Reflectance Research Papers - Academia.edu (original) (raw)

Despite the importance of litter on forest floor albedo and brightness, previous studies have not documented forest floor albedo or litter cover in any detail. Our objective was to describe the seasonal influence of litter on spectral... more

Despite the importance of litter on forest floor albedo and brightness, previous studies have not documented forest floor albedo or litter cover in any detail. Our objective was to describe the seasonal influence of litter on spectral albedos and nadir reflectances of a forest snowpack in a mixed-hardwood stand in the Sleepers River Research Watershed (SRRW) in Danville, Vermont (37°39′ N, 119°2′ W). Experimental measurements in a nearby open area at the Snow Research Station of the SRRW nearly duplicated the spectral trend observed in the forest. Spectral albedo and nadir reflectance measurements in the visible and near infrared (350–2500 nm) transitioned from a gently curved shape through the visible range (for finer-grained, lightly littered snow) to one having a peak in the red/near-infrared (near 760 nm) as the snowmelt season progressed (for coarser-grained, more heavily littered snow). The snowpack became optically thin as surface litter reached high percentages. A point-in-time digital photographic survey of the late-lying snowpacks of three forest stands and the open showed that median litter cover percentages in the coniferous, deciduous, mixed-forest, and an open area were 17·5, 6·1, 1·2, and 0·04 respectively. A Kruskal–Wallis ANOVA on ranks and pairwise comparisons using Dunn's test indicated that the litter covers of the three forest stands were significantly different with >95% confidence. The snowpack was relatively shallow (<1 m), as is typical for this area of Vermont. From a remote-sensing standpoint, and since shallow snow and increased grain size also lower the visible albedo, we can expect that snowpack litter will cause decreased albedo earlier in the snowmelt season, at deeper snow depths, and will tend to shift the maximum albedo peak to the red/NIR range as the melt season progresses. Published in 2001 by John Wiley & Sons, Ltd.

ABSTRACT This work aims at developing a generic and anisotropic point error model, which is capable of computing magnitude and direction of a priori random errors, described in the form of error ellipsoids for each individual point of... more

ABSTRACT
This work aims at developing a generic and anisotropic point error model, which is capable of computing magnitude and
direction of a priori random errors, described in the form of error ellipsoids for each individual point of the cloud. The
direct TLS observations are the range (ρ), vertical (α) and horizontal (θ) angles, each of which is in fact associated with a
priori precision value. A practical methodology was designed and performed in real-world test environments to
determine these precision values. The methodology has two experimental parts. The first part is a static and repetitive
measurement configuration for the determination of a priori precisions of the vertical (𝜎𝛼) and horizontal (𝜎𝜃) angles. The
second part is the measurement of a test stand which contains four plates in white, light grey, dark grey and black colors,
for the determination of a priori precisions of the range observations (𝜎𝜌). The test stand measurement is performed in a
recursive manner so that sensor-to-object distance, incidence angle and surface reflectivity are parameterized. The
experiment was conducted with three TLSs, namely Faro Focus 3D X330, Riegl VZ400 and Z+F 5010x in the same
location and atmospheric conditions. This procedure was followed by the computation of error ellipsoids of each point
using the law of variance-covariance propagation. The direction and size of the error ellipsoids were computed by the
principal components transformation. Validation of the proposed error model was performed in real world scenarios,
which revealed feasibility of the model.
Keywords: TLS (terrestrial laser scanner), range, incidence angle, reflectance, error ellipsoid, anisotropic, error model,
variance-covariance propagation

The albedo of snow is determined in part by the size and shape of snow crystals, especially in the short wave infrared (SWIR). Many models of snow albedo represent snow crystals by spheres of surface/volume (S/V) ratio equal to that of... more

The albedo of snow is determined in part by the size and shape of snow crystals, especially in the short wave infrared (SWIR). Many models of snow albedo represent snow crystals by spheres of surface/volume (S/V) ratio equal to that of snow crystals. However, the actual S/V ratio of snow has never been measured simultaneously with the albedo, for a thorough test of models. Using CH4 adsorption at 77 K, we have measured the specific surface area (SSA) of snow samples, i.e. its ratio S/(V · ρ), where ρ is the density of ice, together with the snow spectral albedo using a field radiometer with nadir viewing, at Ny-Ålesund, Svalbard. Tests are performed at 1310, 1629, 1740 and 2260 nm, and we find a good correlation between the SSA and the snow spectral albedo in the SWIR (linear correlation coefficient R2 > 0.98 for the last 3 wavelengths). Snow samples having varied crystals shapes such as rounded crystals in windpacks and hollow faceted crystals in depth hoar were studied and crystal shape did not affect the correlation in a detectable manner. An interest in using SSA rather than crystal size to predict SWIR albedo is that the reflectance of large hollow crystals such as depth hoar or surface hoar will be correctly predicted from their SSA, while considering their large dimensions would underestimate reflectance. We compare these correlations to those predicted by commonly used optical models. The best agreement is found when we compare our data to the modeled hemispheric reflectance, corrected by an adjustable factor that shows a small wavelength dependence. We propose that, once these results have been confirmed by more studies, it may be possible to design a rapid and simple optical method to measure snow SSA in the field. Our results may also allow a more detailed use of remote sensing data to study snow metamorphism, air–snow exchanges of gases, and climate.

