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Charlie Martin

A detailed timeline of AVAPS.I GPS upgrades from 2007 to 2009, including challenges faced, fixes implemented, and successful flight tests. Lessons learned and key events highlighted.

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Charlie Martin

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  1. AVAPS I: GPS Charlie Martin AVAPS Users MeetingApril 28-29 2009Boulder, Colorado

  2. Timeline Early 2007 July 2007 Jan 2008 April 2008 Sept 2008 Dec 2008 Feb 2009 Aug 2008 April 2009 • Early 2007: • July 2007: • January 2008: • April 2008: • Aug – Sept 2008: • December 2008: • February 2009: • April 2009: • Vaisala informs NCAR GPS module (TIM-LF) will be discontinued in July 2007. • NCAR test drops 4 AVAPS I sondes with the new TIM-4P. No major problems found. • TIM-LF module discontinued • Vaisala Starts production of sondes with TIM-4P module • AVAPS User Conference • T-PARC field project begins to use new sondes with the new TIM-4P module. Could not get good wind data on the newer TIM-4P sondes. • A possible fix is found. Vaisala is instructed to modify 50 AVAPS I rev F sondes and send to NCAR for tests. Once tested, sondes were given to the 53rd to flight test. • Altered TIM-4P based sondes are flown with a very high success rate. • AVAPS User Conference

  3. AVAPS I / uBlox Physical Configs Trimble, P/N 57589 Trimble, P/N 66801 Wi-Sys

  4. AVAPS I GPS Upgrade Steps • NCAR, Vaisala, and NOAA work towards are replacement for the TIM-LF: • December 15th, 2006: uBlox sends out a letter giving a timeline for obsoletion of several production modules. The TIM-LF GPS modules used in AVAPS is affected. • July 12th, 2007: NCAR flight tests four TIM-4P and four TIM-LF based sondes for comparison. The test results are very positive. • July 30th, 2007: The uBlox TIM-LF goes obsolete. • January. 2008: Vaisala begins production of the TIM-4P based sondes.

  5. AVAPS I GPS Upgrade Steps Data Courtesy of June Wang

  6. AVAPS I GPS Upgrade Steps • August to September 2008: NCAR deployed to Guam for T-PARC • Errol finds there are multiple problems with the TIM-4P based sondes: • Winds data is erroneous on many “Good” drops • Extremely long lock up times in the air. • Errol and Laura spent many hours in Guam looking for a fix. Ultimately for a lack of working sondes, they started using TIM-LF based sondes borrowed from the AF 53rd. • After some analysis in Boulder, it was found the GPS configuration was not properly applied. Effectively the TIM-4P’s navigation mode was left as “Auto” instead of “Airborne <2g”. • A fix was applied, but did not solved all problems.

  7. AVAPS I GPS Upgrade Steps • October 2008: NOAA and the AF 53rd contact NCAR with problems about • very long acquire times. • NOAA found sondes in the hanger cannot acquire lock • AF 53rd was having nearly identical problems on the C130’s • November 2008:NCAR traveled to Keesler AFB in Biloxi to further troubleshoot. • NCAR modified and tested a variety of sonde and sonde components in an attempt to isolate the failure point during testing at Keesler. • NCAR replicated the failures the AF 53rd and NOAA experienced, and were able to duplicate them in Boulder.

  8. AVAPS I GPS Upgrade Steps • December 2008: NCAR discovered reradiated GPS signals are deceiving • Proven problematic sondes work well in reradiated areas, but fail when exposes to a true constellation (outside). • Once a systematic roof-top test was constructed, the problem was isolated to RF interference at the GPS antenna. • Once the GPS antenna was exchanged from a Wi-Sys to a Trimble, P/N 57589, nearly all GPS lockup problems evaporated. • January 2009: • 50 Sondes were retrofitted by Vaisala with the new GPS antenna • Sondes were then fully tested with the new methods at NCAR • February 2009: • 50 Sondes were flight tested by the 53rd with a very high success rate

  9. Final Results: Data Courtesy of June Wang

  10. Lessons Learned • Re-radiated GPS signals can mask RF interference problems. • Make sure to fully field test all changes to qualify • Make sure all involved parties are fully aware and on board with changes

  11. Questions or Thoughts?

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