BeiDou Geostationary Earth Orbit Research Articles

Ionospheric behaviors and characteristics in Asian sector during the April 2023 geomagnetic storm with multi-instruments observations

Geomagnetic storms frequently affect satellite navigation, communication and satellite orbits. Monitoring and understanding the ionospheric disturbances and responses to geomagnetic storms are crucial. The detailed ionospheric responses and physical mechanisms to various geomagnetic storms, however, have not yet been extensively studied. In this paper, the ionospheric variation behaviors and features following the April 2023 magnetic storm along the Asian sector are thoroughly studied using multi-instrument observation data, including the Global Navigation Satellite System (GNSS), ionosonde, and other satellites. Large-scale Traveling Ionospheric disturbances (LSTIDs) are observed from BeiDou Geostationary Earth Orbit (GEO) satellites, GPS and GLONASS. LSTIDs traveled with a speed of 760–1300 m/s from high latitude region to low latitude region with a period of about 40 min. The equatorial propagating LSTIDs were generated by coronal mass ejections (CMEs), which occurred in April 2023 with periodic energy input from the auroral area. The poleward LSTIDs are also observed with a velocity of approximately 600–750 m/s and the period is similar. Neutral wind also influenced the characteristics of the ionospheric response. The [O]/[N2] ratio declined during the storm, which led to the formation of the negative storm phases. The largest vertical total electron content (VTEC) is found, and the strengthened region of TEC is mainly centered between ± 20° within geographical latitude. Equatorial Ionospheric Anomaly (EIA) is also observed, which is probably influenced by the electric field. As the time goes on, the peak on the south side of the EIA is disappearing. Meanwhile, the height of the ionospheric maximum electron density rises, and the electron density falls.

The Analysis of Ionospheric TEC Anomalies Prior to the Jiuzhaigou Ms7.0 Earthquake Based on BeiDou GEO Satellite Data

The position between BeiDou geostationary Earth orbit (GEO) satellites and ground-based receiving stations can roughly be considered to be constant with negligible fluctuations; thus, the total electron content (TEC) data over a fixed ionospheric piercing point (IPP) can be continuously acquired, which is advantageous for monitoring ionospheric disturbances. Focused on the Jiuzhaigou Ms7.0 earthquake that occurred on 8 August 2017, the TEC data inverted by the BeiDou GEO satellite were analyzed to extract ionospheric disturbances potentially associated with the earthquake. It was found that significant anomalies in ionospheric TEC occurred 10–11 days, 6–7 days, and 1–9 h prior to the earthquake, which was mainly located in the southeast and southwest directions within about 2500 km distance from the epicenter. Comparing the spatial and temporal characteristics between the ionospheric disturbance and the radon gas near the surface, the atmospheric electric field, and the spectrum of TEC data, it was considered that the chemical and acoustic–gravity wave pathway may play an important role in the lithosphere–atmosphere–ionosphere coupling (LAIC) mechanism.

Structure of Post‐Midnight Enhancements in Electron Density at the Low Latitude F‐Layer Ionosphere

AbstractIt has previously found that at Sanya (109.6°E, 18.3°N) a post‐midnight enhancement in the F2‐layer peak electron density (NmF2) is often accompanied by the increase in the bottom side F layer electron density (Ne) and a reduction in the top side F layer Ne. We conduct a case study to explore the complete spatial coverage of the post‐midnight enhancements of electron density in the low latitude ionosphere. The total electron content (TEC) data are retrieved from the Beidou Geostationary Earth Orbit (GEO) satellite signals recorded by a network of Global Navigation Satellite System (GNSS) receivers in Asia‐Australia. The F2‐layer peak parameters and the altitudinal profiles of Ne are measured by the ionosonde, and incoherent scatter radar at Sanya (109.6°E, 18.3°N). The GEO‐TEC does not always completely follow the enhancement of NmF2. The enhancements may peak roughly simultaneously or with significant time shifts in the west‐east direction, even in the GEO‐TEC series recorded by a GNSS receiver in an event, which indicates possibly the enhancement of different longitudinal scales. Further, in the cases the enhancement is clustered in a limited area. The low latitude enhancements show a hemispheric asymmetry; they occur mainly in the northern hemisphere and usually have no correspondingly magnetic conjugate symmetrical features in the southern hemisphere. The hemispheric asymmetry of the enhancements highlights that both the field‐aligned plasma transport and electric fields are possibly responsible for regulating the limited spatial presence of post‐midnight enhancements in the low latitude ionosphere.

