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In the theoretical part of this work, a calibration strategy for both phase and amplitude calibration of rotating equispaced circular array based on redundant space calibration was introduced. It avoids the challenging implementation of conventional noise-injection networks, especially for a large-scale array, by using the strong self-consistency accomplished by array rotation. This study presents comprehensive simulation results of the proposed calibration strategy, where calibration residuals and image reconstruction errors are evaluated. The phase calibration shows outstanding performance, while the amplitude calibration is found to be biased due to the logarithms used to linearize the system of calibration equations, and the resulting image reconstruction bias is scene-dependent. A bias correction method is proposed accordingly, which requires an a priori regional brightness temperature within the observation scene. The performance of both phase and amplitude calibration take advantage of increasing the number of elements, which promises the system scalability for high spatial resolution applications.
Xi Guo; Adriano Camps; Hyuk Park; Hao Liu; Cheng Zhang; Ji Wu. Phase and Amplitude Calibration of Rotating Equispaced Circular Array for Geostationary Microwave Interferometric Radiometers--Simulation Results and Discussion. IEEE Transactions on Geoscience and Remote Sensing 2021, PP, 1 -19.
AMA StyleXi Guo, Adriano Camps, Hyuk Park, Hao Liu, Cheng Zhang, Ji Wu. Phase and Amplitude Calibration of Rotating Equispaced Circular Array for Geostationary Microwave Interferometric Radiometers--Simulation Results and Discussion. IEEE Transactions on Geoscience and Remote Sensing. 2021; PP (99):1-19.
Chicago/Turabian StyleXi Guo; Adriano Camps; Hyuk Park; Hao Liu; Cheng Zhang; Ji Wu. 2021. "Phase and Amplitude Calibration of Rotating Equispaced Circular Array for Geostationary Microwave Interferometric Radiometers--Simulation Results and Discussion." IEEE Transactions on Geoscience and Remote Sensing PP, no. 99: 1-19.
The calibration strategy for synthetic aperture interferometric radiometers based on noise injection has been successfully demonstrated in the Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) instrument onboard the Soil Moisture and Ocean Salinity (SMOS) mission of the European Space Agency (ESA). With the emerging demands of increasing both array size and frequency bands, the internal calibration hardware becomes more difficult to implement. Although several external calibration methods have been proposed, the so-called phase ambiguity problem was not carefully considered. In this article, a novel calibration strategy for both phase and amplitude calibrations based on redundant space calibration is proposed, which utilizes the unique structure of equispaced circular array and rotational sampling strategy. The original irregular phase ambiguity degenerates to the fixed π-ambiguity, where only two possible solutions to phases are introduced. Both phase and amplitude of visibility can be simultaneously calibrated by the proposed strategy, and no cooperative calibration target is needed.
Xi Guo; Adriano Camps; Hyuk Park; Hao Liu; Cheng Zhang; Ji Wu. Phase and Amplitude Calibrations of Rotating Equispaced Circular Array for Geostationary Microwave Interferometric Radiometers--Theory and Methods. IEEE Transactions on Geoscience and Remote Sensing 2021, PP, 1 -15.
AMA StyleXi Guo, Adriano Camps, Hyuk Park, Hao Liu, Cheng Zhang, Ji Wu. Phase and Amplitude Calibrations of Rotating Equispaced Circular Array for Geostationary Microwave Interferometric Radiometers--Theory and Methods. IEEE Transactions on Geoscience and Remote Sensing. 2021; PP (99):1-15.
Chicago/Turabian StyleXi Guo; Adriano Camps; Hyuk Park; Hao Liu; Cheng Zhang; Ji Wu. 2021. "Phase and Amplitude Calibrations of Rotating Equispaced Circular Array for Geostationary Microwave Interferometric Radiometers--Theory and Methods." IEEE Transactions on Geoscience and Remote Sensing PP, no. 99: 1-15.
CubeSat-based Earth Observation missions have emerged in recent times, achieving scientifically valuable data at a moderate cost. FSSCat is a two 6U CubeSats mission, winner of the ESA S3 challenge and overall winner of the 2017 Copernicus Masters Competition, that was launched in September 2020. The first satellite, 3Cat-5/A, carries the FMPL-2 instrument, an L-band microwave radiometer and a GNSS-Reflectometer. This work presents a neural network approach for retrieving sea ice concentration and sea ice extent maps on the Arctic and the Antarctic oceans using FMPL-2 data. The results from the first months of operations are presented and analyzed, and the quality of the retrieved maps is assessed by comparing them with other existing sea ice concentration maps. As compared to OSI SAF products, the overall accuracy for the sea ice extent maps is greater than 97% using MWR data, and up to 99% when using combined GNSS-R and MWR data. In the case of Sea ice concentration, the absolute errors are lower than 5%, with MWR and lower than 3% combining it with the GNSS-R. The total extent area computed using this methodology is close, with 2.5% difference, to those computed by other well consolidated algorithms, such as OSI SAF or NSIDC. The approach presented for estimating sea ice extent and concentration maps is a cost-effective alternative, and using a constellation of CubeSats, it can be further improved.
