[teqc] teqc mp_CA_AS[%rms]

[Lou Estey]

maybe a stupid question, but what exactly does the -mp_CA_AS[%rms]
switch do?

Best regards
Markus

--------

Dear Markus,

This is, in fact, a good question, especially with L2C and other
signal changes looming.  The -mp_CA_AS[%rms] goes back to some
parameter on the original UNAVCO "QC" Fortran code -- though whether
it was tunable by the user or whether it was hardwired into the
code I don't remember.  The idea was account for noisier data under
certain conditions.  My recollection (without diving into all the teqc
code to verify this) is that during the multipath calculation, if
the coarse acquisition code pseudorange (C1) being used for MP1
(rather than the precise code pseudorange P1) or if antispoofing
was on, then the detection threshold for a multipath slip event
being registered was increased from the default by the given percentage.
(The signal strength of C/A code should be higher than the signal
strength of P1 code, so the decision to bump up the detection
threshold on C1 was based on other criterion.) As you know the
default for this parameter is 100%, so the rms detection is increased
by a factor of two over the defaults of (`teqc +help | grep rms`):

-mp1_rms[cm] #           set expected MP1 rms to # cm (default = 50.00)
-mp2_rms[cm] #           set expected MP2 rms to # cm (default = 65.00)

So if C/A pseudorange (C1) or A/S on, the detection thresholds should
be bumped up to 100 cm and 130 cm for MP1 and MP2 rms, respectively.
This, for example, is how it shows up in the teqc code:

return((double)(teq.udv.mp_sigmas * (1. + teq.udv.mp_CA_AS_rms) * teq.udv.mp_expected_rms[1]));

where teq.udv.mp_CA_AS_rms would have a value of 1 (= 100%) by default.

Chris Rocken, Jim Johnson, John Braun, Teresa vanHove, Chuck Meertens
and possibly others involved with the original development of the
UNAVCO QC algorithm -- from which the qc portion of teqc evolved --
might have more to say on the subject.  And maybe with L2C and
other new signals not too far off in the future, it's a good time
to revisit this topic.

cheers,
--lou