NTSS Navigation Class
1 21Jan2016
Notes
Loran
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
Light List
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
Map-Based Chart Locator By
Region
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.
Miscellaneous Thoughts:
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.