Global Positioning System Techniques Research Articles

The role of policies in land use/cover change since the 1970s in ecologically fragile karst areas of Southwest China: A case study on the Maotiaohe watershed

Study of land use/cover change and its driving forces is one of the most significant fields in global environmental change research. Karst land is a type of important and unique terrain on the Earth's surface because of its extensive distribution, impressive landforms, and high ecological fragility. Recently, more and more researchers have realized that irrational land use practices are leading to a series of alarming environmental issues including rocky desertification in karst areas. Studies on land use/cover change and its driving forces in karst areas are significant in achieving regional ecological construction and sustainable development. Policy has long been considered as one of the major driving forces at national level for land use/cover change. In mainland China, designated and in-depth study on the interaction between land use/cover change and relevant policies is still very limited. Through an integrated technique of geographic information system (GIS), remote sensing (RS), and global positioning system (GPS), the authors attempted to address this issue by using the Maotiaohe watershed in Guizhou province in southwestern China as a case to examine its land use/cover change patterns, and the roles of policies in land use, agriculture, forestry, and eco-environmental protection from 1973 to 2007. The study indicated that land policies contributed largely to the increase of arable land in the 1980s, and helped prevent it from decreasing at the fringe of cities and towns since the 1990s; agricultural policies played active roles in the change of water area and indirectly contributed to the change of construction land. The forestry and eco-environmental policies were found to be the main reasons for the consistent increase of forest land since the 1980s and for the decrease of arable land and rocky desertification land since the 1990s.

Can RTK GPS be Used to Improve Cadastral Infrastructure?

Cadastral surveying is concerned with the process of gathering evidence in the form of position information that is used to define the location of objects or land boundaries for the purposes of identifying ownership and/or the value of land parcels. The advent of Global Navigation Satellite Systems (GNSS), such as the Global Positioning System (GPS), has revolutionised the way 3dimensional positions are determined and GPS surveying techniques, particularly Real Time Kinematic (RTK), are increasingly being adopted by cadastral surveyors. This paper presents a methodology for using RTK GPS observations to improve the existing cadastral survey control infrastructure, based on an extensive survey carried out in New South Wales, Australia. It is shown that accuracies (RMS) of 11 mm in the horizontal and 34 mm in the vertical component (1) can be achieved for this dataset. Calculated bearings and distances agree very well with the official values derived from the state’s survey control database, easily meeting accuracy specifications and survey regulation requirements. 55% of the unestablished marks surveyed were able to be upgraded to cadastral survey control quality. Enhancements in the GPS survey design would have enabled an even higher percentage of marks to be classified as established, showing that the RTK GPS technique is well suited to improving survey control infrastructure for cadastral surveyors.

The Integration of TLS and Continuous GPS to Study Landslide Deformation: A Case Study in Puerto Rico

The Integration of TLS and Continuous GPS to Study Landslide Deformation: A Case Study in Puerto RicoTerrestrial Laser Scanning (TLS) and Global Positioning System (GPS) technologies provide comprehensive information on ground surface deformation in both spatial and temporal domains. These two data sets are critical inputs for geometric and kinematic modeling of landslides. This paper demonstrates an integrated approach in the application of TLS and continuous GPS (CGPS) data sets to the study of an active landslide on a steep mountain slope in the El Yunque National Forest in Puerto Rico. Major displacements of this landslide in 2004 and 2005 caused the closing of one of three remaining access roads to the national forest. A retaining wall was constructed in 2009 to restrain the landslide and allow the road reopen. However, renewed displacements of the landslide in the first half of 2010 resulted in deformation and the eventual rupture of the retaining wall. Continuous GPS monitoring and two TLS campaigns were performed on the lower portion of the landslide over a three-month period from May to August 2010. The TLS data sets identified the limits and total volume of themoving mass, while the GPS data quantified the magnitude and direction of the displacements. A continuous heavy rainfall in late July 2010 triggered a rapid 2-3 meter displacement of the landslide that finally ruptured the retaining wall. The displacement time series of the rapid displacement is modeled using a fling-step pulse from which precise velocity and acceleration time series of the displacement are derived. The data acquired in this study have demonstrated the effectiveness and power of the integrating TLS and continuous GPS techniques for landslide studies.

