1,721,182 research outputs found
gnss-ro/aws-opendata: GNSS-RO AWS Open Data v1.0.0
No full textGNSS Radio Occultation Data in the AWS Clou
A Novel Approach to Evaluate GNSS-RO Signal Receiver Performance in Terms of Ground-Based Atmospheric Occultation Simulation System
No full textThe global navigation satellite system radio occultation (GNSS-RO) is an important means of space-based meteorological observation. It is necessary to test the Global Navigation Satellite System Occultation signal receiver on the ground before the deployment of space-based occultation detection systems. The current approach of testing the GNSS signal receiver on the ground is mainly the mountaintop-based testing approach, which has problems such as high cost and large simulation error. In order to overcome the limitations of the mountaintop-based test approach, this paper proposes an accurate, repeatable, and controllable GNSS atmospheric occultation simulation system and builds a load performance evaluation approach based on the ground-based GNSS atmospheric occultation simulation system on the basis of it. The GNSS atmospheric occultation simulation system consists of the visualization and interaction module, the GNSS-RO simulation signal generation module, the GNSS-RO simulator module, the GNSS-RO signal receiver module, and the GNSS-RO inversion and evaluation module, combined with the preset atmospheric model to generate GNSS-RO simulation signals with a high degree of simulation, and comparing the atmospheric parameters of the inversion performance of the GNSS-RO signal receiver with the parameters of the preset atmospheric model to obtain the error data. The overall performance of the GNSS-RO signal receiver can be evaluated based on the error information. The novel approach to evaluate the GNSS-RO signal receiver performance proposed in this paper is validated by using the FY-3E (FengYun-3E) receiver qualification parts that have been verified in orbit, and the results confirm that the approach can meet the requirements of the GNSS-RO receiver performance test. This study shows that the novel approach to evaluate the GNSS-RO signal receiver performance in terms of the ground-based atmospheric occultation simulation system can efficiently and accurately be used to carry out the receiver test and provides an effective solution for the ground-based test of GNSS-RO signal receivers
Characterisation of residual ionospheric errors in bending angles using GNSS RO end-to-end simulations
No full textGlobal Navigation Satellite System (GNSS) radio occultation (RO) is an innovative meteorological remote sensing technique for measuring atmospheric parameters such as refractivity, temperature, water vapour and pressure for the improvement of numerical weather prediction (NWP) and global climate monitoring (GCM). GNSS RO has many unique characteristics including global coverage, long-term stability of observations, as well as high accuracy and high vertical resolution of the derived atmospheric profiles. One of the main error sources in GNSS RO observations that significantly affect the accuracy of the derived atmospheric parameters in the stratosphere is the ionospheric error. In order to mitigate the effect of this error, the linear ionospheric correction approach for dual-frequency GNSS RO observations is commonly used. However, the residual ionospheric errors (RIEs) can be still significant, especially when large ionospheric disturbances occur and prevail such as during the periods of active space weather. In this study, the RIEs were investigated under different local time, propagation direction and solar activity conditions and their effects on RO bending angles are characterised using end-to-end simulations. A three-step simulation study was designed to investigate the characteristics of the RIEs through comparing the bending angles with and without the effects of the RIEs. This research forms an important step forward in improving the accuracy of the atmospheric profiles derived from the GNSS RO technique
Atmospheric Rivers in Africa Observed with GNSS-RO and Reanalysis Data
No full textAtmospheric Rivers (ARs) transport significant amounts of moisture and cause extreme precipitation events, yet their behavior over Africa is not well understood. This study addresses this gap by analyzing the occurrence, seasonal variability, and spatial dynamics of ARs across the continent from 2009 to 2019. Utilizing ERA5 reanalysis data, Global Navigation Satellite Systems Radio Occultation (GNSS RO) measurements, and the Image-Processing-based Atmospheric River Tracking (IPART) method, distinct seasonal AR patterns are identified. Southern Africa experiences peak activity during austral summer, while AR occurrence in Northern Africa peaks in boreal winter and spring, aligning with regional rainy seasons. Moisture sources include the Atlantic Ocean, the Arabian Sea, and the Red Sea. A comparison of ERA5 Integrated Water Vapor (IWV) estimates with high-resolution GNSS RO data shows that both datasets effectively capture broad-scale moisture patterns. However, ERA5 consistently delivers higher IWV values compared to GNSS RO, which is likely due to underrepresentation of GNSS RO IWV values, since profiles generally do not reach all the way down to the surface—but also due to an overrepresentation of humidity in the ERA5 reanalyses. Understanding AR dynamics in Africa is essential to improve climate resilience, water management and understanding extreme precipitation events
Global GNSS-RO Electron Density in the Lower Ionosphere
