## 3 Current Data
### Multispectral Imagery  
As with historical imagery, near-real-time Landsat imagery is freely available, often for immediate download, making it very easy to consult and employ; both quick-looks and full-resolution imagery are available. Of particular interest to polar researchers, large amounts of Landsat data were combined to form the Landsat Image Mosaic of Antarctica (LIMA; lima.usgs.gov) [66]. Landsat 7 with the Enhanced Thematic Mapper Plus (ETM+) onboard was launched in 1999, and while a scan line corrector failed in 2003 [67], it continues to be in operation and used widely. Landsat 8 was launched in February 2013, with operational imagery beginning in April 2013. Landsat 8 adds three additional bands, reduces spectral autocorrelation, improves the signal-to-noise ratio and radiometric resolution (12-bit data) and has other enhancements [68]. In addition, the high-quality georeferencing of Landsat data is of considerable value to users. Landsat 8 acquisitions for the polar regions and cryosphere are an integral part of the long-term acquisition plan.  
At lower resolution, the MODIS sensors aboard Terra and Aqua continue to collect imagery. As the MODIS sensors are aging, they have already been joined by the VIIRS sensor (Visible Infrared Imaging Radiometer Suite) on Suomi-NPP. Similar to MODIS, VIIRS imagery has high temporal resolution and low spatial resolution. VIIRS products applicable to the polar regions are still under development, but will be available in the future. Current VIIRS imagery and derivative data records are available through NOAA CLASS ([[http://www.nsof.class.noaa.gov/](http://www.nsof.class.noaa.gov/)]([http://www.nsof.class.noaa.gov/](http://www.nsof.class.noaa.gov/))).  
Landsat, MODIS and VIIRS are NASA instruments, but there are many more multispectral imagers on other nationally- and commercially-run platforms. However, access to these often depends on affiliation or is limited by high cost. For example, affiliation with GLIMS (Global Land Ice Measurements from Space; [[http://www.glims.org/](http://www.glims.org/)]([http://www.glims.org/](http://www.glims.org/)) [69]) can enable free ASTER imagery, and U.S. federally-funded researchers can access submeter multispectral imagery through the Polar Geospatial Center's ([[http://www.pgc.umn.edu](http://www.pgc.umn.edu)]([http://www.pgc.umn.edu](http://www.pgc.umn.edu))) RapidIce Viewers ([[http://www.rapidice.org/viewer](http://www.rapidice.org/viewer)]([http://www.rapidice.org/viewer](http://www.rapidice.org/viewer))). Additionally, it is worthwhile noting that airborne multispectral and hyperspectral imagery is available for limited coverage areas from the U.K. Natural Environment Research Council (NERC) Airborne Research and Survey Facility (ARSF) via the NERC Earth Observation Data Centre (NEODC; [[http://www.neodc.rl.ac.uk/](http://www.neodc.rl.ac.uk/)]([http://www.neodc.rl.ac.uk/](http://www.neodc.rl.ac.uk/))). Finally, the IceBridge Digital Mapping System (DMS) provides geolocated and orthorectified high resolution natural color and panchromatic images for many IceBridge flight lines in both the Arctic and the Antarctic ([[http://nsidc.org/data/iodms1b](http://nsidc.org/data/iodms1b)]([http://nsidc.org/data/iodms1b](http://nsidc.org/data/iodms1b))[70]).