NTSS Navigation Class 1 21Jan2016
TERMINATION OF U.S. LORAN-C SIGNALS:
In accordance with the 2010 DHS Appropriations Act, the U.S. Coast Guard terminated the transmission of all U.S. LORAN-C signals on 08 Feb 2010. More Info
U.S. Nears eLoran Decision with Broad International Implications – GNSS Vulnerability Drives Proposal
Inside GNSS, Washington View, March/April 2015 Click Here
Notice to Mariners
Subscription request for Notice to Mariners Local Notice to Mariners
Available by district in pdf 2016 LIGHT LIST VOLUMES
U. S. Chart No. 1
Symbols, Abbreviations and Terms used on Paper and Electronic Navigational Charts (pdf) Chart 1
NOAA Charts for U.S.Waters
Warning: This chart display or derived product can be used as a planning or analysis tool and may not be used as a navigational aid.
NOTE: Use the official, full scale NOAA nautical chart for real navigation whenever possible. Screen captures of the on-line viewable charts available here do NOT fulfill chart carriage requirements for regulated commercial vessels under Titles 33 and 46 of the Code of Federal Regulations.
How does a GPS receiver know what time it is?
A more basic question is, "How does the gps know the travel time so that it can compute the distance?" The satellite sends the current time along with the message so the gps can subtract its knowledge of the current time from the satellite time in the message (which is the time that the signal started its descent) and use this to compute the difference. For this to work the time in your gps must be pretty accurate – to a precision of well under a microsecond. The satellite itself has an atomic clock to keep the time very precisely, but your unit is probably not big enough nor expensive enough to have an atomic clock built in, so your clock is likely to be in error! For this reason our assumptions about the distance calculation are likely to have considerable error and the fourth satellite fix will reveal this to us. However, if we assume the error is caused by an error in our clock then we can adjust our clock a little and recompute all 4 fixes, continuing to do this iteratively until the error disappears! We will then have a good position fix and as a side effect we will also have the correct time to about 200 nanoseconds or so. One of the applications of gps technology is to provide the correct time even when we don't care about our position.