Abstract
Abstract. Time series of brightness temperatures (TB) from the Advanced Microwave Scanning Radiometer–Earth Observing System (AMSR-E) are examined to determine ice phenology variables on the two largest lakes of northern Canada: Great Bear Lake (GBL) and Great Slave Lake (GSL). TB measurements from the 18.7, 23.8, 36.5, and 89.0 GHz channels (H- and V- polarization) are compared to assess their potential for detecting freeze-onset/melt-onset and ice-on/ice-off dates on both lakes. The 18.7 GHz (H-pol) channel is found to be the most suitable for estimating these ice dates as well as the duration of the ice cover and ice-free seasons. A new algorithm is proposed using this channel and applied to map all ice phenology variables on GBL and GSL over seven ice seasons (2002–2009). Analysis of the spatio-temporal patterns of each variable at the pixel level reveals that: (1) both freeze-onset and ice-on dates occur on average about one week earlier on GBL than on GSL (Day of Year (DY) 318 and 333 for GBL; DY 328 and 343 for GSL); (2) the freeze-up process or freeze duration (freeze-onset to ice-on) takes a slightly longer amount of time on GBL than on GSL (about 1 week on average); (3) melt-onset and ice-off dates occur on average one week and approximately four weeks later, respectively, on GBL (DY 143 and 183 for GBL; DY 135 and 157 for GSL); (4) the break-up process or melt duration (melt-onset to ice-off) lasts on average about three weeks longer on GBL; and (5) ice cover duration estimated from each individual pixel is on average about three weeks longer on GBL compared to its more southern counterpart, GSL. A comparison of dates for several ice phenology variables derived from other satellite remote sensing products (e.g. NOAA Interactive Multisensor Snow and Ice Mapping System (IMS), QuikSCAT, and Canadian Ice Service Database) show that, despite its relatively coarse spatial resolution, AMSR-E 18.7 GHz provides a viable means for monitoring of ice phenology on large northern lakes.
Highlights
Lake ice cover is an important component of the terrestrial cryosphere for several months of the year in high-latitude regions (Duguay et al, 2003)
The objectives of this paper are to (i) evaluate the utility of Advanced Microwave Scanning Radiometer–Earth Observing System (AMSR-E) TB measurements for estimating lake ice phenology, (ii) develop a comprehensive algorithm for mapping lake ice phenology variables, and (iii) apply the algorithm over both Great Bear Lake (GBL) and Great Slave Lake (GSL) to investigate the spatio-temporal variability of each lakes ice phonology from 2002 to 2009
In addition to the effect of fall temperature in explaining earlier/later freeze onset (FO) dates, an early ice break-up and warmer summer of the preceding months can result in the late onset of freeze-up for the two large, deep, lakes that store a considerable amount of heat during the open water season (Brown and Duguay, 2010)
Summary
Lake ice cover is an important component of the terrestrial cryosphere for several months of the year in high-latitude regions (Duguay et al, 2003). When energy movement occurs during temperature change, heat transfer (thermodynamics) influences ice thickening as well as the timing and duration of freeze-up and break-up processes, which is referred to as ice phenology (Jeffries and Morris, 2007). Lake ice phenology, which encompasses freeze-onset/melt-onset, ice-on/ice-off dates, and ice cover duration, is largely influenced by air temperature changes and is a robust indicator of climate conditions The large change in emissivity from open water (ε = 0.443– 0.504 at 24 GHz) to ice covered conditions (ε = 0.858–0.908 at 24 GHz) (Hewison and English, 1999; Hewison, 2001) makes the determination of the timing of ice formation and decay on large, deep lakes, feasible from TB measurements. The emissivity of ice, and TB, further increases from its initial formation as the effect of the radiometrically cold water under the ice cover decreases with ice thickening (Kang et al, 2010)
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