David Llaveria; Juan Munoz-Martin; Christoph Herbert; Miriam Pablos; Hyuk Park; Adriano Camps. Sea Ice Concentration and Sea Ice Extent Mapping with L-Band Microwave Radiometry and GNSS-R Data from the FFSCat Mission Using Neural Networks. Remote Sensing 2021, 13, 1139 .
AMA StyleDavid Llaveria, Juan Munoz-Martin, Christoph Herbert, Miriam Pablos, Hyuk Park, Adriano Camps. Sea Ice Concentration and Sea Ice Extent Mapping with L-Band Microwave Radiometry and GNSS-R Data from the FFSCat Mission Using Neural Networks. Remote Sensing. 2021; 13 (6):1139.
Chicago/Turabian StyleDavid Llaveria; Juan Munoz-Martin; Christoph Herbert; Miriam Pablos; Hyuk Park; Adriano Camps. 2021. "Sea Ice Concentration and Sea Ice Extent Mapping with L-Band Microwave Radiometry and GNSS-R Data from the FFSCat Mission Using Neural Networks." Remote Sensing 13, no. 6: 1139.
The Federated Satellite System mission (FSSCat) was the winner of the 2017 Copernicus Masters Competition and the first Copernicus third-party mission based on CubeSats. One of FSSCat’s objectives is to provide coarse Soil Moisture (SM) estimations by means of passive microwave measurements collected by Flexible Microwave Payload-2 (FMPL-2). This payload is a novel CubeSat based instrument combining an L1/E1 Global Navigation Satellite Systems-Reflectometer (GNSS-R) and an L-band Microwave Radiometer (MWR) using software-defined radio. This work presents the first results over land of the first two months of operations after the commissioning phase, from 1 October to 4 December 2020. Four neural network algorithms are implemented and analyzed in terms of different sets of input features to yield maps of SM content over the Northern Hemisphere (latitudes above 45° N). The first algorithm uses the surface skin temperature from the European Centre of Medium-Range Weather Forecast (ECMWF) in conjunction with the 16 day averaged Normalized Difference Vegetation Index (NDVI) from the Moderate Resolution Imaging Spectroradiometer (MODIS) to estimate SM and to use it as a comparison dataset for evaluating the additional models. A second approach is implemented to retrieve SM, which complements the first model using FMPL-2 L-band MWR antenna temperature measurements, showing a better performance than in the first case. The error standard deviation of this model referred to the Soil Moisture and Ocean Salinity (SMOS) SM product gridded at 36 km is 0.074 m
Joan Munoz-Martin; David Llaveria; Christoph Herbert; Miriam Pablos; Hyuk Park; Adriano Camps. Soil Moisture Estimation Synergy Using GNSS-R and L-Band Microwave Radiometry Data from FSSCat/FMPL-2. Remote Sensing 2021, 13, 994 .
AMA StyleJoan Munoz-Martin, David Llaveria, Christoph Herbert, Miriam Pablos, Hyuk Park, Adriano Camps. Soil Moisture Estimation Synergy Using GNSS-R and L-Band Microwave Radiometry Data from FSSCat/FMPL-2. Remote Sensing. 2021; 13 (5):994.
Chicago/Turabian StyleJoan Munoz-Martin; David Llaveria; Christoph Herbert; Miriam Pablos; Hyuk Park; Adriano Camps. 2021. "Soil Moisture Estimation Synergy Using GNSS-R and L-Band Microwave Radiometry Data from FSSCat/FMPL-2." Remote Sensing 13, no. 5: 994.
Global Navigation Satellite System—Reflectometry (GNSS-R) has already proven its potential for retrieving a number of geophysical parameters, including soil moisture. However, single-pass GNSS-R soil moisture retrieval is still a challenge. This study presents a comparison of two different data sets acquired with the Microwave Interferometer Reflectometer (MIR), an airborne-based dual-band (L1/E1 and L5/E5a), multiconstellation (GPS and Galileo) GNSS-R instrument with two 19-element antenna arrays with four electronically steered beams each. The instrument was flown twice over the OzNet soil moisture monitoring network in southern New South Wales (Australia): the first flight was performed after a long period without rain, and the second one just after a rain event. In this work, the impact of surface roughness and vegetation attenuation in the reflectivity of the GNSS-R signal is assessed at both L1 and L5 bands. The work analyzes the reflectivity at different integration times, and finally, an artificial neural network is used to retrieve soil moisture from the reflectivity values. The algorithm is trained and compared to a 20-m resolution downscaled soil moisture estimate derived from SMOS soil moisture, Sentinel-2 normalized difference vegetation index (NDVI) data, and ECMWF Land Surface Temperature.
