A correction method of encoder bias in satellite laser ranging system

In a satellite laser ranging telescope system, well-aligned encoders of the elevation and azimuth axes are essential for tracking objects. However, it is very difficult and time-consuming to correct the bias between the absolute-position indices of the encoders and the astronomical coordinates, especially in the absence of a finder scope for our system. To solve this problem, a method is presented based on the phenomenon that all stars move anti-clockwise around Polaris in the northern hemisphere. Tests of the proposed adjustment procedure in a satellite laser ranging （SLR）system demonstrated the effectiveness and the time saved by using the approach, which greatly facilitates the optimization of a trackin~ svstem.

Progress of the satellite laser ranging system TROS1000

The mobile satellite laser ranging system TROS1000, successfully developed in 2010, achieves a high repetition rate and enables daytime laser ranging. Its measurement range has reached up to 36000 km with an accuracy as precise as 1 cm. Using recent observations in Wuhan, Jiufeng, Xianning, and Rongcheng, Shandong, we introduce the progress made using this mobile observation system.

Influence of Range Gate Width on Detection Probability and Ranging Accuracy of Single Photon Laser Altimetry Satellite

The influence of the single photon laser altimeter range-gate width on the detection probability and ranging accuracy is discussed and analyzed,according to the LiDAR equation,single photon detection equation and the Monte Carlo method to simulate the experiment.The simulated results show that the probability of detection is not affected by the range gate,while the probability of false alarm is relative to the gate width.When the gate width is 100 ns,the ranging accuracy can accord with the requirements of satellite laser altimeter.But when the range gate width exceeds 400 ns,ranging accuracy will decline sharply.The noise ratio will be more as long as the range gate to get larger,so the refined filtering algorithm during the data processing is important to extract the useful photons effectively.In order to ensure repeated observation of the same point for 25 times,we deduce the quantitative relation between the footprint size,footprint,and frequency repetition according to the parameters of ICESat-2.The related conclusions can provide some references for the design and the development of the domestic single photon laser altimetry satellite.

Overview of Satellite Laser Ranging for BeiDou Navigation Satellite System

Satellite laser ranging(SLR)is an unambiguous measurement technique and generates high accuracy satellite orbit data.All satellites in the BeiDou navigation satellite system(BDS)carried laser retro-reflector arrays(LRAs),so they can be tracked by ground SLR stations in order to provide the accurate observation data.The Shanghai astronomical observatory(SHAO)designed the LRAs,and also developed the dedicated SLR systems using a 1 m-aperture telescope and a transportable cabin-based SLR system with a telescopes of 60 cm aperture.These enable BDS satellite ranging during daytime and nighttime with centimeter-level precision,allowing highly accurate estimations of satellite orbits.Moreover,some of the BDS satellites are also equipped with laser time transfer(LTT)payloads,which were developed by the SHAO and China Academy of Space Technology(CAST),providing a highly accurate time comparison between the satellites and ground clocks.This paper describes the dedicated SLR system and the design of the LRAs for BDS satellites,as well as global SLR measurements.The SLR tracking data is used for evaluating the orbit accuracy of BDS satellites and broadcast ephemeris,with an accuracy of less than 1 m.The LTT measurements to BDS satellites for a single shot have a precision of approximately 300 picoseconds,with a time stability of 20 picoseconds in 500 s.

Laser back scatter: Limitation to higher repetition rate [kHz] Satellite Laser Ranging system

Satellite laser ranging(SLR)with higher repetition rate is the recent trend for its various advantages.Laser backscatter(coincidence between recently transmitted pulses and received pulses near the detector)is found to be a constraint for the repetition rates higher than 20 kHz,due to,overlapping with photons returning from a satellite with the present constellation of most of the SLR systems.Such an overlap occurs at every 75 km satellite distance change at 2 kHz repetition rate,and remains for about 7.5 km;for a 20 kHz system however,it will occur after every 7.5 km and remains for 7.5 km,resulting in constant backscatter overlap e leaving no chance to avoid it.The resulting noise is 5 times more than before causing a serious problem in detection and lowers the signal to noise ratio of the overall SLR system.However,decreasing energy per shot at higher repetition rates e assuming a constant power laser e the resulting backscatter may decrease fractionally.

Pre-process algorithm for satellite laser ranging data based on curve recognition from points cloud

The satellite laser ranging （SLR） data quality from the COMPASS was analyzed, and the difference between curve recognition in computer vision and pre-process of SLR data finally proposed a new algorithm for SLR was discussed data based on curve recognition from points cloud is proposed. The results obtained by the new algorithm are 85 % （or even higher） consistent with that of the screen displaying method, furthermore, the new method can process SLR data automatically, which makes it possible to be used in the development of the COMPASS navigation system.

