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Continuous Vis-Near Characterization of snow-ice surface in Ny-Ålesund (SnowIceCReM)
IADC_id: 16
active
Call year: 2015
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The Global Change studies consider the Earth as a complex systems in which the polar areas play a very peculiar role; in particular the analysis of the snow and ice surfaces can offer the best option to monitor changes through time. To continuously monitor the cryosphere, specific satellite missions were scheduled, equipped with sensors able to collect images in the whole spectral range from visible to microwave. rnCoupling remote sensed images and field data it is possible to derive from remote sensed images not only the spatial distribution of snow/ice covers but also information about their physical characteristics. In particular, using images collected by optic passive sensors, that measure the surface reflectance in the wavelength between 400 and 2500nm, it is possible to derive information on micro-physical characteristics of the snow surface or on the presence of liquid water in the first layer of the snow pack. rnSnow optical properties in the visible and near-infrared wavelengths depend on snow grain shape and size, occurrence of impurities (dust, soot, pollen and other plant materials) and liquid water content. In particular, snow reflectance is higher in the visible part of the electromagnetic spectrum, while decreases rapidly at longer wavelengths. Field data and numerical models reveal that the increase of grain size determines a decrease of reflectance all over the spectral range from visible to short wave infrared (350-2500 nm) but it is still hard to define quantitatively how the grain shapes can modify the snow reflectance. Furthermore, the presence of liquid water between snow crystals increases the solar radiation absorption inducing albedo decrease.rnIt is well known as the snow cover in polar areas are extremely sensitive to small variations in weather conditions such as the presence of wind (rounding grain surfaces for saltation) or changes in air temperature (surface melting-freezing , snowpack metamorphism).rnCurrently the continuous monitoring of such areas still presents some problems, first of all the difficulty of obtaining a multi or hyperspectral images without cloud cover. rnWhile measurements of broad band albedo are performed continuously from different observatory, i.e. at the Climate Change tower (CCT) in Ny-Ålesund (www.isac.cnr.it/~radiclim/cctower), observations on the spectral albedo are still limited, for logistical reasons, to short periods. The availability of continuous records of spectral albedo will be extremely useful for studies concerning global change and energy balance because they can allow monitoring the subtle and rapid changes in the snow covers and to better understand the interactions in thesnow/air interface. rnEven in Ny-Ålesund, where the data collected by the scientific community are many and well diversified, continuous monitoring of spectral albedo is still a gap.rnrnThe availability of this data could also be the key for multi and hyperspectral images interpretation, thus the reconstruction of the evolution of snow surface characteristics at different scales is only possible by integrating ground-based observations with remote sensing data.rnA preliminary attempt to monitor continuously the spectral albedo has been carried out in 2014, coupling a field spectroradiometer with a hemispheric webcam. The experiment involved the acquisition of data continuously for about 2 months (May-June-July) and the processing of this data is being completed and it looks promising. rnFor 2015, it is proposed to improve the experimental set-up and to repeat the measurements for a longer time period. This campaign represents a test for the deployment of a fixed-bands albedo monitor that will be compared with the full-range instrumentation. A ground-truth survey will be necessary in order to calibrate the two different hemispherical receivers with bidirectional observations. The field activity will be scheduled during the melting period in order to associate snow metamorphism to spectral variations.
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