Laurentia crustal motion observed using TOPEX/POSEIDON radar altimetry over land

Lee, Hyongki; Shum, C. K.; Yi, Yuchan; Braun, Alexander; Kuo, Chung-Yen

doi:10.1016/j.jog.2008.05.001

Cited by 58 publications

(53 citation statements)

References 44 publications

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“…Only a few researchers have employed retracked altimetry data to monitor solid earth deformation. For example, Lee et al [11] estimated Laurentia crustal motion observed using retracked T/P altimetry with an average uncertainty of 2.9 mm/yr, which is comparable to the 2.1 mm/yr uncertainty of recent GPS solutions. In accordance with their idea, the MTR is excellent for solving the bump in the pre-leading edge of land reflected waveforms.…”

Section: Introductionmentioning

confidence: 75%

“…Many useful retrackers have been developed to improve altimetry measurements in different reflected surfaces, including NASA V4 (β-) retracker [8], offset center of gravity retracker [9], traditional [10] and modified threshold retracker (MTR) [11], ocean and ice retrackers [12], and subwaveform threshold retracker (STR) [13]. Previous studies have applied retracked altimetry to monitor water level changes in inland rivers [14][15][16], lakes, reservoirs [17][18][19][20], and vegetated wetlands [21], as well as to track Antarctic elevation changes [22].…”

Section: Introductionmentioning

confidence: 99%

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Monitoring Vertical Land Motions in Southwestern Taiwan with Retracked Topex/Poseidon and Jason-2 Satellite Altimetry

et al. 2015

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This study successfully uses satellite altimetry, including Topex/Poseidon and Jason-2, retrieved by novel retrackers to monitor vertical land motions in Southwestern Taiwan. Satellite altimetry was originally designed to measure open oceans, so waveform retracking should be applied to overcome the complex waveforms reflected from lands. Modified threshold and improved subwaveform threshold retrackers were used in the study to improve the accuracy of altimetric land surface heights (LSHs) in Southwestern Taiwan. Results indicate that the vertical motion rates derived from both retrackers coincide with those calculated by 1843 precise leveling points, with a correlation coefficient of 0.96 and mean differences of 0.43 and 0.52 cm/yr (standard deviations: 0.61 and 0.69 cm/yr). In addition, wet troposphere delay by precise point positioning with the use of Global Navigation Satellite System data was employed to evaluate the impact of the delay on the estimates of vertical motion rates compared with that traditionally derived from the European Center for Medium-Range Weather Forecasts model when the microwave radiometer is non-functional over lands. The accuracies of retracked altimetric land motion rates corrected by wet troposphere delays derived from both models show no remarkable differences in the Tuku and Yuanchang areas because the accuracy of retracked altimetric LSHs is significantly worse than that of wet troposphere delays.

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Section: Introductionmentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Monitoring Vertical Land Motions in Southwestern Taiwan with Retracked Topex/Poseidon and Jason-2 Satellite Altimetry

et al. 2015

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“…Satellite radar altimetry measurements, originally designed to observe deep-ocean sea level and circulation, have been used to detect solid Earth deformation, e.g., the Laurentian GIA, with an accuracy of several mm yr -1 (Lee et al 2008a(Lee et al , 2008b. The limitation of this technique is that the radar echo loses lock if the terrain is mountainous.…”

Section: Satellite Geodetic Techniquesmentioning

confidence: 99%

“…The height difference from cycle to cycle can reach several hundreds of meters, as can be seen from Fig. 10, and the gradient correction using Shuttle Radar Topography Mission (SRTM) C-band Digital Elevation Model (DEM) as in Lee et al (2008b) could not mitigate the problem. We found that the currently available DEMs, including SRTM and GTOPO DEMs, are not adequate to correct the surface gradient changes for radar altimetry due to the DEM's errors, spikiness, and voids over the extreme terrains in the Qinghai-Tibetan Plateau.…”

Section: Satellite Geodetic Techniquesmentioning

confidence: 99%

Geodetic Constraints on the Qinghai-Tibetan Plateau Present-Day Geophysical Processes

Erkan¹,

Shum²,

Wang³

et al. 2011

Terr. Atmos. Ocean. Sci.

