Earth from orbit

The many roles of satellites at UCAR & NCAR

About 50 years ago, on April 1, 1960, the world’s first successful weather satellite was launched from Cape Canaveral, Florida. Although TIROS I was operational for only 78 days (15 days fewer than planned), it sent back 22,952 images of Earth from orbit, demonstrating the usefulness of satellites for surveying the atmosphere. In the years immediately following TIROS 1, nine more satellites were launched, revolutionizing the science of weather prediction.

Black-and-white satellite image from TIROS compared to modern satellite image.The first-ever satellite photo (upper left) is dwarfed by this 2008 image, which captures Hurricane Ike. It includes clouds from NOAA's Geostationary Operational Environmental Satellite (GOES) with land and ocean data from the Moderate Resolution Imaging Spectroradiometer (MODIS), launched on NASA's Terra satellite in 1999. (Images courtesy NASA.) 

UCAR/NCAR was in its very infancy when TIROS was launched, but space-based meteorology quickly became critical to the organization’s research. As early as 1967, scientists used satellite data during the Line Islands Experiment, NCAR’s first major field program, and again in 1969 during the Barbados Oceanographic and Meteorological Experiment.

Today, nearly every lab or program in the organization interacts with modern satellite technology in some way: testing satellite chemical sensors, measuring India’s groundwater, studying Arctic sea ice, guiding aircraft away from severe weather, discovering solar spicules, and much more. Following are highlights from a few of the organization’s many satellite-related activities.

COSMIC prepares for next round

COSMIC, the joint U.S./Taiwan constellation of six low-Earth orbit satellites launched in 2006, uses a method called radio occultation to measure how much a GPS signal is bent when its satellite is occulted by Earth’s atmosphere. Scientists apply mathematical methods to COSMIC data to determine underlying atmospheric conditions, such as air density, temperature, moisture, and electron density.

COSMIC is the first satellite system to provide a near real-time global snapshot of the atmosphere with high vertical resolution every 100 minutes. It produces about two thousand highly accurate profiles daily, totaling two and a quarter million since launch, most occurring in data-sparse oceanic regions. COSMIC was launched as a research, not operational, system, and yet the technology has been so successful that the data are being used around the world for operational forecasting.

“It’s unprecedented that a new observational system comes online and major global weather centers start assimilating its data within a year after launch,” says COSMIC’s Bill Schreiner. The data have quickly demonstrated their value for weather forecasting, with numerical weather prediction centers assimilating the data into their models and reporting positive impacts on forecasts.

COSMIC satellite in space.An artist’s rendition of the COSMIC satellites. (Illustration courtesy Orbital Sciences Corporation.) 

COSMIC is also aiding predictions of hurricane track and intensity and contributing to upper atmospheric studies of the ionosphere and plasmasphere. It’s poised to boost climate monitoring and model verification, too, by offering a highly accurate, global benchmark data record with full diurnal coverage that scientists will be able to use to determine atmospheric trends—something that no other instruments currently provide. “COSMIC data are so accurate that, given a long enough time series of data, we will be able to determine what the real atmospheric trends are over the long term,” Bill says.

COSMIC’s next step is a follow-on mission, known as COSMIC II, that is included in NOAA’s fiscal year 2011 budget. COSMIC II will place an expressly operational system of 12 satellites into orbit in late 2013 or early 2014, when the current satellites are expected to degrade. The mission is an equal partnership between NOAA and Taiwan’s National Space Organization, which funded much of the current COSMIC system.

“The science community in Taiwan is very supportive of extending the highly successful COSMIC mission to the next stage of the collaboration,” says COSMIC director Bill Kuo.

Tools for using satellite data

The Data Assimilation Research Testbed (DART) was spotlighted in the September 2009 cover story of the Bulletin of the American Meteorological Society. A cross-divisional project that includes collaboration with several dozen NCAR staff, DART provides students, educators, and scientists with access to free, state-of-the-art data assimilation tools.

One of DART’s major activities is helping scientists utilize COSMIC’s growing wealth of data. The testbed’s assimilation systems help scientists incorporate the data into regional models to improve hurricane predictions and into global models to estimate moisture in the atmosphere, particularly over the tropics, which is important for climate model analysis and development.

DART may also help keep satellites in the air—literally. Scientists hope to use its data assimilation products to model the density of the upper atmosphere (ionosphere and thermosphere), where polar-orbiting satellites circle Earth. “If you know the density, you can better predict where satellites are going to move, so you can avoid having satellites smash into each other,” explains DART’s Jeff Anderson.

When TIROS I was launched 50 years ago, Earth’s orbit didn’t see much traffic. Today, thousands of satellites have been launched, putting them at risk of collisions; currently, there is no global air traffic control system that tracks the positions of all satellites. In 2009, a major collision between an inactive Russian military satellite and an active Iridium satellite grabbed headlines. The collision is estimated to have created tens of thousands of pieces of debris that will circle Earth for thousands of years and threaten other satellites. (To learn about a recent close encounter involving a COSMIC satellite, see “Too close for comfort.”)

