Dorota A. Grejner-Brzezinska

Regional Ionosphere Mapping with Kriging and Multiquadric Methods

This paper demonstrates the concept and practical examples of instantaneous mapping of regional ionosphere, based on GPS observations from the State of Ohio continuously operating reference stations (CORS) network. Interpolation/prediction techniques, such as kriging (KR) and the Multiquadric Model (MQ), which are suitable for handling multi-scale phenomena and unevenly distributed data, were used to create total electron content (TEC) maps. Their computational efficiency (especially the MQ technique) and the ability to handle undersampled data (especially kriging) are particularly attractive. Presented here are the preliminary results based on GPS observations collected at five Ohio CORS stations (~100 km sta-tion separation and 1-second sampling rate). Dual frequency carrier phase and code GPS observations were used. A zero-difference approach was used for absolute TEC recovery. The quality of the ionosphere rep-resentation was tested by comparison to the International GPS Service (IGS) Global Ionosphere Maps (GIMs), which were used as a reference.

A Robust Solution to High-Accuracy Geolocation: Quadruple Integration of GPS, IMU, Pseudolite, and Terrestrial Laser Scanning

Reliable and accurate geolocation is essential for airborne and land-based remote sensing applications. The detection, discrimination, and remediation of unexploded ordnance (UXO) and other munitions and explosives of concern (MEC) using the currently available detection and geolocation technologies often yield unsatisfactory results, failing to detect all MEC present at a site or to discriminate between MEC and nonhazardous items. Thus, the goal of this paper is to design and demonstrate a high-accuracy geolocation methodology that will address centimeter-level relative accuracy requirements of a man-portable electromagnetic (EM) sensor system in open and impeded environments. The proposed system design is based on the tight quadruple integration of the Global Positioning System (GPS), the inertial measurement unit (IMU) system, the terrestrial radio-frequency (RF) system pseudolite (PL), and terrestrial laser scanning (TLS) to support high-accuracy geolocation for a noncontact EM mapping system in GPS-challenged environments. The key novel component of the proposed multisensor system is the integration of TLS that can provide centimeter-level positioning accuracy in a local frame and thus enables a GPS/IMU/PL-based navigation system to achieve both high absolute and relative positioning accuracy in GPS-impeded environments. This paper presents the concept design of the quadruple integration system, the algorithmic approach to data integration with a special emphasis on TLS integration with GPS/IMU/PL, and the performance assessment based on real data, where centimeter-level relative geolocation accuracy is demonstrated during the GPS signal blockage.

On improving Navigation accuracy of GPS/INS systems

Direct georeferencing, also referred to as direct platform orientation (DPO), is defined as direct measurement of the imaging sensor external orientation parameters (EOP), using positioning and orientation sensors, such as the Global Positioning System (GPS) and Inertial Navigation System (INS) or Inertial Measurement Unit (IMU). Imaging sensors, most frequently supported by the DPO technique, are digital cameras, lidar systems, multi-spectral or hyper-spectral scanners, or interferometric synthetic aperture radar (INSAR). While for scanning sensors the use of DPO is compulsory, frame digital cameras can also directly benefit from this modern technique of sensor orientation. With direct sensor orientation, the requirement for ground control, tie-point matching and aerotriangulation (AT) is significantly reduced, or even entirely eliminated, resulting in shorter times of data acquisition and processing, and streamlined and highly automated data workflow and quality control. Most of the time, the requirement for ground control points is limited to periodic system calibrations and quality control check. Direct georeferencing is considered a fundamental technology of conventional mobile mapping systems (MMS). Despite significant progress in GSP/INS-based direct georeferencing technology in the last decade, there is still room for improvement in terms of better accuracy and better tolerance to GPS outages. This paper is focused on three error modeling and compensation techniques that could potentially improve GPS/INS systems performance on both land-based and airborne platforms: (1) extended gravity compensation, (2) IMU signal de-noising, and (3) stochastic modeling of IMU errors.

