Accurate acquisition of uncrewed aerial vehicle (UAV) altitude relative to the ground is essential for applications such as aerial mapping and precision agriculture. Although global navigation satellite system reflectometry (GNSS-R) has demonstrated potential for airborne altimetry, its deployment on UAV platforms is limited by payload and power constraints. To the best of our knowledge, this study presents the first miniaturized GNSS-R receiver specifically developed for UAV platforms that supports real-time altimetry. The system enables 5 Hz height inversion with low power consumption and rapid response. A real-time correction framework is implemented to reduce motion-related errors. System performance was evaluated through static and dynamic experiments. The static reservoir water level (WL) test achieved a root-mean-square error (RMSE) of 16.67 cm, while dynamic UAV experiments over a land-based bare soil surface yielded an RMSE of 1.825 m, with retrieval precision improving at higher flight altitudes and degrading at lower altitudes due to waveform aliasing effects. These results demonstrate the reliability and feasibility of the proposed system for UAV-based real-time airborne altimetry, particularly in applications requiring rapid deployment and operational flexibility, such as emergency surveying and environmental monitoring.

This article introduces the Chinese Tianmu-1 Global Navigation Satellite System Reflectometry (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 (CP) 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 (TCs) and flooding. Finally, this article, 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 (SNR) and reflectivity shows that the dual-polarimetric observations follow the trend of theoretical models and hold promise for advancing land remote sensing.

The spaceborne global navigation satellite system reflectometry (GNSS-R) is an emerging GNSS-based passive remote sensing technique, it has become a heated topic around the world in recent years. One type of the direct observables of the spaceborne GNSS-R is the delay-Doppler map (DDM). However, the DDM is often affected by L-band interference from Earth’s surface, due to increasing congestion of frequency spectrum and intensification of geopolitical conflicts. Consequently, this paper proposes a spaceborne GNSS-R DDM-based L-band interference suppression method to remove L-band interference components as much as possible from the spaceborne GNSS-R DDM. Several typical examples based on spaceborne GNSS-R DDM data from Chinese FY3E satellite are presented. Extensive and in-depth analysis requires further discussions and future work.

Sea surface height (SSH) serves as a fundamental geophysical parameter in oceanographic research. In 2023, China successfully launched the world’s first spaceborne interferometric GNSS-R (iGNSS-R) altimeter, which features dual-frequency multi-beam scanning, interferometric processing, and compatibility with three major satellite navigation systems: the BeiDou Navigation Satellite System (BDS), the Global Positioning System (GPS), and the Galileo Satellite Navigation System (GAL). This launch marked the first in-orbit validation of the iGNSS-R altimetry technology. This study provides a detailed overview of the iGNSS-R payload design and analyzes its dual-frequency delay mapping (DM) measurements. We developed a refined DM waveform-matching algorithm that precisely extracts the propagation delays between reflected and direct GNSS signals, enabling the retrieval of global sea surface height (SSH) through the interferometric altimetry model. For validation, we employed an inter-satellite crossover approach using Jason-3 and Sentinel-6 radar altimetry as references, achieving an unprecedented SSH accuracy of 17.2 cm at a 40 km resolution. This represents a breakthrough improvement over previous GNSS-R altimetry efforts. The successful demonstration of iGNSS-R technology opens up new possibilities for cost-effective, wide-swath sea level monitoring. It showcases the potential of GNSS-R technology to complement existing ocean observation systems and enhance our understanding of global sea surface dynamics.

