Global Positioning System Data Loggers Research Articles

Using sutures to attach miniature tracking tags to small bats for multimonth movement and behavioral studies.

Determining the detailed movements of individual animals often requires them to carry tracking devices, but tracking broad-scale movement of small bats (<30 g) has been limited by transmitter technology and long-term attachment methods. This limitation inhibits our understanding of bat dispersal and migration, particularly in the context of emerging conservation issues such as fatalities at wind turbines and diseases. We tested a novel method of attaching lightweight global positioning system (GPS) tags and geolocating data loggers to small bats. We used monofilament, synthetic, absorbable sutures to secure GPS tags and data loggers to the skin of anesthetized big brown bats (Eptesicus fuscus) in Colorado and hoary bats (Lasiurus cinereus) in California. GPS tags and data loggers were sutured to 17 bats in this study. Three tagged bats were recaptured 7 months after initial deployment, with tags still attached; none of these bats showed ill effects from the tag. No severe injuries were apparent upon recapture of 6 additional bats that carried tags up to 26 days after attachment; however, one of the bats exhibited skin chafing. Use of absorbable sutures to affix small tracking devices seems to be a safe, effective method for studying movements of bats over multiple months, although additional testing is warranted. This new attachment method has the potential to quickly advance our understanding of small bats, particularly as more sophisticated miniature tracking devices (e.g., satellite tags) become available.

Performance and Accuracy of Lightweight and Low-Cost GPS Data Loggers According to Antenna Positions, Fix Intervals, Habitats and Animal Movements.

Recently developed low-cost Global Positioning System (GPS) data loggers are promising tools for wildlife research because of their affordability for low-budget projects and ability to simultaneously track a greater number of individuals compared with expensive built-in wildlife GPS. However, the reliability of these devices must be carefully examined because they were not developed to track wildlife. This study aimed to assess the performance and accuracy of commercially available GPS data loggers for the first time using the same methods applied to test built-in wildlife GPS. The effects of antenna position, fix interval and habitat on the fix-success rate (FSR) and location error (LE) of CatLog data loggers were investigated in stationary tests, whereas the effects of animal movements on these errors were investigated in motion tests. The units operated well and presented consistent performance and accuracy over time in stationary tests, and the FSR was good for all antenna positions and fix intervals. However, the LE was affected by the GPS antenna and fix interval. Furthermore, completely or partially obstructed habitats reduced the FSR by up to 80% in households and increased the LE. Movement across habitats had no effect on the FSR, whereas forest habitat influenced the LE. Finally, the mean FSR (0.90 ± 0.26) and LE (15.4 ± 10.1 m) values from low-cost GPS data loggers were comparable to those of built-in wildlife GPS collars (71.6% of fixes with LE < 10 m for motion tests), thus confirming their suitability for use in wildlife studies.

GPS telemetry for parrots: A case study with the Kea (Nestor notabilis)

ABSTRACT Parrots are one of the most complex avian lineages worldwide, yet little is known about their patterns of movement and space use. Such information is vital for understanding the social development and structure of members of this long-lived order, as well as for the establishment of effective conservation and management actions for the many threatened or endangered species. While global positioning system (GPS) telemetry has been employed successfully on a broad range of birds, to date no studies have been published in which this technology has been used on any psittaciform species, most probably due to concerns held by researchers regarding the high cost of GPS units or the perceived ability of members of this order to remove or damage tracking gear. Here, we evaluate the feasibility and performance of animal-borne GPS telemetry as a means of tracking parrots. First, we encased inexpensive (<US$70) archival GPS dataloggers (~19 g) in bite-proof housing, and then we evaluated the effects of the d...

Validity of PALMS GPS scoring of active and passive travel compared with SenseCam.

