Single-frequency Precise Point Positioning (PPP) using a Global Navigation Satellite System (GNSS) has been attracting increasing interest in recent years due to its low cost and large number of users. Currently, the single-frequency PPP technique is mainly implemented using GPS observations. In order to improve the positioning accuracy and reduce the convergence time, we propose the combined GPS/GLONASS Single-Frequency (GGSF) PPP approach. The approach is based on the GRoup And PHase Ionospheric Correction (GRAPHIC) to remove the ionospheric effect. The performance of the GGSF PPP was tested using both static and kinematic datasets as well as different types of precise satellite orbit and clock correction data, and compared with GPS-only and GLONASS-only PPP solutions. The results show that the GGSF PPP accuracy degrades by a few centimetres using rapid/ultra-rapid products compared with final products. For the static GGSF PPP, the position filter typically converges at 71, 33 and 59 minutes in the East, North and Up directions, respectively. The corresponding positioning accuracies are 0·057, 0·028 and 0·121 m in the East, North and Up directions. Both positioning accuracy and convergence time have been improved by approximately 30% in comparison to the results from GPS-only or GLONASS-only single-frequency PPP. A kinematic GGSF PPP test was conducted and the results illustrate even more significant benefits of increased accuracy and reliability of PPP solutions by integrating GPS and GLONASS signals.

This paper proposes an algorithm for the initial alignment method for rocket navigation systems. It uses the inertial freezing alignment to resolve the attitude matrix with respect to its fast and robust characteristics. Due to disturbances from the swaying base environment, such as people walking and wind effect, which would consequently result in a great lever arm effect, a Finite Impulse Response (FIR) filter is utilized to decrease the noise in the accelerometers' measurement. In addition, there are sensor errors in the system; the online estimation of gyroscopes' drift with a Kalman filter is adopted to achieve compensation. Numerical results from a simulated rocket initial alignment experiment are reported to demonstrate the effectiveness of the method.

The liquefaction of nickel ore is widely considered to account for the capsizing and sinking of bulk carriers, but the mechanisms that lead to the incidents still remain uncertain. In this paper, the sloshing motion of fluid with high viscosity in a rectangular tank has been studied; the Level Set Method has been employed to predict the behaviours of fluid sloshing motion under the circumstances of beam seas. In a bid to evaluate the consistency of the numerical solution, a full validation has been performed. The results obtained from the simulations are in good agreement with that from the experiment. The conclusions have also been made that the collapse of the shear resistance of the fluid or increasing heeling moment acquired from the fluid sloshing after liquefaction of the nickel ore may be responsible for the capsizing and sinking of the ships. Hopefully, our conclusions can help ship owners better understand how to take precautions to prevent the ships from capsizing while carrying nickel ore or similar cargos; the results could provide the IMO with the theoretical basis for stipulating new international safe standards for bulk carriers; the numerical methodology can also help engineers to predict sloshing motion of viscous fluids.

As Earth-based radio tracking navigation is severely limited because of communications constraints and low relative navigation accuracy, autonomous optical navigation capabilities are essential for both robotic and manned deep-space exploration missions. Image processing is considered one of the key technologies for autonomous optical navigation to extract high-precision navigation observables from a raw image. New image processing algorithms for deep-space autonomous optical navigation are developed in this paper. First, multiple image pre-processing and the Canny edge detection algorithm are adopted to identify the edges of target celestial bodies and simultaneously remove the potential false edges. Secondly, two new limb profile fitting algorithms are proposed based on the Least Squares method and the Levenberg-Marquardt algorithm, respectively, with the assumption that the perspective projection of a target celestial body on the image plane will form an ellipse. Next, the line-of-sight (LOS) vector from the spacecraft to the centroid of the observed object is obtained. This is taken as the navigation measurement observable and input to the navigation filter algorithm. Finally, the image processing algorithms developed in this paper are validated using both synthetic simulated images and real flight images from the MESSENGER mission.

Inertial Navigation Systems (INS) were large, heavy and expensive until the development of cost-effective inertial sensors constructed with Micro-electro-mechanical systems (MEMS). However, the large errors and poor error repeatability of MEMS sensors make them inadequate for application in many situations even with frequent calibration. To solve this problem, a systematic error auto-compensation method, Rotation Modulation (RM) is introduced and detailed. RM does no damage to autonomy, which is one of the most important characteristics of an INS. In this paper, the RM effects on navigation performance are analysed and different forms of rotation schemes are discussed. A MEMS-based INS with the RM technique applied is developed and specific calibrations related to rotation are investigated. Experiments on the developed system are conducted and results verify that RM can significantly improve navigation performance of MEMS-based INS. The attitude accuracy is improved by a factor of 5, and velocity/position accuracy by a factor of 10.