Troposphere modeling for precise GPS rapid static positioning in mountainous areas

In global navigation satellite system precise positioning, double differencing of the observations is the common approach that allows for significant reduction of correlated atmospheric effects. However, with growing distance between the receivers, tropospheric errors decorrelate causing large residual errors affecting the carrier phase ambiguity resolution and positioning quality. This is especially true in the case of height differences between the receivers. In addition, the accuracy achieved by using standard atmosphere models is usually unsatisfactory when the tropospheric conditions at the receiver locations are significantly different from the standard atmosphere. This paper presents an evaluation of three different approaches to troposphere modeling: (a) neglecting the troposphere, (b) using a standard atmosphere model, and (c) estimating tropospheric delays at the reference station network and providing interpolated tropospheric corrections to the user. All these solutions were repeated with various constraints imposed on the tropospheric delays in the least-squares adjustment. The quality of each solution was evaluated by analyzing the residual height errors calculated by comparing the estimated results to the reference coordinates. Several permanent GPS stations of the EUPOS (European Position Determination System) active geodetic network located in the Carpathian Mountains were selected as a test reference network. The distances between the reference stations ranged from 64 to 122 km. KRAW station served as a simulated user receiver located inside the reference network. The user receiver ellipsoidal height is 267 m and the reference station heights range from 277 to 647 m. The results show that regardless of station height differences, it is recommended to model the tropospheric delays at the reference stations and interpolate them to the user receiver location. The most noticeable influence of the residual (unmodeled) tropospheric errors is observed in the station height component. In many cases, mismodeling of the troposphere disrupts ambiguity resolution and, therefore, prevents the user from obtaining an accurate position.

Pedestrian Tracking and Navigation Using Neural Networks and Fuzzy Logic

The main goal of the research presented here is to develop theoretical foundations and implementation algorithms, which integrate GPS, micro-electro-mechanical inertial measurement unit (MEMS IMU), digital barometer, electronic compass, and human pedometry to provide navigation and tracking of military and rescue ground personnel. This paper discusses the design, implementation and the initial performance analyses of the personal navigator prototype1, with a special emphasis on dead-reckoning (DR) navigation supported by the human locomotion model. To facilitate this functionality, the adaptive knowledge system, based on the Artificial Neural Networks (ANN) and Fuzzy Logic, is trained during the GPS signal reception and used to maintain navigation under GPS-denied conditions. The human locomotion parameters, step frequency (SF) and step length (SL) are estimated during the system calibration period, then the predicted SL, together with the heading information from the compass and gyro, support DR navigation. The current target accuracy of the system is 3-5 m CEP (circular error probable) 50%.

Efficient GPS receiver DCB estimation for ionosphere modeling using satellite-receiver geometry changes

A new and efficient algorithm using the geometry conditions between satellite and tracking receivers is proposed to determine the receiver differential code bias (DCB) using permanent reference stations. This method does not require a traditional single-layer ionosphere model and can be used for estimating DCBs of receivers in a regional network as long as one of the receiver DCBs is already known. The main underlying rationale for this algorithm is that the magnitude of the signal delay caused by the ionosphere is, under normal conditions, highly dependent on the geometric range between the satellite and the receiver. The proposed algorithm was tested with the Ohio Continuously Operating Reference Stations (CORS) sub-network data. The results show that quality comparable to the traditional DCB estimation method is obtainable by implementing this simple algorithm.

Pedestrian tracking and navigation using an adaptive knowledge system based on neural networks

Abstract The primary objective of the research presented here is to develop theoretical foundations and implementation algorithms, which integrate the Global Positioning System (GPS), micro-electromechanical inertial measurement unit (MEMS IMU), digital barometer, electronic compass, and human pedometry to provide navigation and tracking of military and rescue ground personnel. This paper discusses the design, implementation and the performance analyses of the personal navigator prototype, with a special emphasis on dead-reckoning (DR) navigation supported by the human locomotion model. The adaptive knowledge system, based on the Artificial Neural Networks (ANN), is implemented to support this functionality. The knowledge system is trained during the GPS signal reception and is used to support navigation under GPS-denied conditions. The human locomotion parameters, step frequency (SF) and step length (SL), are extracted from GPS-timed impact switches (step frequency) and GPS/IMU data (step length), respectively, during the system calibration period. SL is correlated with several data types, such as acceleration, acceleration variation, SF, terrain slope, etc. that constitute the input parameters to the ANN-based knowledge system. The ANN-predicted SL, together with the heading information from the compass and gyro, support DR navigation. The current target accuracy of the system is 3–5 m CEP (circular error probable) 50%.