Design and analysis of the Macao Science Satellite-1's laser retro-reflector array

The origin and spatial-temporal variation of the Earth’s magnetic field(EMF)is one of the important scientific problems that has long been unsolved.The Macao Science Satellite-1(MSS-1)under construction is China’s first high-precision EMF measurement satellite.To satisfy the highly precise requirements of the MSS-1 orbit measurement,a light,high-precision,four-prism laser retroreflector array was designed.It weighs approximately 285 g,its effective reflection area is greater than 1.77 cm^(2),and its size is 100×100×41 mm.The laser retro-reflector array has excellent performance,and it can achieve a ranging precision at the subcentimeter level for satellite laser ranging.It will be developed and installed on the MSS-1 as a power-free load for high-precision orbit measurement and accurate orbit calibration.The MSS-1 is planned to be brought into the International Laser Ranging Service observations.More than 31satellite laser ranging stations in the International Laser Ranging Service around the world will be able to measure the MSS-1 with long arcs,which will support the scientific mission of high-precision EMF exploration.

Determination of global geodetic parameters using satellite laser ranging to Galileo,GLONASS,and BeiDou satellites

The new Global Navigation Satellite System(GNSS)satellites,including GLONASS,Galileo,and BeiDou system,are equipped with Laser Retroreflector Arrays(LRA)to support Satellite Laser Ranging(SLR)tracking,which contributes to the estimation of global geodetic parameters.In this study,we estimate the global geodetic parameters using the SLR observations to GNSS satellites and also investigate the effects of different data processing strategies on the estimated Earth Rotation Parameters(ERP),geocenter motion,and terrestrial scale.The results indicate that setting range bias parameters for each satellite-station pair can effectively account for the satellite-specific biases induced by LRAs,leading to smaller Root Mean Square Errors(RMSE)of the post-fit SLR residuals.Furthermore,estimating the range biases for each satellite-station pair improves the accuracy of the estimated station coordinates and ERP.We also examine the impact of different arc lengths on the estimates of ERP,geocenter motion,and terrestrial scale.The results show that extending arc length can significantly reduce the formal error of ERP.The 7-day strategy produces the smallest RMSEs of 473 microarcseconds and 495 microarcseconds for the estimated X-and Y-component of pole coordinates,and 52 microseconds for length-of-day,respectively.However,the estimated geocenter motion is less affected by the arc length,even the shortest 1-day arc strategy can capture the seasonal variations of geocenter motion in Z component.For scale estimation,extending the arc length notably improves the accuracy of the estimated station coordinates and scale,but this advantage becomes less noticeable in longer arcs.The 7-day solution also obtains the closet scale results compared to ITRF2014,with the RMSE of 2.10×10^(–9).

The progress of laser ranging technology at Shanghai Astronomical Observatory

As an important station of International Laser Ranging Service(ILRS),Shanghai Astronomical Observatory(SHAO)has upgraded Satellite Laser Ranging(SLR)system with high repetition rate and achieved some technological progress,There are a lot of improvements for overall system performance,such as annual observation passes,measurement precision and quality of observation data.SLR technology with repetition rate of 10 kHz is accomplished firstly in China,and space debris laser ranging technology with200 Hz laser is promoted and proved to be more detective for weak echo,which lead to successful measurement for 40,000 km satellites and space debris within 3000 km.At the same time,SLR based on multi-telescopes and 1064 nm wavelength are planned to make a breakthrough of detection capabilities,and also to expand its application fields.These progresses will be introduced in this paper in detail.

Evaluation of CHAMP Satellite Orbit with SLR Measurements

The technique of Evaluating CHAMP satellite orbit with SLR measurements is presented. As an independent evaluation of the orbit solution, SLR data observed from January 1 to 16, 2002 are processed to compute the residuals after fixing the GFZ’s post science orbits solutions. The SLR residuals are computed as the differences of the SLR measurements minus the corresponding distances between the SLR station and the GPS-derived orbit positions. On the basis of the SLR residuals analysis, it is found that the accuracy of GFZ’s post science orbits is better than 10 cm and that there is no systematic error in GFZ’s post science orbits.

