Q: What can polarimetry tell us about aerosols?
A: Aerosols are a tough problem. Unlike clouds, when looking at Earth from space you really have to look hard to see them. You're often looking at a subtle signal and that makes it hard to be quantitative and accurate. Data from MODIS (radiometers aboard NASA's Terra and Aqua satellites) are of great value, but interpretation of that data depends on educated guesses regarding the types of aerosols in a particular scene, which significantly affects the conclusions.
In the case of aerosols, polarimetry provides a way to estimate their composition from space, which has not previously been possible. With measurements that discriminate the types of aerosols that are present, we eliminate a significant source of uncertainty.
Q: What can polarimetry tell us about clouds?
A: Clouds composed of liquid droplets or ice crystals both modulate the planet's radiation budget and directly affect climate.
For clouds composed of liquid droplets, the size and quantity of the drops determine how much solar radiation they will reflect. For example, low-level stratocumulus clouds cover vast areas of the ocean and strongly regulate the heating of the ocean by blocking solar radiation before it gets to the ocean surface. Polarimetry measurements from various angles offer the promise of more robust measurements of droplet size, which can range in diameter from about 10-30 micrometers or more. Even relatively small differences can be significant for climate.
For clouds composed of ice crystals, the radiative properties of the clouds are quite sensitive to crystal size, quantity and also shape. We learned from previous fieldwork that the size of particles in ice clouds is quite variable, spanning a large range compared to liquid clouds. Cirrus clouds, for example, can be composed of ice crystals
|Contact: Kathryn Hansen|
NASA/Goddard Space Flight Center