ORCID Profile
0000-0002-7464-4592
Current Organisation
University of Tasmania
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Publisher: Springer Science and Business Media LLC
Date: 11-05-2015
DOI: 10.1038/NCLIMATE2635
Publisher: American Geophysical Union (AGU)
Date: 05-2017
DOI: 10.1002/2016JB013698
Publisher: Informa UK Limited
Date: 07-2011
Publisher: American Geophysical Union (AGU)
Date: 06-2021
DOI: 10.1029/2020JC017106
Abstract: Vertical land motion (VLM) is the connection between absolute sea‐level (ASL) from a satellite altimeter (ALT) and relative sea‐level from a tide gauge (TG). VLM is often sparsely observed yet is required for understanding sea‐level rise. Many studies have sought to exploit ALT and TG data to infer VLM, yet regionally correlated systematic errors in altimetry have not been considered. We have developed a Kalman filtering and smoothing framework to simultaneously estimate location‐specific VLM and residual mission‐specific systematic errors in a geocentric reference frame. We used ALT minus TG, ALT crossovers and global positioning system (GPS) bedrock height observations in a multi‐stage solution approach that gradually separated time‐variable parameter estimates in an ill‐posed problem. We evaluated the performance of the method using the Jason‐series along‐track data in the Baltic Sea, where glacial isostatic adjustment is the dominant driver of VLM. We estimated local VLM variability at TGs of up to ∼4.5 mm/yr which is not evident in spatially interpolated GPS velocities. The estimated regional altimeter errors are significant and within the range of ∼±0.5–2.5 mm/yr. Our approach improves agreement between ASL estimates from ALT and TG records, provides a ∼20% decrease in root mean squared error of latitudinal ASL variability at TGs, and a reduction of the ASL rate from altimetry by ∼0.3 mm/yr across the region. This method advances the ALT‐TG approach to determining VLM at TG locations and systematic errors of altimetry, which is broadly applicable to other regional‐ and global‐scale studies.
Publisher: Springer Science and Business Media LLC
Date: 26-06-2017
DOI: 10.1038/NCLIMATE3325
Publisher: Springer Science and Business Media LLC
Date: 18-04-2016
Publisher: Elsevier BV
Date: 05-2018
Publisher: American Geophysical Union (AGU)
Date: 06-04-2016
DOI: 10.1002/2016GL068436
Publisher: MDPI AG
Date: 25-05-2012
DOI: 10.3390/RS4061519
Publisher: Elsevier BV
Date: 09-2017
Publisher: Wiley
Date: 03-2021
Publisher: American Geophysical Union (AGU)
Date: 23-02-2022
DOI: 10.1029/2021GL097232
Abstract: We investigate present‐day bedrock vertical motion using new Global Positioning System (GPS) timeseries from the Totten‐Denman glacier region of East Antarctica (∼77°–120°E) where models of glacial isostatic adjustment (GIA) disagree, glaciers are likely losing mass, and few data constraints on GIA exist. We show that varying surface mass balance loading (SMBL) is a dominant signal, contributing random‐walk‐like noise to GPS timeseries across Antarctica. In the study region, it induces site velocity biases of up to ∼+1 mm/yr over 2010–2020. After correcting for SMBL displacement and GPS common mode error, subsidence is evident at all sites aside from the Totten Glacier region where uplift is ∼1.5 mm/yr. Uplift near the Totten Glacier is consistent with late Holocene ice retreat while the widespread subsidence further west suggests possible late Holocene readvance of the region’s ice sheet, in broad agreement with limited glacial geological data and highlighting the need for s ling beneath the current ice sheet.
