Differential GPS Research Articles

Relative positioning of formation-flying spacecraft using single-receiver GPS carrier phase ambiguity fixing

In recent years, differential carrier phase-based relative positioning (or “baseline determination”) with precision at the millimeter and submillimeter levels has been demonstrated for the GRACE, TanDEM-X and Swarm missions in offline processing. Specific features of such missions have included the use of spacecraft of similar shapes placed in almost identical orbits as well as the use of consistent geodetic-class GPS receivers. These elements have proven to be advantageous for the computation of baseline solutions with such precision levels. Particularly, they have allowed to fully leverage the use of differential GPS techniques, including the estimation and use of carrier phase integer ambiguities. Similarly, the aforementioned spacecraft and orbit characteristics have made it possible to tightly constrain the relative dynamics of formations in the generation of reduced-dynamic solutions. Other than the former examples, prospective formation-flying mission proposals, such as SAOCOM-CS and PICOSAR, may comprise spacecraft with very different characteristics, including dissimilar GPS/GNSS receivers. Such cases may no longer provide favorable conditions for relative orbit determination strategies. As an alternative, absolute orbit solutions may be computed individually for each spacecraft and used for the generation of precise baseline products. This study aims at the assessment of the potential of single-receiver ambiguity fixing for the generation of precise baseline solutions. Results using flight data from the GRACE, TanDEM-X and Swarm missions exhibit baseline accuracy better than 5 mm (3D RMS) for a one-month test period in June 2016. As such, the presented solutions may be considered for prospective formation-flying remote sensing missions with baseline precision requirements at the subcentimeter level. Likewise, the method is considered of particular interest for future multi-spacecraft formations and swarms that require efficient determination of a large number of individual baselines.

Longitudinal distribution of slope and sediment characteristics in headland-bay beaches in Cádiz, Spain

Rodriguez-Polo, S.; Del Rio, L., and Benavente, J., 2018. Longitudinal Distribution of Slope and Sediment Characteristics in Headland-bay Beaches in Cadiz, Spain. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 306–310. Coconut Creek (Florida), ISSN 0749-0208.Headland-bay beaches are systems with an asymmetric curved planform that develop downdrift of a natural or artificial coastal headland. These beaches have some common features found along the coasts of the world, presenting a well differentiated zonation. The main objective of this work is to elucidate how parameters such as grain size, sorting and beachface slope in the different zones (shadow, central and distal sectors) determine the final morphology of the beach. For this purpose, twelve headland-bay systems in the coast of Cadiz (South Spain), with contrasting wave and tide regimes, were monitored in order to analyze the longitudinal gradient in slope and sediment distribution. Topographic surveys were conducted and sediment samples were collected and analyzed for grain size. Shore-normal transects were surveyed with a RTK-DGPS (Real Time Kinematics - Differential Global Positioning System) and beach slope was computed on each sector of the beaches. Three sediment samples were taken in each transect, corresponding to the dry beach, the high intertidal zone and the lower intertidal zone. A total of 152 topographic profiles and about 456 sediment samples were analyzed. All this information has allowed to gain insight into how the different parameters vary along the twelve headland-bays, as well as to establish common trends among them and to see how these parameters affect the final morphology of the beach. In a further step, future work will be focused on the detailed analysis of wave processes on each system, in order to more accurately determine the relations between the above parameters and the hydrodynamic regime.

Quantitative morphometric analysis of the Jama River profile in a tectonically active margin (Northwestern Ecuador)

The longitudinal profile of a river channel can be described in function of mathematical expressions. The logarithmic fit is the most used method to describe the relative equilibrium of a channel elevation profile. Rivers showing zones of high channel gradient and convex-upward profiles can be evaluated in function of the offset distance with respect to the logarithmic curve. The Jama River profile has been constructed using differential GPS data for the downstream reach and 4-m-grid DEM data base for the remaining headward profile. The resulting longitudinal profile shows a prominent knickpoint of about 80 m in elevation characterized by sharp local convexity. The offset distance in vertical direction from the logarithmic plot is interpreted as the successive accumulation of multiple uplift episodes associated with the Jama Fault System activity. The horizontal offset is suggested to represent the remaining retreated distance for the upstream propagation of the Jama knickpoint. The highly resistant Cretaceous rocks outcropping along the Jama knickpoint reach acts as an inflection point between two subprofiles that show well-fitted logarithmic curves, thereby representing a temporary partitioned equilibrium along the Jama River profile.

