Kinematic Differential Global Positioning System Research Articles

Testing Patch, Helix and Vertical Dipole GPS Antennas with without Choke Ring Frame

Abstract: The antenna is the connecting part between Global Positioning System (GPS) satellite and receiver, and it works on transferring the satellite signal propagation to the receiver with minimum interruption. This is beside the main role that GPS antenna can play for accurate and precise positioning. High quality GPS antennas have high gain, systematic radiation pattern, Right Hand Circular Polarization (RHCP), and low directivity. Multipath error is a principal error source connected with GPS positioning and it can be mitigated using better antenna design. GPS antennas tend to be provided with choke ring frame for protection from the reflected RHCP electromagnetic waves. In this paper, the performance of three different types of GPS antenna, namely: Microstrip Patch Antenna (MPA), Helix antenna (HA), and Vertical Dipole antenna (VDA), with and without choke ring frame, has been investigated using single frequency GPS receiver. The antennas have been examined under the same GPS environment, including satellites constellation, geometry, and surroundings, with different heights from the ground reflector surface for multipath evaluation. Short base-line kinematic differential code GPS (DGPS) technique has been used for removing and mitigating the main GPS error sources and focusing on multipath effect. Satellite residuals and the quality of the obtained positioning have been considered for evaluating the performance of each antenna. The results have reflected the ability of choke ring frames to improve the performance of the three GPS antennas with different rates in multipath areas, and illustrate the advantages and limitations of each antenna. Keywords: Micro-strip, Patch, Helix, Vertical Dipole, GPS, Choke Ring Antenna, Multipath.

Foredune formation and evolution on a prograding sea-breeze dominated beach

This study investigates the mechanisms of dune formation and growth on a micro-tidal beach. The study area, located on a barrier island on the northern Yucatan peninsula, is characterized by persistent sea breeze conditions and a wide and shallow continental shelf. Beach topography data was collected over 5 years, on a prograding beach (0.5–7 m y-1), using a Real-Time Kinematic Differential Global Positioning System. The beach surveys (>100) cover from the subaerial beach (seaward from the existing foredune in 2015) to a 1.5 m water depth with a high spatial (0.2 m–0.5 m) and temporal (weekly to bi-weekly) resolution. Thus, shoreline evolution, offshore/onshore inner sandbar migration, and foredune initiation and growth can be analyzed from this data set. Moreover, environmental conditions, obtained from in situ observations and numerical model simulations, allow us to investigate the role of marine and aeolian processes on foredune morphodynamics. A net shoreline advance is observed, induced by the presence of a port's jetty, allowing the formation of a new foredune during the period of study. Field observations suggest that seasonal beach variability is explained by the onshore (offshore) sediment transport during fall-winter (spring-summer). The dune growth rate is well correlated with the monthly mean wind speed that reaches a maximum during spring months, when sea-breezes are more persistent and intense (W > 12 m s-1), the effective fetch length is larger, and the moisture content is lower. Empirical Orthogonal Function (EOF) analysis of beach profiles in the fast progradation area (>1 m y-1) shows that the variability is dominated by sustained beach width increase throughout the study period. On the other hand, at the slow progradation area the first and second EOF modes explain the seasonal beach and foredune variability, respectively. Thus, it is suggested that beach sand supply (during fall-winter) followed by aeolian transport (during spring) control the natural foredune growth in this region.

The technical challenges and outcomes of ground-penetrating radar: A site-specific example from Joggins, Nova Scotia

