Multiple direction/polarisation radiometers
"The category of ‘multiple direction/polarisation instruments’ is used to describe instruments that are custom-built for observing the directional or polarisational characteristics of the target’s signature (either visible/IR or microwave), as a means of deriving geophysical information. Multi-directional radiometers can make observations from more than one incidence angle of the transmitted or diffused radiation emitted by a particular element of Earth’s surface or clouds. In this way, information on anisotropies in the radiation may be identified. The emphasis in these instruments is on spectral (rather than spatial) information, with the result that the detection channels, which typically span the visible to the IR, are precisely calibrated and the spatial resolution is usually about 1 km. Polarimetric radiometers are used for applications in which radiative information is embedded in the polarisation state of the transmitted, reflected or scattered wave. Some polarimetric radiometers also have a multi-directional capability, so that directional information can be determined or used during retrievals of geophysical parameters." (ESA 2015)
European Space Agency (ESA). 2015. “Satellite Earth Observations in Support of Climate Information Challenges.” CEOS Earth Observation Handbook for COP21, 59.