The spatial–temporal sampling errors arising from the differences in geographical locations and measurement times between co-located Global Navigation Satellite System (GNSS) radio occultation (RO) and radiosonde (RS) data represent systematic errors in the three-cornered hat (3CH) method. In this study, we propose a novel spatial–temporal sampling correction method to mitigate the sampling errors associated with both RO–RS and RS–model pairs. We analyze the 3CH processing chain with this new correction method in comparison to traditional approaches, utilizing Fengyun-3E (FY-3E) GNSS Occultation Sounder II (GNOS II) RO data, atmospheric models, and RS datasets from the Hailar and Xisha stations. Overall, the results demonstrate that the improved 3CH method performs better in terms of spatial–temporal sampling errors and the variances of atmospheric parameters, including refractivity, temperature, and specific humidity. Subsequently, we assess the error variances of the FY-3E GNOS II RO, RS and model atmospheric parameters in China, in particular the northern China and southern China regions, based on large ensemble datasets using the improved 3CH data processing chain. The results indicate that the FY-3E GNOS II BeiDou navigation satellite system (BDS) RO and Global Positioning System (GPS) RO show good consistency, with the average error variances of refractivity, temperature, and specific humidity being less than 1.12%2, 0.13%2, and 700%2, respectively. A comparison of the datasets from northern and southern China reveals that the error variances for refractivity are smaller in northern China, while temperature and specific humidity exhibit smaller error variances in southern China, which is attributable to the differing climatic conditions.

Based on delay-Doppler maps (DDMs) in raw counts generated by spaceborne global navigation satellite system reflectometry (GNSS-R) receivers, retrieving ocean surface wind speeds is feasible, so several spaceborne GNSS-R missions have been carried out. However, it is currently troubled by global data latency of several hours or even more due to the bottleneck in the satellite downlink. Consequently, this article, for the first time, presents an algorithm for spaceborne GNSS-R receivers to conduct the DDM calibration in orbit and then to retrieve ocean surface wind speeds in real time, which contributes to not only lightening the burden on downloading a wealth of scientific data but also broadcasting real-time ocean surface wind speeds to users. Since there is a power correlation between direct and reflected signals from the same GNSS satellite with respect to the GNSS-R receiver, this algorithm calibrates direct signal power first, and then it estimates the real-time GNSS transmitter effective isotropic radiated power at the reflected signal according to the normalized antenna pattern of the corresponding GNSS satellite. Afterward, DDMs in raw counts are calibrated. Finally, ocean surface wind speeds are computed using pretrained geophysical model functions. Exploiting the scientific data from the GNOS-II onboard China's FY-3E satellite, this algorithm is validated carefully, and final retrieved ocean surface wind speeds against collocated European Centre for Medium-Range Weather Forecasts wind speeds have an overall root-mean-square error of 1.68 m/s and 1.50 m/s for GPS-R and BDS-R, respectively.

Reflected global navigation satellite system (GNSS) signals from Earth surface can be received by receivers at low Earth orbit for the remote sensing of geophysical parameters. While the technique has been studied for around 30 years, most early spaceborne GNSS reflectometry missions only adapted to receive GPS signals and the studies of reflected Galileo (GAL) signals in space are limited. The Navigation Satellite System Occultation Sounder II (GNOS-II) payload onboard the FY-3E satellite is the first mission that can operationally receive reflected GPS, BeiDou (BDS), and GAL signals at the same time. This letter presents the GAL reflectometry measurements from GNOS-II together with their calibration and wind speed (WS) retrieval methods. Results show that while GAL has a different signal modulation, the observables can be used to retrieve WSs using the same geophysical model functions (GMFs) of GPS after a dedicated calibration. The retrieved WSs from GAL also have a comparable accuracy as those from GPS and BDS.

Copper (Cu) is essential for plant growth and development. IRON MAN (IMA) is a family of small peptides that can bind both iron (Fe) and Cu ions. It was reported that IMAs mediate Fe homeostasis in Arabidopsis thaliana. However, it remains unclear whether IMAs are involved in Cu homeostasis. The transcript abundance of IMA genes decreased in response to Cu deficiency. The combined disruption of all IMA genes caused enhanced tolerance to Cu deficiency and resulted in an increase in the transcript abundance of Cu uptake genes, whereas the overexpression of IMA1 or IMA3 led to the opposite results. Protein interaction assays indicated that IMAs interact with Cu-DEFICIENCY INDUCED TRANSCRIPTION FACTOR1 (CITF1), which is a positive regulator of the Cu uptake genes. Further studies showed that IMAs not only interfere with the DNA binding of CITF1 but also repress the transcriptional activation activity of CITF1, hence resulting in downregulation of the Cu uptake genes. Genetic analyses indicated that IMAs modulate Cu homeostasis in a CITF1-dependent manner. Our findings indicate that IMAs inhibit the functions of CITF1 in regulating Cu deficiency responses, thereby providing a conceptual framework for comprehending the regulation of Cu homeostasis.

