Colloquium: Kirk Knobelspiesse

TITLE: Multi-angle polarimetry: the once and future king (of aerosol remote sensing)

ABSTRACT: One of the largest sources of uncertainty in our understanding of climate is the role of particulate matter in the atmosphere (aka aerosols) and their interactions with clouds. Satellite observations can provide the needed observations to reduce this uncertainty, but existing instruments are fundamentally information limited. This means that assumptions must be made during an observation about aerosol optical properties, which limits the value of such observations for climate. Existing instruments, while incredibly useful, simply cannot measure all that is needed by the climate modeling community.

For these reasons, instruments have been developed that maximize information observed in a scene. They do so by observing a scene at multiple viewing angles, and by determining the polarization state of the reflected radiation. The Aerosol Polarimetry Sensor (APS) on the NASA Glory Mission was once such instrument, which unfortunately did not successfully reach orbit during its 2011 launch. Future NASA missions that may have multi-angle polarimeters include the phase A Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) Mission and the pre-phase A Aerosol/Clouds/Ecosystems Mission. There is also a robust airborne instrument community and international efforts to create such instruments.

I will give an overview of why multi-angle polarimetry is useful, its history in planetary and earth observations, and some details about polarimetric observational units. Inspired by a 2015 Army Research Office sponsored workshop, I’ll also discuss gaps, challenges and future research directions of this community.