Computer Modeling Laboratory 5

Written report due: 4 October

Surface albedo and ocean color.
Examination of true color images.

Lecture 12


Down-looking satellite sensors measure the radiance that is diffuse radiation reflected by the surface and the atmosphere and hence it depends on the combined albedo of the atmosphere-surface system.
A schematic diagram illustrates the ray tracing method that helps to visualize how the successive reflection between the atmosphere and surface contributes to the combined albedo of the atmosphere-surface system.
1) Derive an equation for the combined albedo, ras.
Hint: Recall power series expansion 1/(1-x) = 1+x+x2+...
2) Under what conditions the combined albedo is approximately equal to a sum of the atmospheric albedo plus surface albedo (that is ras = r + rsfc).



You will work with MODIS/Terra data collected near Australia on 21 May 2008 (Day 142).

To get a MODIS RGB image for this case, go to MODIS website
Then go to Atmosphere => Images => Terra L1B Granule Images.
Select 2008, May 21. Select Australia. Clicking on a map with MODIS/Terra orbits, you will see a swath at 01:00 UTC. Find and download a RGB image for this swath.
Examine the image. 1) Mark (or describe in words) areas where in your opinion ocean color will not be retrieved. Briefly explain why.
2) Mark (or describe in words) areas where you would expect to find the largest chlorophyll concentrations. Briefly explain why.

Now to test your predictions, get and examine an ocean color image retrieved for this swath.
Connect to NASA Ocean Color Web
Click on Level 1 and 2 Browser. You will see a webpage where you can visualize ocean color products.
Select 2008, May, 21th.
Select MODIS/Terra.
Select Australia and click on Find Swaths.
Click on T2008142010000.L2_LAC to see retrieved chlorophyll concentrations. Click on the color-scale button to see the legend that relates color in the chlorophyll images to chlorophyll concentration.
Examine the chlorophyll image and relate to your predictions. Were your predictions correct? Why or why not?