Theoretical Limits on Cooperative Positioning in Mixed Traffic

A promising solution to meet the demands on accurate positioning and real-time situational awareness in future intelligent transportation systems (ITSs) is cooperative positioning, where vehicles share sensor information over the wireless channel. However, the sensing and communication technologies required for this will be gradually introduced into the market, and it is, therefore, important to understand what performance we can expect from cooperative positioning systems as we transition to a more modern vehicle fleet. In this paper, we study what effects a gradual market penetration has on cooperative positioning applications, through a Fisher information analysis. The simulation results indicate that solely introducing a small fraction of automated vehicles with high-end sensors significantly improves the positioning quality but is not enough to meet the stringent demands posed by safety critical ITS applications. Furthermore, we find that retrofitting vehicles with low-cost satellite navigation receivers and communication have marginal impact when the positioning requirements are stringent and that the longitudinal road position can be estimated more accurately than lateral

Ground-Based GPS for Validation of Climate Models: The Impact of Satellite Antenna Phase Center Variations

The amount of water vapor in the atmosphere is an important indicator for climate change. Using the Global Positioning System (GPS), it is possible to estimate the integrated water vapor (IWV) above the ground-based GPS receiver. In order to optimally determine the IWV, a correct model of the received signal phase is essential. We have studied the effect of the satellite antenna phase center variations (PCVs) on the IWV estimates by simulating the effect and by studying the estimates of the IWV based on the observed GPS signals. During a period of five years, from 2003 to 2008, a new satellite type was introduced, and it steadily grew in numbers. The antenna PCVs for these satellites deviate from the earlier satellite types and contribute to excess IWV estimates. We find that ignoring satellite antenna phase variations for this time period can lead to an additional IWV trend of about 0.15 kg/m2/year for regular GPS processing

Measurement with Persons: A European Network

The European ‘Measuring the Impossible’ Network MINET promotes new research activities in measurement dependent on human perception and/or interpretation. This includes the perceived attributes of products and services, such as quality or desirability, and societal parameters such as security and well-being. Work has aimed at consensus about four ‘generic’ metrological issues: (1) Measurement Concepts & Terminology; (2) Measurement Techniques: (3) Measurement Uncertainty; and (4) Decision-making & Impact Assessment, and how these can be applied specificallyto the ‘Measurement of Persons’ in terms of ‘Man as a Measurement Instrument’ and ‘Measuring Man.’ Some of the main achievements of MINET include a research repository with glossary; training course; book; series of workshops;think tanks and study visits, which have brought together a unique constellation of researchers from physics, metrology,physiology, psychophysics, psychology and sociology. Metrology (quality-assured measurement) in this area is relativelyunderdeveloped, despite great potential for innovation, and extends beyond traditional physiological metrology in thatit also deals with measurement with all human senses as well as mental and behavioral processes. This is particularlyrelevant in applications where humans are an important component of critical systems, where for instance health andsafety are at stake

Collision-Aware Communication for Intersection Management of Automated Vehicles

Intersection management of automated vehicles relies on wireless communication, whereby communication resources should be allocated to vehicles while maintaining safety. We present a collision-aware resource allocation (CARA) strategy for coordination of automated and connected vehicles by a centralized intersection manager. The proposed strategy is based on a self-triggered approach and proactively reduces the risk of channel congestion by only assigning communication resources to vehicles that are in critical configurations, i.e., when there is a risk for a future collision. Compared with collision-agnostic communication strategies, typically considered for automated intersection management, the CARA strategy aims to bridge the gap between control, sensing, and communication. It is shown to significantly reduce the required amount of communication (albeit with a slight increase in the control cost), without compromising safety. Furthermore, control cost can be reduced by allowing more frequent communication, which we demonstrate through a trade-off analysis between control performance and communication load. Hence, CARA can operate in communication-limited scenarios, but also be modified for scenarios where the control cost is of primary interest

Multiscale InSAR Time Series (MInTS) analysis of surface deformation

We present a new approach to extracting spatially and temporally continuous ground deformation fields from interferometric synthetic aperture radar (InSAR) data. We focus on unwrapped interferograms from a single viewing geometry, estimating ground deformation along the line-of-sight. Our approach is based on a wavelet decomposition in space and a general parametrization in time. We refer to this approach as MInTS (Multiscale InSAR Time Series). The wavelet decomposition efficiently deals with commonly seen spatial covariances in repeat-pass InSAR measurements, since the coefficients of the wavelets are essentially spatially uncorrelated. Our time-dependent parametrization is capable of capturing both recognized and unrecognized processes, and is not arbitrarily tied to the times of the SAR acquisitions. We estimate deformation in the wavelet-domain, using a cross-validated, regularized least squares inversion. We include a model-resolution-based regularization, in order to more heavily damp the model during periods of sparse SAR acquisitions, compared to during times of dense acquisitions. To illustrate the application of MInTS, we consider a catalog of 92 ERS and Envisat interferograms, spanning 16 years, in the Long Valley caldera, CA, region. MInTS analysis captures the ground deformation with high spatial density over the Long Valley region

