Remote sensing of NO2
Satellite measurements of tropospheric NO2
Answer the questions in your head, then click on [Answer] and check your answer with the correct one.
About this exercise type...

 

— What are the marked absorption structures in sunlight called?

[Answer]

 

— What causes these absorption structures?

[Answer]

 

— Why do these structures make ground station observations of trace gases in the atmosphere difficult?

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— Because of this ground station observations initially concentrated on the measurement of strong absorbers in the atmosphere. What species is the principal example of a strong atmospheric absorber?

[Answer]

 

— In what decade were the first ground station measurements of nitrogen dioxide concentrations made?

[Answer]

 

— Given the defects of solar radiation as a light source, what was the key problem for ground station measurements?

[Answer]

 

— What was the main technique used in ground station observations to try to solve this problem?

[Answer]

 

— Satellite-borne spectrometers can measure spectra from three light paths. What are these light paths?

[Answer]

 

— Which of these light paths provides a reference spectrum?

[Answer]

 

 

Fraunhofer lines.
The absorption of particular wavelengths by species on the Sun.
The strong Fraunhofer lines cover up the weak absorptions of trace gases.
Ozone.
The 1970s.
They could not measure the spectrum of sunlight before it entered the Earth's atmosphere, so no reference spectrum was available to compare with the spectrum measured at the surface.
Spectra taken from light paths of different lengths were compared, such as a spectrum at noon with a spectrum at sunrise or sunset.
  • Direct sunlight,
  • sunlight passing through the Earth's atmosphere and
  • 'earthshine', that is sunlight that has been scattered and reflected in the atmosphere and at the surface.
Direct sunlight.
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