空间激光通信与测距一体化研究

【目的】随着卫星技术和通信技术的不断提高,空间激光通信与测距一体化技术也逐渐成熟。而伴随着深空探测、卫星导航等领域的进一步发展,大量的业务及应用需求对星间的通信容量和测距精度又提出了更高的要求。在综合考虑卫星荷载与功耗的前提下,如何在实现激光卫星高速通信的同时,完成测距并进一步提升测距精度,成为亟待解决的课题。【方法】基于双向单程测距原理,设计并实现了一种同时支持正交相移键控(QPSK)和二进制相移键控(BPSK)的相干通信与测距一体化系统,为进一步提升测距性能,又从提升时钟精度入手,通过使用差拍采样方法,使用鉴频与鉴相来获取发送时钟与接收时钟之间的频率差与相位差,以此来获取到更高的时钟精度,从而对测距值进行校正。【结果】该系统能稳定工作在接收光功率大于-48 dBm的环境,针对不同应用需求可设置不同的速率,QPSK模式下最高速率为5 Gbit/s,BPSK模式下速率分别为2.5 Gbit/s、1.25 Gbit/s和625 Mbit/s,系统测距精度理论上可达最小值53 ps,在正常通信时,使用Matlab与Vivado对测距数据进行计算处理,验证了系统测距精度小于0.1 ns。进一步采用差拍采样方法,仿真条件下,测距精度可提升至码元宽度的10^(-3)量级,达±0.36 cm。【结论】所提通信测距一体化系统能够在高速通信的同时实现高精度测距,对未来激光卫星的相关应用具有一定的实际意义。

Performance and observation summary of Changchun Satellite Laser Ranging Station

This note introduces the performance and observation summary of the SLR system at Changcun Observatory, the Chinese Academy of Sciences. The performance of the SLR system has been greatly improved since August 1997. The single shot precision is improved from 5-7 cm to 1-2 cm and the normal point precision reaches 4-7 mm. The long-term stability is better than 1 cm. The amount of observation has been increased from 1000 to over 3000 passes. The whole performance of Changcun SLR system has reached the advanced level among the worldwide SLR stations.

A Raman laser system for multi-wavelength satellite laser ranging

In order to develop a laser system for multi-wavelength satellite laser ranging, the joint group of the Shanghai Astronomical Observatory and the Czech Technical University has studied the conversion efficiency of the Raman-shifting beam and its spatial characteristics. We adopted a 0.53 μm laser with pulse width of 35 ps and peak energy of 35 mJ, the second harmonic of a Nd:YAG actively and passively mode-locked laser, to pump a one-meter-long Raman tube which is full of H2 with high pressure at the Prague-based laboratory. We get the first Stokes laser (0.68 μm): 7 mJ (single pulse) with beam divergence of 40″ (arcsecond) and spatial wobbling of less than 4″; and the first anti-Stokes laser (0.43 μm): 2 mJ (single pulse) with divergence of 56″ and spatial wobbling of less than 4″. The emitting beam from the Raman cell also includes 0.53 μm: 10 mJ (single pulse) with divergence of 40″ and spatial wobbling of less than 7″. According to the radar link equation and based on the above obtained multi-wavelength’s energy, we can estimate the detection probabilities for three colors respectively. It is shown by the result that the developed multi-wavelength Raman laser system has the capability of satellite ranging. The Raman laser system will be installed at the laser station in Shanghai Astronomical Observatory to research the multi-wavelength satellite laser ranging.

Design and observations of satellite laser ranging system for daylight tracking at Shanghai Observatory

The first satellite laser ranging system for daylight tracking in China was set up at Shanghai Observatory, Chinese Academy of Sciences. Both false alarm probability due to strong background noises and detection probability of the laser returns with single photon level from satellite in daylight for our system are analysed. The system design and performance characteristics of subsystems, adopted techniques and satellite ranging observations are given.

Precise orbit determination of Haiyang-2 using satellite laser ranging

With the successful launch and official commissioning of China's first dynamic ocean environment satellite Haiyang-2(HY-2),China's capabilities for oceanic environment monitoring and oceanic resource detecting have been further improved and enhanced.Precise tracking and orbit determination are not only key technical concerns in the ocean dynamic environment satellite project but also necessary conditions for carrying out related oceanic science research using observational data obtained using spaceborne instruments including radar altimeter.In this study,the current available status of international satellite laser ranging(SLR) monitoring on HY-2 was introduced.Six-months of SLR data from HY-2 were processed to obtain precise satellite orbit information using the dynamic orbit determination method.We carried out a detailed assessment of the SLR orbit accuracy by internal evaluation,comparisons with the orbit derived by the French Doppler orbitography and radio-positioning integrated by satellite(DORIS) system,and station-satellite distance validation.These assessments indicate that the three-dimensional orbital accuracy of HY-2 is about 12.5 cm,and the radial accuracy is better than 3 cm.It provides a good example of the application of international SLR monitoring and precise orbit determination in China's earth observation satellite project.

