the advantages of excellent robustness and are easily designed and realized.     

星载GNSS反射信号时-空性能仿真分析

针对星载全球导航卫星系统(GNSS)反射信号时-空性能问题,该文从1阶统计量角度定义了平均空间覆盖次数、全球覆盖面积百分比和平均回访时间3个衡量星载GNSS反射信号时-空性能的指标,并通过建立GNSS和低轨卫星轨道仿真研究了低轨卫星轨道高度、倾角、升交点赤经以及天线波束对星载GNSS反射信号时-空性能的影响。结果表明：单颗卫星无法满足全球探测的任务需求,当轨道高度为1300 km,倾角为98.7°,天线波束为40°时,平均覆盖次数、平均覆盖面积百分比和平均回访时间分别为1.6, 36.5%和8 h;通过单一轨道的卫星组网可有效提高星载GNSS反射信号的时-空性能,当卫星数目为4,高度为635 km,倾角为98.7°,波束宽度为40°时,星载GNSS反射信号的时-空性能指标高于单颗ASCAT卫星24 h覆盖地球65%的指标;当卫星数目增加至8颗时,星载GNSS反射信号可在平均4.5 h内观测地球88.9%的区域。     

Use of Eutectic Fixed Points to Characterize a Spectrometer for Earth Observations

A small palm-sized, reference spectrometer, mounted on a remote-controlled model helicopter is being developed and tested by the National Physical Laboratory (NPL) in conjunction with City University, London. The developed system will be used as a key element for field vicarious calibration of optical earth observation systems in the visible-near infrared (VNIR) region. The spectrometer is hand held, low weight, and uses a photodiode array. It has good stray light rejection and wide spectral coverage, allowing simultaneous measurements from 400 to 900 nm. The spectrometer is traceable to NPL’s primary standard cryogenic radiometer via a high-temperature metal-carbon eutectic fixed-point blackbody. Once the fixed-point temperature has been determined (using filter radiometry), the eutectic provides a high emissivity and high stability source of known spectral radiance over the emitted spectral range. All wavelength channels of the spectrometer can be calibrated simultaneously using the eutectic transition without the need for additional instrumentation. The spectrometer itself has been characterized for stray light performance and wavelength accuracy. Its long-term and transportation stability has been proven in an experiment that determined the “World’s Bluest Sky”—a process that involved 56 flights, covering 100,000 km in 72 days. This vicarious calibration methodology using a eutectic standard is presented alongside the preliminary results of an evaluation study of the spectrometer characteristics.     

Error Analysis and Cycle-Slip Detection Research on Satellite-Borne GPS Observation

According to the application characteristics of low-earth-orbit satellite-borne global positioning system (GPS) receiver, the influence of GPS measurement data error on cycle-slip detection is analyzed. Then a modified TurboEdit preprocessing method is proposed. In the modified method, a weighted factor which closely relates to the GPS satellite elevation angle is introduced in the cycle-slip detection process. The weighted factor estimates the error of measurement data based on the variation of GPS elevation angle and establishes a relationship between the cycle-slip detection process and error of measurement data. Then the cycle-slip detection judgment is adjusted by the weighted factor. The modification algorithm not only reduces the fault rate of cycle-slip detection, but also promotes the autonomous ability of orbit determination by increasing the quantity of measurement data that will participate in low-earth-orbit-satellite orbit determination. Finally, the modified algorithm is verified by GPS measurement data of GRACE satellite formation.