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With the development of Global Navigation Satellite Systems (GNSS), the multipath effect that was once regarded as one error source has been proven can be used to monitor reflecting surface parameters such as water level, snow depth, vegetation water content, and soil moisture using a technology named GNSS-interferometry reflectomety (GNSS-IR). In order to expand monitoring objects and applications of GNSS-IR, this paper proposed the theory and method to retrieve wind speed using ground-based GNSS-IR. The theory includes the signal-to-noise ratio (SNR) multipath oscillation theory, the scattering model theory, and wave spectrum theory. This paper simulated the mathematical model between the SNR cutoff elevation angle and the wind speed, and used the wavelet analysis to extract SNR cutoff elevation angle and a unified method to unify reference of cutoff elevation angle. Data of HKQT station, located in Hong Kong, during the period of "Mangkhut" and "Hato" were used. The results showed that the variations of GPS L5 SNR cutoff elevation angles had a good corresponding relationship with the measured wind speeds, and the correlation coefficient reached 70%~85%. Also, the variations of cutoff elevation angles can describe the change of wind speed from low wind speed to high wind speed and there was a specific mathematical relationship between them. Finally, this paper discussed two difficulties to overcome in the GNSS-IR wind speed retrieval technology.

The ionospheric scintillation, as one of the astronomical disasters occurring frequently in Arctic regions, poses great challenges to GNSS positioning navigation and timing (PNT) services. This calls for an urgent need in studying and effectively monitoring the scintillation to overcome its adverse impact. With the capability of high frequency sampling, ionospheric scintillation monitoring receivers (ISMR) are usually required to monitor the ionospheric scintillation, but the distribution of ISMR restricts the comprehensive monitoring in larger areas (such as the Arctic region). Therefore, based on GNSS observations with 1 Hz sampling, this paper studies the relevant empirical parameters and methods of extracting the ionospheric scintillation signal from the carrier phase observations by using geodetic detrending, precise point positioning and wavelet transform techniques, to construct a new phase scintillation index, which can be used to monitor the ionospheric scintillation. Its effectiveness and accuracy are verified by 188-day observations from 11 stations provided by the Canadian High Arctic Ionospheric Network (CHAIN). The results show that, compared with the commonly used ROTI index, both the scintillation index proposed in this paper and ROTI can effectively detect the occurrence of ionospheric scintillation, but the scintillation index proposed in this paper has a better correlation with the phase scintillation index given by ISMR, especially during periods with strong ionospheric scintillation, indicating that the proposed scintillation index has better ionospheric scintillation monitoring capability.

In general,ionosphere-free model and uncombined model are applied for GNSS precise point positioning (PPP).This paper detailed analyzes the correlation of different parameters of each model,and deducevarious PPP functional model by means of parameterization methods.And uncombined PPP with ionospheric parameter constrains i.e.ionosphere-weighted model can fasten PPP convergence effectively.This paper takes advantage of GPS-only and GPS and BDS combination dataset as example for positioning in different PPP models.In the perspective of positioning accuracy and convergence time,positioning performance are detailed analyzed in both static PPP and simulated dynamic PPP modes.The results demonstrate that GPS-only has the similar accuracy with GPS+BDS combination,and both ionosphere-free model and uncombined model static PPP can achieve the positioning accuracy of millimeter to centimeter level,while the horizontal positioning accuracy of dynamic PPP is superior to 3 cm and the vertical positioning accuracy is superior to 5 cm.In terms of convergence time,ionosphere-free model is superior to uncombined model,and the convergence time of ionosphere-weighted model is the shortest.Compared to the ionosphere-free model,the ionosphere-weighted model can decrease about 15% convergence time,while it can decrease about 34% convergence time compared to the uncombined model in the dynamic positioning.

Real-time high-precise satellite orbit and clock products are needed in real-time GNSS precise point positioning (PPP). In this paper, Estimation model and strategy of multi-GNSS precise satellite clock integrated resolving are researched and BeiDou/GPS real-time precise clock integrated estimation algorithm is realized by filter. Real-time simulation test results show: the STD accuracy of BeiDou/GPS real-time clock estimated in this paper compared to GFZ multi-GNSS precise clock(GBM) is about 0.15ns; horizontal accuracy after convergence of GPS kinematic PPP using simulation real-time clock products estimated in this paper is better than 5cm and vertical accuracy is better than 10cm, respectively; in BeiDou kinematic PPP test, horizontal and vertical accuracy results are same as the results using GFZ multi-GNSS precise clock(GBM) products, and the decimeter positioning can be realized.

