[teqc] dumb clock questions

Jeff Freymueller jfreymue at gi.alaska.edu
Tue Aug 30 11:44:28 MDT 2005


Lou,

Sorry if I was not clear. The jumps truly are 1 millisecond. The 
*estimate* of the jump that you get by differencing the epochs after 
and before are in general not 1 millisecond because of the factors that 
I mentioned. Clockprep has to apply a tolerance to determine whether 
the estimate of a jump is close enough to 1 millisecond to count as a 
detected jump, or if it might represent something else (for example, in 
the phase it could be a cycle slip on one satellite that was not 
flagged by the receiver).

Jeff

On Aug 29, 2005, at 6:59 PM, Lou Estey wrote:

> Jeff Freymueller wrote:
>
>> Geoff's explanation (below) is basically correct. When clockprep 
>> finds an offset in the observables, it is almost never exactly 1 
>> millisecond because of the (physical) change in range between epochs. 
>> In the case of this file, there will also be a component from the 
>> clock drift rate, as it appears that this file (from the clockprep 
>> output Andrew forwarded earlier) has 1 millisecond offsets about 
>> every 50 epochs, or about 5 times an hour. That is a very high rate 
>> of clock drift, but I have seen higher rates before. In this case, 
>> the clock's drift rate is ~0.02 milliseconds per epoch (~6 km), so I 
>> suspect that this effect dominates because clockprep calculates the 
>> offset by averaging across all the satellites, and some satellites 
>> will have range getting larger, others getting smaller so the average 
>> is usually closer to zero than the range change in any one satellite.
>
> That being the case, doing a normal clockprep on a RINEX with ms-jumpy 
> time
> tags and smooth phase and pseudorange is _not_ the same as doing a new 
> `teqc +smtt`
> translation of the data which results in RINEX with smooth time tags 
> and ms-jumpy phase
> and pseudoranges.  `teqc +smtt` applies just an exact ms jump.

Dr. Jeffrey T. Freymueller         Office: 907-474-7286
Geophysical Institute              Fax:    907-474-7290
University of Alaska, Fairbanks    Home:   907-479-3550
PO Box 757320                      Cell:   907-322-7632
Fairbanks, AK 99775-7320           email: jeff at giseis.alaska.edu
URL: http://www.gps.alaska.edu/jeff/jeff.html

Download Alaska GPS data: ftp://gps.alaska.edu/pub/gpsdata/
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