First Assessment of Geophysical Sensitivities from Spaceborne Galileo and BeiDou GNSS-Reflectometry Data Collected by the UK TechDemoSat-1 Mission

The UK’s TechDemoSat-1 (TDS-1), launched 2014, has demonstrated the use of global positioning system (GPS) signals for monitoring ocean winds and sea ice. Here it is shown, for the first time, that Galileo and BeiDou signals detected by TDS-1 show similar promise. TDS-1 made seven raw data collections, recovering returns from Galileo and BeiDou, between November 2015 and March 2019. The retrieved open ocean delay Doppler maps (DDMs) are similar to those from GPS. Over sea ice, the Galileo DDMs show a distinctive triple peak. Analysis, adapted from that for GPS DDMs, gives Galileo’s signal-to-noise ratio (SNR), which is found to be inversely sensitive to wind speed, as for GPS. A Galileo track transiting from open ocean to sea ice shows a strong instantaneous SNR response. These results demonstrate the potential of future spaceborne constellations of GNSS-R (global navigation satellite system–reflectometry) instruments for exploiting signals from multiple systems: GPS, Galileo, and BeiDou.

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Earth Surface Monitoring with Spire’s New GNSS Reflectometry (GNSS-R) CubeSats

10.5194/egusphere-egu2020-13766 ◽

2020 ◽

Author(s):

Vahid Freeman ◽

Dallas Masters ◽

Philp Jales ◽

Stephan Esterhuizen ◽

Ellie Ebrahimi ◽

...

Keyword(s):

Soil Moisture ◽

Spatial Resolution ◽

Precise Orbit Determination ◽

Satellite System ◽

Detection Algorithm ◽

Earth Surface ◽

Wind Speeds ◽

Gnss Reflectometry ◽

The Uk ◽

Global Navigation Satellite

Spire Global operates the world&#8217;s largest and rapidly growing constellation of CubeSats performing GNSS based science and Earth observation. The Spire constellation, performs a variety of GNSS science, including radio occultation (GNSS-RO), ionosphere and space weather measurements, and precise orbit determination. In December 2019, Spire launched two new satellites to perform GNSS reflectometry (GNSS-R). GNSS-R is a relatively new technique based on a passive bistatic radar system. The potential of space-borne GNSS-R observations for ocean and land applications has been demonstrated by other GNSS-R missions, including the NASA Cyclone Global Navigation Satellite System (CYGNSS) and the UK&#8217;s Technology Demonstration Satellite, TechDemoSat (TDS-1).&#160;We present initial results from these new Spire GNSS-R satellites that are primarily focused on retrieving soil moisture but also estimate other Earth surface properties such as ocean wind speeds and flood inundation/wetland mapping. Prior to the launch of Spire&#8217;s GNSS-R satellites and in preparation for Level-2 data production, we developed algorithms and processing chains for land applications. We will present Spire's Soil Moisture (SM) retrieval method using CYGNSS observations. We evaluated the implemented SM change detection algorithm by comparing the Spire&#8217;s daily SM product with NASA&#8217;s Soil Moisture Active Passive (SMAP) observations and in-situ SM measurements. The results of study indicate remarkable retrieval skills of the GNSS-R technique for soil moisture monitoring at a medium spatial resolution. Spire&#8217;s GNSS-R satellites are tuned for land applications with a series of hardware and software optimizations for better signal calibration and acquiring many more data per satellite compared to CYGNSS. A more robust GNSS-R SM retrieval at finer spatial resolution will be possible in the near future after having more Spire satellites in orbit.Spire&#8217;s current and future GNSS-R satellites will provide unprecedented sub-daily global coverage with sub-kilometer spatial resolution. Such intensive data acquisition is of great importance for many land and ocean applications.&#160;

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Inter-comparison of GNSS-Reflectometry measurements from CYGNSS and Spire’s satellites with SMAP soil moisture product

10.5194/egusphere-egu21-15123 ◽

2021 ◽

Author(s):

Vahid Freeman ◽

Philip Jales ◽

Stephan Esterhuizen ◽

Vladimir Irisov ◽

Jessica Cartwright ◽

...