The Carboniferous Joggins Formation is known for its complete succession of fossil-rich, coal-bearing strata, deposited in a fluvial meanderbelt depositional setting. Hence, the Joggins Formation outcrop is an excellent analogue for studying the 2D geological complexities associated with meanderbelt systems. In this research, a conventional ground-penetrating radar system was tested with the intent of imaging near-surface, dipping, strata of the Joggins Formation (potentially with subsequent repeats as annual erosion provides new visual calibrations). The survey was unsuccessful in its primary goal, and for future reference we document the reasons here. However, the overlying near-surface angular unconformity was successfully imaged enabling mapping of the approximately 8 m of overlying glacial till. A successful outcome would have allowed observations from the 2D outcrop to be extended into 3D space and perhaps lead to an increased understanding of the small (e.g., bedform baffles and barriers) and large (e.g., channel bodies) scale architectural elements, meanderbelt geometry, and aspect ratios. The study comprises a 42-line, 3.46 km ground-penetrating radar survey using a Sensors and Software pulseEKKO Pro SmartCart system. It was combined with a real-time kinematic differential global positioning system for the georeferencing of survey lines. The 50 MHz antenna frequency, with a 1 m separation, was chosen to maximize the depth of penetration, while still maintaining a reasonable resolution. The results show that many of the lines are contaminated with diffraction hyperbolae, possibly caused from buried objects near or under the survey lines or surface objects near the survey lines. A total of thirteen unique radar reflectors are described and interpreted from this work. The thick clay-rich soil overlying the Joggins Formation probably contributed to significant signal attenuation and the nature of the Carboniferous strata (dip of the beds, pinching and swelling of the beds, bed thickness, etc.) also contributed to imaging difficulties.

Criteria for the optimal selection of remote sensing optical images to map event landslides

Abstract. Landslides leave discernible signs on the land surface, most of which can be captured in remote sensing images. Trained geomorphologists analyse remote sensing images and map landslides through heuristic interpretation of photographic and morphological characteristics. Despite a wide use of remote sensing images for landslide mapping, no attempt to evaluate how the image characteristics influence landslide identification and mapping exists. This paper presents an experiment to determine the effects of optical image characteristics, such as spatial resolution, spectral content and image type (monoscopic or stereoscopic), on landslide mapping. We considered eight maps of the same landslide in central Italy: (i) six maps obtained through expert heuristic visual interpretation of remote sensing images, (ii) one map through a reconnaissance field survey, and (iii) one map obtained through a real-time kinematic (RTK) differential global positioning system (dGPS) survey, which served as a benchmark. The eight maps were compared pairwise and to a benchmark. The mismatch between each map pair was quantified by the error index, E. Results show that the map closest to the benchmark delineation of the landslide was obtained using the higher resolution image, where the landslide signature was primarily photographical (in the landslide source and transport area). Conversely, where the landslide signature was mainly morphological (in the landslide deposit) the best mapping result was obtained using the stereoscopic images. Albeit conducted on a single landslide, the experiment results are general, and provide useful information to decide on the optimal imagery for the production of event, seasonal and multi-temporal landslide inventory maps.

Evaluating the Performance of Using PPK-GPS Technique in Producing Topographic Contour Map

ABSTRACTThe Global Positioning System (GPS) is considered as one of the most powerful tools that are used in geodetic works. It is increasingly considered as an alternative tool for conventional surveying techniques. The goal of this research paper is to produce a methodology for generating topographic contour maps using the post-processed kinematic differential GPS technique (PPK-GPS). The performance of this technique is assessed by comparing it with the traditional spirit-leveling technique taking into consideration the accuracy, time, and cost. The study area is located along the Mediterranean coast in the Rosetta area of the middle Delta in Egypt with a total area of about 39 km2. The field work includes 14 control points and about 50,000 PPK observations. In addition, 20 check cross sections that extend along the coastal line from Rosetta to El Burullus cities were observed using both spirit-leveling and GPS-PPK techniques. The results of the comparison indicate that the PPK-GPS technique can be used instead of spirit leveling in producing a topographic contour map with an accuracy of about 20 cm in orthometric height. We find that the PPK-GPS technique reduces the estimated time of leveling works in our study area by about 70%.

Application de la technique de photogrammétrie « Structure-from-Motion » pour des levés haute résolution en géomorphologie côtière et fluviale

