GPS/MET mission data reprocessing, May - September, 1997
We are currently reprocessing all GPS/MET data
using the best techniques and software developed during
the course of the mission.
The data currently on our web page were processed using various
versions of software which were continuously being improved as our
understanding increased over the last 3 years. We are now
reprocessing all important observing periods (13 2-3 week periods)
with the same software in an effort to provide a consistant data set
suitable for detection of 1-2 year trends.
The new data will have the following enhancements:
- More general occultation numbering scheme. We have generalized
our numbering scheme to include all occultations observed using
not only high rate data but low and medium rate as well. This will allow
future ionospheric data products to share the same occultation
numbering scheme as our neutral atmospheric data.
This new scheme is based solely on the orbits of
the GPS and LEO satellites, so future changes in processing software
should not affect the occulation numbers. Unfortunately, this change
has rendered our old occulation numbers obsolete. We regret any
inconvenience this change may cause.
- More low level data. On some occasions, there were downlink
problems which resulted in noisy or corrupted level 0 data. Often
better data were subsequently downloaded, but these improved data were
generally not folded into the processing after the first level 1
products were published. The new level 1 products will contain all of
the best level 0 data available.
- New RINEX files will contain precise SNRs. Formerly, LR, MR and
HR 1 second RINEX files contained only 1 digit worth of SNR
information. New RINEX files will have an extension to the RINEX
standard, developed here at UCAR, to provide full resolution SNR data.
- Improved Orbit Determination and Excess Phase Processing.
Several improvements in our precise GPS processing software have led to
increased precision in the GPS orbit, Microlab orbit and excess phase
level 2 data products. The improvements are summarized below:
- GPS orbits consistent with IGS final orbits at the 2-3 cm 3d rms level.
- Microlab orbit overlap precision of < 10 cma 3d rms, < 0.1 mm/sec 3d rms.
- Microlab Excess Phase precision of near 0.1 mm/sec.
- Better handling of data gaps. In the past, a small gap our level 2 data
would spoil the level 3 processing. Newer processing allows the generation
of temperature profiles even in the presence of small gaps.
- More temperature files available. At all stages of processing,
small avoidable errors reduced the number of occultations which were
able to be fully processed. Much effort has been invested in plugging
these 'data leaks', resulting in a greater number of useful occultations.
Data Availability
A schedule for data availability is available and
should be updated shortly.
Due to the large volume
of data to be reprocessed, we will not make most of it (especially low level
products) available on our web site. Instead, we will be distributing
the data on Compact Disc and Exabyte (8mm) tape.
Please direct any requests for low-level reprocessed data to
Doug Hunt (dhunt@ucar.edu)