Publisher: Wiley
Date: 29-09-2020
Publisher: Springer Science and Business Media LLC
Date: 14-03-2013
Publisher: American Society of Civil Engineers (ASCE)
Date: 02-2007
Publisher: American Geophysical Union (AGU)
Date: 28-07-2017
DOI: 10.1002/2017GL073486
Publisher: Springer Science and Business Media LLC
Date: 03-06-2014
Publisher: MDPI AG
Date: 15-10-2018
DOI: 10.3390/S18103465
Abstract: We investigate footprint geolocation uncertainties of a spectroradiometer mounted on an unmanned aircraft system (UAS). Two microelectromechanical systems-based inertial measurement units (IMUs) and global navigation satellite system (GNSS) receivers were used to determine the footprint location and extent of the spectroradiometer. Errors originating from the on-board GNSS/IMU sensors were propagated through an aerial data georeferencing model, taking into account a range of values for the spectroradiometer field of view (FOV), integration time, UAS flight speed, above ground level (AGL) flying height, and IMU grade. The spectroradiometer under nominal operating conditions (8 ∘ FOV, 10 m AGL height, 0.6 s integration time, and 3 m/s flying speed) resulted in footprint extent of 140 cm across-track and 320 cm along-track, and a geolocation uncertainty of 11 cm. Flying height and orientation measurement accuracy had the largest influence on the geolocation uncertainty, whereas the FOV, integration time, and flying speed had the biggest impact on the size of the footprint. Furthermore, with an increase in flying height, the rate of increase in geolocation uncertainty was found highest for a low-grade IMU. To increase the footprint geolocation accuracy, we recommend reducing flying height while increasing the FOV which compensates the footprint area loss and increases the signal strength. The disadvantage of a lower flying height and a larger FOV is a higher sensitivity of the footprint size to changing distance from the target. To assist in matching the footprint size to uncertainty ratio with an appropriate spatial scale, we list the expected ratio for a range of IMU grades, FOVs and AGL heights.
Publisher: MDPI AG
Date: 14-05-2012
DOI: 10.3390/RS4051392
Publisher: American Geophysical Union (AGU)
Date: 06-2021
DOI: 10.1029/2021JB021992
Abstract: GPS observations of ocean tide loading displacements can help infer the regional anelastic properties of the asthenosphere. We estimate M 2 ocean tide loading displacements at 170 GPS sites in New Zealand and compare these to modeled values using a range of numerical tide and radially symmetric (1D) elastic and anelastic Earth models. Regardless of the model combination, we are unable to reduce the strong spatial coherence of the M 2 residuals across the North Island where they reach 0.4 mm (2%). The best fit in the North Island is obtained when combining the FES2014b tide model with spatially variable ocean density and water compressibility, and the STW105 Earth model. The residuals exhibit a change of ∼0.3 mm in magnitude between the Taupo Volcanic Zone and the east coast (∼100 km), suggesting that this region's laterally varying, shallow rheological structure may need to be considered to explain these observations.
Publisher: American Geophysical Union (AGU)
Date: 05-2013
DOI: 10.1002/JGRB.50154
Publisher: Springer Science and Business Media LLC
Date: 12-2022
DOI: 10.1007/S00190-022-01680-3
Abstract: We further developed a space–time Kalman approach to investigate time-fixed and time-variable signals in vertical land motion (VLM) and residual altimeter systematic errors around the Australian coast, through combining multi-mission absolute sea-level (ASL), relative sea-level from tide gauges (TGs) and Global Positioning System (GPS) height time series. Our results confirmed coastal subsidence in broad agreement with GPS velocities and unexplained by glacial isostatic adjustment alone. VLM determined at in idual TGs differs from spatially interpolated GPS velocities by up to ~ 1.5 mm/year, yielding a ~ 40% reduction in RMSE of geographic ASL variability at TGs around Australia. Our mission-specific altimeter error estimates are small but significant (typically within ~ ± 0.5–1.0 mm/year), with negligible effect on the average ASL rate. Our circum-Australia ASL rate is higher than previous results, suggesting an acceleration in the ~ 27-year time series. Analysis of the time-variability of altimeter errors confirmed stability for most missions except for Jason-2 with an anomaly reaching ~ 2.8 mm/year in the first ~ 3.5 years of operation, supported by analysis from the Bass Strait altimeter validation facility. Data predominantly from the reference missions and located well off narrow shelf regions was shown to bias results by as much as ~ 0.5 mm/year and highlights that residual oceanographic signals remain a fundamental limitation. Incorporating non-reference-mission measurements well on the shelf helped to mitigate this effect. Comparing stacked nonlinear VLM estimates and altimeter systematic errors with the El Niño-Southern Oscillation shows weak correlation and suggests our approach improves the ability to explore nonlinear localized signals and is suitable for other regional- and global-scale studies.