Moving Target Detection and Parameter Estimation Using BeiDou GEO Satellites-Based Passive Radar With Short-Time Integration

Owing to the global coverage and high visibility of global navigation satellite systems (GNSS), passive radar using GNSS satellites as transmitters of opportunity has shown great potential for moving target detection, and its possibility to detect short-range maritime targets has been verified. Nevertheless, the existing methods always require tens of seconds for echo integration, which is not ideal for the detection of targets with high maneuverability. To solve this problem, a bistatic configuration using BeiDou geostationary earth orbit (GEO) satellites as illuminators of opportunity, which is suited for short-time coherent integration of echo signals, is presented. In addition, the corresponding signal processing method is introduced. To achieve a more continuous trajectory of the target, a method used to fuse range-Doppler maps obtained individually from multiple BeiDou GEO satellites is also described. The effectiveness and functionality of our proposed algorithms are demonstrated with an experiment in which a ferry was used as a moving target and its real-time location data were adopted as a reference.

Phase Error Analysis and Compensation of GEO-Satellite-Based GNSS-R Deformation Retrieval

Beidou geostationary earth orbit (GEO) satellite-based global navigation satellite system reflectometry (GNSS-R) technique has been developed for measuring surface deformation in a carrier-phase-based, cost-effective, and continuous manner. However, several improper assumptions in the original system and method, such as neglecting the slight GEO satellite movement during angle determination and deeming inter-channel phase difference as time-invariant, can introduce certain errors in estimating the surface deformation. In this work, these issues were analyzed and improved for more accurate estimations. Utilizing a Wilkinson power divider, the inter-channel phase error is estimated and calibrated with direct signal in the master channel. The GEO-motion phase error is theoretically modelled and compensated for based on precise ephemeris. A compensating algorithm of GNSS-R deformation retrieval technique utilizing Beidou GEO satellites is presented, by which encouraging results are yielded from field experiments emulating long-term monitoring. On artificial targets, the retrieval root mean square (RMSE) is better than 8 mm.

Deformation Estimation Using Beidou GEO-Satellite-Based Reflectometry

Deformation monitoring has been brought to the fore and extensively studied in recent years. Global Navigation Satellite System Reflectometry (GNSS-R) techniques have so far been developed in deformation estimation applications, which however, are subject to the influence of mobile satellites. Rather than compensating for the path delay variations caused by mobile satellites, adopting Beidou geostationary Earth orbit (GEO) satellites as transmitters directly eliminates the satellite-motion-induced phase error and thus provides access to stable phase information. This paper presents a novel deformation monitoring concept based on GNSS-R utilizing Beidou GEO satellites. The geometrical properties of the GEO-based bistatic GNSS radar system are explored to build a theoretical connection between deformation quantity and the echo carrier phases. A deformation retrieval algorithm is proposed based on the supporting software receiver, thus allowing echo carrier phases to be extracted and utilized in deformation retrieval. Two field validation experiments are conducted by constructing passive bistatic radars with reflecting plates and ground receiver. Utilizing the proposed algorithm, the experimental results suggested that the GEO-based GNSS reflectometry can achieve deformation estimations with an accuracy of around 1 cm when the extracted phases does not exceed one complete cycle, while better than 3 cm when considering the correct integer number of phase cycles. Consequently, based on the passive bistatic radar system, the potential of achieving continuous, low-cost deformation monitoring makes this novel technique noteworthy.

