Analysis of the Marshall Islands Fireball of February 1, 1994

On February 1, 1994, a large meteoroid impacted over the Pacific Ocean at 2.6° N, 164.1° E. The impact was observed by space based IR sensors operated by the US Department of Defense and by visible wavelength sensors operated by the US Department of Energy. During entry the object broke into several pieces, one of which detonated at 34 km and another at 21 km altitude. The entry velocity of the object is estimated to be 24–25 km/sec. Based on the visible wavelength data, the integrated intensity of the radiated energy of the fireball was approximately 1.3 × 10¹³ joules. Assuming a 6000 K black body and a 30% efficiency for the conversion of the kinetic energy of the body into visible light, we estimate the mass of the body to be between 1.6×10⁵ kg and 4.4×10⁶ kg, and to have a diameter of between 4.4 and 13.5 meters. The object entered at a 45° angle, traveling on a heading of approximately 300°, i.e. from the southeast to the northwest. Calculations using a gross-fragmentation model indicate that the body was most likely a stony object larger than 10 m with an Apollo orbit prior to impact.E T Space SystemsSandia National LaboratoriesOndejov Observatory     

多GNSS精密单点定位性能分析

在实现BDS/GPS/GLONASS组合精密单点定位的基础上,模拟多种遮挡环境;利用3个MGEX测站的数据进行三系统组合PPP试验;并在可见卫星数、PDOP值、定位精度、收敛时间和定位可用性等方面与GPS单系统PPP进行了比较分析。结果表明:在亚太地区,相比于GPS单系统PPP,三系统组合PPP可见卫星数增加了2~3倍,PDOP值显著减小。动态试验中,在无遮挡环境下,三系统组合PPP相较于GPS PPP收敛时间更短,且收敛后定位精度更高;在遮挡环境下,GPS PPP性能急剧下降,三系统组合PPP较好的保证了定位精度,提高了系统定位可用性。     

HLJCORS系统性能测试与分析

通过定位精度测试、可用性测试和兼容性测试,本文分析评估了HLJCORS的实时和事后定位精度、空间可用性、时间可用性以及兼容性。测试表明,HLJCORS测试精度均达到或优于设计要求,可为黑龙江省建立统一的现代化测绘基准提供重要支撑。     

面向地灾应急的国产卫星观测能力分析

针对国产卫星系统在灾害应急观测任务中的覆盖能力并不完全明确的问题,对适用于地质灾害应急观测的国产卫星进行模拟仿真,利用网格点法从空间和时间两个维度对卫星的覆盖情况进行统计分析,深入研究国产卫星在应急响应、重复观测以及复合观测三方面的覆盖能力,并为灾后应急任务制定和我国灾害监测系统的发展提供建议。     

气象卫星发展回顾与展望

回顾了国际气象卫星和中国风云气象卫星的发展,综述了气象卫星在图像解译、定量产品应用和数据同化方面的成就以及辐射校正技术的进步。围绕大气科学,特别是数值天气预报对天基观测的需求,展望了未来气象卫星的技术发展方向。     

海南省临高县调楼乡黄龙港北侧围海工程的自然条件可行性分析

在野外调查的基础上，收集了围填工程海域的气象、水文、地质资料，详细论述了围填区的水动力条件、地质地貌与泥沙运动情况，分析了围填工程对周边设施的影响，得出了围填工程在自然条件下可行的结论。     

Relationship of Caspian tern foraging ecology to nesting success in the Columbia River estuary, Oregon, USA

The prevalence of juvenile salmonids (Oncorhynchus spp.) and marine forage fishes in the diet of Caspian terns (Hydroprogne caspia) nesting in the Columbia River estuary has been established, but the relationship between diet composition, foraging distribution, and productivity of these birds has received little attention. We used radio-telemetry and on-colony observations to relate changes in off-colony distribution to patterns of colony attendance, diet composition, and productivity of adult terns nesting on East Sand Island during two years of different river and prey conditions. Average distance from the East Sand Island colony (located in the marine zone of the estuary) was 38% (6.6 km) greater in 2000 compared to 2001, associated with lower availability of marine forage fish near East Sand Island and lower prevalence of marine prey in tern diets. Colony attendance was much lower (37.0% vs. 62.5% of daylight hours), average trip duration was 40% longer (38.9 min), and nesting success was much lower (0.57 young fledged pair⁻¹ vs. 1.40 young fledged pair⁻¹) in 2000 compared to 2001. Higher proportions of juvenile salmonids in the diet were associated with relatively high use of the freshwater zone of the estuary by radio-tagged terns, which occurred prior to chick-rearing and when out-migrating salmonid smolts were relatively abundant. Lower availability of marine prey in 2000 apparently limited Caspian tern nesting success by markedly reducing colony attendance and lengthening foraging trips by nesting terns, thereby increasing chick mortality rates from predation, exposure, and starvation.     

不同高度截止角下BDS/GPS定位分析

研究了BDS/GPS联合RTK定位的理论和算法,主要包含了BDS/GPS组合系统在不同高度截止角下的可视卫星数与PDOP值的比较;BDS与GPS观测量精度的初步评估;双频联合RTK定位的模糊度解算和定位性能的分析等。得出如下结论:BDS/GPS组合系统的可视卫星数相对单系统明显增多,PDOP值减小,在大高度截止角下,其空间几何强度依然很高;随着高度截止角的增大,BDS与GPS受多路径影响明显减弱,其中GEO卫星受多路径影响最大;BDS观测量精度与GPS相当。BDS/GPS双频联合定位的定位精度相对于GPS或BDS虽没有明显提高,但在大高度截止角下,依然可以成功固定模糊度并实现高精度定位。这将显著改善GPS或BDS单系统双频RTK定位在受遮挡环境下的可用性和可靠性。