Ecological assessment of Phragmites australis wetlands using multi-season SPOT-5 scenes

Ecologists and conservationists need accurate and replicable tools for monitoring wetland conditions in order to develop and implement adaptive management strategies efficiently. The Rhone Delta (Camargue) in southern France encloses 9200 ha of fragmented reed marshes actively managed for reed harvesting, waterfowl hunting or cattle grazing, and holding significant numbers of vulnerable European birds. We used multi-season SPOT-5 data in conjunction with ground survey to assess the predictive power of satellite imagery in modelling indicators of reed structure (height, diameter, density and cover of green/dry stems) relevant to ecosystem management and bird ecology. All indicators could be predicted accurately with a combination of bands (SWIR, NIR) and indices (SAVI, OSAVI, NDWI, DVI, DVW, MSI) issued from scenes of March, June, July, September or December and subtraction between these. All models were robust when validated with an independent set of satellite and field data. The high spatial resolution of SPOT-5 scenes (pixel of 10 × 10 m) permits the monitoring of detailed attributes characterizing the reed ecosystem across a large spatial extent, providing a scientifically-based, replicable tool for managers, stakeholders and decision-makers to follow wetland conditions in the short and long-term. Combined with models on the ecological requirements of vulnerable bird species, these tools can provide maps of potential species ranges at spatial extents that are relevant to ecosystem functioning and bird populations.     

基于卫星信号实现高精度时钟的设计

高精度时钟是通信网时间同步的基础,介绍了接收卫星导航定位系统的定时信号,校正本地晶振的输出,实现高精度时钟的设计方法。从高精度时钟的总体设计、硬件设计,针对硬件实现的关键技术展开阐述,按照ITU-T G．811标准的表征频率精确度和稳定度进行了测试,测试结果分析完全满足标准要求的指标。     

环境减灾卫星影像森林火灾监测技术方法研究

森林火灾是世界性的、频繁发生的重大自然灾害。随着国内外航天科技的迅猛发展,卫星遥感技术特别是红外卫星遥感已成为森林火灾监测的一种有效手段。我国的环境一号卫星A、B星(简称HJ-1A卫星、1B卫星)于2008年9月成功发射,其中的HJ-1B卫星搭载了红外多光谱相机,在森林火灾监测方面具有得天独厚的优势,可在早期的火灾发现、中期的灾害跟踪、后期的灾害损失评估中发挥重要作用。本文主要分析了环境减灾卫星在森林火灾监测方面的优势,对环境减灾卫星森林火灾监测技术和方法进行了研究。     

An Achilles heel: denial of service attacks on Australian critical information infrastructures

Critical, or national, information infrastructure protection, referred to as either CIIP or NIIP, has been highlighted as a critical factor in overall national security by the United States, the United Kingdom, India and the European Community. As nations move inexorably towards so-called ‘digital economies’, critical infrastructure depends on information systems to process, transfer, store and exchange information through the Internet. Electronic attacks such as denial of service attacks on critical information infrastructures challenge the law and raise concerns. A myriad of issues potentially plague the protection of critical information infrastructures owing to the lack of legal regulation aimed at ensuring the protection of critical information infrastructures. This paper will highlight the legal concerns that relate to the denial of service attacks on critical information infrastructures and provide an introductory overview of the law as it relates to CIIP in Australia.     

基于HJ-1高光谱数据的植被覆盖度估测方法研究

植被覆盖度是衡量地表植被状况的一个重要参数,在水文、生态等方面有重要意义,同时,也是影响土壤侵蚀与水土流失的主要因子,是评价土地荒漠化最有效的指标。以环境一号(HJ-1)小卫星上搭载的新型传感器HSI获取的高光谱数据为数据源,通过选择合适的植被指数建立了植被覆盖度反演模型——像元二分模型。然后运用该模型提取了新疆石河子地区的植被覆盖度信息。通过与地面样方数据进行交互比较,对HJ-1/HSI数据反演植被覆盖度的精度进行了评价。研究结果表明,HJ-1/HSI数据能够得到较高精度的植被覆盖度反演结果,在植被动态及全球变化研究领域具有潜在应用价值。     

高分辨率遥感卫星数据传输中信道编码技术分析与研究

根据RS编译码原理,结合高分辨率遥感卫星在轨影像实际数据压缩情况,提出将RS(255,243)和RS(34,26)两种编码算法进行联合使用的方案,以解决数据传输中误码问题,仿真试验证明该方法在解决有干扰条件下的星地数据传输时,可有效防止和减少误码扩散。     

Active disturbance rejection control for high pointing accuracy and rotation speed

This paper presents a design method proposed to design an active disturbance rejection control for the antenna pointing control of a large flexible satellite system. A simplified dynamics model is established using Euler-Lagrange and used to analyze the dynamic stability of the antenna system. The capturing strategy of the antenna is configured and the inner and outer loops of the active disturbance rejection control are then designed to improve pointing accuracy and rotation speed. The design of the active disturbance rejection control is verified through numerical simulation. Simulation results indicate that the proposed method can be used to achieve high pointing accuracy and rotation speed.     

卫星通信系统QOS管理的策略提炼

针对基于策略的DVB—RCS卫星通信系统服务质量管理,提出一种策略提炼模型,结合实例给出目标提炼过程。该模型以线性时态逻辑为基础,在提炼模式的辅助下从高层目标中提取出低层策略,可以有效保证策略提炼过程的正确性、合理性及一致性。在系统设计阶段,该模型用于指导系统功能规划与设计,在系统运行阶段,该模型为网络管理人员提供高层策略向系统设备行为的映射方法。     

Ka频段卫星通信上行链路自适应功率控制

为提高Ka频段（30GHz／20GHz）卫星通信系统上行链路功率控制的可靠性,提出一种上行链路自适应功率控制算法。该方法基于自回归滑动平均模型,能由测量到的下行链路降雨衰减值预测出上行链路的降雨衰减值,从而提高功率控制精度。仿真结果表明,该方法对降雨衰减具有较好的补偿效果。     

Wideband turnstile junction coaxial waveguide orthomode transducer

A wideband turnstile junction coaxial waveguide orthomode transducer (OMT) is presented in this paper, featuring coaxial waveguide input and orthogonal rectangular waveguide outputs. It primarily comprises of a turnstile junction, bending stepped impedance transformers and power combiners. The symmetrical geometry helps achieve wide operating bandwidth and balanced output phases. The OMT covers the whole Ku band from 12 to 18 GHz, which aims at wideband dual‐polarized signal combination and separation within coaxial‐type multi‐band antenna systems. An experimental prototype is manufactured and the measured results confirm that the reflection coefficient is lower than ?15 dB within the whole band, and the port isolation is better than 35 dB. Turnstile junction coaxial waveguide OMTs can be adopted widely in circular/coaxial waveguide hybrid feeding networks for multi‐band satellite communication/remote sensing antenna systems.