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Bathymetry from multibeam sonar surveys showing bottom changes after buoy deployment. Hillshade maps (left column) are illuminated by a light source from west (azimuth angle is 270°, clockwise from north), with an elevation angle of 30°. White annotations on the lower right of (a, b, c, and d) show dates of surveys. Details of the outlined cyan box are shown on the right column. In a1, b1, c1, and d1, background color maps show relative heights with color bars changing from dark purple (deeper) to yellow (shallower); colored dots show daily median estimate of anchor positions with color bar change from wheat, green, to black (located at the bottom of (d1)). In b1, c1, and d1, gray dots show a 15‐second interval GPS positions on corresponding days; centers of red “+” mark anchor position estimates for corresponding days. Note that bathymetry artifact in (c) is due to waves caused by ship turning, white pixels in b1, c1, and d1 are data gaps due to low density of valid sounding measurements. All maps are in the same local reference frame. The multibeam data set used to choose the buoy location from April 2018 was collected with a Reson SeaBat T50‐R dual‐head 200–400‐kHz system, run at 400 kHz. The September 2018 data set was collected with a Reson SeaBat 7125, also run at 400 kHz. All following multibeam data sets were collected with the Reson SeaBat T50‐R dual‐head run at 400 kHz.
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Measuring seafloor motion in shallow coastal water is challenging due to strong and highly variable oceanographic effects. Such measurements are potentially useful for monitoring near‐shore coastal subsidence, subsidence due to petroleum withdrawal, strain accumulation/release processes in subduction zones and submerged volcanoes, and certain fresh...
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Understanding the mechanical evolution of magmatic systems requires careful assessment of their rheological characteristics, particularly in light of the growing evidence that magma reservoirs are dominated by magma‐mush surrounded by thermally‐altered host‐rock. To address this complexity, we develop models for volcano deformation based on a porov...
Citations
... [43,49] Time-lapse gravimetry and pressure Section 3.7 [43,[50][51][52][53][54][55][56] Agisco compensator Section 3.8 [43] Microelectromechanical systems (MEMSs) Section 3.9 [57][58][59] Remote sensing Section 3.10 InSAR (interferometric synthetic aperture RADAR) Section 3.10.1 [20,[60][61][62][63][64][65][66][67][68][69] GNSS (global navigation satellite system) time series Section 3.10.2 [11,20,[70][71][72][73][74][75][76][77][78] GNSS on an anchored spar buoy GNSS on an Anchored Spar Buoy [79] Bottom pressure recorder + GNSS (MEDUSA System) Bottom Pressure Recorder + GNSS (MEDUSA System) [80][81][82][83] ...
... The examined case studies cover diverse geographical localities worldwide, including Anga, Italy [20]; Offshore Italy [74,75]; West Lutong [11]; Malaysia; Indonesia [71]; Tampa Bay, Florida [76]; Ekofisk, Norway [70]; and Harvest, California, USA [77,78]. ...
In view of the ever-increasing global energy demands and the imperative for sustainability in extraction methods, this article surveys subsidence monitoring systems applied to oil and gas fields located in offshore areas. Subsidence is an issue that can harm infrastructure, whether onshore or especially offshore, so it must be carefully monitored to ensure safety and prevent potential environmental damage. A comprehensive review of major monitoring technologies used offshore is still lacking; here, we address this gap by evaluating several techniques, including InSAR, GNSSs, hydrostatic leveling, and fiber optic cables, among others. Their accuracy, applicability, and limitations within offshore operations have also been assessed. Based on an extensive literature review of more than 60 published papers and technical reports, we have found that no single method works best for all settings; instead, a combination of different monitoring approaches is more likely to provide a reliable subsidence assessment. We also present selected case histories to document the results achieved using integrated monitoring studies. With the emerging offshore energy industry, combining GNSSs, InSAR, and other subsidence monitoring technologies offers a pathway to achieving precision in the assessment of offshore infrastructural stability, thus underpinning the sustainability and safety of offshore oil and gas operations. Reliable and comprehensive subsidence monitoring systems are essential for safety, to protect the environment, and ensure the sustainable exploitation of hydrocarbon resources.
... Beck et al., 2022;Chen et al., 2018bChen et al., , 2020Chen et al., , 2022Liu et al., 2017Liu et al., , 2022Liu et al., , 2023 or anthropogenic (Liu et al., 2021;Chen et al., 2023a) perturbations. The TBCOM hindcast products also have been used to support the studies of an anchored spar-buoy seafloor geodetic system at the mouth of Tampa Bay (Xie et al., 2019(Xie et al., , 2021. ...