Publisher: Elsevier BV
Date: 07-2015
Publisher: Elsevier BV
Date: 09-2014
Publisher: American Society of Civil Engineers (ASCE)
Date: 11-2017
Publisher: Elsevier BV
Date: 08-2014
Publisher: Elsevier BV
Date: 07-2021
Publisher: Coastal Education and Research Foundation
Date: 07-2008
DOI: 10.2112/07-0844.1
Publisher: American Geophysical Union (AGU)
Date: 03-04-2010
DOI: 10.1029/2009JB006543
Publisher: American Geophysical Union (AGU)
Date: 11-09-2009
DOI: 10.1029/2009JB006344
Publisher: Springer Science and Business Media LLC
Date: 12-06-2014
Publisher: Springer Science and Business Media LLC
Date: 19-03-2014
Publisher: Copernicus GmbH
Date: 28-08-2018
DOI: 10.5194/ESSD-10-1551-2018
Abstract: Abstract. Global mean sea level is an integral of changes occurring in the climate system in response to unforced climate variability as well as natural and anthropogenic forcing factors. Its temporal evolution allows changes (e.g., acceleration) to be detected in one or more components. Study of the sea-level budget provides constraints on missing or poorly known contributions, such as the unsurveyed deep ocean or the still uncertain land water component. In the context of the World Climate Research Programme Grand Challenge entitled Regional Sea Level and Coastal Impacts, an international effort involving the sea-level community worldwide has been recently initiated with the objective of assessing the various datasets used to estimate components of the sea-level budget during the altimetry era (1993 to present). These datasets are based on the combination of a broad range of space-based and in situ observations, model estimates, and algorithms. Evaluating their quality, quantifying uncertainties and identifying sources of discrepancies between component estimates is extremely useful for various applications in climate research. This effort involves several tens of scientists from about 50 research teams/institutions worldwide (rand-challenges/gc-sea-level, last access: 22 August 2018). The results presented in this paper are a synthesis of the first assessment performed during 2017–2018. We present estimates of the altimetry-based global mean sea level (average rate of 3.1 ± 0.3 mm yr−1 and acceleration of 0.1 mm yr−2 over 1993–present), as well as of the different components of the sea-level budget (0.17882/54854, last access: 22 August 2018). We further examine closure of the sea-level budget, comparing the observed global mean sea level with the sum of components. Ocean thermal expansion, glaciers, Greenland and Antarctica contribute 42 %, 21 %, 15 % and 8 % to the global mean sea level over the 1993–present period. We also study the sea-level budget over 2005–present, using GRACE-based ocean mass estimates instead of the sum of in idual mass components. Our results demonstrate that the global mean sea level can be closed to within 0.3 mm yr−1 (1σ). Substantial uncertainty remains for the land water storage component, as shown when examining in idual mass contributions to sea level.
Publisher: Elsevier BV
Date: 10-2017
Publisher: Oxford University Press (OUP)
Date: 06-2010
Publisher: Cambridge University Press (CUP)
Date: 28-05-2015
DOI: 10.1017/S0954102015000231
Abstract: Monitoring the rate of ice flow into ice shelves is vital to understanding how, where and when mass changes occur in Antarctica. Previous observations of ice surface velocity indicate that the Amery Ice Shelf and tributary glaciers have been relatively stable over the period 1968 to 1999. This study measured the displacement of features on the ice surface over a sequence of Landsat 7 images separated by approximately one year and spanning 2004 to 2012 using the surface feature tracking software IMCORR. The focus is on the region surrounding the southern grounding zone of the Amery Ice Shelf and its primary tributary glaciers: the Fisher, Lambert and Mellor glaciers. No significant changes in surface velocity were observed over this period. Accordingly, the velocity fields from each image pair between 2004 and 2012 were used to synthesize an average velocity dataset of the Amery Ice Shelf region and to compare it to previously published velocity datasets and in situ global positioning system velocity observations. No significant change in ice surface velocities was found between 2004 and 2012 in the Amery Ice Shelf region, which suggests that it continues to remain stable.
Publisher: MDPI AG
Date: 09-01-2018
DOI: 10.3390/RS10010083
Publisher: Informa UK Limited
Date: 07-2003
DOI: 10.1080/714044522
Publisher: American Geophysical Union (AGU)
Date: 02-2020
DOI: 10.1029/2019JB018034
Publisher: International Glaciological Society
Date: 09-2016
DOI: 10.1017/AOG.2016.26
Abstract: Geothermal heat flux (GHF) is one of the key thermal boundary conditions for ice-sheet models. We assess the sensitivity of the Lambert-Amery glacial system in East Antarctica to four different GHF datasets using a regional ice-sheet model. A control solution of the regional model is initialised by minimising the misfit to observations through an optimisation process. The Lambert-Amery glacial system simulation contains temperate ice up to 150 m thick and has an average basal melt of 1.3 mm a −1 , with maximum basal melting of 504 mm a −1 . The simulations which use a relatively high GHF compared to the control solution increase the volume and area of temperate ice, which causes higher surface velocities at higher elevations, which leads to the advance of the grounding line. The grounding line advance leads to changes in the local flow configuration, which dominates the changes within the glacial system. To investigate the difference in spatial patterns within the geothermal datasets, they were scaled to have the same median value. These scaled GHF simulations showed that the ice flow was most sensitive to the spatial variation in the underlying GHF near the ice ides and on the edges of the ice streams.
