A GUIDE TO USING INTERNATIONAL GNSS SERVICE (IGS) PRODUCTS
A GUIDE TO USING INTERNATIONAL GNSS SERVICE (IGS) PRODUCTS
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发表时间：
2003
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通讯作者：
J. Kouba
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作者：
J. Kouba
自1994年以来，国际全球导航卫星系统服务处(全球导航卫星系统)S向太平洋科学界提供了精确的全球定位系统轨道产品，提高了精度和及时性。许多对大地测量定位感兴趣的国家大地测量机构和GPS用户都采用了IGS精密轨道，以达到厘米级的精度，并确保参考坐标系的长期稳定。相对定位方法通常需要至少两个GPS接收器的观测组合，其中至少一个接收器占用一个具有已知坐标的站。然后，可以使用差分载波相位观测值和基线或网络估计方法来相对于一个或多个参考站估计用户位置。差分观测是消除常见GPS卫星和接收机时钟误差的一种常用方法。基线或网络处理在将用户位置与参考站的坐标连接方面是有效的，而精密轨道实际上消除了GPS空间段引入的误差。一个缺点是要求在参考站同时进行用户观测的实际限制。另一种本地后处理方法使用无差双频伪距和载波相位观测值以及IGS精密轨道产品，以实现厘米级精度的独立精密大地测量点定位(静态或动态)。如果利用IGS精密轨道/时钟产品中卫星坐标可用的卫星锁定估计，并模拟导致卫星到用户范围厘米级变化的系统效应，这是可能的。此外，还获得了站对流球天顶路径延迟(mm精度)和GPS接收机时钟估计精度(0.03纳秒)。为了达到最高的准确性和一致性，用户还必须执行全球导航卫星系统通过的特定于全球导航卫星系统的公约和模型。本文描述了这两种后处理方法，总结了平差过程，并详细说明了实现毫米-厘米级定位、对流层天顶路径延迟和闭合解所必须实施的基于地球和空间的模型和惯例。国际全球导航卫星系统服务(IGS)，前身为国际GPS服务，是由80多个国家的200多个捐助组织自愿合作的。由300多个永久的、连续运行的GPS站组成的IGS全球跟踪网络为IGS分析中心提供了丰富的数据集，这些中心制定了S卫星星历和时钟解决方案等精确产品。IGS数据中心免费为任何研究人员提供所有IGS数据和产品。本文着重介绍了IGS精密轨道钟表的优点和使用方法。目前，多达8个IGS分析中心(AC)每天为IGS组合提供超快、快速和最终的GPS球体和时钟解决方案。通过IGS以厘米精度直接计算全球精密GPS轨道和时钟，便于在与当前国际地球参考框架(ITRF)一致的全球综合参考框架内建立直接联系。自2000年以来，最初设计用于服务于气象学应用和支持低地球轨道器(LEO)任务的超快产品已经面市。自那以后，这款超快的产品也对许多其他实时和接近实时的用户有用。有关IGS组合解决方案产品S及其上市的更多信息，请参阅IGS中心局(见http://www.igs.org/components/prods.html).
Since 1994, the International GNSS Service (IGS) ha s provided precise GPS orbit products to the scient ific community with increased precision and timeliness. Many national geodetic agencies and GPS users interested in geodetic positioning have adopted the IGS precise orbits to achieve centimeter level acc uracy and ensure long-term reference frame stability. Rel ative positioning approaches that require the combination of observations from a minimum of two GPS receivers, with at least one occupying a station with known coordinates are commonly used. The user position can then be estimated relative to one or multiple reference stations, using differenced carr ier phase observations and a baseline or network estimation approach. Differencing observations is a popular way to eliminate common GPS satellite an d receiver clock errors. Baseline or network process ing is effective in connecting the user position to the coordinates of the reference stations while the pre cise orbit virtually eliminates the errors introduc ed by the GPS space segment. One drawback is the practical constraint imposed by the requirement that simultaneo us observations be made at reference stations. An alte rnative post-processing approach uses un-difference d dual-frequency pseudorange and carrier phase observations along with IGS precise orbit products, for stand-alone precise geodetic point positioning (sta tic or kinematic) with centimeter precision. This is possible if one takes advantage of the satellite cl ock estimates available with the satellite coordina tes in the IGS precise orbit/clock products and models systema tic effects that cause centimeter variations in the satellite to user range. Furthermore, station tropo spheric zenith path delays with mm precision and GPS receiver clock estimates precise to 0.03 nanosecond are also obtained. To achieve the highest accuracy and consistency, users must also implement the GNSS-specific conventions and models adopted by the IGS. This paper describes both post-processing approaches, summarizes the adjustment procedure and specifies the Earth and space based models and conventions th at must be implemented to achieve mm-cm level positioning, tropospheric zenith path delay and clo ck solutions. The International GNSS Service (IGS), formerly the International GPS Service, is a voluntary collabora tion of more than 200 contributing organizations in more than 80 countries. The IGS global tracking network of more than 300 permanent, continuously-operating GPS stations provides a rich data set to the IGS Analy sis Centers, which formulate precise products such as s atellite ephemerides and clock solutions. IGS Data Centers freely provide all IGS data and products fo r the benefit of any investigator. This paper focus es on the advantages and usage of the IGS precise orbits and clocks. Currently, up to eight IGS Analysis Centers (AC) contribute daily Ultra-rapid, Rapid and Final GPS orb it and clock solutions to the IGS combinations. The da ily computation of global precise GPS orbits and clocks by IGS, with centimeter precision, facilitat es a direct link within a globally integrated, refe rence frame which is consistent with the current Internat ional Terrestrial Reference Frame (ITRF). Since 200 0 the ultra-rapid product originally designed to serve me teorological applications and support Low Earth Orbiter (LEO) missions, has been made available. The ultra-rapid product has since become useful to many other real-time and near real-time users, as well. For mo re information on the IGS combined solution product s and their availability see the IGS Central Bureau ( see http://www.igs.org/components/prods.html).