Bathymetric changes within estuarine and coastal waters can alter the hydrodynamic evolution of sea level and currents, which in turn can influence the ecosystem by altering material property distributions. Here we apply the Tampa Bay Coastal Ocean Model (TBCOM), with an unstructured, high-resolution grid to investigate the hydrodynamic response to bathymetric changes at the periphery of the Tampa Bay mouth over a relatively small area when compared to the whole model domain. Two separate numerical experiments are conducted with the same forcing, one using the original bathymetry and the other employing a revised synthetic bathymetry. The simulated sea level, amplitude and phase of the M2 tide, and associated currents are compared for the two experiments. Significant changes in water level (up to+/-10 cm) and current velocities (up to 20 cm/s) are found in the shallow peripheral area with the two different bathymetric data sets. These bathymetric influences are not limited to the locations where the bathymetric changes occur; they also extend remotely to areas of the bay. Since Tampa Bay bathymetry varies with storm-induced sediment redistributions and human actives such as shipping channel dredging and beach nourishment, these findings emphasize the need for accurate and updated bathymetry for coastal ocean modeling and applications.
... The measurements of both these instruments can be jointly used to recover the sea bottom deformation down to millimeter accuracy in presence of oscillations of the top of the buoy caused by marine and weather conditions (Xie et al. 2019). ...
... Compared to previous works presented in Xie et al. (2019) and De Martino et al. (2020), the novelty of the methodological approach presented in this paper consists in the combination of four main aspects: (i) The estimation of the uncertainties of the compass sensor output angles through a stacking method based on the analysis of the real data coming from the cGPS and the compass and its inclusion in the subsequent data analysis; (ii) The correction of the cGPS data through compass data, ingesting the previous step in the analysis, to account for the pole inclination which, if not taken into account, can alter the horizontal seafloor deformation estimation; (iii) The comparison between the results based on sets of data extracted for different maximum pole inclinations up to 3.5 • and the convergence of the retrieved parameters for increasing pole inclinations; (iv) The analysis of the impact of the main systematic effects on the estimated parameters. ...
... The shift due to the pole inclination vanishes when the buoy stands along the vertical position, characterized by zero values of two tilt (roll and pitch) angles. Differently, it can be evaluated on the basis of the rotation matrix defined by the compass data (Xie et al. 2019). Given the pole length, the rotation matrix allows the computation of the two components, d C E,N , to be subtracted from cGPS horizontal measurements, d G E,N , to obtain the corrected seabed horizontal position, d E,N . ...
Seafloor deformation monitoring is now routinely performed in the marine sector of the Campi Flegrei volcanic area (Southern Italy). The MEDUSA infrastructure is formed by four buoys deployed at a water depth ranging from 40 to 96 m, and equipped with cGPS receivers, accelerometers and magnetic compasses to monitor the buoy status and a seafloor module with a bottom pressure recorder and other onboard instruments. The analysis of the time series data acquired by the MEDUSA monitoring infrastructure system allows to study the seafloor deformation in the Campi Flegrei caldera with geodetic accuracy. In a previous work, we show that the time series acquired by the Campi Flegrei cGPS onland network and MEDUSA over the period 2017–2020 are in good agreement with the ground deformation field predicted by a Mogi model which is widely used to describe the observed deformation of an active volcano in terms of magma intrusion. Only for one of the buoys, CFBA (A), the data differ significantly from the model prediction, at a level of $$\simeq $$ ≃ 6.9 $$\sigma $$ σ and of $$\simeq $$ ≃ 23.7 $$\sigma $$ σ for the seafloor horizontal speed and direction, respectively. For this reason, we devised a new method to reconstruct the horizontal sea bottom displacement considering in the analysis both cGPS and compass data. The method, applied to the CFBA buoy measurements and validated also on the CFBC (C) buoy, uses compass data to correct cGPS positions accounting for the pole inclination. Including also systematic errors, the internal consistency, always within $$\sim $$ ∼ 3 $$\sigma $$ σ for the speed and $$\sim $$ ∼ 2 $$\sigma $$ σ for the angle, between the results derived for different maximum inclinations of the buoy pole (up to 3.5 $$^{\circ }$$ ∘ ) indicates that the method allows to significantly reduce the impact of the pole inclination which, if not properly taken into account, can alter the estimation of the horizontal seafloor deformation. In particular, we find a good