In the visible and near IR spectrum, these instruments allow for improved measurements of the scattering properties of particles such as aerosols, as well as measurement of the angular characteristics of the various contributions to the Earth’s radiation budget, including surface albedo. They also enable accurate measurement of parameters such as Normalised Difference Vegetation Indices (NDVI), which are used to assess vegetation state and crop yield at regional and global scales. MISR, currently flying on NASA’s Terra mission, is providing new types of information for scientists studying Earth’s climate, such as the partitioning of energy and carbon between the land surface and the atmosphere, and the regional and global impacts of different types of atmospheric particles and clouds.

Polarisation information is used to infer a variety of parameters, including the size and scattering properties of liquid water, cloud particles and aerosols, while providing additional information on the optical thickness and phase of clouds. Polarimetric radiometers also provide information on the polarisation state of the radiation backscattered from the Earth’s surface, supplementing measurements obtained from other land and sea imaging instruments. Such measurements are of interest in a range of applications from investigations of albedo and reflectance to agriculture and the classification of vegetation. ESA’s SMOS mission, launched in late 2009, usees an L-band (1.4 GHz) microwave interferometer to measure estimates of soil moisture (a key variable for numerical weather and climate models) and ocean surface salinity (important for ocean circulation models).