Joan Munoz-Martin; Raul Onrubia; Daniel Pascual; Hyuk Park; Miriam Pablos; Adriano Camps; Christoph Rüdiger; Jeffrey Walker; Alessandra Monerris. Single-Pass Soil Moisture Retrieval Using GNSS-R at L1 and L5 Bands: Results from Airborne Experiment. Remote Sensing 2021, 13, 797 .
AMA StyleJoan Munoz-Martin, Raul Onrubia, Daniel Pascual, Hyuk Park, Miriam Pablos, Adriano Camps, Christoph Rüdiger, Jeffrey Walker, Alessandra Monerris. Single-Pass Soil Moisture Retrieval Using GNSS-R at L1 and L5 Bands: Results from Airborne Experiment. Remote Sensing. 2021; 13 (4):797.
Chicago/Turabian StyleJoan Munoz-Martin; Raul Onrubia; Daniel Pascual; Hyuk Park; Miriam Pablos; Adriano Camps; Christoph Rüdiger; Jeffrey Walker; Alessandra Monerris. 2021. "Single-Pass Soil Moisture Retrieval Using GNSS-R at L1 and L5 Bands: Results from Airborne Experiment." Remote Sensing 13, no. 4: 797.
Note: In lieu of an abstract, this is an excerpt from the first page. This paper
Changjiang Hu; Craig Benson; Hyuk Park; Adriano Camps; Li Qiao; Chris Rizos. Addendum: Hu, C.; et al. Detecting Targets above the Earth’s Surface Using GNSS-R Delay Doppler Maps: Results from TDS-1. Remote Sens. 2019, 11, 2327. Remote Sensing 2021, 13, 715 .
AMA StyleChangjiang Hu, Craig Benson, Hyuk Park, Adriano Camps, Li Qiao, Chris Rizos. Addendum: Hu, C.; et al. Detecting Targets above the Earth’s Surface Using GNSS-R Delay Doppler Maps: Results from TDS-1. Remote Sens. 2019, 11, 2327. Remote Sensing. 2021; 13 (4):715.
Chicago/Turabian StyleChangjiang Hu; Craig Benson; Hyuk Park; Adriano Camps; Li Qiao; Chris Rizos. 2021. "Addendum: Hu, C.; et al. Detecting Targets above the Earth’s Surface Using GNSS-R Delay Doppler Maps: Results from TDS-1. Remote Sens. 2019, 11, 2327." Remote Sensing 13, no. 4: 715.
The Flexible Microwave Payload-2 is the GNSS-R and L-band Microwave Radiometer Payload on board 3Cat-5/A, one of the two 6-unit CubeSats of the FSSCat mission, which were successfully launched on 3 September 2020 on Vega flight VV16. The instrument occupies nearly a single unit of the CubeSat, and its goal is to provide sea-ice extension and thickness over the poles, and soil moisture maps at low-moderate resolution over land, which will be downscaled using data from Cosine Hyperscout-2 on board 3Cat-5/B. The spacecrafts are in a 97.5∘ inclination Sun-synchronous orbit, and both the reflectometer and the radiometer have been successfully executed and validated over both the North and the South poles. This manuscript presents the results and validation of the first data sets collected by the instrument during the first two months of the mission. The results of the validation are showing a radiometric accuracy better than 2 K, and a sensitivity lower than the Kelvin. For the reflectometer, the results are showing that the sea-ice transition can be estimated even at short integration times (40 ms). The presented results shows the potential for Earth Observation missions based on CubeSats, which temporal and spatial resolution can be further increased by means of CubeSat constellations.
Joan Munoz-Martin; Lara Fernandez; Adrian Perez; Joan Ruiz-De-Azua; Hyuk Park; Adriano Camps; Bernardo Carnicero Domínguez; Massimiliano Pastena. In-Orbit Validation of the FMPL-2 Instrument—The GNSS-R and L-Band Microwave Radiometer Payload of the FSSCat Mission. Remote Sensing 2020, 13, 121 .
AMA StyleJoan Munoz-Martin, Lara Fernandez, Adrian Perez, Joan Ruiz-De-Azua, Hyuk Park, Adriano Camps, Bernardo Carnicero Domínguez, Massimiliano Pastena. In-Orbit Validation of the FMPL-2 Instrument—The GNSS-R and L-Band Microwave Radiometer Payload of the FSSCat Mission. Remote Sensing. 2020; 13 (1):121.