Lunar/Mars rovers own sun sensors for navigation, however, long-time tracking for the sun impacts on the real-time activity of navigation. Absolute positioning method by observing the sun with a super short tracking period such as 1 or 2 minutes is researched in this paper. Linear least squares model of altitude positioning method is deduced, and the ill-posed problem of celestial positioning using the sun is brought out for the first time. Singular value decomposition method is used to diagnose the ill-posed problem, and different bias estimations are employed and compared by simulative calculations. Results of the calculations indicate the superiority of bias estimations which can effectively improve initial values. However, bias estimations are greatly impacted by initial values, because the initial values converge at a line which passes by the real value and is vertical relative to the orientation of the sun. The research of this paper is of some value to application.

Fixing single-satellite GPS carrier phase ambiguity could significantly improve the orbit accuracy of low earth orbit (LEO) satellite. Currently, the CNES/CLS,Wuhan University and CODE have published GPS integer phase clock products applied to single-satellite ambiguity fixing. In this paper,the integer phase clock method is used for single-satellite ambiguity fixing, and it is applied to the precise orbit determination of LEO satellite. Then, the application performances of integer phase clock products provided by different agencies in single-satellite ambiguity fixing and LEO satellite orbit determination are compared and analyzed. For GRACE-FO formation satellites, about 94% ambiguities could be fixed based on different products provided by the three agencies.Orbit solutions generated using the products from the three agencies can achieve an RMS of around 0.9 cm checked by satellite laser ranging data.Compared with ambiguity-float orbit solutions, the accuracy of absolute orbit determination with single-satellite ambiguity fixing is improved by about 30%.After fixing single-satellite ambiguities using the different products provided by CNES/CLS, WHU and CODE, respectively, the RMS of K-band ranging validation residuals for relative orbit solutions are reduced from 5.7、 5.4 and 5.3 mm to 2.1、 2.0 and 1.5 mm, respectively. The results show that the integer phase clock products provided by different agencies have similar performances in the single-satellite ambiguity fixing and orbit determination of GRACE-FO satellite.

Using dual-frequency satellite-borne GPS observations from May 24 to May 30, 2015, the linear combination of Melbourne-Wübbena and ionosphere-free linear combination, based on the basis of precise point positioning technology, the batch least squares estimation method is used to precisely determine the Swarm undifferenced kinematic orbits with different orbital attitudes. The orbit accuracy is assessed using three methods, which include satellite-borne GPS phase observation residuals analysis, comparison with ESA reduced-dynamic orbits and external evaluation with SLR measurements. The results indicate: ①Swarm satellite-borne GPS phase observation residual RMS is in the range of 6~7 mm level. ②Comparisons with reduced-dynamic orbits computed by European Space Agency (ESA), radial, along-track and cross-track orbit difference RMS are in the range of 2~4 cm level. ③Comparisons with kinematic orbits computed by ESA, Radial, along-track and cross-track orbit difference RMS are in the range of 1~2 cm level. ④The external validation with satellite laser ranging (SLR) measurement shows RMS errors are in the range of 3~4 cm level. Therefore, it is feasible to use the undifferenced kinematic orbit determination method and the orbit determination strategy provided in this paper to carry out the precise orbit determination of swarm series satellites. The orbit determination accuracy is centimeter level.

With the increasing number of high orbit spacecraft, the use of high orbit GNSS technology to a certain extent avoids the limitations of traditional ground-based measurement and orbit determination, reduces the operation burden and maintenance cost of ground-based measurement and communication, and improves the autonomous navigation ability and orbit measurement accuracy of the satellite platform. Therefore, GNSS technology has significant research significance and application value for high earth orbit spacecraft. In this paper, the technology development of GNSS used in high orbit spacecraft is reviewed. Compared with low orbit spacecraft, the characteristics of GNSS in high orbit space are analyzed. From the three aspects of high orbit GNSS availability, on orbit technology verification and high sensitive receiver technology, the characteristics and development of high orbit GNSS autonomous navigation technology are summarized. The new tasks of high orbit post precise orbit determination and formation satellite relative navigation are analyzed. From the perspective of the future development of high orbit spacecraft, the future research prospect of high orbit GNSS technology is given.

