Chapter 5
Priciples of Active and Passive
Remote Measurements of Water
the Atmosphere and at Ground
•
In
Yves Fouquart and Michele Vesperini
Laboratoire d'Optique Atmospherique
Universite des Sciences et Technologies de Lille
59655 Villeneuve d'Ascq Cedex
France
Remote sensing consists in inferring a parameter indirectely from measurements of a dependent quantity. For earth and atmospheric parameters, remote sensing is based on measuring
radiation which contains the signature of the required characteristics and constituents of the
atmosphere (temperature, pressure, absorbing gases, aerosols and cloud), or of the surface
(temperature, moisture, surface wind stress, canopy, etc ... ). Any quantitative interpretation of
remote sensed measurements requires that the emission and the transfer of radiation through
the atmosphere is accurately accounted for. This is a necessary condition to permit geophysical
information to be retrieved from measurements. The first part describes the physical processes
related to emission and transfer of radiation in the atmosphere. In the second part, the characteristics of the different spectral domains are outlined to show which type of information can be
extracted from the different measurements, depending on the wavelength. A special emphasis
is put on water vapour information.
5.1 Radiative Transfer Equation
Let L"(M,.5) be the monochromatic radiance at wavenumber II = 1/>., (in the interval II, 11+
dll) at a point M in the solid angle dw centered on direction.5. L"(M,S) has dimension
[Wm- 2 sr- 1 (cm- 1 )-IJ. Consider a cylindrical volume element which axis is along .5, with surface
dS and length dl. Let choose an axis along .5 and call L"(I, S) and L"(l + dl, S) the radiances at
the entrance and exit of the cylinder.
The photons reaching the exit of the cylinder (L"(I +dl, S)) may have three origins (Figure 5.1):
NATO ASI Series. Vol. 145
Radiation and Water in the Climate System:
Remote Measurements
Edited by Ehrhard Raschke
<1l Springer.Verlag Berlin Heidelberg 1996
Priciples of Active and Passive
Remote Measurements of Water
the Atmosphere and at Ground
•
In
Yves Fouquart and Michele Vesperini
Laboratoire d'Optique Atmospherique
Universite des Sciences et Technologies de Lille
59655 Villeneuve d'Ascq Cedex
France
Remote sensing consists in inferring a parameter indirectely from measurements of a dependent quantity. For earth and atmospheric parameters, remote sensing is based on measuring
radiation which contains the signature of the required characteristics and constituents of the
atmosphere (temperature, pressure, absorbing gases, aerosols and cloud), or of the surface
(temperature, moisture, surface wind stress, canopy, etc ... ). Any quantitative interpretation of
remote sensed measurements requires that the emission and the transfer of radiation through
the atmosphere is accurately accounted for. This is a necessary condition to permit geophysical
information to be retrieved from measurements. The first part describes the physical processes
related to emission and transfer of radiation in the atmosphere. In the second part, the characteristics of the different spectral domains are outlined to show which type of information can be
extracted from the different measurements, depending on the wavelength. A special emphasis
is put on water vapour information.
5.1 Radiative Transfer Equation
Let L"(M,.5) be the monochromatic radiance at wavenumber II = 1/>., (in the interval II, 11+
dll) at a point M in the solid angle dw centered on direction.5. L"(M,S) has dimension
[Wm- 2 sr- 1 (cm- 1 )-IJ. Consider a cylindrical volume element which axis is along .5, with surface
dS and length dl. Let choose an axis along .5 and call L"(I, S) and L"(l + dl, S) the radiances at
the entrance and exit of the cylinder.
The photons reaching the exit of the cylinder (L"(I +dl, S)) may have three origins (Figure 5.1):
NATO ASI Series. Vol. 145
Radiation and Water in the Climate System:
Remote Measurements
Edited by Ehrhard Raschke
<1l Springer.Verlag Berlin Heidelberg 1996