• Stephen Strum

New NOAA Satellite to Improve Weather Predictions

Updated: Jan 31


NOAA's newest weather satellite, GOES 17, is officially operational after months of testing, configuration, and testing. Shortly after the spacecraft launched on March 1, 2018, a problem was discovered with the satellites ABI sensor, which if not corrected would have significantly hobbled the satellite's ability to observe specific data channels. However, engineers have been able to fix and work around nearly all the technical issues with the sensor, and so the satellite is now operating at almost 100%.

Weather satellites don't just take images like your cellphone camera but take data at multiple different wavelengths that allow various aspects of the atmosphere to be analyzed. Visible wavelengths reveal clouds during the daytime, while infrared wavelengths enable cloud detection at night. By observing other wavelengths, GOES 17 can detect aerosols, atmospheric temperature, humidity, and other variables.

Clouds and complex wind flow around the Big Island of Hawaii.

NOAA has both geostationary satellites and polar orbiting satellites. Polar-orbiting satellites orbit at an altitude of about 600 miles, while geostationary satellites orbit at the height of 22,236 miles. Polar-orbiting satellites circle the earth from pole to pole every 90 minutes or so, while geostationary satellites remain over a fixed location on earth. While geostationary satellites are much better for observing a particular region of Earth 24 hours a day, they have a hard time observing high latitudes. Polar-orbiting satellites can see all areas of the earth with equal ability, but generally only pass over the same swath of the planet a couple of times per day, limiting their usefulness.

NOAA generally keeps two satellites in operation over the longitude ranges covering North America, GOES East and GOES West, at the locations shown on the map above. GOES East is currently the GOES 16 satellite which went operational a couple of years ago. GOES 17 will be the new GOES West, replacing the aging GOES 15 satellite. GOES 15 will remain operational for several more months, then be placed in standby mode ready to be used again if there is a problem with one of the new operational satellites.

The oddly specific 22,236-mile altitude required for geostationary orbits is needed because it is the point at which the velocity necessary for a satellite to stay in orbit matches the rotation period of Earth. Satellites or other objects in low earth orbit need to travel about 17,000 miles per hour to balance the downward pull of gravity. However, that speed is much faster than Earth rotates, and so data satellites and other objects like the International Space Station (ISS) will orbit the Earth about once every 90 minutes. However, as the height of the orbit increases, the linear distance a satellite has to travel to complete one lap around the Earth also increases. That, in turn, means it takes longer to complete one orbit. At the magical altitude of 22,236 miles, the time it takes a satellite to complete one orbit around the Earth exactly equals one day. Note that a spacecraft can't merely travel faster or slower to maintain a geostationary orbit at a different altitude. If the satellite slows down, it will gradually spiral down towards the Earth, while if the satellite speeds up, it will spiral progressively further away from the Earth. The plot below shows the altitudes and orbital periods for different orbits.

The new GOES 17 Satellite can observe the Earth at both higher spatial and temporal resolution. Like GOES 16 over the eastern US, the new GOES 17 satellite will be able to take highly detailed imagery of the western US as well as the central and east Pacific. GOES 17 can image the entire region of Earth visible to it every 15 minutes at multiple wavelengths, with far more rapid updates possible over smaller areas.

The image below shows smoke from one of the wildfires in California this past fall as high clouds pass overhead. The high resolution of the new satellite data will allow for fires to be readily spotted when the sky is clear.

With GOES 17 able to provide higher resolution data with rapid update frequency, forecast models will have more accurate and precise data available to help better analyst storm systems and wind flow patterns over the Pacific. That, in turn, will allow for more accurate predictions of storms over the Pacific or approaching the West Coast. Since the same storms frequently travel eastward across the country after reaching the West Coast, that will also help to improve the long-term forecasts of storms that impact central and eastern areas of the US after striking the western US.

So, look for more spectacular imagery from GOES 17 in the weeks and months ahead, including some striking imagery of Pacific hurricanes during the 2019 hurricane season. The satellite will also help to further the steady trend of weather forecast improvements that have been seen over the last 40 years as better observations and increasing computational capacity combine to allow for more accurate weather models.

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