The objective of this study is to assess validity of the personal activity location measurement system (PALMS) for deriving time spent walking/running, bicycling, and in vehicle, using SenseCam (Microsoft, Redmond, WA) as the comparison. Forty adult cyclists wore a Qstarz BT-Q1000XT GPS data logger (Qstarz International Co., Taipei, Taiwan) and SenseCam (camera worn around the neck capturing multiple images every minute) for a mean time of 4 d. PALMS used distance and speed between global positioning system (GPS) points to classify whether each minute was part of a trip (yes/no), and if so, the trip mode (walking/running, bicycling, or in vehicle). SenseCam images were annotated to create the same classifications (i.e., trip yes/no and mode). Contingency tables (2 × 2) and confusion matrices were calculated at the minute level for PALMS versus SenseCam classifications. Mixed-effects linear regression models estimated agreement (mean differences and intraclass correlation coefficients) between PALMS and SenseCam with regard to minutes/day in each mode. Minute-level sensitivity, specificity, and negative predictive value were ≥88%, and positive predictive value was ≥75% for non-mode-specific trip detection. Seventy-two percent to 80% of outdoor walking/running minutes, 73% of bicycling minutes, and 74%-76% of in-vehicle minutes were correctly classified by PALMS. For minutes per day, PALMS had a mean bias (i.e., amount of over or under estimation) of 2.4-3.1 min (11%-15%) for walking/running, 2.3-2.9 min (7%-9%) for bicycling, and 4.3-5 min (15%-17%) for vehicle time. Intraclass correlation coefficients were ≥0.80 for all modes. PALMS has validity for processing GPS data to objectively measure time spent walking/running, bicycling, and in vehicle in population studies. Assessing travel patterns is one of many valuable applications of GPS in physical activity research that can improve our understanding of the determinants and health outcomes of active transportation as well as its effect on physical activity.

Global positioning system data-loggers: a tool to quantify fine-scale movement of domestic animals to evaluate potential for zoonotic transmission to an endangered wildlife population.

Domesticated animals are an important source of pathogens to endangered wildlife populations, especially when anthropogenic activities increase their overlap with humans and wildlife. Recent work in Tanzania reports the introduction of Cryptosporidium into wild chimpanzee populations and the increased risk of ape mortality associated with SIVcpz-Cryptosporidium co-infection. Here we describe the application of novel GPS technology to track the mobility of domesticated animals (27 goats, 2 sheep and 8 dogs) with the goal of identifying potential routes for Cryptosporidium introduction into Gombe National Park. Only goats (5/27) and sheep (2/2) were positive for Cryptosporidium. Analysis of GPS tracks indicated that a crop field frequented by both chimpanzees and domesticated animals was a potential hotspot for Cryptosporidium transmission. This study demonstrates the applicability of GPS data-loggers in studies of fine-scale mobility of animals and suggests that domesticated animal–wildlife overlap should be considered beyond protected boundaries for long-term conservation strategies.

Integrity of estimates of the two-fluid model and gender impacts

This paper summarizes a research study to develop a methodology for utilizing naturalistic Global Positioning System (GPS) driving data for two-fluid model estimation. The two-fluid vehicular traffic flow model describes traffic flow on a street network as a mix of stopped and running vehicles. The parameters of the model essentially represent ‘free flow’ travel time and the level of interaction among vehicles. These parameters have traditionally been used to evaluate roadway networks and corridors with partially limited access. However, the two-fluid model has been found to be a direct result of driver behavior, and can also be used to represent behavioral aspects of driver populations, e.g., aggressiveness, passiveness, etc. Through these behavioral aspects they can also be related to safety on roadways. Due to which the two-fluid model can be considered to be a safety footprint for a particular road or individual driver. Due to which it is critical to understand factors that influence the two-fluid model. In this study, two-fluid models were estimated using naturalistic driving data collected with GPS data loggers in San Luis Obispo (SLO), California. Linear referencing in ArcMap was used to link the GPS data with roadway characteristic data for each element of the roadway network. The linear referencing methodology is the key to relate the GPS driving data with the elements of roadway network. This study explores two fundamental questions: (1) how sensitive are the estimates of the two fluid parameters to various samples? This question is fundamentally important to help define the integrity of the two-fluid model for planning and operational purposes. To this end we use a random sampling approach to address this question. (2) Are there behavioral differences across gender? This provides important behavioral insights on driving behavior across gender. Significant differences were observed between male and female drivers, with female drivers being more aggressive.