Chicago/Turabian StyleJoan Munoz-Martin; Lara Fernandez; Adrian Perez; Joan Ruiz-De-Azua; Hyuk Park; Adriano Camps; Bernardo Carnicero Domínguez; Massimiliano Pastena. 2020. "In-Orbit Validation of the FMPL-2 Instrument—The GNSS-R and L-Band Microwave Radiometer Payload of the FSSCat Mission." Remote Sensing 13, no. 1: 121.
Earth Observation missions have increasingly demanding requirements, i.e. higher spatial resolutions and SNR, and lower revisit times, etc. High resolution images have to be captured with precise pointing accuracy which is achieved by the satellite’s Attitude Determination and Control System (ADCS). This subsystem embeds multiple sensors and actuators capable of changing the satellite attitude by changing the torque applied to the platform. In small satellites, magnetorquers, and more recently reaction wheels as well, are the most frequently used actuators. These components fulfill their main purpose, but exhibit some drawbacks, notably a non-constant jitter that provokes non-desired oscillations of the spacecraft, which may result in blurred images. This work presents a deblurring methodology that uses data coming from the ADCS sensors to infer a spatially variant point-spread function. Moreover, the impact of having a lower temporal resolution than the ideal on the sensors is analyzed and a method is presented to improve it.
David Llaveria; Adriano Camps; Hyuk Park. Correcting the ADCS Jitter Induced Blurring in Small Satellite Imagery. IEEE Journal on Miniaturization for Air and Space Systems 2020, 1, 130 -137.
AMA StyleDavid Llaveria, Adriano Camps, Hyuk Park. Correcting the ADCS Jitter Induced Blurring in Small Satellite Imagery. IEEE Journal on Miniaturization for Air and Space Systems. 2020; 1 (2):130-137.
Chicago/Turabian StyleDavid Llaveria; Adriano Camps; Hyuk Park. 2020. "Correcting the ADCS Jitter Induced Blurring in Small Satellite Imagery." IEEE Journal on Miniaturization for Air and Space Systems 1, no. 2: 130-137.
At L-band (1–2 GHz), and particularly in microwave radiometry (1.413 GHz), vegetation has been traditionally modeled with the τ-ω model. This model has also been used to compensate for vegetation effects in Global Navigation Satellite Systems-Reflectometry (GNSS-R) with modest success. This manuscript presents an analysis of the vegetation impact on GPS L1 C/A (coarse acquisition code) signals in terms of attenuation and depolarization. A dual polarized instrument with commercial off-the-shelf (COTS) GPS receivers as back-ends was installed for more than a year under a beech forest collecting carrier-to-noise (C/N0) data. These data were compared to different ground-truth datasets (greenness, blueness, and redness indices, sky cover index, rain data, leaf area index or LAI, and normalized difference vegetation index (NDVI)). The highest correlation observed is between C/N0 and NDVI data, obtaining R2 coefficients larger than 0.85 independently from the elevation angle, suggesting that for beech forest, NDVI is a good descriptor of signal attenuation at L-band, which is known to be related to the vegetation optical depth (VOD). Depolarization effects were also studied, and were found to be significant at elevation angles as large as ~50°. Data were also fit to a simple τ-ω model to estimate a single scattering albedo parameter (ω) to try to compensate for vegetation scattering effects in soil moisture retrieval algorithms using GNSS-R. It is found that, even including dependence on the elevation angle (ω(θe)), at elevation angles smaller than ~67°, the ω(θe) model is not related to the NDVI. This limits the range of elevation angles that can be used for soil moisture retrievals using GNSS-R. Finally, errors of the GPS-derived position were computed over time to assess vegetation impact on the accuracy of the positioning.
Adriano Camps; Alberto Alonso-Arroyo; Hyuk Park; Raul Onrubia; Daniel Pascual; Jorge Querol. L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and Positioning. Remote Sensing 2020, 12, 2352 .
AMA StyleAdriano Camps, Alberto Alonso-Arroyo, Hyuk Park, Raul Onrubia, Daniel Pascual, Jorge Querol. L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and Positioning. Remote Sensing. 2020; 12 (15):2352.
Chicago/Turabian StyleAdriano Camps; Alberto Alonso-Arroyo; Hyuk Park; Raul Onrubia; Daniel Pascual; Jorge Querol. 2020. "L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and Positioning." Remote Sensing 12, no. 15: 2352.
