Loran System Research Articles

The Loran-C Pseudorange Positioning and Timing Algorithm Based on the Vincenty Formula

To improve the positioning accuracy of the Loran system and meet the requirements of Loran/BDS integrated positioning and timing, it is necessary to enhance the traditional Loran hyperbolic positioning method, making its pseudorange calculation consistent with the BDS positioning and timing solution. The existing pseudorange algorithm based on the Andoyer-Lambert formula has issues such as strict initial value selection range and susceptibility to singularities during calculations. This study proposes a new Loran pseudorange calculation method based on the Vincenty distance formula and conducts a simulation analysis of it. The results show that, in the absence of noise interference, the positioning and timing errors of this pseudorange algorithm are close to zero, demonstrating high accuracy. When subjected to random noise with a standard deviation of less than 100 ns, the latitude and longitude errors are both less than 10 m, and the timing error is less than 10−4 ns, meeting the requirements of Loran positioning and timing. Compared to the pseudorange algorithm based on the Andoyer-Lambert formula, the one based on the Vincenty formula has comparable positioning longitude accuracy but superior timing accuracy. Moreover, the latter offers a wider range of initial value selection and can avoid more singularity issues during calculations.

Two algorithms of geodesic line length calculation considering elevation in eLoran systems

AbstractThe existing LOng RAnge Naviating System stations are mostly used by marine users and are situated at offshore, low‐altitude locations. As a result, the impact of height on the system's positioning accuracy is usually ignored. However, the direct transplantation of low‐altitude calculation methods to high‐altitude areas will bring errors in the positioning results due to the lack of elevation consideration. In order to improve the accuracy of the new enhanced Loran system and reduce the error caused by the calculation of the geodetic line length without considering elevation in high altitude areas, this paper proposes two different algorithms to establish new reference ellipsoids to reduce the height‐caused error, namely the direct algorithm and the expansion ellipsoid algorithm. Experiments show that the error of the calculation results by direct algorithm is smaller, except that it is not applicable when the azimuth is 90° or 270°. The new ellipsoid created by expansion ellipsoid algorithm has smaller changes, and the elevation and geographical coordinates can be considered independent, which is more in line with the Loran system's application requirements.

Evaluation of Height Correction on Loran Signal's Groundwave Transmission Delay Model

With the ongoing construction and development of enhanced long-range navigation (eLoran) system, people's needs for the accuracy of positioning navigation and timing (PNT) service provided by Loran system are increasing. Due to the high altitude at which the new eLoran transmit station will be constructed, the effects of elevation cannot be discounted. Since the existing Loran propagation model (LPM) hasn't systematically taken the impact of elevation into account, new factors have to be added to existing model for users at high-altitude areas. In this letter, the groundwave transmission delay model's (GTDM) height correction factor is provided. Also, by using a modified ellipsoid expansion technique, it is possible to investigate the impact of elevation on the calculation of geodetic line length, a crucial step in the PNT solution of the Loran system. The findings indicate that, in comparison to the built-in algorithm of the current receiver, taking elevation into consideration will result in unavoidable correction for users who are 250 km or less from the transmitter or for users who are more than 500 km away.

Ionospheric delay estimation of Loran skywave using simple cosine model

ABSTRACT Ionospheric delay is the most significant source of error affecting the Loran skywave timing. To improve timing service, we propose a new ionospheric delay estimation method in this paper. It is a cosine model that combines the ionospheric physical characteristics and skywave delay variation law. This semi-empirical and semi-measured model has characteristics of accuracy and simplicity compared with the traditional method. The experimental results show that estimation error of the model is less than 1 µs for a single day and less than 2 µs for 3 days in the stable time. It is sufficient to correct more than 90% of delay when skywave passes through the ionosphere and is less affected by the season. This paper also gives some suggestions on the propagation of ionospheric coefficients required for the model. It allows broadcasting only by modifying the data channel message structure under the normal operation of Loran system.

Simulation-Based Selection of Transmitting Antenna Type for Enhanced Loran System in Selected Location

To improve the coverage and timing capability of enhanced Loran signals, three enhanced Loran transmitters are planned to be built in Western China. The most appropriate antenna configuration can be determined by comparing domestic and foreign mainstream small and radio antennas. By analyzing and comparing the electrical and structural parameters and signal propagation curves of the transmitting antenna, it can be concluded that the single tower umbrella antenna provides the best performance in all evaluation indexes, and the enhanced Loran signal can be transmitted to areas 1000 km away through the single tower umbrella antenna so that the enhanced Loran signal covers most areas of Western China. Therefore, it should be widely used in the construction of enhanced Loran transmitters in the future.