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The Qinghai-Tibetan Plateau is the largest and the highest area in the world with distinct and competing surface and subsurface processes. The entire Plateau has been undergoing crustal deformation and accompanying isostatic uplift as a result of the Cenozoic collision of the Indian and Eurasian continents. Regional secular surface mass changes include the melting of mountain glaciers and ice caps, and permafrost layer degradation due to global warming. There is also a plausible effect of glacial isostatic adjustment due to the removal of a possible Pleistocene ice-sheet. In this article, we present an assessment of the sizes and extents of these competing interior and exterior dynamical processes, and their possible detections using contemporary space geodetic techniques. These techniques include, in addition to GPS, satellite radar altimetry over land, and temporal gravity field measurements from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. These techniques are complementary: land satellite altimetry, similar to GPS, is sensitive only to surface uplift, whereas GRACE is sensitive to both surface uplift and mass changes inside the Earth. Each process may dominate the others in a particular region. Our analysis shows that GRACE data are more sensitive (than GPS or land altimetry) to hydrologic and meteorology signals, some of which are larger than the combined effect of geodynamic processes and permafrost degradation.

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“…The u (obs) data can be obtained by interpreting GPS and tide-gauge observations (Davis & Mitrovica 1996;Braun et al 2008), terrestrial gravity, satellite radar altimetry (Lee et al 2008), traditional levelling or paleo sea level indicator data (e.g. Tushingham & Peltier 1992;Lambeck et al 1998).…”

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confidence: 99%

The forward sensitivity and adjoint-state methods of glacial isostatic adjustment

Martinec

Sasgen

Velı́mský

2014

Geophysical Journal International

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S U M M A R YIn this study, a new method for computing the sensitivity of the glacial isostatic adjustment (GIA) forward solution with respect to the Earth's mantle viscosity, the so-called the forward sensitivity method (FSM), and a method for computing the gradient of data misfit with respect to viscosity parameters, the so-called adjoint-state method (ASM), are presented. These advanced formal methods complement each other in the inverse modelling of GIArelated observations. When solving this inverse problem, the first step is to calculate the forward sensitivities by the FSM and use them to fix the model parameters that do not affect the forward model solution, as well as identifying and removing redundant parts of the inferred viscosity structure. Once the viscosity model is optimized in view of the forward sensitivities, the minimization of the data misfit with respect to the viscosity parameters can be carried out by a gradient technique which makes use of the ASM. The aim is this paper is to derive the FSM and ASM in the forms that are closely associated with the forward solver of GIA developed by Martinec. Since this method is based on a continuous form of the forward model equations, which are then discretized by spectral and finite elements, we first derive the continuous forms of the FSM and ASM and then discretize them by the spectral and finite elements used in the discretization of the forward model equations. The advantage of this approach is that all three methods (forward, FSM and ASM) have the same matrix of equations and use the same methodology for the implementation of the time evolution of stresses. The only difference between the forward method and the FSM and ASM is that the different numerical differencing schemes for the time evolution of the Maxwell and generalized Maxwell viscous stresses are applied in the respective methods. However, it requires only a little extra computational time for carrying out the FSM and ASM numerically. An straightforward approach to compute the gradient of the data misfit is the brute-force method, whereby the partial derivatives of the misfit with respect to model parameters are approximated by the centred difference of two forward model runs. Although the brute-force method is useful for computing the gradient of the data misfit with respect to a small number of model parameters, it becomes expensive for a viscosity model with a large number of parameters. The ASM offers an efficient alternative for computing the gradient of the misfit since the computational time of the ASM is independent of the number of viscosity parameters. The ASM is thus highly efficient for calculating the gradient of the misfit for models with large numbers of parameters. However, the forward-model solution for each time step must be stored, hence the memory demands scale linearly with the number of time steps. This is the main drawback of the ASM.Key words: Numerical solutions; Inverse theory; Sea level change; Rheology: mantle. I N T RO D U C T I O NStudies on glacial isostati...

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Laurentia crustal motion observed using TOPEX/POSEIDON radar altimetry over land

Cited by 58 publications

References 44 publications

Monitoring Vertical Land Motions in Southwestern Taiwan with Retracked Topex/Poseidon and Jason-2 Satellite Altimetry

Monitoring Vertical Land Motions in Southwestern Taiwan with Retracked Topex/Poseidon and Jason-2 Satellite Altimetry

Geodetic Constraints on the Qinghai-Tibetan Plateau Present-Day Geophysical Processes

The forward sensitivity and adjoint-state methods of glacial isostatic adjustment

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