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Evaluation of Tropospheric and Ionospheric Effects on Arctic Navigation Conditions
Abstract
The Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) dataset is evaluated and compared with the JPL GPS Receiver Station Network for use in monitoring and forecasting (simulation/evaluation) tropospheric and ionospheric conditions for GNSS navigation in the arctic maritime environment. Challenges in navigating through arctic seas and harbors include reduced GPS signal availability, increased multi-path and loss-of-lock potential, and changing seasonal coastlines amidst internationally disputed claims to water passageways. Mitigation techniques using auxiliary weather data are explored under degraded arctic GNSS conditions.
A inertial navigation method based on polar stereographic projection was researched to sovle problems that existing inertial navigation methods can not meet the demand for great circle sailing and navigation errors increase in high latitude regions. Ellipsoid grid heading reference model was constructed, drawing from the thought of the polar stereographic projection grid navigation. Then, by using original calculating information of inertial navigation systems (INS), grid heading and grid velocity calculation were achieved. Finally, high latitude navigation parameters performanced evaluation on the basis of the analysis of high-latitude navigation methods inhibition mechanism. Theoretical analysis and simulation results show that this method can effectively improve the navigation performance of INS and meet the demand of carrier sailing in high latitude regions.
To solve the problems that heading error and velocity error of inertial navigation system (INS) increase and the heading angle of the great circle route changes rapidly in polar regions, a calculating method of polar navigation parameters for INS was proposed. First, the polar heading error restraint mechanism was studied and a ellipsoid grid heading reference model was built. Then, the calculating of grid heading and grid velocity was implemented using the calculating navigation parameter information of INS. Finally, the polar navigation performance evaluation of the method was completed. Theoretical analysis and simulation results show that the calculating method is simple, the calculating navigation parameters are conducive to polar sailing monitoring and plotting, and the precision of grid heading and velocity is superior to that of the geographic heading and velocity, which illustrates that the method could meet the requirement of polar navigation and improve the polar navigation performance of the inertial navigation system.
This paper studies the ionospheric response to the major geomagnetic storm of October 18-19, 1995, using the NCAR TIE-GCM simulations and the global ionospheric maps (GIM) of total electron content (TEC) observations from the worldwide network of Global Positioning System (GPS) receivers. The TIE-GCM results show a good agreement with the GPS-GIM in terms of simulating storm-time TEC disturbances over the polar regions. The model indicates that the increase of electron density in the high-latitude E and lower F regions below 200 km is directly related to the magnetospheric energy input through auroral precipitation to the ionosphere, while the decrease of TEC is mainly due to the increase in O 2 and N 2 densities in the upper F region above 200 km. During the recovery phase, both the TIE-GCM and GPS-GIM reveal a distinct hemispheric asymmetry in the TEC integrated above |50°| magnetic latitude, with a 20% decrease in the southern (summer-like) hemisphere and a 30% increase in the northern (winter-like) hemisphere.
New requirements for specification and forecast of the space environment and the availability of unprecedented amounts of real-time data are now driving the development of data assimilation schemes for the thermosphere and ionosphere. Such schemes require accurate knowledge of any biases affecting the models. Finding the biases is not trivial and requires significant effort. Here we present a first step in the validation of a coupled thermosphere ionosphere general circulation model in preparation for its inclusion in a data assimilation scheme. We present a comparison between the Mass Spectrometer Incoherent Scatter (MSIS) radar empirical model neutral temperatures and the Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPE) neutral temperature predictions for three solar cycle conditions (F10.7 = 70, 125, and 200), three geomagnetic activity conditions (Kp = 1, 3, and 7), and three seasons (equinox, summer, and winter). The CTIPE model was run for each case with constant inputs until a diurnally reproducible (“steady state”) global temperature pattern was obtained. MSIS predictions were generated for “perpetually constant” equivalent conditions. The temperature comparisons are performed on a 300 km altitude shell. We present global temperature averages, area-weighted root mean square differences, and zonally averaged temperature comparisons. CTIPE temperatures at 300 km altitude are lower than MSIS if Joule heating calculations do not include small-scale E field variability. This is the first global assessment of a general circulation model for the thermosphere over such a wide range of geomagnetic and solar conditions.
TEC data, obtained from
over 60 GPS stations, were used to study the ionospheric effects of the 12–16
September 1999 magnetic storm over Europe. The spatial and temporal changes of
the ionosphere were analysed as a time series of TEC maps, which present 15 min
averages of TEC. The data set consisting of GPS observations, collected by a
dense network of European stations, with sampling rate of 30 s, enable the
creation of TEC maps with high spatial and temporal resolution. The storm
included the positive as well as the negative phase. The positive phase took
place during the first storm day of 12 September 1999. The short-lived daytime
TEC enhancement was observed at all latitudes. The maximal enhancement reached
a factor of 1.3–1.5. On the second and third days, the negative phase of the
storm developed. The TEC decrease was registered regardless of time of the day.
The TEC depression exceeded 70% relative to quiet days. On the following days
(15 and 16 September), a significant daytime enhancement of TEC was observed
once again. The complex occurrence of the ionospheric storm was probably
related to the features of development of the magnetic storm. We found out that
during the storm the large and medium-scale irregularities developed in the
high-latitude ionosphere. The multi-stations technique, employed to create TEC
maps, was particularly successful while studying the mid-latitude ionospheric
trough. We found out that the essential changes of TEC during the storm, which
were registered at the auroral and sub-auroral ionosphere, were connected with
the effect of the trough and its dynamics, which depends on geomagnetic
activity.Key words. Ionosphere (ionospheric
disturbances; auroral ionosphere; mid-latitude ionosphere)
Although global positioning system (GPS) was originally planned as a satellite-based radio-navigation system for military purposes, civilian users have significantly increased their access to the system for both, commercial and scientific applications. Almost 400 permanent GPS tracking stations have been stablished around the globe with the main purpose of supporting scientific research. In addition, several GPS receivers on board of low Earth orbit satellites fitted with special antennas that focus on Earth's horizon, are tracking the radio signals broadcasted by the high-orbiting GPS satellites, as they rise and set on Earth horizon. The data of these ground and space-born GPS receivers, readily accessible through Internet in a ‘virtual observatory’ managed by the International GPS Service, are extensively used for many researches and might possibly ignite a revolution in Earth remote sensing.
By measuring the changes in the time it takes for the GPS signals to arrive at the receiver as they travel through Earth's atmosphere, scientists can derive a surprising amount of information about the Earth's ionosphere, a turbulent shroud of charged particles that, when stimulated by solar flares, can disrupt communications around the world. This contribution presents a methodology to obtain high temporal resolution images of the ionospheric electron content that lead to two-dimensional vertical total electron content maps and three-dimensional electron density distribution. Some exemplifying results are shown at the end of the paper.
Ionospheric activity is a significant concern for reliable operation of GPS positioning applications, particularly at high latitudes. In order to monitor high latitude ionospheric activity for GPS users, researchers at the University of Calgary have installed the Canadian GPS Network for Ionosphere Monitoring (CANGIM). This network has been operational since 2003 and consists of a number of reference stations, each equipped with a specialized GPS receiver capable of providing near real-time observations of ionospheric parameters and raw GPS data. Potential exists to provide ionospheric warnings and near real-time measures of associated impacts on positioning and navigation applications for GPS users. This paper provides an overview of ionospheric limitations for high latitude GPS users, and describes the ionospheric monitoring services developed for the CANGIM.