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<H1>Sat-nav devices face big errors as solar activity rises </H1>
<P><FONT face=Tahoma>Researchers say the Sun is awakening after a period of low
activity, which does not bode well for a world ever more dependent on satellite
navigation, the BBC News website reports.</FONT></P>
<P><FONT face=Tahoma color=#ff0000>The Sun's irregular activity can wreak havoc
with the weak sat-nav signals we use. </FONT></P>
<P><FONT face=Tahoma><FONT color=#ff0000>The last time the Sun reached a peak in
activity, satellite navigation was barely a consumer product. </FONT></FONT></P>
<P><FONT face=Tahoma><FONT color=#ff0000>But the Sun is on its way to another
solar maximum, which could generate large and unpredictable sat-nav errors.
</FONT></FONT></P><!-- E SF -->
<P><FONT face=Tahoma><FONT color=#ff0000>It is not just car sat-nav devices that
make use of the satellite signals; accurate and dependable sat-nav signals have,
since the last solar maximum, quietly become a necessity for modern
infrastructure</FONT>.<STRONG> </STRONG></FONT></P>
<P><FONT face=Tahoma color=#ff0000>Military operations worldwide depend on them,
although they use far more sophisticated equipment. </FONT></P>
<P><FONT face=Tahoma color=#ff0000>Sat-nav devices now form a key part of
emergency vehicles' arsenals. They are used for high-precision surveying,
docking ships and plans are even underway to incorporate them into commercial
aircraft. </FONT></P>
<P><FONT face=Tahoma><FONT color=#ff0000>Closer to home, more and more trains
depend on a firm location fix before their doors will open.</FONT> </FONT></P>
<P><B><FONT face=Tahoma>Simple geometry</FONT></B></P>
<P><FONT face=Tahoma>The satellite navigation concept is embodied currently by
the US GPS system and Russia's Glonass network, with contenders to come in the
form of Europe's Galileo constellation and China's Compass system. </FONT></P>
<P><FONT face=Tahoma>It depends on what is - at its root - a simple
triangulation calculation. </FONT></P>
<P><FONT face=Tahoma>A fleet of satellites circling the Earth are constantly
beaming a radio signal with two bits of exceptionally precise information: where
exactly they are, and at exactly what time. </FONT></P>
<P><FONT face=Tahoma>A sat-nav receiver on Earth - or on a ship or plane - is
equipped with a fairly precise clock and the means to collect signals from the
satellites that happen to be in its line of sight. </FONT></P>
<P><FONT face=Tahoma>It then works out, based on how long it took those signals
to arrive, how far it is from each of those satellites. Some simple geometry
yields its position.</FONT></P>
<P><FONT face=Tahoma>Read the full BBC News article - </FONT><EM><BR><FONT
face=Tahoma>Sat-nav devices face big errors as solar activity
rises<BR></FONT></EM><A href="http://news.bbc.co.uk/1/hi/sci/tech/8494225.stm"
target=_blank><FONT
face=Tahoma>http://news.bbc.co.uk/1/hi/sci/tech/8494225.stm</FONT></A></P>
<P><FONT face=Tahoma></FONT> </P>
<P><FONT face=Tahoma>Our thanks to <STRONG>Lee, M0HOK</STRONG> for spotting this
item.</FONT></P></DIV></BODY></HTML>