161 research outputs found
Primary drivers of soil moisture spatial variability: a cosmic-ray neutron rover transect study
No full textSupplementary files for: Dong, J., & Ochsner, T. E. (2018). Soil texture often exerts a stronger influence than precipitation on mesoscale soil moisture patterns. Water Resources Research, 54. https://doi.org/10.1002/2017WR02169
Mathematical analysis of heat pulse signals for soil water flux determination
No full text[1] Soil water flux is an important parameter in studies of runoff, infiltration, groundwater recharge, and subsurface chemical transport. Heat pulse sensors have been proposed as promising tools for measuring soil water fluxes. To date, heat pulse methods have required cumbersome mathematical analyses to calculate soil water flux from the measured data. We present a new mathematical analysis showing that a simple linear relationship exists between soil water flux and the natural log of the ratio of the temperature increase downstream from the line heat source to the temperature increase upstream from the line heat source. The simplicity of this relationship makes heat pulse sensors an attractive option for measuring soil water fluxes. In theory, this method is valid for fluxes with magnitudes between 10−4 and 10−7 m s−1. The range of measurable fluxes is defined by temperature measurement resolution at the lower end and by the assumptions used in the analysis at the higher end.This article is published as Wang, Quanjiu, Tyson E. Ochsner, and Robert Horton. "Mathematical analysis of heat pulse signals for soil water flux determination." Water resources research 38, no. 6 (2002). doi: 10.1029/2001WR001089. Posted with permission.</p
Soil Heat Flux Plates
No full textPersistent concern regarding surface energy balance closure encourages increased scrutiny of potential sources of error. Laboratory and field experiments addressed heat flow distortion and thermal contact resistance errors during measurement of soil heat flux (G) using the flux plate technique. Steady-state, one-dimensional heat flow experiments determined flux plate thermal conductivities (λm) and measured the effect of air gaps and thermal heat sink coatings on plate performance. Use of measured instead of manufacturer-specified λm and plate dimensions in a heat flow distortion correction improved the consistency but not the average disagreement between imposed sand G and corrected plate heat flux density (G m). Consistent underestimates of G in dry sand by 20 to 25% after heat flow distortion correction was attributed to thermal contact resistance effects. A convex air gap 0.1 to 1.32 mm thick across 5.9% of the plate face area reduced G m by up to 9.7%. A thin layer of a thermal heat sink compound with λ 0.18 W m−1 K−1 greater than the plate λm (1.0 W m−1 K−1) did not increase G m in a clay soil but increased G m by ∼6% in quartz sand. A 6.5% increase in G mwas also observed for plates treated with the same heat sink compound in a silt loam soil under field conditions. Thermal contact resistance errors are probably G m may occur due to thermal contact resistance in dry sand and due to heat flow distortion when soil λ >> λm.This article is published as Sauer, Thomas J., Tyson E. Ochsner, and Robert Horton. "Soil Heat Flux Plates." Agronomy journal 99, no. 1 (2007): 304-310. doi: 10.2134/agronj2005.0038s. Posted with permission.</p
Soil Heat Storage Measurements in Energy Balance Studies
No full textEnergy balance studies require knowledge of the heat flux at the soil surface. This flux is determined by summing the heat flux at a reference depth (z r) some centimeters below the surface and the rate of change of heat storage in the soil above z r The rate of change of heat storage, or heat storage for short (ΔS), is calculated from soil volumetric heat capacity (C) and temperature. The objectives of this study were to determine how choices regarding z r, Cmeasurements, and ΔS calculations all affect the accuracy of ΔS data. Heat transfer theory and data from three field sites were used toward these ends. In some studies, shallow reference depths have been used and ΔS neglected. Our results indicate that when z r is sufficiently deep to permit accurate heat flux measurements, ΔS is too large to neglect. Three methods for determining C were evaluated: soil sampling, the ThetaProbe soil moisture sensor, and heat pulse sensors. When C was determined using all three methods simultaneously, the estimates agreed to within 6% on average; however, the temporal variability of C was best recorded with the automated heat pulse sensors. Three approaches for calculating ΔS were also tested. The common approach of letting C vary in time but neglecting its time derivative caused errors when soil water content was changing. These errors exceeded 200 W m−2 in some cases. The simple approach of assuming a constant Cperformed similarly. We introduce a third approach that accounts for the time derivative of Cand yields the most accurate ΔS data.This article is published as Ochsner, Tyson E., Thomas J. Sauer, and Robert Horton. "Soil heat storage measurements in energy balance studies." Agronomy journal 99, no. 1 (2007): 311-319. doi: 10.2134/agronj2005.0103S. Posted with permission.</p
Field Tests of the Soil Heat Flux Plate Method and Some Alternatives
