GOES 11 to 15 Transition-FAQ
1. What is happening?
The United States normally operates two environmental satellites positioned over the equator in geostationary orbit, called Geostationary Operational Environmental Satellites (GOES). Each satellite views almost a third of the Earth's surface. GOES-13 (or GOES-East) is positioned at 75 degrees West longitude, and monitors North and South America and most of the Atlantic Ocean. GOES-11 (or GOES-West) was positioned at 135 degrees West longitude, and monitored North America and the Pacific Ocean basin. Together they provided weather observations that covered over 50 percent of the Earth's surface. GOES-15, the National Oceanic and Atmospheric Administration’s (NOAA’s) newest geostationary satellite, replaced GOES-11 as the operational GOES-West satellite on December 6, 2011.
Following launch on March 4, 2010, GOES-15 was positioned in geostationary orbit at a longitude of 89.5 degrees West for testing as a backup spacecraft in standby mode. It is the third and the final satellite in the three current-generation GOES-N series spacecraft. Known as GOES-P before March 16, 2010, GOES-15 forms part of the U.S. NOAA GOES system. The GOES series is developed by a joint NASA-NOAA-Industry partnership, launched by NASA (with industry partners) and operated by NOAA. GOES are not only used for weather applications for the Nation, but also for space weather, oceanography, hazards, data collection, and search and rescue applications.
GOES Flyout Chart [view larger]
2. Why change satellites?
The GOES-11 satellite was nearly out of fuel, which is used to help point the satellite towards Earth. By the time GOES-11 became operational in 2006, it had six years of on-orbit storage. Even though there was at least 10 years worth of station-keeping fuel on board, GOES-11 was kept in cold on-orbit storage during 2000-2006, and it was revived at least once per year for orbit adjustment. In addition, the same amount of fuel must be used to maintain orbit inclination over the equator during this on-orbit storage. Lastly, radiation damage and other simple aging effects are unavoidable, so the risk of instrument performance degradation increases the longer the satellite remains in space.
3. Does this bring any benefits to users?
The GOES-15 switch was needed for the Western Sentinel mission continuity. In addition, the many users of the Western GOES will see improvements with finer spatial resolution (8 to 4 km in the 'Water Vapor' band of the imager), refined radiometerics (better signal-to-noise ratio), stable image navigation and registration (due to the spacecraft bus), and more images (due to a new schedule and fewer eclipse outages). GOES-15 captures higher resolution images of weather patterns and atmospheric measurements than those provided by earlier satellites. The higher resolution images allow forecasters to pinpoint the location of severe weather with greater accuracy.
The operationally significant differences between GOES-11 and GOES-15 are:
- Improved Visible Imagery;
- Higher Resolution Water Vapor Imagery;
- New 13.3 µm Infrared (IR) “CO2” Channel 6;
- All IR channels with 4km resolution and improved calibration;
- Improved Pixel Geolocation;
- Minimized Spring/Fall Eclipse Outages;
- Augmented Scanning Schedule;
- GVAR format changed to support 4km band 6
The GOES Imager is used for a host of applications, ranging from meteorological and climate to oceanographic and hazards. The Sounder is used to estimate temperature and moisture profiles in the atmosphere. It can also derive information on clouds and certain trace gases such as upper-level ozone.
Subsequently, there are new additional scan frames for the West Routine (WRTN) and West Rapid (WRAP) GOES-15 schedules. The new additional frames are the same domain as the current sub-conus taken during the GOES-11 Rapid schedule. In addition, there is a gain of four Super Rapid (SRSO) sectors per hour for non-full disk hours and three per hour for Full Disk hours in the super rapid schedule. Adjusting the frame start times allows better optimization of all GOES West schedules, ensuring better trouble shooting when operational problems arise. There will be NO NEW FRAMES added; only adding repeats of the current SRSO sector.
