Changing of the guard in the skies

Those who watch television weathercasts on the West Coast of the U.S., or in Alaska or Hawaii, or anywhere else around the central and eastern Pacific Ocean, may not have noticed any difference in the presentation between Dec. 5 and 6 of this year, but there was a significant change. The weather satellite known as GOES-11 was removed from regular service during this time while a newer satellite known as GOES-15 began its service. That this transition was virtually unnoticed by most users of the images generated by these satellites speaks volumes about how reliable these spacecraft have been, and also about how observation of the weather from space has become so routine as to be taken for granted by many.

The acronym GOES stands for Geostationary Operational Environmental Satellite. As their name implies, these spacecraft occupy a geostationary orbit around the Earth, which means that they orbit the Earth at the same rate at which the Earth rotates. Therefore, they remain in the same position over the Earth. In order to achieve this orbit, these satellites must fly at an altitude of about 23,500 miles. For comparison, the space shuttle flies in an orbit a couple of hundred miles above the Earth’s surface.

The extreme altitude has a couple of consequences. It means that the satellites can “see” an entire hemisphere of the Earth at one time, which is a benefit for meteorologists. However, it also means that there really is no way for a spacecraft like the space shuttle to go up and repair these satellites should a problem arise. Basically they are on their own, and other than some adjustments which can be remotely executed from ground-based controllers, the spacecraft need to be engineered so they will last through their expected lifetime. In the case of GOES-11, it was launched in May of 2000 with an expected lifetime of five years. It has performed for more than eleven years, exceeding twice its life expectancy.

The new satellite was launched in March of 2010, and has been parked in orbit since then, allowing for its systems to be tested and adjusted. It has now been moved into position over the equator in the middle of the Pacific and since Dec. 6 has been providing regular data and images for use by meteorologists and the public.

As noted above, the availability of satellite observations of the atmosphere has become so ingrained in our lives that it is difficult to remember that not long ago, these observations were not as regularly available, not as comprehensive, and not as reliable. While it is very nice for television viewers to be able to see the movie loops made possible by these satellites, it is really over the oceans that the impact of regular, reliable satellite observations has had the most profound impact. Because there are so few actual observations available over the vast ocean areas of the planet, prior to the satellite age, it was not uncommon for certain atmospheric systems to be undetected until they were noticed by a land or island-based weather station. This significantly reduced the ability of meteorologists to be able to accurately forecast winds and seas over the oceans, and, in turn made ocean voyaging much more hazardous than it is today, both for recreational vessels and commercial vessels. With the availability of satellite information, meteorologists have been able to better understand weather systems over the oceans, and forecast skills have improved significantly.

The newer GOES-15 satellite has significant improvements over its predecessor in terms of meteorological image resolution and quality, and in the amount of data it is able to observe and transmit. This will likely translate into further improvements in forecast accuracy in the coming years. Looking ahead, the next generation of GOES satellites is already being developed, and the first launch is scheduled for 2015. This will certainly mean an even further improvement in observation of the atmosphere from space.

While the pictures that we all see on television are very pleasing to the eye, it is important to remember that these satellites are able to observe much more meteorological data than just these pictures. The GOES satellites are also platforms for instrumentation that is critical for search and rescue operations, adding another dimension to their utility. In many ways, the reliability of the GOES satellites has had more impact on the safety of ocean voyaging than any other single technological advance.

Here are a few links of interest:
The first image from the new GOES-15 satellite taken at 1545 GMT 6-Dec-2011:

The last “full disc” daylight (visible spectrum) image from the retired GOES-11 satellite taken at 2100 GMT 5-Dec-2011

By Ocean Navigator