Open-path active remote sensing instrument


Left: Telescope unit of the Airyx Open Path system. Right: Retro reflector array.

The Airyx open-path remote sensing instrument allows to monitor a wide range of atmospheric trace gases (NO2, SO2, O3, HCHO, HONO, H2O, BrO, OClO) based on the method of Differential Optical Absorption Spectroscopy (DOAS). Light emitted by High Power LEDs (centered at 280, 325, and 365 nm wavelength) covering the UV/vis range from 280 to 380 nm are coupled into a telescope and sent through the atmosphere along light paths of lengths between several 100 m and several km. Optionally, a high-power broadband light source (LDLS) is available extending the spectral range and the maximum measurement path length. The instrument measures the average concentration along the path with high precision (sub ppb range, depending on path length) and high time resolution (few seconds, depending on visibility).

Scheme of the Open path instrument setup. Besides standard high Power LEDS, a broadband Laser Driven Light Source (Xe-lamp) is available.

Although the complex setup, the instrument is very easy to operate: Initial light path alignment is performed by the help of an internal field of view camera combined with precise motors. During operation, the software automatically monitors and optimizes the alignment ensuring constant high-quality measurement without relying on user input. The optional motorized telescope base enables automatized measurements on multiple light paths in different directions and/or heights. Calibration gases are not needed since trace gases are quantified along well-defined light paths using literature absorption data. Automated, frequent lamp reference measurements ensure drift-free, long-term operation at highest precision.


• Spatially averaged trace gas measurement along light paths from several hundred meters to several kilometers

• Emission monitoring (e.g., SO2, NO2, HCHO) / Air quality monitoring

• Studies of atmospheric trace gas chemistry (e.g., O3, BrO, OClO), volcanic plume chemistry or polar halogen chemistry

• Traffic emission monitoring (SO2, NO2) at time resolution of few seconds

• Validation studies for satellite data, passive remote sensing, in situ and spatially high resolved chemistry modelling



*1 Limit of detection depends on path length, data averaging and visibility conditions.

*2 Typical specifications. Spectrometers are equipped with color filters to reduce stray light.

*3 Extension of OP-telescope for motorized elevation change (0 to 30°) and azimuth rotation (-130° to 130°) for application of several vertical light paths.

*4 Number of required arrays depends on application and desired length of light path.


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