In this paper, an algorithm to retrieve surface soil moisture from GNSS-R (Global Navigaton Satellite System Reflectometry) observations is presented. Surface roughness and vegetation effects are found to be the most critical ones to be corrected. On one side, the NASA SMAP (Soil Moisture Active and Passive) correction for vegetation opacity (multiplied by two to account for the descending and ascending passes) seems too high. Surface roughness effects cannot be compensated using in situ measurements, as they are not representative. An ad hoc correction for surface roughness, including the dependence with the incidence angle, and the actual reflectivity value is needed. With this correction, reasonable surface soil moisture values are obtained up to approximately a 30° incidence angle, beyond which the GNSS-R retrieved surface soil moisture spreads significantly.
Adriano Camps; Hyuk Park; Jordi Castellví; Jordi Corbera; Emili Ascaso. Single-Pass Soil Moisture Retrievals Using GNSS-R: Lessons Learned. Remote Sensing 2020, 12, 2064 .
AMA StyleAdriano Camps, Hyuk Park, Jordi Castellví, Jordi Corbera, Emili Ascaso. Single-Pass Soil Moisture Retrievals Using GNSS-R: Lessons Learned. Remote Sensing. 2020; 12 (12):2064.
Chicago/Turabian StyleAdriano Camps; Hyuk Park; Jordi Castellví; Jordi Corbera; Emili Ascaso. 2020. "Single-Pass Soil Moisture Retrievals Using GNSS-R: Lessons Learned." Remote Sensing 12, no. 12: 2064.
As compared to GPS L1C/A signals, L5/E5a Global Navigation Satellite System-Reflectometry (GNSS-R) improves the spatial resolution due to the narrower auto-correlation function. Furthermore, the larger transmitted power (+3 dB), and correlation gain (+10 dB) allow the reception of weaker reflected signals. If directive antennas are used, very short incoherent integration times are enough to achieve good signal-to-noise ratios, allowing the reception of multiple specular reflection points without the blurring induced by long incoherent integration times. This study presents for the first time experimental evidence of the wind and swell waves signatures in the GNSS-R waveforms, and it performs a statistical analysis, a time-domain analysis, and a frequency-domain analysis for a unique data set of waveforms collected by the UPC MIR instrument during a series of flights over the Bass Strait, Australia.
Joan Francesc Munoz-Martin; Raul Onrubia; Daniel Pascual; Hyuk Park; Adriano Camps; Christoph Rüdiger; Jeffrey Walker; Alessandra Monerris. Experimental Evidence of Swell Signatures in Airborne L5/E5a GNSS-Reflectometry. Remote Sensing 2020, 12, 1759 .
AMA StyleJoan Francesc Munoz-Martin, Raul Onrubia, Daniel Pascual, Hyuk Park, Adriano Camps, Christoph Rüdiger, Jeffrey Walker, Alessandra Monerris. Experimental Evidence of Swell Signatures in Airborne L5/E5a GNSS-Reflectometry. Remote Sensing. 2020; 12 (11):1759.
Chicago/Turabian StyleJoan Francesc Munoz-Martin; Raul Onrubia; Daniel Pascual; Hyuk Park; Adriano Camps; Christoph Rüdiger; Jeffrey Walker; Alessandra Monerris. 2020. "Experimental Evidence of Swell Signatures in Airborne L5/E5a GNSS-Reflectometry." Remote Sensing 12, no. 11: 1759.
The functional performance of space-borne instruments must be validated on ground before and after satellite integration. The effects of Radio-Frequency Interference are also becoming more important, even in protected bands for Earth Observation (EO). In this work, a GNSS and GNSS-R signal simulator is developed as part of a testbed of GNSS receivers and GNSS-R payloads' performance in high dynamics, and to study the effects of RFI in the GNSS-R observables. This work describes the different concepts and key enabling techniques that have been developed to support this project.
Adrian Perez; Joan Francesc Munoz-Martin; Jorge Querol; Hyuk Park; Adriano Camps. Implementation of a Testbed for GNSS-R Payload Performance Evaluation. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 2020, 13, 2708 -2715.
AMA StyleAdrian Perez, Joan Francesc Munoz-Martin, Jorge Querol, Hyuk Park, Adriano Camps. Implementation of a Testbed for GNSS-R Payload Performance Evaluation. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 2020; 13 (99):2708-2715.
Chicago/Turabian StyleAdrian Perez; Joan Francesc Munoz-Martin; Jorge Querol; Hyuk Park; Adriano Camps. 2020. "Implementation of a Testbed for GNSS-R Payload Performance Evaluation." IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 13, no. 99: 2708-2715.