Objectives: Using global navigation satellite system（GNSS） reflectometry（GNSS-R） signal to do remote sensing research has become a hotspot in recent years. We has simulated Fengyun 3 E the Ⅱgeneration of GNSS occultation sounder（GNOSⅡ） GNSS-R parameters, which includes the average number of specular points,the maximum number of specular points,the average distance of specular point（SP）-GNSS,the average distance of SP-low Earth orbit（LEO）,the average path lost,the average incident angle on LEO and the average reflected angle on SP.Methods:The relationships between these simulated parameters and antenna parameters（antenna angle, beam width, and inclination direction） are analyzed, and the corresponding results are demonstrated using snow flake method.Results: Through the statistical analysis results, It can be easily learned the conclusion that the beam width has the maximum influence on all of these antenna observations, the antenna angle is the second, and the inclination direction has the minimum influence.Conclusions:The snow flake method mentioned is able to provide a new method for data analysis of GNSS-R especially space-borned ones, and may help to clear some obstacles which obstruct the successful development of corresponding payloads.

The reflected GNSS signals at the L-band is significantly advantageous in soil moisture monitoring as they are sensitive to the dielectric properties determined by the volumetric water content of topsoil, and they can penetrate vegetation, except in very dense forests. The Global Navigation satellite system Occultation Sounder (GNOS-II) with a reflectometry technique onboard the Fengyun-3E (FY-3E) satellite, launched on 5 July 2021, is the first mission that can receive reflected Global Navigation Satellite System (GNSS) signals from GPS, BeiDou and Galileo systems. This paper presents the soil moisture retrieval results from the FY-3E GNOS-II mission using 16 months of data. In this study, the reflectivity observations from different GNSS systems were firstly intercalibrated with some differences analyzed. Observations were also corrected by considering vegetation attenuation for 16 different land cover classifications. Finally, an empirical model was constructed for volumetric soil moisture (VSM) estimation, where the reflectivity of GNOS-II was linearly related to the SMAP reference soil moisture for each 36 km ease grid. The overall root-mean-square error of the retrieved soil moisture is 0.049 compared with the SMAP product, and 0.054 compared with the in situ data. The results of the three GNSS systems show similar levels of accuracy. This paper, for the first time, demonstrates the feasibility of global soil moisture retrieval using multiple GNSS signals.

The Global Navigation Satellite System Occultation Sounder II (GNOS-II) payload onboard the Chinese Fengyun-3E (FY-3E) satellite is the world’s first operational spaceborne mission that can utilize reflected signals from multiple navigation systems for Earth remote sensing. The satellite was launched into an 836-km early-morning polar orbit on 5 July 2021. Different GNSS signals show different characteristics in the observations and thus require different calibration methods. With an average data latency of less than 3 h, many near real-time applications are possible. This article first introduces the FY-3E/GNOS-II mission and instrument design, then describes the extensive calibration methods for the multi-GNSS measurements, and finally presents application results in the remote sensing of ocean surface winds, land soil moisture and sea ice extent. Especially, the ocean surface wind product has been used in operational applications such as assimilation in the numerical weather prediction model and monitoring of tropical cyclones. Currently, GNOS-II has been carried by FY-3E, FY-3F (launched in August 2023) and FY-3G (launched in April 2023). It will be also carried by future follow-on FY series and a more complete multi-GNSS reflectometry constellation will be established.

