Longpath DOAS tomography on a motorway exhaust gas plume: numerical studies and application to data from the BAB II campaign

Laepple, Thomas; Knab, V.; Mettendorf, K. U.; Pundt, I.

doi:10.5194/acp-4-1323-2004

Cited by 27 publications

(20 citation statements)

References 19 publications

(20 reference statements)

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“…First tomographic measurements employing the LP-DOAS technique were carried out to investigate the emissions of a motorway . Using two telescopes and 16 light paths, the NO 2 concentration field perpendicular to the motorway was retrieved and within all errors results are in good agreement with model expectations (Laepple et al, 2004). This study used a discrete approach by approximating the NO 2 concentration field by a finite sum over local piecewise constant (so called box) and Figures…”

Section: Introductionsupporting

confidence: 65%

“…studying sensitivity to measurement errors or investigating different geometries. Furthermore, it contains unavoidable strong functional a priori and was reported to fail for the reconstruction of the motorway emission plume with steep concentration gradients in Laepple et al (2004).…”

Section: Print Versionmentioning

confidence: 99%

“…A i j then stores the lengths of path i in pixel j . With large pixels and small systems of equations, piecewise linear basis functions interpolating linearly between nodes of the discretisation grid, as discussed in Ingesson et al (1998) and used in Laepple et al (2004) reduce discretisation errors.…”

Section: Print Versionmentioning

confidence: 99%

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2-D reconstruction of atmospheric concentration peaks from horizontal long path DOAS tomographic measurements: parametrisation and geometry within a discrete approach

Härtl¹,

Song²,

Pundt³

2005

Preprint

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Abstract. In this study, we theoretically investigate the reconstruction of 2-D cross sections through Gaussian concentration distributions, e.g. emission plumes, from long path DOAS measurements along a limited number of light paths. This is done systematically with respect to the extension of the up to four peaks and for six different measurement setups with 2–4 telescopes and 36 light paths each. We distinguish between cases with and without additional background concentrations. Our approach parametrises the unknown distribution by local piecewise constant or linear functions on a regular grid and solves the resulting discrete, linear system by a least squares minimum norm principle. We show that the linear parametrisation not only allows better representation of the distributions in terms of discretisation errors, but also better inversion of the system. We calculate area integrals of the concentration field (i.e. total emissions rates for non-vanishing perpendicular wind speed components) and show that reconstruction errors and reconstructed area integrals within the peaks for narrow distributions crucially depend on the resolution of the reconstruction grid. A recently suggested grid translation method for the piecewise constant basis functions, combining reconstructions from several shifted grids, is modified for the linear basis functions and proven to reduce overall reconstruction errors, but not the uncertainty of concentration integrals. We suggest a procedure to subtract additional background concentration fields before inversion. We find large differences in reconstruction quality between the geometries and conclude that, in general, for a constant number of light paths increasing the number of telescopes leads to better reconstruction results. It appears that geometries that give better results for negligible measurement errors and parts of the geometry that are better resolved are also less sensitive to increasing measurement errors.

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Section: Introductionsupporting

confidence: 65%

Section: Print Versionmentioning

confidence: 99%

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2-D reconstruction of atmospheric concentration peaks from horizontal long path DOAS tomographic measurements: parametrisation and geometry within a discrete approach

Härtl¹,

Song²,

Pundt³

2005

Preprint

Self Cite

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“…Satellite observations (e.g., GOME, GOME-2, OMI, SCIAMACHY) provide twodimensional distribution patterns on a global scale; however, the resolution is still rather coarse (several tens of km). On smaller scales (several km), tomographic inversion methods have been applied (Laepple et al, 2004;Pöhler, 2010). The resolution of this method depends on the number of light paths, therefore a high spatial resolution can only be achieved by installing a large number of instruments (Hartl et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

