Rapid,high-resolution detection of environmental change over continental scales from satellite data – the Earth Observation Data Cube

The effort and cost required to convert satellite Earth Observation (EO) data into meaningful geophysical variables has prevented the systematic analysis of all available observations. To overcome these problems, we utilise an integrated High Performance Computing and Data environment to rapidly process, restructure and analyse the Australian Landsat data archive. In this approach, the EO data are assigned to a common grid framework that spans the full geospatial and temporal extent of the observations – the EO Data Cube. This approach is pixel-based and incorporates geometric and spectral calibration and quality assurance of each Earth surface reflectance measurement. We demonstrate the utility of the approach with rapid time-series mapping of surface water across the entire Australian continent using 27 years of continuous, 25?m resolution observations. Our preliminary analysis of the Landsat archive shows how the EO Data Cube can effectively liberate high-resolution EO data from their complex sensor-specific data structures and revolutionise our ability to measure environmental change.     

The continental terrace

The continental terrace, defined as the sediment and rock underlying the coastal plain, the continental shelf and continental slope, has been extensively explored during the last decade using seismic techniques. Some facts and theories about its structure and formation are reviewed.The development of the continental terrace is considered in three main stages: first, the formation of the major discontinuity between continent and ocean basin; second, the deposition of sedimentary strata; and third, the Quaternary modification of the continental terrace to form the present topography.The major discontinuity may be formed either by rifting of a continent or by accretion of a large mass of contorted continental terrace and continental rise sediments to a pre-existing edge of a continent. Both types of discontinuity may be either ancient or presently forming in an orogenic area. Sedimentary strata are built generally upwards and outwards but at most places development is modified either by basement structure, by current and slump erosion or by growth of organic and diapiric structures.During the Quaternary Era the terrace has been extensively modified as a result of large fluctuations of sea level. The present wide continental shelf and deep shelf break are at most places the result of wave planation and offshore deposition during the last low sea level and during the subsequent rise of sea level. The final process at many places has been formation of a Holocene coastal plain and deposition of a prism of sediment on the inner continental shelf.Most continental terraces show evidence of continental flexure, which is the seaward tilting of land and seabed with a zero isobase, a line of no vertical movement, close to the shore. The reasons for continental flexure are discussed. The relative positions of the shore line, the zero isobase and the boundary between erosion and deposition are controlled by rates of tilting, by rates of sedimentary processes and by eustatic movements of sea level.From an assessment of the general processes operating today, some conclusions are reached about the changes in form and topography of continental terraces of the past.     

Vector magnetic fields in sunspots

Observations of a round, unipolar sunspot in the Zeeman triplet Fe i 6302.5 with the High Altitude Observatory Stokes Polarimeter are used to derive the vector magnetic field in the spot. The behavior of the magnitude, inclination, and azimuth of the field vector B across the spot is discussed. A linear relation is found between the continuum intensity I _c and the field magnitude B. Time series obtained in the umbra show significant power in the magnitude of the field at a period of t 180 s but the other components of the field vector do not display this behavior.The National Center for Atmospheric Research is sponsored by the National Science Foundation.