Keyword(s):

Soil Moisture ◽

Satellite System ◽

Earth Observation ◽

Regular Grid ◽

Statistical Parameters ◽

Global Soil ◽

Gnss Reflectometry ◽

Level 1 ◽

The Uk ◽

Global Navigation Satellite

The potential of space-borne GNSS-Reflectometry (GNSS-R) technique for soil moisture retrieval has been demonstrated in recent studies using observations from the NASA&#8217;s Cyclone Global Navigation Satellite System (CYGNSS) and the UK&#8217;s Technology Demonstration Satellite, TechDemoSat (TDS-1).Spire Global operates a constellation of CubeSats performing GNSS based science and Earth observation. In December 2019, Spire launched two new satellites with GNSS-R payloads with plans to launch two more follow-on GNSS-R missions in January 2021. In this study, we highlight the capabilities of the Spire&#8217;s current and future GNSS-R missions compared to CYGNSS for global soil moisture monitoring and present the results of an inter-comparison between CYGNSS and Spire GNSS-R observables over land with NASA&#8217;s Soil Moisture Active Passive (SMAP) observations. The comparison of level-1 data and various statistical parameters was performed after data collocation both trackwise and also within a 6km regular grid. The results of the study were used for intercalibration of CYGNSS and Spire&#8217;s GNSS-R measurements for developing a combined GNSS-R soil moisture product.

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From GPS Receiver to GNSS Reflectometry Payload Development for the Triton Satellite Mission

Remote Sensing ◽

10.3390/rs13050999 ◽

2021 ◽

Vol 13 (5) ◽

pp. 999

Author(s):

Yung-Fu Tsai ◽

Wen-Hao Yeh ◽

Jyh-Ching Juang ◽

Dian-Syuan Yang ◽

Chen-Tsung Lin

Keyword(s):

Satellite System ◽

Low Earth Orbit ◽

Export Control ◽

Navigation Systems ◽

Gps Receiver ◽

Design Development ◽

Satellite Mission ◽

Essential Components ◽

Gnss Reflectometry ◽

Global Navigation Satellite

The global positioning system (GPS) receiver has been one of the most important navigation systems for more than two decades. Although the GPS system was originally designed for near-Earth navigation, currently it is widely used in highly dynamic environments (such as low Earth orbit (LEO)). A space-capable GPS receiver (GPSR) is capable of providing timing and navigation information for spacecraft to determine the orbit and synchronize the onboard timing; therefore, it is one of the essential components of modern spacecraft. However, a space-grade GPSR is technology-sensitive and under export control. In order to overcome export control, the National Space Organization (NSPO) in Taiwan completed the development of a self-reliant space-grade GPSR in 2014. The NSPO GPSR, built in-house, has passed its qualification tests and is ready to fly onboard the Triton satellite. In addition to providing navigation, the GPS/global navigation satellite system (GNSS) is facilitated to many remote sensing missions, such as GNSS radio occultation (GNSS-RO) and GNSS reflectometry (GNSS-R). Based on the design of the NSPO GPSR, the NSPO is actively engaged in the development of the Triton program (a GNSS reflectometry mission). In a GNSS-R mission, the reflected signals are processed to form delay Doppler maps (DDMs) so that various properties (including ocean surface roughness, vegetation, soil moisture, and so on) can be retrieved. This paper describes not only the development of the NSPO GPSR but also the design, development, and special features of the Triton’s GNSS-R mission. Moreover, in order to verify the NSPO GNSS-R receiver, ground/flight tests are deemed essential. Then, data analyses of the airborne GNSS-R tests are presented in this paper.

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Potential Applications of GNSS-R Observations over Agricultural Areas: Results from the GLORI Airborne Campaign

Remote Sensing ◽

10.3390/rs10081245 ◽

2018 ◽

Vol 10 (8) ◽

pp. 1245 ◽

Cited By ~ 15

Author(s):

Mehrez Zribi ◽

Erwan Motte ◽

Nicolas Baghdadi ◽

Frédéric Baup ◽

Sylvia Dayau ◽

...

