Global Positioning System Recordings Research Articles

Evaluating predictability in outdoor mobility: A potential pathway to personalized assistance for people with dementia

AbstractBackgroundPeople with dementia (PwD) often become lost, which is commonly attributed to spatial disorientation, one of the earliest symptoms of dementia, particularly of the Alzheimer’s disease type. Spatial disorientation can limit a person's ability to navigate in an outdoor environment. As a result, PwD experience outdoor mobility decline, which, in turn, can have a negative impact on their cognitive functions. Thus, enabling safe outdoor mobility is important for dementia research. Artificial Intelligence (AI) methods in conjunction with Global Positioning System (GPS) data show great potential for supporting the outdoor mobility needs of PwD. The objective of this work is to evaluate the extent to which we can predict future destinations of PwD by learning from their past mobility habits.MethodEight cognitively‐intact older adults (CTL) and seven older adults with dementia completed four weeks of GPS recording. Each participant’s stops and trips were extracted from their trajectories. We determined the predictability of each participant’s mobility patterns using three approaches. First, we assumed each stop is visited with equal probability, thus, disregarding temporal aspects of travel. Next, we built on the previous approach by including stop visitation probability, thus, capturing the heterogeneity of visitations. Finally, to capture the full spatiotemporal characteristics of mobility, we added in‐depth temporal characteristics including the visitation frequency, the order in which the stops were visited, and the time spent at each stop.ResultRelying solely on the spatial dimension of mobility yielded no predictive power across the two groups. Adding the heterogeneity of visitation patterns, we observed an increase in the predictability power; PwD displayed a trend toward higher predictability compared to the CTLs, but the student’s t‐test did not reach statistical significance (0.833±0.085vs.0.768±0.029, t(13)=‐2.06, p=0.06; d=‐1.07). Finally, relying on full spatiotemporal characteristics, a 4‐week record of mobility patterns displayed 95% (SD=2%) and 92% (SD=1%) predictability among PwD and CTLs, respectively. This value was significantly higher among PwD, t(13) = ‐3.39, p<.01; d=‐1.75.ConclusionOur findings offer new perspectives on the predictive mobility models based on GPS data and AI that can be used to provide personalized assistance for outdoor navigation of people with dementia.

The use of GPS data to assess behaviour of red deer hinds over calving: hinds farmed in extensive high-country environments

ABSTRACT Global Positioning System (GPS) technology was used to track movements of extensively farmed red deer hinds over the calving period on two New Zealand high-country farms, during the summers of 2006/07, 2007/08 (Haycocks Station) and 2008/09 (White Rock Station). The goal was to analyse positional data around the expected birthing period to define patterns of hind movement that are potentially descriptive of parturient behaviour. A Hidden Markov model (HMM) was used to identify the time and site of calving based on four pre-defined stages of behaviour described for red deer hinds. These stages are: Late pregnancy (State 1), birth-site searching (State 2), birthing (State 3) and post-birthing (State 4). Previous research on red deer hinds over calving on an intensive lowland farm showed a close alignment between actual calving behaviour and those behaviours inferred from the algorithms developed in the HMM. Hinds in the high-country study conformed to the four-stage model of positional movement patterns. Inferred birthing dates ranged from 8 Nov to 3 Dec. The length of time hinds spent searching for a birthing site (State 2) was highly variable and averaged 16 (SE 3.9) hours, with an average 4-fold increase in distance between consecutive GPS recordings relative to that occurring earlier in late pregnancy (State 1), while in the birthing stage (State 3) there was a 40% reduction in distance between recordings compared with State 1. Although actual incidences of birthing were not observable in this study, it is concluded that definable behavioural characteristics of red deer hinds over the calving period can be discerned from GPS positional data. A key observation of this study was the between-hind variability of duration of these innate behaviours that indicates behavioural plasticity in the face of intraspecific competition for resources or perception of threat within extensive farm environments.

GPS Tracking Technologies to Measure Mobility-Related Behaviors in Community-Dwelling Older Adults: A Systematic Review.

