15.2: Visibility
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Visibility is the final topic on the interaction of light with particles in Earth’s atmosphere covered in this chapter. In general, the topic of visibility is simply a question of what can be seen and how far away it is. When someone says that the visibility today is 10 miles, it means that one can see objects 10 miles away.
In the Arctic, where the air is extremely dry and clean, visibility of 100 miles (161 km) is common. On the other end, when you cannot see objects 100 meters (~330 ft) away this is referred to as zero visibility. As you may imagine, visibility is extremely important for pilots and drivers. Fog in the atmosphere provides the worst conditions for visibility.
Look at the following image of the Great Smoky Mountains. The trees in the front of the image are nearly clear, but with each additional ridge, the mountainside looks whiter and whiter. We assume that each ridge has the same type of foliage as the first. This tells us that objects further away are brighter.
The reason for the change in brightness is particulate matter in the atmosphere. This can come in the form of aerosols or hydrometeors (cloud droplets, rain drops, snow flakes etc.). In the case of the mountain image above, the Great Smoky Mountains are known for emitting plentiful volatile organic compounds (VOCs) that act as cloud condensation nuclei (CCN) and produce clouds near ground level (i.e., low hanging fog). Both the aerosols and the hydrometeors reduce visibility.
Many believe that a lack visibility is caused by objects blocking your view. However, if that were the case, the background would appear darker. Instead, a lack of visibility is caused by objects scattering light towards your eye. With greater distances, your eye has to look through a larger portion of the atmosphere and, therefore, more opportunity for light to scatter towards you. The scattered light is white because Mie scattering is taking place.
Here is another image showing the same scene on a clear and polluted day from the Sequoia and Kings Canyon National Park.
This national park often has issues with pollution from the central valley in California. On polluted days, more aerosols and particulate matter are in the atmosphere, so more particles are available to scatter light toward your eye. Scene details are lost and the mountains in the distance can’t be seen at all. The visible range is shorter on the bottom image as compared to the top.
Chapter 22: Questions to Consider
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Query \(\PageIndex{1}\)
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Query \(\PageIndex{1}\)
- Why is it not possible to see a rainbow on the ground at noon?
- Drag the Sun, Rain Cloud, Rainbow, and Bob to the correct positions in the situation that Bob sees a rainbow when looking East, assuming East is the right side of the picture:
Query \(\PageIndex{1}\)
- What causes low visibility? What type of scattering is this an example of?
Selected Practice Question Answers:
Query \(\PageIndex{1}\)