Multi axis differential optical absorption spectroscopy (MAX-DOAS)

Abstract

Abstract. Multi Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) in the atmosphere is a novel measurement technique that represents a significant advance on the well-established zenith scattered sunlight DOAS instruments which are mainly sensitive to stratospheric absorbers. MAX-DOAS utilizes scattered sunlight received from multiple viewing directions. The spatial distribution of various trace gases close to the instrument can be derived by combining several viewing directions. Ground based MAX-DOAS is highly sensitive to absorbers in the lowest few kilometres of the atmosphere and vertical profile information can be retrieved by combining the measurements with Radiative Transfer Model (RTM) calculations. The potential of the technique for a wide variety of studies of tropospheric trace species and its (few) limitations are discussed. A Monte Carlo RTM is applied to calculate Airmass Factors (AMF) for the various viewing geometries of MAX-DOAS. Airmass Factors can be used to quantify the light path length within the absorber layers. The airmass factor dependencies on the viewing direction and the influence of several parameters (trace gas profile, ground albedo, aerosol profile and type, solar zenith and azimuth angles) are investigated. In addition we give a brief description of the instrumental MAX-DOAS systems realised and deployed so far. The results of the RTM studies are compared to several examples of recent MAX-DOAS field experiments and an outlook for future possible applications is given.

Quantitative bias estimates for tropospheric NO<sub>2</sub> columns retrieved from SCIAMACHY, OMI, and GOME-2 using a common standard for East Asia

“…Here we briefly describe ground-based MAX-DOAS measurements -scattered sunlight observations in the UV/visible at several elevation angles between the horizon and zenith (e.g., Hönninger and Platt, 2002;Hönninger et al, 2004) -performed at three sites in Japan and three sites in China (Table 1 and Fig. 1).…”

Intercomparison of slant column measurements of NO<sub>2</sub> and O<sub>4</sub> by MAX-DOAS and zenith-sky UV and visible spectrometers

“…1 (Hönninger and Platt, 2002;Hönninger et al, 2004;Wittrock et al, 2004). Because the path to the last scattering point is confined to lower altitudes at elevations close to the horizon, measurements at several elevations down almost to the horizon yield information about the vertical profile of the absorber within the troposphere.…”

NO<sub>2</sub> observations over the western Pacific and Indian Ocean by MAX-DOAS on <i>Kaiyo</i>, a Japanese research vessel

“…Hönninger et al, 2004;Wagner et al, 2004;Wittrock et al, 2004;Sinreich et al, 2005;Frieß et al, 2006). It is useful for measuring a priori profiles for satellite retrievals and for validating chemical transport models.…”