Global positioning system (GPS) technology has been increasingly used in aging research as a tool for reliably capturing the level and patterns of mobility among older adults. This article aims to systematically review the current state of GPS-based mobility research with community-dwelling older adults. Twenty-nine studies from 2008 to 2019 are included. Included studies examined various forms of temporal and spatial mobility measures. This review provides a synthesis of the current evidence on the risk factors or correlates of GPS-driven mobility limitations, such as demographic, cognitive, physical, psychological, and environmental factors. There is variability in types of GPS technology and GPS-derived mobility measures, GPS recording methods, data processing, and correlates of mobility limitation across studies. Future research should focus on identifying meaningful GPS-derived mobility measures and developing standardized protocols for GPS administration and data analytics for comparison across studies.

A 20-yr database (1997-2017) of co-seismic displacements from GPS recordings in the Aegean area and their scaling with Mw and hypocentral distance

We describe and make available a dataset of 64 data points of Global Positioning System (GPS) displacements for significant, shallow earthquakes in Greece during the period 1997-2017. The displacement data can be used by earthquake geologists, engineers and seismologists in an effort to better understand the faulting process, the rupture mechanics, the pattern of ground-motions, and in engineering applications. We include recordings from GNSS networks at near-source to regional distances (2–132 km) for 11 earthquakes between global CMT moment magnitudes (Mw) 5.5 and 6.9. We also model the magnitude scaling properties of peak ground horizontal displacements (PGD and PGD-S) for these events using L1-norm minimisation regression. Our data indicate an almost linear attenuation of seismic strain with distance for this range of seismic magnitudes. We developed a set of relationships based on PGD (in cm) and distance to hypocentre R (in km), which may be used for the rapid estimation of the earthquake magnitude in near real-time.MwPGD = [LOG(PGD) + 8.2849]/(1.6810 – 0.2453LOGR)MwPGD-S = [LOG(PGD-S) + 8.0839]/(1.6793 – 0.2447LOGR)

Field trial of a photonics‐based dual‐band fully coherent radar system in a maritime scenario

This study reports the experimental validation of the first photonics-based dual-band radar system in a real maritime scenario, detailing the operation principles as well as the implementation of the demonstrator. The prototype, exploiting photonics for both the generation and the detection of the radar signals, is able to simultaneously handle two radar waveforms in the S-band and the X-band, ensuring also their reciprocal phase coherence. The proposed system implementation is fully detailed and its characterisation is reported, demonstrating a minimum detectable signal of −124 dBm. Finally, the system is tested in a real scenario, nearby the port of Livorno (Italy), where it successfully detects multiple naval targets, and tracks a cooperative vessel for 8 NM. The obtained results are compared with reference data from automatic identification system and global positioning system recorders, showing a perfect match in terms of range and velocity, both in the S- and X-band. Moreover a theoretical analysis of the power budget, considering also the radar cross section in the different frequency bands, is carried out and supported by the experimental observations. Beyond the actual implementation of the proposed system, the outcomes of these tests confirm that the photonics-based approach can lead new advances in radar architecture, through the development of frequency-agile photonic transceivers.

A decade of progress in observing and modelling Antarctic subglacial water systems.

In the decade since the discovery of active Antarctic subglacial water systems by detection of subtle surface displacements, much progress has been made in our understanding of these dynamic systems. Here, we present some of the key results of observations derived from ICESat laser altimetry, CryoSat-2 radar altimetry, Operation IceBridge airborne laser altimetry, satellite image differencing and ground-based continuous Global Positioning System (GPS) experiments deployed in hydrologically active regions. These observations provide us with an increased understanding of various lake systems in Antarctica: Whillans/Mercer Ice Streams, Crane Glacier, Recovery Ice Stream, Byrd Glacier and eastern Wilkes Land. In several cases, subglacial water systems are shown to control ice flux through the glacier system. For some lake systems, we have been able to construct more than a decade of continuous lake activity, revealing internal variability on time scales ranging from days to years. This variability indicates that continuous, accurate time series of altimetry data are critical to understanding these systems. On Whillans Ice Stream, our results from a 5-year continuous GPS record demonstrate that subglacial lake flood events significantly change the regional ice dynamics. We also show how models for subglacial water flow have evolved since the availability of observations of lake volume change, from regional-scale models of water routeing to process models of channels carved into the subglacial sediment instead of the overlying ice. We show that progress in understanding the processes governing lake drainage now allows us to create simulated lake volume time series that reproduce time series from satellite observations. This transformational decade in Antarctic subglacial water research has moved us significantly closer to understanding the processes of water transfer sufficiently for inclusion in continental-scale ice-sheet models.

