What is NASA's Atmospheric Infrared Sounder (AIRS)?

The Atmospheric Infrared Sounder (AIRS) is one of five primary instruments on NASA’s Aqua satellite, which launched in 2002 and continues to operate today. The sensor measures the heat radiance reflected from Earth’s surface or emitted as radiation from its atmosphere, which aids in monitoring weather patterns, detecting wildfires, and measuring long-term climate processes.

Together with the Moderate Resolution Imaging Spectroradiometer (MODIS), AIRS also makes up the primary payload of the advanced polar-orbiting satellites called the Aqua remnant. Together with two other visible-light-band sensors on this spacecraft, the Visible Sensor (VIIRS) and the Mid-Infrared Sensor (MIRAS), these instruments allow scientists to observe Earth at three different wavelengths simultaneously. Here are some facts about AIRS.

How It Works

AIRS operates at infrared wavelengths longer than what human eyes can detect. It detects heat radiance from the Earth’s surface and from the atmosphere above it at five different wavelengths.

There is a 10.7 micrometer (μm) wavelength, a 13.3 μm wavelength, and a 15.33 μm wavelength, as well as two shortwave infrared (SWIR) channels at 1.64 μm and 2.08 μm. The sensor features an onboard computer that uses information from all five wavelengths to create an image of the Earth. It can do this, even though each wavelength can penetrate the atmosphere to a different degree.

The 10.7 μm wavelength is the longest and can penetrate the atmosphere the deepest. This can be helpful to scientists who want to measure the temperature of the lower troposphere, which is the bottom six miles of the atmosphere. The 15.33 μm wavelength can penetrate the atmosphere the least but can still be used to measure the temperature of the mid-troposphere, about three miles up.

This wavelength can also be helpful in monitoring the amount of water vapor in the lower troposphere. The 1.64 μm and 2.08 μm wavelengths can be used in conjunction with the 10.7 μm and 15.33 μm wavelengths to create false-color images.

Science Behind AIRS

It’s helpful to understand what a “wedge” is to know how AIRS does its job. This is a term coined by scientists who study the atmosphere and refer to a wedge as the area of the atmosphere between two infrared bands. AIRS measures a wedge that begins at the surface and extends upward, having a different temperature at each level.

The infrared band at 10.7 μm measures the surface temperature and the temperature of the lowest part of the atmosphere. The infrared band at 15.33 μm measures the temperature of the middle part of the atmosphere. The infrared bands at 1.64 μm and 2.08 μm measure the temperature of the highest part of the atmosphere.

Key Features of AIRS

Coverage

The AIRS coverage is approximately 40% of the global total. The image resolution is approximately 1.5 km.

Geolocation accuracy

The AIRS geolocation accuracy is approximately 8 km.

Sample time

The AIRS samples the atmosphere every 10 seconds.

Data rates and spatial resolution

The AIRS data rate is approximately 100 Kilobytes per second. The spatial resolution is approximately 1.5 km.

Latitude coverage

The latitude coverage range is from 85 to 85.5 degrees north and from 75 to 75.5 degrees south.

Longitude coverage

The longitude coverage range is from 65.5 degrees west to 102.5 degrees east.

Chlorine measurement

The AIRS can be used to measure the total chlorine in the atmosphere.

Limitations of AIRS

No surface winds or surface temperature information

The AIRS can measure surface temperature but cannot measure surface winds, pressure, or other weather-related variables.

No surface pressure information

The AIRS can measure surface pressure, but not with the same level of accuracy as instruments like the Advanced Hyronometer specifically designed to measure surface pressure.

No surface ozone measurements

The AIRS can measure surface ozone, but with a level of accuracy that is not yet sufficient for some applications.

No carbon monoxide measurements

The AIRS can measure carbon monoxide, but with a level of accuracy that is not yet sufficient for some applications.

No sulfur dioxide measurements

The AIRS can measure sulfur dioxide, but with a level of accuracy that is not yet sufficient for some applications.

No carbon dioxide measurements

The AIRS can measure carbon dioxide, but with a level of accuracy that is not yet sufficient for some applications.

Uses of AIRS Data

Scientists use data from the AIRS to study global climate change and weather patterns. The data is valuable to both short-term forecasting and long-term climate studies. For example, data from the AIRS helps scientists identify where carbon dioxide is increasing in the atmosphere, which allows them to understand better how the greenhouse effect is changing our climate. The AIRS data can also provide early warning of drought and wildfire.