Exploiting the Potential of Coastal GNSS-R for Improving Storm Surge Modeling

The potential mymargin for improving storm surge simulation is demonstrated by using winds derived from ground-based Global Navigation Satellite System Reflectometry (GNSS-R) that uses BeiDou geostationary Earth orbit (GEO) satellite signals. We reconstruct wind fields by blending GNSS-R coastal winds with the European Center for Median Weather Forecasts (ECMWF) reanalysis product. The reconstructed winds agree well with the weather station data collected at Yangjiang in Guangdong, China. The ECMWF winds and the reconstructed winds are used to force a storm surge model off the Chinese coast during typhoon Utor 2013, respectively. The model storm surges forced by the reconstructed winds agree substantially better with tide-gauge observations than those forced by the ECMWF winds. The average error has been reduced by 30.5% from 24.3 cm with the ECMWF winds to 16.9 cm with the reconstructed winds. This letter suggests that GNSS-R coastal winds can have a positive impact on the accuracy of storm surge hindcasting directly and forecasting indirectly by improving the initial conditions.

Multi-Instrumental Observations of Early Morning Equatorial Plasma Depletions During the 2017 Memorial Weekend Storm

We investigate an equatorial plasma depletion (EPD) event in Japan near the early morning sector (04:30–7:30 LT) during the recovery phase of a geomagnetic storm occurred on Memorial weekend (May 28) 2017 by using multi-instrumental measurements, including ground-based Global Navigation Satellite Systems (GNSS) network, ionosonde stations, and space-based Swarm and Defense Meteorological Satellite Program (DMSP) missions. The detailed 2-D evolution of the early morning EPD is well observed using GNSS ROTI maps with high temporal-spatial resolution. Moreover, ROTI data from BeiDou Geostationary Earth Orbit satellites are used to detect the EPD signature for the first time. The dawn EPD signature was also observed at the topside ionosphere by in situ electron density (Ne) measurements and ROTI results by space-borne Swarm Alpha (A), Charlie (C), and DMSP F17 satellites, indicating that the equatorial depletions arose to higher altitudes. We suggest that both the eastward disturbance dynamo electric field and overshielding electric field near the early morning sector created a favorable condition for the growth of the Rayleigh–Taylor (R-T) instability, and thus result in the generation of the dawn EPD.

Improved IRI-2016 model based on BeiDou GEO TEC ingestion across China

Due to the quasi-invariant orbital locations of the BeiDou geostationary earth orbit (GEO) satellites, the BeiDou GEO total electron content (TEC) is not influenced by the contamination of ionospheric spatial and temporal gradient variations. We ingest BeiDou GEO TEC observations across China into the IRI-2016 model for the first time by developing effective hourly ionospheric global indices (IG), which were estimated based on the assumption that BeiDou GEO TEC is equal to the updated IRI TEC for the given location and time. When the retrieved hourly IG indices are used to drive the IRI-2016 model, the resulting near real-time ionospheric parameters are externally evaluated by other data sources, including (1) the Center for Orbit Determination of Europe (CODE) Global Ionosphere Maps (GIM) TEC products and extra BeiDou GEO TEC, (2) Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) electron density (Ne) profiles and F2 layer maximum electron density (NmF2) and (3) ionosonde Ne profiles and critical frequency (foF2) observations under both geomagnetic quiet and active conditions. The validation results show that the proposed ingestion technique successfully pushes the standard IRI model toward being usable for near real-time weather predictions. Moreover, a general improvement in accuracy of the updated IRI model regarding TEC, Ne, NmF2 and foF2 can be obtained during September 2–12, 2017, as expected: (1) updated TEC BIAS/RMS reduces from − 3.20/4.86 to − 0.10/1.86 TECU compared to CODE GIM, and from − 2.84/4.63 TECU to 0.75/1.05 TECU compared to external BeiDou GEO TEC. (2) Topside electron density from updated IRI matches better with that from the COSMIC than the standard IRI; the STD/RMS/BIAS versus COSMIC NmF2 decreases from 2.195/2.313/0.845 to 2.083/2.043/− 0.092 (unit: 105 cm−3). (3) Bottomside electron density from the updated IRI is much closer to the ionosonde measurement than the standard IRI; updated IRI foF2 also exhibits relatively minor improvements compared with ionosonde measurements, i.e., STD/RMS/BIAS reduces from 1.070/1.268/0.681 to 1.019/1.061/− 0.298 MHz.

