[IGSMAIL-6298] Reprocessed IGS Trop Product now available with Gradients

[Yoaz Bar-Sever]

Authors: Yoaz Bar-Sever and Sung Byun


Dear Colleagues:

We'd like to announce the availability the reprocessed IGS 
tropospheric product. The reprocessed product is based on IGS 
reprocessed orbit and clock from 1995 to 2007.

The reprocessed product, and all products going forward from 2007 now 
include estimates of the North and East delay gradients, in addition 
to the zenith path delay.

The only other change to the estimation approach was the replacement 
of the Niell mapping function with GMF. A summary of the estimation 
approach is provided below.

While retaining the naming convention of the trop product files, the 
format has been expanded slightly to accommodate the addition of 
gradients, hopefully in a transparent manner:

The "SOLUTION_FIELDS_1" line of the Header now specify the gradient 
fields. For example:

+TROP/DESCRIPTION
*KEYWORD______________________ VALUE(S)______________
  SAMPLING INTERVAL                                300
  SAMPLING TROP                                    300
  ELEVATION CUTOFF ANGLE                           7.0
  TROP MAPPING FUNCTION         GMF
  SOLUTION_FIELDS_1             TROTOT STDDEV N_GRAD STDEV E_GRAD STDEV
-TROP/DESCRIPTION


The main body of the file which contains data now looks as follows 
(eg, for ALGO site on 2010-123):

+TROP/SOLUTION
*SITE EPOCH_______ TROTOT STDEV  N_GRAD  STDEV  E_GRAD  STDEV
  ALGO 10:123:00000 2421.4   1.9  -4.634  3.733  -0.861  2.125
  ALGO 10:123:00300 2421.3   1.9  -4.614  3.692  -0.883  2.106
  ALGO 10:123:00600 2421.5   1.8  -4.541  3.617  -0.793  2.091
  ALGO 10:123:00900 2421.8   1.7  -4.490  3.539  -0.527  2.069
  ALGO 10:123:01200 2421.9   1.7  -4.508  3.456  -0.397  2.035

Note that all units are in mm. These files are available at both JPL 
and CDDIS sites.

At JPL:
ftp://sideshow.jpl.nasa.gov/pub/igs_trop/trop_zpd/repro1/yxxxx (from 
1995 to 2007)
ftp://sideshow.jpl.nasa.gov/pub/igs_trop/trop_zpd/yxxxx (from 2008 to present)

At CDDIS:
ftp://cddis.gsfc.nasa.gov/pub/gps/products/troposphere/zpd/repro1/xxxx 
(from 1995 to 2007)
ftp://cddis.gsfc.nasa.gov/pub/gps/products/troposphere/zpd/xxxx 
(from 2008 to present)

With this reprocessing we now have 15 years of consistently derived 
trop products from hundreds of sites.

Summary of estimation approach:
Fixed orbits and clocks: IGS Final Re-Analyzed Combined (1995-2007), 
and IGS Final Combined 2008-Current
Earth orientation: IGS Final Re-Analyzed Combined (1995-2007), and 
IGS Final Combined (2008-Current)
Transmit antenna phase center map: IGS Standards
Receiver antenna phase center map: IGS Standards
Elevation angle cutoff: 7 degrees
Mapping function (hydrostatic and wet): GMF
A priori delay (m): hyd = 1.013*2.27*e -0.116*ht wet = 0.1
Data arc: 24 hours
Data rate : 5 minutes
Estimated parameters: station clock (white noise), station position, wet zenith
delay (3 cm/hour random walk), delay gradients (0.3 cm/hour 
random walk), phase biases (white noise)

Contact Sung Byun <<mailto:byun at jpl.nasa.gov>byun at jpl.nasa.gov> or 
Yoaz Bar-Sever 
<<mailto:Yoaz.E.Bar-Sever at jpl.nasa.gov>Yoaz.E.Bar-Sever at jpl.nasa.gov> 
with any question
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