Get PDFLack of instrument sensitivity to low electron density (Ne) concentration makes it difficult to measure sharp Ne vertical gradients (four orders of magnitude over 30 km) in the D/E-region. A robust algorithm is developed to retrieve global D/E-region Ne from the high-rate GNSS radio occultation (RO) data, to improve spatiotemporal coverage using recent SmallSat/CubeSat constellations. The new algorithm removes F-region contributions in the RO excess phase profile by fitting a linear function to the data below the D-region. The new GNSS-RO observations reveal many interesting features in the diurnal, seasonal, solar-cycle, and magnetic-field-dependent variations in the Ne morphology. While the D/E-region Ne is a function of solar zenith angle (χ), it exhibits strong latitudinal variations for the same χ with a distribution asymmetric about noon. In addition, large longitudinal variations are observed along the same magnetic field pitch angle. The summer midlatitude Ne and sporadic E (Es) show a distribution similar to each other. The distribution of auroral electron precipitation correlates better with the pitch angle from the magnetosphere than from one at 100 km. Finally, a new TEC retrieval technique is developed for the high-rate RO data with a top reaching at least 120 km. For better characterization of the E- to F-transition in Ne and more accurate TEC retrievals, it is recommended to have all GNSS-RO acquisition routinely up to 220 km
Global GNSS-RO Electron Density in the Lower Ionosphere
No full textLack of instrument sensitivity to low electron density (Ne) concentration makes it difficult to measure sharp Ne vertical gradients (four orders of magnitude over 30 km) in the D/E-region. A robust algorithm is developed to retrieve global D/E-region Ne from the high-rate GNSS radio occultation (RO) data, to improve spatiotemporal coverage using recent SmallSat/CubeSat constellations. The new algorithm removes F-region contributions in the RO excess phase profile by fitting a linear function to the data below the D-region. The new GNSS-RO observations reveal many interesting features in the diurnal, seasonal, solar-cycle, and magnetic-field-dependent variations in the Ne morphology. While the D/E-region Ne is a function of solar zenith angle (χ), it exhibits strong latitudinal variations for the same χ with a distribution asymmetric about noon. In addition, large longitudinal variations are observed along the same magnetic field pitch angle. The summer midlatitude Ne and sporadic E (Es) show a distribution similar to each other. The distribution of auroral electron precipitation correlates better with the pitch angle from the magnetosphere than from one at 100 km. Finally, a new TEC retrieval technique is developed for the high-rate RO data with a top reaching at least 120 km. For better characterization of the E- to F-transition in Ne and more accurate TEC retrievals, it is recommended to have all GNSS-RO acquisition routinely up to 220 km
Improvement of reflection detection success rate of GNSS RO measurements using artificial neural network
No full textGlobal Navigation Satellite System (GNSS) radio occultation (RO) has been widely used in the prediction of weather, climate, and space weather, particularly in the area of tropospheric analyses. However, one of the issues with GNSS RO measurements is that they are interfered with by the signals reflected from the earth's surface. Many RO events are subject to such interfered GNSS measurements, which are considerably difficult to extract from the GNSS RO measurements. To precisely identify interfered RO events, an improved machine learning approach- A gradient descent artificial neural network (ANN)-aided radio-holography method-is proposed in this paper. Since this method is more complex than most other machine learning methods, for improving its efficiency through the reduction in computational time for near-real-time applications, a scale factor and a regularization factor are also adjusted in the ANN approach. This approach was validated using Constellation Observing System for Meteorology, Ionosphere, and Climate/FC-3 atmPhs (level 1b) data during the period of day of year 172-202, 2015, and its detection results were compared with the flag data set provided by Radio Occultation Meteorology Satellite Application Facilities for the performance assessment and validation of the new approach. The results were also compared with those of the support vector machine method for improvement assessment. The comparison results showed that the proposed method can considerably improve both the success rate of GNSS RO reflection detection and the computational efficiency
Advancing GNSS-RO Detection of Ionospheric Irregularities Using Refined Back Propagation and GOLD Data
No full textThis paper investigates on the detection and localization of ionospheric irregularities using GNSS Radio Occultation (GNSS-RO). We propose a new segmented phase screen (PS) approach to improve vertical and horizontal localization and remove the presence of outliers. The study focused on the May 2024 geomagnetic solar storm is presented, consisting of a comparison of the GNSS-RO back propagation (BP) irregularity positioning against the data of NASA’s Globalscale Observations of the Limb and Disk (GOLD) mission. This study is performed for validation purposes and examines the presence of equatorial plasma bubbles (EPBs) at predicted locations. Experimental RO data from EUMETSAT’s MetOp satellites is used to demonstrate the method’s capability to characterize the distribution of ionospheric irregularities. Results validate the segmented approach's capabilities of detecting irregularity structures and identifying their centroids with improved performance compared with the previous version of the algorithm.
다중 안테나 기반 데이터 보상을 통한 GNSS RO 전리권 전자밀도 산출 기법 연구
No full text학위논문(박사) - 한국과학기술원 : 항공우주공학과, 2023.8,[vii, 113 p. :]Global Navigation Satellite System (GNSS) Radio Occultation (GNSS RO) is a remote sensing technique that observes the Earth's atmosphere, including the ionosphere, based on the degree of refraction and delay of GPS signals received from Low Earth Orbit (LEO) satellites. GNSS RO has the advantage of being able to providing high-resolution ionospheric information over the global range and altitude. Due to this advantage, the demand for GNSS RO data is increasing in various fields that require ionospheric monitoring. In Korea, the RO receiver is on board on Korea Multi-Purpose Satellite 5 (KOMPSAT-5) and is in operation. In order to obtain precise atmospheric profiles from the RO data and process the RO data not only from the domestically developed RO system, but also from other international RO missions, a new algorithm considering the characteristics of RO data from each mission and its own software are required.
