2000年度上海天文台卫星激光测距观测报告

介绍了 2 0 0 0年度上海天文台卫星激光测距观测和系统的改进情况     

一种新的激光点云数据精简方法

三维激光扫描技术是最近几年在测量方面发展起来的一个研究热点。提出利用点云模型中相邻三角形夹角的大小来对点云数据进行直接精简的方法,在matlab平台下,通过编程实现点云数据的压缩。将精简的点云数据通过编程重新构建三角网,最后在Geomagic软件中建模,通过与原始模型进行对比,新方法的压缩效果比较理想。     

Optical attenuation in fog at a wavelength of 1.55 micrometers

As part of a series of studies on laser propagation for terrestrial free space optical (FSO) telecommunications or laser telecommunications, an experiment was conducted to determine the relationship between visibility in fog and optical attenuation (dB/km) at a laser wavelength of 1.55 μm. In the telecommunications industry, a semi-empirical equation, called the Kruse formula [Kruse, P.W., McGlauchlin, L., McQuistan, R.B., 1962. Elements of infrared technology: generation, transmission, and detection. John Wiley and Sons, New York] is typically used to calculate expected attenuation for a given meteorological visibility. The Kruse formula, however, was developed to relate meteorological visibility to optical attenuation over wavelengths from the visible to the near infrared (IR), and for dust and small particle aerosols with dimensions much smaller than the wavelength. Typically, suspended small aerosols have diameters that average about 0.1 μm while fog droplets have diameters that range upward from 2.5 μm with mean diameters that exceed 10 μm in some fogs. Therefore, application of the Kruse formula to attenuation in fog is not appropriate since fogs consist mainly of particles much larger than the laser wavelength. As part of the experiment, a transmissometer with an 85-m baseline and a dynamic range of 60 dB operated for thirteen months in an area prone to radiation fog. A commercial visibility sensor, similar to those used at airports, was located near the middle of the optical path of the transmissometer and operated over the same period. The largest attenuation measured at this site was just over 300 dB/km, corresponding to a visibility of 32 m. The key finding of the study is that the generally accepted Kruse formula relating visibility and optical attenuation may be too pessimistic at low visibilities, and actual attenuation values for a given visibility may be more than 20% lower than previously thought. At visibilities exceeding about 650 m, the Kruse formula gives a good estimate of optical attenuation.     

Geomorphic expression of neotectonic activity in a low relief area in an Airborne Laser Scanning DTM: A case study of the Little Hungarian Plain (Pannonian Basin)

The NW corner of the Little Hungarian Plain, which lies at the junction of the Eastern Alps, the Pannonian Basin and the Western Carpathians, is a neotectonically active region linking the extrusional tectonics of the Eastern Alps with the partly subsiding Little Hungarian Plain. The on-going deformation is verified by the earthquake activity in the region. An extremely flat part of the area, east of Neusiedlersee, the so-called Seewinkel, has been investigated with Airborne Laser Scanning (ALS, also known as airborne LiDAR) techniques, resulting in a digital terrain model (DTM) with a 1 m grid resolution and vertical precision of better than 10 cm. The DTM has been compared with known and inferred neotectonic features.Potential neotectonic structures of the DTM have been evaluated, together with geological maps, regional tectono-geomorphic studies, geophysical data, earthquake foci, as well as geomorphological features and the Quaternary sediment thickness values of the Seewinkel and the adjacent Parndorfer plateau. A combined evaluation of these data allows several tectonic features with a relief of < 2 m to be recognized in the DTM. The length of these linear geomorphological structures ranges from several hundred meters up to several kilometers. The most prominent feature forms a 15 km long, linear, 2 m high NE–SW trending ridge with gravel occurrences having an average grain size of ca. 5 cm on its top. We conclude this feature to represent the surface expression of the previously recognized Mönchhof Fault. In general, this multi-disciplinary case study shows that ALS DTMs are extremely important for tectono-geomorphic investigations, as they can detect and accurately locate neotectonic structures, especially in low-relief areas.     

基于GRACE-FO的微波与激光星间测距数据的重力场模型对比分析

为分析GRACE-FO微波测距系统KBR及激光干涉测距系统LRI对时变重力场结果的影响,以动力学方法为基础,分别采用KBR数据和LRI数据反演2019-01~2021-08的90阶无约束时变重力场模型APM_KBR和APM_LRI,并进行对比分析。 从重力场模型阶方差和等效水柱高的空间分布来看,在两类测距数据完整且质量较好的前提下,两者精度处于同一水平,而当发生较多月卫星机动或其他卫星事件时会使LRI数据缺失,从而导致APM_LRI模型在该月得到的等效水柱高时间序列信噪比略低。由后验残差结果可知,APM_LRI后验残差RMS比APM_KBR减少约50%,且在高频处(大于等于60 CPR)LRI的后验残差显著低于KBR。总体来说,在现有条件下,由于背景场模型等其他因素影响,两类测距数据反演重力场的阶方差和等效水柱高结果基本一致,但后验残差上LRI测距具有更低的噪声。因此,未来可直接使用LRI测距数据探测、分析较弱的地球物理信号。     