Application of Ultra Narrow Band Modulation in Enhanced Loran System

The Enhanced Loran (eLoran) system is valued for its important role in the positioning, navigation, and timing fields; however, with its current modulation methods, low data rate restricts its development. Ultra narrow band (UNB) modulation is a modulation method with extremely high spectrum utilization. If UNB modulation can be applied to the eLoran system, it will be very helpful. The extended binary phase shift keying modulation in UNB modulation is selected for a detailed study, parameters and application model are designed according to its unique characteristics of signal time and frequency domains, and it is verified through simulation that the application of this modulation not only meets the design constraints of the eLoran system but also does not affect the reception of the respective signals of both parties. Several feasible schemes are compared, analyzed, and selected. Studies have revealed that application of UNB modulation in the eLoran system is feasible, and it will increase the data rate of the system by dozens of times.

High-Accuracy Positioning Based on Pseudo-Ranges: Integrated Difference and Performance Analysis of the Loran System.

The Long Range Navigation (Loran) system as a backup of the Global Navigation Satellite System (GNSS) is a good choice. The dominant deterioration factors of position accuracy are the pseudo-range measurement errors and the geometric dilution of precision (GDOP). This paper focuses on the algorithm integrated difference with pseudo-ranges to improve the position accuracy. Firstly, the theoretical prediction of propagation delay and raw measurement are compared. The results show that the measured pseudo-range consists of a constant term and a temporal term, which reflect the propagation situation along the true path. Secondly, a position solution algorithm based on a pseudo-range and difference is presented, exceeding the limit of a single chain. Finally, some simulation tests are implemented utilizing the new proposed position algorithm to verify the differential performance. This method can reduce the GDOP conveniently through increasing the number of transmitters. In view of the amplitude and characteristics of errors in measurement, systematic error and random noise are distinguished and discussed. The absolute accuracy responds to the pseudo-range bias that is different from geometric distance and repeatable accuracy is mainly influenced by random noise. The difference method can improve the absolute accuracy via the correction degree without changing the geometry of the transmitters.

ASF 예측모델과 실측치를 이용한 영일만 해상 ASF 맵 생성기법

In order to establish eLoran system it needs the betterment of a receiver and a transmitter, the add of data channel to loran pulse for loran system information and the differential Loran for compensating Loran-c signal. Precise ASF database map is essential if the Loran delivers the high absolute accuracy of navigation demanded at maritime harbor entrance. In this study we developed the ASF mapping method using predicted ASFs compensated by the measured ASFs for maritime in the harbor. Actual ASF is measured by the legacy Loran signal transmitted from Pohang station in the GRI 9930 chain. We measured absolute propagation delay between the Pohang transmitting station and the measurement points by comparing with the cesium clock for the calculation of the ASFs. Monteath model was used for the irregular terrain along the propagation path in the Yeongil Bay. We measured the actual ASFs at the 12 measurement points over the Yeongil Bay. In our ASF-mapping method we estimated that the each offsets between the predicted and the measured ASFs at the 12 spaced points in the Yeongil. We obtained the ASF map by adjusting the predicted ASF results to fit the measured ASFs over Yeungil bay.

9930M국 로란-C 신호를 이용한 내륙 ASF 측정 연구

The LORAN system had been used widely and it was an essential navigation aid for ships in the ocean until the GPS is adopted actively. In particular, it was essential functionality for the ships to sail the oceans. According to the advancement of industry, however, the current accuracy of traditional Loran is insufficient for the utilization of harbour approach, land navigation, and the field of survey and timing. Therefore it is necessary that the study on the improvement of the positioning accuracy of Loran. The one of the improving methods is to measure and compensate the propagation time delay between the transmitter and user`s receiver, which is called as additional secondary factor (ASF). In this study, we measured the ASF between the Pohang master transmitting station (9930M) and four points where locate within 33 km apart from the transmitting station, using the measuring technique of the absolute time delay without a time of coincidence (TOC) table. As the result of measurement, the ranging error caused by the propagation delay was about 210 m at 33 km, however it can be reduced up to 40 m with ASF compensation.