Precise Orbit Determination for BeiDou GEO/IGSO Satellites during Orbit Maneuvering with Pseudo-Stochastic Pulses

In order to provide better service for the Asia-Pacific region, the BeiDou navigation satellite system (BDS) is designed as a constellation containing medium earth orbit (MEO), geostationary earth orbit (GEO), and inclined geosynchronous orbit (IGSO). However, the multi-orbit configuration brings great challenges for orbit determination. When orbit maneuvering, the orbital elements of the maneuvered satellites from broadcast ephemeris are unusable for several hours, which makes it difficult to estimate the initial orbit in the process of precise orbit determination. In addition, the maneuvered force information is unknown, which brings systematic orbit integral errors. In order to avoid these errors, observation data are removed from the iterative adjustment. For the above reasons, the precise orbit products of maneuvered satellites are missing from IGS (international GNSS (Global Navigation Satellite System) service) and iGMAS (international GNSS monitoring and assessment system). This study proposes a method to determine the precise orbits of maneuvered satellites for BeiDou GEO and IGSO. The initial orbits of maneuvered satellites could be backward forecasted according to the precise orbit products. The systematic errors caused by unmodeled maneuvered force are absorbed by estimated pseudo-stochastic pulses. The proposed method for determining the precise orbits of maneuvered satellites is validated by analyzing data of stations from the Multi-GNSS Experiment (MGEX). The results show that the precise orbits of maneuvered satellites can be estimated correctly when orbit maneuvering, which could supplement the precise products from the analysis centers of IGS and iGMAS. It can significantly improve the integrality and continuity of the precise products and subsequently provide better precise products for users.

Precise time and frequency transfer combined BeiDou\u2019s RDSS and RNSS signals

Unlike other satellite navigation systems such as GPS (Global Positioning System), the BeiDou satellite navigation system broadcasts RDSS (Radio Determination Satellite Service) and RNSS (Radio Navigation Satellite Service) signals simultaneously on its GEO (geostationary earth orbit) satellites and provides related navigation services. This paper studies the method of using the RDSS and RNSS signals of BeiDou to achieve accurate frequency and time transmission. We analyze the generation mechanism of RDSS signal and RNSS signal of BeiDou GEO satellite, establish a mathematical model of RDSS and RNSS signal frequency transfer, and derive an equation based on BeiDou’s RDSS and RNSS signals for accurate frequency and time transmission. We also verified the relevant performance of the method through computer simulation. The results show that the combination of RDSS and RNSS signals from the BeiDou satellite system provides a new solution for its application in precise time and frequency transmission. This method is different from other satellite navigation systems such as GPS and is unique to the BeiDou system, with high accuracy and low dependence on satellite orbit accuracy.

A Novel Method for Ocean Wind Speed Detection Based on Energy Distribution of Beidou Reflections.

