Combined Global Positioning System Research Articles

Combining global positioning system and accelerometer data to determine the locations of physical activity in children

National trends indicate that children and adolescents are not achieving sufficient levels of physical activity. Combining global positioning system (GPS) technology with accelerometers has the potential to provide an objective determination in locations where youth engage in physical activity. The aim of this study was to identify the optimal methods for collecting combined accelerometer and GPS data in youth, to best locate where children spend time and are physically active. A convenience sample of 24 mid-school children in Massachusetts was included. Accelerometers and GPS units were used to quantify and locate childhood physical activity over 5 weekdays and 2 weekend days. Accelerometer and GPS data were joined by time and mapped with a geographical information system (GIS) using ArcGIS software. Data were collected in winter, spring, summer in 2009-2010, collecting a total of 26,406 matched datapoints overall. Matched data yield was low (19.1% total), regardless of season (winter, 12.8%; spring, 30.1%; summer, 14.3%). Teacher-provided, pre-charged equipment yielded the most matched (30.1%; range: 10.1-52.3%) and greatest average days (6.1 days) of data. Across all seasons, children spent most of their time at home. Outdoor use patterns appeared to vary by season, with street use increasing in spring, and park and playground use increasing in summer. Children spent equal amounts of physical activity time at home and walking in the streets. Overall, the various methods for combining GPS and accelerometer data provided similarly low amounts of combined data. No combined GPS and accelerometer data collection method proved superior in every data return category, but use of GIS to map joined accelerometer and GPS data can demarcate childhood physical activity locations.

MOBILE PHONES AS PERSONAL ENVIRONMENTAL SENSING PLATFORMS: DEVELOPMENT OF THE CALFIT SYSTEM

Background and Aims: Mobile phones are pervasive computing technologies that offer opportunities for sensing personal behaviors and exposures to environmental hazards. The CalFit system uses the combination of global positioning system (GPS) and accelerometry on mobile phones for continuous measurements of an individual’s time-activity patterns, which can greatly inform spatial and temporal variations in exposures for environmental health studies. As a research platform, CalFit was designed for flexibility, allowing its use in air pollution epidemiology, built environment, and active living research. Here, we describe the development of CalFit’s algorithm for estimating energy expenditure for physical activity and minute ventilation for air pollution studies. Methods: We describe the capabilities of the CalFit software that runs on Android mobile phones, which includes time-location tracking using GPS and the estimation of energy expenditure from triaxial accelerometry. To develop the energy expenditure algorithm, the CalFit phone was compared against the COSMED cardiopulmonary exercise monitor for 24 adult subjects (10 men and 14 women aged 19-59 years) who wore both systems simultaneously during a series of prescribed activities (four levels on treadmill spanning 1-6 mph, stair climbing, sit to stand, lie to stand, jump, and 6-minute walk test). Generalized linear equations were used to estimate COSMED measured energy expenditure and ventilation rate from the CalFit phone’s vertical and horizontal accelerometry counts. Results: In the linear model, CalFit vertical and horizontal accelerometry counts/min were significant predictors (ß=0.623 P<0.001 and ß=1.65 P<0.001, respectively) of COSMED energy expenditure (R2=0.80). Inclusion of 2-minute counts improved the linear model (R2=0.86), as did generalizing the model to account for differences between subjects (R2=0.81). Moreover, energy expenditure and minute ventilation were linearly related (R2=0.80). Conclusions: Environmental epidemiology studies that require the combined assessment of energy expenditure from physical activity, minute ventilation, and time-location patterns may benefit from the CalFit phone system.

Research on Integrated Navigation Algorithm Based on ANFIS

Combination of Global Positioning System (GPS) and Inertial Navigation System (INS) can improve the navigation performance that is superior to either one. This paper proposed and discussed an INS/GPS integrated navigation method based on adaptive neuro-Fuzzy Inference System (ANFIS) to fuse INS and GPS data. In this method, an ANFIS network was trained to mimic the error dynamical model of INS when GPS signals were available. If GPS outages occur, the trained ANFIS network is utilized to bridge the GPS outages. Simulations in INS/GPS integrated navigation system show the proposed method can reduce the positioning error during GPS outages.