ASF 예측치와 실측치 비교

대부분의 응용분야에서 GNSS가 주 측위 시스템으로 활용되고 있으나, 방해전파에 대한 취약성으로 인해 최근에 몇몇 국가에서 eLoran 시스템을 GNSS 백업용으로 사용하기 위한 연구를 진행 중이다. eLoran 시스템의 구축을 위해서는 기존 Loran 시스템에서 설비의 업그레이드, 데이터 채널 사용, dLoran 사이트 추가 구성, 전파 지연오차 보상을 통한 성능 향상이 필요하다. eLoran 신호를 이용한 측위 시에 정확도 성능에 가장 큰 영향을 미치는 오차요소는 육지를 통해 전파될 때 겪는 부가적인 지연요소인 ASF이다. ASF는 지상파 신호가 전파시에 가변적인 고도, 유전율, 도전율 특성을 갖는 육지를 통과하며 발생하는 지연요소이다. 따라서 지상파를 이용한 항법 시에 ASF에 대한 보상모델을 설정하는 것은 매우 중요하다. 본 논문에서는 몬테쓰 모델 (Monteath's Model)을 사용하여 ASF 예측치를 모델링하고, Loran 신호를 이용한 실측을 통해 ASF 실측치를 측정한 후, ASF 예측치와 실측치를 비교하고 특성을 도출하였다. 실험대상 지역은 대전 KRISS와 포항 근방이며, GRI 9930 체인 중 주국인 포항 송신국의 신호를 사용하였다. 실험을 통해 ASF 실측치의 반복성을 확인하고, ASF 예측치와 실측치 간에 일정한 추이를 보이는 것을 확인하였다. In the almost application parts, GNSS being used the primary navigation system on world-widely. However, some of nations attempt or deliberate to enhance current Loran system, as a backup to satellite navigation system because of the vulnerability to the disturbance signal. Loran interests in supplemental navigation system by the development and enhancement, which is called eLoran, and that consists of advancement of receiver and transmitter and of differential Loran in order to increase the accuracy of current Loran-C. A significant factor limiting the ranging accuracy of the eLoran signal is the ASF in the TOAs observed by the receiver. The ASF is mostly due to the fact that the ground-wave signal is likely to propagate over paths of varying conductivity and topography. This paper presents comparison results between the predicted ASF and the measured ASF in a southern east region of Korea. For predicting ASF, the Monteath model is used. Actual ASF is measured from the legacy Loran signal transmitted Pohang station in the GRI 9930 chain. The test results showed the repeatability of the measured ASF and the consistent characteristics between the predicted and the measured ASF values.

소프트웨어 기반 Loran-C 신호 처리

With GPS being the primary navigation system, Loran use is in steep decline. However, according to the final report of vulnerability assessment of the transportation infrastructure relying on the global positioning system prepared by the John A. Volpe National Transportation Systems Center, there are current attempts to enhance and re-popularize Loran as a GPS backup system through the characteristic of the ground based low frequency navigation system. To advance the Loran system such as Loran-C modernization and eLoran development, research is definitely needed in the field of Loran-C receiver signal processing as well as Loran-C signal design and the technology of a receiver. We have developed a set of Matlab tools, which implement a software Loran-C receiver that performs the receiver's position determination through the following procedure. The procedure consists of receiving the Loran-C signal, cycle selection, calculation of the TDOA and range, and receiver's position determination through the Least Square Method. We experiences the effect of an incorrect cycle selection and various error factors (ECD, ASF, sky wave, CRI, etc.) from the result of the Loran-C signal processing. It is apparent that researches which focus on the elimination and mitigation of various error factors need to be investigated on a software Loran-C receiver. These aspects will be explored in further work through the method such as PLL and Kalman filtering.

