We present a new approach to remote sensing of water vapor based on the global positioning system (GPS). Geodesists and geophysicists have devised methods for estimating the extent to which signals propagating from GPS satellites to ground-based GPS receivers are delayed by atmospheric water vapor. This delay is parameterized in terms of a time-varying zenith wet delay (ZWD) which is retrieved by stochastic filtering of the GPS data. Given surface temperature and pressure readings at the GPS receiver, the retrieved ZWD can be transformed with very little additional uncertainty into an estimate of the integrated water vapor (IWV) overlying that receiver. Networks of continuously operating GPS receivers are being constructed by geodesists, geophysicists, government and military agencies, and others in order to implement a wide range of positioning capabilities. These emerging GPS networks offer the possibility of observing the horizontal distribution of IWV or, equivalently, precipitable water with unprecedented coverage and a temporal resolution of the order of 10 min. These measurements could be utilized in operational weather forecasting and in fundamental research into atmospheric storm systems, the hydrologic cycle, atmospheric chemistry, and global climate change. Specially designed, dense GPS networks could be used to sense the vertical distribution of water vapor in their immediate vicinity. Data from ground-based GPS networks could be analyzed in concert with observations of GPS satellite occultations by GPS receivers in low Earth orbit to characterize the atmosphere at planetary scale.

/pdf/gps-meteorology-remote-sensing-of-atmospheric-water-vapor-56jequkh8e.pdf

GPS Meteorology: Remote Sensing of Atmospheric Water Vapor Using the Global Positioning System

A location reporting paging communication system comprising space satellites, ground stations and a remote receiving unit adapted to resolve a global position from signals transmitted from a communication transmitter. The subscriber in possession of the remote receiving unit updates the paging network with global positioning information. A caller paging a subscriber in possession of the remote receiving unit may request the global location of the remote receiving unit. The paging network could divulge or block such information from a caller depending on the requirements of the subscriber.

Location reporting satellite paging system with optional blocking of location reporting

Emerging networks of Global Positioning System (GPS) receivers can be used in the remote sensing of atmospheric water vapor. The time-varying zenith wet delay observed at each GPS receiver in a network can be transformed into an estimate of the precipitable water overlying that receiver. This transformation is achieved by multiplying the zenith wet delay by a factor whose magnitude is a function of certain constants related to the refractivity of moist air and of the weighted mean temperature of the atmosphere. The mean temperature varies in space and time and must be estimated a priori in order to transform an observed zenith wet delay into an estimate of precipitable water. We show that the relative error introduced during this transformation closely approximates the relative error in the predicted mean temperature. Numerical weather models can be used to predict the mean temperature with an rms relative error of less than 1%.

/pdf/gps-meteorology-mapping-zenith-wet-delays-onto-precipitable-1f1pjto6t8.pdf

GPS Meteorology: Mapping Zenith Wet Delays onto Precipitable Water

Vehicle tracking data is an essential "raw" material for a broad range of applications such as traffic management and control, routing, and navigation. An important issue with this data is its accuracy. The method of sampling vehicular movement using GPS is affected by two error sources and consequently produces inaccurate trajectory data. To become useful, the data has to be related to the underlying road network by means of map matching algorithms. We present three such algorithms that consider especially the trajectory nature of the data rather than simply the current position as in the typical map-matching case. An incremental algorithm is proposed that matches consecutive portions of the trajectory to the road network, effectively trading accuracy for speed of computation. In contrast, the two global algorithms compare the entire trajectory to candidate paths in the road network. The algorithms are evaluated in terms of (i) their running time and (ii) the quality of their matching result. Two novel quality measures utilizing the Frechet distance are introduced and subsequently used in an experimental evaluation to assess the quality of matching real tracking data to a road network.

/pdf/on-map-matching-vehicle-tracking-data-1antqwrzot.pdf

On map-matching vehicle tracking data

Precision agriculture is the application of technologies and principles to manage spatial and temporal variability associated with all aspects of agricultural production for the purpose of improving crop performance and environmental quality. Success in precision agriculture is related to how well it can be applied to assess, manage, and evaluate the space-time continuum in crop production. This theme is used here to assess the current and potential capabilities of precision agriculture. Precision agriculture is technology enabled. It is through the integration of specific technologies that the potential is created to assess and manage variability at levels of detail never before obtainable and, when done correctly, at levels of quality never before achieved. The agronomic feasibility of precision agriculture has been intuitive, depending largely on the application of traditional management recommendations at finer scales, although new approaches are appearing. The agronomic success of precision agriculture has been limited and inconsistent although quite convincing in some cases, such as N management in sugar beet (Beta vulgaris L.). Our analysis suggests prospects for current precision management increase as the degree of spatial dependence increases, but the degree of difficulty in achieving precision management increases with temporal variance. Thus, management parameters with high spatial dependence and low temporal variance (e.g., liming, P, and K) will be more easily managed precisely than those with large temporal variance (e.g., mobile insects). The potential for economic, environmental, and social benefits of precision agriculture is complex and largely unrealized because the space-time continuum of crop production has not been adequately addressed.