The Global Navigation Satellite System Reflectometry (GNSS-R) technique exploits the characteristics of reflected GNSS signals to estimate the geophysical parameters of the earth’s surface. This paper focuses on investigating the wind speed retrieval method using ocean scattered signals from a Beidou Geostationary Earth Orbit (GEO) satellite. Two new observables are proposed by computing the ratio of the low energy zone and the high energy zone of the delay waveform. Coastal experimental raw data from a Beidou GEO satellite are processed to establish the relationship between the energy-related observables and the sea surface wind. When the delay waveform normalized amplitude (this will be referred to as “threshold” in what follows) is 0.3, fitting results show that the coefficient of determination is more than 0.76 in the gentle wind scenario (<10 m/s), with a root mean square error (RMSE) of less than 1.0 m/s. In the Typhoon UTOR scenario (12.7 m/s~37.3 m/s), the correlation level exceeds 0.82 when the threshold is 0.25, with a RMSE of less than 3.10 m/s. Finally, the impact of the threshold and coherent integration time on wind speed retrieval is discussed to obtain an optimal result. When the coherent integration time is 50 milliseconds and the threshold is 0.15, the best wind speed retrieval error of 2.63 m/s and a correlation level of 0.871 are obtained in the UTOR scenario.

Continuous precise ephemerides for Beidou-2 maneuvered satellites based on a new thrust force model

Beidou geostationary earth orbit (GEO) and inclined geosynchronous orbit (IGSO) satellites are frequently maneuvered to keep them in the designed orbits by thrust forces. As the thrust forces are generally unknown, precise satellite orbits are difficult to be determined during maneuver periods. At present, precise ephemerides are not available or not complete for the satellite on the day of maneuver, and sometimes even the day after. This study aims to provide continuous precise orbit for Beidou-2 satellites during the maneuver period through better modeling of the thrust forces. We firstly present a thrust model based on the thrust behavior of Beidou-2 satellites detected in our previous study. Then, for the maneuvered satellite, the precise orbit is determined by estimating the extra thrust model parameters, together with other orbit parameters of initial satellite state and solar radiation pressure (SRP). Using observations from the Multi-GNSS Experiment (MGEX) network in Sep and Oct 2017, we have detected 10 GEO in-plane, 1 GEO and 3 IGSO out-of-plane maneuvers among the 5 GEO and 6 IGSO satellites; precise orbit determination (POD) is conducted for all the GEO in-plane and IGSO maneuvered satellites. The accuracy of our recovered orbit has been evaluated by comparing to a concatenation of the dynamic orbit before/after the maneuver and kinematic orbit during the maneuver. The RMSs of orbit differences before/after maneuvers are about 0.30, 2.34 and 0.42 m in the radial, along-track, and cross-track (RAC) directions for GEOs, and 0.33, 0.62 and 0.26 m for IGSOs. A similar level of accuracy has also been achieved during maneuvers as shown by the orbit differences and the stable POD residuals during the whole maneuver day. The recovered orbit accuracy is comparable to that of the normal Beidou-2 precise ephemerides from International GNSS Service (IGS) analysis centers (WHU/GFZ).

A novel predictive algorithm for double difference observations of obstructed BeiDou geostationary earth orbit (GEO) satellites

Transmission link disturbances and device failure cause global navigation satellite system (GNSS) receivers to miss observations, leading to poor accuracy in real-time kinematic (RTK) positioning. Previously described solutions for this problem are influenced by the length of the prediction period, or are unable to account for changes in receiver state because they use information from previous epochs to make predictions. We propose an algorithm for predicting double difference (DD) observations of obstructed BeiDou navigation system (BDS) GEO satellites. Our approach adopts the first-degree polynomial function for predicting missing observations. We introduce a Douglas-Peucker algorithm to judge the state of the rover receiver to reduce the impact of predictive biases. Static and kinematic experiments were carried out on BDS observations to evaluate the proposed algorithm. The results of our navigation experiment demonstrate that RTK positioning accuracy is improved from meter to decimeter level with fixed ambiguity (horizontal < 2 cm, vertical < 18 cm). Horizontal accuracy is improved by over 50%, and the vertical accuracies of the results of the static and kinematic experiments are increased by 47% and 27% respectively, compared with the results produced by the classical approach. Though as the baseline becomes longer, the accuracy is weakened, our predictive algorithm is an improvement over existing approaches to overcome the issue of missing data.

