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High DOP Alert for All-in-View Users Confirmed

Posted by Jim on September 11, 2009 at 1:31pm
High DOP Alert for All-in-View Users Confirmed--------------------------------------------------------------------------------The USCG NavCen has issued a high DOP warning for tomorrow for certain locations in the U.S., Asia, and Oceania, which GPS World reported Wednesday.GPS World's Innovation editor Richard Langley explains why the warning affects all-in-view users:"The warning is based on a 'best four' satellite scenario; i.e., what the DOPs would be if we only used the best four satellites (the combination providing the lowest DOP value) of all the satellites in view at a particular location."However, most civil receivers these days track 8 or 10 or even all satellites in view. Therefore, I contacted the Coast Guard about this. After I contacted them, they did another analysis and confirmed DOP spikes for all-in-view users too. Prompted by that, I did my own analyses and found that with PRN31 out of action for the delta-V and PRN01 not yet declared healthy, only five satellites above 5° elevation angle (and almost colinear in the sky) will be visible at the stated locations and times, resulting in GDOP spikes approaching 100!"So, in this case, the warning is for all users in the affected areas, not just receivers with only four channels."NavCen originally reported that GPS may be unreliable in certain parts of the world for short periods on September 11 as a result of a routine Delta-V maneuver with satellite #52 (PRN-31), reporting that GPS users may experience a temporary degradation in GPS reception in parts of the southwest and central United States from 13:02 UTC to 13:23 UTC on September 11.The following areas in the United States may be affected:Southern NebraskaKansasOklahomaSouthwestern ArkansasEastern TexasWestern LouisianaRelated Links :USCG Nav Center Issues High Horizontal Dilution of Precision Advisory
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