For the second Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-2) Global Positioning System radio occultation (GPS RO) neutral atmosphere retrieval, ionosphere error correction on bending angle is performed by combining either L2C or L2P signals with L1 at the University Corporation for Atmospheric Research (UCAR), Boulder, CO, USA. While the L2C is a civil signal, the encrypted L2P signal from high-noise occultations will lead to low-accuracy bending angle profiles. This study distinguishes high-noise COSMIC-2 L2P occultations using the L2P signal-to-noise ratio (SNR) and proposes an alternative ionosphere correction method by fitting and extrapolating the difference between the L1 bending angle and the bending angle derived from the MSIS 00 model above 35 km (${\alpha }_{\text {L1+M}}$). Statistical validations are performed based on over 110159 L2P occultations from January 2023 to June 2023. The comparison of$ {\alpha }_{\text {L1+M}}$and L1 and L2P bending angle, derived from L2P occultations with SNR below 200 v/v (${\alpha }_{\text {{L}1}+{\text {ML}}}$and${\alpha }_{\text {{L}1+L}{2}{\text {PL}}}$), shows that the percentage passed quality control increased from 40.8% (39.5%) to 73.6% (69.0%) for rising (setting) occultations. The mean standard deviation (SD) of${\alpha }_{\text {L1+M}}$is 2.0% (1.9%) on impact heights between 19 and 30 km for rising (setting) occultations, which is obviously smaller than 2.6% (2.5%) for${\alpha }_{\text {L1+L2PL}}$profiles. Hence, it can be concluded that the proposed ionosphere correction method can be utilized for retrieving COSMIC-2 L2P occultations, and combined with L2P high SNR occultations, the COSMIC-2 L2P occultations can further enrich the amounts of effective profiles on numerical weather prediction (NWP) and climate research.

This paper introduces the Chinese Tianmu-1 GNSS-R constellation of 22 small satellites launched in 2023–2024 and comprehensively evaluates the latest version of the in-orbit data. First, the mission design and instrument technology are described, which largely builds on the Fengyun-3/GNOS-II missions. Notable innovations include full-GNSS compatibility and dual-polarization antenna. Then, the spatiotemporal characteristics of the constellation are analyzed—specifically, coverage percentage and mean revisit time at different latitudes. Next, the accuracy of its science products including ocean surface winds and land soil moisture has been assessed, with two application cases demonstrating the mission’s utility for monitoring tropical cyclones and flooding. Finally, this paper for the first time evaluates Tianmu’s polarized observations including Horizontal (H), Vertical (V), Left-Hand Circularly-Polarized (LHCP) and Right-Hand Circularly-Polarized (RHCP). Analysis of the signal-to-noise ratio and reflectivity shows that the dual-polarimetric observations follow the trend of theoretical models and hold promise for advancing land remote sensing.

Based on the daily measured data of meteorological stations and the reanalysis data of forecast factors, a statistical downscaling and a decision tree model were used to predict the future change of extreme climate index in the Yellow River Delta region of China, and the two models’ performance were compared. The results showed that the decision tree was more accurate in predicting extreme climate at regional scale than those of the statistical downscaling model.

Global Navigation Satellite System Reflectometry (GNSS-R) is a burgeoning remote sensing observation technology that can retrieve global sea surface wind speeds using satellite signals reflected from the sea surface. The improvement of data quality and the accumulation of data volume of this technology provides data support for constructing interdisciplinary-based retrieval models. This article constructs a hybrid deep neural network model based on deep learning for wind speed retrieval, which can receive and perform feature mining on the entire delay waveform while simultaneously supporting multiple auxiliary features input and achieving joint fitting. Then a bias correction method based on cumulative distribution function (CDF) matching is introduced to mitigate bias, especially at high wind speeds. We verify the contribution of different attribute features in wind speed retrieval by designing a feature ablation analysis. The fluctuation variation of the retrieval accuracy in the time dimension and the retrieval results distribution in space are compared and analyzed. The root mean square error (RMSE) of retrieval results is 1.486m/s and can reach 1.399m/s under the 94.25% wind speed condition. After bias correction based on CDF matching, the retrieval accuracy at high wind speed is improved by 7.19%. Besides, this model also has good temporal stability and can reproduce large-scale wind fields while effectively mitigating retrieval bias on a global scale, showing great potential for operational applications.

