64 research outputs found
Inferring Glaciological Attributes of Thwaites Glacier Using GPS-Interferometric Reflectometry and Precise Point Positioning
We use two continuous GPS stations located on Thwaites glacier to estimate the rate of snow accumulation through GPS interferometric reflectometry and separately examine details of the motions of the glacier. We find an 8-year snow accumulation rate in meters water equivalent for the station Upper Thwaites of 0.44±0.03 m.w.e./yr and a 7-year rate for the station Lower Thwaites of 0.56±0.06 m.w.e./yr. Averages at both GPS sites match the European Centre for Medium-Range Weather Forecasts reanalysis accumulation rate, derived from integrated snowfall over the same period. We used precise point positioning to obtain daily station positions and modeled the observed movement of the glacier towards the Amundsen Sea using a constant acceleration and periodic fluctuations about this background motion. Lower Thwaites exhibits statistically significant deviations from this model that may be related to emptying and refilling of a nearby subglacial lake
Measuring Snow Liquid Water Content with Low-Cost GPS Receivers
The amount of liquid water in snow characterizes the wetness of a snowpack. Its temporal evolution plays an important role for wet-snow avalanche prediction, as well as the onset of meltwater release and water availability estimations within a river basin. However, it is still a challenge and a not yet satisfyingly solved issue to measure the liquid water content (LWC) in snow with conventional in situ and remote sensing techniques. We propose a new approach based on the attenuation of microwave radiation in the L-band emitted by the satellites of the Global Positioning System (GPS). For this purpose, we performed a continuous low-cost GPS measurement experiment at the Weissfluhjoch test site in Switzerland, during the snow melt period in 2013. As a measure of signal strength, we analyzed the carrier-to-noise power density ratio (C/N-0) and developed a procedure to normalize these data. The bulk volumetric LWC was determined based on assumptions for attenuation, reflection and refraction of radiation in wet snow. The onset of melt, as well as daily melt-freeze cycles were clearly detected. The temporal evolution of the LWC was closely related to the meteorological and snow-hydrological data. Due to its non-destructive setup, its cost-efficiency and global availability, this approach has the potential to be implemented in distributed sensor networks for avalanche prediction or basin-wide melt onset measurements
Analytical and Experimental Methods for the Characterization of Field Propagation in Non-Standard Conditions
The electromagnetic propagation is totally and fully assessed in free space, in standard working conditions. However there exists peculiar propagation environments in which the propagation has not been studied but in which it could be fully exploited in order to assess specic needs or to provide new sensing tools. In particular the research activity describes in this thesis has been devoted to the study of the propagation in non-standard condition
Soil Moisture & Snow Properties Determination with GNSS in Alpine Environments: Challenges, Status, and Perspectives
Moisture content in the soil and snow in the alpine environment is an important factor, not only for environmentally oriented research, but also for decision making in agriculture and hazard management. Current observation techniques quantifying soil moisture or characterizing a snow pack often require dedicated instrumentation that measures either at point scale or at very large (satellite pixel) scale. Given the heterogeneity of both snow cover and soil moisture in alpine terrain, observations of the spatial distribution of moisture and snow-cover are lacking at spatial scales relevant for alpine hydrometeorology. This paper provides an overview of the challenges and status of the determination of soil moisture and snow properties in alpine environments. Current measurement techniques and newly proposed ones, based on the reception of reflected Global Navigation Satellite Signals (i.e., GNSS Reflectometry or GNSS-R), or the use of laser scanning are reviewed, and the perspectives offered by these new techniques to fill the current gap in the instrumentation level are discussed. Some key enabling technologies including the availability of modernized GNSS signals and GNSS array beamforming techniques are also considered and discussed
An assessment of sub-snow GPS for quantification of snow water equivalent
Global Navigation Satellite Systems (GNSS) contribute to various
Earth observation applications. The present study investigates the potential
and limitations of the Global Positioning System (GPS) to estimate in situ
water equivalents of the snow cover (snow water equivalent, SWE) by using
buried GPS antennas. GPS-derived SWE is estimated over three seasons
(2015/16–2017/18) at a high Alpine test site in Switzerland. Results are
validated against state-of-the-art reference sensors: snow scale, snow
pillow, and manual observations. SWE is estimated with a high correspondence
to the reference sensors for all three seasons. Results agree with a median
relative bias below 10 % and are highly correlated to the mean of the three
reference sensors. The sensitivity of the SWE quantification is assessed for
different GPS ambiguity resolution techniques, as the results strongly depend
on the GPS processing.</p
Geodetic Sciences
Space geodetic techniques, e.g., global navigation satellite systems (GNSS), Very Long Baseline Interferometry (VLBI), satellite gravimetry and altimetry, and GNSS Reflectometry & Radio Occultation, are capable of measuring small changes of the Earth�s shape, rotation, and gravity field, as well as mass changes in the Earth system with an unprecedented accuracy. This book is devoted to presenting recent results and development in space geodetic techniques and sciences, including GNSS, VLBI, gravimetry, geoid, geodetic atmosphere, geodetic geophysics and geodetic mass transport associated with the ocean, hydrology, cryosphere and solid-Earth. This book provides a good reference for geodetic techniques, engineers, scientists as well as user community
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