School of Surveying, University of Otago. PO Box 56, Dunedin, New Zealand; CSIR-NRE Earth Observation Research Group, Building 33, PO Box 395, Pretoria, 0001, South Africa; IRD-Great Ice, Laboratoire de Glaciologie et Géophysique de l'Environnement, 54 Rue Molière, 38402 Saint Martin d'Heres cedex, France
Sirguey, P., School of Surveying, University of Otago. PO Box 56, Dunedin, New Zealand; Mathieu, R., School of Surveying, University of Otago. PO Box 56, Dunedin, New Zealand, CSIR-NRE Earth Observation Research Group, Building 33, PO Box 395, Pretoria, 0001, South Africa; Arnaud, Y., IRD-Great Ice, Laboratoire de Glaciologie et Géophysique de l'Environnement, 54 Rue Molière, 38402 Saint Martin d'Heres cedex, France
This study describes a comprehensive method to produce routinely regional maps of seasonal snow cover in the Southern Alps of New Zealand (upper Waitaki basin) on a subpixel basis, and with the MODerate Resolution Imaging Spectroradiometer (MODIS). The method uses an image fusion algorithm to produce snow maps at an improved 250 m spatial resolution in addition to the 500 m resolution snow maps. An iterative approach is used to correct imagery for both atmospheric and topographic effects using daily observations of atmospheric parameters. The computation of ground spectral reflectance enabled the use of image-independent end-members in a constrained linear unmixing technique to achieve a robust estimation of subpixel snow fractions. The accuracy of the snow maps and performance of the algorithm were assessed carefully using eight pairs of synchronic MODIS/ASTER images. 'Pixel-based' metrics showed that subpixel snow fractions were retrieved with a Mean Absolute Error of 6.8% at 250 m spatial resolution and 5.1% after aggregation at 500 m spatial resolution. In addition, a 'feature-based' metric showed that 90% of the snowlines were depicted generally within 300 m and 200 m of their correct position for the 500-m and 250-m spatial resolution snow maps, respectively. A dataset of 679 maps of subpixel snow fraction was produced for the period from February 2000 to May 2007. These repeated observations of the seasonal snow cover will benefit the ongoing effort to model snowmelt runoff in the region and to improve the estimation and management of water resources. © 2008 Elsevier Inc. All rights reserved.
Agglomeration; Atmospherics; Conformal mapping; Data fusion; Fusion reactions; Hydraulic models; Image fusion; Maps; Optical projectors; Spectrometers; Water management; Water resources; Accuracy assessments; Atmospheric parameters; Comprehensive methods; End-members; Fusion algorithms; Iterative approaches; Linear unmixing; Mean absolute errors; Moderate resolution imaging spectro radiometers; MODIS; MODIS/ASTER; Mountainous terrain; New zealand; Regional maps; Robust estimations; Seasonal snow covers; Snowmelt runoffs; Spatial resolution.; Spatial resolutions; Spectral reflectances; Spectral unmixing; Sub pixels; Subpixel snow fraction; Topographic effects; Precipitation (meteorology); accuracy assessment; algorithm; alpine environment; environmental monitoring; mapping method; MODIS; pixel; snow cover; spatial resolution; Australasia; New Zealand; South Island; Southern Alps
