Methodology:

Surface melt occurrence was estimated from brightness temperature (Tb) measurments from the following spaceborne sensors:

- Scanning Microwave Multichannel Radiometer (SMMR) onboard the Nimbus-7 satellite (1978-1987);

- Special Sensor Microwave/Imager (SSM/I) onboard successive satellites (F-8, F-11, and F13) from the Defense Meteorological Satellite Program (DMSP; 1987-2009);

- Special Sensor Microwave Imager Sounder (SSMIS) onboard DMSP F-17 satellite (2006-present).

The data were obtained from the National Snow and Ice Data Center on its South-Hemisphere Equal-Area Scalable Earth (EASE) Grid with a nominal resolution of 25 km, corresponding to NSIDC datasets 0071 (Armstrong et al., 1994) and 0032 (Knowles et al., 2000).

To identify surface melt, we used horizontally polarized Tb data in the K-band (18 GHz for SMMR, 19 GHz for SSM/I-SSMIS). These data were available twice-daily (from the ascending and descending satellite passes). Data gaps were filled (only if they did not exceed one day) by linearly interpolating the data from the two adjacent days. This was particularly important for SMMR data, which are available only every other day. To ensure temporal consistency of the melt data across the various sensors, all SMMR and SSM/I data were calibrated with respect to SSMIS F-17 using the regression coefficients derived by Jezek et al. (1991), Abdalati et al. (1995), Stroeve et al. (1998), and Nicolas et al. (2017).

The melt detection algorithm is similar to the one used by Nicolas et al. (2017). For a given grid cell and a given day, melt was identified as soon as one of the two daily Tb observations exceeded a threshold value (Tb melt) defined as Tb melt = Tb ref + deltaT, where deltaT = 30 K and Tb ref is a reference temperature. The value of deltaT was based on the work from Tedesco (2009). Tb ref was calculated as the 12-month average from 1 April-31 March after filtering out all melt days, as in Torinesi et al. (2003).

The data are provided on a reduced 200 x 300 grid (referred to as 'es25r grid') that is a subset of NSIDC's original 721 x 721 25-km South-Hemisphere EASE Grid (https://nsidc.org/data/ease). In our es25r grid, the first row corresponds to row 257 of the original grid and the first column corresponds to column 251 of the original grid. The resolution is 25 x 25 km.

The es25r grid covers the full range of longitudes (180°W to +180°E), and extends from the South Pole (90°S) to cover the Antarctic continent and ice shelves, with a Northern boundary at varying latitudes between 68.5°S and 53.8°S.

Data collection:

Instrumentation:

SMMR - Scanning Microwave Multichannel Radiometer

SSM/I - Special Sensor Microwave/Imager

SSMIS - Special Sensor Microwave Imager Sounder

Data quality:

Uncertainties could not be estimated for this dataset.