916 research outputs found
The Eddy Experiment: accurate GNSS-R ocean altimetry from low altitude aircraft
During the Eddy Experiment, two synchronous GPS receivers were flown at 1 km
altitude to collect L1 signals and their reflections from the sea surface for
assessment of altimetric precision and accuracy. Wind speed (U10) was around 10
m/s, and SWH up to 2 m. A geophysical parametric waveform model was used for
retracking and estimation of the lapse between the direct and reflected signals
with a 1-second precision of 3 m. The lapse was used to estimate the SSH along
the track using a differential model. The RMS error of the 20 km averaged
GNSS-R absolute altimetric solution with respect to Jason-1 SSH and a GPS buoy
measurement was of 10 cm, with a 2 cm mean difference. Multipath and retracking
parameter sensitivity due to the low altitude are suspected to have degraded
accuracy. This result provides an important milestone on the road to a GNSS-R
mesoscale altimetry space mission.Comment: All Starlab authors have contributed significantly; the Starlab
Author list has been ordered randoml
Detecting Targets above the Earth's Surface Using GNSS-R Delay Doppler Maps: Results from TDS-1
: 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.Peer ReviewedPostprint (published version
Sea state monitoring using coastal GNSS-R
We report on a coastal experiment to study GPS L1 reflections. The campaign
was carried out at the Barcelona Port breaker and dedicated to the development
of sea-state retrieval algorithms. An experimental system built for this
purpose collected and processed GPS data to automatically generate a times
series of the interferometric complex field (ICF). The ICF was analyzed off
line and compared to a simple developed model that relates ICF coherence time
to the ratio of significant wave height (SWH) and mean wave period (MWP). The
analysis using this model showed good consistency between the ICF coherence
time and nearby oceanographic buoy data. Based on this result, preliminary
conclusions are drawn on the potential of coastal GNSS-R for sea state
monitoring using semi-empirical modeling to relate GNSS-R ICF coherence time to
SWH.Comment: All Starlab authors have contributed significantly; the Starlab
author list has been ordered randomly. Submitted to GR
The GNSS-R Eddy Experiment II: L-band and Optical Speculometry for Directional Sea-Roughness Retrieval from Low Altitude Aircraft
We report on the retrieval of directional sea-roughness (the full directional
mean square slope, including MSS, direction and isotropy) through inversion of
Global Navigation Satellite System Reflections (GNSS-R) and SOlar REflectance
Speculometry (SORES)data collected during an experimental flight at 1000 m. The
emphasis is on the utilization of the entire Delay-Doppler Map (for GNSS-R) or
Tilt Azimuth Map (for SORES) in order to infer these directional parameters.
Obtained estimations are analyzed and compared to Jason-1 measurements and the
ECMWF numerical weather model.Comment: Proceedings from the 2003 Workshop on Oceanography with GNSS
Reflections, Barcelona, Spain, 200
Improved gnss-r altimetry methods: Theory and experimental demonstration using airborne dual frequency data from the microwave interferometric reflectometer (mir)
Altimetric performance of Global Navigation Satellite System - Reflectometry (GNSS-R) instruments depends on receiver’s bandwidth and signal-to-noise ratio (SNR). The altimetric delay is usually computed from the time difference between the peak of the direct signal waveform and the maximum of the derivative of the reflected signal waveform. Dual-frequency data gathered by the airborne Microwave Interferometric Reflectometer (MIR) in the Bass Strait, between Australia and Tasmania, suggest that this approach is only valid for flat surfaces and large bandwidth receivers. This work analyses different methods to compute the altimetric observables using GNSS-R. A proposed novel methodThis work was funded by the Spanish Ministry of Science, Innovation and Universities,
“Sensing with Pioneering Opportunistic Techniques”, grant RTI2018-099008-B-C21/AEI/10.13039/
501100011033, and the grant for recruitment of early-stage research staff FI-DGR 2015 of the AGAUR—
Generalitat de Catalunya (FEDER), Spain, and the grant for recruitment of early-stage research staff
FI 2018 of the AGAUR—Generalitat de Catalunya (FEDER), Spain, and Unidad de Excelencia MarĂa
de Maeztu MDM-2016-060Postprint (published version
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