Cryospheric and Polar Processes Seminar

Remote sensing of seasonal snow water equivalent: instruments of opportunity, systemic inertia, curiosity-driven science and future prospects

 by Dr. Richard Kelly - Department of Geography and Environmental Management, University of Waterloo, Ontario, Canada

The estimation of seasonal snow from space typically can be categorized into three variables of interest: snow presence, snow mass (or snow water equivalent, SWE) and snow wetness. The spectral signatures used to identify snow presence and snow wetness have a high contrast with non-snow surfaces that enable robust mapping of these variables for science and human applications. However, the recovery of satellite observation-based seasonal snow mass, or SWE, has been a more challenging aspiration of the snow remote sensing science community since 1978 when the Scanning Multichannel Microwave Radiometer (SMMR) instrument was launched. The objectives of SMMR, along with those of the more recent passive microwave instruments (SSMI, AMSR-E, AMSR2, etc.) typically do not consider SWE as a primary goal. Yet these instruments represent the most significant systems available for global long-term satellite SWE applications. While the signature physics of the microwave emission of snow at the local in situ scale is tractable, passive microwave snow emission signatures at the multi-kilometre satellite observation scales are complex on account of the mixing of spatially and time varying signatures across heterogenous snow-covered landscapes. Consequently, satellite passive microwave observing systems have offered tantalizing opportunities to estimate SWE and have succeeded in providing insights into dynamical snow-covered landscapes in some instances, but in other cases they struggle.  Yet arguably they have also contributed to systemic inertia in instrument science development; SWE is observable so why develop something new? Despite these impediments, the acknowledged value of these instruments of opportunity (the continuous passive microwave record is now 38 years long), and the absence of a dedicated global seasonal snow mission have impelled an increasing body of curiosity-driven and applied research into better understanding snow microphysics and landscape-scale distribution of SWE, and how snow interacts with active and passive visible-infrared and microwave radiation. This presentation provides a Canadian perspective on recent advances in knowledge from observation and modelling experiments in the microwave domain, and how future prospects for the satellite observation-based science can benefit.