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The Airborne imaging differential opticalabsorption spectroscopy (DOAS) instrument for Measurements of AtmosphericPollution (AirMAP) has been developed for the purpose of trace gasmeasurements and pollution mapping. The instrument has been characterized andsuccessfully operated from aircraft. Nitrogen dioxide (NO2) columnswere retrieved from the AirMAP observations. A major benefit of the push-broom imaging instrument is the spatially continuous, gap-free measurementsequence independent of flight altitude, a valuable characteristic formapping purposes. This is made possible by the use of a charge coupleddevice (CCD) frame-transfer detector. A broad field of view across track of around 48° isachieved with wide-angle entrance optics. This leads to a swath width ofabout the same size as the flight altitude. The use of fibre coupled lightintake optics with sorted light fibres allows flexible instrument positioningwithin the aircraft and retains the very good imaging capabilities. Themeasurements yield ground spatial resolutions below 100 m depending onflight altitude. The number of viewing directions is chosen from a maximum of35 individual viewing directions (lines of sight, LOS) represented by 35individual fibres. The selection is adapted to each situation by averagingaccording to signal-to-noise or spatial resolution requirements. Observationsat 30 m spatial resolution are obtained when flying at 1000 m altitude andmaking use of all 35 viewing directions. This makes the instrument a suitabletool for mapping trace gas point sources and small-scale variability. Theposition and aircraft attitude are taken into account for accurate spatialmapping using the Attitude and Heading Reference System of the aircraft. Afirst demonstration mission using AirMAP was undertaken in June 2011. AirMAPwas operated on the AWI Polar-5 aircraft in the framework of the AIRMETH-2011campaign. During a flight above a medium-sized coal-fired power plant innorth-west Germany, AirMAP clearly detected the emission plume downwind fromthe exhaust stack, with NO2 vertical columns around2 × 1016 molecules cm−2 in the plume centre. NOxemissions estimated from the AirMAP observations are consistent with reportsin the European Pollutant Release and Transfer Register. Strong spatialgradients and variability in NO2 amounts across and along flightdirection are observed, and small-scale enhancements of NO2 above amotorway are detected

A wide field-of-view imaging DOAS instrument for two-dimensional trace gas mapping from aircraft