Photogrammetry is an old remote sensing technique that has undergone significant new developments related to the emergence of new computer vision algorithms, notably the workflow technique called Structure-from-Motion (SfM photogrammetry). These innovations facilitate the utilization of this technique by non-specialists. SfM photogrammetry now enables the production of high-resolution morphometric 3D models and derived products such as digital surface models (DSMs) and orthophotographs. We conducted three SfM-photogrammetric experiments, in French Guiana on an embayed beach in Cayenne and on a small mudflat sector of a coastal mud bank near the Sinnamary estuary, and finally in the French southern Alps on a section of the braided Buech River near Sisteron. We developed a simple field protocol based on subvertical aerial photography from a microlight aircraft at low altitude (1000 feet). We generated DSMs and the other products with user-friendly Agisoft Photoscan Professional © software. These SfM implementations were aimed at highlighting the subtle morphological variations characterising these features and some of the processes involved in morphological change. The DSMs were produced at a resolution of 5 to 10 cm per pixel and had a mean vertical accuracy less than 10 cm compared to the Real-Time Kinematic Differential Global Positioning System (RTK-DGPS) control points, with a maximum of 20 cm in marginal sectors near high vegetation such as trees and shrubs and on wet surfaces close to water-filled channels or in the lower intertidal zone. Low-cost, user-friendly SfM photogrammetry offers interesting new perspectives in the fields of coastal and fluvial geomorphology requiring high-resolution topographic data. The technique combines the advantages of the reproducibility of GPS topographic surveys and the high density and accuracy of airborne LIDAR, but at very advantageous cost compared to the latter.

Can recreational echosounder-chartplotter systems be used to perform accurate nearshore bathymetric surveys?

This work intends to determine if low-cost surveying techniques based on recreational echosounders can be used to perform nearshore bathymetry for analysing evolution of coastal sectors. For that purpose, two hydrographic surveying techniques were compared, i.e. (1) a real-time kinematic differential global positioning system (RTK-DGPS) synchronised with a single beam echosounder with real-time tidal elevation correction and (2) a low-cost recreational echosounder-chartplotter system using Global Navigation Satellite Systems (GNSS) with real-time European Geostationary Navigation Overlay Service (EGNOS) augmentation services and depth values post-processed using measured sea level. Two bathymetric data sets were obtained, one by each method, for the same area and survey lines at an ebb tidal delta (Tavira Inlet, Ria Formosa Portugal). Vertical differences were determined assuming no morphological variations between surveys. Results showed that depth elevation differences between bathymetric surfaces were of 0.10 ± 0.16 m, slightly higher but within the same order of the error attributable to the used interpolator (0.00 ± 0.11 m, triangular surface fitting). The differences between surveys performed with two different equipment sets and using different methodologies for correcting water elevations are very small both quantitative and qualitatively. Those differences can be diminished by improving the tidal level correction and uncertainties associated to different tidal slopes throughout the survey area. Pitch/roll corrections performed with low-cost GPS receivers would be also a valuable addition to the accuracy and precision of the method. It is then concluded that navigation with EGNOS augmentation services and sounding devices ten times cheaper than combined RTK-DGPS with single beam echosounders allow to measure and monitor accurately the nearshore bathymetry.

Experimental assessment of post-processed kinematic Precise Point Positioning method for structural health monitoring

Monitoring the response of engineering structures, such as tall buildings, tower and large-scale bridges, under severe loading conditions, such as strong earthquake or wind storm, is an important requirement to verify their design and construction and to evaluate structural condition and reliability. In the last two decades, high-rate real-time or post-processed kinematic differential Global Positioning System (DGPS) has been widely used in dynamic displacement measurements of civil engineering structures. In recent years, interest has increased for Precise Point Positioning (PPP) due to its capability to generate positioning solutions as accurate as DGPS. In this study, the potential of post-processed kinematic PPP in terms of monitoring dynamic displacement response of a structure has been explored based on free damped oscillation events obtained from a model structure, which is able to vibrate in the fundamental and higher modes of vibration. A number of experiments have been carried out and five events, each of which is different character, have been selected to compare PPP results with DPGS results in the time and frequency domain. The results clearly demonstrate that the PPP method, like the DGPS method, offers great potential for the measurement of horizontal and vertical dynamic movement of structures. The impact of a short period (one minute) of observation length on the result of the kinematic PPP method was also investigated in terms of sensing the dynamic movement of a structure. Twenty selected one-minute data-sets extracted from a one-hour original data-set were processed by Canadian spatial reference system PPP and each one-minute PPP solution was compared with the corresponding segment obtained from the one-hour PPP solution. The results show that the one-minute PPP solution is able to extract the fundamental natural frequency of the oscillation in the horizontal and vertical component just like the one-hour PPP solution after the offset is removed and the lower frequency trend component is filtered out.

