От astro-02
К Zamir Sovetov
Дата 04.04.2007 15:14:09
Рубрики Космос;

Re: ЕМНИП это...


>
>сигнал несёт в себе информацию о "загрублённых" географических районах и при наличии приёмника в предалах района координаты начинают "гулять". На Северном Кавказе такая петрушка происходила во время войны в Чечне.

Ищу источники. По-моему, байка.
От RuLavan
К astro-02 (04.04.2007 15:14:09)
Дата 04.04.2007 16:02:33

Вот такой вот источник есть

Говорят что...

Про Чечню наверняка байка, а про загрубление гражданского сигнала можно тут почитать http://www.ostp.gov/html/0053_2.html

"STATEMENT BY THE PRESIDENT REGARDING
THE UNITED STATES’ DECISION TO STOP DEGRADING
GLOBAL POSITIONING SYSTEM ACCURACY

Today, I am pleased to announce that the United States will stop the intentional degradation of the Global Positioning System (GPS) signals available to the public beginning at midnight tonight. We call this degradation feature Selective Availability (SA). This will mean that civilian users of GPS will be able to pinpoint locations up to ten times more accurately than they do now. GPS is a dual-use, satellite-based system that provides accurate location and timing data to users worldwide. My March 1996 Presidential Decision Directive included in the goals for GPS to: “encourage acceptance and integration of GPS into peaceful civil, commercial and scientific applications worldwide; and to encourage private sector investment in and use of U.S. GPS technologies and services.” To meet these goals, I committed the U.S. to discontinuing the use of SA by 2006 with an annual assessment of its continued use beginning this year.

The decision to discontinue SA is the latest measure in an on-going effort to make GPS more responsive to civil and commercial users worldwide. Last year, Vice President Gore announced our plans to modernize GPS by adding two new civilian signals to enhance the civil and commercial service. This initiative is on-track and the budget further advances modernization by incorporating some of the new features on up to 18 additional satellites that are already awaiting launch or are in production. We will continue to provide all of these capabilities to worldwide users free of charge.

My decision to discontinue SA was based upon a recommendation by the Secretary of Defense in coordination with the Departments of State, Transportation, Commerce, the Director of Central Intelligence, and other Executive Branch Departments and Agencies. They realized that worldwide transportation safety, scientific, and commercial interests could best be served by discontinuation of SA. Along with our commitment to enhance GPS for peaceful applications, my administration is committed to preserving fully the military utility of GPS. The decision to discontinue SA is coupled with our continuing efforts to upgrade the military utility of our systems that use GPS, and is supported by threat assessments which conclude that setting SA to zero at this time would have minimal impact on national security. Additionally, we have demonstrated the capability to selectively deny GPS signals on a regional basis when our national security is threatened. This regional approach to denying navigation services is consistent with the 1996 plan to discontinue the degradation of civil and commercial GPS service globally through the SA technique.

Originally developed by the Department of Defense as a military system, GPS has become a global utility. It benefits users around the world in many different applications, including air, road, marine, and rail navigation, telecommunications, emergency response, oil exploration, mining, and many more. Civilian users will realize a dramatic improvement in GPS accuracy with the discontinuation of SA. For example, emergency teams responding to a cry for help can now determine what side of the highway they must respond to, thereby saving precious minutes. This increase in accuracy will allow new GPS applications to emerge and continue to enhance the lives of people around the world."

В Вики принцип действия SA описывается так, за точность правда не ручаюсь:
http://en.wikipedia.org/wiki/GPS
"Selective availability

The GPS includes a feature called Selective Availability (SA) that introduces intentional errors between 0 meters and up to a hundred meters (300 ft) into the publicly available navigation signals, making it difficult to use for guiding long range missiles to precise targets. Additional accuracy was available in the signal, but in an encrypted form that was only available to the United States military, its allies and a few others, mostly government users.

SA typically added signal errors of up to about 10 meters (30 ft) horizontally and 30 meters (100 ft) vertically. The inaccuracy of the civilian signal was deliberately encoded so as not to change very quickly, for instance the entire eastern U.S. area might read 30 m off, but 30 m off everywhere and in the same direction. In order to improve the usefulness of GPS for civilian navigation, Differential GPS was used by many civilian GPS receivers to greatly improve accuracy.

During the Gulf War, the shortage of military GPS units and the wide availability of civilian ones among personnel resulted in a decision to disable Selective Availability. This was ironic, as SA had been introduced specifically for these situations, allowing friendly troops to use the signal for accurate navigation, while at the same time denying it to the enemy. But since SA was also denying the same accuracy to thousands of friendly troops, turning it off or setting it to an error of 0 meters (effectively the same thing) presented a clear benefit.

In the 1990s, the FAA started pressuring the military to turn off SA permanently. This would save the FAA millions of dollars every year in maintenance of their own radio navigation systems. The military resisted for most of the 1990s, but SA was eventually "discontinued"; the amount of error added was "set to zero"[11] in 2000 following an announcement by U.S. President Bill Clinton, allowing users access to an undegraded L1 signal. Per the directive, the induced error of SA was changed to add no error to the public signals (C/A code). Selective Availability is still a system capability of GPS, and error could, in theory, be reintroduced at any time. In practice, in view of the hazards and costs this would induce for US and foreign shipping, it is unlikely to be reintroduced, and various government agencies, including the FAA,[12] have stated that it is not intended to be reintroduced.

The US military has developed the ability to locally deny GPS (and other navigation services) to hostile forces in a specific area of crisis without affecting the rest of the world or its own military systems.[11]

One interesting side effect of the Selective Availability hardware is the capability to correct the frequency of the GPS Cs and Rb clocks to approximately two parts in ten to the thirteenth frequency accuracy. This represented a significant improvement over the raw accuracy of the clocks.[citation needed]"

Врут, поди, как всегда...
От kinetic
К RuLavan (04.04.2007 16:02:33)
Дата 04.04.2007 20:56:29

Re: Вот такой...

"selectively deny GPS signals on a regional basis" - вполне может означать и выключение и загрубление.
От Гегемон
К kinetic (04.04.2007 20:56:29)
Дата 05.04.2007 00:43:46

Я подобное слышал от археологов

Скажу как гуманитарий

>"selectively deny GPS signals on a regional basis" - вполне может означать и выключение и загрубление.
Использовать приемники для привязки раскопа не имело смысла из-за определения места по 3 точкам. Традиционными способами получалось лучше

С уважением