Showing papers by "Jouni Peltoniemi published in 2015"
TL;DR: In this paper, a series of spectral reflectance measurements were conducted to quantify the effects of absorbing contaminants on snow, a remarkable feature is the fact that the absorbing contaminants enhanced the metamorphism of snow under strong sunlight in their experiments.
Abstract: . In order to quantify the effects of absorbing contaminants on snow, a series of spectral reflectance measurements were conducted. Chimney soot, volcanic sand, and glaciogenic silt were deposited on a natural snow surface in a controlled way as a part of the Soot on Snow (SoS) campaign. The bidirectional reflectance factors of these soiled surfaces and untouched snow were measured using the Finnish Geodetic Institute's Field Goniospectropolariradiometer, FIGIFIGO. A remarkable feature is the fact that the absorbing contaminants on snow enhanced the metamorphism of snow under strong sunlight in our experiments. Immediately after deposition, the contaminated snow surface appeared darker than the natural snow in all viewing directions, but the absorbing particles sank deep into the snow in minutes. The nadir measurement remained the darkest, but at larger zenith angles, the surface of the contaminated snow changed back to almost as white as clean snow. Thus, for a ground observer the darkening caused by impurities can be completely invisible, overestimating the albedo, but a nadir-observing satellite sees the darkest points, underestimating the albedo. Through a reciprocity argument, we predict that at noon, the albedo perturbation should be lower than in the morning or afternoon. When sunlight stimulates sinking more than melting, the albedo should be higher in the afternoon than in the morning, and vice versa when melting dominates. However, differences in the hydrophobic properties, porosity, clumping, or size of the impurities may cause different results than observed in these measurements.
58 citations
01 Jan 2015
TL;DR: In this paper, the authors provide a set of reliable references by measuring various known terrestrial and planetary targets for Earth Observation projects and for collecting more accurate knowledge on the Earth, universe, and environment.
Abstract: An important factor for reducing the amount of data acquired by Earth Observation projects and for collecting more accurate knowledge on the Earth, universe, and environment is to provide a set of reliable references by measuring various known terrestrial and planetary targets.
29 citations
TL;DR: The model is a Lommel–Seeliger type model, representing a medium composed of individual scatterers with small single-scattering albedo, suitable for dark regolith surfaces such as the Moon and many classes of asteroids.
13 citations
TL;DR: In this paper, an inhomogeneous irregular-particle model for reproducing the typical light-scattering features of cometary dust such as the negative polarization near the backscattering direction, and the weak increase of the back scattering intensity was introduced.
9 citations
TL;DR: The linear and circular polarization ratios for clusters of spherical particles averaged over multiple orientations show a systematic pattern as a function of the refractive index and the size parameter, and this work shows that the pattern is relatively invariable in terms of the number of particles.
Abstract: The linear and circular polarization ratios for clusters of spherical particles averaged over multiple orientations show a systematic pattern as a function of the refractive index and the size parameter. We show that, at backscattering, the depolarizing behavior of orientation-averaged clusters of spheres can be approximated by second-order scattering of bispheres. The pattern is relatively invariable in terms of the number of particles. We also demonstrate the significance of the near-field effects for polarization at backscattering.
8 citations
TL;DR: In this paper, a series of experiments in which they deposited different soot concentrations onto natural snow in different regions of Finland, and thereafter monitored the changes of the snowpack through the melting season.
Abstract: . Light-absorbing impurities affect snow and ice via a decrease in albedo and a consequent disturbance to the radiative energy balance. Experimentally, these matters have only been examined in a few studies. Here we present results from a series of experiments in which we deposited different soot concentrations onto natural snow in different regions of Finland, and thereafter monitored the changes of the snowpack through the melting season. Measurements of the particulates in the snow indicated concentrations in the range of thousands of ppb to have clear effects on the snow properties, including the albedo, the physical snow characteristics, and an increased melt rate. For soot concentrations in the hundreds of ppb range, the effects were not as clearly visible, and it was more difficult to attribute the effects solely to the soot on the snow. Comparisons between our experimental data and the widely used Snow, Ice and Aerosol Radiation (SNICAR) model showed a general agreement when the model was specifically tuned to our measurements. This study highlights the importance of additional experimental studies, to further articulate and quantify the effects of light-absorbing impurities on snow.
5 citations
TL;DR: In this article, Finnish Geodetic Institute, PO Box 15, 02431 Masala, Finland b Department of Physics, University of Helsinki, PO box 14, 00014, Finland c Laboratory of Geo-Information Science and Remote Sensing, Wageningen University, The Netherlands d Mikes/Aalto University, Finland e Department of Physical Methods and Devices for Quality Control, Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russia
Abstract: a Finnish Geodetic Institute, PO Box 15, 02431 Masala, Finland b Department of Physics, University of Helsinki, PO Box 14, 00014, Finland c Laboratory of Geo-Information Science and Remote Sensing, Wageningen University, The Netherlands d Mikes/Aalto University, Finland e Department of Physical Methods and Devices for Quality Control, Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russia