Multi-UAV Carrier Phase Differential GPS and Vision-based Sensing for High Accuracy Attitude Estimation

This paper presents a cooperative navigation technique which exploits relative vision-based sensing and carrier-phase differential GPS (CDGPS) among antennas embarked on different flying platforms, to provide accurate UAV attitude estimates in real time or in post-processing phase. It is assumed that all UAVs are under nominal GPS coverage. The logical architecture and the main algorithmic steps are highlighted, and the adopted CDGPS processing strategy is described. The experimental setup used to evaluate the proposed approach comprises two multi-rotors and two ground antennas, one of which is used as a benchmark for attitude accuracy estimation. Results from flight tests are presented in which the attitude solution obtained by integrating CDGPS and vision (CDGPS/Vision) measurements within and Extended Kalman Filter is compared with estimates provided by the onboard navigation system and with the results of a formerly developed code-based differential GPS (DGPS/Vision) approach. Benchmark-based analyses confirm that CDGPS/Vision approach outperforms both onboard navigation system and DGPS/Vision approach.

Terrace sequence along the Yushanguxi River in the southern piedmont of Tian Shan and its relationship to climate and tectonics in northwestern China

Controversies persist regarding the formation of terraces under the control of tectonic factors or climatic changes. This work focuses on the Yushanguxi River in the southern piedmont of Tian Shan, which is an intense tectonic uplift area where the terraces are very developed and the river has deeply downcut. Nine main terraces are distinguished (labelled T1 to Th, from youngest to oldest) based on the interpretation of a high-resolution remote sensing image, field investigations and detailed surveying with differential GPS. The results of the determination of 10Be exposure and 14C show abandoned ages of ~2.1 ka for T1, ~4.1 ka for T2, ~4.2 ka for T3, ~8.2 ka for T4, ~18.1 ka for T5, ~18.8 ka for T6, ~102.1 ka for T7, ~100.6 ka for T81, ~113.9 ka for T82, ~144.6 ka for Th1, ~210.7 ka for Th2, and ~284.3 ka for Th3. Since ~18 ka, the incision rate began to increase from ~0.6 mm a−1 to ~12 mm a−1, which is obviously higher than the fault slip rate of ~0.7 mm a−1. We suggest that the rapid downcutting along the Yushanguxi River during the Holocene has mainly been caused by frequent climate fluctuations.

Multi-Temporal DInSAR to Characterise Landslide Ground Deformations in a Tropical Urban Environment: Focus on Bukavu (DR Congo)

Landslides can lead to high impacts in less developed countries, particularly in tropical environments where a combination of intense rainfall, active tectonics, steep topography, and high population density can be found. However, the processes controlling landslide initiation and their evolution through time remains poorly understood. Here we show the relevance of the use of the multi-temporal differential radar interferometric (DInSAR) technique to characterise ground deformations associated with landslides in the rapidly-expanding city of Bukavu (DR Congo). We use 70 COSMO-SkyMed synthetic aperture radar images acquired between March 2015 and April 2016 with a mean revisiting time of eight days to produce ground deformation rate maps and displacement time series using the small baseline subset approach. We find that various landslide processes of different ages, mechanisms, and states of activity can be identified. Ground deformations revealed by DInSAR are found consistent with field observations and differential GPS measurements. Our analysis highlights the ability of DInSAR to grasp landslide deformation patterns affecting the complex tropical-urban environment of the city of Bukavu. However, longer time series will be needed to infer landside responses to climate, seismic, and anthropogenic drivers.

