Imaging differential optical absorption spectroscopy

A camera that measures what comes out of a flare.

Imaging DOAS points a spectrometer at a plume from a few hundred meters away and builds a two-dimensional picture of the gas inside it. Add wind data and we convert that picture into an emission rate in kilograms per hour, from outside the fence, without sampling the stack.

The instrument splits its field of view into 50 vertical rows and reads each as its own spectrum. A scanning mirror steps the fan sideways across the plume, so one scan returns a 2D map of gas column density instead of a single number.

Fifty spectrometers in one exposure

Conventional open-path DOAS gives one concentration averaged over one light path. Imaging DOAS treats each of 50 detector rows as a separate spectrometer, so a single exposure returns 50 stacked measurements up the height of the plume. Sweep the mirror sideways and those columns build into an image.

Scattered sunlight is the light source

A 45° elliptical mirror collects skylight coming from behind the plume, so you need no transmitter or reflector on the far side. The instrument works on sources you cannot get near.

Absorption identifies the gas

Formaldehyde, SO₂, NO₂ and others each absorb ultraviolet wavelengths in their own pattern. We fit those patterns against reference spectra to get a differential slant column density for every row, each with its own error.

Geometry and wind convert it to a flux

We sum the column densities into a vertical slice through the plume and subtract the upwind background. Distance, wind speed and wind direction then turn that slice into an emission rate in kilograms per hour.

Measuring something you can’t reach?

Tell us the source and the compound. We’ll tell you whether Imaging DOAS is the right instrument for it.

Talk to our team