Spatial and temporal patterns of habitat use by Eurasian oystercatchers (Haematopus ostralegus) in the eastern Wadden Sea revealed using GPS data loggers

Detailed knowledge on species–habitat relationships is of crucial importance for the understanding of processes in marine ecosystems. Being top-predators, birds are important bio-indicators for marine systems. The aim of this study was to elucidate precise information on foraging habitat use and foraging times of oystercatchers (Haematopus ostralegus) on wide tidal flats using global positioning system (GPS) data loggers. The study was conducted to collect hints for the negative population trends in oystercatchers in the Wadden Sea. It is the first time that GPS technique has been used in a shorebird species. Although oystercatchers are known to exhibit foraging site fidelity, a number of individuals visited multiple sites. Foraging trips at night were longer, and the targeted sites were further away than those used during the day. These patterns were likely to be caused by higher risks of clutch predation by avian predators during the day that led adults to reduce their absence to defend their clutches. Our methodological approach enabled the subtle spatio-temporal patterns of habitat use to be determined on a very fine spatio-temporal scale. We suggest further potential studies using GPS data loggers that may help to reveal the reasons for the current declines in oystercatcher populations in the German Wadden Sea.

Preparing to Replace the Official Horizontal and Vertical Datums in the United States: Federal Geospatial Summit on Improving the National Spatial Reference System; Silver Spring, Maryland, 11–12 May 2010

The National Spatial Reference System (NSRS) contains both the official “horizontal” and “vertical” datums of the United States: the North American Datum of 1983 (NAD83) and the North American Vertical Datum of 1988 (NAVD88). Horizontal datums provide reference latitude and longitude on Earth's surface; vertical datums are used for describing elevation. The responsibility for defining, maintaining, and providing access to these datums falls to the National Geodetic Survey (NGS), an office within the National Oceanic and Atmospheric Administration (NOAA).These datums were created to correct deficiencies in the previous (1920's era) datums. Still, they relied almost exclusively on terrestrial surveying and the use of passive marks for their realization. Once the Global Positioning System (GPS) and other space geodetic techniques were widely operational, some significant issues became apparent. First, NAD83 has a nongeocentricity (i.e., its origin differs from the known center of Earth's mass) of approximately 2.2 meters. Second, the use of NAVD88's unmonitored passive control benchmarks to determine elevations lacks critical vertical velocity information. Additionally, the zero‐elevation surface of NAVD88 is now known to be biased (50 centimeters) and tilted (2 meters from Florida to Alaska) relative to the geoid.

GPS/INS navigation precision and its effect on airborne radio occultation retrieval accuracy

An airborne radio occultation (RO) system has been developed to retrieve atmospheric profiles of refractivity, moisture, and temperature. The long-term objective of such a system is deployment on commercial aircraft to increase the quantity of moisture observations in flight corridors in order to improve weather forecast accuracy. However, there are several factors important to operational feasibility that have an impact on the accuracy of the airborne RO results. We investigate the effects of different types of navigation system noise on the precision of the retrieved atmospheric profiles using recordings from the GNSS Instrument System for Multistatic and Occultation Sensing (GISMOS) test flights, which used an Applanix POS/AV 510 Global Positioning System (GPS)/Inertial Navigation System (INS). The data were processed using a carrier phase differential GPS technique, and then the GPS position and inertial measurement unit data were combined in a loosely coupled integrated inertial navigation solution. This study quantifies the velocity precision as a function of distance from GPS reference network sites, the velocity precision with or without an inertial measurement unit, the impact of the quality of the inertial measurement unit, and the compromise in precision resulting from the use of real-time autonomous GPS positioning. We find that using reference stations with baseline lengths of up to 760 km from the survey area has a negligible impact on the retrieved refractivity precision. We also find that only a small bias (less than 0.5% in refractivity) results from the use of an autonomous GPS solution rather than a post-processed differential solution when used in an integrated GPS/INS system. This greatly expands the potential range of an operational airborne radio occultation system, particularly over the oceans, where observations are sparse.

Global positioning system and associated technologies in animal behaviour and ecological research

Biologists can equip animals with global positioning system (GPS) technology to obtain accurate (less than or equal to 30 m) locations that can be combined with sensor data to study animal behaviour and ecology. We provide the background of GPS techniques that have been used to gather data for wildlife studies. We review how GPS has been integrated into functional systems with data storage, data transfer, power supplies, packaging and sensor technologies to collect temperature, activity, proximity and mortality data from terrestrial species and birds. GPS 'rapid fixing' technologies combined with sensors provide location, dive frequency and duration profiles, and underwater acoustic information for the study of marine species. We examine how these rapid fixing technologies may be applied to terrestrial and avian applications. We discuss positional data quality and the capability for high-frequency sampling associated with GPS locations. We present alternatives for storing and retrieving data by using dataloggers (biologging), radio-frequency download systems (e.g. very high frequency, spread spectrum), integration of GPS with other satellite systems (e.g. Argos, Globalstar) and potential new data recovery technologies (e.g. network nodes). GPS is one component among many rapidly evolving technologies. Therefore, we recommend that users and suppliers interact to ensure the availability of appropriate equipment to meet animal research objectives.