Satellite instrumentation

Scientists in NESL/ACD have long depended on satellites to get a sense of the global sweep of atmospheric gases far above Earth's surface. The MOPITT (Measurements Of Pollution In The Troposphere) instrument has now been measuring carbon monoxide for 10 years from its perch on NASA’s Terra satellite.

HIRDLS instrument.A model of the HIRDLS instrument.

“The 10-year data record is unique and gives us a chance to look at variability over a long period, to see the effects of things like the El Niño/Southern Oscillation and variability in biomass burning and boreal fires from year to year,” says John Gille, MOPITT’s principal investigator.

The MOPITT team recently released a fourth, improved version of the instrument’s data to the scientific community. In addition, the researchers are currently refining a technique for determining surface carbon monoxide from measurements of solar radiation reflected from the Earth’s surface. Preliminary results allow the researchers to pinpoint individual cities in Asia that stand out as major sources of carbon monoxide pollution, something that wasn’t possible before, according to John.

HIRDLS (High Resolution Dynamics Limb Sounder), another ACD-built instrument aboard a NASA satellite, measures atmospheric chemicals and temperatures. The instrument stopped transmitting scientific data in March 2008 due to a malfunctioning chopper. The team is hopeful that it will be able to restart the chopper with a new approach it plans to apply this spring.  

The researchers are about to release a fifth version of the HIRDLS data, which scientists are using for studies of the upper troposphere and lower stratosphere. The data are particularly applicable to this region because of their unprecedented 1-kilometer vertical resolution and regular global coverage. The team is also working to boost the accuracy of the instrument’s signal, which is partially blocked by a piece of plastic film that tore during launch in 2004.

“We’re working very hard to improve the accuracy of the correction for the signal coming from the blockage,” John says. “Our hope is to be able to add measurements of water vapor, methane, and nitrogen dioxide to our present suite of temperature, ozone, nitric acid, and the CFCs 11 and 12.”

Training and education

“We have a long and active history of providing satellite-related training,” says COMET project manager Wendy Abshire.

The program’s MetEd distance learning component currently offers more than 50 relevant modules in English, eight in Spanish, and five in French (see “On the Web”). About 20,000 user sessions were logged on these modules in 2009. The two most most recent satellite-related modules cover using satellites to monitor the ocean and explaining the benefits to weather forecasting that would result from putting a high spectral resolution infrared sounder into orbit.

One of COMET’s ongoing efforts to support the satellite community is the Environmental Satellite Resource Center, a community-driven website launched in September 2008 that provides access to a wide variety of educational materials for all knowledge levels. Anyone in the global satellite community can contribute to the site; COMET provides quality assurance as well as quick access to COMET modules. This spring, the site will be available in Spanish as well as English.

Another ongoing project involves collaborating with the Meteorological Service of Canada on modules for helping users interpret satellite data and apply it to forecasting, particularly with regard to winter weather.

Although most of the MetEd satellite training materials are geared toward professionals and students, the program’s “GOES-R: Benefits of Next-Generation Environmental Monitoring” module is designed for the public, decision makers, and forecasters, with especially striking visuals. “It explains the amazing leaps forward we will take when we have the capabilities associated with the next generation of geostationary satellites,” Wendy says.


Too close for comfort

On February 28, the U.S. Joint Space Operations Center warned that at 3:56 a.m. Mountain Standard Time the next day, a close encounter over the eastern United States would occur between one of COSMIC’s satellites and a satellite for amateur ham radios.

The two satellites' orbits, both about 500 miles (800 kilometers) high, were separated by a mere 128 feet (39 meters). However, timing was everything. Because of the satellites' positions along their orbits, their actual closest pass was a more comfortable 3,127 feet (953 meters), ensuring a happy outcome.


Satellites in the 2010s: A gloomy outlook turns more hopeful

UCAR president Rick Anthes spent many long hours working with Berrien Moore (University of New Hampshire) to chair a National Research Council report on the future of Earth monitoring via satellite. Informally called the “decadal survey,” the report—Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond—was issued in 2007. It warned of a looming crisis for Earth science: older U.S. satellite systems were nearing the end of their useful lives, and their replacements weren’t being adequately funded. The report laid out proposed timelines and costs for 17 missions deemed to be the most important.

There are signs of progress, Rick says. “Berrien and I have been pleased at the response to the decadal survey and its recommendations, not only by NASA and NOAA but also by Congress and the press.” However, bringing U.S. satellites up to speed isn’t easy or cheap. Since the 2007 NRC report was issued, it’s become clear that the costs of some systems were underestimated, while other proposals have been upgraded. The result is that most of the NASA missions will cost two to three times as much as expected. Similarly, the National Polar-orbiting Operational Environmental Satellite System (NPOESS) being built by NOAA, NASA, and the Air Force is now estimated to cost about $14 billion, compared to the original 2002 estimate of $6.5 billion.

President Barack Obama’s budget request for NASA and NOAA for fiscal year 2011 and beyond shows significant increases for Earth science satellites. “If these increases come through, it is a good sign for implementing the recommendations from the decadal survey,” Rick says.