Transcript PHY2505-Lecture14

Atmospheric Radiation – Lecture 14
PHY2505 - Lecture 14
IR temperature retrieval
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Atmospheric Radiation – Lecture 14
Line shape – altitude dependence
Emission
Re-absorption
Z
n
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Atmospheric Radiation – Lecture 14
15um CO2 band and temperature of Mars
1 2 3
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3
2
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Atmospheric Radiation – Lecture 14
Retrieval methods
Even under cloud free conditions, with a noise free
radiometer that measures all l, a unique solution for T(z) is
not guaranteed
With instrument noise and a limited number of l, an infinite
numbers of solutions is possible.
We want to find a temperature profile that satisfies the RTE
and approximates the true profile as closely as possible
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Atmospheric Radiation – Lecture 14
Three classes of methods
Physical methods: Chahine’s method – uses RTE &
weighting functions & non-linear iteration (Liou 7.4.3.1)
Statistical methods: no RTE (no physics!), regression
between radiances and training set of temperature profile
solutions - (Liou 7.4.3.2)
Hybrid retrievals: – uses RTE and weighting functions
and linearisation of the RTE to allow use of matrix inversion
( Liou 7.4.3.2)
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Atmospheric Radiation – Lecture 14
Physical methods
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Atmospheric Radiation – Lecture 14
Physical methods: Chahine’s method
(Liou 7.4.3.1)
Ii
Ti(pi)
Iterate the relaxation equation
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Atmospheric Radiation – Lecture 14
Chahine’s method – relaxation equation
derivation (Liou 7.4.3.1)
Liou equation 7.4.25a
Approximate the observed radiance using the mean value theorem
Dividing expected by observed:
as low dependence on
temperature
Can approximate by
relaxation equation
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Atmospheric Radiation – Lecture 14
Chahine’s method outline– (Liou 7.4.3.1)
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Atmospheric Radiation – Lecture 14
Chahine’s method outline– how good is
it?
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Atmospheric Radiation – Lecture 14
Statistical methods – (Liou 7.4.3.2)
First operational
measurements
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Atmospheric Radiation – Lecture 14
Hybrid methods – (Liou 7.4.3.2)
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