Upcoming Low Earth Orbit Satellite Networks will provide low-latency and high downlink capacity necessary for future broadband communications and Earth Observation missions. This architecture was proposed at the beginning of the 90’s, although it has just recently re-gained popularity thanks to the so-called Mega-Constellations. This network is composed of satellites that have Inter-Satellite Links (ISL) to communicate between them. Due to the satellite motion, an ISL is a temporal contact between two satellites characterized by a lifetime in which the communication remains feasible. The determination of a route between distant satellites is a challenging problem in this context. However, the satellite follows a well-known deterministic orbit trajectory, being feasible the prediction of its position by propagating a trajectory model over time. The Contact Graph Routing protocol uses this feature to determine the evolution of the routes by pre-computing on-ground a planning of the satellite contacts. This centralized grounddependent solution cannot be directly applied in the Internet of Satellites paradigm, which proposes the autonomous deployment of heterogeneous satellite networks without pre-assuming any specific satellite system architecture. Following this concept, the present work proposes a distributed algorithm by which a satellite predicts neighbor contacts, and generates a global contact plan without trajectory propagation. To achieve this solution, an ISL has been modeled as a "close approach" between two satellites, which is characterized by their relative motion. The present work details the predictive algorithm, and evaluates its performance in two scenarios with a hybrid satellite constellation and a mega-constellation.
Joan A. Ruiz-De-Azua; Victoria Ramirez; Hyuk Park; Anna Calveras Auge; Adriano Camps. Assessment of Satellite Contacts Using Predictive Algorithms for Autonomous Satellite Networks. IEEE Access 2020, 8, 100732 -100748.
AMA StyleJoan A. Ruiz-De-Azua, Victoria Ramirez, Hyuk Park, Anna Calveras Auge, Adriano Camps. Assessment of Satellite Contacts Using Predictive Algorithms for Autonomous Satellite Networks. IEEE Access. 2020; 8 (99):100732-100748.
Chicago/Turabian StyleJoan A. Ruiz-De-Azua; Victoria Ramirez; Hyuk Park; Anna Calveras Auge; Adriano Camps. 2020. "Assessment of Satellite Contacts Using Predictive Algorithms for Autonomous Satellite Networks." IEEE Access 8, no. 99: 100732-100748.
As opposed to monostatic radars where incoherent backscattering dominates, in bistatic radars, such as Global Navigation Satellite Systems Reflectometry (GNSS-R), the forward scattered signals exhibit both an incoherent and a coherent component. Current models assume that either one or the other are dominant, and the calibration and geophysical parameter retrieval (e.g., wind speed, soil moisture, etc.) are developed accordingly. Even the presence of the coherent component of a GNSS reflected signal itself has been a matter of discussion in the last years. In this work, a method developed to separate the leakage of the direct signal in the reflected one is applied to a data set of GNSS-R signals collected over the ocean by the Microwave Interferometer Reflectometer (MIR) instrument, an airborne dual-band (L1/E1 and L5/E5a), multi-constellation (GPS and Galileo) GNSS-R instrument with two 19-elements antenna arrays with 4 beam-steered each. The presented results demonstrate the feasibility of the proposed technique to untangle the coherent and incoherent components from the total power waveform in GNSS reflected signals. This technique allows the processing of these components separately, which increases the calibration accuracy (as today both are mixed and processed together), allowing higher resolution applications since the spatial resolution of the coherent component is determined by the size of the first Fresnel zone (300–500 meters from a LEO satellite), and not by the size of the glistening zone (25 km from a LEO satellite). The identification of the coherent component enhances also the location of the specular reflection point by determining the peak maximum from this coherent component rather than the point of maximum derivative of the incoherent one, which is normally noisy and it is blurred by all the glistening zone contributions.
Joan Francesc Munoz-Martin; Raul Onrubia; Daniel Pascual; Hyuk Park; Adriano Camps; Christoph Rüdiger; Jeffrey Walker; Alessandra Monerris. Untangling the Incoherent and Coherent Scattering Components in GNSS-R and Novel Applications. Remote Sensing 2020, 12, 1208 .
AMA StyleJoan Francesc Munoz-Martin, Raul Onrubia, Daniel Pascual, Hyuk Park, Adriano Camps, Christoph Rüdiger, Jeffrey Walker, Alessandra Monerris. Untangling the Incoherent and Coherent Scattering Components in GNSS-R and Novel Applications. Remote Sensing. 2020; 12 (7):1208.
Chicago/Turabian StyleJoan Francesc Munoz-Martin; Raul Onrubia; Daniel Pascual; Hyuk Park; Adriano Camps; Christoph Rüdiger; Jeffrey Walker; Alessandra Monerris. 2020. "Untangling the Incoherent and Coherent Scattering Components in GNSS-R and Novel Applications." Remote Sensing 12, no. 7: 1208.