Improving Loran Coverage with Low Power Transmitters

Enhanced Loran (eLoran) is currently being implemented to provide back up to global navigation satellite systems (GNSS) in many critical and essential applications. In order to accomplish this, eLoran needs to provide a high level of availability throughout its desired coverage area. While the current Loran system is generally capable of accomplishing this, worldwide, there remain a number of known areas where improved coverage is desirable or necessary. One example is in the middle of the continental United States where the transmitter density is not adequate for providing the desired availability for applications such as aviation in some parts. This paper examines the use of lower power, existing assets such as differential GPS (DGPS) and Ground Wave Emergency Network (GWEN) stations to enhance coverage and fill these gaps. Two areas covered by the paper are the feasibility and performance benefits of using the antennas at these sites.Using DGPS, GWEN or other existing low frequency (LF) broadcast towers requires the consideration of several factors. The first is the ability of the transmitting equipment to efficiently broadcast on these antennas, which are significantly shorter than those at a Loran station. Recent tests at the US Coast Guard Loran Support Unit (LSU) demonstrated the performance of a more efficient transmitter. This technology allows for the effective use of smaller antennas at lower power levels. Second is the ability to broadcast a navigation signal that is compatible with the Loran system and the potential DPGS broadcast (when using a DGPS antenna). The paper examines some possibilities for navigation signals. The goal is to develop a suitable low power signal that enhances navigation and is feasible for the transmission system.The second part of the paper examines the benefits of using these stations. The benefits depend on the location of the stations and the ability seamlessly to integrate them within the existing Loran infrastructure. Analysis of these factors is presented and the coverage benefits are examined.

Differential LORAN for 2005

A multimodal group of engineers, scientists, and industry representatives, including the U.S. Coast Guard (USCG) and Federal Aviation Administration (FAA) completed a major effort to define and analyze the performance of a new Enhanced Loran system as a backup for the navigation and timing services provided by the NAVSTAR Global Positioning System (GPS) provided services. Each mode of transportation has defined requirements that the new Enhanced Loran must meet to be acceptable in the radionavigation mix of systems. The group developed a set of requirements for Loran maritime navigation in terms of availability, accuracy, integrity and continuity for the Harbor Entrance and Approach (HEA) requirements defined in the Federal Radionavigation Plan (FRP). This paper discusses the goals of the Loran Support Unit for Fiscal Year 2005 (FY05), and the program to support these goals. The factors related to achieving the objective of moving Differential Loran from the proof-of-concept stage to an operational status will be discussed. Also covered are the results of an initial survey of the Inner Harbor at Boston, MA, USA.

Performance of DSP-Loran/H-Field Antenna System and Implications for Complementing GPS

ABSTRACT: In light of the September 2001 terrorist attacks and the Department of Transportation's (DOT) Volpe Study on national vulnerabilities associated with overdependence on GPS, the importance of objectively assessing the capabilities of a modern Loran system has greatly increased. The Federal Aviation Administration (FAA) has an active program to investigate Loran as a complement to GPS, and the United States Coast Guard (USCG) is modernizing its Loran infrastructure. This paper reviews the development status and capabilities of a new H-field antenna and digital signal processing (DSP)–based Loran receiver system undergoing assessment by the FAA, and presents test results from side-by-side comparisons with GPS and legacy Loran receivers. Empirical results suggest Loran is a logical choice to become the national complement to GPS.

Eastward sulfur flux from the Northeastern United States

During January and February 1986 the concentrations of sulfur dioxide (SO 2) and particulate sulfate (SO 4 2−) were measured from an instrumented aircraft 80–120 km east of the New England coast. The average concentration of SO 2 in the boundary layer (BL) was 10 μg m −3; the maximum 30-min average was 26 μg m −3. The average and maximum values in the free troposphere (FT) were 3.9 and 31 μg m −3, respectively. The concentrations of non-sea-salt SO 4 2− averaged 2.0 and 0.7 μg m −3 in the BL and FT, and the maximum concentrations were 7.7 and 3.2 μg m −3. Continuous wind speed records from the aircraft LORAN system were used to estimate altitude profiles of the offshore fluxes of SO 2 and SO 4 2− for the duration of the study. The estimated advection flux, is (3.5 ± 0.4) × 10 −3 Tg(S)day −1 from the coastal segment between 41 and 43°N latitudes. Most (89%) of the S flux was found to be in the form of SO 2; the remainder corresponded to particulate SO 4 2−. The ratio of aerosol to gas-phase S in the BL was found to be similar tó that in the FT, despite the fact that removal of SO 2 from the BL is expected to be much faster than that from the FT.