Morphodynamic change analysis of bedforms in the Lower Orinoco River, Venezuela

Abstract. The Orinoco River has the third largest discharge in the world, with an annual mean flow of 37 600 m3 s−1 at its outlet to the Atlantic Ocean. Due to the presence of the Guiana Shield on the right bank, the lower reach of the Orinoco has a plan form characterized by contraction and expansion zones. Typical 1–1.5 km wide narrow reaches are followed by 7–8 km wide reaches. A complex pattern of bed aggradation and degradation processes takes place during the annual hydrological regime. A series of Acoustic Doppler Current Profiler (ADCP) transects were collected on an expansion channel in the Orinoco River, specifically over a fluvial island, representative of the lower Orinoco. In this study, temporal series of bathymetric cartography obtained by ADCP profiles combined with Differential Global Position System (DGPS) measurements (with dual-frequency), were used to recover the local displacement of bed forms in this island. The principal aims of this analysis were: (1) to understand the dynamics and evolution of sand waves and bars at this section and (2) to quantify the volume (erosion vs. accretion) of a mid-channel bar with dunes by applying DEM of Difference (DoD) maps on time series of bathymetric data. This required sampling with ADCP transects during the months of: May 2016; November 2016 and April 2017. Each bathymetric transect was measured twice, 1 day apart and on the same trajectory obtained by a GPS receptor. The spatial analysis of these ADCP transects is presented as a novel tool in the acquisition of time series of bathymetry for a relatively deep section (∼20 m) and under variable flow conditions.

Role of Geographic Information System in Assessing Determinants of Cardiovascular Disease: An Experience From a Low- and Middle-Income Country.

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the world. The determinants of CVD in an urban population using conventional and geographic information system techniques were attempted as a community-based census-type cross-sectional study in Kerala, India, among 1649 individuals residing in 452 households. Sociodemographic details, risk factor exposures, and self-reported disease prevalence were determined. Location of houses, wells from which subjects drew drinking water, and distances of the house from the outer road (proxy for air pollution) were mapped using differential global positioning system and pH of water samples determined. Prevalence of CVD was 5.8%. Significant predictors of CVD were male gender, diabetes mellitus, hypertension, and hypothyroidism. Statistically significant spatial association was found between CVD and groundwater pH. Geographic information system technology is useful in identification of spatial clustering and disease hotspots for designing preventive strategies targeting CVD.

Quantification of groundwater recharge and river bed clogging by daily water level measurements in a check dam

Check dams are one of the methods of managed aquifer recharge to augment groundwater storage in regions with non-perennial rivers. The objectives of this study were to quantify the groundwater recharge from a check dam in the Arani River, north of Chennai, India, and to assess the clogging of the riverbed. The water level in the check dam was measured daily for 3 years from 2010 to 2013. Other field investigations carried out include measurement of the topographic elevation of the riverbed using the differential global positioning system. Based on the water balance method, the quantity of water evaporated and recharged was estimated. A comparison of 3-year daily water level measurements indicated that there is no clogging in the riverbed during the study period, as this check dam is fitted with a sluice gate which is operated at appropriate times to flush out the sediments.

Variability in Rates of Coastal Change Along the Yukon Coast, 1951 to 2015

AbstractTo better understand the reaction of Arctic coasts to increasing environmental pressure, coastal changes along a 210‐km length of the Yukon Territory coast in north‐west Canada were investigated. Shoreline positions were acquired from aerial and satellite images between 1951 and 2011. Shoreline change rates were calculated for multiple time periods along the entire coast and at six key sites. Additionally, Differential Global Positioning System (DGPS) measurements of shoreline positions from seven field sites were used to analyze coastal dynamics from 1991 to 2015 at higher spatial resolution. The whole coast has a consistent, spatially averaged mean rate of shoreline change of 0.7 ± 0.2 m/a with a general trend of decreasing erosion from west to east. Additional data from six key sites shows that the mean shoreline change rate decreased from −1.3 ± 0.8 (1950s–1970s) to −0.5 ± 0.6 m/a (1970s–1990s). This was followed by a significant increase in shoreline change to −1.3 ± 0.3 m/a in the 1990s to 2011. This increase is confirmed by DGPS measurements that indicate increased erosion rates at local rates up to −8.9 m/a since 2006. Ground surveys and observations with remote sensing data indicate that the current rate of shoreline retreat along some parts of the Yukon coast is higher than at any time before in the 64‐year‐long observation record. Enhanced availability of material in turn might favor the buildup of gravel features, which have been growing in extent throughout the last six decades.