No full textHeat flux plates are commonly used to measure soil heat flux, a component of the surface energy balance. The plate method is simple and precise, but several previous studies have demonstrated the potential for relatively large errors. Here we present the results of in situ tests of the plate method, and we describe some promising alternative methods. Summertime soil heat flux was measured with heat flux plates and with two alternative methods at each of three sites. In total, three alternative methods were used: a single probe gradient method, a three needle gradient method, and a self-calibrating plate method. The standard plate method underestimated the magnitude of the heat flux by 18 to 66% depending on the site and type of plate. Agreement between the alternative methods was good with discrepancies ranging from 2 to 6%. The plates underestimate flux apparently due to a combination of low plate thermal conductivity, thermal contact resistance, and latent heat transfer effects. The three needle gradient method for measuring heat flux performed well at all three sites, providing a good alternative to the standard plate method. The self-calibrating plate method performed well at the one site where it was tested and may also be a good alternative. Increased adoption of these methods should lead to more accurate soil heat flux and surface energy balance data.This article is published as Ochsner, Tyson E., Thomas J. Sauer, and Robert Horton. "Field tests of the soil heat flux plate method and some alternatives." Agronomy journal 98, no. 4 (2006): 1005-1014. doi: 10.2134/agronj2005.0249. Posted with permission.</p
Gina Ochsner
No full textGina Ochsner graduated from George Fox in 1992 and quickly became one of the school’s most critically acclaimed fiction writers. Her 2002 book of short stories, The Necessary Grace to Fall, won the Flannery O’Connor Award for Short Fiction, and her 2005 follow-up, People I Wanted to Be, was recipient of the Oregon Book Award. A novel, The Russian Dreambook of Colour and Flight, received the Grub Street Book Prize in 2011 and was long listed for the Orange Prize in 2010. In all, she has won more than 20 awards for her writing, including the Pacific Northwest Booksellers Association Book Award. Her short stories have been featured in The New Yorker magazine and The Best American Nonrequired Reading. Gina Ochsner is an educator and prolific writer who has received widespread praise for her work. She is the author of the short story collection The Necessary Grace to Fall, winner of the Flannery O’Connor Award for Short Fiction, and the story collection People I Wanted to Be. Both books received the Oregon Book Award. In addition, her novel The Russian Dreambook of Colour and Flight was longlisted for the Orange Award (UK). Ochsner lives in Keizer, Ore., and divides her time between teaching at Corban University and writing. She is the recipient of grants from the Oregon Arts Commission, the National Endowment for the Arts and the Howard Foundation.Since her graduation in 1992, Gina has been a part of numerous volunteer and ministry outreaches. She has worked with the Roma Outreach Ministries (BBI, YWAN Slavic Ministries, and the Cooperative Baptist Fellowship); the Romainian/Moldovan Outreach (Bridge Builders, and the Cooperative Baptist Fellowship); and the Latvian Missions (Bridge Builders International, YWAN, and the Lavitican Public School Cooperation). Her volunteer experience includes work in Roma through Global Missions and Cooperative Baptist Fellowship (short term teams), Youth with a Mission (Slavic short term teams), as a writer/intern for, For God’s Children International with ministries at Bucharest’s Children’s Hospital and Zabil home for the disabled and the Children’s Home in Moldova, a speaker/ workshop leader at the Slavic school in Salem, a speaker/workshop leader for the Public School Conference’s “Integrating Biblical Principles in Education,” in Riga, Latvia. She has also volunteered with the Oregon Writers Colony, Simonka House for Women, as an English Language tutor, for the Northwest Review staff reader, and as a mentor/ workshop leader facilitating with middle and high school grades with an emphasis on creative writing with Title 1 and rural schools.https://digitalcommons.georgefox.edu/noteable_individuals/1088/thumbnail.jp
Threats to the Lugert-Altus Irrigation District: Untangling the Effects of Drought, Land Use Change, and Groundwater Development
No full textFinal Report – Ochsner et al. USGS 104b Project FY2015Start Date: 3/1/2015End Date: 2/29/2016Congressional District: 3rdFocus Category: AG, DROU, GW, SW, WQN, WUDescriptors: Streamflow, groundwater, climate.Students: non
Use of the Dual‐Probe Heat‐Pulse Technique to Monitor Soil Water Content in the Vadose Zone
No full textThe dual-probe heat-pulse (DPHP) technique is emerging as a useful technique for measuring soil volumetric water content (θ). However, few published data are available regarding the performance of the DPHP technique under field conditions. The objective of this study is to evaluate the effectiveness of the DPHP technique for measuring θ under field conditions. We used 24 DPHP sensors to monitor θ in a soybean [Glycine max (L.) Merr.] field during the 2001 and 2002 growing seasons. The DPHP sensors demonstrated durability in field conditions and clear sensitivity to temporal and spatial variations of θ at the scale of measurement. The mean θ measured by the DPHP sensors (θDPHP) was on average 0.040 m3 m−3 larger than the mean θ measured by soil sampling (θSS). The response of the DPHP sensors was linear. Regressions of θDPHP vs. θSS yielded r 2 values of 0.949 and 0.843 at depths of 7.5 and 37.5 cm. The DPHP technique showed good resolution with RMSE values for the regression of 0.009 and 0.011 m3 m−3 at the two measurement depths. The slopes of the regressions were 0.75 rather than 1.0. Errors in θSS are a likely cause of this low slope. We shifted all the θ values for each sensor up or down by a constant value to make the first θ measurement from each sensor equal θ determined from soil sampling near that sensor at the time of installation. This simple matching point procedure improved the accuracy of the DPHP technique, resulting in a −0.024 m3 m−3 average difference between θDPHP and θSS Also, the matching point procedure markedly reduced the variability between sensors, reducing the average SD from 0.063 to 0.026 m3 m−3 This procedure requires no additional soil sampling and is recommended for field applications of the DPHP technique.This article is published as Ochsner, Tyson E., Robert Horton, and Tusheng Ren. "Use of the dual-probe heat-pulse technique to monitor soil water content in the vadose zone." Vadose Zone Journal 2, no. 4 (2003): 572-579. doi: 10.2136/vzj2003.5720. Posted with permission.</p
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