[转帖]从日本军用地图说开去

glass

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静思

[这个贴子最后由静思在 2002/12/08 04:03pm 编辑]

      Navigation satellite systems-1: 美国的GPS      lt;pgt;       GPS(Global Positioning System, 全球定位系统) is funded by and controlled by the U. S. Department of Defense (DOD). While there are many thousands of civil users of GPS world-wide, the system was designed for and is operated by the U. S. military.
       GPS provides specially coded satellite signals that can be processed in a GPS receiver, enabling the receiver to compute position, velocity and time.
       Four GPS satellite signals are used to compute positions in three dimensions and the time offset in the receiver clock.

静思

The first actual GPS satellite, named quot;Navstarquot;, was launched by a US Air Force (USAF) Atlas-Centaur booster in February 1978. That satellite, plus the ten after it, were designated quot;Block Iquot;, and were built by Rockwell International.
      The first quot;Block IIquot; operational satellite was launched by an Air Force Delta booster on 14 February 1989.
      The full 24-satellite operational constellation was finally completed with the launch of a Block IIA satellite on 9 March 1994. The Block II/IIA satellites have a design lifetime of over 7 years.
      Replacement satellites, designated quot;Block IIRquot; and built by Lockheed Martin, are being launched as needed to maintain the constellation. The first Block IIR satellite was launched on a Delta II booster on 27 March 1996, and six Block IIR satellites have been launched as of early 2001.
      A total of 20 Block IIR spacecraft were produced and stockpiled, with the last scheduled to be launched in 2009. After manufacture of the Block IIR spacecraft, the Air Force then decided to initiate a degree of improvement in GPS services, and so the last twelve of the batch are being modified to the quot;Block IIR-Mquot; (quot;Mquot; for quot;Modernizedquot;) standard, with additional GPS signals. The first Block IIR-M satellite is currently scheduled for launch in 2003.
      The Block IIR / IIR-M satellites will be be followed by further improved quot;Block IIFquot; satellites, with the first Block IIF spacecraft scheduled to be launched in 2005. A total of 12 Block IIF spacecraft will be built by Boeing, which bought Rockwell\'s space assets in 1996.

静思

Block IIR-M GPS satellite

静思

Both Japan and the European Space Agency (ESA) are now working on GPS augmentation systems, with the main function of both networks being air traffic control.
      The Japanese system is known as quot;MTSAT (Multifunction Transport Satellite) Space-based Augmentation Systemquot; or quot;MSASquot;, and is being implemented by the Japanese Meteorological Agency and the Japanese Ministry of Transport, hence the name of the satellite. The MTSAT spacecraft will be a combination meteorological and communications satellite, and will be placed in geostationary orbit over the eastern Pacific. The satellite will relay GPS augmentation and integrity data to aircraft, along with other communications services.
       The first MTSAT launch was in November 1999, but the spacecraft failed to reach orbit. A replacement spacecraft, designated quot;MTSAT-1Rquot;, will be launched in the late summer of 2003, with a second, similar satellite designated quot;MTSAT-2quot; scheduled for launch in the summer of 2004. The satellites are built by Space Systems / Loral, and are based on standard Loral satellite buses. lt;pgt;      The ESA network is known as the quot;European Geostationary Navigation Overlay System (EGNOS)quot;. Like MSAS, EGNOS will transmit augmentation and integrity data to aircraft through geostationary communications satellites. It is currently scheduled to go into operation in 2003, and will use the INMARSAT AOR-E and IOR commercial communications satellites and the European Space Agency Artemis experimental communications satellite. The satellites will provide coverage of subpolar areas ranging from the east coast of the United States to Japan.

静思

Navigation satellite systems-2: 俄罗斯（前苏联）的GLONASSlt;pgt;      The Soviets gave their own answer to GPS, with the English name of quot;Global Navigation Satellite System (GLONASS)quot;.
      Like GPS, the full GLONASS network is to include 24 satellites, consisting of 21 operational satellites and three spares. All the satellites are to transmit identical codes but at different frequencies, exactly the reverse of the scheme used for GPS.
      The orbits are at an altitude of 19,100 kilometers, slightly lower than that of the GPS satellites, with the satellites placed in three orbital planes, each containing eight satellites. Each satellite completes an orbit in 11 hours 15 minutes. The planes have orbital inclinations of 64.8 degrees. GLONASS is supposed to have location accuracy capabilities roughly similar to those of GPS, but it does not impose selective availability on civilian users.
      GLONASS launches began in 1982, but due to the troubled circumstances of the Soviet and successor Russian states, the full constellation has never been implemented. As of mid-2002, only eight GLONASS satellites are operational. The Russians are planning to launch more when they can get the money.
      They are also working on a next-generation quot;GLONASS-Mquot; satellite, with improved signal characteristics and a design lifetime of up to eight years, rather than the current 3 year design lifetime. They ultimately hope to go to quot;GLONASS-Kquot;, which will be smaller and will have a design lifetime of ten years.

