SGP/VCEIL/B4 - Window contamination

During this period, the VCEIL window repeatedly became contaminated by bird droppings 
shortly after each cleaning. Detection of clouds was intermittently limited. The window 
warnings are contained in the status_flag data.

The cleaning frequency was increased and then bird deterrent spikes were installed on 
3/24/2009. 

Cloud height measurements are suspect when the status_string field contains the "Window 
contaminated" warning.

• Lowest cloud base height detected(first_cbh)
• Third cloud base height(third_cbh)
• Aerosol volume backscattering coefficient at 355 nm(backscatter)
• Vertical visibility(vertical_visibility)
• Second lowest cloud base height(second_cbh)