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

Abstract

Abstract. For the purpose of trace gas measurements and pollution mapping, the Airborne imaging DOAS instrument for Measurements of Atmospheric Pollution (AirMAP) has been developed, characterised and successfully operated from aircraft. From the observations with the AirMAP instrument nitrogen dioxide (NO2) columns were retrieved. A major benefit of the pushbroom imaging instrument is the spatially continuous, gap-free measurement sequence independent of flight altitude, a valuable characteristic for mapping purposes. This is made possible by the use of a frame-transfer detector. With a wide-angle entrance objective, a broad field-of-view across track of around 48° is achieved, leading to a swath width of about the same size as the flight altitude. The use of fibre coupled light intake optics with sorted light fibres allows flexible positioning within the aircraft and retains the very good imaging capabilities. The measurements yield ground spatial resolutions below 100 m. From a maximum of 35 individual viewing directions (lines of sight, LOS) represented by 35 single fibres, the number of viewing directions is adapted to each situation by averaging according to signal-to-noise or spatial resolution requirements. Exploitation of all the viewing directions yields observations at 30 m spatial resolution, making the instrument a suitable tool for mapping trace gas point sources and small scale variability. For accurate spatial mapping the position and aircraft attitude are taken into account using the Attitude and Heading Reference System of the aircraft. A first demonstration mission using AirMAP was undertaken. In June 2011, AirMAP has been operated on the AWI Polar-5 aircraft in the framework of the AIRMETH2011 campaign. During a flight above a medium sized coal-fired power plant in North-West Germany, AirMAP clearly detects the emission plume downwind from the exhaust stack, with NO2 vertical columns around 2 × 1016 molecules cm−2 in the plume center. The emission estimates are consistent with reports in the pollutant transfer register. Strong spatial gradients and variability in NO2 amounts across and along flight direction are observed, and small-scale enhancements of NO2 above a motorway are detected. The present study reports on the experimental setup and characteristics of AirMAP, and the first measurements at high spatial resolution and wide spatial coverage are presented which meet the requirements for NO2 mapping to observe and account for the intrinsic variability of tropospheric NO2.

High-resolution measurements from the airborne Atmospheric Nitrogen Dioxide Imager (ANDI)

“…Therefore, the VCD (Eq. 7) may be defined as the ratio of the SCD to the AMF (Solomon et al, 1987) VCD = SCD AMF .…”

“…how this change might impact the AOD and in turn the AMF, the OPAC aerosol model (Hess et al, 1998) was used to estimate the impact with a continental average aerosol configuration. The results showed that an increase in RH from 50 % to 60 % would lead to an 8 % increase in AOD at 450 nm.…”

Liquid water absorption and scattering effects in DOAS retrievals over oceans

“…CHOCHO, from space (e.g., Burrows et al, 1999;Martin et al, 2002;Richter et al, 2005;Wittrock et al, 2006;Schön-hardt et al, 2008;De Smedt et al, 2008) as well as from the ground, ships and aircafts (e.g., Wittrock et al, 2004;Heckel et al, 2005;Peters et al, 2012;Pinardi et al, 2013;Groß-mann et al, 2013;Schönhardt et al, 2014).…”

Atmospheric remote sensing constraints on direct sea-air methane flux from the 22/4b North Sea massive blowout bubble plume

“…These data can be used for top-down estimates of atmospheric surface fluxes of local sources via inverse modeling (Krings et al, 2011(Krings et al, , 2013. In addition to the MAMAP instrument, also a push-broom imaging DOAS spectrometer instrument for remote sensing measurements of nitrogen dioxide (NO 2 ) was installed on the aircraft, as described in Schönhardt et al (2014).…”