Aspects of precision agriculture

Elements of Satellite Surveying The Global Positioning System Adjustment Computations Least-Squares Adjustment Examples Links to Physical Observations The Three-Dimensional Geodetic Model GPS Observables Propagation Media, Multipath, and Phase Center Processing GPS Carrier Phases Network Adjustments Ellipsoidal and Conformal Mapping Models Useful Transformations Datums, Standards, and Specifications Appendices References Abbreviations for Frequently Used References Indexes.

GPS satellite surveying

The integration of GPS with GLONASS may be considered a major milestone in satellite-based positioning, because it can dramatically improve the reliability and productivity of said positioning. However, unlike GPS, GLONASS satellites transmit signals at different frequencies, which result in significant complexity in terms of modeling and ambiguity resolution for integrated GPS and GLONASS positioning systems. In this paper, a variety of mathematical and stochastic modeling methodologies and ambiguity resolution strategies are analyzed, and some remaining research challenges are identified. The exercise, of developing mathematical models and processing methodologies for integrated systems based on more than one satellite system, is a valuable one as it identified crucial issues concerned with the combination of any two or more microwave positioning systems, be they satellite-based or terrestrial. Hence these are experiences that can be applied to future projects that might integrate GPS with Galileo, or GLONASS and Galileo, or all three. © 2001 John Wiley & Sons, Inc.

GPS and GLONASS Integration: Modeling and Ambiguity Resolution Issues

Models used in geodesy to transform two sets of coordinates are studied and distortions in geodetic networks are investigated. Commonly used transformation models are first reviewed and most of them are interpreted. Differences between various models are discussed. Pitfalls in partial solutions are then considered. It is shown that only as many chords and/or directional elements can be used in the computation as are needed to completely determine the size or shape of the polyhedron implied in the set of Cartesian coordinates. Each additional element causes the normal matrix to be singular provided that all correlations between the chords are used. A number of tables and maps indicating distortions in the NAD 27, Precise Traverse M-R '72, AUS, and SAD 69 geodetic datums are also included. The residuals of the coordinates are scanned for systematic patterns after transforming each geodetic system to the NWL9D Doppler system. Also, an attempt is made to show scale distortions in the NAD 27.

https://ntrs.nasa.gov/api/citations/19760017591/downloads/19760017591.pdf

On Similarity Transformation and Geodetic Network Distortions Based on Doppler Satellite Observations

Double differencing of the carrier phases is a popular technique in global positioning system (GPS) surveying for eliminating receiver and satellite clock errors. However, because each global navigation satellite system (GLONASS) satellite transmits a different carrier frequency, it is not straightforward to constrain double difference integer ambiguities from GLONASS carrier phases. Various solutions are reviewed, following the formalism traditionally applied to GPS observations and focusing on the receiver clock errors. Mixed GPS/GLONASS data are used to demonstrate the impact of receiver clock errors on GLONASS double differences carrier phases.

GLONASS Satellite Surveying

The GLONASS (ICD-92) double difference carrier
observables must be transformed to either a common
frequency or to linear distances in order for the relative
receiver clock errors to cancel. Such a scaling causes the
double difference equations to contain single difference
ambiguities whose coefficients depend on the GLONASS
frequencies. Pseudoranges are used to compute an
approximate single difference ambiguity value for the base
satellite. This additional step, which is not required for
GPS, allows the double difference ambiguity formulation.
However, this initial approximation of the single difference
ambiguity must meet certain accuracy limitations. Dual-
frequency pseudoranges and carrier phase observations to
5 GLONASS satellites are used to verify software
implementation and to draw conclusions such as the need
for frequency-dependent hardware delay calibrations and
the need for accurate pseudoranges.

Alfred Leick

Papers

GPS satellite surveying

GPS and GLONASS Integration: Modeling and Ambiguity Resolution Issues

On Similarity Transformation and Geodetic Network Distortions Based on Doppler Satellite Observations

GLONASS Satellite Surveying

Processins GLONASS Carrier Phase Observations - Theory and First Experience