# Presentation: 449480

## Ocean Surface Topography Science Team Meeting
Venice, Italy:  March 16 - 18, 2006

John Lillibridge
NOAA Laboratory for Satellite Altimetry

Gregg Jacobs & Kirk Whitmer
Naval Research Laboratory - Stennis Space Center

*Venice, Italy:  March 16 - 18, 2006*
- John Lillibridge
*NOAA Laboratory for Satellite Altimetry*
- Gregg Jacobs & Kirk Whitmer
*Naval Research Laboratory - Stennis Space Center*

- Geosat Follow-On Mission & Status

## GFO Spacecraft & Sensors

- Ku-band Altimeter
- Dual-ƒ Radiometer
- 4 GPS Receivers
- Doppler Beacon
- Laser Retro-reflector
- Fixed Solar Array
- Solid State Memory

## Navy GFO Ground Segment

## A Brief History

- Launch: 10-Feb-1998 from Vandenberg AFB
- 8-year nominal lifetime, celebrated 8th anniversary in 2006
- Initial hardware difficulties
- Onboard CPU resets during first two years
- GPS receivers failed in spite of 4-unit redundancy
- Loss of primary orbit determination system
- Loss of precision time-tagging
- Ground-based time-tag unit at NAVSOC: June, 1999
- Precision orbit determination based on SLR tracking
- CPU reset problems solved: November, 1999
- Navy acceptance: November 29, 2000
- Momentum wheel anomalies - temperature sensitivity

## Altimetry Data Return

## Interagency Participation

- U.S. Navy
- SPAWAR
- Program management
- Navy Cal/Val team
- NAVSOC
- Satellite Command/Control
- Data Telemetry
- Operational Doppler orbits
- NAVO/NRL - Stennis
- Payload Operations Center - ADFC
- Near real-time altimetry -> GODAE
- Military data requests

- NASA
- Wallops Flight Facility
- Instrument performance monitoring & Cal/Val
- Goddard Space Flight Center
- Precise Orbit Determination from laser ranging
- Ice-sheet monitoring via altimeter waveforms
- NOAA
- Final Science-quality GDRs
- Near real-time IGDRs
- Civilian Data Requests (Foreign & National)
- Funding OSU Cal/Val team & GSFC Orbits
- Funded CLS for sea-state bias model

## European Partners

- CNES - Corsica absolute calibration
- CLS - Real-time “DUACS” system
- Validation of all corrections
- Editing thresholds and engineering flags
- Sea surface height, SWH, Wind & Attitude
- S.O.S. (U.K.) - SWH/Wind Buoy validation

## Near Real-Time AVISO Processing - GFO

- Courtesy:
- M-H. de Launay
- CLS

## Near Real-Time Navy ADFC Processing

## GFO Precise Orbit Statistics

## GFO & T/P Sea Surface Height

- SSH-MSS residuals: 11 cm for GFO; 10 cm for T/P
- Geocenter offsets applied (B. Beckley/GSFC)

## Improved Mesoscale Sampling

- Pascual, A., Y. Fauge`re, G. Larnicol, and P.-Y. Le Traon (2006),
- Improved description of the ocean mesoscale variability by combining four satellite altimeters, Geophys. Res. Lett., 33, 2006.

## East Australia Current Analysis - CSIRO

- Courtesy:
- D. Griffin -CSIRO

## GFO contributes to GSLR records

## Hurricane Katrina & Altimetry

- Scharroo, Smith and Lillibridge, EOS, 86(40), 2005

## GFO Waveform Data Collection

## NOAA Lab. for Satellite Altimetry GFO Site

## Navy/NRL Data Access

## U.S. GODAE Server - NAVO Products

## AVISO/DUACS GFO Products

## Continuing GFO Operations

- GFO has reached its nominal 8-year lifetime
- Navy, NOAA, & NASA will continue operations as long as possible
- Two significant hardware issues to face:
- Thermal sensitivity of reaction wheels
- Wheel #1 taken offline: may still be viable, but requires further study
- Wheel #3 sensitive to overheating
- Reduced operations when orbit in “full-sun” orientation
- Battery aging effects
- Will reach manufacturer’s spec. on charge/discharge cycles this year
- During orbital eclipse voltages approach undervoltage limit
- Direct Downlink mode has been terminated (transmitter off)
- Implement ‘one-failed-cell’ battery mode to lower UV limits
- Place altimeter in standby for portion of eclipse (each rev...)
- Power off Water Vapor Radiometer for extended periods of time