The Heidelberg Airborne Imaging DOAS Instrument (HAIDI) – a novel imaging DOAS device for 2-D and 3-D imaging of trace gases and aerosols

et al. 2014

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Abstract. Many relevant processes in tropospheric chemistry take place on rather small scales (e.g., tens to hundreds of meters) but often influence areas of several square kilometer. Thus, measurements of the involved trace gases with high spatial resolution are of great scientific interest. In order to identify individual sources and sinks and ultimately to improve chemical transport models, we developed a new airborne instrument, which is based on the well established Differential Optical Absorption Spectroscopy (DOAS) method. The Heidelberg Airborne Imaging DOAS Instrument (HAIDI) is a passive imaging DOAS spectrometer, which is capable of recording horizontal and vertical trace gas distributions with a resolution of better than 100 m. Observable species include NO 2 , HCHO, C 2 H 2 O 2 , H 2 O, O 3 , O 4 , SO 2 , IO, OClO and BrO.Here we give a technical description of the instrument including its custom-built spectrographs and CCD detectors. Also first results from measurements with the new instrument are presented. These comprise spatial resolved SO 2 and BrO in volcanic plumes, mapped at Mt. Etna (Sicily, Italy), NO 2 emissions in the metropolitan area of Indianapolis (Indiana, USA) as well as BrO and NO 2 distributions measured during arctic springtime in context of the BRomine, Ozone, and Mercury EXperiment (BROMEX) campaign, which was performed 2012 in Barrow (Alaska, USA).

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“…in Laepple et al (2004) and Hartl et al (2006) and to stratospheric ozone profile retrieval from limb scatter satellite observations in Degenstein et al (2009). Since MAX-DOAS observations are essentially tomographic measurements, we believe that their analysis might benefit from this more specialised approach.…”

Section: A Hartl and M O Wenig: Max-doas Regularisation Studymentioning

confidence: 99%

Regularisation model study for the least-squares retrieval of aerosol extinction time series from UV/VIS MAX-DOAS observations for a ground layer profile parameterisation

Härtl

Wenig

2013

Atmos. Meas. Tech.

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Abstract. The retrieval of tropospheric aerosol extinctions from MAX-DOAS observations of O4 using a small number of three or four extinction profile parameters suitable for boundary layer reconstruction is investigated with respect to the following questions. First, to what extent does this nominally over-constrained pure least-squares problem for the inversion of the radiative transfer equation require regularisation and how should parameters of the regularisation be chosen? Second, how can a lack of information in the under-constrained case be best compensated by using the information contained in a sequence of observations and by explicitly including intensities into the fit? The forward model parameterises the optical properties of the boundary layer aerosol by its extinction profile, single-scattering albedo and a Henyey–Greenstein phase function. Forward calculations are carried out online, i.e. without look-up tables. The retrieval uses a Tikhonov regularisation combined with an approximate L-curve criterion and empirical a priori information from the retrieval sequence based on previous valid solutions. The consistency of the approach is demonstrated in selected model case studies assuming a polluted urban scenario and westward viewing direction of the instrument. It is shown that a dynamic choice of the regularisation parameter is crucial for high aerosol load and large diurnal variations. The quality of the retrieval can be improved significantly if the retrieval sequence and thus the a priori is chosen according to the information content of the measurement series. Additional intensities improve the solution for all solar angles if suitably weighted. This flexible retrieval algorithm allows for reconstruction of aerosol profiles in the boundary layer for a wide range of viewing directions and extinctions. It can thus be applied to observational geometries scanning the sky in two angular dimensions and to retrieve further aerosol optical parameters in the boundary layer.

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Longpath DOAS tomography on a motorway exhaust gas plume: numerical studies and application to data from the BAB II campaign

Cited by 27 publications

References 19 publications

2-D reconstruction of atmospheric concentration peaks from horizontal long path DOAS tomographic measurements: parametrisation and geometry within a discrete approach

2-D reconstruction of atmospheric concentration peaks from horizontal long path DOAS tomographic measurements: parametrisation and geometry within a discrete approach

The Heidelberg Airborne Imaging DOAS Instrument (HAIDI) – a novel imaging DOAS device for 2-D and 3-D imaging of trace gases and aerosols

Regularisation model study for the least-squares retrieval of aerosol extinction time series from UV/VIS MAX-DOAS observations for a ground layer profile parameterisation

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