NSCAT-Derived Antarctic Sea-Ice Extent -------------------------------------- OVERVIEW -------- This data set consists of files of ice masked SIRF images of the Arctic and Antarctic as well as the lat,lon extent of Arctic and Antarctic sea ice from JD 258, 1996 through JD 179, 1997. Each file represents an "average" ice extent over a 6 day periods. The time periods overlap on 3 day centers. However, until about 1996 JD 300 the data set is not continuous due to periods of missing NSCAT data early in the mission. In some cases, the ice mapping algorithm obviously failed in small localized regions of the ice edge. In such situations, the edges were manually edited to improve the quality of the edges. When editing has been performed, it is noted in the header information of the SIR files. The ASCII files contain latitude/longitude pairs which represent the contour points of the estimated sea ice edge (including edited changes to the edge when they exist). Each line entry in the file consists of two values: a longitude and a lattitude. The longitude values range from -180 to +180. Multiple contours are separated by a '0 0' entry. IMAGE RECONSTRUCTION METHODOLOGY -------------------------------- The ice extent maps were made from enhanced resolution backscatter images created by the Microwave Earth Remote Sensing (MERS) Laboratory at Brigham Young University (BYU) using the Scatterometer Image Reconstruction with Filtering (SIRF) resolution enhancement algorithm. The multivariate SIRF algorithm is a non-linear resolution enhancement algorithm based on modified algebraic reconstruction and maximum entropy techniques. The algorithm is described in detail in: Long, D.G., P.J. Hardin, and P.T. Whiting, "Resolution Enhancement of Spaceborne Scatterometer Data," IEEE Trans. Geoscience Remote Sens., Vol. 31, No. 3, pp. 700-715, May 1993. The SIRF algorithm has been successfully applied to SASS and NSCAT measurements to study tropical vegetation and glacial ice. Variants of SIRF has been successfully applied to ERS-1 scatterometer and various radiometers (SSM/I and SMMR). For scatterometers, the multivariate form of the SIRF algorithm models the dependence of sigma-0 on incidence angle as sigma-0 (in dB) = A + B * (Inc Ang - 40 deg) over the incidence angle range of 15 to 60 deg. The output of the SIRF algorithm is images of the A and B coefficients. A represents the "incidence angle normalized sigma-0" (effectively the sigma-0 value at 40 deg incidence angle). The units of A are dB. The B coefficient describes the incidence angle dependence of sigma-0 and has the units of dB/deg. SEA ICE MAPPING METHODOLOGY --------------------------- The polarization ratio (AV-AH in dB), vertical incidence angle dependence (BV), and the sigma-0 estimate error standard deviation were used to perform the sea ice/ocean discrimination. The ice/ocean modes of the bimodal AV-AH vs. BV distribution were separated using linear and quadratic techniques. The sigma-0 estimate error standard deviation threshold was used as the deciding factor when the linear and quadratic extent estimates disagreed. Residual misclassification noise was reduced using binary image processing techniques such as region growing, erosion, and dilation resulting in a low pass filtered version of the edge. The resulting edge closely matches the NSIDC SSM/I-derived 30% ice concentration edge. The lat/lon values in the ASCII edge files were obtained by computing the lat/lon location of each pixel along the edge of the binary ice mask. Note that in cases obvious algorithm ice extent errors, the edges have been manually edited. For a more detailed description of the ice extent algorithm see: Remund, Q.P., Long, D.G., "Automated Antarctic Ice Edge Detection Using NSCAT Data," Proc. IGARSS'97, pp. 1841-1843, Singapore, 4-8 August, 1997. Remund, Q.P., Long, D.G., "Sea-Ice Extent Mapping Using Ku-Band Scatterometer Data," to appear, Journal of Geophysical Research, 1998. DATA USE -------- (c) Data is copyright 1998 by David G. Long at Brigham Young University. Any use of these images should include a citation to appropriate paper(s) below and the following acknowledgement: "Ice extent images (or maps) are courtesy of David G. Long at Brigham Young University generated from data obtained from the PO.DAAC." Remund, Q.P., Long, D.G., "Sea-Ice Extent Mapping Using Ku-Band Scatterometer Data," to appear, Journal of Geophysical Research, 1998. Long, D.G., P.J. Hardin, and P.T. Whiting, "Resolution Enhancement of Spaceborne Scatterometer Data," IEEE Trans. Geoscience Remote Sens., Vol. 31, No. 3, pp. 700-715, May 1993 Please send copies of all papers, reports, or presentations using this data to the JPL PO.DAAC and David Long. Use of this data is contingent on meeting these requirements. ============================================================================== Dr. David G. Long long@ee.byu.edu Associate Professor voice: (801) 378-4383 Electrical and Computer Engineering Department fax: (801) 378-6586 459 Clyde Building Brigham Young University Provo, Utah 84602 BYU Electrical and Computer Engineering home page: http://www.ee.byu.edu/ BYU Microwave Earth Remote Sensing (MERS) Laboratory home page: http://www.ee.byu.edu/ee/mers/ or http://mers.byu.edu/ ============================================================================== Last revised: 19 Nov. 1998