Effect of habitat use and diet on the gastrointestinal parasite community of an avian omnivore from an urbanized environment

With urbanization, anthropogenic foods have grown in importance for several species. A shift away from natural foods is likely to affect trophically transmitted parasites, although this has received limited attention in urban-adapted avian omnivores. We examined the effect of habitat use and diet on gastrointestinal parasite assemblages of Ring-billed Gulls (Larus delawarensis Ord, 1815) breeding in an urbanized region (Montréal, Quebec, Canada) using three approaches depicting different temporal scales. Birds were fitted with global positioning system data loggers to determine habitat-use patterns during a 2–3 day period. Stomach contents were examined, providing dietary information during the preceding hours. Liver carbon (δ13C) and nitrogen (δ15N) stable isotope signatures served as proxy of nutrient assimilation during the preceding 10 days. Endoparasite community variations were best explained by δ13C and δ15N ratios. Individuals with lower δ15N had lower parasite abundance, while δ13C was enriched in birds with less diverse parasites (fewer helminth genera). Tissue depletion in15N in Ring-billed Gulls from this colony has previously been associated with predominant consumption of human-related foods. The present study supports the hypothesis that Ring-billed Gulls exhibiting preference for anthropogenic food sources encounter fewer trophically transmitted parasites, which may have contributed, in part, to their population expansion during the last century.

Real-Time Transportation Mode Detection Using Smartphones and Artificial Neural Networks: Performance Comparisons Between Smartphones and Conventional Global Positioning System Sensors

Traditionally, traffic monitoring requires data from traffic cameras, loop detectors, or probe vehicles that are usually operated by dedicated employees. In efforts to reduce the capital and operational costs associated with traffic monitoring, departments of transportation have explored the feasibility of using global positioning system (GPS) data loggers on their probe vehicles that are postprocessed for analyzing the traffic patterns on desired routes. Furthermore, most cell phones are equipped with embedded assisted-GPS (AGPS) chips, and if the mode of transportation the phone is in can be anonymously identified, the phones can be treated as if they are probe vehicles that are voluntarily hovering throughout the city, at minimal additional costs. Emerging cell phones known as “smartphones” are equipped with additional sensors including an accelerometer and magnetometer. The accelerometer can directly measure the acceleration values, as opposed to having acceleration values derived from speed values in conventional GPS sensors. The magnetometer can measure mode-specific electromagnetic levels. Smartphones are subscribed with roadside Internet data plans that can provide an essential platform for real-time traffic monitoring. In this article, neural network-based artificial intelligence is used to identify the mode of transportation by detecting the patterns of distinct physical profile of each mode that consists of speed, acceleration, number of satellites in view, and electromagnetic levels. Results show that newly available values in smartphones improve the mode detection rates when compared with using conventional GPS data loggers. When smartphones are in known orientations, they can provide three-dimensional (3-D) acceleration values that can further improve mode detection accuracies.

Feasibility study to objectively assess activity and location of Hispanic preschoolers: a short communication

Both physical and social environmental factors influence young children's physical activity, yet little is known about where Hispanic children are more likely to be active. We assessed the feasibility of simultaneously measuring, then processing objective measures of location and physical activity among Hispanic preschool children. Preschool-aged Hispanic children (n = 15) simultaneously wore QStarz BT100X global positioning system (GPS) data loggers and Actigraph GT3X accelerometers for a 24- to 36-hour period, during which time their parents completed a location and travel diary. Data were aggregated to the minute and processed using the personal activity location measurement system (PALMS). Children successfully wore the GPS data loggers and accelerometers simultaneously, 12 of which yielded data that met quality standards. The average percent correspondence between GPS- and diary-based estimates of types of location was high and Kappa statistics were moderate to excellent, ranging from 0.49-0.99. The between-method (GPS monitor, parent-reported diary) correlations of estimated participant-aggregated minutes spent on vehicle-based trips were strong. The simultaneous use of GPS and accelerometers to assess Hispanic preschool children's location and physical activity is feasible. This methodology has the potential to provide more precise findings to inform environmental interventions and policy changes to promote physical activity among Hispanic preschool children.