A Piecewise Approach to Epipolar Resampling of Pushbroom Satellite Images Based on RPC

Epipolar line determination and image resampling are important steps for stereo image processing. Unlike frame cameras that have well-known epipolar geometry, the pushbroom camera does not produce straight epipolar lines and the epipolar pair does not exist for the entire scene. These properties make it difficult to establish epipolar geometry of the pushbroom camera for epipolar image resampling. Therefore, some researchers have adopted approximate models to avoid these problems. In this study, a new method for the conjugate epipolar curve pair determination and epipolar resampling of spaceborne pushbroom images based on RPC is proposed. The proposed method assumes that the conjugate epipolar curve pairs exist approximately for the local scene area and the global epipolar pairs can also exist if the local pairs are sequentially linked. Then, epipolar image resampling is established by reassigning the generated conjugate epipolar curve pair points to satisfy the epipolar resampling image condition. Ikonos stereo images are tested for the evaluation, and the proposed method showed a maximum y-parallax of 1.25 pixels for manually measured tie points, while the resampling method by the parallel projection model showed a maximum of 4.59 pixels.

THE IMPACT OF THE IONOSPHERIC CORRECTION LATENCY ON LONG-BASELINE INSTANTANEOUS KINEMATIC GPS POSITIONING

Abstract The primary objective of this paper is to estimate the influence of the double-difference (DD) ionospheric corrections latency on the instantaneous (one-epoch) ambiguity resolution (AR) in longrange RTK under typical ionospheric conditions. The key to the success in integer AR rests mainly in the mitigation of the atmospheric errors, i.e., the ionospheric and tropospheric delays. Between these two, the former has the greatest influence on the AR, since both ambiguities and ionospheric delay are frequency-dependent. Instantaneous RTK is presently one of the most challenging topics in precise GPS applications. The research presented here addresses this topic through the development and testing of a multiple reference station approach implemented in the MPGPS™ (Multi Purpose GPS Processing Software) software. Atmospheric corrections are used in order to obtain a high quality RTK position over long distances. In our approach, DD ionospheric correction prediction derived from the previous correctly resolved epoch is applied. Yet, at the beginning of the session, a short initialization period is still required in order to produce the initial prediction. After the initialization the method is based on single epoch solution. This method assures a high success rate of the instantaneous AR for long baselines (over 100 km). Since the previous-epoch ionospheric delay is used, and instantaneous mode is applied in the algorithm, the proposed method is robust against cycle slips and data gaps, and still capable of producing centimetre-level RTK positions. The RTK solution was simulated in the post-processing mode. Namely, different DD ionospheric delay correction latencies were simulated in 10 s increments and sent to the (simulated) rover in order to test the AR performance. The AR results were compared and analyzed, and the performance of the RTK positioning was assessed based on the static true solution. Several hours of GPS data, collected by the State of Israel permanently tracking network, were processed. The analyses show that about 90 s latency may exist while the instantaneous ambiguities could still be resolved correctly. The numerical tests presented in this study show the centimetre-level positioning results for mobile receiver.

From mobile mapping to telegeoinformatics: Paradigm shift in geospatial data acquisition, processing, and management

Technological advances in positioning and imaging sensors, combined with the explosion in wireless mobile communication systems that occurred during the last decade of the twentieth century, practically redefined and substantially extended the concept of mobile mapping. The advent of the first mobile mapping systems (MMS) in the early 1990s initiated the process of establishing modern, virtually ground-control-free photogrammetry and digital mapping. By the end of the last decade, mobile mapping technology had made remarkable progress, evolving from rather simple land-based systems to more sophisticated, real-time multitasking and multisensor systems, operational in land and airborne environments. New specialized systems, based on modern imaging sensors, such as CCD (charge-coupled device) cameras, lidar (Light Detection and Ranging) and hyperspectral/multispectral scanners, are being developed, aimed at automatic data acquisition for geoinformatics, thematic mapping, land classification, terrain modeling, emergency response, homeland security, etc. This paper provides an overview of the mobile mapping concept, with a special emphasis on the MMS paradigm shift from the post-mission to near-real-time systems that occurred in the past few years. A short review of the direct georeferencing concept is given, and the major techniques (sensors) used for platform georegistration, as well as the primary radiolocation techniques based on wireless networks, are presented. An overview of the major imaging sensors and the importance of multisensor system calibration are also provided. Future perspectives of mobile mapping and its extension towards telegeoinformatics are also discussed. Some examples of mobile geospatial technology used in automatic object recognition, real-time highway centerline mapping, thematic mapping, and city modeling with lidar and multispectral imagery are included.