Direct-Ranging Loran Model Identification and Performance Predictions

With the availability of modern data processing techniques and lowcost stable time references, the use of Loran in a direct-ranging mode offers certain potential advantages. In order to generate reliable direct-ranging Loran (DRL) performance projections and system designs, however, accurate system error models are required. This paper first describes the processing of airborne flight data from a DRL receiver to identify models for significant DRL system errors. These models are then used in a Kalman filter covariance simulation to generate performance predictions for an optimally integrated DRL system. Comparisons with conventional hyperbolic Loran are also given. DRL is shown to be capable of substantially improved position accuracy over that of conventional hyperbolic Loran, especially in regions of poor geometry. A stationary ground-align technique for improving DRL performance is also discussed.

Explicit (Noniterative) Loran Solution

the main computational requirement for LORAN navigation systems is the transformation to geographic latitude and longitude of time difference measurements made by the LORAN receiver. It is desirable to maintain a computational accuracy of less than one second of arc to avoid degradation of the inherently attainable LORAN system accuracy. It is therefore necessary to take into account the effect of a non-spherical earth (ellipticity correction) and variable velocity of propagation (secondary phase correction.) Incorporation of these corrections into the analysis results in two non-linear equations in two unknowns. This paper presents a derivation and discussion of an explicit, noniterative, LORAN mechanization of very high accuracy (approximately one second of arc). The advantages of this explicit solution are as follows: 1. No initial guess as to receiver position is required. This provides for a self-sufficient LORAN system. 2. Perfect computational repeatability is achieved. 3. With the explicit solution, it is always possible to select the proper solution of the two possible solutions. 4. The simple explicit equations lead to reduced computational time and memory storage requirements for the computer. This technique has been programmed on the RECOMP III Computer. It was tested for accuracy by comparison with the National Bureau of Standards computations [2] for the East Coast LORAN Net. Representative samples of the results are given.

Loran-Inertial Navigation Systems for Long-Range Use

Loran C, a long-range hyperbolic navigation system, is currently used in transoceanic aircraft only to provide periodic position up-dating of primary self-contained navigation systems. The successful development and flight testing of an automatic coordinate converter has recently shown that the potential of the Loran system of navigation is vastly greater than past utilization has indicated. This paper briefly discusses the advantages of combining an increased capability Loran sub-system and an unsophisticated inertial sub-system within the framework provided by a heavy logistics support aircraft.

Navigation and Control from Loran-C

The position fixing capability of the Loran system has been well recognized for use in transport aircraft as a navigation system monitor. The role of Loran-C as a navigation and control system has not been recognized, however, primarily because of the unwieldly time difference coordinates of the system. With the successful development of cockpit operable auto-track receivers and proof of the feasibility of automatic coordinate conversion, it now becomes possible to discuss the potential of Loran-C as a system capable of providing navigation control in the horizontal plane. To this end, three separate tracks across the North Atlantic area are analyzed to show the accuracy of positional, track and steering information that is available from the proper processing of Loran-C signals. From the analysis, it is evident that within its coverage area the system is capable of being used as a primary navigation system or, on a supersonic transport, it can be used in conjunction with an inertial navigator to obtain dual operational redundancy of the navigation systems.

Technical Advances in the Loran System and its Future Development

The Loran System came into being during the war and played its part in the achievement of ultimate victory. During that period, expediency was the motif, but this was accompanied by some improvements over early equipment. Technical refinement and development have continued up to the present time. In transmitting equipment, emphasis has been placed on reduction of equipment failures, accuracy of synchronization, reduction of adjacent channel interference to other services, ability to operate with a small signal to noise ratio, reduction in costs through unattended operation, and increased range through higher power and optimized antennas. New receivers contain such features as increased stability, direct reading dials, greater range in the presence of noise and interference through narrower bandwidth, automatic pulse locking, automatic pulse tracking, remote indicators and miniaturization. Future receiver developments, of which some exploratory work has been done, aim divergently at simplification and price reduction and at (along with further refinement of transmitting equipment) a manifold increase in navigational accuracy. Possible future developments, now only in the planning stage, are described. Covered also are actual special applications such as official speed determinations of the SS UNITED STATES and other vessels, aid to fishermen, navigation at great distances from stations by multihop signals and Coast Guard ocean station and ice patrol activities. The present Loran service is described.