Copyright (c) 2013 University of Connecticut All rights reserved. http://digitalcommons.uconn.edu/nrme_articles Recent documents in Department of Natural Resources and the Environment Articles en-us Tue, 09 Apr 2013 18:35:33 PDT 3600 http://digitalcommons.uconn.edu/nrme_articles/12 http://digitalcommons.uconn.edu/nrme_articles/12 Thu, 08 Jul 2010 08:01:19 PDT Comparing published NAVD 88 Helmert orthometric heights of First-Order bench marks against GPS-determined orthometric heights showed that GEOID03 and GEOID09 perform at their reported accuracy in Connecticut. GPS-determined orthometric heights were determined by subtracting geoid undulations from ellipsoid heights obtained from a network least-squares adjustment of GPS occupations in 2007 and 2008. A total of 73 markers were occupied in these stability classes: 25 class A, 11 class B, 12 class C, 2 class D bench marks, and 23 temporary marks with transferred elevations. Adjusted ellipsoid heights were compared against OPUS as a check. We found that: the GPS-determined orthometric heights of stability class A markers and the transfers are statistically lower than their published values but just barely; stability class B, C and D markers are also statistically lower in a manner consistent with subsidence or settling; GEOID09 does not exhibit a statistically significant residual trend across Connecticut; and GEOID09 out-performed GEOID03. A "correction surface" is not recommended in spite of the geoid models being statistically different than the NAVD 88 heights because the uncertainties involved dominate the discrepancies. Instead, it is recommended that the vertical control network be re-observed.

]]> Thomas H. Meyer et al. http://digitalcommons.uconn.edu/nrme_articles/11 http://digitalcommons.uconn.edu/nrme_articles/11 Wed, 09 Sep 2009 05:20:30 PDT A study was conducted to empirically determine the degradation of survey-grade GPS horizontal position measurements due to the effects of broadleaf forest canopies. The measurements were taken using GPS/GLONASS-capable receivers measuring C/A and P-codes, and carrier phase. Fourteen survey markers were chosen in central Connecticut to serve as reference markers for the study. These markers had varying degrees of sky obstruction due to overhanging tree canopies. Sky obstruction was measured by photographing the sky with a 35mm reflex camera fitted with a hemispherical lens. The negative was scanned and the image mapped using an equal- area projection to remove the distortion caused by the lens. The resulting digital image was thresholded to produce a black-and-white image in which a count of the black pixels is a measure of sky-area obstruction. The locations of the markers were determined independently before the study. During the study, each marker was occupied for four 20-minute sessions over the period of one week in mid-July, 1999. The location of the study markers produced relatively long baselines, as compared with similar studies. We compared the accuracy of GPS-only vs. GPS&GLONASS as a function of sky obstruction. Based on our results, GLONASS observations did not improve or degrade the accuracy of the position measurements. There is a loss of 2mm of accuracy per percent of sky obstruction for both GPS only and GPS&GLONASS.

]]> Thomas H. Meyer et al. http://digitalcommons.uconn.edu/nrme_articles/10 http://digitalcommons.uconn.edu/nrme_articles/10 Wed, 12 Nov 2008 13:03:27 PST Dust exposure in and near farm fields is of increasing concern for human health and may soon be facing new emissions regulations. Dust plumes of this nature have rarely been documented due to the unpredictable nature of the dust plumes and the difficulties of accurately sampling the plumes. This article presents a dynamic random‐walk model that simulates the field‐scale PM10 (particle diameter <10 >um) dust dispersion from an agriculture disking operation. The major improvements over traditional plume models are that it can simulate moving sources and plume meander. The major inputs are the friction velocity (u*), wind direction in the simulation period, atmospheric stability, and source strength (ug s-1). In each time step of the model simulation, three instantaneous wind velocities (x, y, and z directions) are produced based on friction velocity, mean wind speed, and atmospheric stability. The computational time step is 0.025 times the Lagrangian time scale. The resulting instantaneous wind vectors transport all the individual particles. The particle deposition algorithm calculates if a particle is deposited based on the particle settling speed and vertical wind velocity when it touches the ground surface. The particle mass based concentration in 3‐D can be obtained at any instant by counting the particle numbers in a unit volume and then converting to mass based on the particle size and density. Simulations from this model are verified by comparison with dust dispersion and plume concentrations obtained by an elastic backscatter LIDAR. The simulated plume spread parameters (oy, oz) at downplume distances up to 160 m were within ±73% of those measured with a remote aerosol LIDAR. Cross‐correlations between a modeled plume and LIDAR measurements of the actual plume were as high as 0.78 near the ground and decreased to 0.65 at 9 m above ground, indicating close pattern similarity between the modeled and measured plumes at lower heights but decreasing with elevation above the ground.