In order to analyze the relationship between the waterbirds spatial distributions and climate change, Statistical Downscaling Model (SDSM) and Maximum Entropy model have been applied here to predict the future climate change and future spatial distributions of waterfowls in Xianghai. The results show that in the next four periods, the average temperature in Xianghai will be increasing year by year; daily precipitation will be more concentrated in summer and will be significantly reduced in spring and autumn; sunshine hours will continue to increase, resulting in lower humidity and drier climate. With the exception of Larus argentatus, the overall area of Tadorna ferruginea, Vanellus vanellus and Anas crecca has decreased, shrinking toward the center in the future.

The GNOS (GNSS Occultation Sounder) is the China's second GNSS (Global Navigation Satellite System) radio occultation payload for atmospheric and ionospheric sounding onboard FY-3D (Fengyun-3D) satellite meteorological satellite, which was launched on November 15th2017. This paper presents the technical characters of flight module manufactured by National Space Science Center (NSSC), Chinese Academy of Sciences, and the on-orbit performance of the FY-3D GNOS instrument. Firstly, we show the main technical parameters, including constellations and frequencies, position and occultation antenna gain, channel number, clock stability and so on. The on-orbit test result of the carrier phase accuracy and the precise orbit determination is shown. Meanwhile, the ability of occultation events received per day and the preliminary reversion accuracy are introduced in this paper.

Global Navigation Satellite System Occultation Sounder II (GNOS II) is an integrated GNSS remote sensing instrument which combines POD (Precise Orbit Determination), GNSS Radio Occultation (GNSS-RO) and GNSS Reflectometry (GNSS-R). It will provide more and higher quality radio occultation data and new reflected GNSS signal Delay Doppler Mapping (DDM), compared with its predecessor GNOS which were used in FY3C and FY3D satellites. GNOS II will be used on-board FY3E satellite since 2020 to monitor the ionosphere, neutral atmosphere, sea wave and wind field of earth. This paper presents the latest status and progress of Fengyun-3E GNOS II mission. Main features and parameters of the GNOS II , especially the improvements during the development of the GNOS II Flight Model, are illustrated.

Global Navigation Satellite System (GNSS) Radio Occultation measurements can remote sensing Earth's neutral atmosphere and ionosphere. Meanwhile, another GNSS remote sensing technique named GNSS Reflectometry (GNSS-R) has been developed rapidly, which can retrieve sea surface wind speed. The GNSS Occultation Sounder (GNOS) II instrument has been designed to integrate these two GNSS remote sensing techniques in one payload of the third batch FengYun-3 (FY-3) satellites. This paper presents the advancements in research of GNOS II and instrument performance. The qualified module of GNOS II has been manufactured by National Space Science Center (NSSC), Chinese Academy of Sciences. We show that the phase center variety is low enough for the new designed precise orbit determination (POD) antenna to increase the accuracy of precise orbit determination. A wide coverage atmosphere occultation antenna and a 65nm technics ASIC are used in the new generation GNOS instrument. As an important improvement, the GNOS II can generate Delay Doppler Maps (DDMs) of GNSS signals scattered from the ocean surface. The result of test shows that the GNOS II instrument has high performance in precision of code, carrier phase and real-time navigation.

The Global Navigation Satellite System (GNSS) radio occultation (RO) observation data is widely used for numerical weather prediction (NWP) and global climate monitoring (GCM). However, the residual higher-order ionospheric error (RIE) can still be significant. To further mitigate the RIEs, characterization and quantification of RIEs in bending angles have been performed by using end-to-end simulations. In this study, the seasonal characteristics of the RIEs in bending angles were analyzed by using larger ensembles of profiles from end-to-end simulations. The results indicated that the RIE is a major source of the bending angle in lower mesosphere and upper stratosphere (LMUS), and its bias has a clear negative tendency that in line with our previous studies. The preliminary analysis showed that, globally the average bias and standard deviation of RIEs changed slightly, while regionally they changed obviously. For the northern hemisphere middle latitude (NHM) region, the largest average bias and standard deviation of RIEs happened in summer, while the smallest ones happened in winter. This study helps to inform future RIE mitigation schemes for ensuring benchmark quality stratospheric RO data.

GNOS is a scientific instrument for monitoring the Earth's neutral atmosphere and ionosphere. It provides vertical profiles of atmospheric temperature, pressure and humidity, as well as ionospheric electron density. GNOS is one of the important payloads on Fengyun3-D low-earth orbit satellite launched at November 15th2017, and began to work on November 25th2017. GNOS on FY3-D improved a lot in both function and performance compared with GNOS on FY3-C satellite that had been launched in September 2013. This paper introduces the FY3-D GNOS's improvements compared with FY3-C GNOS, and describes the expected results of FY3-D GNOS. In-orbiting validation is ongoing, and the assessment of the FY3-D GNOS will be finished in the first half of next year. Preliminary results will be given in the conference.

