Welcome

As we prepare to meet the challenges of global climate change and pollution, we urgently need to improve our understanding of the atmosphere's chemistry. TES is making a vital contribution to this effort as one of four instruments aboard NASA's Aura satellite. TES focuses on the troposphere, the layer of atmosphere that stretches from the ground to the altitude at which airplanes fly. With very high spectral resolution, TES can distinguish concentrations of gases at different altitudes, a key factor in understanding their behavior and impact. It's the first orbiting instrument able to do this with ozone, a very important chemical with regard to both global warming and air pollution.

Chemical clues

After the sun warms the Earth, the planet radiates that energy back into space in a range of infrared wavelengths. But before reaching space, the energy passes through the atmosphere, where various gases absorb and re-radiate portions of it -- in effect stamping the energy with their own spectral signatures. From its vantage point in orbit, TES measures radiation coming out of the top of Earth's atmosphere in a range that includes the signature wavelengths of ozone, carbon monoxide, water vapor, and methane. Those data enables scientists to deduce valuable information about global warming and climate change, Earth's water cycle, and air pollution on a local, regional, and global scale.

Ozone

Ozone's impact is all about location. High in the stratosphere, ozone shields us from the sun's harmful UV rays. But beneath that, at the top of the troposphere, it acts as a greenhouse gas and contributes to global warming. In the middle of the troposphere, it plays a key role in a chemical process that cleans the air of certain pollutants. But at the bottom of the troposphere, where we live and breathe, it contributes to smog and is toxic to plants and animals. TES lets us track the abundance, creation, destruction, and movement of this critical chemical at various altitudes in the troposphere.

Global warming and climate change

Greenhouse gases contribute to global warming by trapping some of the energy that Earth radiates after being warmed by the sun. TES scientists are currently able to calculate how much energy is trapped at various altitudes by ozone and they're in the process of doing the same with water vapor, the most abundant greenhouse gas. Upcoming work with TES data may similarly reveal the effects of methane.

Global water cycle

Understanding how water travels between Earth's surface and atmosphere is crucial to being able to predict the climate and the availability of water in various parts of the world, and to formulating plans to help people adapt to climate changes brought about by global warming. TES helps to deepen our understanding of the water cycle by providing one important piece of the puzzle.

Biomass burning

Biomass burning is the widespread practice, especially in the tropics, of using fire to clear forests and grassland for agriculture and to dispose of crop residue. Among its environmental impacts, biomass burning releases large amounts of carbon monoxide (CO) into the atmosphere, where it reacts with other chemicals to produce ozone. Other instruments observe and measure CO, but only TES measures both CO and ozone -- at the same time and at various altitudes. This enables scientists to see the extent to which biomass burning contributes to ozone in the troposphere.

Local and regional air pollution

TES feeds data about ozone concentrations to local agencies and decision-makers, and helps them use the data in climate-modeling tools. Since TES is the only remote-sensing instrument currently flying that can distinguish ozone at altitudes where it does harm from altitudes where it is beneficial, TES data can be uniquely valuable to local and regional air-pollution analysis and forecasting.

What is TES?

TES is an infrared spectrometer flying aboard the Aura satellite, which currently orbits Earth. Its high spectral resolution enables it to measure concentrations of ozone, carbon monoxide, water vapor and methane at various altitudes in the atmosphere, which reveals important information about global warming and climate change, the water cycle, and air pollution.

Detecting altitudes

Every kind of chemical absorbs and emits a characteristic pattern of energy wavelengths that serves as its spectral fingerprint. These wavelengths vary slightly with the changes in temperature and air pressure found at different altitudes. TES' predecessors were not sensitive enough to detect those variations, but TES has such high spectral resolution, it can tell the difference between the wavelength pattern of a chemical at one altitude from the pattern of the same chemical at a different altitude. This makes the instrument uniquely valuable for measuring ozone, for example, which is harmful at some altitudes and beneficial at others.

Sun-synchronous orbit

Sunlight plays a critical role in many of the chemical reactions that TES scientists study, and keeping the sun at a nearly constant angle for each observation of the same location simplifies interpretation of the data. So TES (as part of the Aura satellite) flies a sun-synchronous orbit that takes it over each part of the Earth at the same "solar mean time" in each orbit. For example, the instrument flies over the equator at about 1:45 p.m. local time with each 100-minute orbit. It takes TES 16 orbits to survey the entire planet, except for small regions around each pole.

Nadir and limb views

TES observes both straight down (nadir view) and at an angle that just skims the surface of the planet (limb view). Each view has its advantages. Limb viewing provides a much longer path through the atmosphere, and looking through a larger mass of air improves the chances of observing sparsely distributed substances that might be missed in the nadir view. Limb viewing's angle also makes it easier to determine the altitudes of the observed chemicals. But nadir viewing is less obscured by clouds, is able to reach the lowest parts of the troposphere, and enables scientists to study changes across distances as short as tens of kilometers.

Night vision

During every 100-minute orbit, TES crosses from Earth's dayside to nightside and back again. If it relied on reflected sunlight, it would be useless half the time. But TES senses light in the infrared part of the electromagnetic spectrum, like night-vision goggles. So TES can observe both day and night, including the long nights of the polar regions.

TES Science
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