The BDS triple-frequency carrier phase ambiguity resolution is greatly affected by the residual of atmospheric error between long range stations, and GEO satellites are also unfavorable for carrier phase ambiguity resolution relative to geostationary. Taking advantage of the relatively stable signal path of GEO satellites and the influence of atmospheric delay which do not change with the space position of satellites, the constraint of atmospheric delay errors more in line with actual conditions for GEO satellites are carried out. Using the linear relationship of carrier phases ambiguities of GEO satellites B2 and B3 to reduce the effect of single-difference ionospheric delay error between stationson the ambiguity candidates, the candidates of carrier phases ambiguity of B2 and B3 areselected. The linear relationship of triple-frequency phase ambiguity which does not include the influence of errors makes evaluation of the ambiguity candidates, and the ambiguity search space can be constrained. The ambiguity candidates of the GEO satellites are used to determine the residual change of the ionospheric delay between adjacent epochs, and the parameter estimation of GEO satellites is more constrained in accordance with actual situation.The method of long range BDS triple-frequency carrier phase ambiguity resolution with actual atmospheric delay variation constraints and the integer ambiguity constraints of GEO satellite is studied.And determining the ionospheric delay constraint value by using the candidates of ambiguity between epochs is proposed, adjusting the constraint value of the random walk between GEO satellite according to the actual situation.The experimental results show that the method in this paper can improve the efficiency of the triple-frequency carrier phase ambiguity resolution and the accuracy of positioning.

The method of long range network RTK is the main means to improve the accuracy of real-time kinematic positioning of GPS/BDS. The fast fixing of carrier phase integer ambiguity with GPS/BDS between long range reference stations was significant. The algorithm of multi-frequency carrier phase integer ambiguity resolution with GPS/BDS between long range network RTK reference stations was studied in this paper. The GPS wide-lane ambiguities were fixed by the double frequency observation data of reference station network. And the extra-wide-lane ambiguities of B2 and B3 frequency were fixed by using B2 and B3 frequency observation data at the same time. Then the solution model including GPS double difference carrier phase integer ambiguities and atmospheric errors can be established, the carrier phase integer ambiguity can be fixed by this solution model and the constraint of wide-lane ambiguities. Then the spatial correlation model of atmospheric delay error was established. And the computation model of BDS double difference carrier phase integer ambiguity including atmospheric delay error was established by the extra-wide-lane ambiguities of B2 and B3 frequency. The BDS carrier phase integer ambiguity resolution was constrained by the spatial correlation model of atmospheric errors. Therefore the influence of ambiguities fixing by using ionosphere free observation can be eliminated. The test of the algorithm was carried out by the GPS/BDS data with long range reference station network. The results of experiment indicate that the rapidly fixing of carrier phase integer ambiguity with GPS/BDS between long range reference stations was achieved by this algorithm.

This paper presents a review of the advances, products and applications of lunar photogram-metric mapping using orbital images. It mainly introduces the key techniques such as construction and refinement of geometric models of lunar orbital images, co-registration of lunar orbital image and digital elevation model, optimal selection of multiple images, and large area mapping. Engineering and science applications of lunar photogrammetric mapping products are described, with more emphases on the Chang'E lunar exploration missions. Finally, the future research directions are discussed.

The traditional single-frequency carrier phase smoothing pseudo-range algorithm is prone to divergence and precision degradation due to the influence of ionospheric delay. However, the existing solutions have limited accuracy improvement or need external data support. In this paper, the regularity of ionospheric variation is studied and a regressive model is established. On this basis, a self-modelling algorithm for single-frequency carrier phase smoothing pseudorange with ionospheric delay variation is proposed. The algorithm uses the ionospheric delay information contained in the pseudo-range and carrier observations to model the ionospheric delay, and deducts the ionospheric delay variation between epochs from the smooth pseudo-range, thus effectively avoiding the divergence of the smooth pseudo-range. Carrier smoothing pseudo-range algorithm of ionospheric self-modeling is realized by using GNSSer software. Static and dynamic observation data are used to carry out positioning experiment and precision analysis. The example shows that:① the long period regular Hatch filtering is seriously affected by the ionosphere; ② the precision of the self-modelling ionospheric delay can reach centimeter level, and the linear moving window fitting method is the best in the 30-minute window; ③ self-modeling ionospheric correction can effectively eliminate the influence of smooth pseudo-range ionosphere. With the increase of time window, the precision does not decrease; ④ the proposed algorithm is used for epoch-by-epoch single-frequency smoothing pseudo-range single-point positioning, and the positioning accuracy reaches sub-decimeter level in both static and dynamic NEU directions. In the dynamic positioning test, the horizontal and elevation direction accuracy is 6.25 cm and 10.4 cm, which are 5.4 times and 3.3 times higher than the original pseudo-range respectively.