Dynamics of the Douro estuary sand spit before and after breakwater construction

The Douro estuary sand spit (NW Portugal) is an important natural defence against the impact of storm events. Aiming to improve navigation safety, a breakwater was built to stabilise the spit. In 2001, a monitoring programme was set up to understand the dynamics of the sand spit and, later, to evaluate breakwater efficiency on stabilising the spit's shape and volume. Nine years of periodic, accurate 3D digital elevation models obtained from kinematic differential Global Positioning System surveys were used to assess spatial and temporal changes in the spit morphology before and after the breakwater construction. Temporal and spatial spit dynamics were further related to river discharge flows, wave action and wind energy. Although the breakwater had a stabilising effect on most of the spit's area and volume, it caused a clear change in the morphology of the spit's head and in the previously observed patterns of erosion and accretion. Before breakwater construction, erosion was significantly correlated with extreme river discharge and wind conditions; accretion was significantly correlated with extreme wind conditions; and spit area and volume at 1–2 m elevation with extreme wave conditions. After breakwater construction, these correlations were not found, but the eastern (inland) face of the spit and particularly its southern part became more susceptible to the observed extreme river discharge flows, wave and wind conditions. The instability in the SE part of the spit may pose a threat to an existing local Nature Reserve. Furthermore, before breakwater construction, the spit often breached during severe floods favouring river discharges. The strengthening of the spit after breakwater construction may reduce the likelihood of breaching and lead to more severe flood effects in the estuary.

Morphology and composition of beach-cast Posidonia oceanica litter on beaches with different exposures

Posidonia oceanica seagrass litter is commonly found along sandy shores in the Mediterranean region, forming structures called banquettes, which are often removed in order to allow the beach to be used for tourism. This paper evaluates the relationship between the morphology and composition of banquettes and beach exposure to dominant waves. A Real Time Kinematic Differential Global Positioning System was used to evaluate the variability of banquettes and beach morphology over a period of 1year. Banquette samples, collected at two different levels of the beach profile (i.e. foreshore and backshore), were used to evaluate the contribution of leaves, rhizomes and sediments to the total weight. Banquettes showed a higher volume, thickness and cross-shore length on exposed beaches, whereas narrower litter deposits were found on the sheltered beach. On exposed beaches, banquettes were deposited in beach zones characterized by changes in elevation. These changes in elevation were mainly due to the deposition and erosion of sediments and secondly to the deposition and or erosion of leaf litter. On sheltered beaches, the variability in beach morphology was low and was restricted to areas where the banquettes were located. The leaf/sediment ratio changed along the cross-shore profile. On the backshore, banquettes were a mixture of sediments and leaves, whereas leaves were the main component on the foreshore, independently of the beach exposure. The processes which control the morphodynamics in the swash zone could explain the variability of banquette composition along the cross-shore profile. Finally, this study highlighted that Posidonia oceanica seagrass litter plays an important role in the geomorphology of the beachface and its removal can have a harmful impact on the beaches.

Thematic information content assessment of the ASTER GDEM: a case study of watershed delineation in West Java, Indonesia

This study assesses the thematic information content using subwatershed boundaries mapped using advanced spaceborne thermal emission and reflection (ASTER) global digital elevation model (GDEM), shuttle radar topography mission (SRTM) DEM and a topographic map (Topo-DEM), and verifies the absolute elevation accuracy by the use of a real-time kinematic differential global positioning system (RTK-DGPS) survey. Subwatershed boundaries extracted from the three different DEMs exhibit a high degree of congruency especially in upstream areas. In these areas, SRTM exhibits lower root mean square errors (RMSEs) than the ASTER GDEM. The discrepancies were larger at lower altitudes. The vertical accuracy assessment using the RTK-DGPS data showed strong correlation with the three DEMs at some stations but the accuracy varied from one area to another. The ASTER GDEM and SRTM had lower accuracy than the Topo-DEM due to the influence of artefacts as shown by their total average RMSE (4.42, 3.30 and 3.13 m, respectively). The average RMSE values also indicate that SRTM is comparatively more accurate than ASTER GDEM.