Keyword(s):

Soil Moisture ◽

Signal To Noise Ratio ◽

Soil Surface ◽

Satellite System ◽

Area Index ◽

Vegetation Height ◽

Study Sites ◽

Global Navigation Satellite ◽

Vegetation Characteristic ◽

Agricultural Areas

The aim of this study is to analyze the sensitivity of airborne Global Navigation Satellite System Reflectometry (GNSS-R) on soil surface and vegetation cover characteristics in agricultural areas. Airborne polarimetric GNSS-R data were acquired in the context of the GLORI’2015 campaign over two study sites in Southwest France in June and July of 2015. Ground measurements of soil surface parameters (moisture content) and vegetation characteristics (leaf area index (LAI), and vegetation height) were recorded for different types of crops (corn, sunflower, wheat, soybean, vegetable) simultaneously with the airborne GNSS-R measurements. Three GNSS-R observables (apparent reflectivity, the reflected signal-to-noise-ratio (SNR), and the polarimetric ratio (PR)) were found to be well correlated with soil moisture and a major vegetation characteristic (LAI). A tau-omega model was used to explain the dependence of the GNSS-R reflectivity on both the soil moisture and vegetation parameters.

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High-rate altimetry in SNR-based GNSS-R: Proof-of-concept of a synthetic vertical array

10.36227/techrxiv.14186930 ◽

2021 ◽

Author(s):

Mauricio Kenji Yamawaki ◽

Felipe Geremia-Nievinski ◽

João Francisco Monico

Keyword(s):

Sea Level ◽

Signal To Noise Ratio ◽

Satellite System ◽

High Rate ◽

Proof Of Concept ◽

Radio Waves ◽

Vertical Array ◽

Remote Sensing Technique ◽

Single Antenna ◽

Global Navigation Satellite

Global Navigation Satellite System Reflectometry (GNSS-R) has emerged as a promising remote sensing technique for coastal sea level monitoring. The GNSS-R based on signal-to-noise ratio (SNR) observations employs a single antenna and a conventional receiver. It performs best for low elevation satellites, where direct and reflected radio waves are very similar in polarization and direction of arrival. One of the disadvantages of SNR-based GNSS-R for sea level altimetry is its low temporal resolution, which is of the order of one hour for each independent satellite pass. Here we present a proof-of-concept based on a synthetic vertical array. It exploits the mechanical movement of a single antenna at high rate (about 1 Hz). SNR observations can then be fit to a known modulation, of the order of the antenna sweeping rate. We demonstrate that centimetric altimetry precision can be achieved in a 5-minute session. [©2021 IEEE]

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Investigation of the Occurrence of Nighttime Topside Ionospheric Irregularities in Low-Latitude and Equatorial Regions Using CYGNSS Satellites

Sensors ◽

10.3390/s20030708 ◽

2020 ◽

Vol 20 (3) ◽

pp. 708 ◽

Cited By ~ 1

Author(s):

Liang Huang ◽

Yi Liu ◽

Qiong Tang ◽

Guanyi Chen ◽

Zhuangkai Wang ◽

...

Keyword(s):

Signal To Noise Ratio ◽

Global Analysis ◽

Satellite System ◽

Ionospheric Irregularities ◽

Wave Number ◽

Significant Finding ◽

Low Latitude ◽

Zonal Wave Number ◽

Global Navigation Satellite ◽

Maximum Occurrence

By using multi-satellite observations of the L1 signal-to-noise ratio (SNR) from the Cyclone Global Navigation Satellite System (CYGNSS) taken in 2017, we present the occurrence of nighttime topside ionospheric irregularities in low-latitude and equatorial regions. The most significant finding of this study is the existence of longitudinal structures with a wavenumber 4 pattern in the topside irregularities. This suggests that lower atmospheric waves, especially a daytime diurnal eastward-propagating zonal wave number-3 nonmigrating tide (DE3), might play an important role in the generation of topside plasma bubbles during the low solar minimum. Observations of scintillation events indicate that the maximum occurrence of nighttime topside ionospheric irregularities occurs on the magnetic equator during the equinoxes. The current work, which could be regarded as an important update of the previous investigations, would be readily for the further global analysis of the topside ionospheric irregularities.