convergence of the retrieved velocity and deformation angle as we include in the analysis data from increasing values of the buoy pole inclination. Taking the result derived assuming the maximum allowed cutoff and accounting for statistical and systematic errors, we found a speed $$v$$ v = (3.521 ± 0.039 ( stat ) ± 0.352 ( syst )) cm/yr and a deformation direction angle $$\alpha $$ α = ( $$-115.159$$ - 115.159 ± 0.670 ( stat ) ± 7.630 ( syst )) $$^{\circ }$$ ∘ (statistical errors at 1 $$\sigma $$ σ quoted from the rms of their values, main systematic errors added linearly). The relative impact of the main potential systematic (statistical) effects increases (decreases) with the cutoff. Our analysis provides a horizontal speed consistent with the model at a level of $$\simeq $$ ≃ 5.2 $$\sigma $$ σ ( stat only) or of $$\simeq $$ ≃ 0.5 $$\sigma $$ σ ( stat and syst added linearly), and a deformation angle consistent with the model at $$\simeq $$ ≃ 4.3 $$\sigma $$ σ level ( stat only) or at $$\simeq $$ ≃ 0.3 $$\sigma $$ σ level ( stat and syst added linearly). Correspondingly, the module of the vectorial difference between the velocity retrieved from the data and the velocity of the adopted Mogi model diminishes by a factor of $$\simeq $$ ≃ 7.65 ± 1.23 ( stat ) or ± 5.78 ( stat + syst ) with respect to the previous work. A list of potential improvements to be implemented in the system and instruments is also discussed.
... The measurements of both these instruments can be jointly used to recover the sea bottom deformation down to millimetre accuracy in presence of oscillations of the top of the buoy caused by marine and weather conditions (Xie et al. (2019)). ...
... Compared to previous works presented in Xie et al. (2019) and De Martino et al. (2020), the novelty of the methodological approach presented in this paper consists in the combination of four main aspects: i) the estimation of the uncertainties of the compass sensor output angles through a stacking method based on the analysis of the real data coming from the cGPS and the compass and its inclusion in the subsequent data analysis; ii) the correction of the cGPS data through compass data, ingesting the previous step in the analysis, to account for the pole inclination which, if not taken into account, can alter the horizontal seafloor deformation estimation; iii) the comparison between the results based on sets of data extracted for different maximum pole inclinations up to 3.5 • and the convergence of the retrieved parameters for increasing pole inclinations; iv) the analysis of the impact of the main systematic effects on the estimated parameters. ...
... The shift due to the pole inclination vanishes when the buoy stands along the vertical position, characterized by zero values of two tilt (roll and pitch) angles. Differently, it can be evaluated on the basis of the rotation matrix defined by the compass data (Xie et al. (2019)). Given the pole length, the rotation matrix allows the computation of the two components, d C E,N , to be subtracted from cGPS horizontal measurements, d G E,N , to obtain the corrected seabed horizontal position, d E,N . ...
Seafloor deformation monitoring is now performed in the marine sector of the Campi Flegrei volcanic area. MEDUSA infrastructure consists of 4 buoys at depths of 40-96m equipped with cGPS receivers, accelerometers and magnetic compasses to monitor buoy status and a seafloor module with a bottom pressure recorder. We study the seafloor deformation in the caldera. Previously we show that cGPS onland network and MEDUSA timeseries for the years 2017-2020 are in agreement with the deformation predicted by a Mogi model describing the observed deformation of an active volcano. Only for buoy A data differ significantly from model, at 6.9sigma and 23.7sigma for the horizontal speed (v) and direction. We devised a new method to reconstruct the sea bottom displacement including cGPS and compass data. The method, applied to buoy A and validated also on C, uses compass data to correct cGPS positions accounting for pole inclination. Including systematic errors, the internal consistency, within 3sigma (2sigma) for the speed (angle), between the results derived for different maximum inclinations of the buoy pole up to 3.5deg shows that the method allows to significantly reduce the impact of the pole inclination which can alter the estimation. We find good convergence of the velocity and deformation angle for increasing values of the buoy pole inclination. We found v=3.521+-0.039(stat)+-0.352(syst)cm/yr and an angle -115.159+-0.670(stat)+-7.630(syst)deg. The relative impact of potential systematics (statistical) effects increases (decreases) with cutoff. Our analysis gives v consistent with Mogi at 5.2sigma(stat) or 0.5sigma(stat and syst), and a deformation angle consistent at 4.3sigma(stat) or at 0.3sigma. The module of the vectorial difference between v from the data and Mogi diminishes by a factor 7.65+-1.23(stat) or +-5.78(stat+syst) compared with previous work. Potential improvements are discussed.