Research Spotlight: Tectonic plates relocked after 2005 earthquake in northeastern Japan

In August 2005 a magnitude 7.2 earthquake shook northeastern Japan. The quake occurred on the boundary of the North American plate and the Pacific plate off Miyagi prefecture. Earthquakes with a magnitude of about 7.5 have been occurring in this area approximately every 37 years. Sato et al. used seafloor geodetic observations from a combination of Global Positioning System (GPS) and acoustic measurements to detect seafloor movements during and after the earthquake. They focused on the movement of a seafloor reference point located about 10 kilometers east of the epicenter of the 2005 quake. (Geophysical Research Letters, doi:10.1029/2010GL045689, 2011)

Overall Impacts of Off-Hour Delivery Programs in New York City Metropolitan Area

This paper examines the chief findings of research conducted on policies to foster off-hour deliveries (OHDs) in the New York City metropolitan area. The goal was to estimate the overall impacts of eventual full implementation of an OHD program. As part of the research, a system of incentives was designed for the receivers of deliveries the system combined Global Positioning System (GPS) remote sensing monitoring with GPS-enabled smart phones to induce a shift of deliveries to the off-hours from 7:00 p.m. to 6:00 a.m. The concept was pilot tested in Manhattan by 33 companies that switched delivery operations to the off-hours for a period of 1 month. At the in-depth interviews conducted after the test, the participants reported being very satisfied with the experience. As an alternative to road pricing schemes that target freight carriers, this was the first real-life trial of the use of financial incentives to delivery receivers. The analyses indicate that the economic benefits of a full implementation of the OHD program are in the range of $147 to $193 million per year, corresponding to savings on travel time and environmental pollution for regular-hour traffic as well as productivity increases for the freight industry. The pilot test also highlighted the great potential of unassisted OHD—that is, OHD made without personnel from the receiving establishment present—because almost all participants who used this modality decided to continue receiving OHD even after the financial incentive ended.

GNSS geodetic techniques for time and frequency transfer applications

We performed an initial analysis of the pseudorange data of the GIOVE-B satellite, one of the two experimental Galileo satellites currently in operation, for time transfer. 1 The time transfer technique specified herein does not refer to the definition of Galileo Common View as set up by the European Space Agency, the Royal Observatory of Belgium and Timing Expert, nor the Common View GPS standard practice for BIPM. 1 For this specific aim, software was developed to process the GIOVE-B raw pseudoranges and broadcast navigation messages collected by the Galileo Experimental Sensor Stations (GESS) tracking network, yielding station clock phase errors with respect to the Experimental Galileo System Time (EGST). The software also allows processing the Global Positioning System (GPS) P1 and P2 pseudorange data with broadcast navigation message collected at the same stations to obtain the station clock phase errors with respect to the GPS system time (GPST). Differencing these solutions between stations provides two independent means of GNSS time transfer. We compared these time transfer results with Precise Point Positioning (PPP) method applied to GPS data in combined carrier-phase and pseudorange mode as well as in pseudorange-only mode to show their relative merits. The PPP solutions in combined carrier-phase and pseudorange mode showed the least instability of the methods tested herein at all scales, at few parts in 10 15 at 1 day for the stations processed, following a tau −½ interval dependency. Conversely, the PPP solutions in pseudorange-only mode are an order of magnitude worst (few parts in 10 14 at 1 day for the stations processed) following a tau −1 power-law, but slightly better than the single-satellite raw GPS time transfer solutions obtained using the developed software, since the PPP least-squares solution effectively averages the pseudorange noise. The pseudorange noise levels estimated from PPP pseudorange residuals and from clock solution comparisons are largely consistent, providing a validation of our software operation. The raw GIOVE-B time transfer, as implemented in this work, proves to be slightly better than single-satellite raw GPS satellite time transfer, at least in the medium term. However, one of the processed stations shows a combined GPS P1 and P2 pseudorange noise level at 2 m, a factor 2 worst than usually seen for geodetic receivers, so the GPS time transfer results may not be at their best for the cases processed. Over the short term, the GPS single-satellite time transfer instability outperforms the GIOVE-B by an order of magnitude at 1 s interval, which would be due to the different characteristics of the tracking loop filters for GPS P1 and P2 on one hand and the GIOVE-B signals on the other. Even at this preliminary stage and using an experimental satellite system, results show that the GIOVE-B (and hence Galileo) signals offer interesting perspectives for high precision time transfer between metrological laboratories.