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Detecting Targets above the Earth’s Surface Using GNSS-R Delay Doppler Maps: Results from TDS-1

Remote Sensing ◽

10.3390/rs11192327 ◽

2019 ◽

Vol 11 (19) ◽

pp. 2327 ◽

Cited By ~ 2

Author(s):

Changjiang Hu ◽

Craig Benson ◽

Hyuk Park ◽

Adriano Camps ◽

Li Qiao ◽

...

Keyword(s):

Specular Reflection ◽

Satellite System ◽

Low Earth Orbit ◽

Earth Orbit ◽

Navigation Satellite ◽

Reflection Point ◽

Leo Satellites ◽

Gnss Reflectometry ◽

Global Navigation Satellite ◽

Remotely Sense

Global Navigation Satellite System (GNSS) reflected signals can be used to remotely sense the Earth’s surface, known as GNSS reflectometry (GNSS-R). The GNSS-R technique has been applied to numerous areas, such as the retrieval of wind speed, and the detection of Earth surface objects. This work proposes a new application of GNSS-R, namely to detect objects above the Earth’s surface, such as low Earth orbit (LEO) satellites. To discuss its feasibility, 14 delay Doppler maps (DDMs) are first presented which contain unusually bright reflected signals as delays shorter than the specular reflection point over the Earth’s surface. Then, seven possible causes of these anomalies are analysed, reaching the conclusion that the anomalies are likely due to the signals being reflected from objects above the Earth’s surface. Next, the positions of the objects are calculated using the delay and Doppler information, and an appropriate geometry assumption. After that, suspect satellite objects are searched in the satellite database from Union of Concerned Scientists (UCS). Finally, three objects have been found to match the delay and Doppler conditions. In the absence of other reasons for these anomalies, GNSS-R could potentially be used to detect some objects above the Earth’s surface.

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Derivation of global ionospheric Sporadic E critical frequency ( f o Es) data from the amplitude variations in GPS/GNSS radio occultations

Royal Society Open Science ◽

10.1098/rsos.200320 ◽

2020 ◽

Vol 7 (7) ◽

pp. 200320 ◽

Cited By ~ 1

Author(s):

Bingkun Yu ◽

Christopher J. Scott ◽

Xianghui Xue ◽

Xinan Yue ◽

Xiankang Dou

Keyword(s):

Critical Frequency ◽

Detection Threshold ◽

Low Frequency ◽

Satellite System ◽

Global Scale ◽

Satellite Mission ◽

Frequency Detection ◽

Sporadic E ◽

The Uk ◽

Global Navigation Satellite

The ionospheric sporadic E (Es) layer has a significant impact on the global positioning system (GPS)/global navigation satellite system (GNSS) signals. These influences on the GPS/GNSS signals can also be used to study the occurrence and characteristics of the Es layer on a global scale. In this paper, 5.8 million radio occultation (RO) profiles from the FORMOSAT-3/COSMIC satellite mission and ground-based observations of Es layers recorded by 25 ionospheric monitoring stations and held at the UK Solar System Data Centre at the Rutherford Appleton Laboratory and the Chinese Meridian Project were used to derive the hourly Es critical frequency ( f o Es) data. The global distribution of f o Es with a high spatial resolution shows a strong seasonal variation in f o Es with a summer maximum exceeding 4.0 MHz and a winter minimum between 2.0 and 2.5 MHz. The GPS/GNSS RO technique is an important tool that can provide global estimates of Es layers, augmenting the limited coverage and low-frequency detection threshold of ground-based instruments. Attention should be paid to small f o Es values from ionosondes near the instrumental detection limits corresponding to minimum frequencies in the range 1.28–1.60 MHz.