静思

DFH-3
Credit: via Chen Lan
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      Navigation satellite systems-3: 中国的北斗lt;pgt;      Beidou (\'Big Dipper\') was the satellite component of an independent Chinese satellite navigation and positioning system. This was to be achieved by launching a satellite constellation in stages during 2000-2010 while developing the relevant application systems. The end result would be a Chinese indigenous satellite navigation and positioning industry. Experimental launch of the first two indigenous Beidou navigation satellites was in 2000. Beidou began in 1983 with a proposal by Chen Fangyun to develop a Twinsat regional navigation system using two geostationary satellites. The concept was proven in 1989 in a test using two in-orbit DFH-2/2A communcations satellites. This test showed that the precision of the Twinsat system would be comparable to the American Global Positioning System. In 1993, the Beidou program was officially started. Beidou used the DFH-3 bus and had similar basic performance. The final Beidou constellation was to consist of four geosynchronous satellites, two operational and two backups.      
      The quot;Beidou (Big Dipper) Navigation Test Satellite 1quot; was launched by a Chinese Long March 3M booster on 31 October 2000, into a geostationary orbit slot at 140 degrees East Longitude, to the east of China.
      It was followed by quot;Beidou 1Bquot; on 21 December 2000, which was placed in a geostationary slot at 80 degrees East longitude. This allows the two satellites to provide navigational coverage over the entire country.
      Beidou is the first in a series of satellites for a system that will provide all-weather, round-the-clock navigation information for highways, railways and shipping. The satellite was developed by China\'s Research Institute of Space Technology. No information was provided on when the network will be operational. The 2200 kg (4849 lbm) satellite is based on the DFH-3 bus.
      Beidou joins a U.S. navigation system called Global Positioning System (GPS) and the Russian\'s operate a system called Global Navigation Satellite System (GLONASS). China is concerned about becoming too dependent on foreign technology.
      Beidou is the Chinese name for the constellation which many westerner\'s refer to as Ursa Major. Specific details of the system have not been released, but the Chinese state that they are working on a second-generation navigation satellite system.

静思

就民用而言，GPS已得到了广泛的应用。在日本，花１４万日圆，约９３００多人民币即可在私人汽车内装上一台GPS接收器，使用时在９inch大小的显示屏上可见所处地域，街道和邻近建筑的名称，本车的动态位置，目的地的方位距离以及前方路况等等，对于我这种路盲来说尤其方便。手机也可装载GPS接收器。不知GPS在国内的应用情况具体如何（指民用，军方早就在学习研究了，理论和实验进展多多，但离实用还差得远）？

DingDang

下面引用由乡长在 2002/12/07 00:54am 发表的内容：
哈哈哈哈哈....我要笑死了,就知道这点也来跟我讨论地图?
GPS是美国的卫星,日本屁都没有,美国政府已经在2000年5月1日停止对GPS加扰,
所以现在一般民用GPS能达到的精度是15米左右,实际上,由于卫星上星载铯原子
钟　...

lt;pgt;nod，偶知道的本来也不多，
日本本来就是租用美国的GPS，lt;pgt;你的信息很专业嘛，偶是没法和你比的，不过你好像忘记了，
我说的是民用技术，而不是满口的专业词汇。lt;pgt;你试着告诉我国内的应用技术吧，而不是在这里用满口的专业词汇来糊弄大多数。lt;pgt;地图么，谁没做过？专业词汇，谁不会一堆，说出来唬人的吗？lt;pgt;我知道的确实不多，足够我做出些什么来。。。lt;pgt;既然这里这么多同行，区区不才，也献丑一把。
接触这个行业没多久，不过一年半而已。lt;pgt;有说错的多指教咯。lt;pgt;多谢静思，找出这么多信息来。：）lt;pgt;国内导航还在起步阶段，主要是地图处理方面进展得力不从心，
数据收集整理工作是政府的工作，并非一个公司可以做好的。lt;pgt;目前也有一些号称导航的产品问世，如果你打算买，那么十年之内不要去看国外的导航产品，不然会捶胸顿足满是怒气。lt;pgt;好了，废话到此为止吧。其实有的时候，我们应该学习一下谦虚怎么写。
而不是一味的自我膨胀。
俺们不是还有句古话叫做三人行必有我师么。实行起来，真的比较难吧。lt;pgtS：有些信息落伍了就帮我刷新叻吧，我已经离开这个行业半年多辣～～

乡长

我也有一台GPS,台湾产的，我觉得没什么难的，中国有很多好的专业GPS系统，
但是民用的GPS几乎没有，我想关键还是中国没有这方面的市场，而且半导体
产业落后，芯片没法跟上的缘故。前面有人说要14万日元,好像太贵了点吧？
一般的带电子地图的民用机也就一两千人民币。lt;pgt;关于北斗一号，我了解一些，本来要发射四颗，现在发射了两颗，估计另外两
颗不会发射了。lt;pgt;我前面说了，导航卫星的关键是星载原子钟，原子钟有三类，铷钟，铯钟，氢钟。
氢钟精度最高，但长期稳定性差，铯钟精度差，但是长期稳定性最好。所以目前
卫星上基本上用铯钟，因为这样可以避免做频繁的星历修正。美国生产的星载铯
钟重两公斤，无故障时间超过五年。目前还没有第二家能生产这种东西。lt;pgt;中国氢钟比较厉害，主要是上海天文台在做，而且还出口多个发达国家。但是铯钟
几乎一片空白，所以，中国的北斗一号上面也不可能用国产铯钟，上面的原子钟是
从美国进口的铷钟，铷钟最差，是美国淘汰的产品，不过就是这个，也对中国禁运
的，所以我说，另外两颗北斗一号基本上不会发射了。由于用的是铷钟，北斗一号
的精度大概比美国GPS差五倍。lt;pgt;现在星载原子钟的发展趋势是氢钟，估计计划5年后中国将发射北斗二号导航卫星
会使用国产小型氢钟，目前上海天文台和北大物理系两家在争。lt;pgt;另外说一下，其实这个世界上就美国会做小型铯钟，中国整个国家的时间同步网络
都是依赖美国的小型铯钟（当然现在也用一部分上海天文台生产的小型氢钟），哪
天打仗了，也许整个国家的计算机网络，长途电话网络，中国联通的CDMA移动电话
网络都会瘫痪。大家收音机电视机上的报时信号，其实也来源于中央电视台的一台
从美国进口的铯钟。