Commentary on ‘Test-retest Reliability of GPS derived Measurements in Patients with Claudication’

In their paper, Gernigon et al. 1 evaluated the test-retest reliability of Global Positioning System (GPS) derived measurements in patients with claudication under community walking conditions. They showed that the reliability of greatest walking distance and average of walking speeds are high, despite the variability of the different measured distances between two symptom limited stops during a 1 hour stroll. This suggests that GPS technology offers new perspectives in the individual evaluation of walking ability and that it might help in objectively evaluating the severity and the impact of claudication in a patient in his daily life. However, we would like to make some points on the paper. The first point isthatthe methodology suffers from several limitations. Twenty patients were included over a 30 month periodandthreeofthemwereexcludedbecauseofsomeGPS issues. Moreover, there was no standardization between the two series of evaluations, with the second test being performed within 30 days of the first, under potentially different environmental conditions. Total time walking duration was sometimes longer than 1 hour and it is possible that walking 25% longer could change the results. The small sample size, thelong duration ofthestudy,the outdoorstroll, andthe lack of standardization could have influenced biased the results. The second point is the logistics of these measurements. The authors mentioned that the potential advantages of GPS technology in the setting of claudication include price of the test and the time saving. However, the cost of the GPS device, the time needed to equip the patient and explain the procedures, and the time to learn how to analyze the GPS recording were not taken into consideration. The authors also described some adjunctive procedures that could help in improving GPS data interpretation (heart rate, near infrared spectroscopy, temperature), but it is expected that the cost of GPS devices able to record such physiological parameters would be high. Finally, it has already been demonstrated that exercise therapy with hospital or community based training under the supervision of a physical therapist or other trained medical personnel is superior to other forms of exercise therapy, and that increased supervision tends to lead to a greater improvement in walking distance. 2 As a result, supervised exercise has been given a class I, level of evidence A recommendation by the American College of Cardiology/American Heart Association. 3 Moreover, supervised exercise therapy is more cost-effective. 4 In any case, this paper opens the door towards remote evaluation of multiple variables associated with physical activity in claudicants and could help to objectively measure the impact of a given treatment in the patient’s specific daily life conditions. Patients merely have to remember not to leave their smartphone at home!

Applicability of global positioning system for the assessment of walking ability in patients with arterial claudication

This study determined for the first time the clinical applicability of a global positioning system (GPS)-monitored community-based walking ability assessment in a large cohort of patients with peripheral artery disease (PAD). A multicenter study was conducted among PAD patients who complained of intermittent claudication. Patients equipped with a GPS device performed a community-based outdoor walk. We determined the number of technically satisfactory GPS recordings (attempt No. 1). Patients with unsatisfactory GPS recordings were asked to perform a second attempt (attempt No. 2). From the satisfactory recordings obtained after attempts No. 1 and No. 2, we analyzed several GPS parameters to provide clinical information on the patients' walking ability. Results are reported as median (interquartile range). A total of 218 patients performed an outdoor walk. GPS recordings were technically satisfactory in 185 patients (85%) and in 203 (93%) after attempts No. 1 and No. 2, respectively. The highest measured distance between two stops during community walking was 678m (IQR, 381-1333m), whereas self-reported maximal walking distance was 250m (IQR, 150-400m; P< .001). Walking speed was 3.6km/h (IQR, 3.1-3.9km/h), with few variations during the walk. Among the patients who had to stop during the walk, the stop durations were<10minutes in all but one individual. GPS is applicable for the nonsupervised multicenter recording of walking ability in the community. In the future, it may facilitate objective community-based assessment of walking ability, allow for the adequate monitoring of home-based walking programs, and for the study of new dimensions of walking in PAD patients with intermittent claudication.