A Novel Wind Speed Estimation Based on the Integration of an Artificial Neural Network and a Particle Filter Using BeiDou GEO Reflectometry.

Oceanographic remote sensing, which is based on the sensitivity of reflected signals from the Global Navigation Satellite Systems (GNSS), so-called GNSS-Reflectometry (GNSS-R), is very useful for the observation of ocean wind speed. Wind speed estimation over the ocean is the core factor in maritime transportation management and the study of climate change. The main concept of the GNSS-R technique is using the different times between the reflected and the direct signals to measure the wind speed and wind direction. Accordingly, this research proposes a novel technique for wind speed estimation involving the integration of an artificial neural network and the particle filter based on a theoretical model. Moreover, particle swarm optimization was applied to find the optimal weight and bias of the artificial neural network, in order to improve the accuracy of the estimation result. The observation dataset of the reflected signal information from BeiDou Geostationary Earth Orbit (GEO) satellite number 4 was used as an input for the estimation model. The data consisted of two phases with I and Q components. Two periods of BeiDou data were selected, the first period was from 3 to 8 August 2013 and the second period was from 12 to 14 August 2013, which corresponded to events from the typhoon Utor. The in situ wind speed measurement collected from the buoy station was used to validate the results. A coastal experiment was conducted at the Yangjiang site located in the South China Sea. The results show the ability of the proposed technique to estimate wind speed with a root mean square error of approximately 1.9 m/s.

Empirically derived model of solar radiation pressure for BeiDou GEO satellites

A key limitation in the precise orbit determination (POD) of BeiDou geostationary Earth orbit (GEO) satellites is the relatively static observation geometry, which results in strong correlations between orbital elements, solar radiation pressure (SRP) parameters, and ambiguities. Satellite laser ranging (SLR) residuals of BeiDou G01 satellite orbits display a clear dependence on the Sun elongation angle e, as well as a bias of approximately − 40 cm. These indicate the low performance of BeiDou GEO orbits. In this study, we confirmed that the perturbation caused by the communication antenna generates the e-angle-dependent variation and the bias of approximately − 14.9 cm in BeiDou G01 SLR residuals. Besides, the orbit-normal (ON) attitude mode used by BeiDou GEO satellites as well as an orbital inclination of nearly 0° results in strong linear correlations between the POD estimated parameters, i.e., satellite’s initial position on the Z-axis and the constant Y-bias along the cross-track direction. Hence, the solar pressure models, such as Extended CODE Orbit Model (ECOM) in ON mode, with the Y-axis along the cross-track direction are deficient for SRP estimation of BeiDou GEO satellites. In this study, an empirical a priori SRP model was established for BeiDou GEO satellites to enhance the ECOM using an empirical fitting approach. This proposed model is expressed in DYB frame using eight parameters. With this model, precise BeiDou GEO orbits in 2016 were determined. SLR validation indicated that the systematic e-angle-dependent error was reduced and the large negative bias almost vanished. In general, better than 10-cm root-mean-square of SLR validation was achieved, and also an improvement of 4–5 times over the five-parameter ECOM model was obtained.

Construction of a BDSPHERE solar radiation pressure model for BeiDou GEOs at vernal and autumn equinox periods

