Individual scans from our NOVAC scanning-DOAS (Differential Optical Absorption Spectroscopy) instruments can be downloaded via our data API. Full instructions can be found here.

Volcanoes emit a large array of gases, either actively during eruptions from a vent or directly from erupted lava as it degasses, or passively through the a vent or directly through the volcanic edifice as melts migrate, evolve, and degas in the sub-surface plumbing system. Many of these gases may be harmful if breathed in for extended periods of time. Depending on the prevailing conditions, these gases—collectively known as a volcanic plume—can be blown towards local population centres and are thus critical for monitoring and understanding municipal air quality.

Changes in the volume flux of certain volcanic gases, such as sulphur dioxide (SO2) can indicate changes in the subsurface conditions, with increases often being tied to upticks in unrest from other geophysical observables. Tracking the evolution of gas fluxes through time is thus an important aspect of monitoring.

The volumes of gases emitted by any given volcanic system depends on a number of factors, particularly properties of the magma such as its viscosity—how 'runny' it is—which controls how easily gases can escape from the melt. Some volcanic systems (e.g. Cleveland volcano, in the Aleutian arc) exhibit persistent plumes, even during inter-eruption period.

In recent years, satellites—such as the OMI satellite—have been launched that are capable of measuring fluxes of volcanic gases (e.g. SO2), but there are a number of caveats. Images captured by these satellites have reasonably long repeat times based on their orbits, they need a sky clear of things like clouds, and their current resolution is quite low, with most volcanic systems entirely encompassed by a handful of pixels. Consequently, there is still a lot of value in ground-based instrumentation.

Scanning DOAS (Differential Optical Absorption Spectroscopy) systems are a type of instrument that can be used to monitor volcanic emissions. DOAS systems use spectroscopy to measure the concentration of gases in the air by analyzing the absorption of light at specific wavelengths. This allows them to detect a wide range of gases, including sulfur dioxide (SO2), which is a common gas emitted by active volcanoes. Scanning DOAS systems are often used in combination with other instruments, such as cameras and thermal sensors, to provide a more complete picture of a volcano's activity. They can help to identify changes in gas emissions that may indicate an increased likelihood of an eruption, allowing for more effective monitoring and eruption forecasting.

DOAS systems use spectroscopy to measure the concentration of gases in the air by analyzing the absorption of light at specific wavelengths. This means that they are sensitive to specific colors or wavelengths of light, depending on the gases they are designed to detect. For example, a DOAS system designed to measure sulfur dioxide (SO2) emissions from a volcano would be sensitive to light in the ultraviolet (UV) range, as SO2 strongly absorbs UV light at certain wavelengths. DOAS systems typically use a light source, such as a lamp or laser, to illuminate the gas of interest, and a spectrometer to analyze the light that is absorbed by the gas. The resulting data can be used to calculate the concentration of the gas in the air.

Differential optical absorption spectroscopy (DOAS) is a technique that has been used in a variety of scientific and industrial applications for several decades. The basic principles of DOAS were first developed in the early 1900s, but the first practical DOAS systems were not developed until the 1950s. These early systems were used primarily for atmospheric research and air pollution monitoring, and were relatively large and complex. Over time, DOAS technology has evolved and become more sophisticated, with the development of smaller, more portable systems that are easier to use and more widely applicable. Today, DOAS systems are used in a variety of fields, including environmental monitoring, industrial process control, and medical diagnostic imaging.

There are several environmental factors that can impact the effectiveness of DOAS systems when used to monitor volcanic emissions. One of the most important factors is the presence of other gases or particles in the air that can interfere with the detection of the gas of interest. For example, volcanic plumes often contain a complex mixture of gases and particles, including water vapor, ash, and other pollutants. These other substances can absorb light at the same wavelengths as the gas being measured, which can make it more difficult to accurately detect the gas using DOAS. Additionally, weather conditions such as fog, clouds, and rain can affect the ability of DOAS systems to collect accurate data by scattering or absorbing the light used for measurement. Finally, the distance between the DOAS system and the source of the volcanic emissions can also impact the accuracy of the measurements, as the concentration of the gas may vary over distance. These and other environmental factors must be carefully considered when using DOAS systems to monitor volcanic activity.

There are several potential challenges that could arise when trying to telemeter data from a scanning DOAS system deployed on a remote volcano, such as Cleveland volcano in the Aleutian Islands. One of the main challenges is the need to establish a reliable communication link between the DOAS system and the monitoring station. This could involve the use of satellite or radio communication systems, which may be subject to interference or other disruptions. Additionally, the remote location of the volcano may make it difficult to physically access the DOAS system for maintenance or repair, if necessary. Furthermore, the harsh and unpredictable weather conditions in the Aleutian Islands may pose challenges for the DOAS system, such as exposure to high winds, snow, and extreme temperatures. These and other factors must be carefully considered when deploying a DOAS system on a remote volcano.