The remote sensing technique using X band and K band microwave signals between two Low-Earth-Orbit(LEO-LEO) satellites can characterize atmosphere temperature, humidity and pressure from low troposphere up to mesosphere without auxiliary background information. This paper firstly introduces the principle of the technique and then our LEO-LEO occultation system is presented. To achieve demanded amplitude and phase measurement precision, the structure and features of the LEO-LEO receiver are introduced. The transmitter and receiver have been basically completed. The ground test will be done within a few months.

Since Global Navigation Satellite System (GNSS) signals were not designed for remote sensing, GNSS Reflection (GNSS-R) signals from the earth surface are so weak, especially for space borne GNSS-R receiver cases, which limits its application for earth surface remote sensing. To achieve stronger GNSS-R signals, this thesis analyzed the effect of GNSS Left-Hand Circularly Polarized (LHCP) antenna's central beam direction on the ocean reflected signals' SNR around Specular utilizing GREEPS simulator. It was found that the available maximum SNR and the corresponding incident angle was varied when the LHCP's central beam direction was different. The greatest maximum SNR was available when central beam direction's nadir off-pointing was 26° and the corresponding incident angle was 32° .The added SNR compared with the case with central beam direction's nadir off-pointing being 0° and the corresponding incident angle being 4° was more than 3 dB.

GOPA is a radiation hardened GNSS baseband ASIC produced on the 65 nm 7-layer metal process technology. GOPA is capable of processing signals from GPS and BDS. A lot of lab tests had been carried out after tape-out of GOPA. The experiment results showed that the performances of GOPA were in good agreement with the design goals, the TID, SEL and SEU of the ASIC fulfilled the design requirements. GOPA will be used in the following GNOS series. The first flight of GOPA on GNOS series will be in 2018.

In Global Navigation Satellite System Radio Occultation (GRO), the tropospheric temperature and humidity can only be retrieved separately from refractivity by co-using a priori humidity or temperature information. Fortunately, the LEO-LEO (Low Earth Orbit) microwave occultation (LMO) exploits both the refraction and absorption of signals to solve the temperature-humidity ambiguity, and so it can retrieve the pressure, temperature, and humidity profiles independently. Furthermore, using LMO, ozone profiles can be retrieved by the signals around ozone absorption lines, and the liquid water and ice cloud variables can also be retrieved as by-products. In this paper, the measurement principle and capabilities of LMO technique are provided as an overview based on available literature; and then a pre-study of LMO including orbit design, frequency channels selection, performance analysis, and transmitter and receiver design/development is presented. The encouraging performance prospects of LMO give us confidence that it is highly worthwhile to pursue a space-borne demonstration mission.

Global Navigation Satellite System (GNSS) Occultation Sounder (GNOS) instruments were designed for the FengYun-3 (FY-3) series of meteorological satellites for sounding the Earth's atmosphere and ionosphere by radio occultation. Meanwhile, another GNSS remote sensing technique named GNSS reflectometry (GNSS-R) has been developed rapidly as well. To integrate these two GNSS remote sensing techniques in one payload, to help save the satellite's space, power and mass, a new instrument named GNOS II has been designed for the FY-3E satellite. The FY-3E satellite is anticipated to monitor the ionosphere, neutral atmosphere, sea wave and wind field by using GNSS signals in the future. So far, these two functional modules have been validated by ground-based, airborne or space-based campaigns. The GNOS II configuration and main performances characteristics are presented in this paper. According to its demonstrated performance, one can draw the conclusion that GNOS II will provide more and higher quality radio occultation data and new reflected GNSS signal delay Doppler maps (DDMs) for sea wave and wind field detection.

In order to understand the space-borne GNSS Reflection (GNSS-R) performance, an end to end simulator named GREEPS (GNSS-R End-to-End Performance Simulator) was developed by National Space Science Center (NSSC), Chinese Academy of Sciences. The simulator consists of four functional modules: Mission analysis module, forward modeling module, observation system modeling module and inversion/retrieval and precision Analysis module. This paper introduces each module's structure and capabilities. The preliminary simulation results are shown, including average and maximum number of simultaneously reflected GNSS satellites for 24 hours, coverage ratio between the ± inclination of LEO for 24 hours, the sensitivity of Delay Doppler Map (DDM) to the wind field, and wind field and ocean altimetry retrieval precision analysis. GREEPS is a powerful and useful simulation software for space-borne GNSS-R mission and payload design, it will speed up the space-borne GNSS-R applications in China.

