Browsing by Author "Koenig, Lora S."
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Item Brief communication: Mapping Greenland's perennial firn aquifers using enhanced-resolution L-band brightness temperature image time series(EGU, 2020-09-02) Miller, Julie Z.; Long, David G.; Jezek, Kenneth C.; Johnson, Joel T.; Brodzik, Mary J.; Shuman, Christopher; Koenig, Lora S.; Scambos, Ted A.Enhanced-resolution L-band brightness temperature (Tʙ) image time series generated from observations collected over the Greenland Ice Sheet by NASA’s Soil Moisture Active Passive (SMAP) satellite are used to map Green land’s perennial firn aquifers from space. Exponentially decreasing L-band Tʙ signatures are correlated with perennial firn aquifer areas identified via the Center for Remote Sensing of Ice Sheets (CReSIS) Multi-Channel Coherent Radar Depth Sounder (MCoRDS) that was flown by NASA’s Operation IceBridge (OIB) campaign. An empirical algorithm to map extent is developed by fitting these signatures to a set of sigmoidal curves. During the spring of 2016, perennial firn aquifer areas are found to extend over ∼ 66 000 km².Item A Satellite-Derived Climate-Quality Data Record of the Clear-Sky Surface Temperature of the Greenland Ice Sheet(AMS, 2012-07-15) Hall, Dorothy K.; Comiso, Josefino C.; DiGirolamo, Nicolo E.; Shuman, Christopher; Key, Jeffrey R.; Koenig, Lora S.The authors have developed a climate-quality data record of the clear-sky surface temperature of the Greenland Ice Sheet using the Moderate-Resolution Imaging Spectroradiometer (MODIS) ice-surface temperature (IST) algorithm. Daily and monthly quality-controlled MODIS ISTs of the Greenland Ice Sheet beginning on 1 March 2000 and continuing through 31 December 2010 are presented at 6.25-km spatial resolution on a polar stereographic grid along with metadata to permit detailed accuracy assessment. The ultimate goal is to develop a climate data record (CDR) that starts in 1981 with the Advanced Very High Resolution Radiometer (AVHRR) Polar Pathfinder (APP) dataset and continues with MODIS data from2000 to the present, and into the Visible Infrared Imager Radiometer Suite (VIIRS) era (the first VIIRS instrument was launched in October 2011). Differences in the APP and MODIS cloud masks have thus far precluded merging the APP and MODIS IST records, though this will be revisited after the APP dataset has been reprocessed with an improved cloud mask. IST of Greenland may be used to study temperature and melt trends and may also be used in data assimilation modeling and to calculate ice sheet mass balance. The MODIS IST climate-quality dataset provides a highly consistent and well-characterized record suitable for merging with earlier and future IST data records for climate studies. The complete MODIS IST daily and monthly data record is available online.Item Variability in the surface temperature and melt extent of the Greenland ice sheet from MODIS(AGU, 2013-02-12) Hall, Dorothy K; Comiso, Josefino C.; DiGirolamo, Nicolo E.; Shuman, Christopher; Box, Jason E.; Koenig, Lora S.Satellite-derived moderate-resolution imaging spectro-radiometer (MODIS) ice-surface temperature (IST) of the Greenland ice sheet shows a positive trend and two major melt events from 2000 to present. IST increased by ~0.55 ± 0.44°C/decade, with the greatest increase (~0.95 ± 0.44°C/decade) found in northwestern Greenland where coastal temperatures and mass loss are also increasing and outlet glaciers are accelerating. IST shows the highest rates of increase during summer (~1.35 ± 0.47°C/decade) and winter (~1.30 ± 1.53°C/decade), followed by spring (~0.60 ± 0.98°C/decade). In contrast, a decrease in IST was found in the autumn (~-1.49 ± 1.20°C/decade). The IST trends in this work are not statistically significant with the exception of the trend in northwestern Greenland. Major surface melt (covering 80% or more of the ice sheet) occurred during the 2002 and 2012 melt seasons where clear-sky measurements show a maximum melt of ~87% and ~95% of the ice sheet surface, respectively. In 2002, most of the extraordinary melt was ephemeral, whereas in 2012 the ice sheet not only experienced more total melt, but melt was more persistent, and the 2012 summer was the warmest in the MODIS record (-6.38 ± 3.98°C). Our data show that major melt events may not be particularly rare during the present period of ice sheet warming. Citation: Hall, D. K., J. C. Comiso, N. E. DiGirolamo, C. A. Shuman, J. E. Box, and L. S. Koenig (2013), Variability in the surface temperature and melt extent of the Greenland ice sheet from MODIS, Geophys. Res. Lett., 40, 2114–2120, doi:10.1002/grl.50240.