Passive Microwave Melt Onset Retrieval Based on a Variable Threshold: Assessment in the Canadian Arctic Archipelago

Abstract

The Canadian Arctic Archipelago (CAA) presents unique challenges to the determination of melt onset (MO) using remote sensing data. High spatial resolution data is required to discern melt onset among the islands and narrow waterways of the region. Current passive microwave retrievals use daily averaged 19 GHz and 37 GHz data from the multi-channel microwave radiometer (SMMR) and/or the special sensor microwave/imager (SSM/I). The development of a new passive microwave melt onset method capable of using higher resolution data is desirable. The new passive microwave melt onset method described here, named the Dynamic Threshold Variability Method (DTVM), uses higher resolution data from the 37 GHz vertically-polarized channel from the advanced microwave scanning radiometers (AMSR-E and AMSR-2). The DTVM MO detection methodology differs from previously presented passive microwave Arctic MO methods in that it does not use a fixed threshold of a brightness temperature parameter. Instead, the DTVM determines MO dates based on the distribution of dates corresponding to the exceedance of a range of brightness temperature variability thresholds. The method also uses swath data instead of daily averaged brightness temperatures, which is found to lead to improved melt detection. Two current passive microwave MO methods are compared and evaluated for applicability in the CAA alongside the DTVM. The DTVM provides MO dates at a higher spatial resolution than earlier methods in addition to higher correlation with MO dates from surface air temperature (SAT) reanalyses. It is found that, for some years, MO dates in the CAA exhibit a latitudinal dependence, while in other years the MO dates in the CAA are relatively uniform across the domain.

Sea ice and snow phenology in the Canadian Arctic Archipelago from 1997 to 2018

“…While first open water will be later than sea ice melt onset, the weak negative trend in first open water dates (-2.91 d decade -1 , p > 0.05) is consistent with findings from previous studies, highlighting that no significant trends in melt onset dates were found in the CAA (e.g. Mahmud et al 2016;Marshall et al 2019); while other Arctic regions (e.g. Baffin Bay, Eastern Greenland, Barents Sea, Beaufort Sea, and Chukchi Sea) have shown significantly earlier melt onset by 2.3 to 6.9 d decade -1 (e.g.…”

Estimating Meltwater Drainage Onset Timing and Duration of Landfast Ice in the Canadian Arctic Archipelago Using AMSR-E Passive Microwave Data

“…Figure 3 shows the time series of the AMSR-E MPF and daily average 2 m air temperature in the ERA5 dataset provided by the European Centre for Medium-Range Weather Forecasts (ECMWF, https://www.ecmwf.int/). The MO date is obtained by using the dynamic threshold variability method based on 36.5 GHz vertically polarized T B data [20]. The FO date is retrieved from the melt/freeze-up algorithm, using 19 and 37 GHz vertically polarized T B data [18].…”

“…These data points outside the possible melt season are problematic and are not to be included; we only used the realistic time series over 10/10 ice concentration and between the MO and FO dates, as the black circles in Figure 3 show. If the threshold of the MO is not determined due to the high inter-quartile range in the histogram of the potential MO [20], a data point of more than 0 • C air temperature is used for determining a realistic time series.…”

“…Satellite passive microwave and optical remote sensing is useful for monitoring the entire polar regions daily [15,16], although optical remote sensing is limited by cloud cover when observing sea ice conditions. Although the timing of melt onset (MO) has been derived using passive microwave remote sensing [17][18][19][20], little is known about large-scale DO timing and DD in the melt season.…”

Potential of Melt Pond Fraction Retrieval From High Spatial Resolution AMSR-E/2 Channels

“…[11], respectively. In 2012, the MO detections using [9] are not possible since the AMSR2 data are available from 4 July. MO in 2012 is instead detected using the melt/freeze-up algorithm 10].…”