Soil Water Flux Estimates from Streaming Potential and Penta-Needle Heat Pulse Probe Measurements

Better management of water resources is a growing concern with increasing stress on natural resources. Despite technological improvements in the past decades, a method to instantaneously measure soil water flux remains elusive, especially at a resolution adequate for monitoring natural processes (i.e. 1 mm d-1). The objectives of this research were to evaluate and improve two emerging methods for water flux estimates, 1) streaming potential and 2) heat pulse measurements, as tools to perform at these low flux rates. Streaming potential measures a voltage between two electrodes resulting from water with charged particles generating a current as it flows between the charged surfaces of the soil. Heat pulse measurements, performed with a penta-needle heat pulse probe (PHPP), measure the transport rate and direction of a heat pulse as it propagates from a central needle to surrounding thermistors through soil. Water moving past this sensor carries heat and this allows estimation of water flux from measured heat flux. Streaming potential experimentation demonstrated a clear voltage response to low flow rates. Unfortunately, inconsistent results coupled with measurement complications – susceptibility to electromagnetic noise, drifting, etc. – led to difficulties when trying to establish a congruent relationship between flow rate and voltage behavior. We concluded that the necessary steps to potentially improve measurement consistency made streaming potential less desirable to pursue compared to other emerging tools for water flux measurements. Heat pulse work focused on modifying design parameters to improve low flux rate determination. We tested the effect of increasing heater needle diameter (from 2 mm to 5 mm), increasing heating time (from 8 to 24 and 40 seconds), and doubling heat input (from 120 W m-1 to 240 W m-1) in saturated sand. Results indicated that using larger heater needles and higher heat input improve flux estimation but increasing heating time resulted in marginal improvement. By using a PHPP with a 5 mm heater needle, 24 second heating time, and 240 W m-1 heating input, fluxes were resolved down to 1 cm d-1. Refinement of calibration procedures and inconsistencies between probes used must be resolved if measurement resolution is to be improved further

Maximizing the hyperpolarizability of one-dimensional systems

Previous studies have used numerical methods to optimize the hyperpolarizability of a one-dimensional quantum system. These studies were used to suggest properties of one-dimensional organic molecules, such as the degree of modulation of conjugation, that could potentially be adjusted to improve the nonlinear-optical response. However, there were no conditions set on the optimized potential energy function to ensure that the resulting energies were consistent with what is observed in real molecules. Furthermore, the system was placed into a one-dimensional box with infinite walls, forcing the wavefunctions to vanish at the ends of the molecule. In the present work, the walls are separated by a distance much larger than the molecule's length; and, the variations of the potential energy function are restricted to levels that are more typical of a real molecule. In addition to being a more physically-reasonable model, our present approach better approximates the bound states and approximates the continuum states - which are usually ignored. We find that the same universal properties continue to be important for optimizing the nonlinear-optical response, though the details of the wavefunctions differ from previous result.Comment: 10 pages, 5 figure

Instrumentation Enhancement at the T.W. Daniel Experimental Forest: A Drought Management Initiative Project

Work at Utah State University\u27s T.W. Daniel Experimental Forest (TWDEF) has been helpful in increasing understanding of the fate of water in native ecosystems. TWDEF is at an elevation of 2600m, and is a montane forest-meadow mosaic of conifers, aspen, sagebrush and grass-forb communities; providing an ideal setting for comparison of how different vegetation and soil properties affect snowmelt infiltration and soil water storage. At the core of the research site are twelve instrument clusters (3 in each vegetation type) that continuously monitor above ground meteorological and below ground soil conditions at each location. Complementing these stations are 1) a tower mounted eddy covariance system to quantify the surface fluxes of heat, water vapor and C02, as well as the surface radiation balance, 2) four lysimeters providing snowmelt rate data, and 3) a NRCS SN0TEL site which monitors snowpack and related climatic variables to provide year-round precipitation and winter snow water equivalent measurements. Presented are the past year\u27s improvements to the instrumentation infrastructure and several examples of the ongoing work and processing of the collected data. Recent developments in the processing of the eddy flux data have provided waterloss estimates from: 1) sublimation when snow is present, and 2) evapotranspiration during other times of the year. A re-instrumented soil heat flux sensor system has also been implemented at the eddy flux site helping provide consistent data, and, along with net radiation data, has allowed for preliminary energy budget calculations. The project website is located at http://danielforest.usu.edu and the SnoTel URL is: http://www.wcc.nrcs.usda.gov/snotel/snotel.pl?sitenum=1098&state=ut. Carlisle, J, S.B. P. Szafruga, V. Mahat, B. Mace, K. Schreuders, S. B. Jones, D.G. Tarboton, L. Hipps and J.L. Boettinger. 2010.lnstrumentation Enhancement at the T.W. Daniel Experimental Forest: A Drought Management lnitiative Project. Spring Runoff Conference. Utah State University, Apr. 20-21