Structures oscillations monitoring with global positioning system and adaptive filtering techniques

PurposeThis paper aims to detect small dynamic displacements by analysis of L1 Global Positioning System carrier frequency using an improved method for collecting data and filtering techniques on monitoring large structures. It is proposed to analyze the phase residuals directly from the raw phase observable data collected in a short baseline during a limited time span, in lieu of obtaining the residual data file from regular GPS processing programs.Design/methodology/approachThe approach of this paper is an update on the method based on the interferometer idea for analyzing the Global Positioning Systems signals applying adaptive filtering techniques on the phase residuals computed through the double difference adjusted by the 3rd order polynomial. The method is based on the frequency domain analysis of the phase residuals resulted from the L1 double difference static data processing of only two satellites.FindingsThis research improves the ability to characterize the dynamic behavior of large structures though the detection of millimeter‐level data of structural amplitude oscillation response and its frequency value.Practical implicationsSupport of Civil Engineers by collaboration on monitoring oscillations of spans and towers of large bridges; determination of amplitude oscillations value and low‐frequency modal values. The paper presents two trials to verify the proposed methodology for using GPS as a tool for monitoring large structures.Originality/valueThe paper presents a comprehensive framework and implementation approach to demonstrate the capabilities of Global Positioning System as a tool for monitoring large structures providing accurate response data at high levels of precision.

An inter-comparison of zenith tropospheric delays derived from DORIS and GPS data

Doppler Orbitography Radiopositioning Integrated by Satellite (DORIS) and Global Positioning System (GPS) techniques are similarly affected by propagation delays in the neutral atmosphere (troposphere) and hence make use of similar data processing strategies for reducing this effect. We compare Zenith Tropospheric Delays (ZTDs) estimated from 52 DORIS and GPS station pairs co-located at 35 sites over the 2005–2008 period. We find an overall systematic negative mean bias of −4 mm and a median bias of −2 mm, with a large site-to-site scatter and especially stronger biases over South America, potentially linked to remaining problems related to the South Atlantic Anomaly (SAA) in the current DORIS data processing. The standard deviation of ZTD differences is in the range 4–12 mm over the globe (8 mm on average), with larger values located in the southern hemisphere. The spatial variability of differences is consistent with previous work but remains largely unexplained. DORIS is shown to be much less sensitive to instrumental changes than GPS (only the switch from Alcatel to Starec antenna at Toulouse is detected as an offset of −4 mm in the ZTD time series). On the opposite, discontinuities and spurious annual signals are found in the GPS ZTD solutions. A discontinuity of +5 mm is found on 5 November 2006, linked to the switch from relative to absolute GPS antenna models used in the data processing. The use of modified GPS antennas (e.g. at GODE) or improved antenna models is shown to reduce the spurious annual signal (e.g. from 5 mm to 2 mm at METS). Overall, the agreement between both techniques is good, though DORIS shows a significantly larger random scatter. The high stability and good spatial and temporal coverage make DORIS a potential candidate technique for meteorology and climate studies as long as reasonable time averaging can be applied (e.g. differences are reduced from 8.6 to 2.4 mm with 5-day averages) and no real-time application is considered. This technique could be considered as a potential contributor to Global Geodetic Observing System (GGOS) for climatology.

GPR and GPS data integration: examples of application in Antarctica

Ground Penetrating Radar (GPR) and Global Positioning System (GPS) techniques were employed in snow accumulation studies during the Italian leg of the International Trans-Antarctic Scientific Expedition (ITASE). The acquired data were useful both for glaciological and climatological studies. This paper presents some results obtained by GPR and GPS data integration employed to determine accumulation/ablation processes along the profile of the traverse that show how the snow-sublayer thickness can vary quickly in just a few kilometres. Some examples of data integration employed in detection and characterisation of buried crevasses are also presented.