Fine scale biologging of an inshore marine animal

We compared the results of two biologging techniques used to study the foraging behaviour of a colony of small inshore predators, little penguins (Eudyptula minor). The first technique involved the use of satellite transmitters and diving loggers deployed on separate individuals, which has been the conventional method of tracking the movements and behaviour of this species for >10years. The second technique combined a diving logger and a global positioning system (GPS) logger deployed on the same individual, which is similar to the biologging methods presently being developed and used for many other species. We then considered the value of each technique as a conservation tool operating at the small scale (foraging area <5000ha and duration <1day).We found that the separately deployed satellite transmitters significantly underestimated the penguins' foraging area size. However, the size of the foraging area and other foraging parameters, such as total distance travelled, were influenced by the degree of GPS location sub-sampling. Furthermore, only the combined diving and GPS loggers could confidently describe the diving behaviour of the penguins in relation to the sea floor and identify that they were using small areas of conservation interest (shipping channel) inside their foraging area.Hence, the method employed to assess habitat use at fine scales can influence conservation measures that rely upon the data collected. We suggest that researchers fast-track their adoption of high resolution multi-loggers for increased data confidence when tracking animals at a fine scale, but also consider the potential effect of sampling rate on the calculation of parameters of interest.

A Multi-Constellations Satellite Selection Algorithm for Integrated Global Navigation Satellite Systems

The U.S. Global Positioning System (GPS) is currently the only fully operational global navigation satellite system (GNSS) that has been widely utilized in navigation and data collection, among other applications. In the near future, there will be other GNSSs such as the Russian GLONASS, the European Galileo, and the Chinese Compass that provide compatible services with GPS and will be available to all users. Besides operating in the single GNSS mode, future GNSS receivers will have the capability to operate in an integrated GNSS mode where they will be able to couple satellites from all available constellations for positioning solutions. However, tracking all visible satellites simultaneously increases the computational load of the receivers. This is particularly true with low-cost and compact receivers, which have limited computational resources and are commonly used in real-time intelligent transportation system (ITS) applications such as automatic vehicle location, route guidance, fleet management, vehicle dispatch, traveler information, and car navigation. These real-time applications also impose time constraints on positional updates (maximum required time interval between two epochs) while requiring high accuracy positioning solutions. To mitigate such burdens while maintaining benefits of the combined system, this article presents a new heuristic algorithm called a multi-constellations satellite selection algorithm (MCSSA). The algorithm allows an integrated GNSS receiver to track only a smaller set of visible satellites that can provide acceptable positioning solutions in the required time intervals. The MCSSA considers the geometric arrangements of visible satellites and selects the ones that spread evenly over the observed sky view. The performance of the MCSSA was validated by simulating the combined GPS and Galileo constellations. The accuracy and computation time of the MCSSA were compared with selected existing satellite selection algorithms. The results indicate that the MCSSA provides the set of satellites with near-optimal geometries giving high positional accuracy in a reasonably small computation time and thus is suitable for real-time applications.

Measurement-Level Integration of Carrier-Phase GPS and Laser-Scanner for Outdoor Ground Vehicle Navigation

This paper introduces a navigation system based on combined global positioning system (GPS) and laser-scanner measurements for outdoor ground vehicles. Using carrier-phase differential GPS, centimeter-level positioning is achievable when cycle ambiguities are resolved. However, GPS signals are easily attenuated or blocked, so their use is generally restricted to open-sky areas. In response, in this work we augment GPS with two-dimensional laser-scanner measurements. The latter is available when GPS is not and further enables obstacle detection. The two sensors are integrated in the range domain for optimal navigation performance. Nonlinear laser observations and time-correlated code and carrier-phase GPS signals are processed in a unified and compact measurement-differencing extended Kalman filter. The resulting algorithm performs real-time carrier-phase cycle ambiguity estimation and provides absolute vehicle positioning throughout GPS outages, without a priori knowledge of the surrounding landmark locations. Covariance analysis, Monte Carlo simulations, and experimental testing in the streets of Chicago demonstrate that the performance of the range-domain integrated system far exceeds that of a simpler position-domain implementation, in that it not only achieves meter-level precision over extended GPS-obstructed areas, but also improves the robustness of laser-based simultaneous localization and mapping.

