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Markus, T, Neumann T, Martino A, Abdalati W, Brunt K, Csatho B, Farrell S, Fricker H, Gardner A, Harding D, Jasinski M, Kwok R, Magruder L, Lubin D, Luthcke S, Morison J, Nelson R, Neuenschwander A, Palm S, Popescu S, Shum CK, Schutz BE, Smith B, Yang YK, Zwally J.  2017.  The Ice, Cloud, and land Elevation Satellite-2 (ICESat-2): Science requirements, concept, and implementation. Remote Sensing of Environment. 190:260-273.   10.1016/j.rse.2016.12.029   AbstractWebsite

The Ice, Cloud, and land Elevation Satellite (ICESat) mission used laser altimetry measurements to determine changes in elevations of glaciers and ice sheets, as well as sea ice thickness distribution. These measurements have provided important information on the response of the cryopshere (Earth's frozen surfaces) to changes in atmosphere and ocean condition. ICESat operated from 2003 to 2009 and provided repeat altimetry measurements not only to the cryosphere scientific community but also to the ocean, terrestrial and atmospheric scientific communities. The conclusive assessment of significant ongoing rapid changes in the Earth's ice cover, in part supported by ICESat observations, has strengthened the need for sustained, high accuracy, repeat observations similar to what was provided by the ICESat mission. Following recommendations from the National Research Council for an ICESat follow-on mission, the ICESat-2 mission is now under development for planned launch in 2018. The primary scientific aims of the ICESat-2 mission are to continue measurements of sea ice freeboard and ice sheet elevation to determine their changes at scales from outlet glaciers to the entire ice sheet, and from 105 of meters to the entire polar oceans for sea ice freeboard. ICESat carried a single beam profiling laser altimeter that produced similar to 70 m diameter footprints on the surface of the Earth at similar to 150 m along-track intervals. In contrast, ICESat-2 will operate with three pairs of beams, each pair separated by about 3 km cross-track with a pair spacing of 90 m. Each of the beams will have a nominal 17 m diameter footprint with an along -track sampling interval of 0.7 m. The differences in the ICESat-2 measurement concept are a result of overcoming some limitations associated with the approach used in the ICESat mission. The beam pair configuration of ICESat-2 allows for the determination of local cross -track slope, a significant factor in measuring elevation change for the outlet glaciers surrounding the Greenland and Antarctica coasts. The multiple beam pairs also provide improved spatial coverage. The dense spatial sampling eliminates along -track measurement gaps, and the small footprint diameter is especially useful for sea surface height measurements in the often narrow leads needed for sea ice freeboard and ice thickness retrievals. The ICESat-2 instrumentation concept uses a low energy 532 nm (green) laser in conjunction with single-photon sensitive detectors to measure range. Combining ICESat-2 data with altimetry data collected since the start of the ICESat mission in 2003, such as Operation IceBridge and ESA's CryoSat-2, will yield a 15+ year record of changes in ice sheet elevation and sea ice thickness. ICESat-2 will also provide information of mountain glacier and ice cap elevations changes, land and vegetation heights, inland water elevations, sea surface heights, and cloud layering and optical thickness. Published by Elsevier Inc. This is an open access article under the CC BY license

Lubin, D, Lynch S, Clarke R, Morrow E, Hart S.  2003.  Increasing reflectivity of the Antarctic ocean-atmosphere system: Analysis of Total Ozone Mapping Spectrometer (TOMS) and passive microwave data for 1979-1994. Journal of Geophysical Research-Atmospheres. 108   10.1029/2002jd002702   AbstractWebsite

Measurements of Lambert equivalent reflectance at 380 nm from the Total Ozone Mapping Spectrometer (TOMS) instrument have shown increases in reflectivity between 1979 and 1994 over much of the Southern Ocean, encompassing 280degrees in longitude. These trends represent a possible change in the state of the Antarctic ocean-atmosphere system related to recent climate warming. To determine if these reflectivity trends are due to changes in cloud cover or sea ice, or both, the TOMS data were collocated with a contemporaneous passive microwave satellite data set from the scanning multichannel microwave radiometer and the Special Sensor Microwave Imager. The passive microwave data sets specify total sea ice concentration, retrieved by a uniform method for all years using the NASA Team algorithm. To first order the locations of TOMS reflectivity increases coincide with regions where sea ice concentration has increased over the past 2 decades, signifying that the TOMS trends are the result of trends in underlying sea ice and not cloud cover. However, when the TOMS reflectivity measurements are sorted into fixed sea ice concentration bins of 0.1 width, the TOMS data also show increasing reflectivity trends in regions where sea ice extent has been decreasing (Amundsen and Bellingshausen Seas and the Western Antarctic Peninsula). Over open water, TOMS reflectivity trends are less convincing and may be artifacts related to uncertainties in passive microwave sea ice identification. These results suggest that a significant component of the Southern Ocean TOMS reflectivity trends may be a gradual increase in the albedo of the underlying sea ice. This could be caused by a gradual lengthening of the sea ice season, with a concomitant increase in the persistence of dry snow on the sea ice cover.

Lubin, D.  1994.  Infrared Radiative Properties of the Maritime Antarctic Atmosphere. Journal of Climate. 7:121-140.   10.1175/1520-0442(1994)007<0121:irpotm>;2   AbstractWebsite

The longwave radiation environment of the Antarctic Peninsula and Southern Ocean has been investigated using radiometric Fourier Transform Infrared (FTIR) measurements of atmospheric emission in conjunction with detailed radiative transfer theory. The California Space Institute FTIR Spectroradiometer was deployed at Palmer Station, Antarctica (64 degrees 46'S, 64 degrees 04'W), where it made zenith sky emission measurements several times daily between 25 August 1991 and 17 November 1991. Emission spectra covered the entire middle infrared (5-20 mu m) with one inverse centimeter spectral resolution. For FTIR data obtained under cloudy skies, a least-squares algorithm is used to match the emission spectra with discrete-ordinate radiative transfer calculations that are based on marine cloud microphysics. This algorithm provides a determination of cloud emissivity, and useful estimates of cloud optical depth and equivalent radius of the droplet size distribution. Temperatures in the lower troposphere between 259 K and 273 K diminish the radiative importance of water vapor and enhance the importance of clouds and CO2 relative to midlatitudes. Springtime variability in stratospheric temperature and ozone abundance has a small but noticeable impact of about 1.0 W m(-2) on surface longwave flux under clear skies. The mid-IR window emissivities of low stratiform clouds are most often between 0.90 and 0.98, with few as large as unity. Most low stratiform clouds appear to have moderate mid-IR optical depth (5-10), but relatively large equivalent radius (9-11 mu m). However, clouds with base height between 1 and 2 km have noticeably smaller emissivities and optical depths. The emissivity of maritime antarctic clouds is determined to be smaller for a given liquid water path than the parameterization used in the NCAR Community Climate Model (CCM1), and an appropriate mass absorption coefficient for antarctic clouds is 0.065 m(2) g(-1) for the mid-IR window.