[IGSSTATION-5385] some receivers misreporting satellite health bits

[Jake Griffiths - NOAA Federal]

Author: Analysis Center Coordinator

Dear Colleagues,

A scan of the GPS navigation RINEX files at NASA/CDDIS for April 23, 2013
(yyyy=2013 doy=113) highlights an ongoing issue with several receiver types
reporting incorrect health bits for PRN30/SVN35. According to NANU 2013022
(e.g., http://www.navcen.uscg.gov/?Do=gpsShowNanu&num=2013022), this satellite
was set unusable until further notice (UNUSUFN) on March 28, 2013.

The following receiver types:

   AOA BENCHMARK ACT
   ASHTECH UZ-12
   LEICA CRS1000
   LEICA GRX1200
   LEICA GRX1200GGPRO
   LEICA GRX1200PRO
   TPS E_GGD
   TRIMBLE 4000SSE
   TRIMBLE 4700
   TRIMBLE 5700
   TRIMBLE NETR5
   TRIMBLE NETRS

at the following IGS stations:

alic barh brft brmu bzrg cagl cas1 cedu chum coco conz darw dav1 drao hert hnpt
hob2 holb joz2 joze karr lck2 lcki mate maw1 mobs morp nano nico ohi3 pbr2 pbri
pdel pert pgc5 rcmn sfer str1 str2 tid1 tow2 wes2 wtzr xmis yar3 yebe

however continue to report PRN30/SVN35 as "healthy".

The main reason to report this is that the navigation files from IGS stations
are assembled to form the global broadcast file (brdc${ddd}0.${yy}n) at the
Data Centers. Having some stations misreport the health status causes confusion
when a user attempts to examine the health bits for the entire constellation
over an extended period of time. The following table is a nice example:

Summary for the Health Bits for all PRNs ('.'=healthy; '1'=unhealthy)
-------------------------------------------------------------------------
wwwwd hh  0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3
           1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
-------------------------------------------------------------------------
17372 00  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . 1 . .
17372 02  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . 1 . .
17372 04  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . 1 . .
17372 06  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . . .
17372 08  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . . .
17372 10  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . . .
17372 12  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . . .
17372 14  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . . .
17372 16  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . . .
17372 18  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . 1 . .
17372 20  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . 1 . .
17372 22  . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . 1 . .
-------------------------------------------------------------------------
wwwwd hh  0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3
           1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
-------------------------------------------------------------------------

Incorrect health bits can also cause issues for software that resamples and
transforms the broadcast ephemerides into ECEF coordinates.

I suspect the issue arises from a firmware bug or that the receivers need their
memory flushed. Though, of course, any mitigating action should be taken so as
to minimize the impacts to users.

FYI,
jake

-- 
Jake Griffiths, Ph.D.
Geodesy & Geomechanics
IGS Analysis Coordinator
Chief, CORS Branch
NOAA National Geodetic Survey
1315 East-West Highway, N/NGS22
Silver Spring, MD 20910 USA

p: (301) 713-3205  ext.153
f: (301) 713-4324
e: jake.griffiths at noaa.gov