Autonomous navigation using a robot platform in a sugar beet field

An RTK-DGPS (Real Time Kinematic Differential Global Positioning System) based autonomous field navigation system including automated headland turns was developed to provide a method for crop row mapping combining machine vision, and to evaluate the benefits of a behaviour based reactive layer in a hybrid deliberate systems architecture. Two experiments were performed at the same time: following of pre-planned paths reconstructed from crop row positions based on RTK-DGPS and crop row mapping by combining vision-based row detection with RTK-DGPS information. The standard deviation, mean, minimum and maximum lateral error of the robot vehicle while following a straight path on the field with RTK-DGPS at a speed of 0.3 m s−1 were respectively 1.6, 0.1, −4.5 and 3.4 cm. The standard deviation, mean, minimum and maximum of the heading error were 0.008, 0.000, −0.022 and 0.023 rad. The point-in-polygon algorithm proved to be a suitable method for detection in which part of the field the actuator position coordinates or the field of view of the camera are located. A smooth headland path that connected to the subsequent path along the crop was generated in realtime using a spline based algorithm. The hybrid deliberate software architecture with a behaviour based reactive layer allowed a convenient evaluation of the robot performance. Results from the field experiments showed that the implement can be guided along a defined path with cm precision using an autonomous robot navigating in a field.

A path following algorithm for mobile robots

This paper considers path following control for a robotic platform. The vehicle used for the experiments is a specially designed robotic platform for performing autonomous weed control. The platform is four-wheel steered and four-wheel driven. A diesel engine powers the wheels via a hydraulic transmission. The robot uses a Real Time Kinematic Differential Global Positioning System to determine both position and orientation relative to the path. The deviation of the robot to the desired path is supplied to two high level controllers minimizing the orthogonal distance and orientation to the path. Wheel angle setpoints are determined from inversion of the kinematic model. At low level each wheel angle is controlled by a proportional controller combined with a Smith predictor. Results show the controller performance following different paths shapes including a step, a ramp, and a typical headland path. A refined tuning method calculates controller settings that let the robot drive as much as possible along the same path to its setpoint, but also limit the gains at higher speeds to prevent the closed loop system to become unstable due to the time delay in the system. Mean, minimum and maximum orthogonal distance errors while following a straight path on a paving at a speed of 0.5 m/s are 0.0, −2.4 and 3.0 cm respectively and the standard deviation is 1.2 cm. The control method for four wheel steered vehicles presented in this paper has the unique feature that it enables control of a user definable position relative to the robot frame and can deal with limitations on the wheel angles. The method is very well practical applicable for a manufacturer: all parameters needed are known by the manufacturer or can be determined easily, user settings have an easy interpretation and the only complex part can be supplied as a generic software module.

Error Analysis in a Stereo Vision-Based Pedestrian Detection Sensor for Collision Avoidance Applications

This paper presents an analytical study of the depth estimation error of a stereo vision-based pedestrian detection sensor for automotive applications such as pedestrian collision avoidance and/or mitigation. The sensor comprises two synchronized and calibrated low-cost cameras. Pedestrians are detected by combining a 3D clustering method with Support Vector Machine-based (SVM) classification. The influence of the sensor parameters in the stereo quantization errors is analyzed in detail providing a point of reference for choosing the sensor setup according to the application requirements. The sensor is then validated in real experiments. Collision avoidance maneuvers by steering are carried out by manual driving. A real time kinematic differential global positioning system (RTK-DGPS) is used to provide ground truth data corresponding to both the pedestrian and the host vehicle locations. The performed field test provided encouraging results and proved the validity of the proposed sensor for being used in the automotive sector towards applications such as autonomous pedestrian collision avoidance.