According to scientists at NOAA's Cooperative Institute for Meteorological Satellite Studies(CIMSS) at The University of Wisconsin- Madison (UW), the GOES-15 imager visible channel is a narrower channel that is centered at 0.63 µm (compared to the broader 0.65 µm visible channel on GOES-11) and as such the visible imagery may appear a bit "darker" in clear-regions, in comparison (because the 0.63 µm channel sees less of the "brighter" portion of the grass/vegetation spectrum). In addition, the narrower 6.7 µm water vapor channel on GOES-11 imager will be replaced by a much broader 6.5 µm water vapor channel on GOES-15. In clear skies, the weighting function of the GOES-15 imager water vapor channel will peak lower in the troposphere, so in general the water vapor brightness temperatures will be a few degrees warmer (from features slightly lower in the atmosphere) compared to GOES-11.
Lastly, ground equipment may require adjustments to the satellite ID, but the transition timeline and plans are intended to minimize disruptions to users who acquire the GOES-15 GVAR signal via an antenna.
4. How does the transition work?
On August 22, 2011, GOES-15 began executing GOES-West frames to accommodate advanced user testing of GOES-15 data. On October 18, 2011 at 0321 UTC,GOES-15 began a westward drift from 89.5 degrees West to 135 degrees West at a rate ~ 0.78 degrees/day.
On December 6, 2011, moving from 1550 UTC to 1600 UTC and approaching 129 degrees West, GOES-15 replaced GOES-11 as the GOES-West operational spacecraft, and GOES-15 GOES Variable (GVAR) data began flowing through GOES-11 communication links, thus, GOES-15 data became operational but is received through the GOES-11 downlink. In other words, the data in GVAR are relayed through GOES-11. Users pointing to GOES-11 started receiving GOES-15 data. Ancillary communication services (Data Collection System/Low Rate Information Transmission/Emergency Managers Weather Information Network/Search And Rescue) will remain on GOES-11. Users did not re-point antennae. At this point GOES-15 data are considered operational, but had significant problems occurred, GOES-11 data could have been reestablished quickly.
On December 14-16, 2011, GOES-15 GVAR flowed directly through GOES-15 communication links and GOES-11was decommissioned. Intricate steps are necessary to provide a continuous flow of data, with minimal impact to users. There was no need to readjust antenna.
Finally, on December 14, 2011 at 0130 UTC the GOES-15 drift stop maneuver was performed. The GOES-11 signal was turned off and GOES-15 data are acquired directly from GOES-15. GOES-15 GVAR data was relayed through GOES-15. Ancillary communication services (DCS/LRIT/EMWIN/SAR) switched from GOES-11 to GOES-15.
Pending successful arrival of GOES-15 at 135 degrees West, GOES-11 performed de-orbit maneuver #1 on December 16, 2011 at 0230 UTC. At 1430 UTC, on the same day, GOES-11 performed de-orbit maneuver #2 and final decommissioning.
GOES-11did not re-enter Earth's atmosphere. It was “retired” from service through a final burn from its booster, which moved it approximately 300 km above its current geostationary orbit where it will not interfere with other satellites.
For more information, please visit the following websites:
http://www.ospo.noaa.gov/Operations/GOES/schedules.html for GOES schedule information;
http://www.oso.noaa.gov/goesstatus/ for GOES status;
http://rsd.gsfc.nasa.gov/goes/text/databook/databook.pdf for GOES-L (11) data book;
http://www.osd.noaa.gov/GOES/GOES-P_Databook.pdf for GOES-P (15) data book;
http://www.noaasis.noaa.gov/cemscs/gostbus.txt for the location of GOES-15 (WMO header TBUS10 KWBC);
http://www.osd.noaa.gov/GVAR_Downloads/gvar_downloads.html and http://www.oso.noaa.gov/goes/goes-calibration/ for GVAR information;
http://www.class.ncdc.noaa.gov/saa/products/welcome for Comprehensive Large Array-Data Stewardship System (CLASS);
and http://rammb.cira.colostate.edu/projects/goes-p/GOES-15_Technical_Report_draft_2011-11.pdf for NOAA GOES-15 Science Test;
http://cimss.ssec.wisc.edu/goes/blog/archives/category/goes-15 for CIMSS Satellite Blog;
Select satellite image animations can be found at:
Improved spatial resolution of the imager water vapor band (better see jet streaks, atmospheric flow):
Improved navigation (knowing where you are looking):
Improved visible imagery:
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