]]> Thomas H. Meyer http://digitalcommons.uconn.edu/nrme_articles/9 http://digitalcommons.uconn.edu/nrme_articles/9 Tue, 14 Oct 2008 12:46:55 PDT The State of Connecticut owns a LIght Detection and Ranging (LIDAR) data set that was collected in 2000 as part of the State’s periodic aerial reconnaissance missions. Although collected eight years ago, these data are just now becoming ready to be made available to the public. These data constitute a massive “point cloud”, being a long list of east-north-up triplets in the State Plane Coordinate System Zone 0600 (SPCS83 0600), orthometric heights (NAVD 88) in US Survey feet. Unfortunately, point clouds have no structure or organization, and consequently they are not as useful as Triangulated Irregular Networks (TINs), digital elevation models (DEMs), contour maps, slope and aspect layers, curvature layers, among others. The goal of this project was to provide the computational infrastructure to create a first cut of these products and to serve them to the public via the World Wide Web. The products are available at http://clear.uconn.edu/data/ct_lidar/index.htm.

]]> Thomas H. Meyer http://digitalcommons.uconn.edu/nrme_articles/8 http://digitalcommons.uconn.edu/nrme_articles/8 Tue, 08 Jul 2008 05:55:33 PDT The Everglades Depth Estimation Network (EDEN) is an integrated network of realtime water-level monitoring, ground-elevation modeling, and water-surface modeling that provides scientists and managers with current (2000-present), online water-stage and water-depth information for the entire freshwater portion of the Greater Everglades. Continuous daily spatial interpolations of the EDEN network stage data are presented on grid with 400-square-meter spacing. EDEN offers a consistent and documented dataset that can be used by scientists and managers to: (1) guide large-scale field operations, (2) integrate hydrologic and ecological responses, and (3) support biological and ecological assessments that measure ecosystem responses to the implementation of the Comprehensive Everglades Restoration Plan (CERP) (U.S. Army Corps of Engineers, 1999). The target users are biologists and ecologists examining trophic level responses to hydrodynamic changes in the Everglades. The first objective of this report is to validate the spatially continuous EDEN water-surface model for the Everglades, Florida developed by Pearlstine et al. (2007) by using an independent field-measured data-set. The second objective is to demonstrate two applications of the EDEN water-surface model: to estimate site-specific ground elevation by using the validated EDEN water-surface model and observed water depth data; and to create water-depth hydrographs for tree islands. We found that there are no statistically significant differences between model-predicted and field-observed water-stage data in both southern Water Conservation Area (WCA) 3A and WCA 3B. Tree island elevations were derived by subtracting field water-depth measurements from the predicted EDEN water-surface. Water-depth hydrographs were then computed by subtracting tree island elevations from the EDEN water stage. Overall, the model is reliable by a root mean square error (RMSE) of 3.31 cm. By region, the RMSE is 2.49 cm and 7.77 cm in WCA 3A and 3B, respectively. This new landscape-scale hydrological model has wide applications for ongoing research and management efforts that are vital to restoration of the Florida Everglades. The accurate, high-resolution hydrological data, generated over broad spatial and temporal scales by the EDEN model, provides a previously missing key to understanding the habitat requirements and linkages among native and invasive populations, including fish, wildlife, wading birds, and plants. The EDEN model is a powerful tool that could be adapted for other ecosystem-scale restoration and management programs worldwide.

]]> John C. Volin et al. http://digitalcommons.uconn.edu/nrme_articles/7 http://digitalcommons.uconn.edu/nrme_articles/7 Thu, 19 Jun 2008 06:46:32 PDT Height of instrument (HI) blunders in GPS measurements cause position errors. These errors can be pure vertical, pure horizontal, or a mixture of both. There are different error regimes depending on whether both the base and the rover both have HI blunders, if just the base has an HI blunder, or just the rover has an HI blunder. The resulting errors are on the order of 30 cm for receiver separations of 1000 km for an HI blunder of 2 m. Given the complicated nature of the errors, we believe it would be difficult, if not impossible, to detect such errors by visual inspection. This serves to underline the necessity to enter GPS HIs correctly.

]]> Thomas H. Meyer et al. http://digitalcommons.uconn.edu/nrme_articles/6 http://digitalcommons.uconn.edu/nrme_articles/6 Mon, 31 Mar 2008 12:32:22 PDT Laying out a sampling transect in the field is a common task when researching natural systems and resources. With widespread availability of global navigation satellite systems (GNSS), such as the US global positioning system (GPS), it is becoming more common to resurvey legacy transects to establish them in globally referenced coordinate systems such as geodetic latitude/longitude or planimetric systems such as the Universal Transverse Mercator (UTM) or the State Plane Coordinate System (SPCS). Transforming local coordinates into a globally referenced coordinate system allows (1) disparate legacy surveys to be combined into a common geographic information system (GIS) database, (2) new GPS measurements to be incorporated into that same database, and (3) GPS-based navigation to be used for plot establishment and resampling. This article presents the mathematics necessary to determine the globally referenced planimetric coordinates of established linear, rectangular, or nominally rectangular transects (such as a rhombus) using formulas that are easily implemented on a spreadsheet. In addition, methods are given to determine the planimetric coordinates of new transects. Copyright © 2007 by the Society ot American Foresters.