Theoretical analysis and numerical solution of laser pulse transformation for satellite laser ranging

The processes of the pulse transformation in satellite laser ranging (SLR) are analyzed,the analytical expressions of the transformation are deduced,and the effects of the transformation on Center-of-Mass corrections of satellite and ranging precision are discussed.The numerical solution of the transformation and its effects are also given.The results reveal the rules of pulse transformation affected by different kinds of factors.These are significant for designing the SLR system with millimeter accuracy.

Satellite laser ranging experiment with sub-centimeter single-shot ranging precision at Shanghai Observatory

The Shanghai Astronomical Observatory, Chinese Academy of Sciences, incollaboration with the Czech Technical University, carried out the experiment of satellite laser ranging with sub-centimeter precision in Shanghai in August 2001. A pico-second event timer was used for the measurement of the time interval between the transmitted and returned laser pulses for Lageos 1, 2, Starlette, Stella, Topex/Poseiden and ERS-2 in coordination with the existing laser transmitting and receiving system at the Shanghai Observatory. The analysis of the measurement showed that the single-shot ranging precision with these satellites is 7-8 mm. In order to compare ranging precision, the existing ranging system has tracked simultaneously these satellites and obtained the ranging precision of 12-15 mm. It means that the ranging precision with the new system is 80% better thanthe existing system. The systematic biases with the existing system have also been checked in the experiment.

高海拔1.2 m望远镜的瓦级皮秒激光空间目标测距研究

高精度的空间碎片测量,可以提供更精确的碎片目标实时信息,增强卫星对空间碎片的规避预警实效性。通过对青海口径1.2 m量子通信望远镜(海拔3200 m)进行改造,采用单脉冲能量1.2 mJ、重复频率1 kHz皮秒激光开展了卫星激光测距(SLR)与空间碎片激光测距(DLR)试验,其中合作卫星的探测范围由低轨扩展至同步轨道,测距精度优于2 cm;空间碎片目标测量最远距离1620.5 km,雷达散射截面积(RCS)为2.41 m^(2),测距精度达到10.64 cm,实现了单套激光器系统既可开展合作目标厘米级高精度测距,又可实现空间碎片观测。这是目前为止国际首次采用高重频低功率激光测距系统实现对空间碎片目标高精度测量,体现了皮秒激光及高海拔大口径望远镜测量优势,为我国西部开展空间目标的激光测距提供参考,以及为空间碎片激光测距系统选址与空间碎片监视能力的提升提供了有效途径。

超高重频卫星激光测距时序电路实现及应用

高重频卫星激光测距(Satellite Laser Ranging,SLR)具有精度高、捕获快、观测数据量大、可靠性高等优势。但随着重复频率提升至百千赫兹以上,现有测量时序电路无法达到系统运行处理速度和实时后向散射规避等要求。本文提出超高重频卫星激光测距时序电路设计方法,采用FPGA代替控制计算机进行门控距离实时计算,精确产生门控信号控制探测器开启,并使用了收发交替的方式实时调整激光点火信号以规避后向散射干扰。能够自主完成激光测距中距离门控输出时刻的计算、存储和信号输出,最高工作频率大于500 kHz,满足百千赫兹超高频率测距的要求。该系统已成功应用于上海天文台100 kHz重复率SLR,标准点精度突破200μm,验证了基于FPGA的测距时序电路的正确性和潜力。该电路设计简单、分辨率高、上位机交互方便,为百kHz~MHz的超高重频SLR系统时序控制电路设计提供有效解决方案。

FCM测站定权的LAGEOS-2卫星精密定轨影响分析

由于卫星激光测距(satellite laser ranging, SLR)台站的测距精度和稳定性存在差异,精密定轨中需要对不同性能的台站赋予不同权重。本文将模糊C均值(fuzzy C-means, FCM)聚类定权应用于LAGEOS-2精密定轨,并比较原始测站定权和FCM定权对轨道精度的影响。结果表明:1)相较于原始测站定权,FCM定权更能反映各SLR台站的性能,提高定轨精度和观测值数量;2)对于ILRS四个质量分析机构,原始测站定权下JCET发布的质量报告在定轨精度上略优于其他中心,采用FCM定权后,以4个机构发布的质量报告进行定轨的结果在同一水平,轨道精度为4.83~4.86 cm。