Map matching is an important algorithm for any location-based service, especially in navigation and tracking systems and services. Identifying the relevant road segments accurately and efficiently, given positioning data, is the first and most important step in any map matching algorithm. This paper proposes a new approach to searching for road candidates by clustering and then searching road segments through a constructed hierarchical clustering tree, rather than using indexing techniques to query segments within a fixed search window. A binary tree is created based on the hierarchical clustering tree and adaptive searches are conducted to identify candidate road segments given GPS positions. The approach was validated using road maps with different scales and various scenarios in which moving vehicles were located. Both theoretical analysis and experimental results confirm that the proposed approach can efficiently find candidate road segments for map matching.

Unmanned Air Systems (UAS) navigate using Global Navigation Satellite Systems (GNSS), but GNSS vulnerability precludes its use as the only means of navigation and requires a secondary means of navigation. A differentiating characteristic of UAS is their periodic communications with the ground station. This paper analyses the adequacy of employing UAS Command, Control and Communications (C3) as a secondary means of navigation. With no additional infrastructure, an Extended Kalman Filter (EKF) is used to process C3 messages and to obtain the positions of the UAS. Navigation accuracy and integrity are calculated in a scenario with three UAS. The obtained results meet the International Civil Aviation Organization (ICAO) Performance-Based Navigation (PBN) requirements.

This study describes the estimation of spherical wave parameters that appears in Synthetic Aperture Radar (SAR) images acquired over the coast of Chukk, Micronesia. The main causes for the interaction of SAR signals with ocean waves can be retrieved through the Bragg scattering mechanism. Dominant wavelengths were retrieved by means of Fast Fourier Transform (FFT) analysis in terms of peak frequency responses. Sea surface slopes were then obtained from the dispersion relation with consideration of different water wave conditions for each subset area, and wave heights were estimated with the use of dominant wavelengths and sea surface slopes. The work presented in this paper may be useful to retrieve the various wave parameters over different regions. The method used is a novel technique to correlate the relationship between SAR image parameters and dispersion relation.

The process used to create charted depictions of aviation instrument approach procedures in the United States is examined. The rapid growth of iPad®-like mobile technologies is discussed relative to the historical context of chart implementation. Notional new methods of electronic chart generation are introduced, demonstrating both the functional possibilities and concerns not directly addressed by existing regulation for private aircraft operators. These concerns suggest a ‘yin-yang’ of the stifling of innovation versus the creation of latent safety hazards. The article concludes by recommending regulatory oversight review of approach chart implementation. A glossary of terms is included at the end of this paper. The facts, analysis, and opinions offered in this article represent an independent effort of the author and do not reflect the opinions of any academic institution or government agency. The author also has a limited financial interest in certain iOS® applications.

Despite continuous efforts to improve shipping safety, groundings are still the prime cause of large scale oil pollution of the marine environment. As the bridge operator remains the most important part of navigation, the provision of tools which promote his understanding of the threats which lie ahead of the ship has become a permanent challenge. In this work, the use of a hull-mounted forward-looking sonar as a navigational aid for grounding avoidance and ultimately as an associated oil-spill risk control option for oil tankers is examined according to the Formal Safety Assessment (FSA) approach. In this context, the sonar's oil-spill risk reduction potential and its overall cost were estimated and assessed against the Cost of Averting a Ton of oil Spilled (CATS) criterion. It was found that the currently available sonar technology has a maximum detection range which is adequate for the avoidance of powered groundings in the case of small-sized oil tankers only. However, for this ship size category, the attained oil-spill risk reduction was found to be low and sonar use was proved to be cost ineffective. However, it was found that sonar technology will offer sizable oil-spill risk reduction in large-sized oil tankers and their requirement for longer sonar detection range can be easily met cost-effectively as an oil-spill risk control option for ships of this size.

This paper presents the design and implementation of a Chip Scale Atomic Clock (CSAC) driven dual-channel Digitally Configurable Receiver (DCR) for Global Navigation Satellite Systems (GNSS). The receiver is intended to be used for research applications such as; multipath mitigation, scintillation assessment, advanced satellite clock and spatial frame transformation modelling, Precise Point Positioning (PPP) as well as rapid development and assessment of novel circuits and systems for GNSS receivers. A novel sub-Nyquist sampling (subsampling) receiver architecture incorporating dual-band microstrip RF filters is employed in order to minimize the complexity of the multi-frequency Radio Frequency (RF) front-end. Moreover, the digital receiver incorporates a novel and complexity-reduced Fast Fourier Transform (FFT) core for signal acquisition as well as COordinate Rotation DIgital Computer (CORDIC) cores for the code/carrier discriminators in order to minimize the resource allocation on the FPGA. The receiver also provides easy access to enable adjustment of its internal parameters such as; RF gain, position update rate, tracking channel correlator spacing and code/carrier loop noise bandwidth. Correlator outputs, code/carrier error, Carrier-to-Noise Ratio (C/N0), navigation and RINEX data are provided to the end-user in real-time. This paper collectively highlights and reports on the implementation, test and validation of the novel techniques, elements and approaches in both the RF and digital part of the DCR that comprise the multi-constellation receiver.