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.

Design of a GPS data logger device with street-level map interface

The Global Positioning System (GPS) has now become a widely used aid to navigation and it is commonly used in many navigational applications such as land surveying, shipping, piloting, route guidance, map making, study of earthquakes, precise time reference, and hobbies and games such as geocaching. One of the problems with the early GPS system was its low accuracy which prevented it to be used in applications requiring high accuracy, such as piloting and street-level route guidance. With the recent introduction of the sophisticated error correction techniques such as the WAAS/EGNOS, the horizontal accuracy of a GPS system is nowadays around 10 m. This study describes the design of a microcontroller based GPS data logger device with Secure Data (SD) card storage and Google Map mapping interface. The device collects the user co-ordinates in a file on an SD card, and then the Google Map software is used to draw the track of the user on a street-level map.

Real-Time Transportation Mode Detection via Tracking Global Positioning System Mobile Devices

This article presents a methodology for identifying travelers' transportation modes by tracking Global Positioning System (GPS)-equipped mobile devices in the traffic stream. Various mobile phone service providers have location-based services (LBS) that track the locations of their mobile phones. One major concern in using mobile phones for traffic monitoring is that the phones are not necessarily in passenger vehicles. The mobile device can be in a car, bus, or other modes that have distinct speed and acceleration profiles. In addition, querying the mobile device has monetary cost implications, and the higher the number of location queries from the server the higher the associated cost. This article focuses on the feasibility of using the characteristics of the trail of GPS data stream to identify the mode on which the mobile device is located. Currently available LBS in Toronto can only provide GPS data once every 5 min. Because of the sampling limitation, a GPS data logger is used to collect the trip data and the logged data is sampled at varying frequencies as if they are coming from the mobile phones. The analysis is conducted using neural networks (NNs) to determine the transportation mode. The analysis also examines the impact of varying sampling rates (number of pings per unit time) and monitoring duration (time length of data trail) on mode classification accuracy. In total, 60 h of GPS data were collected while traveling on various transportation modes throughout the Greater Toronto Area. Results confirm the potential of neural networks to successfully detect transportation modes from GPS data, both in peak and nonpeak periods. The results indicate that higher sampling frequency and longer monitoring duration result in higher mode detection rates. In addition, the route-specific neural networks perform better than the universal neural networks.

Tracking fish using ‘buoy-based’ GPS telemetry

The marine environment imposes severe constraints on the means by which location information can be obtained from submerged, freely swimming animals. Standard methods of tracking marine organisms are often labour intensive, expensive, or of low spatial and temporal resolution. Here, we describe a new method by which larger species of fish that live in shallow or surface waters can be tracked using an inexpensive telemetry device based on the global positioning system (GPS). We fixed small GPS data-logger units configured to record position fixes at 90 to 150 s intervals to low-drag tow-bodies and then attached these units by means of a tether to New Zealand eagle rays Myliobatis tenuicaudatus. After deployment periods lasting up to 29 h we recovered the tracking gear and downloaded the location data, which were stored onboard. The GPS units worked well, with mean fix-success rates >90%, and allowed accurate reconstruction of the movements of the rays throughout an estuary in Northland, New Zealand. Although our method is restricted to animals that swim on or near the surface of the water, it does provide a means of cheaply describing the movement patterns of suitable species for substantial periods of time at heretofore unprecedented spatial and temporal scales.

