Recalibration of Coupled Optical/Thermal MODIS Infrared Surface Melt Magnitude Retrieval During the Spatially-Extensive 2012 Greenland Ice Sheet Melt Event

Satellite based assessments of melt from passive microwave systems are typically used to detect the presence of surface melt on ice sheets and ice shelves, although they are limited in that they only provide an indication of melt occurrence and have coarse spatial resolution. This works further develops an algorithm for retrieving surface melt magnitude using coupled near-IR and thermal surface measurements from MODIS, calibrated by estimates of liquid water fraction (LWF) in the upper 1cm of the firn derived from a one-dimensional thermal snowmelt model (SNTHERM). SNTHERM was forced by hourly meteorological data from automatic weather station (AWS) data at several reference sites spanning a range of melt conditions across the Greenland Ice Sheet during the most extensive melt season in the MODIS satellite record, 2012. Effective melt magnitude or LWF was derived for 8-day composite periods covering the summer months of July and August at a 1km resolution over the entire ice sheet. This work represents a step forward in characterizing not only melt occurrence and duration but also melt magnitude, and at a higher spatial resolution than current passive microwave melt detection methods. Calibration using the 2012 melt season will allow detection of a wider range of surface melt conditions than prior assessments.