Boundary layer remote sensing with combined active and passive techniques: GPS radio occultation and high-resolution visible imaging (WindCam) small satellite concept

Observation of the cloudy boundary layer from satellite poses enormous remote sensing challenges. Sensor systems must resolve fine scale structure in the lowest few km of the atmosphere (horizontal scales < 10 km, vertical < 200 m), often in the presence of partial or complete cloud cover. A new concept is being developed that combines high vertical resolution active sounding (GPS radio occultation–GPSRO) with high horizontal resolution multi-angle visible imaging (WindCam). The Decadal Survey missions planned over the next 1-2 decades do not directly address observations of the cloudy boundary layer, despite the fact that boundary layer processes are known to play a key role in climate feedback. The following missions will benefit from improved BL observations: SMAP, ICESAT-2, CLARREO, ASCENDS and OCO-2. The GPSRO+WindCam concept will significantly improve the overall science return from these and other missions, and yet it is implementable as a pair of small satellites. Significant remote sensing challenges in developing the concept must be addressed, including improved RO retrievals of temperature and water vapor in the boundary layer. RO retrievals must be combined with WindCam-like observations of cloud top heights and winds. We present case studies of combined RO with MISR observations to describe candidate retrieval methods being developed.