A modification to the extended CLEAN deconvolution method for passive microwave interferometric radiometers is presented to account for the interferometer beam patterns that vary depending on the source position within the interferometer field of view. This method is developed for the newly proposed multisatellite rotating microwave interferometric radiometer concept for geostationary atmospheric sounding, which is found to have a spatially varying beam pattern. The proposed method is implemented by the piecewise application of Fast Fourier Transform (FFT)-based convolution, i.e., the image is divided into discrete segments, where the beam pattern is assumed to be constant within each segment. This approach allows the proposed method to exploit the speed advantage of the FFT. Applying this method to the proposed multisatellite interferometer shows a twofold improvement in the radiometric accuracy of the restored brightness temperature map, as compared with the constant beam pattern CLEAN.
Ahmed Kiyoshi Sugihara El Maghraby; Hyuk Park; Adriano Camps; Angelo Grubisic; Camilla Colombo; Adrian Tatnall. An FFT-Based CLEAN Deconvolution Method for Interferometric Microwave Radiometers With Spatially Variable Beam Pattern. IEEE Geoscience and Remote Sensing Letters 2020, 18, 341 -345.
AMA StyleAhmed Kiyoshi Sugihara El Maghraby, Hyuk Park, Adriano Camps, Angelo Grubisic, Camilla Colombo, Adrian Tatnall. An FFT-Based CLEAN Deconvolution Method for Interferometric Microwave Radiometers With Spatially Variable Beam Pattern. IEEE Geoscience and Remote Sensing Letters. 2020; 18 (2):341-345.
Chicago/Turabian StyleAhmed Kiyoshi Sugihara El Maghraby; Hyuk Park; Adriano Camps; Angelo Grubisic; Camilla Colombo; Adrian Tatnall. 2020. "An FFT-Based CLEAN Deconvolution Method for Interferometric Microwave Radiometers With Spatially Variable Beam Pattern." IEEE Geoscience and Remote Sensing Letters 18, no. 2: 341-345.
The relative phase and amplitude calibration between individual receiving elements are one of the key challenges in interferometric microwave radiometry. For monolithic interferometers, for example the Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) on board the Soil Moisture and Ocean Salinity (SMOS) mission, the calibration of these two parameters is accomplished by correlated noise injection, where a noise signal from a central noise source is distributed to multiple elements in phase, and any measured phase and amplitude differences can be measured and compensated. As new multisatellite interferometers are being proposed, a new strategy capable of calibrating these errors between the free-flying antennas as well as any antenna position errors is required. In this article, a new calibration scheme is proposed which uses a set of microwave beacons in place of the central noise source, placed at known locations within the interferometer's field of view. The visibility function produced by these point-sources can be precalculated, and any errors between the calculated and the measured visibility samples can be attributed to the errors to be determined. Since the phase of the measured visibility is a function of phase and antenna position errors, this technique is capable of calibrating these two parameters simultaneously. Calibration equations for far- and near-field beacons are presented. Using these expressions, five interferometric calibration routines are proposed and examined for geostationary formation flight microwave radiometers. Although this technique is ideal for multisatellite interferometers with variable antenna positions, it is also applicable to monolithic interferometers that can undergo substantial array deformation.
Ahmed Kiyoshi Sugihara El Maghraby; Hyuk Park; Adriano Camps; Angelo Grubisic; Camilla Colombo; Adrian Tatnall. Phase and Baseline Calibration for Microwave Interferometric Radiometers Using Beacons. IEEE Transactions on Geoscience and Remote Sensing 2020, 58, 5242 -5253.
AMA StyleAhmed Kiyoshi Sugihara El Maghraby, Hyuk Park, Adriano Camps, Angelo Grubisic, Camilla Colombo, Adrian Tatnall. Phase and Baseline Calibration for Microwave Interferometric Radiometers Using Beacons. IEEE Transactions on Geoscience and Remote Sensing. 2020; 58 (8):5242-5253.
Chicago/Turabian StyleAhmed Kiyoshi Sugihara El Maghraby; Hyuk Park; Adriano Camps; Angelo Grubisic; Camilla Colombo; Adrian Tatnall. 2020. "Phase and Baseline Calibration for Microwave Interferometric Radiometers Using Beacons." IEEE Transactions on Geoscience and Remote Sensing 58, no. 8: 5242-5253.
Hyuk Park; Adriano Camps; Jordi Castellvi; Jorge Muro. Generic Performance Simulator of Spaceborne GNSS-Reflectometer for Land Applications. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 2020, 13, 3179 -3191.
AMA StyleHyuk Park, Adriano Camps, Jordi Castellvi, Jorge Muro. Generic Performance Simulator of Spaceborne GNSS-Reflectometer for Land Applications. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 2020; 13 ():3179-3191.
Chicago/Turabian StyleHyuk Park; Adriano Camps; Jordi Castellvi; Jorge Muro. 2020. "Generic Performance Simulator of Spaceborne GNSS-Reflectometer for Land Applications." IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 13, no. : 3179-3191.
