> ## Documentation Index
> Fetch the complete documentation index at: https://data.avert.ldeo.columbia.edu/llms.txt
> Use this file to discover all available pages before exploring further.

# Background

Scanning Differential Optical Absorption Spectroscopy (DOAS) is used to measure sulfur dioxide (SO₂) in volcanic plumes. The technique relies on the fact that SO₂ absorbs ultraviolet light at specific wavelengths. By comparing observed spectra with calibrated references, SO₂ concentrations along a line of sight can be derived.

At Cleveland volcano, Scanning DOAS provides the **first continuous SO₂ monitoring in the Aleutians**, a region with frequent explosive activity. Measuring SO₂ fluxes here is critical because persistent degassing at Cleveland has been a hallmark of activity, and flux increases often precede eruptive events.

<Frame
  caption="Processed scan data from the CLNE and CLES scanning DOAS instruments for a period of elevated gas emissions from June
21–July 3, 2024. SO₂ emission rates, in tons per day, are indicated by the green (CLNE) and orange (CLES) circles. Wind speeds are
indicated by the grey triangles."
>
  <img src="https://mintcdn.com/avert/6D1_XNdzck93VGdT/images/figure-14.png?fit=max&auto=format&n=6D1_XNdzck93VGdT&q=85&s=6c9a4c5de4355fa31e16eb28791cb6d1" width="1352" height="462" data-path="images/figure-14.png" />
</Frame>