Modelling and analysis of the flood risk at Cavaillon City, Haiti

In Haiti, the vulnerability of urban populations in river flood corridors has disastrous socio-economic consequences on the living conditions of these communities. Mapping of areas prone to this type of risk is not sufficiently developed in Haiti, which complicates the implementation of strategies for the effective management of flood risk. This paper presents a methodological approach allowing to draw up a risk map of the city of Cavaillon, which is confronted to periodic flooding by the Cavaillon river flowing through the city. The reconstruction of the riverbed and floodplain geometry using a differential GPS and a novel drone-based photogrammetry technique made it possible to construct a hydraulic model of the river and to calculate the flow in the river for scenarios corresponding to different periods of return. The vulnerability of the different areas in the city was established using an Analytic Hierarchy Process. Various criteria of vulnerability were identified and their respective weight progressively determined from discussions between local decision-makers. Finally, considering the extent of the inundated area following recent Hurricane Matthew that particularly affected the zone, a vulnerability mapping was drawn for the town of Cavaillon.

Comparison of different GPS's used in different areas in our country's forestry

Aim of study: Terrestrial measurements have an important place in the production of spatial databases for use in forestry activities in Turkey. Terrestrial methods develop in parallel to the advancing technology while the mechanical measuring devices used in the past are replaced by computer-assisted digital measuring devices.Area of study:. The Forestry Faculty area of Istanbul University at the European side of province of Istanbul was determined as study area for the present study.Material and Methods: Global positioning systems (GPS) developed to collect satellite-based spatial data are among the devices derived from this technology. This study explored the possibilities to use this technology for forestry purposes and the performance of hand held Global Positioning System, Differential Global Positioning System (DGPS), DGPS-Continuously Operating Reference Stations (CORS) and Total Station on the areas representing the very closed forest area, open area and forest boundary selected for the study was assessed.Main results: According to the results, DGPS CORS type GPS is the most accurate one for all three areas types. It was most accurate in closed forest area as the error margin in dense foliage was 3,41 m in horizontal and 3,88 m in vertical; 0,06 m in horizontal and 0,05 m in vertical for open area; 0,62 m in horizontal and 1,16 m in vertical for forest boundary.Research highlights: It is predicted that DGPS CORS systems to be preferred in forestry operations requiring high sensitivity, whereas usage of hand held GPS systems for time saving.

Learning Driver Braking Behavior Using Smartphones, Neural Networks and the Sliding Correlation Coefficient: Road Anomaly Case Study

This paper focuses on the automated learning of driver braking “signature” in the presence of road anomalies. Our motivation is to improve driver experience using preview information from navigation maps. Smartphones facilitate, due to their unprecedented market penetration, the large-scale deployment of advanced driver assistance systems. On the other hand, it is challenging to exploit smartphone sensor data because of the fewer and lower quality signals, compared to the ones on board. Methods for detecting braking behavior using smartphones exist, however, most of them focus only on harsh events. Additionally, only a few studies correlate longitudinal driving behavior with the road condition. In this paper, a new method, based on deep neural networks and the sliding correlation coefficient, is proposed for the spatio-temporal correlation of road anomalies and driver behavior. A unique deep neural network structure, that requires minimum tuning, is proposed. Extensive field trials were conducted and vehicle motion was recorded using smartphones and a data acquisition system, comprising an inertial measurement unit and differential GPS. The proposed method was validated using the probabilistic Receiver Operating Characteristics method. The method proves to be a robust and flexible tool for self-learning driver behavior.

Validation of Pleiades Tri-Stereo DSM in Urban Areas

We present an accurate digital surface model (DSM) derived from high-resolution Pleiades-1B 0.5 m panchromatic tri-stereo images, covering an area of 400 km2 over the Athens Metropolitan Area. Remote sensing and photogrammetry tools were applied, resulting in a 1 m × 1 m posting DSM over the study area. The accuracy of the produced DSM was evaluated against measured elevations by a differential Global Positioning System (d-GPS) and a reference DSM provided by the National Cadaster and Mapping Agency S.A. Different combinations of stereo and tri-stereo images were used and tested on the quality of the produced DSM. Results revealed that the DSM produced by the tri-stereo analysis has a root mean square error (RMSE) of 1.17 m in elevation, which lies within the best reported in the literature. On the other hand, DSMs derived by standard analysis of stereo-pairs from the same sensor were found to perform worse. Line profile data showed similar patterns between the reference and produced DSM. Pleiades tri-stereo high-quality DSM products have the necessary accuracy to support applications in the domains of urban planning, including climate change mitigation and adaptation, hydrological modelling, and natural hazards, being an important input for simulation models and morphological analysis at local scales.