Geostationary Earth Orbit (GEO) satellites are important components of the BeiDou System (BDS). Long-term orbit ephemeris accuracy monitoring in the Operational Control System (OCS) of BDS indicates that the orbit accuracy for the BDS GEOs is unstable and degraded by several meters during the vernal and autumn equinox periods of each year. The SPHERE solar radiation pressure (SRP) model does not do a good job of reflecting the characteristics of the SRP during equinox periods. In view of this problem, this study proposes to replace SPHERE with BDSPHERE for the BDS GEOs during both equinox and non-equinox periods. We smooth the orbits of the BDS GEOs provided in SP3 precise orbit file format of Wuhan University (WHU, Wuhan, China) in the Multi-GNSS Pilot Project (MGEX), re-estimate the SRP parameter over a 2-year period and construct a 2-year continuous time series of the SRP model parameter. By analyzing the time series, a BDSPHERE model is constructed. The polynomial coefficients during the equinox periods are determined based on historical data and new data. Experiments with Beidou data show that during the equinox periods the orbit-only contribution to the signal-in-space range error (SISRE(ORB)) using the BDSPHERE model for GEOs in orbit determination arc and the 8-h and 24-h orbit predictions arc are 0.77, 0.80 and 1.62 m, respectively, which are smaller than those of the conventional SPHERE model by 53%, 60% and 61%, respectively. An evaluation based on global satellite laser ranging (SLR) data shows that during the equinox periods the BDSPHERE model can provide a radial orbit accuracy of 0.61 m, which is 70% better than that of the SPHERE model, and reach the SPHERE model's orbit accuracy in non-eclipsing periods. The BDSPHERE model during equinox periods considerably improves the orbit accuracy and stability of the BDS GEOs. This paper can provide technical support for constructing SRP models for the BDS.

Initial Results of Typhoon Wind Speed Observation Using Coastal GNSS-R of BeiDou GEO Satellite

Sea surface-reflected signals of global navigation satellite system (GNSS) were collected during a coastal experiment to evaluate the potential use of these signals on typhoon investigation. This work focuses on processing the signals from BeiDou geostationary Earth orbit (GEO) satellites and assessing the sensitivities of waveform observables to the wind speed evolution during the typhoons. After the processing of the raw samples, both the delay- and spectral-related observables are obtained from the complex waveforms and then compared with in situ wind measurement collected during two tropical cyclones. Results from the data analysis are presented, confirming that the proposed observables are well correlated with the wind speed evolution and suitable for coastal wind speed retrieval.

Phase Altimetry Using Reflected Signals From BeiDou GEO Satellites

With the development of the Chinese BeiDou satellite navigation system, the applications of BeiDou reflected (BeiDou-R) signals would play a key role in Global Navigation Satellite System reflected signals. Different from other navigation systems, the BeiDou satellite navigation system has certain unique characteristics, and the Geostationary Earth Orbit (GEO) satellite is one of them. The aim of this letter is to prove the feasibility of coastal ocean phase altimetry using BeiDou GEO reflected signals. The coastal experiment was performed from October 18, 2014, to October 19, 2014, in Dayang Shan, Zhejiang, China. This is the first coastal ocean phase altimetry experiment using BeiDou GEO reflected signals. The phase altimetry results can invert the slope of ocean surface height variation (in time), and its highest accuracy can reach centimeter level.

Basic performance of space-surface bistatic SAR using BeiDou satellites as transmitters of opportunity

The basic performance of space-surface bistatic synthetic aperture radar (SS-BSAR) using BeiDou satellites as transmitters of opportunity is presented. The transmitted signal, the satellite trajectory, and the observation time are analyzed to demonstrate the potential of BeiDou satellites to be used as transmitters of SS-BSAR. When a BeiDou medium earth orbit (MEO) satellite is used, the signal-to-noise ratio and the resolution are examined for different SS-BSAR cases, where the receiver is fixed on the ground or mounted on a moving platform. Since the parameters of the BeiDou geostationary earth orbit (GEO) satellite and the inclined geosynchronous satellite orbit (IGSO) satellite are different from those of the MEO satellite, the peculiarities of SS-BSAR with the GEO or IGSO satellite as transmitter are analyzed and then compared with the case of MEO satellite. In order to show the performance difference of SS-BSAR with BeiDou satellites as transmitters, comparisons with other global navigation satellite system (GNSS) transmitters are also made. The theoretical results show that SS-BSAR using BeiDou satellites as transmitters can achieve different sounding performance and can provide some new potential applications compared to other GNSS transmitters.