... TBCOM also helped to guide dead fish cleanup operations by Pinellas County during the major red tide event that ensued subsequent to the Piney Point release. Other recent applications include the works of Xie et al. (2019Xie et al. ( , 2021 describing the precision of GPS observations on a spar buoy anchored at the mouth of Tampa Bay. ...
With a large salinity gradient existing between the rivers and the ocean, the saline environment of an estuary is crucial to its ecosystem functionality. For Tampa Bay, the Howard F. Curren Advanced Wastewater Treatment Plant (HFCAWTP) presently yields an outflow of nearly freshwater to the Hillsborough Bay portion of Tampa Bay. In order to estimate the potential impact that the removal of this outflow may have on the salinity and flow fields of Hillsborough Bay, as part of the Tampa Augmentation Project, both numerical circulation model and Knudsen theorem applications are made. The numerical model study compares the instantaneous and nontidal, mean estuarine circulation and salinity distributions for the Hillsborough Bay on the basis of the HFCAWTP outflow being either included with, or excluded from, the freshwater inflows. It is found that the potential reduction of the treated reclaimed water inflow to the bay from the HFCAWTP will not significantly affect the circulation or the salinity distributions of Hillsborough Bay or of the larger Tampa Bay. The estimation through a Knudsen theorem application shows an 0.13 psu increase of salinity after removing the HFCAWTP outflow when averaged within Hillsborough Bay. Thus, both approaches demonstrate that the effects of HFCAWTP outflow removal are very small when compared with variations that occur naturally.
... Campi Flegrei offers an important natural laboratory for geodetic studies of caldera systems. The coastal setting has stimulated the development of submarine volcano deformation measurements, since most of the caldera system is submerged (Iannaccone et al. 2018;Xie et al. 2019). Geodetic studies of Campi Flegrei have also inspired worldwide investigations of calderas. ...
Over the first century of the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI), volcano geodesy grew from roots as an accidental and incidental system of measurements to an important method for monitoring volcanic activity and forecasting eruptions. The first practitioners in volcano geodesy were experts in other disciplines, and it was not until the latter half of the twentieth century that specialists in the field emerged—scientists who developed new methods, measured geodetic change at volcanoes, and quantitatively interpreted the results in terms of magmatic processes. Much of the early work in the field was restricted to a few volcanoes and involved techniques that had been adapted from other applications; relatively few methods were developed specifically for use on volcanoes. These volcanoes, however, provided the natural laboratories needed to advance the field. By the start of the twenty-first century, geodetic studies, especially using space-based techniques, contributed to the recognition of deformation and gravity change at hundreds of volcanoes on Earth. In coming years, IAVCEI researchers will focus on comprehensive exploitation of the growing volumes of geodetic data to better model, forecast, and track activity at volcanoes worldwide. Meanwhile, the field needs to become more diverse, better representing people who live in the shadows of volcanoes around the globe.
... From left to right, top to down: the seafloor multi-instrumented observatory; the underwater view of the floating from the bottom by an UHD submerged camera; a diving operator who performs an inspection on the electro-mechanical cable that ensures the connection of the seafloor observatory to the top of buoy (for the powersupply, Ethernet link and the GPS communication for the time-marking of the data acquired); the buoy ballast on the seabed (see alsoXie et al., 2019). ...
The InSEA project (“Initiatives in Supporting the consolidation and enhancement of the EMSO research infrastructure consortium (ERIC) and related Activities”) has the objective, as the full name of the project indicates, to consolidate and strengthen the infrastructures concerning the EMSO (“European Multidisciplinary Seafloor and water column Observatory”) ERIC (European Research Infrastructure Consortium) and all those technical-scientific activities related to it. In particular, the project is upgrading localized and distributed marine infrastructures, laboratories, observatories and spatial measurement activities in Southern Italian seas to support those activities of surveys in fixed time series points of observation of EMSO ERIC. The project is developing according to six implementation Objectives of Research (OR) that involve four National research Institutions: INGV, ISPRA, OGS and Anton Dohrn Zoological Station of Naples. The paper illustrates with more details the relevant objectives of the InSEA project and its most significant implementation phases.
... The system was designed for measuring three-component seafloor motion, with the GPS antenna placed on top of the spar, and the bottom of the spar connected to a heavy ballast by a shackle. A float is integrated into the spar to provide buoyancy, keeping the buoy near vertical (Xie et al., 2019). This design is much less expensive compared to construction and deployment of massive rigid spars, and can be redeployed when necessary. ...