Methodology for Automating the Identification and Localization of Construction Components on Industrial Projects

Even though engineered components, such as pipe spools and structural steel elements, generally account for a significant percentage of the total installed cost of an industrial project, current industry practices still rely on human ability to track thousands of these components individually after they are received at the job site. These site-tracking practices are inefficient and error prone. This paper presents an approach for automating the identification and localization of construction components on large industrial projects. The proposed approach combines advanced sensing devices and localization mechanisms. The appropriate combination of global positioning system and radio-frequency identification (RFID) facilitates an infrastructure-free data collection process capable of detecting a large number of RFID-tagged components in short amounts of time. Based on the collected data, localization mechanisms precisely estimate the coordinates of the tagged components. Field experiments on real construction scenarios demonstrated the feasibility of the proposed methodology.

A multirange architecture for collision‐free off‐road robot navigation

AbstractWe present a multilayered mapping, planning, and command execution system developed and tested on the LAGR mobile robot. Key to robust performance under uncertainty is the combination of a short‐range perception system operating at high frame rate and low resolution and a long‐range, adaptive vision system operating at lower frame rate and higher resolution. The short‐range module performs local planning and obstacle avoidance with fast reaction times, whereas the long‐range module performs strategic visual planning. Probabilistic traversability labels provided by the perception modules are combined and accumulated into a robot‐centered hyperbolic‐polar map with a 200‐m effective range. Instead of using a dynamical model of the robot for short‐range planning, the system uses a large lookup table of physically possible trajectory segments recorded on the robot in a wide variety of driving conditions. Localization is performed using a combination of global positioning system, wheel odometry, inertial measurement unit, and a high‐speed, low‐complexity rotational visual odometry module. The end‐to‐end system was developed and tested on the LAGR mobile robot and was verified in independent government tests. © 2008 Wiley Periodicals, Inc.

Driving with tentacles: Integral structures for sensing and motion

AbstractIn this paper we describe a LIDAR‐based navigation approach applied at both the C‐Elrob (European Land Robot Trial) 2007 and the 2007 DARPA Urban Challenge. At the C‐Elrob 2007 the approach was used without any prior knowledge about the terrain and without global positioning system (GPS). At the Urban Challenge the approach was combined with a GPS‐based path follower. At the core of the method is a set of “tentacles” that represent precalculated trajectories defined in the ego‐centered coordinate space of the vehicle. Similar to an insect's antennae or feelers, they fan out with different curvatures discretizing the basic driving options of the vehicle. We detail how the approach can be used for exploration of unknown environments and how it can be extended to combined GPS path following and obstacle avoidance allowing safe road following in case of GPS offsets. © 2008 Wiley Periodicals, Inc.

Prediction of Activity Mode with Global Positioning System and Accelerometer Data

The primary aim of this pilot study was to assess how well the combination of global positioning system (GPS) and accelerometer data predicted different activity modes. Ten adults (seven male, three female; 23-51 yr) simultaneously wore a GPS unit and accelerometer during bouts of walking, jogging/running, bicycling, inline skating, or driving an automobile. Discriminant function analysis was used to identify a parsimonious combination of variables derived from accelerometer counts and steps and GPS speed that best classified mode. A total of 29 bouts were used to develop this classification criterion. This criterion was validated using two datasets generated from the complete collection of minute-by-minute values from all bouts. Model development with "calibration" data showed that two accelerometer variables alone (median counts and steps) resulted in 26 of 29 bouts (90%) being correctly classified. Prediction of activity mode using counts and steps in a minute-by-minute "validation" dataset (N = 200) was 86.5%. Using three variables from the accelerometer and GPS (median counts, steps and speed) resulted in correct classification in 27 of 29 activity bouts in the "calibration" data (93%). In the "validation" dataset comprising 200 min, the combination of accelerometer counts and steps and GPS speed were able to correctly classify 91% of the observations. Walking and bicycling minutes were correctly classified most frequently (96%). In another "validation" dataset consisting of activity bouts, this combination of variables resulted in correct classification in 42 of 43 bouts (98%). This pilot study provides evidence that the addition of GPS to accelerometer monitoring improves physical activity mode classification to a small degree. Larger studies among free-living individuals and with an expanded range of activities are needed to replicate the current findings and further determine the merits of using GPS with accelerometers for mode identification.