An Automated Cost-effective System for Real-time Slope Mapping in Commercial Wild Blueberry Fields

The development of site-specific agriculture has increased the need for knowledge regarding within-field variability in factors such as soil/plant characteristics and topography that influence wild blueberry (Vaccinium angustifolium) production. Surface soil properties are the first type of information most frequently used by blueberry producers in developing management plans. Topographic features are not yet routinely used to guide within-field management. The majority of blueberry fields in eastern Canada have gentle to severe topography. An automated slope measurement and mapping system (SMMS) consisting of low-cost accelerometers used as tilt sensors, differential global positioning system (DGPS), and laptop and custom software was developed. The SMMS was mounted on an all-terrain vehicle for real-time slope measurement and mapping. Six commercial wild blueberry fields were surveyed in central Nova Scotia to evaluate the performance of SMMS. The automatically sensed slopes (SS) were also compared with manually measured slopes (MS) at 20 randomly selected points in each field to examine the accuracy of SMMS. The SMMS measured slope reliably in the selected fields with root mean square error ranging from 0.12 to 0.56 degrees and correlations of SS with MS of R2 = 0.95 to 0.99. The selected fields had substantial variation in slope (ranging from 0.8 to 31.0 degrees). Therefore, the use of low-cost and reliable accelerometers with a DGPS is a better option than expensive real-time kinematic DGPS for developing cost-effective SMMS to quantify and map slopes (real-time) for planning site-specific management practices in commercial fields. The SS maps or real-time SMMS could also be used to adjust vehicle speed at particularly steep slopes.

A low-cost integrated positioning system for autonomous off-highway vehicles

This article reports a method for integrating a low-cost positioning system, constructed using a Garmin N17 global positioning system (GPS) and an integrated inertial sensor unit, consisting of three single-axis microelectromechanical system (MEMS) gyros and one triaxial MEMS accelerometer, for autonomous off-highway vehicle use. Based on a vehicle position—velocity—attitude (PVA) model, a data fusion algorithm was formulated to extract more accurate and reliable positioning information from the raw data sensed by the GPS and inertial sensor unit. The developed integrated positioning system (IPS) was evaluated on an agricultural utility vehicle on three different sites. A real-time kinematic (RTK) differential GPS unit, capable of providing 2–3cm dynamic positioning accuracy while the position dilution of precision is low enough, was installed on the test vehicle to provide accurate positioning references in those evaluation tests. Results obtained from those tests showed that, when the vehicle was travelling on paved roads near buildings and/or under the trees, the maximum positioning error of the developed IPS was 0.50m, and that this maximum error level was reduced to 0.30m when the vehicle was travelling in open fields. The IPS could provide a position update rate at 50Hz; even the GPS could provide only a 1Hz update rate. Test results also revealed that this system could continuously provide accurate position signals when the GPS signal is lost for up to 30s. This research verified that a low-cost IPS could provide satisfactory position information for autonomous off-highway vehicle uses.

Sistema de Posicionamiento para Vehículos Autónomos

Uno de los objetivos más importantes de los Sistemas Inteligentes de Transporte (ITS) es evitar la pérdida de precisión en el posicionamiento y guiado del vehículo, debido a la disminución en la calidad de la señal del Sistema de Posicionamiento Global (GPS). En este artículo, se presenta un sistema de posicionamiento formado por la combinación de un GPS con una unidad de medida inercial ayudada por los sensores embarcados en el coche para realizar el guiado. En función de la precisión proporcionada por el GPS, el sistema discrimina entre tres posibles comportamientos: 1) Si la precisión es centimétrica, el GPS se encarga en solitario del guiado. 2) Si no se recibe la señal GPS, el control lo toma la unidad inercial. 3) Si la precisión de la señal del GPS no es centimétrica, la posición del vehículo se calcula mediante una combinación de ambas medidas. El sistema se ha instalado en un Citroën C3 Pluriel. Los resultados muestran un correcto comportamiento del vehículo en diferentes situaciones y prueban la necesidad de integrar la información sensorial para realizar un control de navegación óptimo.

Fifty years of coastal erosion and retrogressive thaw slump activity on Herschel Island, southern Beaufort Sea, Yukon Territory, Canada

