Aerial perspective

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Aerial perspective (photography), fading and bluing of the colors of distant objects. Landscape in Nepal.

The aerial perspective (English: aerial perspective) describes the visibility conditions in a landscape, caused by the air. The appearance is also known as opalescence . An object looks bluish, lighter or browner (due to smog) with increasing distance. The reason for this is the (diffuse) reflection and the (selective) absorption of the light rays by the air particles, which can be explained with the help of physics. On the one hand, the aerial perspective refers to the everyday experience that distant mountains appear light blue. On the other hand, it denotes the possibility that artists can achieve a desired long-distance effect in their paintings by grading the color values ​​towards blue and white. Since the color contributes to the spatial effect of the aerial perspective, it can be understood as a special form of the color perspective.

Aerial perspective (photography). Brownish colors from smog. Street in Prague (Czech Republic).

In photography, the aerial perspective sometimes also refers to an image that shows an object from above. This is also known as an aerial view , bird's eye view, or top view.

The composition of the air

The air or the earth's atmosphere consists of very different air particles. It is a (heterogeneous) mixture of gases, atmospheric water and aerosols.

  • Aerial perspective (painting). Ferdinand Hodler: Lake Geneva from Chexbres , 1904.
    The gases in the air are mainly nitrogen (N 2 , 78% relative volume fraction) and oxygen (O 2 , 21%). Other gases, such as argon or carbon dioxide, only occur in small quantities. The gas molecules are very small. They have a diameter of around 10 −7 cm (= 0.001 µm).
  • The atmospheric water (H 2 O) can be solid (ice crystals, ice fog, hail, frost, snow crystals), liquid (haze, fog droplets, raindrops, clouds) or gaseous (water vapor = humidity). Depending on the weather, the proportion varies greatly in terms of space and time. The maximum value of water vapor in the humid tropics is 4% (relative volume fraction). Depending on their condition, water particles can take on very different sizes, from the smallest water vapor particles to 4 cm large hailstones.
  • The air also contains aerosols . These are solid or liquid suspended particles such as fine dust, pollen, smoke, soot, salt crystals, smog, dust, droplets or volcanic ash. The aerosols are relatively large. They have a size of 10 −4 to 10 −2 cm (= 1 to 100 µm).
Aerial photography. Gardens of Nordkirchen Castle (North Rhine-Westphalia).
Rayleigh scattering. Blue light is preferentially scattered by the air particles, while red, yellow and green light is absorbed or transmitted.

The radiation balance in the air

The sunlight hits the earth's air envelope in parallel. There the rays are let through, reflected or absorbed.

  • Some of the rays (around 30%) are let through (transmission) and reach the earth's surface undisturbed. This is direct sunlight .
  • Another part (about 25%) is absorbed (swallowed). Through this selective absorption , the radiation energy is absorbed by the air particles and converted into thermal energy.
  • The remaining part is reflected by the air particles in all possible directions. This all-round, undirected scattering of the radiation is called diffuse reflection . About 20% of these diffusely reflected rays reach the earth and form the diffuse light from the sky. About 25% radiate back into space.

The physical explanation

The visible light from the sun (solar radiation with a wavelength of 0.38 to 0.78 µm) falling into the earth's atmosphere is a mixture of all colors. If the rays hit air particles, they experience selective absorption or diffuse reflection. The strength and type of absorption and reflection depend on the size of the air particles and the wavelength of the light. Two cases can be distinguished.

The Rayleigh scattering

The English physicist John William Strutt, 3rd Lord Rayleigh (1842–1919) recognized how the blue of the sky comes about. The smaller air particles, mainly the oxygen and nitrogen molecules (but also tiny water droplets and aerosols), are around 100 times smaller than the wavelength of light. It would be ideal for a reflection if the molecule were just as large as the wavelength. After all, the size ratio of molecule to wavelength is more favorable for blue (and violet), short-wave light. Therefore, the air molecules reflect (scatter) the blue light 16 times more strongly than the long-wave, red. Green, yellow and red are absorbed to a greater extent. Thus the clear, cloudless sky appears blue. The higher you go and the thinner the atmosphere, the less this effect is and the darker the sky becomes - up to space black.

The Mie scatter

The German physicist Gustav Adolf Mie (1868–1957) recognized how the white of the sky comes about. If the air particles are about the same size or larger than the wavelength of light (that is, the aerosols or the atmospheric water), they scatter all of the white sunlight. This results in a brightening of the sky in the vicinity of the sun. Because the aerosol and water concentration in the layers close to the ground is greater than in the height, this whitish blue is found especially near the horizon.

Sharp contours of distant mountains in sunny weather. San Andreas Fault (USA).
Sharp contours of distant tree trunks in fog. Bruderwald (Bamberg)
High renaissance. Detail from: Leonardo da Vinci: Rock Grotto Madonna , 1495–97.
Dutch baroque. Willem van de Velde the Younger, Dutch Ships in a Calm , around 1665.

The contours

In a landscape in sunny weather, objects far away appear lighter and more bluish. We perceive details, color contrasts , plasticity and structures of the objects less and less because the different colors dissolve into a uniform light blue. But even if the distant mountain appears flat and uniformly light blue, its outer contour remains sharp as long as its silhouette contrasts with the color of the sky. Only at extreme distance or high humidity do the colors blend. But then the mountain can no longer be seen.

Something similar happens in fog, but over a shorter distance. Even at a short distance, objects can only be recognized as flat, but sharply contoured (!) Silhouettes. The uniform gray color is more and more similar to the white or light gray of the fog color, until the object finally disappears completely.

