Volcanic Ash Detection Techniques

Satellite imagery from satellites can be used without enhancement to detect volcanic ash plumes. An example is this spectacular NASA true colour view of the eruption of Ruang, in Indonesia, in September 2002.

However, high resolution images such as this are relatively rare, and as the ash clouds disperse they can become quite difficult to track using conventional satellite imagery.

Operational multi-spectral satellite techniques rely principally on differences in absorption and radiation between water/ice and ash clouds in key infrared bands. Using these techniques, we are able to identify areas of volcanic ash, and process the satellite imagery to show where an apparent ash signature exists.

The image below shows a night-time infrared image from the same eruption, processed to highlight volcanic ash. The strength of the ash cloud signal is indicated by the colour. At this stage, the ash cloud is in two main portions, with the westward portion drifting over Borneo, and the eastward ash/gas cloud (higher up in the atmosphere) remaining nearly stationary near the site of the eruption. A third area of ash is nearly invisible near the bottom centre of the image; because the ash cloud also contained ice, this portion was difficult to distinguish from normal cloud.

An animation of geostationary imagery of this eruption from Ruang is in our imagery archives.