Celestial positioning is an important method in positioning and navigation, which is widely used in the fields of geodetic astrometry and celestial navigation. The selection of stars in this method affects the accuracy of positioning. At present, there is a lack of research on the optimal selection of stars for the celestial positioning algorithm which determinates longitude and latitude simultaneously. With the improvement of the automation level of observation instruments, the acquisition of observation data becomes more efficient. Therefore, it is necessary to study the optimal selection of stars to achieve the highest accuracy of positioning. Based on the concept of geometric dilution of precision (GDOP) in satellite navigation, this paper studies the influence of the number and distribution of stars in zenith-method on the accuracy of positioning. Finally, the conclusion is verified by the simulation experiment and the measured data. When the statistical characteristic of observation error on zenith distance is fixed, GDOP can be used to describe the effect of star distribution on the accuracy of positioning, and the error of positioning is minimal when the azimuth of stars is uniformly distributed. Considering that the residual error of atmospheric refraction correction of zenith distance of stars with different heights is different, the stars with equal zenith distance and azimuth distributed evenly should be used as far as possible in actual measurement.

By using the theory of infinite series and the Lagrange inversion theorem, the infinite expansions of the auxiliary latitudes in geodesy and cartography with respect to the geodetic latitude are given, which are the power series of the first eccentricity of the reference ellipsoid. The inverse solutions of the isometric and the conformal latitudes can be obtained from the recurrences of a number of known coefficients. The forward expansion of the conformal latitude is proposed on the basis of the Taylor expansion of the Gudermannian function, and the forward expansion of the rectifying latitude is given in which the coefficient can be expressed as a explicit determinant by the division of power series. Compared the coefficients of the auxiliary latitudes expansions at order e0 to e40 with the results by the computer algebra system Mathematica and the corresponding cost time, the algorithm of this paper is verified to be correct and fast. By taking CGCS2000 reference ellipsoid, the numerical experiment is made for the expansions and then the correctness is further proved.

In this paper,the variations of ECOM solar radiation pressure model parameters were analyzed for BeiDou satellites through orbit fitting using 3 years precise ephemeris data. The ECOM parameter selection strategies for the three types of BeiDou satellites were confirmed. Based on the satellite attitude control modes,satellite illumination was theoretically analyzed. We pointed out that solar panels are perpendicular illuminated,and then solar radiation pressure has the periodic component associated with the orbital period when satellite is at orbit-normal attitude control mode. Periodic parameters of D direction need to be added to enhance the ECOM 5 parameters. Orbit determination tests were carried out using MGEX global network data. Tests prove that using ECOM 7 parameters the orbit overlap accuracy improvement could reach up to 50%~80%.

A rapid and efficient orbit numerical integration algorithm with high accuracy is needed in multi-GNSS rapid precise orbit determination. In order to improve the compute efficiency, an adaptive step-changed Admas integration method and a synchronous integration algoritm for multi-GNSS satellites are developed in this paper. To validate the precision and efficiency of the proposed method, the multi-GNSS precise orbit products calculated by Wuhan University (WHU) and Center for Orbit Determination in Europe (CODE) are used for orbit fitting. Results show that, the average 3DRMS of GPS, GLONASS, BDS and Galileo satellites are all below 20 mm. Comparing with the traditional step-fixed orbit integraion method applied for each satellite separately, the computational efficiency of the proposed method is improved significantly:without damaging the accuracy, it takes only 0.09 s for a single satellite, which is 14 times faster than the traditional method. Besides, further improvement can be achieved when the number of satellites is increased.

Ionospheric delay correction is the core issue of LEO satellite single-frequency precise orbit determination. At present, "the method of ionosphere scale factor" is mainly adopted in the LEO satellite ionospheric delay correction, but the method doesn't consider the electron density peak height along with the variation of factors, such as latitude and longitude, day and night, seasons, solar activity, etc. IRI2012 model while considering the influence of the above factors on the electron density peak height, but because of the height criteria inconsistent with ionosphere single layer model, there is usually a systematic deviation and can't be used directly. Therefore, this paper puts forward to an improved ionospheric delay correction method, the ionosphere thin layer height as the constraint condition of IRI2012 model of electron density peak height of the mean parameter estimation. Based on Swarm satellite single-frequency observation data, the effectiveness of the method was verified. The results showed that: with the improved model of the ionosphere, the precision of Swarm satellite obit radial, tangential and normal was improved in varying degrees, especially for the radial and normal most obviously, improved on average by 31.6% and 32.0%, respectively. At the same time, the systemic deviation of the orbit reduced significantly, especially for the radial and normal, reduced on average by 65.0% and 54.7%, respectively.

