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20 CHAPTER 2. ATMOSPHERE AND REMOTE SENSING 2.1.3 Airborne Imaging DOAS Klaus-Peter Heue (Stephen Broccardo 2 , Stuart Piketh 2 , Ulrich Platt, Kristy Ross 3 ) 2 University of Witwatersrand Johannesburg, 3 ESKOM, South Africa Abstract Two dimensional distribution of a several trace gases were mapped by a ground based imaging DOAS instrument build in 2003. Now a modified instrument for airborne measurements was realised and first measurements were performed in a test campaign in the Highveld region South Africa in October 2006. N u m b e r o f p ix e l 5 1 0 1 5 2 0 2 5 D is ta n c e [m ] 0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 3 8 0 4 3 8 5 4 3 9 0 4 3 9 5 4 4 0 0 4 4 0 5 4 4 1 0 4 4 1 5 4 4 2 0 N u m b e r o f s p e c tru m 8 0 0 6 0 0 4 0 0 2 0 0 0 -2 0 0 -4 0 0 -6 0 0 -8 0 0 w in d d ire c tio n flig h t d ire c tio n Figure 2.3: NO2 SCD distribution below the aircraft close to the power station in Majuba, South Africa, which is indicated by the circle (preliminary result). Background In most atmospheric investigations information about the two dimensional distribution of tropospheric trace gases is highly desirable. A typical use is the identification of source areas, emission plumes, or the validation of chemical transport models. In the past various attempts have been made on different spatial scales, e.g. DOAS tomography on local scales (10 km), or satellite measurements on a global scale. We build an instrument based on imaging spectroscopy to map the 2D distribution of a series of relevant trace gases including NO2, glyoxal, H2O, O4 and BrO. It is installed on an aeroplane and observes the local distribution with a spatial resolution of 100 m. The Imaging DOAS instrument Lohberger et al. [2004] consists of an imaging spectrometer combined with a two dimensional detector (i.e. a CCD camera) analysing sun-light backscattered from the earth’s surface. The CCD camera records the spectral information in one dimension (x) and spatial information in the other dimension (y) perpendicular to the aircraft’s flight direction. The spectra are analysed using the DOAS technique ?, to retrieve the concentration integrated along the light paths which is called slant column densities (SCD’s). Thereby 2D-maps of the trace gas’s SCD are recorded. The newly build instrument was installed on an Aero Commander (ZS-JRA) of the South D is ta n c e [m ] a t g ro u n d le v e l re la tiv e to th e p lu m b lin e African Meteorological Service for a research campaign in the Highveld (ZA) in early October 2006. The instrument’s total field of view was 24.5 o (corresponding to a swath width of e.g. 1900 m at 4400 m flight altitude above ground). Methods and results First results are shown in figure 2.3 depicting the recorded NO2 columns when the aeroplane passed over a power station. The prevailing wind (indicated by the arrow) blew the plume across the flight track as it is clearly visible in the reconstructed NO2 SCD map. Outlook/Future work The existing instrument has to be further improved until next spring when the second part of the campaign will take place. In cooperation with the Anhui <strong>Institut</strong>e of Optics & Fine Mechanics (Hefei, China) new improved instruments will be build and employed on a high altitude research aircraft. Meanwhile the construction of a more sophisticated instrument for the new research aircraft HALO (Gulfstream 550) has just begun. Funding The measurements in South Africa were funded by the South African electricity supply company (Eskom). The instrument was funded by the <strong>Institut</strong>e. 2 ] N O 2 S C D [1 0 1 6 m o le c /c m 2 2 2 0 1 8 1 6 1 4 1 2 1 0 8 6 4 2 0
2.1. TROPOSPHERIC RESEARCH GROUP 21 2.1.4 Auto-MAX DOAS measurements for Tropospheric NO2 in Europe O. W. Ibrahim (Thomas Wagner, Torsten Stein and Ulrich Platt) Abstract Detection and retrieval of Vertical Column Densities of tropospheric air pollutant trace gas NO2 was carried on in industrial/traffic/urban areas in Europe. Measurements have been performed using the Automobile Multi Axis Differential Optical Absorption Spectroscopy technique(Auto-MAX DOAS) Figure 2.4: Panel (A): The route of driving with Auto-MAX DOAS from Brussels (Belgium) to Heidelberg (Germany). Panel(B):The Vertical Column Densities (VCDs) along the route retrieved from these measurements. Background Measurements of tropospheric pollutant trace gases in urban and industrial areas need a suitable spatial resolution. Although Satellites and airplanes can perform tropospheric columns measurements , their spatial resolution is still of the order of several kilometers. The Automobile Multi Axis Differential Optical Absorption Spectroscopy technique (Auto-MAX DOAS) has a more suitable spatial resolution (ranging between few tens of meters and few hundred meters). Making it an attractive tool for the measurements of trace gases on the scale of cities. The Auto-MAX DOAS fills the knowledge gap of tropospheric pollution between the local scale of cities and regional scale. Methods and results The use of UV/Vis spectroscopy with a miniature instrument installed on a car roof enables the detection and quantification of trace gases such as NO2, SO2, HONO, and CH2O in the troposphere. The time resolution of measurements is about 20-30 seconds and the spatial resolution from this method is ranging between tens of meters and a few hundred meters depending on the actual integration time and the driving speed of the car. The detection limit of NO2 is about 1 ppb, depending on the observation geometry. In contrast to in-situ techniques, from continuous Auto-MAX DOAS observations the integrated amount of trace gases (integrated over the altitude) is derived. Here we present the results of NO2 Vertical Column Densities (VCDs) from Auto-MAX DOAS measurements. Figure 2.4(A): the route of the Auto-MAX DOAS when driving from Brussels (Belgium) to Heidelberg (Germany), (B) The Vertical Column Densities (VCDs) along the route retrieved from these measurements. The VCDs retrieved by this method can be used for comparison/evaluation of satellite measurements over Urban areas with the advantage of having a better spatial resolution (i.e. the ability to see the gradients of the trace gases within the satellite pixel). Outlook/Future work Further improvement of the Auto-MAX DOAS is planned for the near future. This includes optimization of time resolution and spatial resolution. The expected improvement in time resolution will be achieved by using a newer generation of spectrometers with detectors (QE65000) with a higher quantum efficiency (up to 90 percent) and a better light throughput compared to the one used here. This will reduce the total integration time (i.e.improve the time resolution) by about one order of magnitude which will also improve the spatial resolution of the Auto-MAX DOAS. Funding International Max Plank Research School scholarship. Main publications Under preparation.
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2.6. CARBON CYCLE GROUP 87 2.6.4 In
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3.1. SOIL PHYSICS 97 3.1.1 Unstable
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3.1. SOIL PHYSICS 99 3.1.3 Physical
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3.1. SOIL PHYSICS 101 3.1.5 Install
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3.2. ICE AND CLIMATE 111 3.2.4 Prog
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3.2. ICE AND CLIMATE 113 Weller, R.
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Overview Werner Aeschbach-Hertig Su
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Bibliography 177
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180 CHAPTER 7. BIBLIOGRAPHY Butz, A
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182 CHAPTER 7. BIBLIOGRAPHY Leigh,
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184 CHAPTER 7. BIBLIOGRAPHY Wang, P
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186 CHAPTER 7. BIBLIOGRAPHY Kühl,
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7.5. INVITED TALKS 193 Invited Talk
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