High-speed gallop locomotion in the Thoroughbred racehorse. I. The effect of incline on stride parameters

During locomotion up an incline, power is required to elevate the centre of mass. This is provided when the animal's limbs are in contact with the ground. Measurements of stride timing variables from multiple limbs during high speed, over-ground locomotion would enhance our understanding of locomotor powering during changes in terrain. This study measured foot-on and foot-off times from galloping horses using a previously validated system of limb-mounted accelerometers and a global positioning system data logger. A detailed track survey provided incline information from all areas of the track. Measurements were made from six horses over a speed range of 9 to 13 m s(-1). Foot-fall timings were used to calculate variables, which included stance duration, protraction duration, stride frequency and duty factor. The relationship between track incline and measured variables was assessed. Stride variables from horses galloping on level (0-2% incline) and incline (8-12% incline) sections of the track were compared. Fore- and hindlimb protraction durations were significantly reduced across the speed range during incline galloping (P=0.001). This resulted in a mean increase in stride frequency from 2.01 to 2.08 strides s(-1) at 9.5 m s(-1) and 2.10 to 2.17 strides s(-1) at 12.5 m s(-1) during incline galloping. Duty factor was significantly greater for the hindlimbs during incline galloping (P<0.001), increasing from 0.31 to 0.32 at 9.5 m s(-1) and 0.28 to 0.29 at 12.5 m s(-1). Peak limb force was calculated from duty factor and assumed fore- to hindlimb impulse distributions. Smaller peak vertical forces were calculated in the forelimbs and increased peak vertical forces were calculated in the hindlimbs when galloping on an incline. Measured changes in stride timing variables differ from those reported in trotting horses. We propose that horses increase their stride frequency at a given speed during incline galloping to provide power for moving the centre of mass up the slope.

Vehicle Activity Patterns and Emissions in Pune, India

India continues to experience substantial economic growth, with increased travel demand for both passengers and goods. As a result, roadway congestion is increasing in many cities and putting significant pressure on India's transportation infrastructure. One key concern is air pollution related to the increased transportation activity. To understand the transportation impacts on air quality, it is necessary to develop and apply appropriate modeling tools to the area of concern. Recently, a new on-road mobile source emissions model designed for use in developing countries has been developed: the international vehicle emissions (IVE) model. The IVE model was developed jointly by researchers at the International Sustainable Systems Research Center and the University of California at Riverside. This paper describes a research program that applied the IVE modeling approach to the city of Pune, India. As part of the approach, an extensive vehicle activity–fleet composition study took place in Pune; it consisted of videotaping and measuring traffic patterns, tracking representative vehicles with Global Positioning System data loggers, monitoring start–stop patterns in instrumented vehicles, and conducting surveys in the field. In this paper, the methodology and results of the study are described in detail, followed by mobile-source emissions predictions based on the calibrated IVE model. This overall effort was designed to support estimates of the air pollution impacts of on-road transportation in Pune that can now be used extensively in the development of air quality and transportation management plans for the region. It is also hoped that the collected data can be extrapolated to other Indian cities to support further environmental improvement efforts.