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Spaceborne GNSS-R Observation of Global Lake Level: First Results from the TechDemoSat-1 Mission

Remote Sensing ◽

10.3390/rs11121438 ◽

2019 ◽

Vol 11 (12) ◽

pp. 1438 ◽

Cited By ~ 2

Author(s):

Liwen Xu ◽

Wei Wan ◽

Xiuwan Chen ◽

Siyu Zhu ◽

Baojian Liu ◽

...

Keyword(s):

Satellite System ◽

Temporal Variations ◽

Strong Correlations ◽

Lake Levels ◽

The Caspian Sea ◽

First Results ◽

The Uk ◽

Global Navigation Satellite ◽

Inland Water Bodies ◽

First Time

Spaceborne global navigation satellite system reflectometry (GNSS-R) data collected by the UK TechDemoSat-1 (TDS-1) satellite is applied to retrieve global lake levels for the first time. Lake levels of 351 global lakes (area greater than 500 km2 and elevation lower than 3000 m each) are estimated using TDS-1 Level 1b data over 2015–2017. Strong correlations (overall R2 greater than 0.95) are observed among lake levels derived from TDS-1 and other altimetry satellites such as CryoSat-2, Jason, and Envisat (the latter two are collected by Hydroweb), although with large root-mean-square error (RMSE) (tens of meters) mainly due to the fact that TDS-1 is not dedicated for altimetry measuring purpose. Examples of the Caspian Sea and the Poyang Lake show consistent spatial and temporal variations between TDS-1 and other data sources. The results in this paper provide supportive information for further application of GNSS-R constellations to measure altimetry of inland water bodies.

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Experimental results of multipath behavior for GPS L1-L2 and Galileo E1-E5b in static and kinematic scenarios

Journal of Applied Geodesy ◽

10.1515/jag-2019-0010 ◽

2019 ◽

Vol 13 (4) ◽

pp. 279-289 ◽

Cited By ~ 1

Author(s):

Alexandra Avram ◽

Volker Schwieger ◽

Noha El Gemayel

Keyword(s):

Signal To Noise Ratio ◽

Measurement Data ◽

Absolute Error ◽

Autonomous Driving ◽

Satellite System ◽

Natural Environments ◽

Navigation Systems ◽

Global Navigation Satellite ◽

The Impact ◽

Measurement Campaigns

Abstract Current trends like Autonomous Driving (AD) increase the need for a precise, reliable, and continuous position at high velocities. In both natural and man-made environments, Global Navigation Satellite System (GNSS) signals suffer challenges such as multipath, attenuation, or loss-of-lock. As Highway Assist and Highway Pilot are AD next steps, multipath knowledge is necessary for this typical user-case and kinematic situations. This paper presents a multipath performance analysis for GPS and Galileo satellites in static, slow, and high kinematic scenarios. The data is provided from car test-drives in both controlled and unrestricted, near-natural environments. The Code-Minus-Carrier (CMC) and cycle-slip implementations are validated with measurement data from consecutive days. Multipath statistical models based on satellite elevation are evaluated for the three investigated scenarios. Static models derived from the car setup measurements for GPS L1, L2 and Galileo E1 and E5b show a good agreement with a state-of-the-art model as well as the enhanced Galileo signals performance. Slow kinematic multipath results in a controlled environment showed an improvement for both navigation systems compared to the static measurements at the same place. This result is confirmed by static and slow kinematic multipath simulations with the same GNSS receiver. Post-processing analysis on highway measurements revealed a bigger multipath bias, compared to the open-sky static and slow kinematic measurement campaigns. Although less critical as urban or rural, this indicates the presence of multipath in this kind of environment as well. The impact of different parameters, including receiver architecture and Signal-to-noise ratio (SNR) are analyzed and discussed. Differential position (DGNSS) based on code is computed for each epoch and compared against GNSS/INS integrated position for all three measurement campaigns. The most significant 3D absolute error occurs where the greatest multipath envelope is found.

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