Tide model accuracy in the Amundsen Sea, Antarctica, from radar interferometry observations of ice shelf motion

This study assesses the accuracy of tide model predictions in the Amundsen Sea sector of West Antarctica. Tide model accuracy in this region is poorly constrained, yet tide models contribute to simulations of ocean heat transfer and to the removal of tidal signals from satellite observations of ice shelves. We use two satellite-based interferometric synthetic aperture radar (InSAR) methods to measure the tidal motion of the Dotson Ice Shelf at multiple epochs: a single-difference technique that measures tidal displacement and a double-difference technique that measures changes in tidal displacement. We use these observations to evaluate predictions from three tide models (TPXO7.1, CATS2008a-opt, and FES2004). All three models perform comparably well, exhibiting root-mean-square deviations from the observations of ∼9 cm (single-difference technique) and ∼10 cm (double-difference technique). Care should be taken in generalizing these error statistics because (1) the Dotson Ice Shelf experiences relatively small semidiurnal tides and (2) our observations are not sensitive to all tidal constituents. An error analysis of our InSAR-based methods indicates measurement errors of 7 and 4 cm for the single-and double-difference techniques, respectively. A model-based correction for the effect of fluctuations in atmospheric pressure yields an ∼6% improvement in the agreement between tide model predictions and observations. This study suggests that tide model accuracy in the Amundsen Sea is comparable to other Antarctic regions where tide models are better constrained. These methods can be used to evaluate tide models in other remote Antarctic waters

Evidence for cross rift structural controls on deformation and seismicity at a continental rift caldera

In continental rifts structural heterogeneities, such as pre-existing faults and foliations, are thought to influence shallow crustal processes, particularly the formation of rift faults, magma reservoirs and surface volcanism. We focus on the Corbetti caldera, in the southern central Main Ethiopian Rift. We measure the surface deformation between 22nd June 2007 and 25th March 2009 using ALOS and ENVISAT SAR interferograms and observe a semi-circular pattern of deformation bounded by a sharp linear feature cross-cutting the caldera, coincident with the caldera long axis. The signal reverses in sign but is not seasonal: from June to December 2007 the region south of this structure moves upwards 3 cm relative to the north, while from December 2007 until November 2008 it subsides by 2 cm. Comparison of data taken from two different satellite look directions show that the displacement is primarily vertical. We discuss potential mechanisms and conclude that this deformation is associated with pressure changes within a shallow (<1 km) fault-bounded hydrothermal reservoir prior to the onset of a phase of caldera-wide uplift. Analysis of the distribution of post-caldera vents and cones inside the caldera shows their locations are statistically consistent with this fault structure, indicating that the fault has also controlled the migration of magma from a reservoir to the surface over tens of thousands of years. Spatial patterns of seismicity are consistent with a cross-rift structure that extents outside the caldera and to a depth of ∼30 km, and patterns of seismic anisotropy suggests stress partitioning occurs across the structure. We discuss the possible nature of this structure, and conclude that it is most likely associated with the Goba–Bonga lineament, which cross-cuts and pre-dates the current rift. Our observations show that pre-rift structures play an important role in magma transport and shallow hydrothermal processes, and therefore they should not be neglected when discussing these processes

Studies of Atmospheric Water Vapor Using the Global Positioning System

Atmospheric water vapor is of fundamental interest in the Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) techniques. These techniques are based on the timing of radio waves propagating through the atmosphere. The received signals are delayed by the water vapor mainly located in the lower part of the atmosphere called the troposphere. In order to achieve accurate positioning, such effects have to be corrected for. This can be done by estimating the delay from the signals themselves. From these results it is possible to derive the amount of water vapor in the atmosphere. The GPS and VLBI techniques can thus be used both for positioning and for determination of the amount of atmospheric water vapor. This thesis deals mainly with the technique to estimate the amount of water vapor in the atmosphere with GPS. Modeling of the atmosphere is treated as well as how to convert the signal delay estimates from GPS to the water vapor amount. The results obtained are assessed through comparisons with independent techniques, such as radiosondes and a microwave radiometer. The results in this thesis show that it is possible to measure the atmospheric water vapor with GPS with an accuracy comparable to techniques presently in use for that purpose. GPS gives, however, a better temporal and spatial resolution as well as being more cost-effective than the present radiosonde launches. This may prove to be useful for the meteorological community, as water vapor is an important factor in numerical weather prediction, and in climate studies since it is one of the most important greenhouse gases. Improved modeling of the water vapor and assessment of the results will also benefit positioning with GPS, which is useful, for example, in the determination of the land uplift after the last glaciation period