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remote sensing

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    NIWA maintains a retrieval system and a large archive for New Zealand satellite images. These satellite data are for sea surface temperature, chlorophyll analysis and satellite cloud imagery.

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    This Report assembles an eleven year time series for the period 2001 to 2011 of snow cover area in New Zealand. A dataset is prepared based on the MODIS/Terra Snow Cover 8-Day L3 Global 500m Grid, Version 5 data (MOD10A2.5, available from the National Snow and Ice Data Center NSIDC, Boulder, Colorado USA). The MOD10A2.5 dataset indicates the maximum snow cover extent over an eight-day compositing period. It provides a seamless coverage of snow presence at regularly spaced time intervals, while minimizing the obscuration by clouds. Each year is composed of 46 epochs, each of 8 consecutive days starting on the first day of the year and extending in to the next year. An algorithm based on a trajectory analysis of land cover through time is used to infer the status of remaining pixels obscured by cloud in the composite period. This leads to a time series of virtually cloud-free composite snow cover maps that are readily imported into GIS packages for analysis of spatial and temporal variability.