TES is the first satellite instrument to provide simultaneous concentrations of carbon monoxide, ozone, water vapor and methane throughout Earth’s lower atmosphere. This lower atmosphere (the troposphere) is situated between the surface and the height at which aircraft fly, and is an important part of the atmosphere that we often impact with our activities. This is also where gases such as ozone (O3) are formed, transported, and interact with other gases, and where much of the atmospheric water cycle is dictated. Understanding the distribution and movement of these and other trace gases is vital if we are to understand and correctly represent climate and air quality. TES makes measurements of infrared radiances used to derive the vertical distribution of important pollutant and greenhouse gases. TES is measuring trace gases that play an important role in the troposphere's chemistry, its interaction with living things, and its exchange of gases with the stratosphere. The location of these substances is mapped in three dimensions - not only with regard to latitude and longitude, but also altitude. TES also measures how conditions vary over time, at global, regional, and local scales.
What TES Measures
Routine standard products from TES include vertically-resolved profiles for ozone, carbon monoxide, water vapor, deuterated water vapor and methane. TES makes use of a variety of special observations that provide denser spatial sampling along orbits, and a continuous-coverage mode (called a transect) to detect air pollution. Ozone profiles, atmospheric temperature, concentrations of water vapor and deuterated water vapor, carbon monoxide and methane, nitric acid, effective cloud pressure and optical depth, surface temperature and land emissivity are all derived from TES radiance spectra.
How Does TES Work?
TES is a Fourier Transfer Infrared Spectrometer (FTIR) that measures the infrared-light energy (radiance) emitted by Earth’s surface and by gases and particles in the troposphere. The basic principle of FTIR's is to split and recombine a beam of light such that the recombined beam produces a wavelength-dependent interference pattern. Every substance (so long as it is warmer than absolute zero) emits infrared radiation at certain signature wavelengths — emissivity is a measure of a material’s ability to absorb and radiate energy. The emission wavelengths of Earth’s atmosphere vary with cloud cover and the concentration of the various gases and particles that absorb and emit infrared energy, and according to the pressures and temperatures at which these are found. Since the emission wavelengths vary with temperature and pressure, and temperature and pressure vary with altitude, if emission spectra are measured very precisely, we can infer the altitude of the chemical species
The TES instrument was designed with very fine spectral resolution, making one scan every 4 or 16 seconds at a spectral resolution of 0.1 cm-1 or 0.025 cm-1, respectively. This fine spectral resolution enables TES to pinpoint the wavelengths at which key substances are emitting and measure their pressure-broadened infrared absorption lines in the troposphere. These lines are used to identify the substances and determine their altitude within the troposphere.
TES measurements are also helping to determine local atmospheric temperature and humidity profiles (see global water cycle), local surface temperatures, and local surface reflectance and emittance (that is, the amount of sunlight reflected, and the amount of heat emitted by Earth’s surface). In response to the ever-changing cloud properties within a TES observed footprint and the changing thermal properties of the atmosphere and Earth’s surface, the amount of vertical sensitivity in the TES retrievals changes from scan to scan. The averaging kernel is an important measure for understanding the vertical sensitivity of a TES profile and these averaging kernels are provided in the data product for each TES scan. Another important metric for understanding TES retrievals is the degrees of freedom for signal (or DOFS).
Validation reports, data user’s guides and algorithm theoretical basis documents, and other documents are available to further understand TES retrievals.
Next: Chemical clues
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.