Active transport between home and school assessed with GPS: a cross-sectional study among Dutch elementary school children

BackgroundActive transport to school is associated with higher levels of physical activity in children. Promotion of active transport has therefore gained attention as a potential target to increase children’s physical activity levels. Recent studies have recognized that the distance between home and school is an important predictor for active travel among children. These studies did not yet use the promising global positioning system (GPS) methods to objectively assess active transport. This study aims to explore active transport to school in relation to the distance between home and school among a sample of Dutch elementary school children, using GPS.MethodsSeventy-nine children, aged 6-11 years, were recruited in six schools that were located in five cities in the Netherlands. All children were asked to wear a GPS receiver for one week. All measurements were conducted between December 2008 and April 2009. Based on GPS recordings, the distance of the trips between home and school were calculated. In addition, the mode of transport (i.e., walking, cycling, motorized transport) was determined using the average and maximum speed of the GPS tracks. Then, proportion of walking and cycling trips to school was determined in relation to the distance between home and school.ResultsOut of all school trips that were recorded (n = 812), 79.2% were classified as active transport. On average, active commuting trips were of a distance of 422 meters with an average speed of 5.2 km/hour. The proportion of walking trips declined significantly at increased school trip distance, whereas the proportion of cycling trips (β = 1.23, p < 0.01) and motorized transport (β = 3.61, p < 0.01) increased. Almost all GPS tracks less than 300 meters were actively commuted, while of the tracks above 900 meters, more than half was passively commuted.ConclusionsIn the current research setting, active transport between home and school was the most frequently used mode of travel. Increasing distance seems to be associated with higher levels of passive transport. These results are relevant for those involved in decisions on where to site schools and residences, as it may affect healthy behavior among children.

Source Rupture Models for the Mw 9.0 2011 Tohoku Earthquake from Joint Inversions of High-Rate Geodetic and Seismic Data

Research Article| May 01, 2013 Source Rupture Models for the Mw 9.0 2011 Tohoku Earthquake from Joint Inversions of High‐Rate Geodetic and Seismic Data Han Yue; Han Yue Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar Thorne Lay Thorne Lay Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar Bulletin of the Seismological Society of America (2013) 103 (2B): 1242–1255. https://doi.org/10.1785/0120120119 Article history first online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Han Yue, Thorne Lay; Source Rupture Models for the Mw 9.0 2011 Tohoku Earthquake from Joint Inversions of High‐Rate Geodetic and Seismic Data. Bulletin of the Seismological Society of America 2013;; 103 (2B): 1242–1255. doi: https://doi.org/10.1785/0120120119 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract The space–time history of fault slip during the 11 March 2011 Tohoku earthquake (Mw 9.0) is determined using high sample rate three‐component Global Positioning System (GPS) recordings from regional stations across Japan, teleseismic broadband P waves, global R1 source time functions determined by empirical Green’s function deconvolutions of short‐arc Rayleigh waves, and ocean‐bottom deformation observations. Least‐squares inversions are performed for models with prescribed rupture‐front expansion velocity. Joint inversion yields improved resolution of slip compared with inversions using any single data type for both checkerboard rupture simulations and the actual data. Joint inversion stabilizes inversions with respect to some key parameters, such as the rupture expansion velocity and subfault total rupture durations, due to lower dependence on these parameters of some datasets (mainly the high sample rate [1 sample/s] three‐component GPS recordings [hr‐GPS] data). The preferred joint inversion model has a seismic moment estimate of 4.2×1022 N·m (Mw 9.0), with a primary large‐slip patch with maximum slip of ∼50–60 m located up‐dip of the hypocenter on the shallow megathrust and distributed slip of 20–30 m near the hypocenter. A down‐dip low‐slip extension to the south is also resolved, with centroid source time later than 110 s.Online Material: Figures of inverted slip distributions and associated source time functions and centroid times, and waveform fits. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Rupture History of the 2011 M 9 Tohoku Japan Earthquake Determined from Strong-Motion and High-Rate GPS Recordings: Subevents Radiating Energy in Different Frequency Bands