Use in painting

  • Since the High Renaissance , artists have been using the air and color perspective in addition to the central perspective in order to depict depth. You want to reproduce the visible reality in a credible way. Leonardo da Vinci recognizes that the distant blue stain and paleness comes from the medium of air. Presumably he was the first to describe this phenomenon as an aerial perspective.
  • Romance. Caspar David Friedrich: Bohemian landscape with the Milleschauer , 1809.
    The watercolors from Albrecht Dürer's second trip to Italy are evidence of the artist's trust in the visual impression. He paints distant mountains in light blue, although in truth (that is, in the vicinity) they have the colors of the forest, stone or snow.
  • The Dutch baroque painters in particular graduate their landscape paintings from warm to cold. They use warm brown, red and yellow in the foreground, a cold steel blue in the background and green color gradations in the middle ground between the two.
  • The painters of the Romantic period put feeling and the internalized experience of nature against the sobriety and severity of classicism. They increasingly turn to landscape painting. The aerial perspective plays a major role in depicting the feeling of loneliness and the longing for the distance.
  • From the Renaissance onwards, the aerial, color and central perspective retained their undisputed validity until Impressionism. Since then, artists have also used multi-perspective and aperspective modes of representation.

literature

  • Reinhard Breuer (Editor-in-Chief): Spectrum of Science. Special: color . 1. unchanged new edition. Spectrum of Science Verlagsgesellschaft mbH, Heidelberg 2004, ISBN 3-936278-80-6 .
  • Martin Kappas: Climatology. Climate Research in the 21st Century - a Challenge for Natural and Social Sciences . 1st edition. Spektrum Akademischer Verlag, Heidelberg 2009, pp. 78–81.
  • Walter Roedel: Physics of our environment. The atmosphere . 2nd Edition. Springer-Verlag, Berlin et al. 1994, ISBN 3-540-57885-4 .
  • Wolfgang Weischet, Wilfried Endlicher: Introduction to climatology . 7th edition. Gebr. Borntraeger Verlagbuchhandlung, Berlin / Stuttgart 2008, ISBN 978-3-443-07142-4 , pp. 48–51.

Web links

Commons : Atmospheric perspective  - collection of images, videos and audio files

Individual evidence

  1. Marcel Minnaert: Light and color in nature . 1st edition. Birkhäuser Verlag, Basel / Boston / Berlin 1992, ISBN 3-7643-2496-1 , p. 321 .
  2. ^ Karl Mütze (ed.): Brockhaus. ABC of optics . 1st edition. VEB FA Brockhaus Verlag, Leipzig 1961, p. 729, keyword: spatial perception .
  3. Peter Wiench (editorial): Keyser's great antiques lexicon . Book club Ex Libris, Zurich et al. 1983, p. 167 .
  4. ^ Stefan Brönnimann: Climatology . 1st edition. Haupt Verlag, Bern 2018, ISBN 978-3-8252-4819-2 , p. 43 .
  5. Wolfgang Weischet, Wilfried Endlicher: Introduction to climatology . 7th edition. Gebr. Borntraeger Verlagbuchhandlung, Berlin, Stuttgart 2008, ISBN 978-3-443-07142-4 , p. 48 .
  6. Wolfgang Weischet, Wilfried Endlicher: Introduction to climatology . 7th edition. Gebr. Borntraeger Verlagbuchhandlung, Berlin, Stuttgart 2008, ISBN 978-3-443-07142-4 , p. 85-86 .
  7. Martin Kappas: Climatology. Climate Research in the 21st Century - a Challenge for Natural and Social Sciences . 1st edition. Spektrum Akademischer Verlag, Heidelberg 2009, ISBN 978-3-8274-1827-2 , p. 78 .
  8. ^ Stefan Brönnimann: Climatology . 1st edition. Haupt Verlag, Bern 2018, ISBN 978-3-8252-4819-2 , p. 48 .
  9. Wolfgang Weischet, Wilfried Endlicher: Introduction to climatology . 7th edition. Gebr. Borntraeger Verlagbuchhandlung, Berlin, Stuttgart 2008, ISBN 978-3-443-07142-4 , p. 50 .
  10. Martin Kappas: Climatology. Climate Research in the 21st Century - a Challenge for Natural and Social Sciences . 1st edition. Spektrum Akademischer Verlag, Heidelberg 2009, ISBN 978-3-8274-1827-2 , p. 78 .
  11. Reinhard Breuer (editor-in-chief): Spectrum of science. Special: color . 1st edition. Spectrum of Science Verlagsgesellschaft mbH, Heidelberg 2004, ISBN 3-936278-80-6 , p. 16 .
  12. ^ Rainer Schönhammer: Introduction to the psychology of perception. Senses, body, movement . 2nd Edition. Facultas.wuv Universitätsverlag, Vienna 2013, ISBN 978-3-8252-4076-9 , p. 194 .
  13. Perspective - pictorial means: The aerial perspective (blue, sfumato). Accessed December 30, 2019 (German).
  14. ^ Eva Maria Kaifenheim: Aspects of Art. A textbook and workbook for art education . 1st edition. Verlag Martin Lutz GmbH, Munich 1979, ISBN 3-87501-060-4 , p. 37 and 39 .
  15. ^ Winfried Nerdinger: Perspektiven der Kunst. From the Carolingian era to the present . 3. Edition. Oldenbourg Schulbuchverlag GmbH, Munich, Düsseldorf, Stuttgart 2006, ISBN 978-3-486-87517-1 , p. 507 .
  16. ^ Eva Maria Kaifenheim: Aspects of Art. A textbook and workbook for art education . 1st edition. Verlag Martin Lutz GmbH, Munich 1979, ISBN 3-87501-060-4 , p. 36 .