MODIS-based Mosaic of Antarctica (MOA) data sets: Continent-wide surface morphology and snow grain size

摘要

We present digital image mosaics of surface morphology and optical snow grain size for the Antarctic continent and surrounding islands, assembled from 260 Moderate-resolution Imaging Spectroradiometer (MODIS) images. The products are derived from MODIS band 1 (red light: ～647 nm) and band 2 (infrared: ～857 nm) orbit swath data acquired during the 2003-2004 austral summer. Multiple images of all areas are combined in a data cumulation scheme to improve spatial resolution and increase radiometric content of the mosaics. The component images were de-striped, geo-registered, and re-sampled to the projection grid using the MODIS Swath-to-Grid Toolbox (MS2GT) software. A 125 m ground-equivalent polar stereographic projection was used, identical to previous radar image mosaics and similar to several other continent-wide data sets. Geo-location accuracy of the final mosaics is better than 125 m. Swath acquisition times were limited to the range 05:00-13:30 UT to provide broad but uniform mosaic illumination. Regions of cloud cover, blowing snow, and intense forward scattering were masked prior to compositing. The MOA snow grain size data set image provides the first continent-wide semi-quantitative map of mean summer snow, firn, and blue ice grain size. Optical grain size (radius) was determined using a normalized difference index derived from MODIS band 1 and band 2 rad values. Atmospheric correction, adjustments for directional reflectance variation and snow grain size estimation were accomplished by a look-up table, generated by a combination of published models of snow spectral reflectance and atmosphere radiative transfer. Validation of the snow grain size image is provided by in situ spectra of snow-covered sea ice made in October, 2003. We use the new data sets to determine major ice shelf areas, and shelf edge, coastline, and ice grounding line vector files, and determine areas of selected blue ice regions. These data sets are available for download at http:/sidc.org/data/moa/.