Improvement of the Temperature and Moisture Retrievals in the Lower Troposphere Using AIRS and GPS Radio Occultation Measurements

Abstract Accurate temperature and water vapor profiles in the middle and lower troposphere (LT) are crucial for understanding the water cycle, cloud systems, and energy balance. Global positioning system (GPS) radio occultation (RO) is the first technique that can provide a high-vertical-resolution all-weather refractivity profile, which is a function of pressure, temperature, and moisture. However, in the moist LT over the Tropics, the refractivity retrievals from GPS RO data are often significantly negatively biased because of tracking errors and propagation effects related to sharp vertical moisture gradients that may result in superrefraction (SR). The Atmospheric Infrared Sounder (AIRS) is a nadir-viewing sounder that can measure vertical temperature and moisture profiles with about 1–2-km vertical resolution. However, AIRS observations cannot usually obtain accurate temperature and water vapor profiles in the planetary boundary layer (PBL) because of the poor resolving power in the LT. This study uses simulations based on radiosonde profiles by combining the AIRS and the GPS RO measurements to obtain the best temperature and moisture retrievals in the LT. Different approaches are used for the drier LT and the moist LT. For the drier LT, where GPS RO data are not affected by SR errors, a multivariable regression algorithm for inverting the combined AIRS and GPS RO measurements is used. In the moist LT (e.g., SR on top of PBL), the combined AIRS and GPS RO regression inversion above the LT is used as the first guess for AIRS-only physical retrieval, which is extended into the LT. The results show that combining AIRS and GPS RO data effectively constrains the individual solutions, and therefore significantly improves inversion results. The algorithm is also applied for all available radiosonde profiles (19 profiles) over a 1-month period from the site characterized by strong SR on top of the PBL. Retrieved temperature and water vapor profiles yield unbiased low-resolution refractivity profiles in the PBL.

An integrated framework to map animal distributions in large and remote regions

ABSTRACTIn this paper we show how new technologies can be incorporated from the gathering of field data on wildlife distribution to the final stage of producing distribution maps. We describe an integrated framework for conducting wildlife censuses to obtain data to build predictive models of species distribution that when integrated in a GIS will produce a distribution map. Field data can be obtained with greater accuracy and at lower costs using a combination of Global Positioning System, Personal Digital Assistant, and specific wildlife recording software. Sampling design benefits from previous knowledge of environmental variability that can be obtained from free remote sensing data. Environmental predictors derived from this remote sensing information alone, combined with automatic procedures for predictor selection and model fitting, can render cost‐effective predictive distribution models for wildlife. We show an example with guanaco distribution in the Patagonian steppes of Santa Cruz province, Argentina.

Investigation of physical and bathymetric characteristics of Lakes Abaya and Chamo, Ethiopia, and their management implications

AbstractThe purpose of this study was to investigate the physical parameters of Lakes Abaya and Chamo in the Ethiopian rift lakes system, including such physical characteristics as depth, water resources capacity, hydrology, water balances, and impacts of water use and degradation of their watersheds. These parameters have not previously been studied for these two lakes to any significant extent. This study describes the bathymetry survey undertaken for these two lakes, and the morphometric characteristics derived from it. This study is part of a research project developed to provide further details on such parameters as hydrology, water quality, sediment inflows and deposition, lake hydrodynamics and consumptive water uses. The bathymetric survey was conducted, utilizing a combination of global positioning system (GPS) and echo sounder. To calculate the morphometric characteristics, the background lake map was digitized, and the surveyed primary data were developed as digital values. The digital values were interpolated, generating grids of the elevation surface. The elevation area and elevation volume curves (capacity curves) of the two lakes were developed from the digital values, describing the water resources capacity of the lake water basins. The results of this study increase our understanding of the water resources of these two lakes, as well as provide better understanding of their vulnerability to human activities because of their shallow depths. Immediate application of the results, as a basis for continuation of this study, also is highlighted.

Use of a global positioning and heart rate monitoring system to assess training load in a group of Thoroughbred racehorses

Training is an important variable for determining athletic success. Nonetheless, there has been minimal scientific evaluation of racehorse training programmes. Training of racehorses focuses on running the horses at certain speeds using a combination of a stopwatch and rider's 'feel' for a horse's work intensity. Consequently, actual work intensity for individual horses is not clearly defined. To 1) utilise a combined global positioning system (GPS) and heart rate monitor system to quantify training intensity and physiological responses of a group of racehorses undergoing training and racing; and 2) compare the workload measured by the GPS to that timed and recorded daily by a racehorse trainer. Nineteen racehorses age 3 years were followed through a traditional training and racing programme over a 4 month period. Daily GPS and heart rate data together with the trainer's timing and distance data were collected while the horses were trained. Data were analysed using an ANOVA for repeated measures. The combined GPS/heart rate monitoring system detected different heart rate responses in individual horses subjected to the same training workouts. The average speeds detected with the GPS system were in agreement with average speeds timed by the trainer. However, peak speeds reached during training were significantly greater (P<0.05) than those estimated with stopwatch timing. The horses average training speeds increased significantly over the duration of the training period. The results from this study show that a GPS/heart rate monitor system provides a reliable measure of daily workload in horses during training. This technology provides a detailed picture of horses' training sessions and has the potential to provide a greater insight into the types of training that may predispose horses to injury.