Local effects of redundant terrestrial and GPS-based tie vectors in ITRF-like combinations

Tie vectors (TVs) between co-located space geodetic instruments are essential for combining terrestrial reference frames (TRFs) realised using different techniques. They provide relative positioning between instrumental reference points (RPs) which are part of a global geodetic network such as the international terrestrial reference frame (ITRF). This paper gathers the set of very long baseline interferometry (VLBI)–global positioning system (GPS) local ties performed at the observatory of Medicina (Northern Italy) during the years 2001–2006 and discusses some important aspects related to the usage of co-location ties in the combinations of TRFs. Two measurement approaches of local survey are considered here: a GPS-based approach and a classical approach based on terrestrial observations (i.e. angles, distances and height differences). The behaviour of terrestrial local ties, which routinely join combinations of space geodetic solutions, is compared to that of GPS-based local ties. In particular, we have performed and analysed different combinations of satellite laser ranging (SLR), VLBI and GPS long term solutions in order to (i) evaluate the local effects of the insertion of the series of TVs computed at Medicina, (ii) investigate the consistency of GPS-based TVs with respect to space geodetic solutions, (iii) discuss the effects of an imprecise alignment of TVs from a local to a global reference frame. Results of ITRF-like combinations show that terrestrial TVs originate the smallest residuals in all the three components. In most cases, GPS-based TVs fit space geodetic solutions very well, especially in the horizontal components (N, E). On the contrary, the estimation of the VLBI RP Up component through GPS technique appears to be awkward, since the corresponding post fit residuals are considerably larger. Besides, combination tests including multi-temporal TVs display local effects of residual redistribution, when compared to those solutions where Medicina TVs are added one at a time. Finally, the combination of TRFs turns out to be sensitive to the orientation of the local tie into the global frame.

Accuracy of Static Differential GPS Techniques; Implications for Structural Deformation Monitoring

In recent years, the need to monitor for Deformation in Engineering Structures such as Dams, Bridges and Tall buildings have become more necessary as a result of reported failures of many of these structures with catastrophic consequences globally. Global Positioning System (GPS) is highly automated and less labour intensive than other conventional techniques used in structural deformation monitoring. For most applications, such as National Geodetic Control Network, Urban Control Network and other Engineering Control Network, an accuracy in the cm level for most GPS work is quite adequate. For Structural deformation monitoring however, the required accuracy is in millimeters. In this paper, the use of Static Differential GPS method with multiple receivers for high precision measurement was investigated using the monitoring Stations at Ikpoba Dam as case study Scenerio. Four units of LEICA 300 Dual Frequency GPS receivers were deployed for code and carrier phase measurements with observation session of 1hr at a sampling rate of 15 sec. Baseline Processing and Least Squares Adjustment of observation was carried out in WGS 84 and NTM reference frames using the LEICA SKI-PRO Processing software and Move. Analysis of the results revealed that the number of outliers in the observation were <5% and the accuracy of horizontal and vertical coordinates were 4mm maximum for horizontal and 2mm maximum for vertical. The study revealed that in areas with favourable satellite constellation and appropriate reduction or elimination of multipath and other noise like errors, Static Differential GPS techniques with a combination of code and carrier phase measurement gives good results for structural deformation monitoring.

The 4D microgravity method for waterflood surveillance: Part 3 — 4D absolute microgravity surveys at Prudhoe Bay, Alaska

The 4D microgravity method is becoming a mature technology. A project to develop practical measurement and interpretation techniques was conducted at Prudhoe Bay, Alaska, from 1994 through 2002. Beginning in 2003 these techniques have been systematically applied to monitor a waterflood in the gas cap of the Prudhoe Bay reservoir. Approximately 300 stations in a [Formula: see text] area are reoccupied in each survey year with sub-[Formula: see text] precision absolute gravity and centimeter precision Global Positioning System (GPS) geodetic measurements. The 4D gravity measured over epochs 2005–2003, 2006–2003, and 2007–2003 has been successfully modeled to track the mass of water injected since late in 2002. A new and improved version of the A-10 field-portable absolute gravity meter was developed in conjunction with this project and has proven to be a key element in the success of the 4D methodology. The use of an absolute gravity meter in a field survey of this magnitude is unprecedented. There are substantial differences between a 4D absolute microgravity survey and a conventional gravity survey in terms of station occupation procedures, GPS techniques, and the 4D elevation correction. We estimate that the overall precision of the 4D gravity signal in each epoch is less than [Formula: see text].

