A satellite-based snow cover climatology (1985–2011) for the European Alps derived from AVHRR data

Abstract

Abstract. Seasonal snow cover is of great environmental and socio-economic importance for the European Alps. Therefore a high priority has been assigned to quantifying its temporal and spatial variability. Complementary to land-based monitoring networks, optical satellite observations can be used to derive spatially comprehensive information on snow cover extent. For understanding long-term changes in alpine snow cover extent, the data acquired by the Advanced Very High Resolution Radiometer (AVHRR) sensors mounted onboard the National Oceanic and Atmospheric Association (NOAA) and Meteorological Operational satellite (MetOp) platforms offer a unique source of information.In this paper, we present the first space-borne 1 km snow extent climatology for the Alpine region derived from AVHRR data over the period . The objective of this study is twofold: first, to generate a new set of cloudfree satellite snow products using a specific cloud gap-filling technique and second, to examine the spatiotemporal distribution of snow cover in the European Alps over the last 27 yr from the satellite perspective. For this purpose, snow parameters such as snow onset day, snow cover duration (SCD), melt-out date and the snow cover area percentage (SCA) were employed to analyze spatiotemporal variability of snow cover over the course of three decades. On the regional scale, significant trends were found toward a shorter SCD at lower elevations in the south-east and south-west. However, our results do not show any significant trends in the monthly mean SCA over the last 27 yr. This is in agreement with other research findings and may indicate a deceleration of the decreasing snow trend in the Alpine region. Furthermore, such data may provide spatially and temporally homogeneous snow information for comprehensive use in related research fields (i.e., hydrologic and economic applications) or can serve as a reference for climate models.

Snow Extent Variability in Lesotho Derived from MODIS Data (2000–2014)

“…It has been shown that the occurrence of single snowfall events, followed by rapid melting, necessitates a daily snow product to detect the amount of coverage in the country. The post-processing step is essential to fill gaps caused by cloud cover and to generate a continuous time series [12]. The combination of previously implemented methods, temporal filling of missing information and elevation based filling (SNOWL) is capable of reducing the amount of gaps significantly as shown by [50,53,56].…”

“…The primary objective is to reduce cloud cover (i.e., by making assumptions about the surface condition beneath the cloud cover). The following post-processing procedure is based on the application of a combination of spatial and temporal filters [12].…”

“…The accuracy of this method was assessed by [13] with data from 754 climate stations over Austria; the SNOWL method was found to produce robust snow cover maps, even under abundant cloud cover (i.e., 90% coverage). This method was also successfully applied by [12] to the European Alps using medium resolution AVHRR sensor data.…”

“…During the last years, many studies showed the benefit of remote sensing derived snow maps [10,11] for mountainous areas with ephemeral snow dynamic. Unfortunately, in this regions prevailing cloud cover limits monitoring of the ground but post-processing considering temporal and spatial characteristics of the snow cover minimizes these gaps [12,13]. Especially the MODIS sensor with 36 spectral bands and a reasonable resolution of 250 m-1000 m is an appropriate tool to monitor snow cover in mountains [14].…”

On the Importance of High-Resolution Time Series of Optical Imagery for Quantifying the Effects of Snow Cover Duration on Alpine Plant Habitat

“…Optical remote sensing provides the opportunity to address the question of snow cover regime changes at the regional scale, particularly in the context of mid-latitude study areas [13]. A decrease in snow-covered areas has been globally observed in the Northern Hemisphere since the end of the 1970s, when the first space borne optical sensors began to monitor the Earth's surface [14,15].…”