Abstract Strong‐motion records from KiK‐net and K‐NET, along with 1 sample/s Global Positioning System (GPS) records from GEONET, were analyzed to determine the location, timing, and slip of subevents of the M 9 2011 Tohoku earthquake. Timing of arrivals on stations along the coast shows that the first subevent was located closer to the coast than subevent (2), which produced the largest slip. A waveform inversion of data from 0 to 0.2 Hz indicates that the first subevent primarily ruptured down‐dip and north of the hypocenter and had an M of 8.5. The areas of this subevent that generated the low ( 0.2 Hz) frequency energy are located in the same vicinity. The inversion result for the second subevent ( M 9.0) has large slip on the shallow part of the fault with peak slip of about 65 m above about 25 km depth. This slip generated the tsunami. The preferred inversion has initiation of subevent 2 on the shallow portion of the fault so that rupture proceeded down‐dip and mainly to the south. Subevent 2 started about 35 s after subevent 1, which allows for the possibility of dynamic triggering from subevent 1. The slip model predicts displacements comparable to those found from ocean‐bottom transducers near the epicenter. At frequencies that most affect tall buildings (0.1–0.5 Hz), there is a strong pulse (subevent 3) in the strong‐motion records that arrives after the near‐field ramp from subevent 2. High‐frequency subevent 3 was located down‐dip and south of the high‐slip portion of subevent 2 and was initiated as rupture from subevent 2 proceeded down‐dip. The compact pulse for subevent 3 is modeled with an M 8.0 source in a 75 by 30 km area that ruptured down‐dip and to the south with a high slip velocity, indicating high stress drop.

Refining spatial resolution and spillovers of a micro-econometric analysis of adapting portfolios to climate change using the global positioning system

This paper refines the spatial resolution and spillover effects of a micro-econometric analysis of adaptation of agricultural portfolios to climate change using the Global Positioning System (GPS). From the household surveys collected across South America by the World Bank, the GPS recordings of exact farm locations such as latitude, longitude, and altitude are matched with high resolution grid cell climate data from the Climate Research Unit as well as geographically referenced soils and geography data from the Food and Agriculture Organization. The choice of agricultural systems at the farm level is estimated using spatial Logit model and the conditional land value is estimated for each system of agriculture after correcting for selection bias and spatial spillovers. Future choices and land values are simulated using the fine resolution climate scenarios by the UKMO (United Kingdom Meteorological Office) and GISS (Goddard Institute for Space Studies). This paper finds that, under the UKMO HadGEM1 (Hadley Center Global Environmental Model 1) scenario by around 2060, the choices of the specialized systems are expected to fall, but the mixed system would increase. The land value of the crops-only falls by 29 %, but the mixed system land value falls only by 12 %. Under a milder GISS ER (ModelE-R) scenario, the land value of the mixed system increases by 6 %. With full adaptations of agricultural systems, the expected land value falls by 17 %. Without adaptations, the damage increases. This paper demonstrates that adaptation behaviors can be best studied by a fine resolution micro-econometric analysis of agricultural portfolios using the GPS reference.

Automated time activity classification based on global positioning system (GPS) tracking data

BackgroundAir pollution epidemiological studies are increasingly using global positioning system (GPS) to collect time-location data because they offer continuous tracking, high temporal resolution, and minimum reporting burden for participants. However, substantial uncertainties in the processing and classifying of raw GPS data create challenges for reliably characterizing time activity patterns. We developed and evaluated models to classify people's major time activity patterns from continuous GPS tracking data.MethodsWe developed and evaluated two automated models to classify major time activity patterns (i.e., indoor, outdoor static, outdoor walking, and in-vehicle travel) based on GPS time activity data collected under free living conditions for 47 participants (N = 131 person-days) from the Harbor Communities Time Location Study (HCTLS) in 2008 and supplemental GPS data collected from three UC-Irvine research staff (N = 21 person-days) in 2010. Time activity patterns used for model development were manually classified by research staff using information from participant GPS recordings, activity logs, and follow-up interviews. We evaluated two models: (a) a rule-based model that developed user-defined rules based on time, speed, and spatial location, and (b) a random forest decision tree model.ResultsIndoor, outdoor static, outdoor walking and in-vehicle travel activities accounted for 82.7%, 6.1%, 3.2% and 7.2% of manually-classified time activities in the HCTLS dataset, respectively. The rule-based model classified indoor and in-vehicle travel periods reasonably well (Indoor: sensitivity > 91%, specificity > 80%, and precision > 96%; in-vehicle travel: sensitivity > 71%, specificity > 99%, and precision > 88%), but the performance was moderate for outdoor static and outdoor walking predictions. No striking differences in performance were observed between the rule-based and the random forest models. The random forest model was fast and easy to execute, but was likely less robust than the rule-based model under the condition of biased or poor quality training data.ConclusionsOur models can successfully identify indoor and in-vehicle travel points from the raw GPS data, but challenges remain in developing models to distinguish outdoor static points and walking. Accurate training data are essential in developing reliable models in classifying time-activity patterns.