The FengYun-3E Global Navigation Satellite System (GNSS) occultation sounder II (FY-3E GNOS II) was launched on 5 July 2021. For the first time, based on the new GNOS II sensor, this mission realizes radio occultation (RO) and reflectometry observations using the navigation signals from the third-generation BeiDou System (BDS-3), and it is hence important to assess and analyze the BDS-3 remote sensing performances relative to other systems. Here, we assessed FY-3E GNOS II RO atmospheric retrievals by inter-comparing with corresponding data from the NCEP FNL global atmospheric analysis and FY-3D GNOS mission. The GNOS RO data quality and consistency of the different FY-3 meteorological satellites, i.e., FY-3D and FY-3E, as well as different GNSS systems (GPS, BDS-2, BDS-3) were analyzed. We find that the FY-3E GNOS II RO data exhibit better quality than FY-3D GNOS, particularly in the number, penetration height toward surface, and global coverage by BDS RO profiles, due to the integration of BDS-2 and BDS-3. Additionally, comparing with co-located NCEP FNL analysis profiles, the mean difference (and standard deviation) of the FY-3E GNOS II RO atmospheric refractivity profile retrievals is found to be smaller than 0.2% (and 1%), in the upper troposphere and lower stratosphere, from 5 to 30 km, and remains consistent at this accuracy and precision level with the FY-3D GNOS RO data. These features provide clear evidence for a high utility of the new GNOS II RO data for weather and climate research and applications.

The vigorous development of the global navigation satellite system (GNSS) has led to a boom in GNSS radio occultation (GNSS RO) and GNSS reflectometry (GNSS-R) techniques. Consequently, we have proposed an innovative signal processing scheme for spaceborne integrated GNSS remote sensors (SIGRS), combining a GNSS RO and a GNSS-R module. In the SIGRS, the GNSS-R module shares one precise orbit determination (POD) module with the GNSS RO module, and the GNSS-R module first achieves compatibility with GPS, BDS, and Galileo. Moreover, the programmable non-uniform delay resolution was introduced and first used by the SIGRS to generate the output DDM, which achieves a high delay resolution in the DDM central region around the specular point to improve the accuracy of basic observables but requires fewer delay bins than the conventional DDM with uniform delay resolution. The SIGRS has been successfully used to design the GNOS II onboard the Chinese FY-3E satellite, and the results of in-orbit operation validate the performance of the SIGRS, which means the SIGRS is an economically and technically efficient design and has become the first successful signal processing scheme for spaceborne integrated GNSS remote sensors around the world.

The spherical satellite is Chinese first spherical small satellite, integrating atmospheric composition, atmospheric density detection and precision orbit determination. The payload is the Orbital Atmosphere Detector, which was launched into a near-circular polar orbit with the orbit altitude of 520 km and an inclination angle of 97.4° on 14 October, 2021. The scientific objectives, operating principle and the ground calibration results of the Orbital Atmosphere Detector are presented in this paper. The preliminary in-situ observed results are analyzed and discussed. The observed mass densities are strongly correlated with F10.7 and Kp. The peak-tovalley ratio of observed mass densities during the quiet period of solar and geomagnetic activity on 3 November 2021 was 3.02; the peak of observed mass density increased from 2.8×10 -13 to 8.0×10 -13 kg/m~3 during the strong geomagnetic storm event on 4 November, 2021, an increase of 2.857 times compared to the MSIS00 model of 1.316 times. The observed data show that the increase in atmospheric density started at the South Pole and spread to the middle and low latitudes, while the MSIS00 model only shows a weak symmetrically increase between the northern and southern hemispheres during the storm. The observed results show that the observed data objectively reflect the spatial and temporal distribution of thermosphere density during the quiet period and the geomagnetic storm event, and thermosphere atmospheric model correction can be implemented based on a large amount of observed data.