日长的十年尺度变化研究

用高精度的日长资料和由人卫激光测距（ＳＬＲ） 解算出的地球引力场系数Ｊ２ 的变化序列ΔＪ２ ,证明地球各圈层的物质迁移对日长１０ 年尺度变化贡献仅占日长１０ 年尺度变化的４ ％ ,可以忽略;认为１０ 年尺度变化主要来源于地球各圈层的内力矩或相对角动量部分,其优点是可以不顾及地球各圈层物质迁移复杂的物理机制     

Sea-floor positioning with global positioning system–acoustic link system

The present study describes a new system designed and developed for observing crustal deformation on the sea floor. The system consists of two parts, the kinematic positioning by global positioning system (GPS) and acoustic ranging techniques. Since the location of a site at the ocean bottom relative to a reference site on land cannot be determined directly, the procedure was divided into two steps. First, the position of a vessel was determined using differential and kinematic GPS techniques, and then the position of a reference point at the ocean bottom was located relative to the vessel using the acoustic ranging technique. Thus, the location of the ocean-bottom station is determined relative to the reference sites on land in the global reference system. The accuracy was tested in several ways. In one experiment, a buoy was used as the surface station which linked the positions of a GPS receiver to the acoustic transponder. Assuming a simple sound velocity profile of the seawater, the position of an ocean-bottom reference point was estimated with an accuracy of several meters. Thus, with the present system, it is difficult to observe ocean-bottom crustal deformations generated by typical plate motions. Methods are being investigated to improve the observation system for more accurate sea floor positioning.     

四种海水透明度现场测量方法的对比分析及发展趋势研究

随着海洋探测的不断发展,海水透明度作为海水光学性质的一个重要参量,也越来越受到人们的关注。文章对比分析了4种海水透明度现场测量方法:透明度盘法~([1])、光纤式高光谱剖面测量法~([2])、激光衰减测量法~([3])和基于双光路原理的海水IOPs高光谱测量法~([4]),主要分析了4种方法的测量原理,对比各自的优缺点,并提出了海水透明度测量未来发展设想。     

东喜马拉雅构造结气候构造作用下热史演化的40Ar/39Ar年代学记录

以喜马拉雅山系为典型实例,究竟是气候作用还是构造作用引起山体隆升的问题已经成为地球系统科学研究中的重要前沿问题。无论是气候因素还是构造因素引起山体隆升,二者都与一个共同的地表过程——剥蚀作用相关,剥蚀作用对山体中地质体的影响可以用岩石矿物经历的热史演化来描述,所以,在造山作用研究中,山体或山脉的热史演化是揭开地质体经历地质过程、山体隆升研究的重要途径。利用河砂组成矿物来研究流域的地质过程和构造演化已经成为现代地质科学的重要手段。本文采集了雅鲁藏布江下游墨脱县以南约50 km处地东河段内的现代河砂,对其中的角闪石、白云母、黑云母及钾长石等四种矿物进行了高精度单颗粒激光⁴⁰Ar/³⁹Ar年代学测试,并进行了概率统计。地东河段河砂中富钾矿物⁴⁰Ar/³⁹Ar年代学统计结果显示,大峡谷流域的热史演化可以确定有多个阶段,分别可以识别出70~69、61~60、43~42、35~34、26~25、25~23、22~20、20~18、17~14、12~11、8~6、5~4及<2Ma等13个热史演化阶段。通过将上述热史信息与印度大陆与欧亚大陆碰撞角度和碰撞速率变化曲线的对比,可以确定70~69、61~60、43~42、35~34、22~20和12~11Ma等6个阶段的年代学信息是两大陆碰撞角度和碰撞速率变化事件在东喜马拉雅构造结热史上的记录;通过与全球深海氧、碳同位素记录曲线的对比,可以认为26~25、25~23、17~14、8~6、5~4和<2Ma等6个阶段的年代学信息是气候变化在东喜马拉雅构造结热史上的记录。东喜马拉雅构造结地质体热史演化是构造与气候相互作用的结果。     

地震电磁卫星精密定轨方法研究

高精度卫星轨道是提高卫星应用水平的基础,卫星精密定轨方法主要基于卫星轨道动力学理论．通过跟踪卫星轨迹的测轨技术,将几何和动力学信息进行融合。地震电磁卫星拟采用星载GPS和综合轨道求解方法进行精密定轨．并辅之以人卫激光测距,其定轨的精度可达厘米级。