AUTOMATIC TIME-ACTIVITY CLASSIFICATION BASED ON GLOBAL POSITIONING DATA

Background and Aims: Air pollution epidemiological studies are increasingly using global positioning system (GPS) to collect time-location data. However, remarkable uncertainties in GPS data create challenges for reliably characterizing time-activity patterns from the raw GPS data. We aimed to develop models to classify people’s major time- activity patterns directly from the GPS tracking. Methods: We collected 131 person-days of GPS time-activity data in 2008 for 47 residents in Southern California. Time-activity patterns were coded for each subject based on GPS recordings, time-activity diary logs, and follow-up interviews. Using similar methods, 7-day validation data were collected from three research staff in 2010. We developed, evaluated, and compared two models for extracting time-activity patterns (i.e. indoor static, outdoor static, outdoor walking, and in-vehicle travel) from the GPS data. A rule-based model developed user-defined rules based on time, speed, and spatial relationship of the GPS points, while a logistic model trees (LMT) model required minimal user-input by using existing software that combined a tree structure with logistic regression. Results: Indoor static, outdoor static, outdoor walking and in-vehicle travel accounted for 82.7%, 6.1%, 3.2% and 7.2% of the points in the main dataset, respectively. Both the rule-based and the LMT models correctly classified more than 90% of reported indoor static points and more than 70% of reported in-vehicle travel points, with Type 1 error (over-estimation) and Type 2 error (underestimation) &lt;9% for indoor static classification and &lt;29% for in-vehicle travel classification. Both models performed the worst in identifying outdoor static points. The performance of the LMT model improved significantly when using training data from the 7-day validation dataset likely because of more accurate diary data. Conclusion: Our models can successfully identify static and in-vehicle travel points from raw GPS data. It is more challenging to separate outdoor static from indoor static points.

Grazing behavior of sheep at different stocking rates in the Inner Mongolian steppe, China

In free-ranging or grazing animals, physical activity can account for a substantial proportion of their total energy requirement with considerable consequences for animals at low production level. This study evaluated the effect of grazing intensity (GI) on behavior and walking distance of sheep grazing the Inner Mongolian steppe, China. In July 2008, 70 female fat-tailed breed sheep were randomly assigned to one of six GI plots, which were used according to the following herbage allowance (HA) classes: >12, 6–12, 4.5–6, 3–4.5, 1.5–3, and <1.5 kg dry matter kg −1 live weight corresponding to very light (GI 1), light (GI 2), light-moderate (GI 3), moderate (GI 4), heavy (GI 5), and very heavy (GI 6) grazing. The sheep were continuously on the plots throughout the grazing season until September 2008. Behavior of two sheep per plot was monitored by visual observation during daylight on two days in the beginning of each month. Walking distance was measured by global positioning system recorders between 12:00 h and 24:00 h. Organic matter (OM) intake was estimated in six sheep per plot using titanium dioxide as external fecal marker as well as the diet OM digestibility derived from fecal crude protein concentration. Two main grazing periods were observed at all GIs with afternoon grazing being longer than morning grazing. GI had no effect on the animals’ ruminating time and walking distance. However, with increasing GI sheep spent more time grazing and less time resting during daylight. Similarly, the animals tended to decrease their resting time in order to maintain their grazing time when daylight became shorter with advancing vegetation period. Thereby, they succeeded in maintaining their OM intake as GI increased from GI 1 to GI 5 despite lower HAs at high GIs. Nevertheless, OM intake was lower in GI 6 than in GI 2 and GI 3 sheep. Therefore, both, reduced feed intake and higher energy requirements for activity, will outweigh the expected profit from highly intensive grazing.

