"NARROW-LANE" COMBINATION |
The L6 or "narrow-lane" observable is obtained by adding the two
phase equations (L1+L2) expressed in cycles:
 |
(6.4-18) |
The effective wavelength of this observable is very small: 
0.10
metres. The n6 ambiguity is n1 + n2, and
is therefore still an integer.
In metric units, upon multiplying eqn (6.4-18) by the wavelength 
6:
 |
(6.4-19a) |
or in terms of the L1 ionospheric delay (using eqn (6.4-2)):
 |
(6.4-19b) |
The L6 ionospheric effect is approximately 1.28 times that on L1 (1.28
f1 / f2). However the noise on the L6 observables
is very small (Table in section 6.4.6).
Another expression for the L3 ionosphere-free observable is to sum eqns (6.4-17) and (6.4-19) and divide by two:
 |
(6.4-20a) |
Similarly, an expression for the P3 ionosphere-free combination is:
 |
(6.4-20b) |
In the case of pseudo-range observations the equivalent narrow-lane expression is:
 |
(6.4-21) |
(Hint: convert eqns (6.4-10)
to cycles, sum the expressions and then scale them back to metric units
using 6). The narrow-lane pseudo-range is therefore delayed
by the ionosphere (range too long), while the narrow-lane phase is advanced
by the ionosphere (phase-range too short). This is the opposite to what
happens with the wide-lane observables.
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© Chris Rizos, SNAP-UNSW, 1999