Quaternary tectonic activity of Maradona Fault System, Central Precordillera, Argentina

Several parallel east verging thrusts with Quaternary tectonic activity have been identified in the eastern piedmont of Cordón de Las Osamentas, Central Precordillera of Argentina. We grouped these structures into the Maradona Fault System (MFS). The main morphostructural units, called mountainous and transitional, were analyzed. The form and evolution of these units are closely related to the geological structure of the area. With the morphotectonic analysis, we estimated the length of MFS and the affected alluvial levels. Besides, the morphology of the escarpments was determined through detailed transversal topographic profiles made in a sector where the alluvial levels are affected by the faults. This analysis allowed the recognition of several fault segments and the selection of the points that would present the best natural exposures of the fault- sedimentary deposits relationships. Topographic profiles performed with differential GPS let to identify centimetric fault scarps through slope changes observed in each transect orthogonal to the direction of the structures. Five natural exposures were identified allowing determination of the kinematics of the different fault sections and the deposits affected by these structures. In all the analyzed exposures, faults are reverse with low angle (thrust), dipping to the west and affecting Neogene deposits and alluvial units assigned to the late Pleistocene-Holocene. The Maradona fault system affects younger alluvial levels to the east, showing the gradual migration of the Andean deformation eastward. The progression of the deformation in this sector of Central Precordillera would have evolved according to a pattern of thrusts with angles in surface near 45°, with sequences of internal deformation and reactivation during the Pleistocene-Holocene. Finally, the SFM is regarded as a potential seismogenic source capable to produce earthquakes with magnitude >Mw 6 and hit the main populated centers of the province of San Juan (>700,000 inhabitants), and several dams built along the San Juan River.

Study on Robust Lateral Controller for Differential GPS-Based Autonomous Vehicles

Recently, technological advancements in autonomous vehicle development have continued to accelerate. In this paper, we propose a lateral controller and navigation algorithm for autonomous vehicles based on the Differential Global Positioning System (DGPS), core technology of autonomous vehicles. In this study, an H-infinity (H∞) controller was designed lateral controller to ensure nominal safety and robustness against noise, external disturbances and structural and non-structural errors in vehicle modeling. Meanwhile, the “pure pursuit” approach which geometrically follows a path was employed as a path-tracking technique for the proposed navigation algorithm. A vehicle modeling simulation was conducted to evaluate the performance of the proposed method using a twodegrees- of-freedom linear model. The lateral H∞ controller and navigation algorithm were applied to an actual vehicle, Their performances were evaluated by comparing the path tracking error at various speeds of autonomous vehicles with that of the proportional-integral-derivative (PID) controller.

Kinematic-PPP using Single/Dual Frequency Observations from (GPS, GLONASS and GPS/GLONASS) Constellations for Hydrography

Abstract Global Positioning System (GPS) technology is ideally suited for inshore and offshore positioning because of its high accuracy and the short observation time required for a position fix. Precise point positioning (PPP) is a technique used for position computation with a high accuracy using a single GNSS receiver. It relies on highly accurate satellite position and clock data that can be acquired from different sources such as the International GNSS Service (IGS). PPP precision varies based on positioning technique (static or kinematic), observations type (single or dual frequency) and the duration of observations among other factors. PPP offers comparable accuracy to differential GPS with safe in cost and time. For many years, PPP users depended on GPS (American system) which considered the solely reliable system. GLONASS's contribution in PPP techniques was limited due to fail in maintaining full constellation. Yet, GLONASS limited observations could be integrated into GPS-based PPP to improve availability and precision. As GLONASS reached its full constellation early 2013, there is a wide interest in PPP systems based on GLONASS only and independent of GPS. This paper investigates the performance of kinematic PPP solution for the hydrographic applications in the Nile river (Aswan, Egypt) based on GPS, GLONASS and GPS/GLONASS constellations. The study investigates also the effect of using two different observation types; single-frequency and dual frequency observations from the tested constellations.