Objective Mobility Documentation Using Emerging Technologies

Historically, rehabilitation clinicians who work with people who are visually impaired (that is, are blind or have low vision) have relied on subjective checklists and clinical assessments to document the capacity of individuals to perform various tasks, including mobility, and to assess the impact of rehabilitation. Numerous instruments have been developed to measure functional outcomes and the quality of life of people who are visually impaired (De l'Aune, Williams, Watson, Schuckers, & Ventimiglia, 2004; Haymes, Johnston, & Heyes, 2001). The continued development and implementation of such instruments represents a major achievement in the coordination and standardization of measurements of functional outcomes. This article highlights a unique, objective method for assessing the mobility of clients who are visually impaired by using a combination of GPS (Global Positioning System), GIS (Geographic Information Systems), and accelerometer technologies. The use of these technologies facilitates a highly objective and reliable measurement of both indoor (accelerometer) and outdoor (GPS and accelerometer) mobility and travel patterns. Moreover, measures of mobility can be used in conjunction with other commonly used self-report and clinician-assessed measures of mobility-related behaviors, including those that assess the impact of vision loss on mobility. GPS AND GIS TECHNOLOGY GPS technology, which provides information on the spatial coordinates of a given geographic location or traveler that is derived from signals received simultaneously from multiple GPS satellites, is often used in conjunction with GIS, which provides digital mapping and other important information about a specific location. In simple terms, GPS determines an individual's geographic location, travel paths, and speeds, while GIS provides a multilayered platform that is typically displayed in maps that can be used to interpret GPS data. GPS technology has been used to investigate details about personal travel behavior (Wolf, Guensler, & Bachman, 2001; Wolf, Loechl, Thompson, & Arce, 2003) and the relationships between physical activity and travel patterns. By equipping participants who are visually impaired with GPS data loggers, investigators can process data on second-by-second GPS positions, time, and speed within a GIS framework to obtain in-depth information about various outdoor behaviors, including travel times, modes of travel, the duration of stops, the length of trips, speed profiles, routes, and types of travel environments. This information can then be augmented with information on the specific purposes of travel and levels of independence that is gathered from self-report travel diaries and assessment interviews. These behaviors are closely related to the goals associated with orientation and mobility. GIS technology involves spatial analysis software platforms that are used to manage and evaluate geographically referenced data (Brainard, Bateman, & Lovett, 1995; Brainard, Lovett, & Parfitt, 1996; Lee & Stucky, 1998; Loh, Van Stipdonk, Holtfrerich, & Hsieh, 1996; Lovett, Parfitt, & Brainard, 1997). It can be used to generate detailed information on travel routes that an individual who is visually impaired has collected via GPS. In addition, extensive comments or notes about specific features of various GIS themes, such as bus routes, commercial and entertainment districts, and other relevant community information, can be integrated into the data system. METHODS This study was conducted by researchers at the Atlanta VA Rehabilitation Research and Development Center and at GeoStats () to evaluate the efficiency of the procedures, the quality of the data, and the effectiveness of the concepts of the three technologies. It was approved by the Emory University Internal Review Board, and the participants signed informed-consent forms before they participated. …

Effect of speed on stride parameters in racehorses at gallop in field conditions

Stride duration, stance duration and protraction duration are key variables when describing the gaits of terrestrial animals. Together, they determine the duty factor (the fraction of the stride for which the limb maintains contact with the ground surface), from which the peak vertical force can be estimated. When an animal changes speed, these variables change at different proportions. Limited measurements of these variables and predictions of peak limb force have been undertaken for large mammals performing high-speed over-ground exercise. This study set out to make such measurements, employing a previously validated system consisting of limb-mounted accelerometers and a Global Positioning System data logger. Measurements were made on nine elite Thoroughbred racehorses during gallop locomotion over a range of speeds from 9 to 17 m s(-1). No statistically significant differences were seen in any variables between the lead and non-lead limbs for either the fore or hind pairs of limbs. Mean stance durations of 131 and 77 ms in the forelimbs and 143 and 94 ms in the hindlimbs were recorded at speeds of 9 and 17 ms(-1), respectively. Equivalent values for protraction duration were 364 and 342 (fore) and 355 and 326 ms (hind). Peak limb forces (from duty factor) at 17 ms(-1) were 24.7 N kg(-1) body weight (range 22.6 to 26.0 N kg(-1) body weight) for the forelimbs and 15.3 N kg(-1) (range 13.7-16.2 N kg(-1) body weight) for the hindlimbs. The duration of the aerial phase of the stride (when no limbs are in contact with the ground) was independent of speed. Overlap time (when more than one leg is on the ground) dropped with speed and approached zero at maximum speed.