Schoolyard physical activity in 14-year-old adolescents assessed by mobile GPS and heart rate monitoring analysed by GIS

Environmental settings seem to influence the activity patterns of children in neighbourhoods and schoolyards, the latter being an important arena to promote physical activity (PA) in school children. New technology has made it possible to describe free-living PA in interaction with the environment. This study focused on how schoolyard environments influenced the activity patterns and intensity levels in 14-year-old children and whether PA levels in adolescents complied with official recommendations. Another objective was to introduce methodology of using a mobile global positioning system (GPS) device with synchronous heart rate (HR) recordings as a proxy for PA level and a geographical information system (GIS) for spatial analyses. The sample constituted of 81 children (aged 14 years) from two schools. Movement patterns and activity levels were recorded during lunch break applying a GPS Garmin Forerunner 305 with combined HR monitoring and analysed in a GIS by an overlaid grid and kriging interpolation. Spatial data from GPS recordings showed particular movement patterns in the schoolyards. Low activity levels (mean HR < 120 bpm) dominated in both schools with no gender differences. Activities located to a handball goal area showed the highest monitored HR (>160 bpm) with higher intensity in girls than in boys. Movement patterns and PA generated in GIS for visualisation and analysis enabled direct and realistic description of utilising of schoolyard facilities and activity levels. Linking GPS data and PA levels to spatial structures made it possible to visualise the environmental interaction with PA and which environments promoted low or high PA.

Variability and short-term determinants of walking capacity in patients with intermittent claudication

Global positioning system (GPS) recordings can provide valid information on walking capacity in patients with peripheral arterial disease (PAD) and intermittent claudication (IC) during community-based outdoor walking. This study used GPS to determine the variability of the free-living walking distance between two stops (WDBS), induced by lower-limb pain, which may exist within a single stroll in PAD patients with IC and the potential associated parameters obtained from GPS analysis. This cross-sectional study of 57 PAD patients with IC was conducted in a university hospital. The intervention was a 1-hour free-living walking in a flat public park with GPS recording at 0.5 Hz. GPS-computed parameters for each patient were WDBS, previous stop duration (PSD), cumulated time from the beginning of the stroll, and average walking speed for each walking bout. The coefficient of variation of each parameter was calculated for patients with the number of walking bouts (N(WB)) >or=5 during their stroll. A multivariate analysis was performed to correlate WDBS with the other parameters. Mean (SD) maximal individual WDBS was 1905 (1189) vs 550 (621) meters for patients with N(WB) <5 vs N(WB) >or= 5, respectively (P < .001). In the 36 patients with N(WB) >or= 5, the coefficient of variation for individual WDBS was 43%. Only PSD and cumulated time were statistically associated with WDBS in 16 and 5 patients, respectively. A wide short-term variability of WDBS exists and likely contributes to the difficulties experienced by patients with IC to estimate their maximal walking distance at leisurely pace. Incomplete recovery from a preceding walk, as estimated through PSD, seems to dominantly account for the WDBS in patients with IC.

Patterns of GPS measured time outdoors after school and objective physical activity in English children: the PEACH project

BackgroundObservational studies have shown a positive association between time outdoors and physical activity in children. Time outdoors may be a feasible intervention target to increase the physical activity of youth, but methods are required to accurately measure time spent outdoors in a range of locations and over a sustained period. The Global Positioning System (GPS) provides precise location data and can be used to identify when an individual is outdoors. The aim of this study was to investigate whether GPS data recorded outdoors were associated with objectively measured physical activity.MethodsParticipants were 1010 children (11.0 ± 0.4 years) recruited from 23 urban primary schools in South West England, measured between September 2006 and July 2008. Physical activity was measured by accelerometry (Actigraph GT1M) and children wore a GPS receiver (Garmin Foretrex 201) after school on four weekdays to record time outdoors. Accelerometer and GPS data were recorded at 10 second epochs and were combined to describe patterns of physical activity when both a GPS and accelerometer record were present (outdoors) and when there was accelerometer data only (indoors). ANOVA was used to investigate gender and seasonal differences in the patterns of outdoor and indoor physical activity, and linear regression was used to examine the cross-sectional associations between GPS-measured time outdoors and physical activity.ResultsGPS-measured time outdoors was a significant independent predictor of children's physical activity after adjustment for potential confounding factors. Physical activity was more than 2.5 fold higher outdoors than indoors (1345.8 ± 907.3 vs 508.9 ± 282.9 counts per minute; F = 783.2, p < .001). Overall, children recorded 41.7 ± 46.1 minutes outdoors between 3.30 pm and 8.30 pm, with more time spent outdoors in the summer months (p < .001). There was no gender difference in time spent outdoors. Physical activity outdoors was higher in the summer than the winter (p < .001), whilst there was no seasonal variation in physical activity indoors.ConclusionsDuration of GPS recording is positively associated with objectively measured physical activity and is sensitive to seasonal differences. Minute by minute patterning of GPS and physical activity data is feasible and may be a useful tool to investigate environmental influences on children's physical activity and to identify opportunities for intervention.