Patterns of coastal erosion in the Arctic differ dramatically from those coasts in more temperate environments. Thick sea ice and shore-fast ice limit wave-based erosional processes to a brief open water season, however despite this, permafrost coasts containing massive ice, ice wedges and ice-bonded sediments tend to experience high rates of erosion. These high rates of erosion reflect the combined thermal–mechanical processes of thawing permafrost, melting ground ice, and wave action. Climate change in the Arctic is expected to result in increased rates of coastal erosion due to warming permafrost, increasing active layer depths and thermokarst, rising sea levels, reduction in sea ice extent and duration, and increasing storm impacts. With the most ice-rich permafrost in the Canadian Arctic, the southern Beaufort Sea coast between the Tuktoyaktuk Peninsula and the Alaskan border is subject to high rates of erosion and retrogressive thaw slump activity. Under many climate change scenarios this area is also predicted to experience the greatest warming in the Canadian Arctic. This paper presents results of a remote sensing study on the long-term patterns of coastal erosion and retrogressive thaw slump activity for Herschel Island in the northern Yukon Territory. Using orthorectified airphotos from 1952 and 1970 and an Ikonos image from 2000 corrected with control points collected by kinematic differential global positioning system and processed using softcopy photogrammetric tools, mean coastal retreat rates of 0.61 m/yr and 0.45 m/yr were calculated for the periods 1952–1970 and 1970–2000, respectively. The highest coastal retreat rates are on north–west facing shorelines which correspond to the main direction of storm-related wave attack. During the period 1970–2000 coastal retreat rates for south to south–east facing shorelines displayed a distinct increase even though these are the most sheltered orientations. However, south to south–east facing shorelines correspond to the orientations where the highest densities of retrogressive thaw slumps are observed. Differences in rates of headwall retreat of retrogressive thaw slumps and coastal erosion results in the formation of larger thermokarst scars and the development of polycyclic thaw slumps on south to south–east exposures. The number and the total area of retrogressive thaw slumps increased by 125% and 160%, respectively, between 1952 and 2000. As well, the proportion of active retrogressive thaw slumps increased dramatically. Polycyclic retrogressive thaw slumps appear to develop in a periodic fashion, related to retrogressive thaw slump stage and maximum inland extent.

Seasonal and Interannual Influences on the Patterns of Shoreline Changes in Rio Grande do Sul, Southern Brazil

Changes in shoreline positions along the Rio Grande do Sul coast, southern Brazil, are analyzed to determine the spatial and temporal variability of shoreline movements at a regional scale. Using a kinematic Differential Global Positioning System (DGPS) survey method, the 618-km long shoreline of Rio Grande do Sul has been mapped on five occasions between November 1997 and April 2002. These data show that the coastline responds differently to hydrodynamic and meteorological forcing along the three major coastal sectors. The observed differences occur especially in the magnitude of changes, in the time interval in which the shoreline returns to a previous position, and in the length scale of dominant shoreline changes. Here changes in shoreline position are examined with respect to grain size, shoreline orientation, storms, El Nino–Southern Oscillation (ENSO) events, and gradients of longshore sediment transport. Data analyses and modeling indicate that the alongshore variability in the patterns of shoreline change through time is closely related to shoreline orientation and the associated gradients of longshore sediment transport. Results indicate also that variability in wave energy and storminess influence seasonal changes, whereas ENSO events influence interannual changes. This study demonstrates the importance of understanding the drivers of shoreline change at a regional scale and has applications in studies concerned with coastal engineering and shoreline response to climate change.

Power-Steering Control Architecture for Automatic Driving

The unmanned control of the steering wheel is, at present, one of the most important challenges facing researchers in autonomous vehicles within the field of intelligent transportation systems (ITSs). In this paper, we present a two-layer control architecture for automatically moving the steering wheel of a mass-produced vehicle. The first layer is designed to calculate the target position of the steering wheel at any time and is based on fuzzy logic. The second is a classic control layer that moves the steering bar by means of an actuator to achieve the position targeted by the first layer. Real-time kinematic differential global positioning system (RTK-DGPS) equipment is the main sensor input for positioning. It is accurate to about 1 cm and can finely locate the vehicle trajectory. The developed systems are installed on a Citroe/spl uml/n Berlingo van, which is used as a testbed vehicle. Once this control architecture has been implemented, installed, and tuned, the resulting steering maneuvering is very similar to human driving, and the trajectory errors from the reference route are reduced to a minimum. The experimental results show that the combination of GPS and artificial-intelligence-based techniques behaves outstandingly. We can also draw other important conclusions regarding the design of a control system derived from human driving experience, providing an alternative mathematical formalism for computation, human reasoning, and integration of qualitative and quantitative information.