Computer Modeling Laboratory 9

Written report due: 12 November

Passive remote sensing of clouds.

Lecture 10

Platnick, S., et al., 2003: The MODIS cloud products: Algorithms and examples from Terra. IEEE Trans. Geosci. Remote Sens., 41, 459-473.
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Instruction:to compute the TOA radiances click on RUN RT code

The solar reflectance technique enables to retrieve the optical depth and effective drop size of clouds using 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.



In this task, you will be analyzing MODIS cloud products using a web interface that provides access to the Level 1 and Atmosphere Archive and Distribution System (LAADS). Go to Images, Granule Browser. Select Nov.1 2008, Terra MODIS, parameter RGB, and get granule images of a 10x10 degrees box over the Northern Africa (10N,-10S), (-10W,10E). This selection includes three day-time granules (10:25; 10:30 and 12:00).
Select (click on image) the 10:25 am granule. By clicking on View Side by Side Parameter Comparison, you can see cloud and some other atmospheric products retrieved for this granule. Download images for cloud fraction, cloud-top pressure, cloud optical depth and effective particle radius. Download the same cloud products for other two granules.
1) Analyze cloud fraction images against by comparing two RGB images for 10:25; 10:30 and 12:00 granules. Find a few instances when cloud fraction was retrieved incorrectly. Briefly discuss the possible reasons.
2) Using cloud-top-pressure and cloud optical depth images, identify a stratus cloud over ocean and over land. Compare retrieved effective particle radius for these cases. Do retrievals look reasonable (refer to table 5.1, Lecture 5)?
3) Identify a few cirrus clouds in RGB images and analyze retrieved cloud products, if any. Do the retrieved products look reasonable? Briefly discuss what might be causing problems in retrievals of ice clouds.