The GNOS instruments are GNSS radio occultation payloads for atmospheric and ionospheric sounding onboard FY-3 meteorological satellites. The first GNOS instrument has been in orbit since September 23, 2013 when the FY-3C satellite was launched. The next generation GNOS instrument is being developed for the 3rd batch of FY-3 series satellites. This paper presents the new instrument's characteristics in design and main performance in occultation tracking. We show that the phase center variety is low enough for the choke-ring antenna new designed to increase the accuracy of precise orbit determination. A wide coverage atmosphere occultation antenna and a 65nm technology ASIC are used in the new generation GNOS instrument. The new GNOS instrument will acquire higher quality occultation data due to its better performance.

With the development of global navigation satellite system (GNSS) remote sensing, radio occultation (RO) has become an important atmospheric observation technique that mainly be used for numerical weather prediction (NWP) and global climate monitoring (GCM). However, residual ionopheric error (RIE) can still be significant after an ionospheric error elimination by linear combination of dual-frequency RO bending angles. Lots of quantification and analysis of RO bending angle RIEs has been conducted by using quasi-realistic end-to-end simulations. In this study, the RIEs in RO observations have been investigated by comparative analysis of COSMIC RO measurements and ECMWF model data. The results illustrate that the RIE is a major source of the bending angle in lower mesosphere and upper stratosphere, and its bias has a clear negative tendency that in line with our empirical studies based on simulation RO data. This study helps to inform future RIE mitigation schemes for ensuring benchmark quality stratospheric RO data.

GNOS (GNSS Occultation Sounder) is an instrument developed by National Space Science Center (NSSC), Chinese Academy of Sciences. It was first successfully launched in September 23, 2013, as a payload of FY3C. More than 700 occultation events were received every day. The modified GNOS will also be on-board the FY3D satellite scheduled to launch in 2016. It contains three major improvements including increasing occultation channel numbers, employing open loop tracking on GPS L2C and Compass B1I and improving the gain of the antenna. In order to confirm the performance of GNOS instrument, a mountain-based experiment was carried out in China's Hebei Province on Mt. Wuling (40.598°N, 117.478°E) from June 16thto June 18th, 2015. By analyzing the experimental data, the performance of open-loop tracking on GPS L2C and Compass B1I was well validated.

Global Navigation Satellite System Reflectometry (GNSS-R) was regarded as a promising way to observe atmospheric duct by utilizing low elevation angle ocean surface reflected signals. To invest the Delay maps' feature of low elevation angle reflected signals in the atmospheric duct, a shipborne GNSS-R campaign was conducted in July, 2015 by the scientific investigation ship called Shiyan 3 on the South China Sea. During the campaign, the atmospheric temperature, pressure, and relative humidity which were used to detect atmospheric duct were recorded by GPS radiosondes and meteorological recorder. The GNSS-R payload developed by National Space Science Center (NSSC) and fixed on the rail of Shiyan3 was used to generate Delay maps. Preliminary results showed that atmospheric duct, especially evaporation duct, existed almost all the time in the experimental ocean region. Ocean surface reflected signals with elevation angle less than 10° were received and formed delay maps successfully. Affected by the direct signal and specular reflected signal's strong interference, apparent code correlation peaks appeared on Delay maps' tail. The experimental values of correlation peaks and simulated code autocorrelation were synthetically used to fit the curve of direct signal and specular reflected signal's strong interference utilizing the least square method. After removing the interference, cleaner reflected signals without direct and specular reflection signals were obtained.

This paper presents the error characteristics of MSISE-90, and data analysis is performed using statistical comparison. In this experiment, the absolute error, root mean square error and standard deviation of temperature and pressure for each month, latitude and geometric height are calculated, and the curve of annual global error characteristics is obtained at the same time. The result shows that there are obvious monthly periodic variations of the temperature and pressure error data. The annual global error increases with height: the annual global error of temperature is more than 3% at the height of 70km, while the annual global error of pressure is more than 15% at the same height. This article get a detailed monthly and annual average error characteristics of MSISE-90 model, which lay the foundation for using MSISE-90 model as a priori background field in the accurate processing of remote sensing data.