This data set provides sea ice extent for the Arctic (60-90 degrees North) and Antarctic (52-90 degrees South) in Scatterometer Image Reconstruction (SIR) binary image format, along with ASCII text files containing latitude and longitude coordinates along the sea ice edge, and browse images of SIR files in Graphics Interchange Format (GIF) format. Ancillary products include daily-averaged total ... sea ice extent in ASCII format. Estimates of sea ice extent were produced from daily-averaged QuikSCAT sigma-0 measurements and extend from 19 July 1999 to 31 December 2009. QuikSCAT obtains 12 individual radar normalized backscatter (sigma-0) measurements, called slices, for each footprint as it scans over a 1800 km wide swath. Slices are typically 4 to 6 km long by 20 km wide. The summed measurements of the slices are called egg measurements. The effective resolution and shape of each egg measurement is approximately 20 by 30 km, depending on the antenna beam and instrument mode. This data set contains both slice and egg images for each day. The Microwave Earth Remote Sensing (MERS) group at Brigham Young University (BYU) developed a SIR-with-filtering (SIRF) algorithm that combines forward- and aft-looking sigma-0 measurements to produce enhanced-resolution backscatter images over various azimuth angles. The polarization ratio, incidence angle dependence, and the sigma-0 estimate error standard deviation were used to discriminate between sea ice and ocean. Sea ice extent was estimated for both slice and egg images. The nominal pixel resolution of the slice images is 2.225 km with an estimated effective resolution of approximately 4 km. Egg images have a nominal pixel resolution of 4.45 km with an estimated effective resolution of approximately 8 to 10 km. Data and browse images are available via FTP, along with C, Fortran, and Interactive Data Language (IDL) tools to read and display the SIR images.
Sea ice extent images were manually checked for spatial and temporal consistency. NSIDC noticed some inconsistencies in the ice extents from QuikSCAT. Slice images appear much noisier than egg images in the Arctic, particularly in 2003 and 2004. Antarctic ice extents should match well between QuikSCAT and Special Sensor Microwave/Imager (SSM/I) using a 30% ice concentration threshold, but a ... preliminary analysis shows they match well even with a 15% threshold. In the Arctic, SSM/I shows much greater winter ice extents compared to QuikSCAT. The differences in arctic ice extent between SSM/I and QuikSCAT may relate to the physical properties of the ice, in the sense that QuikSCAT does not 'see' the first-year ice as readily as it sees the more highly scattering multiyear ice. In the Antarctic -- where pancake ice, frazil ice formation, and refrozen snow slush at the snow/ice interface are prevalent -- scattering is sufficient enough to yield similar extent results between SSM/I and QuikSCAT scatterometer data. This data set is unchanged from the original format. An improved version of this data set will be available in the future.
Any use of images or data should include the following acknowledgement and citations: 'Ice extent images (or maps) are courtesy of David G. Long at Brigham Young University, generated by the Scatterometer Climate Record Pathfinder project from data obtained from the PO.DAAC.' Early, D.S., and and D.G. Long. 2001. Image reconstruction and enhanced resolution imaging from irregular samples. IEEE ... Transactions on Geoscience and Remote Sensing 39(2): 291-302. Long, D.G. 2004. NASA SCP arctic and antarctic ice extent from QuikSCAT, 1999-2004. Boulder, CO, USA: National Snow and Ice Data Center. Digital media. Remund, Q.P., and D.G. Long. 1999. Sea ice extent mapping using Ku-band scatterometer data. Journal of Geophysical Research 104(C5): 11515-11527. Please send reprints of papers, reports, or presentations using these data to NSIDC User Services, the Physical Oceanography Distributed Active Archive Center (PO.DAAC) and David Long.
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Early, D.S., and and D.G. Long. 2001. Image Reconstruction and Enhanced Resolution Imaging from Irregular Samples. IEEE Transactions on Geoscience and Remote Sensing 39(2): 291-302. Jet Propulsion Laboratory. 2001. QuikSCAT Science Data Product User's Manual, Version 2.2.View PDF (346 KB). Kramer, H.J. 1994. Observation of the Earth and its Environment. New York: Springer-Verlag. Long, D. 2000. ... Standard BYU QuikScat/Seawinds Land/Ice Image Products, Revision 2.0. Unpublished report. Provo, UT: Microwave Earth Remote Sensing Laboratory, Brigham Young University. View PDF (1.2 MB). Long, D.G., and M.R. Drinkwater. 2000. Azimuth Variation in Microwave Scatterometer and Radiometer Data over Antarctica. IEEE Transactions on Geoscience and Remote Sensing 38(4): 1857-1870. Long, D.G., and M.R. Drinkwater. 1999. Cryosphere Applications of NSCAT Data. IEEE Transactions Geoscience and Remote Sensing 37(3): 1671-1684. Long, D.G., P.J. Hardin, and P.T. Whiting. 1993. Resolution Enhancement of Spaceborne Scatterometer Data. IEEE Transactions on Geosciences and Remote Sensing 32(3): 700-715. Remund, Q.P., and D.G. Long. 2000. Iterative Estimation of Antarctic Sea Ice Extent Using SeaWinds Data. Proceedings of the International Geoscience and Remote Sensing Symposium, Honolulu, HI, 24-28 July 2000, pp. 491-493. Remund, Q.P., and D.G. Long. 1999. Sea Ice Extent Mapping Using Ku-band Scatterometer Data. Journal of Geophysical Research 104(C5): 11515-11527. Remund, Q.P., and D.G. Long. 1998. Sea Ice Mapping Algorithm for QuikSCAT and Seawinds. Proceedings of the International Geoscience and Remote Sensing Symposium, Seattle, WA, 6-10 July 1998, pp. 1686-1688. Remund, Q.P., and D.G. Long. 1997. Automated Antarctic Ice Edge Detection Using NSCAT Data. Proceedings of the International Geoscience and Remote Sensing Symposium, Singapore, 4-8 August 1997, pp. 1841-1843. Scatterometer Climate Record Pathfinder (SCP). 'General BYU SIR file naming scheme.' 2004. http://www.scp.byu.edu/docs/SIRfilename.html. Accessed January 2005. Scatterometer Climate Record Pathfinder (SCP). 'NSCAT-Derived Antarctic Sea-Ice Extent.' 2004. http://www.scp.byu.edu/data/NSCAT/iceproduct/doc/sea-ice-extent. Accessed January 2005. Scatterometer Climate Record Pathfinder (SCP). 'QuikSCAT Ice Extent Products.' 2004. http://www.scp.byu.edu/data/Quikscat/Ice/Quikscat_ice.html. Accessed January 2005. Spencer, M.W., C. Wu, and D.G. Long. 2000. Improved Resolution Backscatter Measurements with the SeaWinds Pencil-beam Scatterometer. IEEE Transactions on Geoscience and Remote Sensing 38(1): 89-104.