Impact of 3D radiative transfer on airborne NO<sub>2</sub> imaging remote sensing over cities with buildings
<p>Airborne imaging remote sensing is increasingly used to map the spatial distribution of nitrogen dioxide (<span class="inline-formula">NO<sub>2</sub></span>) in cities. Despite the small ground-pixel size of the sensors, the measured <span class="in...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2021-10-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/14/6469/2021/amt-14-6469-2021.pdf |
| _version_ | 1819135414043148288 |
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| author | M. Schwaerzel M. Schwaerzel D. Brunner F. Jakub C. Emde C. Emde B. Buchmann A. Berne G. Kuhlmann |
| author_facet | M. Schwaerzel M. Schwaerzel D. Brunner F. Jakub C. Emde C. Emde B. Buchmann A. Berne G. Kuhlmann |
| author_sort | M. Schwaerzel |
| collection | DOAJ |
| description | <p>Airborne imaging remote sensing is increasingly used to map the spatial distribution of nitrogen dioxide (<span class="inline-formula">NO<sub>2</sub></span>) in cities. Despite the small ground-pixel size of the sensors, the measured <span class="inline-formula">NO<sub>2</sub></span> distributions are much smoother than one would expect from high-resolution model simulations of <span class="inline-formula">NO<sub>2</sub></span> over cities. This could partly be caused by 3D radiative transfer effects due to observation geometry, adjacency effects and effects of buildings.
Here, we present a case study of imaging a synthetic <span class="inline-formula">NO<sub>2</sub></span> distribution for a district of Zurich using the 3D MYSTIC (Monte carlo code for the phYSically correct Tracing of photons In Cloudy atmospheres) solver of the libRadtran radiative transfer library. We computed <span class="inline-formula">NO<sub>2</sub></span> slant column densities (SCDs) using the recently implemented 3D-box air mass factors (3D-box AMFs) and a new urban canopy module to account for the effects of buildings.
We found that for a single ground pixel (50 m <span class="inline-formula">×</span> 50 m) more than 50 % of the sensitivity is located outside of the pixel, primarily in the direction of the main optical path between sun, ground pixel, and instrument. Consequently, <span class="inline-formula">NO<sub>2</sub></span> SCDs are spatially smoothed, which results in an increase over roads when they are parallel to the optical path and a decrease otherwise. When buildings are included, <span class="inline-formula">NO<sub>2</sub></span> SCDs are reduced on average by 5 % due to the reduced sensitivity to <span class="inline-formula">NO<sub>2</sub></span> in the shadows of the buildings. The effects of buildings also introduce a complex pattern of variability in SCDs that would show up in airborne observations as an additional noise component (about 12 <span class="inline-formula">µmol m<sup>−2</sup></span>) similar to the magnitude of typical measurement uncertainties.
The smearing of the SCDs cannot be corrected using 1D-layer AMFs that assume horizontal homogeneity and thus remains in the final <span class="inline-formula">NO<sub>2</sub></span> map. The 3D radiative transfer effects by including buildings need to be considered to compute more accurate AMFs and to reduce biases in <span class="inline-formula">NO<sub>2</sub></span> vertical columns obtained from high-resolution city-scale <span class="inline-formula">NO<sub>2</sub></span> remote sensing.</p> |
| first_indexed | 2024-12-22T10:18:42Z |
| format | Article |
| id | doaj.art-ecb0f25bcee24777a95f2f9802a13cee |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-22T10:18:42Z |
