scholarly journals Comparison of traditional and optical grain-size field measurements with SNOWPACK simulations in a taiga snowpack

2015 ◽  
Vol 61 (225) ◽  
pp. 151-162 ◽  
Author(s):  
L. Leppänen ◽  
A. Kontu ◽  
J. Vehviläinen ◽  
J. Lemmetyinen ◽  
J. Pulliainen
Keyword(s):  
Grain Size ◽  
Snow Cover ◽  
Electromagnetic Waves ◽  
Field Measurements ◽  
Scaling Factor ◽  
Field Conditions ◽  
Meteorological Forcing ◽  
Sensing Applications ◽  
Variable Nature ◽  
Snow Microstructure

AbstractKnowledge of snow microstructure is relevant for modelling the physical properties of snow cover and for simulating the propagation of electromagnetic waves in remote-sensing applications. Characterization of the microstructure in field conditions is, however, a challenging task due to the complex, sintered and variable nature of natural snow cover. A traditional measure applied as a proxy of snow microstructure, which can also be determined in field conditions, is the visually estimated snow grain size. Developing techniques also allow measurement, for example, of the specific surface area (SSA) of snow, from which the optical-equivalent grain size can be derived. The physical snow model SNOWPACK simulates evolution of snow parameters from meteorological forcing data. In this study we compare an extensive experimental dataset of measurements of traditional grain size and SSA-derived optical grain size with SNOWPACK simulations of grain-size parameters. On average, a scaling factor of 1.2 is required to match traditional grain-size observations with the corresponding SNOWPACK simulation; a scaling factor of 2.1 was required for the optical equivalent grain size. Standard deviations of scaling factors for the winters of 2011/12 and 2012/13 were 0.36 and 0.42, respectively. The largest scaling factor was needed in early winter and under melting conditions.

Effect of Grain Size on Strain in a Copper Oxide Nanofilm for Gas Sensing Applications

2019 ◽  
Vol 11 (5) ◽  
pp. 05040-1-05040-4
Author(s):  
Sumanta Kumar Tripathy ◽  
◽  
Sanjay Kumar ◽  
Divya Aparna Narava ◽  
◽  
...  
Keyword(s):  
Grain Size ◽  
Copper Oxide ◽  
Gas Sensing ◽  
Sensing Applications

scholarly journals Retrieval of snow grain size and albedo of Western Himalayan snow cover using satellite data

2011 ◽  
Vol 5 (1) ◽  
pp. 605-653 ◽  
Author(s):  
H. S. Negi ◽  
A. Kokhanovsky
Keyword(s):  
Grain Size ◽  
Snow Cover ◽  
Western Himalaya ◽  
Sensor Data ◽  
Art Theory ◽  
Grain Sizes ◽  
Spectral Bands ◽  
Steep Slopes ◽  
Different Parts ◽  
Good Agreement

Abstract. In the present study we describe the retrievals of snow grain size and spectral albedo (plane and spherical albedo) for Western Himalayan snow cover using Hyperion sensor data. The asymptotic radiative transfer (ART) theory was explored for the snow retrievals. To make the methodology operational only five spectral bands (440, 500, 1050, 1240 and 1650 nm) of Hyperion were used for snow parameters retrieval. The bi-spectral method (440 nm in the visible and 1050/1240 nm in the NIR region) was used to retrieve snow grain size. Spectral albedos were retrieved using satellite reflectances and estimated grain size. A good agreement was observed between retrieved snow parameters and ground observed snow-meteorological conditions. The satellite retrieved grain sizes were compared with field spectroradiometer retrieved grain sizes and close results were found for Lower Himalayan snow. The wavelength 1240 nm was found to be more suitable compared to 1050 nm for grain size retrieval along the steep slopes. The methodology was able to retrieve the spatial variations in snow parameters in different parts of Western Himalaya which are due to snow climatic and terrain conditions of Himalaya. This methodology is of importance for operational snow cover and glacier monitoring in Himalayan region using space-borne and air-borne sensors.

scholarly journals A Possible Relation Between Grain Size, Density, and Light Attenuation in Natural Snow Cover

1970 ◽  
Vol 9 (55) ◽  
pp. 154-156
Author(s):  
James D. Bergen
Keyword(s):  
Grain Size ◽  
Porous Medium ◽  
Specific Surface ◽  
Snow Cover ◽  
Extinction Coefficient ◽  
Light Attenuation ◽  
Empirical Relation ◽  
Air Permeability ◽  
Fair Agreement ◽  
Natural Snow

AbstractThe extinction coefficient for the transmission of light through snow cover is related to the grain size and density of the snow cover. The connection is made by means of an empirical relation between the latter parameters and the air permeability and by the Carmen–Kozney relation between the air permeability and specific surface of a porous medium. The results are compared with a set of measurements found in the literature with fair agreement between the predicted and measured values of the extinction coefficient.

