Article Abstract
Understanding GNSS Availability and How it Impacts Maritime Safety
Author(s):
A. Grant, P. Williams, G. Shaw, M. De Voy, N. Ward
Published in:
Proceedings of the 2011 International Technical Meeting of The Institute of Navigation
January 24 - 26, 2011
Catamaran Resort Hotel San Diego, CA
Cite this article:
Grant, A., Williams, P., Shaw, G., De Voy, M., Ward, N., "Understanding GNSS Availability and How it Impacts Maritime Safety," Proceedings of the 2011 International Technical Meeting of The Institute of Navigation, San Diego, CA, January 2011, pp. 687-695.
Full Paper:
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The General Lighthouse Authorities of the United Kingdom and Ireland (GLAs) provide marine aids-to-navigation (AtoNs) for the benefit and safety of all mariners within their waters. These AtoNs range from traditional lighthouses and buoys through to radionavigation systems, such as marine radiobeacon DGPS. It is widely recognised that Global Navigation Satellite Systems (GNSS), particularly GPS, have become the primary means of obtaining position, navigation and timing information at sea. Mariners have been conditioned to believe that GPS is infallible, yet this is not the case. This paper reports on recent investigations by the GLAs on three specific threats to GNSS namely the effects of intentional interference and GPS jamming, the impact of a reduced number of available satellites and finally the effect of space weather.
Over the past few years the GLAs have conducted a number of GPS jamming trials, investigating the effect of GPS service denial on a number of GLA vessels, their bridge systems and also on the GLAs’ own AtoNs. The implications of jamming can be severe, particularly when the strength of the jamming signal is comparable to the true GPS signal. During such conditions, hazardously misleading information (HMI) has been observed. Moreover, GPS service denial results in multiple alarms and the simultaneous failure of many bridge systems including the ship’s radar, gyro-compass and Automatic Identification System (AIS). It is nowadays taken for granted by mariners that these systems provide accurate situational awareness, and are often regarded as the backup upon which to rely in the event of GNSS failure, and yet they are themselves vulnerable to the failure of GNSS.
This paper also considers the impact of the 2009 US Government Accountability Office (GAO) report which predicts ‘significant challenges in sustaining and upgrading widely used capabilities’ of GPS due to the struggle to meet launch schedules for GPS IIR replacement and IIF follow-on satellites. The GAO report concluded that the probability of maintaining a constellation of at least 24 useable GPS satellites would fall below 80% by 2011 and that this probability would not return consistently above 95% until 2015. More recent GAO predictions in September 2010 indicate (with 95% confidence) that the number of satellites should not fall below 24 in the medium term, but concerns remain over the effects of satellite ageing and the rate of replacement.
The paper reports on the results of initial investigations into the effects of a reduced GPS constellation on maritime GPS-based navigation. Navigation accuracy performance may be significantly impaired, with the receiver output position being lost or, observed to freeze during prolonged GPS outages. In such conditions there is again the possibility of hazardously misleading information being produced by the ship’s navigation system and this could pose a real threat to maritime navigation.
In a time when GPS jamming units are becoming more common, when satellite constellations are changing and as we approach the solar maximum in 2013, understanding GNSS availability and its effects is crucial to maintaining safe navigation.