Geotechnical Survey, Dredgeability Of Soil Sediments And Siltation Volume Of Brimsu Water Reservoir

The water supply for the Cape Coast Metropolis of Ghana comes from Brimsu reservoir. The accumulation of soil sediments in the reservoir since construction and commissioning in 1928 has resulted in a drastic reduction of the storage capacity of the reservoir leading to perennial water shortages to the community. A dredging syst-em to desilt the sediments and to improve the storage capacity was investigated. The volume of siltation was determined by hydrographic and topographical surveys using Global Positioning System and Total Station Tec-hniques to obtain data on the area and thickness of the sediments. The rate of siltation had more than doubled since the construction. The geotechnical characteristics of the sediments showed the sediments were of unifor-mly graded sand with admixtures of clay and silt. The dredgeability of the sediments was characterized by geo-technical descriptor terms, indicating that the sediments could be dredged using cutter-type dredger for excava-tion, and transported by hydraulic pipelines to disposal sites. The study established that sustainable environme-ntal management is required to minimize the siltation of the reservoir and ensure regular water supply. Journal of Applied Science and Technology Vol. 12 (1&2) 2007: pp. 71-77

Carrier-Phase Differential Global Positioning System Navigation Filter for High-Altitude Spacecraft

A new navigation Kalman filter has been developed which uses carrier-phase differential Global Positioning System techniques in a framework that includes integer ambiguities to estimate the relative states of high-altitude, formation-flying spacecraft. This model-based approach to relative navigation allows spacecraft formations to use carrier-phase techniques above the Global Positioning System constellation. The filter uses dynamics models for the spacecraft orbits, receiver clocks, ionospheric total electron content, and Global Positioning System satellite residual position and clock errors. The process noise driving the orbital dynamics is separated into a common-mode part and lower intensity differential-mode part to better model how disturbances influence formations. The ionospheric total electron content model contains information that allows the filter to decide when to use the dual-frequency measurements to correct for the ionosphere and when to use them to aid in integer ambiguity resolution. The filter tracks undifferenced carrier-phase ambiguities, but still resolves the double-differenced integer ambiguities for use in the relative navigation solution. Monte Carlo simulations are used to evaluate the filter's performance. In geostationary scenarios, the filter's mean relative position error magnitude is 1.2 cm, and its maximum error magnitude is 6 cm. In high-Earth-orbit scenarios at an apogee distance of 18 Earth radii, the filter's mean error magnitude is 11 cm, and its maximum error magnitude is 54 cm. The correct integer ambiguities are resolved in one or two 30 s measurement steps in most cases.

Assessment of wetland fragmentation in the Tarim River basin, western China

The wetlands in the middle and lower reaches of the Tarim River are a rich area of biodiversity and natural resources in the inland arid region of China. However, this wetland area has decreased in size during the past several decades. Water quality and biodiversity has declined due to expanded agricultural activities since 1960s. Using remote sensing (RS), geographic information system (GIS) and global positioning system (GPS) techniques, we investigated the dynamics, spatial patterns and fragmentation of the wetlands in the middle and lower reaches of the Tarim River from 1980 to 2000. We found that the total area of the wetlands was reduced by 45.8% and the density of the patches increased four times from 1980 to 1990. From 1990 to 2000, though the total area of the wetlands slightly increased the number of the patches increased three times and the density of the patches doubled. Based on the analyses of transition matrixes, diversity and fragmentation indexes, and spatial distribution alternation of the wetlands, we found the landscape diversity and fragmentation indices increased while wetland dominance index decreased dramatically. Among the wetland types, the areas of the river-channel, reservoir and pond wetlands increased while the areas of the lake and marsh wetlands decreased continuously.

High-Altitude Satellite Relative Navigation Using Carrier-Phase Differential Global Positioning System Techniques

A new carrier-phase differential global positioning system relative navigation estimator has been developed that extends the use of carrier-phase differential global positioning system techniques to spacecraft formations that operate at geostationary altitudes and above. The estimator achieves rapid convergence to the carrier-phase ambiguities and incorporates a cycle slip detection and recovery algorithm. It solves a linearized problem using least-squares square-root information processing that does not require spacecraft dynamics models. In this context, integer ambiguities are resolved using an integer least-squares algorithm. The cycle slip algorithm identifies the slip channel by statistical hypothesis testing and estimates the magnitude of the slip. Global positioning system receiver-in-the-loop tests with simulated low-Earth orbit data show nearly instantaneous convergence to the correct integer ambiguities and relative position error magnitudes of less than 3 mm. Truth-model simulations are used to simulate geostationary orbits and high-Earth orbit scenarios. The geostationary orbit scenario produces nearly instantaneous convergence to the ambiguities and error magnitudes of less than 0.1 m. The high-Earth orbit case at a radial distance of 17.8 Earth radii converges in minutes with error magnitudes of less than 3 m. Cycle slips, present in the hardware-in-the-loop simulations, are detected and corrected without significant accuracy degradation.

