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

2. Timeline Early 2007 Early 2007: July 2007: January 2008: April 2008: Aug – Sept 2008: December 2008: February 2009: April 2009: July 2007 April 2008 April 2009 Aug 2008 Sept 2008 Feb 2009 Dec 2008 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 53 rd to flight test. Altered TIM-4P based sondes are flown with a very high success rate. AVAPS User Conference Jan 2008

3. AVAPS I / uBlox Physical Configs Sonde TypeuBlox ModuleGPS AntennaDates Produced AVAPS I, rev FTIM-LFWI-SYSUp to Jan 2008 AVAPS I, rev FTIM-4PWI-SYSJan - Oct 2008 AVAPS I, rev FTIM-4PTrimble, P/N 57589Dec 2008 and on AVAPS II, rev -TIM-5HTrimble, P/N 66801-- Trimble, P/N 66801 Trimble, P/N 57589 Wi-Sys

4. AVAPS I GPS Upgrade Steps Sondes AffecteduBlox ModuleGPS AntennaDates Produced AVAPS I, rev FTIM-LFWI-SYSUp to Jan 2008 NCAR, Vaisala, and NOAA work towards are replacement for the TIM-LF: December 15 th, 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 12 th, 2007: NCAR flight tests four TIM-4P and four TIM-LF based sondes for comparison. The test results are very positive. July 30 th, 2007: The uBlox TIM-LF goes obsolete. January. 2008: Vaisala begins production of the TIM-4P based sondes. NCAR, Vaisala, and NOAA work towards are replacement for the TIM-LF: December 15 th, 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 12 th, 2007: NCAR flight tests four TIM-4P and four TIM-LF based sondes for comparison. The test results are very positive. July 30 th, 2007: The uBlox TIM-LF goes obsolete. January. 2008: Vaisala begins production of the TIM-4P based sondes.

5. AVAPS I GPS Upgrade Steps Sondes AffecteduBlox ModuleGPS AntennaDates Produced AVAPS I, rev FTIM-4PWI-SYSJan - Oct 2008 Data Courtesy of June Wang

6. AVAPS I GPS Upgrade Steps Sondes AffecteduBlox ModuleGPS AntennaDates Produced AVAPS I, rev FTIM-4PWI-SYSJan - Oct 2008 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 53 rd. 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. 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 53 rd. 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 Sondes AffecteduBlox ModuleGPS AntennaDates Produced AVAPS I, rev FTIM-4PWI-SYSDec 2008 and on October 2008: NOAA and the AF 53 rd contact NCAR with problems about very long acquire times. NOAA found sondes in the hanger cannot acquire lock AF 53 rd 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 53 rd and NOAA experienced, and were able to duplicate them in Boulder. October 2008: NOAA and the AF 53 rd contact NCAR with problems about very long acquire times. NOAA found sondes in the hanger cannot acquire lock AF 53 rd 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 53 rd and NOAA experienced, and were able to duplicate them in Boulder.

8. AVAPS I GPS Upgrade Steps Sondes AffecteduBlox ModuleGPS AntennaDates Produced AVAPS I, rev FTIM-4PWI-SYSDec 2008 and on 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 53 rd with a very high success rate 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 53 rd with a very high success rate

9. Final Results: Sondes AffecteduBlox ModuleGPS AntennaDates Produced AVAPS I, rev FTIM-4PTrimble, P/N 57589Dec 2008 and on Configuration AVAPS I, rev F TIM-4P Trimble P/N 57589 AVAPS I, rev F TIM-4P Wi-SYS Data Source50 drops by 53 rd T-PARC Number Dropped4512 Good Drops436 % Good95.56%50.00% Drop Problems 1 Fast Fall 1 No GPS lock 1 Erroneous GPS (very odd) 1 No GPS lock 3 Only Tracked 6 SVs and never changed 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?