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.
Changjiang Hu; Craig Benson; Hyuk Park; Adriano Camps; Li Qiao; Chris Rizos. Detecting Targets above the Earth’s Surface Using GNSS-R Delay Doppler Maps: Results from TDS-1. Remote Sensing 2019, 11, 2327 .
AMA StyleChangjiang Hu, Craig Benson, Hyuk Park, Adriano Camps, Li Qiao, Chris Rizos. Detecting Targets above the Earth’s Surface Using GNSS-R Delay Doppler Maps: Results from TDS-1. Remote Sensing. 2019; 11 (19):2327.
Chicago/Turabian StyleChangjiang Hu; Craig Benson; Hyuk Park; Adriano Camps; Li Qiao; Chris Rizos. 2019. "Detecting Targets above the Earth’s Surface Using GNSS-R Delay Doppler Maps: Results from TDS-1." Remote Sensing 11, no. 19: 2327.
This work analyzes the satellite cross-talk observed by the microwave interferometric reflectometer (MIR), a new global navigation satellite system (GNSS) reflectometer, during an airborne field campaign in Victoria and New South Wales, Australia. MIR is a GNSS reflectometer with two 19-element, dual-band arrays, each of them having four steerable beams. The data collected during the experiment, the characterization of the arrays, and the global positioning system (GPS) and Galileo ephemeris were used to compute the expected delays and power levels of all incoming signals, and the probability of cross-talk was then evaluated. Despite the MIR highly directive arrays, the largest ever for a GNSS-R instrument, one of the flights was found to be contaminated by cross-talk almost half of the time at the L1/E1 frequency band, and all four flights were contaminated ∼5–10% of the time at the L5/E5a frequency band. The cross-talk introduces an error of up to 40 cm of standard deviation for altimetric applications and about 0.24 dB for scatterometric applications.
Raul Onrubia; Daniel Pascual; Hyuk Park; Adriano Camps; Christoph Rüdiger; Jeffrey P. Walker; Alessandra Monerris. Satellite Cross-Talk Impact Analysis in Airborne Interferometric Global Navigation Satellite System-Reflectometry with the Microwave Interferometric Reflectometer. Remote Sensing 2019, 11, 1120 .
AMA StyleRaul Onrubia, Daniel Pascual, Hyuk Park, Adriano Camps, Christoph Rüdiger, Jeffrey P. Walker, Alessandra Monerris. Satellite Cross-Talk Impact Analysis in Airborne Interferometric Global Navigation Satellite System-Reflectometry with the Microwave Interferometric Reflectometer. Remote Sensing. 2019; 11 (9):1120.
Chicago/Turabian StyleRaul Onrubia; Daniel Pascual; Hyuk Park; Adriano Camps; Christoph Rüdiger; Jeffrey P. Walker; Alessandra Monerris. 2019. "Satellite Cross-Talk Impact Analysis in Airborne Interferometric Global Navigation Satellite System-Reflectometry with the Microwave Interferometric Reflectometer." Remote Sensing 11, no. 9: 1120.
This manuscript describes the Microwave Interferometric Reflectometer (MIR) instrument, a multi-beam dual-band GNSS-Reflectometer with beam-steering capabilities built to assess the performance of a PAssive Reflectrometry and Interferometry System—In Orbit Demonstrator (PARIS-IoD) like instrument and to compare the performance of different GNSS-R techniques and signals. The instrument is capable of tracking up to 4 different GNSS satellites, two at L1/E1 band, and two at L5/E5 band. The calibration procedure of the up- and down-looking arrays is presented, the calibration performance is evaluated, and the results of the validation experiments carried out before the field experiments are shown in this paper.
Raul Onrubia; Daniel Pascual; Jorge Querol; Hyuk Park; Adriano Camps. The Global Navigation Satellite Systems Reflectometry (GNSS-R) Microwave Interferometric Reflectometer: Hardware, Calibration, and Validation Experiments. Sensors 2019, 19, 1019 .
AMA StyleRaul Onrubia, Daniel Pascual, Jorge Querol, Hyuk Park, Adriano Camps. The Global Navigation Satellite Systems Reflectometry (GNSS-R) Microwave Interferometric Reflectometer: Hardware, Calibration, and Validation Experiments. Sensors. 2019; 19 (5):1019.
Chicago/Turabian StyleRaul Onrubia; Daniel Pascual; Jorge Querol; Hyuk Park; Adriano Camps. 2019. "The Global Navigation Satellite Systems Reflectometry (GNSS-R) Microwave Interferometric Reflectometer: Hardware, Calibration, and Validation Experiments." Sensors 19, no. 5: 1019.