Skip Navigation
menu close modal

AIRS Rapid Response:
Latest Sulfur Dioxide and
Dust Detection

Detection Time: 2021/08/13, UTC 03:59:21

Region plotted represents one AIRS data granule.

SO2 DETECTION

About | KMZ | GeoTIFF

Sulfur dioxide brightness temperature difference is calculated by differencing the values reported between two AIRS channels, one that is sensitive to SO2 and one that is not. Larger differences imply greater SO2 absorption, which in turn implies a stronger volcanic signal. Please refer to the opening paragraph on this page for a better understanding of what this measurement implies.

DUST DETECTION

About | KMZ | GeoTIFF

Dust score is determined from multiple tests that compare radiances. Higher scores indicate more certainty that dust is present. Dust is probable when the score is above 380.

CLOUDS

Total Cloud Fraction
About | KMZ

The cloud fraction reported by AIRS is the product of cloud emissivity and areal coverage. Low fraction can indicate either small, highly emissive clouds or more extensive but less emissive clouds. The cloud fraction shown here has a spatial resolution of 45 km at nadir. AIRS can sense up to two cloud decks in a column of atmosphere, and this plot shows the cloud fraction of all cloud decks present.

Cloud Top Altitude
About | KMZ

Cloud top altitude is calculated from the natural logarithm of the AIRS cloud top pressure assuming a surface pressure of 1000 hPa and a scale height of 6 km. The cloud altitude shown here has a spatial resolution of 45 km at nadir. AIRS can sense up to two cloud decks in a column of atmosphere, but in this plot only the higher of the two decks is depicted.

VISIBLE AND INFRARED

Visible Image (daytime only)
About

This image is created using data from AIRS’ visible/near-infrared light sensor, Vis/NIR, and is available for daytime acquisitions only. Please note the green rectangular border defines the area of one granule of AIRS data on Earth’s surface that is observed by AIRS’ primary set of IR sensors. The viewing area for the Vis/NIR instrument is slightly different than the primary sensors, which explains the misalignment of the visible image and the green border.

Infrared Image
About

AIRS' infrared sensor measures radiometric temperature (brightness temperature) at the top of the atmosphere over a wide spectral range, allowing determination of air temperature throughout the atmospheric column either above the clouds or at Earth's surface when not blocked by cloud. Useful for assessing cloud cover (clouds are colder than the underlying surface).

OVERLAY TOOL

  • Use this tool to overlay sulfur dioxide (SO2), dust, cloud fraction, and cloud top height derived from AIRS data plus AIRS visible light and infrared imagery.
  • Set the visibility and opacity of individual layers to see where quantities intersect and to facilitate interpretation.
  • Clouds can obscure the AIRS SO2 signal. By combining SO2, cloud fraction, and cloud height you can see can where meteorological clouds interfere with AIRS detections of SO2.

About the AIRS Products

Volcanic eruptions can release large volumes of sulphur dioxide (SO2) gas and pulverized rock known as volcanic ash. The SO2 and dust browse products derived from AIRS observations can indicate the possibility of volcanic activity, but more detailed analysis is required to confirm the presence of volcanic clouds or estimate the composition and quantity of materials in the clouds.

What the measurements imply

Volcanic SO2 and ash plumes absorb the energy in infrared wavelengths of light, or radiances, passing through them in transit from the surface of the Earth to space. This absorption is controlled by the composition of a plume and quantity of the components within the plume, together with other important factors such as cloud cover, surface temperature and emissivity. We detect SO2 and ash plumes by comparing the radiance measured in spectral channels that are sensitive to SO2 or ash to the radiance measured in channels that are not sensitive.

In the case of SO2, we represent differences between the radiance in two channels as a difference in radiometric, or brightness, temperature. Larger brightness temperature differences (BTD) imply stronger SO2 absorption. In the case of ash, we represent differences between several pairs of channels as a dust score. Larger dust scores imply stronger ash absorption. It’s important to note that clouds can block the detection of the SO2 signal by the AIRS instrument.

About the data and rapid response system

These rapid response images are generated from AIRS radiance observations (Level 1B data) obtained in six-minute periods that are received within three hours of the original observation. An automated process divides each six-minute data collection into 54 separate sub-regions (each 250 km on a side and containing 225 observations) and searches for the presence of SO2 alone or a physically-contiguous combination of SO2 and dust. If either of these tests produce a positive, a plume event is declared and images are produced. Each image covers the entire six-minute data granule.