GPS Seismology: Application to the 2002 Mw 7.9 Denali Fault Earthquake

Abstract The 2002 Denali fault, Alaska, earthquake ( M w 7.9) caused one or more components of most broadband seismometers in western Canada to clip, yet did not trigger strong-motion instruments, thus leaving a substantial gap in the seismic record of this event. However, the large-amplitude surface waves generated by this event were well recorded by the Global Positioning System (GPS) in the same region, out to epicentral distances of more than 3000 km. In this article, we explore the capabilities of GPS seismology, specifically how the relative strengths of GPS and seismic data sets can be exploited in order to more effectively study earthquake source characteristics and wave-propagation effects. High-rate (1-Hz) GPS data from 23 stations throughout western North America have been analyzed to derive displacement waveforms for this event, and the impact of instrumentation (GPS receiver model) and error-reduction strategy (modified sidereal and spatial filtering) on the noise characteristics of displacement time series at each GPS site was assessed. After applying error-reduction methods to GPS displacements, the final average noise floors of 0.5 cm in the horizontal and 1.5 cm in the vertical indicate that large dynamic displacements are observable by GPS. We validate the GPS displacements by comparing broadband seismic recordings (integrated to displacement) with GPS recordings for four effectively colocated sets of instruments. We show excellent agreement between the unclipped seismic and GPS recordings of the surface waves from the Denali earthquake over the period range of 10–50 sec and for ground displacements exceeding about 1.0 cm. Thus, a large GPS displacement data set is now available for western North America, an area where records of this event were previously missing or incomplete. The final GPS seismograms are archived at Incorporated Research Institutions for Seismology (IRIS) for public use in future studies of the 2002 Denali earthquake.

GPS Collar Sampling Frequency: Effects on Measures of Resource Use

A challenge in animal behavior studies using Global Positioning System (GPS) collars is selecting a sampling frequency to accomplish desired goals. High data resolution (i.e., frequent sampling) is appealing, because it maximizes behavioral information garnered. Extended sampling might be needed, however, to describe long term behaviors or seasonal dynamics. Because tradeoffs exist between high data resolution and sampling duration, we evaluated the effects of variable GPS sampling intervals on proportions of pastures used by cattle and distance traveled per day. This was accomplished with GPS collars configured to record cattle positions every 5 min for 15 d in three 829–864-ha pastures. Data were iteratively reduced to simulate increasingly longer GPS recording intervals from once every 10 min up to once daily. Two techniques were used to measure the percentage of pastures accessed by cattle. The first counted only pixels containing GPS coordinates. The second counted pixels containing coordinates and/or traversed by lines between vertices. Expansion of GPS recording intervals decreased (P , 0.01) estimates of the proportion of pastures visited by cattle with rates of decline best fit by exponential decay functions for both line and point techniques (R 2 5 0.93 and 0.97, respectively). Spatial errors accompanying less frequent sampling intervals, however, were extremely large with the line technique and misrepresented areas visited by cattle. Expansion of GPS sampling intervals decreased (P , 0.001) distance traveled per day by cattle about 10% with each iteration. If travel corridors or accurate assessments of resources accessed are of critical concern, then longer GPS integration intervals should be avoided because they propagate flawed spatial interpretations. Similarly, if accurate measures of travel distances are critical, we suggest using a relatively frequent GPS recording interval.