Publisher: American Geophysical Union (AGU)
Date: 03-2018
DOI: 10.1002/2017JC013655
Publisher: Oxford University Press (OUP)
Date: 18-09-2014
DOI: 10.1093/GJI/GGU325
Abstract: Secular motion of Earth's rotation pole results in large-scale secular deformation of Earth. Here, we investigate the magnitude of the deformation that has resulted from the rapid motion of the rotation pole to the east since ∼2005. We show that geodetic (GNSS, DORIS, VLBI and SLR) estimates of vertical velocity since ∼2005 have been biased by up to ±0.38 mm yr–1 relative to the longer-term deformation pattern. The largest signals occur within regions that include the U.S. Pacific Coast, Europe and South Pacific islands where geodetic measurements provide essential measurements of tide-gauge vertical movement and important constraints on models of glacial isostatic adjustment. Consequently, geodetic vertical velocities based on recent data should not be interpreted as being identical to centennial or longer term vertical land movement. Since 2010 the effect is further lified by the overprediction of the IERS polar motion model relative to the ongoing secular change in pole position—during this time geodetic vertical velocities based on the IERS pole tide model are not just biased relative to the long-term rates but also from actual post-2010 Earth deformation. For geophysical or reference frame studies seeking geodetic vertical velocities that are representative of decadal timescales, where interannual variation is considered noise, the correction for this non-linear effect is straightforward, requiring an elastic computation using a reference rate of polar motion that is linear over the timescales of interest.
Publisher: American Geophysical Union (AGU)
Date: 18-06-2020
DOI: 10.1029/2020GL087493
Abstract: The emergence of new, statistically robust trends in Antarctic surface mass balance (SMB) requires an understanding of the underlying SMB variability (noise). We show that simple white or AR[1] noise models do not adequately represent the variability of SMB in both the RACMO2.3p2 SMB model output (1979–2017) and composite ice core records (1800–2010), underestimating low‐frequency variability. By testing a range of noise models, we find that a Generalized Gauss Markov (GGM) model better approximates the noise around a linear trend. The general preference for GGM noise applies over spatial scales from the total ice sheet down to in idual drainage basins. Over the longest timescales considered, trend uncertainties are 1.3–2.3 times larger using a GGM model compared to using an AR1 model at the ice sheet scale. Overall, our results suggest that larger trends or longer periods are required before new SMB trends can be robustly separated from background noise.
Publisher: Springer Berlin Heidelberg
Date: 10-08-2010
Publisher: Elsevier BV
Date: 2017
Publisher: American Geophysical Union (AGU)
Date: 07-08-2009
DOI: 10.1029/2009GL038718
Publisher: American Geophysical Union (AGU)
Date: 18-02-2011
DOI: 10.1029/2010JB008157
Publisher: Wiley
Date: 16-09-2020
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2014
Publisher: American Geophysical Union (AGU)
Date: 2006
DOI: 10.1029/2005GL025538
Publisher: American Geophysical Union (AGU)
Date: 02-2008
DOI: 10.1029/2007GL032252
Publisher: Elsevier BV
Date: 09-2018
Publisher: Informa UK Limited
Date: 2004
Publisher: American Geophysical Union (AGU)
Date: 24-12-2021
DOI: 10.1029/2021GL097065
Abstract: We constrain viscoelastic Earth rheology and recent ice‐mass change in the northern Marguerite Bay region of the Antarctic Peninsula. Global Positioning System (GPS) time series from Rothera and San Martin stations show bedrock uplift range of ∼−0.8–1.8 mm/year over 1999–2005 and 2016–2020 but ∼3.5–6.0 mm/year over ∼2005–2016. Digital elevation models reveal substantial surface lowering, but at a lower rate since ∼2009. Using these data, we show that an elastic‐only model cannot explain the non‐linear uplift of the GPS sites but that a layered viscoelastic model can. We show close agreement between GPS uplift changes and viscoelastic models with effective elastic lithosphere thickness and upper‐mantle viscosity ∼10–95 km and ∼0.1−9 × 10 18 Pa s, respectively. Our viscosity estimate is consistent with a north‐south gradient in viscosity suggested by previous studies focused on specific regions within the Antarctic Peninsula and adds further evidence of the low viscosity upper mantle in the northern Antarctic Peninsula.
No related grants have been discovered for Christopher Watson.