Accuracy of non-differential GPS for the determination of speed over ground

Accurate determination of speed is important in many studies of human and animal locomotion. Some global positioning system (GPS) receivers can data log instantaneous speed. The speed accuracy of these systems is, however, unclear with manufacturers reporting velocity accuracies of 0.1–0.2 ms −1. This study set out to trial non-differential GPS as a means of determining speed under real-life conditions. A bicycle was ridden around a running track and a custom-made bicycle speedometer was calibrated. Additional experiments were performed around circular tracks of known circumference and along a straight road. Instantaneous speed was determined simultaneously by the custom speedometer and a data logging helmet-mounted GPS receiver. GPS speed was compared to speedometer speed. The effect on speed accuracy of satellite number; changing satellite geometry, achieved through shielding the GPS antenna; speed; horizontal dilution of precision and cyclist position on a straight or a bend, was evaluated. The relative contribution of each variable to overall speed accuracy was determined by ANOVA. The speed determined by the GPS receiver was within 0.2 ms −1 of the true speed measured for 45% of the values with a further 19% lying within 0.4 ms −1 ( n=5060). The accuracy of speed determination was preserved even when the positional data were degraded due to poor satellite number or geometry. GPS data loggers are therefore accurate for the determination of speed over-ground in biomechanical and energetic studies performed on relatively straight courses. Errors increase on circular paths, especially those with small radii of curvature, due to a tendency to underestimate speed.

Elimination of the Travel Diary: Experiment to Derive Trip Purpose from Global Positioning System Travel Data

Several recent pilot studies combined Global Positioning System (GPS) technology with travel survey data collection to evaluate opportunities for improving the quantity and accuracy of travel data. These studies used GPS to supplement traditional data elements collected in paper or electronic travel diaries. Although many traditional trip elements can be obtained from the GPS data, trip purpose has remained an important element, requiring the use of a diary to continue. Presented are the results of a proof-of-concept study conducted at the Georgia Institute of Technology that examined the feasibility of using GPS data loggers to completely replace, rather than supplement, traditional travel diaries. In this approach, all GPS data collected must be processed so that all essential trip data elements, including trip purpose, are derived. If this processing is done correctly and quickly, then the computer-assisted telephone interview retrieval call could be shortened significantly, reducing both respondent burden and telephone interview times. The study used GPS data loggers to collect travel data in personal vehicles. The GPS data were then processed within a geographic information system (GIS) to derive most of the traditional travel diary elements. These derived data were compared with data recorded on paper diaries by the survey participants and were found to match or exceed the reporting quality of the participants. Most important, this study demonstrated that it is feasible to derive trip purpose from the GPS data by using a spatially accurate and comprehensive GIS.

Design and Testing of a Global Positioning System‐Based Radiometer for Precision Mapping of Pearl Millet Total Dry Matter in the Sahel

The nondestructive determination of plant total dry matter (TDM) in the field is greatly preferable to the harvest of entire plots in areas such as the Sahel where small differences in soil properties may cause large differences in crop growth within short distances. Existing equipment to nondestructively determine TDM is either expensive or unreliable. Therefore, two radiometers for measuring reflected red and near‐infrared light were designed, mounted on a single wheeled hand cart and attached to a differential Global Positioning System (GPS) to measure georeferenced variations in normalized difference vegetation index (NDVI) in pearl millet fields [Pennisetum glaucum (L.) R. Br.]. The NDVI measurements were then used to determine the distribution of crop TDM. The two versions of the radiometer could (i) send single NDVI measurements to the GPS data logger at distance intervals of 0.03 to 8.53 m set by the user, and (ii) collect NDVI values averaged across 0.5, 1, or 2 m. The average correlation between TDM of pearl millet plants in planting hills and their NDVI values was high but varied slightly depending on solar irradiance when the instrument was calibrated. There also was a good correlation between NDVI, fractional vegetation cover derived from aerial photographs and millet TDM at harvest. Both versions of the rugged instrument appear to provide a rapid and reliable way of mapping plant growth at the field scale with a high spatial resolution and should therefore be widely tested with different crops and soil types.