scholarly journals Upscaling from Instantaneous to Daily Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) for Satellite Products

2020 ◽  
Vol 12 (13) ◽  
pp. 2083
Author(s):  
Siyuan Chen ◽  
Liangyun Liu ◽  
Xue He ◽  
Zhigang Liu ◽  
Dailiang Peng
Keyword(s):  
Zenith Angle ◽  
Photosynthetically Active Radiation ◽  
Solar Zenith Angle ◽  
Field Measurements ◽  
Area Index ◽  
Active Radiation ◽  
Sensing Applications ◽  
Typical Satellite ◽  
Absorbed Photosynthetically Active Radiation ◽  
Local Noon

The fraction of absorbed photosynthetically active radiation (FAPAR) is an essential climate variable (ECV) widely used for various ecological and climate models. However, all the current FAPAR satellite products correspond to instantaneous FAPAR values acquired at the satellite transit time only, which cannot represent the variations in photosynthetic processes over the diurnal period. Most studies have directly used the instantaneous FAPAR as a reasonable approximation of the daily integrated value. However, clearly, FAPAR varies a lot according to the weather conditions and amount of incoming radiation. In this paper, a temporal upscaling method based on the cosine of the solar zenith angle (SZA) at local noon ( c o s ( S Z A n o o n ) ) is proposed for converting instantaneous FAPAR to daily integrated FAPAR. First, the diurnal variations in FAPAR were investigated using PROSAIL (a model of Leaf Optical Properties Spectra (PROSPECT) integrating a canopy radiative transfer model (Scattering from Arbitrarily Inclined Leaves, SAIL)) simulations with different leaf area index (LAI) values corresponding to different latitudes. It was found that the instantaneous black sky FAPAR at 09:30 AM provided a good approximation for the daily integrated black sky FAPAR; this gave the highest correlation (R2 = 0.995) and lowest Root Mean Square Error (RMSE = 0.013) among the instantaneous black sky FAPAR values observed at different times. Secondly, the difference between the instantaneous black sky FAPAR values acquired at different times and the daily integrated black sky FAPAR was analyzed; this could be accurately modelled using the cosine value of solar zenith angle at local noon ( c o s ( S Z A n o o n ) ) for a given vegetation scene. Therefore, a temporal upscaling method for typical satellite products was proposed using a cos(SZA)-based upscaling model. Finally, the proposed cos(SZA)-based upscaling model was validated using both the PROSAIL simulated data and the field measurements. The validated results indicated that the upscaled daily black sky FAPAR was highly consistent with the daily integrated black sky FAPAR, giving very high mean R2 values (0.998, 0.972), low RMSEs (0.007, 0.014), and low rMAEs (0.596%, 1.378%) for the simulations and the field measurements, respectively. Consequently, the cos(SZA)-based method performs well for upscaling the instantaneous black sky FAPAR to its daily value, which is a simple but extremely important approach for satellite remote sensing applications related to FAPAR.

scholarly journals Analysis of QualitySpec Trek Reflectance from Vertical Profiles of Taiga Snowpack

Geosciences ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 404 ◽  
Author(s):  
Leena Leppänen ◽  
Anna Kontu
Keyword(s):  
Grain Size ◽  
Surface Area ◽  
Near Infrared ◽  
Sample Surface ◽  
Short Wave ◽  
Optical Remote Sensing ◽  
Mass Ratio ◽  
Data Set ◽  
Hemispherical Reflectance ◽  
Snow Microstructure

Snow microstructure is an important factor for microwave and optical remote sensing of snow. One parameter used to describe it is the specific surface area (SSA), which is defined as the surface-area-to-mass ratio of snow grains. Reflectance at near infrared (NIR) and short-wave infrared (SWIR) wavelengths is sensitive to grain size and therefore also to SSA through the theoretical relationship between SSA and optical equivalent grain size. To observe SSA, the IceCube measures the hemispherical reflectance of a 1310 nm laser diode from the snow sample surface. The recently developed hand-held QualitySpec Trek (QST) instrument measures the almost bidirectional spectral reflectance in the range of 350–2500 nm with direct contact to the object. The geometry is similar to the Contact Probe, which was previously used successfully for snow measurements. The collected data set includes five snow pit measurements made using both IceCube and QST in a taiga snowpack in spring 2017 in Sodankylä, Finland. In this study, the correlation between SSA and a ratio of 1260 nm reflectance to differentiate between 1260 nm and 1160 nm reflectances is researched. The correlation coefficient varied between 0.85 and 0.98, which demonstrates an empirical linear relationship between SSA and reflectance observations of QST.

scholarly journals Retrieval of snow grain size and albedo of western Himalayan snow cover using satellite data