]]> Mark Rudnicki et al. http://digitalcommons.uconn.edu/nrme_articles/5 http://digitalcommons.uconn.edu/nrme_articles/5 Thu, 15 Feb 2007 07:27:54 PST This is the final paper in a four-part series examining the fundamental question, “What does the word height really mean?” The creation of this series was motivated by the National Geodetic Survey’s (NGS) embarking on a height modernization program as a result of which NGS will publish measured ellipsoid heights and computed Helmert orthometric heights for vertical bench marks. Practicing surveyors will therefore encounter Helmert orthometric heights computed from Global Positioning System (GPS) ellipsoid heights and geoid heights determined from geoid models as their published vertical control coordinate, rather than adjusted orthometric heights determined by spirit leveling. It is our goal to explain the meanings of these terms in hopes of eliminating confusion and preventing mistakes that may arise over this change. The first paper in the series reviewed reference ellipsoids and mean sea level datums. The second paper reviewed the physics of heights culminating in a simple development of the geoid in order to explain why mean sea level stations are not all at the same orthometric height. The third paper introduced orthometric heights, geopotential numbers, dynamic heights, normal heights, and height systems. This fourth paper is composed of two sections. The first considers the stability of the geoid as a datum. The second is a review of current best practices for heights measured with the Global Positioning System (GPS), essentially taking the form of a commentary on NGS’ guidelines for high-accuracy ellipsoid and orthometric height determination using GPS.

]]> Thomas H. Meyer et al. http://digitalcommons.uconn.edu/nrme_articles/4 http://digitalcommons.uconn.edu/nrme_articles/4 Fri, 02 Feb 2007 08:28:38 PST Digital terrain models (DTM) typically contain large numbers of postings, from hundreds of thousands to billions. Many algorithms that run on DTMs require topological knowledge of the postings, such as finding nearest neighbors, finding the posting closest to a chosen location, etc. If the postings are arranged irregu- larly, topological information is costly to compute and to store. This paper offers a practical approach to organizing and searching irregularly-space data sets by presenting a collection of efficient algorithms (O(N),O(lgN)) that compute important topological relationships with only a simple supporting data structure. These relationships include finding the postings within a window, locating the posting nearest a point of interest, finding the neighborhood of postings nearest a point of interest, and ordering the neighborhood counter-clockwise. These algorithms depend only on two sorted arrays of two-element tuples, holding a planimetric coordinate and an integer identification number indicating which posting the coordinate belongs to. There is one array for each planimetric coordinate (eastings and northings). These two arrays cost minimal overhead to create and store but permit the data to remain arranged irregularly.

]]> Thomas H. Meyer http://digitalcommons.uconn.edu/nrme_articles/3 http://digitalcommons.uconn.edu/nrme_articles/3 Thu, 14 Sep 2006 12:10:06 PDT Education in Geographic information science (GIS/LIS) happens in the United States both within surveying-related academic programs and in other academic programs that use spatially oriented data and information. This article presents an overview of two such programs. The first is a four-year Bachelor of Science degree program in Geographic Information Science at Texas A&M University-Corpus Christi. The second is a concentration with a four-year Bachelor of Science degree program in Natural Resources at the University of Connecticut (UConn). Geographic information science is the primary focus of the Texas A&M program, whereas GIS/LIS is an emphasis of the UConn program. Both approaches are presented for comparison.

]]> Gary Jeffress et al. http://digitalcommons.uconn.edu/nrme_articles/2 http://digitalcommons.uconn.edu/nrme_articles/2 Thu, 14 Sep 2006 12:05:59 PDT This is the third paper in a four-part series considering the fundamental question, “what does the word “height” really mean?” The first paper reviewed reference ellipsoids and mean sea level datums. The second paper reviewed the physics of heights culminating in a simple development of the geoid and explained why mean sea level stations are not all at the same orthometric height. This third paper develops the principle notions of height, namely measured, differentially deduced changes in elevation, orthometric heights, Helmert orthometric heights, normal orthometric heights, dynamic heights, and geopotential numbers. We conclude with a more in-depth discussion of current thoughts regarding the geoid.

]]> Thomas H. Meyer et al. http://digitalcommons.uconn.edu/nrme_articles/1 http://digitalcommons.uconn.edu/nrme_articles/1 Thu, 22 Jun 2006 08:35:42 PDT We investigated tree sway and crown collision behavior of even-aged lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stands of different structure in Alberta, Canada, to examine how these factors might affect loss of leaf area as stands mature. The Two Creeks stand (TC) had high density and slender trees, while the Chickadee stand (CH) had stout trees. The TC stand was then thinned (TCT) to reduce the stand density. For each stand, simultaneous tree sways of a group of 10 trees were monitored with biaxial clinometers during wind speed of 5 m/s (canopy top). Crown collisions were reconstructed by combining sway displacement of individual trees with their respective crown dimensions. Comparing the sway statistics between stands with contrasting mean bole slenderness (TC and CH) indicated that more slender trees have greater sway displacements, faster sway speeds, and a greater depth of collision. Disturbance by thinning increased sway displacements, sway speeds, and depth of collisions at TCT. Tree sway patterns were circular in shape and not aligned with wind direction, but patterns were elongated after thinning. This demonstrates the high frequency of crown collision experienced by stands with slender trees and supports the notion that crown collisions result in empty space between crowns of trees.

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