B2a信号是北斗三号(BeiDou-3 satellite navigation system,BD-3)新增的高宽带信号,具备非常高的伪距测量精度,适合开展基于全球导航卫星系统反射信号(global navigation satellite system-reflectometry,GNSS-R)的水面高度测量.由于BD-3近两年才开始为全球提供服务,基于BD-3反射信号的研究较少.中国科学院国家空间科学中心研发了具备自主知识产权的GNSS-R接收机,接收机专门增加了 BD-3 B2a的捕获跟踪功能,可以对直射和反射B2a信号同时进行捕获和跟踪.接收机同时具备了交叉定标功能,能够有效消除由电缆和接收机通道间差异引起的系统偏差.在中国北京市怀柔开展的岸基实验过程中,累计获取了BD-3 B2a、北斗二号(BeiDou-2 satellite navigation system,BD-2)B1I和全球定位系统(global positioning sys-tem,GPS)L1C/A反射信号的相关波形数据,成功反演了水面高度并进行了系统偏差消除.数据处理结果表明,基于BD-3B2a的水面高度在30 s非相干积分时间条件下反演精度达到了 5.9 cm,比BD-2B1I的高度测量精度提高了 13 cm,比GPS L1C/A信号的高度测量精度提高了 20 cm.

FIT (FER-LIKE IRON DEFICIENCY- INDUCED TRANSCRIPTION FACTOR) and four bHLH Ib transcription factors (TFs) bHLH38, bHLH39, bHLH100 and bHLH101, are the master regulators of Fe uptake genes, and they interact with each other to activate the Fe uptake systems. However, it remains unclear why FIT and bHLH Ib depend on each other to regulate the Fe deficiency response. By analyzing Fe deficiency phenotypes and Fe uptake genes, we found that the quadruple bhlh4x mutants ( bhlh38 bhlh39 bhlh100 bhlh101 ) mimic the fit mutant. Subcellular localization analyses indicate that bHLH38 and bHLH39 are preferentially expressed in the cytoplasm whereas bHLH100 and bHLH101 in the nucleus. Transcriptome data show that the genes involved in Fe signaling pathway show the same expression trends in bhlh4x and fit . Genetic analyses suggest that FIT and bHLH Ib depend each other to regulate the Fe deficiency response. Further biochemical assays indicate that bHLH Ib TFs possess the DNA binding ability and FIT has the transcription activation ability. This work concludes that FIT and bHLH Ib form a functional transcription complex in which bHLH Ib is responsible for target recognition and FIT for transcription activation, explaining why FIT and bHLH Ib interdependently regulate Fe uptake.

The polar-orbiting spherical experimental satellite of China for atmospheric density detection with an altitude of ~520 km was successfully launched on 14 October 2021. Based on the dynamic inversion method for atmospheric density and the precise orbit determination data obtained by its GNSS, we inverted the orbital atmospheric density during the severe geomagnetic storm in early November 2021. In this paper, we compared the atmospheric density data obtained by the spherical satellite with the simulations of the MSISE00 and the DTM, evaluated their error distribution, and analyzed the response of the atmospheric density during the severe geomagnetic storm in the dawn–dusk orbit of 520 km altitude. The properties and the physical processes for the atmospheric density of the time evolutions in different latitudes and the global distributions during the severe geomagnetic storm were obtained. We found that the substantial disturbance enhancement and recovery of the atmospheric density of the dawn–dusk orbit have a close correlation with the geomagnetic indexes Kp and Dst. The elevation extends from the poles to the equator, and the relative variation in two hemispheres demonstrates a bimodal nearly symmetric growth structure. The maximum relative variation of the two hemispheres both occurred in the middle latitude, and, for this case, the enhancement of atmospheric density in the mid-latitude region accounted for a larger proportion. The asymmetry between the northern and southern hemispheres is demonstrated by the fact that the absolute value and absolute change in the southern hemisphere in summer are larger than those in the northern hemisphere, and the bimodal structure of the relative variation is inclined to the northern hemisphere.