| publishDate | 2021-10-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-ecb0f25bcee24777a95f2f9802a13cee2022-12-21T18:29:41ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482021-10-01146469648210.5194/amt-14-6469-2021Impact of 3D radiative transfer on airborne NO<sub>2</sub> imaging remote sensing over cities with buildingsM. Schwaerzel0M. Schwaerzel1D. Brunner2F. Jakub3C. Emde4C. Emde5B. Buchmann6A. Berne7G. Kuhlmann8Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, SwitzerlandEnvironmental Remote Sensing Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne, SwitzerlandEmpa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, SwitzerlandMeteorological Institute, Ludwig Maximilian University of Munich, Munich, GermanyMeteorological Institute, Ludwig Maximilian University of Munich, Munich, GermanyGerman Aerospace Center (DLR), Oberpfaffenhofen, GermanyEmpa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, SwitzerlandEnvironmental Remote Sensing Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne, SwitzerlandEmpa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland<p>Airborne imaging remote sensing is increasingly used to map the spatial distribution of nitrogen dioxide (<span class="inline-formula">NO<sub>2</sub></span>) in cities. Despite the small ground-pixel size of the sensors, the measured <span class="inline-formula">NO<sub>2</sub></span> distributions are much smoother than one would expect from high-resolution model simulations of <span class="inline-formula">NO<sub>2</sub></span> over cities. This could partly be caused by 3D radiative transfer effects due to observation geometry, adjacency effects and effects of buildings. Here, we present a case study of imaging a synthetic <span class="inline-formula">NO<sub>2</sub></span> distribution for a district of Zurich using the 3D MYSTIC (Monte carlo code for the phYSically correct Tracing of photons In Cloudy atmospheres) solver of the libRadtran radiative transfer library. We computed <span class="inline-formula">NO<sub>2</sub></span> slant column densities (SCDs) using the recently implemented 3D-box air mass factors (3D-box AMFs) and a new urban canopy module to account for the effects of buildings. We found that for a single ground pixel (50 m <span class="inline-formula">×</span> 50 m) more than 50 % of the sensitivity is located outside of the pixel, primarily in the direction of the main optical path between sun, ground pixel, and instrument. Consequently, <span class="inline-formula">NO<sub>2</sub></span> SCDs are spatially smoothed, which results in an increase over roads when they are parallel to the optical path and a decrease otherwise. When buildings are included, <span class="inline-formula">NO<sub>2</sub></span> SCDs are reduced on average by 5 % due to the reduced sensitivity to <span class="inline-formula">NO<sub>2</sub></span> in the shadows of the buildings. The effects of buildings also introduce a complex pattern of variability in SCDs that would show up in airborne observations as an additional noise component (about 12 <span class="inline-formula">µmol m<sup>−2</sup></span>) similar to the magnitude of typical measurement uncertainties. The smearing of the SCDs cannot be corrected using 1D-layer AMFs that assume horizontal homogeneity and thus remains in the final <span class="inline-formula">NO<sub>2</sub></span> map. The 3D radiative transfer effects by including buildings need to be considered to compute more accurate AMFs and to reduce biases in <span class="inline-formula">NO<sub>2</sub></span> vertical columns obtained from high-resolution city-scale <span class="inline-formula">NO<sub>2</sub></span> remote sensing.</p>https://amt.copernicus.org/articles/14/6469/2021/amt-14-6469-2021.pdf |
| spellingShingle | M. Schwaerzel M. Schwaerzel D. Brunner F. Jakub C. Emde C. Emde B. Buchmann A. Berne G. Kuhlmann Impact of 3D radiative transfer on airborne NO<sub>2</sub> imaging remote sensing over cities with buildings Atmospheric Measurement Techniques |
| title | Impact of 3D radiative transfer on airborne NO<sub>2</sub> imaging remote sensing over cities with buildings |
| title_full | Impact of 3D radiative transfer on airborne NO<sub>2</sub> imaging remote sensing over cities with buildings |
| title_fullStr | Impact of 3D radiative transfer on airborne NO<sub>2</sub> imaging remote sensing over cities with buildings |
| title_full_unstemmed | Impact of 3D radiative transfer on airborne NO<sub>2</sub> imaging remote sensing over cities with buildings |
| title_short | Impact of 3D radiative transfer on airborne NO<sub>2</sub> imaging remote sensing over cities with buildings |
| title_sort | impact of 3d radiative transfer on airborne no sub 2 sub imaging remote sensing over cities with buildings |
| url | https://amt.copernicus.org/articles/14/6469/2021/amt-14-6469-2021.pdf |
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