Ionospheric delay is a major problem in the process of ambiguity resolution over medium and long baselines that the time consuming is barely satisfactory and the success rate is not high. This paper proposes a new ambiguity resolution method which combines the RNSS and RDSS observations of BeiDou to reduce the ionospheric delay. Firstly, two optical virtual observations with small total noise level and ionospheric delay coefficient are selected by analyzing the RNSS and RDSS combination signals. Then, the NL integers of GEO are solved using geometry-independent and ionosphere-free model which are formed by new virtual observations. Finally, the NL integers of non-GEO are solved with known GEO NL integers. This method is verified using simulated data. Test results show that, the new method has higher success rate and less consuming time compared with traditional method.

GNSS precise point positioning (PPP) has become the research hotspot in the most recent years due to its capability of obtaining precise position with single receiver. Usually, three models are used in PPP, that is,uncombined model, Uofc model and ionosphere-free combination model. The relationships between the these models are described in detail in this paper. On the one hand, it is clarified that the uncombined model is equivalent to the Uofc model and both of them are better than the ionosphere-free model in the sense of ambiguity resolution. On the other hand, in comparison with the Uofc model that eliminates the ionosphere delay by using the equivalence principle, the uncombined model that takes the ionosphere delay as the parameter has its advantage that it can provide the users with the prior constrained conditions for the ionosphere. As a result, the model can be converted to the ionosphere-weighted model easily. In the circumstance of fixing the wide-lane, when comparing with the ionosphere-free model by using ambiguity dilution of precision (ADOP) from the aspect of fixing ambiguity, Uofc model has many advantages such as small noise, origin information preserving etc.,while the ionosphere-weighted model can improve the ambiguity resolution significantly when the high precise prior ionosphere information is available.

A kind of single-frequency precise point positioning (PPP) algorithm based on the raw observations is presented in this paper. By this algorithm, the ionospheric delays were corrected efficiently by means of adding the ionospheric delay prior information and the virtual observation equations with the spatial and temporal constraints, and they were estimated as the unknown parameters simultaneously with other positioning parameters. Then, a dataset of 178 International GNSS Service (IGS) stations at day 72 in 2012 was used to evaluate the convergence speed, the positioning accuracy and the accuracy of the retrieved ionospheric VTEC. The series of results have shown that the convergence speed and stability of the new algorithm are much better than the traditional PPP algorithm, and the positioning accuracy of about 2-3 cm and 2-3 dm can be achieved respectively for static and kinematic positioning with the single-frequency observations' daily solution. The average bias of ionospheric total electron content retrieved by the single-frequency PPP and dual-frequency PPP is less than 5 TECU. So the ionospheric total electron content can be used as a kind of auxiliary products in GPS positioning.

Solar radiation pressure (SRP) model is the basis of high precise orbit determination and positioning of navigation satellites. At present, it is not uncommon for the study of SRP model of BDS satellite. However, the establishment and application of comprehensive analytical SRP model based on satellite physical parameters are rare. Different from other conservative force and non-conservative force, SRP is closely related to the satellite's physical parameters and in-orbit state, which has obviously individual differences. On the basis of the physical mechanism of solar radiation, BDS satellite physical parameters, in-orbit attitude control mode, and so on, comprehensive analytical model has been modeled in this paper. Based on precise ephemeris and laser ranging data, the precision of comprehensive analytical model has been verified. And the precision of orbit determination is decimeter using this comprehensive analytical SRP model. According to the satellite conservation theorem of angular momentum and change of in-orbit telemetry parameters, the difference between comprehensive analytical model and actual in-orbit interference force has been analyzed and calculated. The addition of empirical items on the comprehensive analytical model has been proposed in section 4. Taking C08, C10 satellite of BDS as an example, the precision of satellite laser ranging (SLR) checking precision of them is 0.078 m and 0.084 m respectively. Compared with using the improved CODE empirical model, precision orbit accuracy of them has increased by 0.021 m and 0.045 m respectively.