The 4D microgravity method for waterflood surveillance: Part II — Gravity measurements for the Prudhoe Bay reservoir, Alaska

Between 1994 and 2002, a series of experiments was conducted at Prudhoe Bay, Alaska, aimed at the development of an effective 4D (or time-lapse) gravity technique. Theoretical investigations had pointed out the potential for monitoring water injection in the [Formula: see text]-deep reservoir, but it was not clear that gravity measurements of sufficient accuracy could be made in the arctic environment. During the course of these experiments, new techniques and instrumentation were introduced and perfected for both gravity and position measurements. Gravity stations are located using high-precision global positioning system (GPS) techniques without permanent monuments. Robust methods for meter drift control have improved noise resistance in relative gravimeter surveys. Absolute gravity measurements with a field-portable instrument maintain absolute gravity levels among surveys. A 4D gravity-difference noise of [Formula: see text] standard deviation has been established at Prudhoe Bay for GPS-controlled relative gravimeter surveys. The lessons learned are now being applied to full-scale waterflood monitoring at Prudhoe Bay. The basic technique is applicable to microgravity surveys and 4D microgravity surveys for any purpose.

MODES-2D—Method of detecting strike-shift shear zones

One of the goals of using the Global Positioning System (GPS) and other geodetic survey techniques in tectonics has been to detect boundaries such as faults or shear zones between rigid or mildly deforming crustal masses. The calculation of infinitesimal strains and rotations with GPS data has been widely used to detect shear zones but it has been largely unsuccessful because infinitesimal strain and rotation, although useful in many other ways, is non-diagnostic of shear zones or faults. Our approach is to work with components of deformation, not strain, and to design specifically a diagnostic method of detecting shear zones. This paper introduces the first part of our method, the detection of two-dimensional, strike-shift shear zones (MODES-2D). The MODES-2D method has three elements: (1) determination of the orientation of a suspected strike-shift shear zone by analyzing components of a deformation tensor derived from a data set of displacements in an arbitrary coordinate system; (2) resolution of the deformation tensor into the coordinate system parallel and normal to the detected shear zone; and (3) exploration of the resolved data set for evidence for a belt of inhomogeneous deformation, which is an essential characteristic of a shear zone. The operation of MODES-2D is illustrated herein with a theoretical survey network across an ideal shear zone developed with a buried dislocation-fault and with a survey network afforded by the crossing of the Kaynaşlı viaduct by the 1999 Düzce–Bolu earthquake rupture in Turkey.

Quantification of spontaneous locomotion activity in foals kept in pastures under various management conditions

To describe spontaneous locomotion activity of foals kept under various management conditions and assess the suitability of global positioning system (GPS) technology for recording foal activity. Animals-59 foals. During the foals' first 4 months of life, 921 observation periods (15 minutes each) were collected and analyzed for locomotion activities. The GPS system was evaluated by simultaneously carrying out field observations with a handheld computer. Foals spent 0.5% of total observed time cantering, 0.2% trotting, 10.7% walking, 32.0% grazing, 34.8% standing, and 21.6% lying down. Total observed daytime workload (velocity x distance) in the first month was approximately twice that in the following months. Locomotion activity decreased with increasing age. Colts had more activity than fillies in certain periods, and foals that were stabled for some portion of the day had compensatory locomotion activity, which was probably insufficient to reach the level of foals kept continually outside. The GPS recordings and handheld-computer observations were strongly correlated for canter, trot, and walk and moderately correlated for standing and lying. Correlation for grazing was low. Results indicated that domestically managed foals, when kept 24 h/d at pasture, will exercise at a level comparable with feral foals. High workload during the first month of life might be important for conditioning the musculoskeletal system. The GPS technique accurately quantified canter, trot, and walk activities; less accurately indexed resting; and was unsuitable for grazing because of the wide array of velocities used while foraging.