In this dissertation, an algorithm for retrieving the ionospheric electron density through multi-antenna data filling was proposed. In the case of satellites such as Challenging Ministration Payload (CHAMP), Gravity Recovery and Climate Experiment (GRACE) and KOMPSAT-5, which use occultation antenna for monitoring the ionosphere, uncertainty may be included because the total electron content (TEC) outside the LEO orbit (auxiliary side TEC) is built through modeling during the TEC calibration process. Instead of using modeled auxiliary-side TEC, the proposed method uses the auxiliary-side TEC observed by a precision orbit determination (POD) and connects the data by modeling the gap between the POD antenna and the occultation antenna.
Second, this dissertation develops a software for retrieving the ionospheric electron density from GNSS RO data. The algorithm in the software was based on the existing COSMIC Data Analysis and Archive Center (CDAAC)’s algorithm. As a result of comparative analysis with CDAAC’s algorithm, it was confirmed that the 1st Constellation System for Meteorology Ionosphere and Climate (COSMIC-1) electron density retrieved by the developed software are within the tolerance range accuracy requirement. In addition, the electron density profiles from GRACE RO retrieved by the proposed algorithm have similar trends with the CDAAC’s output, and also have good agreement with the electron density profiles observed by the collocated incoherent scatter radar (ISR).
Third, the performance assessment of the ionospheric electron density retrieved from KOMPSAT-5 RO by applying the proposed algorithm has been done. To validate the output from KOMPSAT-5 RO with reliable truth observations, digital ionosonde (digisonde) data, the incoherent scatter radar and COSMIC-2 RO data were used as reference dataset. The comparisons between digisonde NmF2 and KOMSPAT-5 RO NmF2 reveal a high degree of correlation of 0.90. The comparisons with both observations from ISR and COSMIC-2 RO show that the profiles retrieved from KOMPSAT-5 RO data have good agreement with the electron density profiles from the both ISR and COSMIC-2 RO.
Lastly, this dissertation proposes the methodology for assessing the performance of RO data, and applies the methodology to assess the performance of GeoOptics’ Community Initiative for Cellular Earth Remote Observation (CICERO) CubeSat RO by comparing it with the COSMIC missions. The results from performance assessment demonstrate that the miniature version of the GNSS RO receiver could satisfy certain accuracy requirements of the GNSS RO measurements.한국과학기술원 :항공우주공학과
Stratospheric gravity waves in a post-limb sounder era: can GNSS-RO be used to extend the SABER QBO-driving record?
Get PDFThe quasi-biennial oscillation (QBO) is a slowly repeating cycle of winds which dominates tropical lower-stratospheric dynamics and has been described as the “heartbeat of the stratosphere”. However, it is challenging to represent in weather and climate models because its periodicity and magnitude are controlled by small-scale gravity waves (GWs) that cannot be resolved on model grids. To quantify this GW driving we require high-resolution measurements, ideally from satellites to ensure full spatial coverage. Since 2002, the SABER instrument on the TIMED satellite has provided such data, facilitating long-term studies of QBO GW driving. However, SABER is expected to be decommissioned later this year, and no replacement is planned. Here, we assess the possibility of using GNSS-RO data to extend the 23-year SABER record. GNSS-RO cannot be used as a simple replacement for long-term studies because data volumes are too low before 2006 and for most of the late 2010s, and thus, we ideally wish to supplement rather than replace the SABER record. However, while the two datasets have broadly similar lower stratospheric resolutions when compared to the full Earth observation constellation, GNSS-RO measurements are higher resolution in all three dimensions than SABER and are oriented differently in 3D space. As a result of this, GNSS-RO GW measurements exhibit much larger GW potential energies (GWPE) and shorter vertical wavelengths than those from SABER. To understand these differences, we use a high-resolution run of the GEOS model to produce synthetic GW measurements, then systematically vary the measurement characteristics between those of the two real instruments. This allows us to identify the key drivers of the different GW properties they measure. We demonstrate that the differences between QBO-driving GW properties measured by the two instruments are primarily due to vertical resolution, with horizontal resolution (either along or across line of sight) and orientation angle playing a negligible role. We further demonstrate that, with a simple vertical smoothing of the GNSS-RO data in the vertical before analysis for GWs, the measured GW properties become near-identical, allowing us to use SABER and GNSS-RO data near-equivalently for this use case. Since GNSS-RO data are now a crucial component of the global numerical weather prediction constellation and are hence highly likely to be available in the long term, this allows us to produce a consistent long-term record of QBO GW forcing from 2002 onwards without key gaps which would be otherwise present in the early 2000s and late 2010s.</p
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