Abstract
Abstract. We publish and describe a surface spectral reflectance data record of seasonal snow (dry, wet, shadowed), forest ground (lichen, moss) and forest canopy (spruce and pine, branches) constituting the main elements of the boreal landscape. The reflectances are measured with spectro(radio)meters covering the wavelengths from visible (VIS) to short-wave infrared (SWIR) (350 to 2500 nm). In this paper, we describe the instruments used and how the spectral observations at different scales along with the concurrent in situ reference data have been collected, processed and archived. Information on the quality of the data and factors causing uncertainty are discussed. The main experimental site is located in the Sodankylä Arctic Space Centre in northern Finland (67.37∘ N, 26.63∘ E; 179 m a.s.l) and the surrounding region. The collection includes highly controlled snow and conifer branch laboratory spectral measurements, portable field spectroradiometer observations of snow and snow-free ground at different locations, and continuous mast-borne reflectance time series data of a pine forest and forest opening. In addition to the surface level spectral reflectance, data from airborne imaging spectrometer campaigns over the Sodankylä boreal forest and Saariselkä fell region at selected spectral bands are included in the collection. All measurements of the data record correspond to a typical polar-orbiting satellite observation event in the high-latitude spring season regarding their Sun or illumination source (calibrated lamp) zenith angle and close-to-nadir instrument viewing angle. For all measurement geometries, observations are given in surface reflectance quantity corresponding to the typical representation of a satellite observation quantity to facilitate their comparison with other data sources. The openly accessible spectral reflectance data at multiple scales are suitable to climate and hydrological research and remote sensing model validation and development. To facilitate easy access to the data record the four datasets described here are deposited in a permanent data repository (http://www.zenodo.org/communities/boreal_reflectances/) (Hannula et al., 2019). Each dataset of a distinct scale has its own unique DOI – laboratory: https://doi.org/10.5281/zenodo.3580078 (Hannula and Heinilä, 2018a); field: https://doi.org/10.5281/zenodo.3580825 (Heinilä et al., 2019a); mast-borne: https://doi.org/10.5281/zenodo.3580096 (Hannula and Heinilä, 2018b); and airborne: https://doi.org/10.5281/zenodo.3580451 (Heinilä, 2019a) and https://doi.org/10.5281/zenodo.3580419 (Heinilä, 2019b).
Highlights
High-latitude regions are facing fundamental and rapid changes in climate and hydrology due to raising mean annual temperatures (ACIA, 2005; AMAP, 2017)
We describe the instruments used and how the spectral observations at different scales along with the concurrent in situ reference data have been collected, processed and archived
The Analytical Spectral Devices (ASD) FieldSpec Pro spectroradiometer was installed on a 33 m high mast in the intensive observation area (IOA) of the Finnish Meteorological Institute’s Sodankylä Arctic Space Centre (FMI-ARC) for the optical remote sensing validation studies
Summary
High-latitude regions are facing fundamental and rapid changes in climate and hydrology due to raising mean annual temperatures (ACIA, 2005; AMAP, 2017). Several approaches have been used to estimate the FSC from satellite imagery (Klein et al, 1998; Hall and Riggs, 2007; Dozier et al, 2009; Nolin, 2010; Dietz et al, 2012; Frei et al, 2012; Metsämäki et al, 2015) These methods, such as the semiempirical-reflectance-model-based method SCAmod (Metsämäki et al, 2005, 2012), used for the detection of snow cover in forested areas, have benefited from accurate reference spectral measurements enabling better characterization of the model parameters (i.e. spectral endmembers). Reference spectroscopy measurements are valuable in defining the spectral endmembers of the satellite scene reflectance, namely snow, snow-free terrain after melting and forest cover. These data can be obtained from controlled-condition laboratory spectroradiometer observations, portable field spectroscopy campaigns, mast-borne spectral monitoring and aerial surveys. The discussion of possible sources of error and uncertainty is accompanied with conclusions and recommendations for data utilization
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