Computer Modeling Laboratory 10

Written report due: 10 April

Passive remote sensing of clouds.

Lecture 12



The detection of clouds is a first key step not only in retrievals of cloud properties, but also in many remote sensing applications that require cloud-free conditions. A combination of solar and IR observations are commonly used to overcome the inherent problems in detecting clouds with either solar or IR remote sensing alone.

  1. Give three examples when clouds will be hard to detect from the visible imagery.
    HINT: Recall expression for a combined reflectance of the cloud-underlying surfcae system. The albedo of cloud itself (for conservative scattering) can be approximated as Rcl = [(1-g)τ]/[1+(1-g)τ]
  2. You analyze a satellite image of two different clouds with one appearing brighter at the visible wavelengths. In general, would you expect more, less, or unknown infrared radiance emitted by the brighter-looking cloud?
  3. This animation helps to visualize the effect of clouds on remote sensing in the IR.
    Answer the questions listed under the animation figure.


Instruction:to compute TOA radiances click on RUN RT code

The solar reflectance technique enables to retrieve the optical depth and effective drop size of clouds from radiances measured by a passive satellite sensor in the solar spectrum (see Lecture 12).

Using MODIS 2.1 and 0.86 μm channels, investigate whether this technique is capable of retrieving the optical depth and effective particle size of low level clouds over bright deserts (Asur = 0.3). Both MODIS channels have a band width of 0.05 μm. Take same solar and viewing zenith angles as in Figure 12.9, Lecture 12.