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Shields of Strength――这是信仰
爱车：暂无
财产: 10307 爱卡币
来自: 北京市|北京市
Shields of Strength――这是信仰
Shields of Strength 是美国德克萨斯州的一个将运动与宗教相结合的品牌，他的项链将力量美完美展现，深受全世界健身爱好者喜爱，当然啦也包括我~
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onmousewheel="return imgzoom(this);" alt="" />
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onmousewheel="return imgzoom(this);" alt="" />
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[每日热点]:
爱车：暂无
财产: 10307 爱卡币
来自: 北京市|北京市
项链的款式不多，主要有5种比较受欢迎，分别是哑铃、杠铃片、壶铃、飞鞋和军牌，吊坠上的文字有3种可供选择，都是出自于《新约》的章节，到底买哪条这就要看个人喜好了。
760) {this.resized= this.width=760; this.alt='Click here to open new window';}" onmouseover="if(this.width>760) {this.resized= this.width=760; this.style.cursor='hand'; this.alt='Click here to open new window';}" onclick="window.open('.cn/bbs/photo/.htm')" longdesc=".cn/bbs/photo/.htm" title="点击进入图库"
onmousewheel="return imgzoom(this);" alt="" />
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onmousewheel="return imgzoom(this);" alt="" />
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onmousewheel="return imgzoom(this);" alt="" />
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onmousewheel="return imgzoom(this);" alt="" />
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[每日热点]:
爱车：暂无
财产: 10307 爱卡币
来自: 北京市|北京市
我喜欢杠铃片形状的，文字选了Phil 4:13: I can do all things through CHRIST who strengthens me,虽然从远处看隐约有点像铜钱。。。
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onmousewheel="return imgzoom(this);" alt="" />
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onmousewheel="return imgzoom(this);" alt="" />
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[每日热点]:
爱车：暂无
财产: 10307 爱卡币
来自: 北京市|北京市
福利时间到，从tb搜罗了几张买家秀~~~
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onmousewheel="return imgzoom(this);" alt="" />
760) {this.resized= this.width=760; this.alt='Click here to open new window';}" onmouseover="if(this.width>760) {this.resized= this.width=760; this.style.cursor='hand'; this.alt='Click here to open new window';}" onclick="if(!this.resized) {} else {window.open('/large/69be05fejw1es8prhl1efj20hs08w0t8.jpg');}" onmousewheel="return imgzoom(this);" alt="" />
[每日热点]:
财产: 767 爱卡币
来自: 吉林省|吉林市
[每日热点]:
财产: 2 爱卡币
项链的款式不多，主要有5种比较受欢迎，分别是哑铃、杠铃片、壶铃、飞鞋和军牌，吊坠上的文字有3种可供选择，都是出自于《新约》的章节，到底买哪条这就要看个人喜好了。
760) {this.resized= this.width=760; this.alt='Click here to open new window';}" onmouseover="if(this.width>760) {this.resized= this.width=760; this.style.cursor='hand'; this.alt='Click here to open new window';}" onclick="if(!this.resized) {} else {window.open('.cn/attachments/a/day_c36d945c66ae940d9Fhdk4fhSRQyC.jpg');}" onmousewheel="return imgzoom(this);" alt="" />
760) {this.resized= this.width=760; this.alt='Click here to open new window';}" onmouseover="if(this.width>760) {this.resized= this.width=760; this.style.cursor='hand'; this.alt='Click here to open new window';}" onclick="if(!this.resized) {} else {window.open('.cn/attachments/a/day_c845b10ee2a868cb3w2czP5vMy3Ld.jpg');}" onmousewheel="return imgzoom(this);" alt="" />
760) {this.resized= this.width=760; this.alt='Click here to open new window';}" onmouseover="if(this.width>760) {this.resized= this.width=760; this.style.cursor='hand'; this.alt='Click here to open new window';}" onclick="if(!this.resized) {} else {window.open('.cn/attachments/a/day_ba76d54e4bec0e307YTBSW0yUdB3k.jpg');}" onmousewheel="return imgzoom(this);" alt="" />... 亲，在哪买的啊？多少钱一个啊？?
[每日热点]:
财产: 77630 爱卡币
来自: 贵州省|贵阳市
[每日热点]:
财产: 77630 爱卡币
来自: 贵州省|贵阳市
正在开始接触健身
[每日热点]:
财产: 77630 爱卡币
来自: 贵州省|贵阳市
原来还有这么好玩的东西
[每日热点]:
财产: 77630 爱卡币
来自: 贵州省|贵阳市
百度不到多少内容
[每日热点]:
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