Computationally Efficient Radio Frequency Source Localization for Radio Interferometric Arrays

AbstractRadio frequency interference (RFI) is an ever‐increasing problem for remote sensing and radio astronomy, with radio telescope arrays especially vulnerable to RFI. Localizing the RFI source is the first step to dealing with the culprit system. In this paper, a new localization algorithm for interferometric arrays with low array beam sidelobes is presented. The algorithm has been adapted to work both in the near field and far field (only the direction of arrival can be recovered when the source is in the far field). In the near field the computational complexity of the algorithm is linear with search grid size compared to cubic scaling of the state‐of‐the‐art 3‐D MUltiple SIgnal Classification (MUSIC) method. The new method is as accurate as 3‐D MUSIC. The trade‐off is that the proposed algorithm requires a once‐off a priori calculation and storing of weighting matrices. The accuracy of the algorithm is validated using data generated by low‐frequency array while a hexacopter was flying around it and broadcasting a continuous‐wave signal. For the flight, the mean distance between the differential GPS positions and the corresponding estimated positions of the hexacopter is 2 m at a wavelength of 6.7 m.

Precise Orbit and Baseline Determination for the SAOCOM-CS Bistatic Radar Mission

This paper presents an overview of the SAOCOM-CS synthetic aperture radar (SAR) interferometry mission and the use of GPS/GNSS for precise orbit and baseline determination. Compared to X-band SAR interferometry missions, the use of L-band SAR in SAOCOM-CS poses less stringent (sub-centimeter rather than mm-level) requirements on the baseline accuracy. At the same time, however, the use of dissimilar spacecraft and GNSS receivers implies a less than optimal precondition for carrier phase differential GPS (CDGPS) navigation and is likely to degrade the baseline determination accuracy compared to ideal conditions. Based on GPS data collected in previous formation flying missions, the achievable baseline performance in SAOCOM-CS is assessed and recommendations for the most suitable processing scheme are given. Copyright © 2018 Institute of Navigation

Test of methodology for developing a large wood budget: A 1-year example from a regulated gravel bed river following ordinary floods

Wood budgeting is a current approach for quantifying the spatial and temporal variations of in-channel large wood (LW). Despite its importance for a proper LW management, the assessment of LW budget is still a challenge because of the complexity of LW dynamics. Focusing on a 3.7 km-long gravel-bed reach of the Piave River (North-eastern Italy), this study proposes an attempt to assess a short-term (1 year) LW budget as a consequence of ordinary floods (RI < 1 yr). Lateral recruitment, mobilization and deposition of LW were investigated by two field surveys conducted at the beginning and end of the study period. The lateral input was evaluated by measuring, positioning and tagging all standing trees (diameter ≥ 0.1 m) within a 20 m-wide buffer strip along the floodplain and island perimeters. Bank erosion was checked by measuring the riverbanks with a differential Global Positioning System (dGPS), during the first and second survey. Contemporarily, the position and characteristics of each fluvial wood element (diameter ≥ 0.1 m and length ≥ 1 m) within the active channel was determined. These short-term analyses revealed that ordinary floods are not able to induce relevant variations in the LW abundance and redistribution of in-channel wood. Nevertheless, the results highlighted the role of riverbank erosion in supplying LW to the active channel. Episodic inputs of LW from bank erosion were also observed during ordinary flood events, introducing 33% (0.21 m3·km−1) of the total LW input amount. Results on LW transport showed that, in the Piave River, both deposition and mobilization of LW may also occur during low flow conditions (i.e. 14% of bankfull stage) without causing important variations in the wood quantity. However, the low magnitude of floods was reflected in the small amount of LW involved in the input (0.4 m3·km−1) and output (0.7 m3·km−1) processes, pointing out that sites for deposition and mobilization of LW are conditioned by flood magnitude and morphological settings. The combination of recruitment, mobilization and deposition processes resulted in a slight decrease of LW storage (−0.07%), while including also the anthropic removal of LW the amount of wood storage decreased to −9.7%. Despite the short-term investigation, this work sheds further light on LW processes, providing useful results for the management of LW in wide piedmont rivers.