The Global Navigation Satellite System Reflectometry (GNSS-R) technique can measure ocean surface winds and other geophysical parameters from forward scattered Global Navigation Satellite System (GNSS) (Global Positioning System (GPS), BeiDou (BDS), Galileo, etc.) signals. However, most early spaceborne missions only captured GPS signals while the study of spaceborne BDS reflectometry (BDS-R) is limited. The Global Navigation Satellite System Occultation Sounder II (GNOS-II) payload onboard China’s FY-3E satellite has been operationally collecting a large number of BDS-R data since July 10, 2021. BDS is different from GPS in the orbit, signal frequency, chipping rate, and effective isotropic radiated power (EIRP). Furthermore, the BDS satellites have different generations and orbits. This article, for the first time, comprehensively characterizes the spaceborne BDS-R observations over the ocean using the FY-3E GNOS-II data from different BDS satellite types including BDS-2 inclined geosynchronous orbit (IGSO), BDS-2 medium Earth orbit (MEO), BDS-3 IGSO, and BDS-3 MEO. Their spatial coverage, spatial resolution, effective scattering area (ESA), incidence angle, range corrected gain (RCG), EIRP, and signal-to-noise ratio (SNR) have been analyzed and compared with those of GPS-R. Spaceborne BDS-R shows a lot of uniquenesses compared with GPS-R. The BDS-R observables are then calibrated separately for each type. An intercalibration is also applied to correct extra calibration errors. After calibration, BDS-R observables and retrieved winds are consistent between each type and compared with those of GPS-R. Calibrated observables from FY-3E GNOS-II are also evaluated by comparing them to those measured by the Cyclone GNSS (CYGNSS) mission and a theoretical model. The results of this article can provide a reference for future BDS-R studies and spaceborne GNSS-R mission design.

FengYun-3E (FY3E), launched on 5 July 2021, is one of China’s polar-orbiting meteorological satellite series. The GNOS II onboard FY3E is an operational GNSS remote sensor that for the first time combines GNSS radio occultation (GNSS RO) and GNSS reflectometry (GNSS-R). It has eight reflection channels that can track eight specular points at the same time, receiving reflected signals from multiple GNSS systems, including GPS, BeiDou and Galileo. The basic GNSS-R output generated by GNOS II is a 122 × 20 non-uniform delay-Doppler map whose high resolution portion captures more information near the specular point. This paper introduces the GNSS-R aspect of the FengYun-3E GNOS II, including the instrument, power calibration and wind speed retrieval algorithm. Preliminary validation results for its first four months of data are also presented. After preliminary quality control, the overall wind speed error is less than 2 m/s at wind speeds below 20 m/s for data from both GPS satellites and BeiDou satellites when compared to the ECMWF reanalysis winds.

Iron (Fe) homeostasis is essential for plant growth and development. Many transcription factors (TFs) play pivotal roles in the maintenance of Fe homeostasis. bHLH11 is a negative TF that regulates Fe homeostasis. However, the underlying molecular mechanism remains elusive. Here, we generated two loss-of-function bhlh11 mutants in Arabidopsis (Arabidopsis thaliana), which display enhanced sensitivity to excess Fe, increased Fe accumulation, and elevated expression of Fe deficiency responsive genes. Levels of bHLH11 protein, localized in both the cytoplasm and nucleus, decreased in response to Fe deficiency. Co-expression assays indicated that bHLH IVc TFs (bHLH34, bHLH104, bHLH105, and bHLH115) facilitate the nuclear accumulation of bHLH11. Further analysis indicated that bHLH11 represses the transactivity of bHLH IVc TFs toward bHLH Ib genes (bHLH38, bHLH39, bHLH100, and bHLH101). The two ethylene response factor-associated amphiphilic repression motifs of bHLH11 provided the repression function by recruiting the TOPLESS/TOPLESS-RELATED (TPL/TPRs) corepressors. Correspondingly, the expression of Fe uptake genes increased in the tpr1 tpr4 tpl mutant. Moreover, genetic analysis revealed that bHLH11 has functions independent of FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR. This study provides insights into the complicated Fe homeostasis signaling network.