Ultra-high temperature ceramics (UHTCs) are interesting materials for a large variety of applications under extreme conditions. This paper reports on the production and extensive characterization of highly dense, pure zirconium and... more

Ultra-high temperature ceramics (UHTCs) are interesting materials for a large variety of applications under extreme conditions. This paper reports on the production and extensive characterization of highly dense, pure zirconium and tantalum diborides, with particular interest to their potential utilization in the thermal solar energy field. Monolithic bulk samples are produced by Spark Plasma Sintering starting from elemental reactants or using metal diboride powders previously synthesized by Self-propagating High-temperature Synthesis (SHS). Microstructural and optical properties of products obtained by the two processing methods have been comparatively evaluated. We found that pure diborides show a good spectral selectivity, which is an appealing characteristic for solar absorber applications. No, or very small, differences in the optical properties have been evidenced when the two investigated processes adopted for the fabrication of dense TaB 2 and ZrB 2 , respectively, are compared.

The color change in dried apricots at various moisture contents was studied. Dried apricots originally at 19.32% moisture were first dried to 15.49% and then rehydrated to 20.10%, 25.21% and finally 30.20% moisture levels. The CIE L*, a*,... more

The color change in dried apricots at various moisture contents was studied. Dried apricots originally at 19.32% moisture were first dried to 15.49% and then rehydrated to 20.10%, 25.21% and finally 30.20% moisture levels. The CIE L*, a*, and b* color variables were measured to determine the color of dried apricots, and C* (chroma) and h* (hue) values were calculated from a* and b* values. A linear relationship was found between the color variables and moisture contents at 15.49–30.20%. As the moisture content increased, the L* (lightness), b* (yellowness), C* and h* color values increased while the a* (redness) value decreased for the dried apricots at all moisture levels. Results showed that the moisture content of dried fruits should be specified once the reflectance color variables are reported.

Aluminum doped zinc oxide (AZO) nanometric particles were synthesized by hydrothermal method. Aluminum nitrate hydrate, aluminum sec-butoxide and zinc nitrate hydrate were used as the starting materials, and n-propanol and 2-butanol were... more

Aluminum doped zinc oxide (AZO) nanometric particles were synthesized by hydrothermal method. Aluminum nitrate hydrate, aluminum sec-butoxide and zinc nitrate hydrate were used as the starting materials, and n-propanol and 2-butanol were used as solvents. Ratio of Al2O3 in ZnO was kept at 10 wt%. Reaction was conducted in a Teflon autoclave at 175–225 °C for 5 h. Ratios of alcohol, H2O and HCl to zinc nitrate hydrate were altered and 6 different sets of parameters were investigated. Obtained products were subjected to powder-XRD, particle size measurement, TEM examination and AAS analysis. Single phase AZO particles were obtained at alcohol to zinc nitrate ratio of 35, acid to zinc nitrate ratio of 0.2, at 225 °C. Particle size was determined as 3.2 ± 0.4 nm from TEM examinations and as 1–2 nm from dynamic light scattering. Synthesized particles have amphiphilic character, thus they can be dispersed in both polar and non-polar media. It was seen from the UV-diffuse reflectance spectra that the AZO powder had low reflectance in the UV region and high reflectance in the visible region. The obtained powder has the potential to be utilized in the form of thin films for optical and electronic purposes.

Two different configurations of a shortwave infrared water stress index (SIWSI) are derived from the MODIS near-and shortwave infrared data. A large absorption by leaf water occurs in the shortwave infrared wavelengths (SWIR) and the... more

Two different configurations of a shortwave infrared water stress index (SIWSI) are derived from the MODIS near-and shortwave infrared data. A large absorption by leaf water occurs in the shortwave infrared wavelengths (SWIR) and the reflectance from plants thereby is ...

Wetland vegetation plays a key role in the ecological functions of wetland environments. Remote sensing techniques offer timely, up-to-date, and relatively accurate information for sustainable and effective management of wetland... more

Wetland vegetation plays a key role in the ecological functions of wetland environments. Remote sensing techniques offer timely, up-to-date, and relatively accurate information for sustainable and effective management of wetland vegetation. This article provides an overview on the status of remote sensing applications in discriminating and mapping wetland vegetation, and estimating some of the biochemical and biophysical parameters of wetland vegetation. Research needs for successful applications of remote sensing in wetland vegetation mapping and the major challenges are also discussed. The review focuses on providing fundamental information relating to the spectral characteristics of wetland vegetation, discriminating wetland vegetation using broad- and narrow-bands, as well as estimating water content, biomass, and leaf area index. It can be concluded that the remote sensing of wetland vegetation has some particular challenges that require careful consideration in order to obtain successful results. These include an in-depth understanding of the factors affecting the interaction between electromagnetic radiation and wetland vegetation in a particular environment, selecting appropriate spatial and spectral resolution as well as suitable processing techniques for extracting spectral information of wetland vegetation.

Reflectance is a method borrowed from coal studies which can estimate the absolute burn temperature of charcoals. Studies examining the usefulness of reflectance in archaeology are underway in a number of areas. This report details first... more

Reflectance is a method borrowed from coal studies which can estimate the absolute burn temperature of charcoals. Studies examining the usefulness of reflectance in archaeology are underway in a number of areas. This report details first results from reflectance testing of archaeological charcoals from known Irish Bronze Age cremations, which included calcinated bone. As calcination of bone occursat 650 °C to ≥ 800 °C (Wahl, 1982), it was expected that the charcoals would reflect this temperature. This was not the case for identified charcoals > 2mm, nor for micro-charcoals of ca. 250 μ m. Cultural depositional modalities, combustion completeness and taphonomic influences may have all played a part in this result which suggests that the usefulness of reflectance will depend on depositional circumstances and charcoal collection strategies