The total electron content (TEC) measurements of the Global Navigation Satellite System (GNSS) revealed traveling ionospheric disturbances (TID) that locate North Korea's underground nuclear explosion (UNE) of 25 May 2009 to within about 3.5 km of its seismically determined epicenter. The random chance for this pattern of TIDs to register across the eleven GNSS stations is roughly 1 in 19 billion. Monte Carlo analysis of nearly 1,300 TIDs from a 7‐station subset of the 11 GNSS stations supports the statistical strength of the array's signature. The UNE was also detected by seismic stations and possibly a local infrasound network of the International Monitoring System (IMS) of the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), but no radionuclide evidence was found. Thus, global GNSS infrastructure enables mapping spatial and temporal variations of TEC that augment and complement other methods of detecting and locating clandestine UNEs.
Abstract. 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 station 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 representation was tested by comparison to the International GPS Service (IGS) Global Ionosphere Maps (GIMs), which were used as a reference.
INTRODUCTIONThe primary objective of a mobile mapping system (MMS) is to provide automatic acquisition of directly oriented (georeferenced) digital imagery for mapping and geographic information system (GIS) data collection. The direct georeferencing is most commonly facilitated by the integration of differential GPS (DGPS) and inertial navigation systems (INS), providing nearly continuous (up to 256 Hz) positioning and attitude information of the imaging sensor(s). The navigation data can be processed in near real time or in postmission mode to determine the best estimates of the image exterior orientation. Directly oriented images are then used in photogrammetric processing to extract the feature data, together with their positional information. In the past 10 years, MMSs have evolved toward multisensor and multitasking systems, comprising four primary modules: (1) the control module, (2) the positioning (georeferencing) module, (3) the imaging module, and (4) the data postprocessing module. The modular design creates a system capable of handling numerous concurrent operations in real time and in postprocessing.The MMS presented in this paper is designed for high-accuracy, near-real-time mapping of highway center and edge lines [1]; the system development is currently supported by the Ohio Department of Transportation. The positioning module of this system is based on a tight integration of dual-frequency DGPS carrier phases and raw inertial measurement unit (IMU) data provided by a medium-accuracy, high-reliability strapdown Litton LN-100 INS. The LN-100 is based on a Zero-lock TM Laser Gyro (ZLG TM ) and A-4 accelerometer triad (0.8 nmi/h circular error probable [CEP], gyro bias 0.003 deg/h, accelerometer bias 25 g). An optimal 21-state centralized Kalman filter estimates errors in position, velocity, and attitude, as well as in the inertial and GPS measurements. Under favorable GPS constellations (minimum of 5 -6 satellites) and short to medium baselines, the estimated standard deviations are at the level of 2 -3 cm for position coordinates, and 10 arcsec and 10 -20 arcsec for attitude and heading components, respectively.As a land-based MMS, the system operates primarily in urban environments, where frequent losses of GPS signal lock occur. To prevent major degradation in navigation accuracy and to support ambiguity resolution after GPS signal reacquisition, the loss-of-lock events must be controlled in real time. The MMS control module tracks the duration of the loss of lock (or extended partial satellite blockage) and, based on empirical knowledge of the positioning error growth, provides a warning to the operator that a ZUPT (zero velocity update) is needed (see Figure 1). This empirical information is derived from the system calibration and testing, and facilitates a reference input to the control system. This paper presents the calibration results for the static INS used to derive the empirical information for the system's controls, including observability characteristics. Special emphasis is placed on...
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