This paper describes the Magnetic Electron Ion Spectrometer (MagEIS) instruments aboard the RBSP spacecraft from an instrumentation and engineering point of view. There are four magnetic spectrometers aboard each of the two spacecraft, one low-energy unit (20-240 keV), two medium-energy units (80-1200 keV), and a high-energy unit (800-4800 keV). The high unit also contains a proton telescope (55 keV-20 MeV).The magnetic spectrometers focus electrons within a selected energy pass band upon a focal plane of several silicon detectors where pulse-height analysis is used to determine if the energy of the incident electron is appropriate for the electron momentum selected by the magnet. Thus each event is a two-parameter analysis, an approach leading to a greatly reduced background.The physics of these instruments are described in detail followed by the engineering implementation. The data outputs are described, and examples of the calibration results and early flight data presented.

No abstract

A saturated riparian buffer (SRB) is an edge-of-field conservation practice that reduces nitrate export from agricultural lands by redistributing tile drainage as shallow groundwater and allowing for denitrification and plant uptake. We propose an approach to improve the design of SRBs by analyzing a tradeoff in choosing the SRB width, and we apply the approach to six sites with SRBs in central Iowa. A larger width allows for more residence time, which increases the opportunity for removing nitrate that enters the buffer. However, because the SRBs considered here treat only a portion of the tile flow when it is large, for the same difference in hydraulic head, a smaller width allows more of the total tile flow to enter the buffer and therefore treats more of the drainage. By maximizing the effectiveness of nitrate removal, defined as the ratio of total nitrate removed by the SRB to total nitrate leaving the field in tile drainage, an equation for the optimal width was derived in terms of soil properties, denitrification rates, and head difference. All six sites with existing SRBs considered here have optimal widths smaller than the current width, and two are below the minimum width listed in current design standards. In terms of uncertainty, the main challenges in computing the optimal width for a site are estimating the removal coefficient for nitrate and determining the saturated hydraulic conductivity. Nevertheless, including a width that accounts for site conditions in the design standards would improve water quality locally and regionally.

No abstract

Erosion and sediment controls on construction sites minimize environmental impacts from sediment-laden stormwater runoff. Silt fence, a widely specified perimeter control practice on construction projects used to retain sediment on-site, has limited performance-based testing data. Silt fence failures and resultant sediment losses are often the result of structural failure. To better understand silt fence performance, researchers at the Auburn University-Erosion and Sediment Control Testing Facility (AU-ESCTF) have evaluated three silt fence options to determine possible shortcomings using standardized full-scale testing methods. These methods subject silt fence practices to simulated, in-field conditions typically experienced on-site without the variability of field testing or the limited application of small-scale testing. Three different silt fence practices were tested to evaluate performance, which included: (1) Alabama Department of Transportation (ALDOT) Trenched Silt Fence, (2) ALDOT Sliced Silt Fence, and (3) Alabama Soil and Water Conservation Committee (AL-SWCC) Trenched Silt Fence. This study indicates that the structural performance of a silt fence perimeter control is the most important performance factor in retaining sediment. The sediment retention performance of these silt fence practices was 82.7%, 66.9% and 90.5%, respectively. When exposed to large impoundment conditions, both ALDOT Trench and Sliced Silt Fence practices failed structurally, while the AL-SWCC Trenched Silt Fence did not experience structural failure.