The Atmospheric Infra-Red Sounder (AIRS) instrument suite, along with several other instruments, are on-board NASA's Earth Observing System (EOS) Aqua satellite. The AIRS Project Instrument Suite measures the Earth’s atmospheric water vapor and temperature profiles over the entire world every day. Before the AIRS Project Instrument Suite, these measurements required radiosondes (weather balloons).
An atmospheric sounder measures how the physical properties of a column of air vary with altitude. The measurement as a function of altitude is sometimes called a “profile”, a “sounding”, or a “retrieval”. The term "sounder" refers to measuring how the temperature and salinity are similarly measured in the ocean using sound waves. See Atmospheric Sounding for more information.
The AIRS suite also measures clouds and abundances of trace components in the atmosphere (See here for a list). The AIRS suite also detects suspended dust particles, but measurements of dust are not reported by the AIRS project as a data product.
The AIRS Project Instrument Suite comprises four individual instruments:
- Atmospheric Infra-Red Sounder (AIRS)
- Advanced Microwave Sounding Unit (AMSU-A1 and AMSU-A2)
- Humidity Sounder for Brazil (HSB)
The high spectral resolution infrared of AIRS results in good vertical resolution, however the resolution degrades in the presence of clouds. Microwave energy sensed by the AMSU and HSB microwave instruments has lower vertical resolution, but is insensitive to clouds and provides valuable soundings in all weather conditions. Combining data from AIRS and the microwave instruments provides highly accurate soundings in all cloud conditions. The result is a daily global snapshot of the state of the atmosphere.
The AIRS Project Instrument Suite primarily measures the Earth’s atmospheric water vapor and temperature profiles over the entire world every day. However, all the atmospheric components from space to the ground, including the ground itself, have some effect on the data. The atmospheric components include clouds, dust, and trace gasses. Some of these components are reported by the AIRS project, while other components are left to the wider scientific community.
Specifically, the AIRS Project Instrument Suite measures and reports (AIRS v6) the following as a function of altitude
The AIRS Project Instrument Suite also measures and reports (AIRS v6)
- Surface properties (e.g., temperature, emissivity, type [land, ocean, ice, etc])
- Cloud properties
- CO2 – carbon dioxide
- SO2 – sulfur dioxide (experimental; as a presence flag; no quantitative product).
The AIRS Project Instrument Suite also can measure, but does not report
- NH3 – ammonia (Level 3 available at GES-DISC)
- Dust – particulates
- HDO – deuterated water vapor (working to include in AIRS v7)
- HNO3 – nitric acid (processed with NOAA NUCAPS algorithm)
- N2O – nitrous oxide (processed with NOAA NUCAPS algorithm).
Many other trace gasses are detected by the AIRS Project Instrument Suite, but may be at low resolution or low sensitivity.
Clarisse, L. et al., 2010: Retrieving radius, concentration, optical depth, and mass of different types of aerosols from high-resolution infrared nadir spectra, Appl. Opt., 49, 3713-3722, doi:10.1364/AO.49.003713