Validating improved-MODIS products from spectral mixture-Landsat snow cover maps in a mountain region in southern Spain
2018
Abstract. Remote sensing is the only feasible data source for distributed
modelling of snow in mountain regions on medium to large scales, due to the
limited access to these areas together with the lack of dense ground
monitoring stations for snow variables. Observations worldwide identify snow
cover persistence together with snowfall occurrence as the most affected
variables by global warming. In Mediterranean regions, the spatiotemporal
evolution of the snow cover can experiment quick changes that result in
different accumulation-ablation cycles during the cold season. High frequency
sensors are required to adequately monitor such shifts; however, for trend
analyses, the Landsat time series constitute the only available source of
data, being their frequency low for this regime, especially when cloudy
conditions limit the available images. On the other hand, the MODIS daily
series provide more than 15 years of continuous snow maps, despite the
spatial resolution may pose a constraint in areas with abrupt topography;
several approaches have been done to improve their spatial resolution from
combining different information. This work presents a methodological approach
to validate the improved MODIS daily snow cover maps from Notarnicola et al. (2013a, b),
with 250 m spatial resolution, in Sierra Nevada (southern Spain),
from a reference data set obtained by spectral mixture analyses of Landsat TM
data by Pimentel et al. (2017b). This reference time series of fractional
snow maps, with 30 m spatial resolution, were validated from high resolution
local time series of snow maps obtained by terrestrial time-lapse cameras.
The results show a significantly high correlation between the two snow map
products both on a global and basin scales in the Sierra Nevada area.
Selected areas and time periods are shown to address the convergence and
divergence between both products and assess the development of a fusion
algorithm to retrieve daily Landsat-resolution snow maps on a long term
basis.
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