In this paper the minimum ship domain in which a navigator feels comfortable is estimated. That is, we estimate the free space surrounding a ship into which no other ship or object should enter. This is very useful when estimating the maximum flow through a channel or a bridge span. The paper benefits from the introduction of Automatic Identification System (AIS) data as it is now much easier to conduct studies involving a large number of observations. Our observations are based on ships sailing in southern Danish waters during a four year period, and from the observations we estimate how closely ships pass each other and fixed objects in open sea navigation. The main result is the establishment of an empirical minimum ship domain related to a comfortable navigational distance.

In kinematic Global Navigation Satellite Systems (GNSS) navigation, the Kalman Filter (KF) solution relies, to a great extent, on the quality of the dynamic model that describes the moving object's motion behaviour. However, it is rather difficult to establish a precise dynamic model that only connects the previous state and the current state, since these high-order quantities are usually unavailable in GNSS navigation receivers. To overcome such limitations, the Window-Recursive Approach (WRA) that employs the previous multiple states to predict the current one was developed in Zhou et al., (2010). Its essence is to adaptively fit the moving object's motion behaviour using the multiple historical states in a short time span. Up to now, the WRA method has been performed only using GNSS pseudorange measurements. However, in GNSS navigation fields, the strength of pseudorange observation model is usually weak due to various reasons, e.g., multi-path delay, outliers, insufficient visible satellites. As an important complementary measurement, Doppler can be used to aid Position and Velocity (PV) estimation. In this contribution, implementation of WRA will be developed using the pseudorange and Doppler measurements. Its corresponding state transition matrix is constructed based on the Newton's Forward Difference Extrapolation (NFDE) and Definite Integral (DI) methods for the efficient computation. The new implementation of WRA is evaluated using the real kinematic vehicular GNSS data with two sampling rates. The results show that:

1. (i) aided by GNSS Doppler measurement, the new implementation of WRA significantly improves the accuracy compared with the pseudorange-only WRA.

2. (ii) In high sampling rate, the WRA works best in the case of 2 epochs in time window, while in the low sampling rate, it obtains better solutions if more epochs involved in time window.

3. (iii) Compared with KF with constant velocity dynamic model, the WRA demonstrates better in the self-adaptation and validity.

4. (iv) As a benefit of WRA itself, the NFDE/DI-based state transition matrix for WRA can be previously computed offline without increasing the computation burdens.

An algorithm of alignment calibration for Ultra Short Baseline (USBL) navigation systems was presented in the companion work (Part I). In this part (Part II) of the paper, this algorithm is tested on the sea trial data collected from USBL line surveys. In particular, the solutions to two practical problems referred to as heading deviation and cross-track error in the USBL line survey are presented. A field experiment running eight line surveys was conducted to collect USBL positioning data. The numerical results for the sea trial data demonstrated that the proposed algorithm could robustly and effectively estimate the alignment errors. Comparisons of the experimental result with the analytical prediction of roll misalignment estimation in Part I is drawn, showing good agreement. The experimental results also show that an inappropriate estimation of roll alignment error will significantly degrade the quality of estimations of heading and pitch alignment errors.

This paper will demonstrate that the Master Pilot Exchange (MPX) is a document of debatable value in pilotage waters. The MPX exists in many formats which are designed to reflect local navigational challenges and port requirements. A generic form exists which can aid the design of local MPX forms. Both the generic and port MPX forms may require the recording of information that has a neutral outcome on the planned act of pilotage. Analysis of significant incidents suggests that investigation recommendations are not consistently reflected in MPX forms and there is a gap between what should be recorded and reality.

Ships navigate freely when in the open sea, but their freedom of movement is reduced in areas with intense traffic, restricted draught or obstacles. In such cases, a traffic separation scheme (TSS) can be established to guide the ship traffic. This paper is based on work performed in connection with a proposed bridge across Fehmarnbelt between Denmark and Germany, and the purpose is to estimate the efficiency of a TSS guiding traffic through the main bridge openings. The efficiency in terms of getting the traffic through the traffic lanes without the TSS hindering traffic flow is an important decision parameter in the bridge design process. In this paper, we present a new “free flow” paradigm based on an innovative, dynamic application of the ship domain theory.

This note commences with the adoption by the newly invented steam ships, of the sailing ship's custom of referring helm orders to the direction in which the tiller was to be shifted. It records something of the early resiling of the non-English speaking nations from this counter intuitive custom and draws attention to the confusion which the lack of an international approach created, especially for a ship under pilotage. The note concludes with the international uniformity achieved for helm orders by Convention in 1929.