Modification of vehicle handling characteristics via steer-by-wire

While changing the handling characteristics of a conventional vehicle normally requires physical modification, a vehicle equipped with steer-by-wire can accomplish the same effect through active steering intervention. This paper presents an intuitive method for altering a vehicle's handling characteristics by augmenting the driver's steering command with full vehicle state feedback. The vehicle can be made more or less responsive depending on the driver's preference and particular operating conditions. Achieving a smooth, continuous change in handling quality requires both accurate state estimation and well-controlled steering inputs from the steer-by-wire system. Accurate estimates of vehicle states are available from a combination of global positioning system (GPS) and inertial navigation system (INS) sensor measurements. By canceling the effects of steering system dynamics and tire disturbance forces, the steer-by-wire system is able to track commanded steer angle with minimal error. Experimental results verify that with precise steering control and accurate state information, the handling modification is exactly equivalent to changing the front tire cornering stiffness.

Measuring the onset of locking in the Peru–Chile trench with GPS and acoustic measurements

The subduction zone off the west coast of South America marks the convergence of the oceanic Nazca plate and the continental South America plate. Nazca-South America convergence over the past 23 million years has created the 6-km-deep Peru-Chile trench, 150 km offshore. High pressure between the plates creates a locked zone, leading to deformation of the overriding plate. The surface area of this locked zone is thought to control the magnitude of co-seismic release and is limited by pressure, temperature, sediment type and fluid content. Here we present seafloor deformation data from the submerged South America plate obtained from a combination of Global Positioning System (GPS) receivers and acoustic transponders. We estimate that the measured horizontal surface motion perpendicular to the trench is consistent with a model having no slip along the thrust fault between 2 and 40 km depth. A tsunami in 1996, 200 km north of our site, was interpreted as being the result of an anomalously shallow interplate earthquake. Seismic coupling at shallow depths, such as we observe, may explain why co-seismic events in the Peruvian subduction zone create large tsunamis.

Rapid uplift of southern Alaska caused by recent ice loss

SUMMARY Extreme uplift rates and sea level changes in southern Alaska have been documented by Global Positioning System (GPS) surveys, tide gauge measurements and studies of raised shorelines. The movements detected in a network of 45 GPS survey points describe a broad pattern of rapid regional uplift. The majority of the study area is uplifting at a rate faster than 10 mm yr −1 , with several sites uplifting more rapidly than 25 mm yr −1 . New tide gauge data presented here consist of repeat occupations of 18 temporary gauge sites. Sea level rates at these sites agree with similar measurements in southern Alaska taken ∼50 yr earlier, and also with the pattern of uplift derived from the GPS data. Raised shoreline studies at 14 sites document total sea level change, with a maximum change in sea level of −5.7 m found in upper Lynn Canal. The start of the ongoing uplift episode that raised these shorelines has been dated with dendrochronology and found to be coincident with the start of the collapse of the Glacier Bay Icefield, at ca. 1750 AD. The pattern of total sea level change is in general agreement with upliftrate measurements, with greater sea level change found at the sites closest to the peak uplift rates in upper Glacier Bay. We use a viscoelastic earth model subjected to an ice load history built upon observations of glacial change to predict uplift rates at the tide gauge and GPS sites as well as the total uplift at the raised shoreline sites. Our modelling exercises are limited to an ice load model based on independent studies of the region’s glacial history over the past 1.7 kyr, to evaluate whether the uplift observations can be explained by simple earth models subjected to this load history. Two-layer earth models, consisting of an elastic crust and a low-viscosity upper mantle half-space, can be adjusted to fit either the raised shoreline data or the combined GPS and tide gauge uplift-rate data, but cannot fit all the data with a single set of earth model parameters. However, all three data sets are consistent with an approximated three-layer earth model. The combined model is constrained by a total of 77 uplift measurements, which at the 95 per cent confidence level require a low-viscosity asthenosphere [ηA = (1.4 ± 0.3) × 10 19 Pa s and thickness 110 +20