... Height changes of the antenna above water reflect a combination of vertical motion of the anchor, spar tilt, and water level changes, although after several months of settling anchor vertical motion is minimal. The system can be deployed in shallow offshore waters, several kilometers or more from the coastline (Xie et al., 2019). Since only GPS data are used in this study, we refer to the method as GPS-IR unless noted. ...
... Water levels are calculated by H = H g − H r , where H, H g , and H r denote water level, elevation of the GPS antenna phase center, and reflecting height (vertical distance between GPS antenna phase center and the water surface), respectively. Kinematic GPS processing to estimate H g was reported in Xie et al. (2019); we follow the same method here: GPS positions are determined using Precise Point Positioning method provided by the Canadian Spatial Reference System (CSRS, https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ ppp.php?locale, last access on September 5, 2021). Typical formal error of H g for a single epoch is 3-5 cm. ...
Conventional tide gauges are usually housed along the coast. Satellite altimetry works well in the open ocean but poorly near the coast due to signal contamination by land returns. These limitations lead to an observational gap in the transition zone between the coast and open ocean. Using data collected by a GPS installed on top of an anchored spar‐buoy in Tampa Bay, we retrieved water levels through a combination of precise positioning and interferometric reflectometry. Individual water level retrievals agree with a nearby acoustic tide gauge (19.5 km distance) at ∼15 cm level. Amplitude and phase of the major tidal constituents are well recovered by the GPS spar‐buoy measurements. Over a 2.9‐year period, agreement of de‐tided daily mean sea levels measured by the GPS spar‐buoy and the nearby acoustic tide gauge is 4.4 cm. When sea level data measured by the GPS spar‐buoy are included in the local coastal ocean circulation model, low‐frequency error propagated from the open boundary is significantly reduced.
... We determined kinematic site positions from three on-ice GNSS stations (JEME, LMID, and JNIH) using TRACK software which uses carrier-phase differential processing relative to bedrock mounted base stations (Text S3; Herring et al., 2010;Xie et al., 2019). We used GNSS stations KAGA (28 km baseline length) and ROCK (36 km baseline) as reference stations ( Figure S3). ...
Plain Language Summary
Meltwater produced on the surface of the Greenland Ice Sheet reaches the bed by flowing into crevasses or moulins, vertical holes that connect to the ice sheet's base. Early in the summer, meltwater that reaches the bed increases water pressures within the drainage system underneath the ice sheet, increasing sliding speeds. However, later in the summer, ice sliding speeds often slowdown despite continued meltwater inputs. While these slowdowns have been attributed to the growth of subglacial conduits, recent observations suggest the drainage of hydraulically isolated cavities—pockets of water formed by ice sliding over bedrock bumps—may instead be responsible. Here, we measure surface ice motion and water pressures within moulins located several kilometers away from rapidly draining supraglacial lakes. We show the passing of a floodwave underneath the ice sheet slowed sliding to wintertime speeds without enlarging subglacial channels connected to our instrumented moulin. Instead, our results indicate the drainage of isolated cavities may be responsible for slowdowns that occur during the melt season. Accordingly, our results, similar to others, suggest increased channelization of the subglacial drainage system appears unlikely to buffer GrIS ice velocity against future meltwater inputs.
Due to the blockage of seawater, seafloor displacement cannot be directly measured by space geodesy. The combination of Global Navigation Satellite Systems‐acoustic ranging (GNSS‐A) has been used to overcome the electromagnetic barrier, so that a GNSS‐determined sea surface vessel's coordinates can be transformed to seafloor benchmarks in a global reference frame. Due to the high cost and science priorities, previous GNSS‐A studies mainly targeted relatively deep water and a minimum of three transponders were used to form an array, equivalent to a precision geodetic station. With recent developments in unmanned autonomous surface vessels, low cost GNSS‐A surveys are poised to become practical. Here we demonstrate that with a carefully designed surveying trajectory, Wave Glider‐based GNSS‐A surveying of a single transponder in shallow water can provide centimeter‐level accuracy on horizontal seafloor positioning, even if the sound speed model deviates from the actual value by a few meters per second. Results from a nine‐month experiment conducted at ∼54 m water depth show that the repeatability of the seafloor horizontal positioning is better than 2 cm. When conditions allow, the acoustic observations should be collected symmetrically about the transponder and data redundancies are recommended to reduce the error associated with time‐dependent variations in sound speed.