2011 ◽  
Vol 5 (4) ◽  
pp. 831-847 ◽  
Author(s):  
H. S. Negi ◽  
A. Kokhanovsky
Keyword(s):  
Grain Size ◽  
Snow Cover ◽  
Western Himalaya ◽  
Sensor Data ◽  
Art Theory ◽  
Grain Sizes ◽  
Spectral Bands ◽  
Steep Slopes ◽  
Different Parts ◽  
Good Agreement

Abstract. In the present study we describe the retrievals of snow grain size and spectral albedo (plane and spherical albedo) for western Himalayan snow cover using Hyperion sensor data. The asymptotic radiative transfer (ART) theory was explored for the snow retrievals. To make the methodology operational only five spectral bands (440, 500, 1050, 1240 and 1650 nm) of Hyperion were used for snow parameters retrieval. The bi-spectral method (440 nm in the visible and 1050/1240 nm in the NIR region) was used to retrieve snow grain size. Spectral albedos were retrieved using satellite reflectances and estimated grain size. A good agreement was observed between retrieved snow parameters and ground observed snow-meteorological conditions. The satellite retrieved grain sizes were compared with field spectroradiometer retrieved grain sizes and close results were found for lower Himalayan snow. The wavelength 1240 nm was found to be more suitable compared to 1050 nm for grain size retrieval along the steep slopes. The methodology was able to retrieve the spatial variations in snow parameters in different parts of western Himalaya which are due to snow climatic and terrain conditions of Himalaya. This methodology is of importance for operational snow cover and glacier monitoring in Himalayan region using space-borne and air-borne sensors.

Brightness temperature simulation of snow cover based on snow grain size evolution usingin situdata

2016 ◽  
Vol 10 (3) ◽  
pp. 036016 ◽  
Author(s):  
Lili Wu ◽  
Xiaofeng Li ◽  
Kai Zhao ◽  
Xingming Zheng ◽  
Tao Jiang
Keyword(s):  
Grain Size ◽  
Brightness Temperature ◽  
Snow Cover ◽  
Size Evolution

scholarly journals A new Snow-SVAT to simulate the accumulation and ablation of seasonal snow cover beneath a forest canopy

2004 ◽  
Vol 50 (169) ◽  
pp. 171-182 ◽  
Author(s):  
Melody J. Tribbeck ◽  
Robert J. Gurney ◽  
Elizabeth M. Morris ◽  
David W. C. Pearson
Keyword(s):  
Solar Radiation ◽  
Snow Cover ◽  
Forest Canopy ◽  
Correlation Coefficients ◽  
Field Measurements ◽  
Radiation Model ◽  
Physically Based ◽  
Boreal Ecosystem ◽  
Snow Model

AbstractA new snow—soil—vegetation—atmosphere transfer (Snow-SVAT) scheme, which simulates the accumulation and ablation of the snow cover beneath a forest canopy, is presented. The model was formulated by coupling a canopy optical and thermal radiation model to a physically based multi-layer snow model. This canopy radiation model is physically based yet requires few parameters, so can be used when extensive in situ field measurements are not available. Other forest effects such as the reduction of wind speed, interception of snow on the canopy and the deposition of litter were incorporated within this combined model, SNOWCAN, which was tested with data taken as part of the Boreal Ecosystem—Atmosphere Study (BOREAS) international collaborative experiment. Snow depths beneath four different canopy types and at an open site were simulated. Agreement between observed and simulated snow depths was generally good, with correlation coefficients ranging between r2 = 0.94 and r2 = 0.98 for all sites where automatic measurements were available. However, the simulated date of total snowpack ablation generally occurred later than the observed date. A comparison between simulated solar radiation and limited measurements of sub-canopy radiation at one site indicates that the model simulates the sub-canopy downwelling solar radiation early in the season to within measurement uncertainty.

scholarly journals A Possible Relation Between Grain Size, Density, and Light Attenuation in Natural Snow Cover

1970 ◽  
Vol 9 (55) ◽  
pp. 154-156 ◽  
Author(s):  
James D. Bergen
Keyword(s):  
Grain Size ◽  
Porous Medium ◽  
Specific Surface ◽  
Snow Cover ◽  
Extinction Coefficient ◽  
Light Attenuation ◽  
Empirical Relation ◽  
Air Permeability ◽  
Fair Agreement ◽  
Natural Snow

Abstract The extinction coefficient for the transmission of light through snow cover is related to the grain size and density of the snow cover. The connection is made by means of an empirical relation between the latter parameters and the air permeability and by the Carmen–Kozney relation between the air permeability and specific surface of a porous medium. The results are compared with a set of measurements found in the literature with fair agreement between the predicted and measured values of the extinction coefficient.

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