Sequential Ground Research Articles

Implications of spatial distributions of snow mass and melt rate for snow-cover depletion: observations in a subarctic mountain catchment

AbstractSpatial statistics of snow water equivalent (SWE) and melt rate were measured using spatially distributed, sequential ground surveys of depth and density in forested, shrub and alpine tundra environments over several seasons within a 185 km2 mountain catchment inYukonTerritory, Canada.When stratified by slope/aspect sub-units within landscape classes, SWE frequency distributions matched the log-normal, but multiclass surveys showed a more bimodal distribution. Within-class variability of winter SWE could be grouped into (i) windswept tundra and (ii) sheltered tund ra/forest regimes. During melt, there was little association between the standard deviation and mean of SWE. At small scales, a negative correlation developed between spatial distributions of pre-melt SWE and melt rate where shrubs were exposed above the snow. This was not evident in dense-forest, alpine-tundra or deep-snowdrift landscape classes. At medium scales, negative SWE and melt-rate correlations were also found between mean values from adjacent slope sub-units of the tundra landscape class. Themedium-scale correlation was likely due to slope effects on insolation and blowing-snow redistribution. At the catchment scale, the correlation between mean SWE and melt rate from various landscape classes reversed to a positive one, likely influenced by intercepted and blowing regimes, shrub exposure during melt and adiabatic cooling with elevation rise. Covariance at the catchment scale resulted in a 40% acceleration of snow depletion. These results suggest that the spatial variability and covariability of both SWE and melt rate are scale- and landscape-class-specific and need to be considered in a landscape-stratified manner at the appropriate scale when snow depletion is described and the snowmelt duration predicted.

Improving solar cell efficiencies by up-conversion of sub-band-gap light

A system for solar energy conversion using the up-conversion of sub-band-gap photons to increase the maximum efficiency of a single-junction conventional, bifacial solar cell is discussed. An up-converter is located behind a solar cell and absorbs transmitted sub-band-gap photons via sequential ground state absorption/excited state absorption processes in a three-level system. This generates an excited state in the up-converter from which photons are emitted which are subsequently absorbed in the solar cell and generate electron-hole pairs. The solar energy conversion efficiency of this system in the radiative limit is calculated for different cell geometries and different illumination conditions using a detailed balance model. It is shown that in contrast to an impurity photovoltaic solar cell the conditions of photon selectivity and of complete absorption of high-energy photons can be met simultaneously in this system by restricting the widths of the bands in the up-converter. The upper limit of the energy conversion efficiency of the system is found to be 63.2% for concentrated sunlight and 47.6% for nonconcentrated sunlight.

The Analysis of Sequential ground Faults on a Six Phase Generator in Phase Co-ordinates.(Dept.E)

Transmission of bulk power over high phase order transmission lines KPOT, is being considered as a potential alternative to the conventional three phase lines. Lo practical, six phase systems appear to be favored. Should HPOT prove to be economically and technically viable, the problem of fault analysis, in particular the analysis of sequential faults on HPOT system appears to be a complicated one. When a ground fault on power system involves more than one terminal, tire fault usually develops in sequence. This paper presents a generalized treatment of sequential ground faults on the terminal of an initially unloaded six phase symmetrical generator. No restriction is placed either on the sequence in which the ground fault develops or on Tie instants at which the various phases are grounded. Expressions for transient phase currents and transient terminal voltages have been given. An expression for the neutral current which is an important variable for any protection scheme bas also been given. The method given in the paper can be applied to a power system of any number of phases by suitably adjusting the summation index in general equations. The analysis has been done in actual phase variable. Finally, the results for an arbitrary sequential ground fault on the terminals of a fictitious six phase generator have been given.

The analysis of random sequential ground faults on a high phase order (six-phase) power system in phase coordinates

High phase order transmission (HPOT) lines are considered a potential alternative to the conventional three-phase lines for the transmission of bulk power. In particular, six- and twelve-phase systems appear to be favoured for this purpose. Should HOPT prove to be economically and technically viable, the problem of fault analysis, in particular the analysis of random sequential ground faults on these systems, appears to be a complicated one. When a ground fault on a power system involves more than one terminal, the fault usually develops in sequence. This paper presents a generalized analysis of random sequential ground faults on the terminals of an initially unloaded six-phase symmetrical generator. No restriction is placed either on the sequence in which the ground fault develops or on the instants at which the various phases are grounded. Single equations from which all transient phase currents and transient terminal voltages can be calculated are given. An expression for the transient neutral current which is an important variable for any protection scheme against ground faults is also given. The method in this paper can be applied to a power system of any number of phases by suitably adjusting the summation indices in the general equations. The analysis has been done in actual phase variables. Finally, the results for an arbitrary sequential ground fault on the terminals of a fictitious six-phase generator are given.

The impact, control, and mitigation of off-road vehicle activity in Hungry Valley, California

Hungry Valley, and arid basin situated within the Transverse Ranges of Southern California, has been utilized by off-road vehicles (ORVs) since 1971. Loss of vegetation, severe soil erosion and gullying, alluvial fan formation, and increased sediment discharge are the direct results of ORV activity in the valley. These hydrologic-geologic effects have been documented and monitored utilizing sequential aerial photographs, ground surveys, and sediment transport measurements. Despite the increased usage of ORVs on public lands, and the well-documented short-term physical environmental impacts, little data exists on erosion or sediment transport rates in disturbed vs. adjacent undisturbed areas, the ability of natural vegetation to re-establish itself, or the feasibility of site rehabilitation techniques or methods.

Phenological evaluations using Landsat?1 sensors

For a 16-month period starting in July 1972 multispectral scanner (MSS) data from the ERTS-1 (Landsat-1) satellite was evaluated to find if the phenological development of forest and agricultural vegetation at 14 test sites in the eastern half of the United States could be detected. Sequential ground photography taken at each site provided a ground comparison for the analysis. Imagery from MSS band 5 (red) and 7 (near infrared) was selected for densitometric measurement and correlation with known site seasonal changes. Image densities were corrected for instrument error, photographic variations, solar elevation differences and atmospheric influences using linear regression equations. Band Density Ratios (BDR) calculated using the corrected densities in the equation: Band Density Ratio = Band 5 Density − Band 7 Density/Band 5 Density + Band 7 Density correlated well with the phenological conditions recorded on the ground photography. The height of summer vegetational development was typically indicated by a BDR near 0.3 while winter vegetational stages were indicated with a BDR of approximately 0.08.