Geodetic Elevation Research Articles

Spatial heterogeneity, terminus environment effects and acceleration in mass loss of glaciers and ice caps across Greenland

Greenland's peripheral glaciers and ice caps (GICs) contribute significant amounts of meltwater to the oceans but also affect local economies and livelihoods. Here we created multi-temporal geodetic elevation change datasets to compute mass changes for 6149 glaciers around the entire periphery of Greenland. These glaciers have lost a total of at least 276 ± 55 Gt of ice, or 0.76 ± 0.15 mm sea level equivalent, from their ablation areas between 1978 and 2015. If we assume no mass loss within accumulation areas, then the mean mass balance has been at least −0.10 ± 0.02 m w.e. yr−1. In general, west Greenland glaciers have had a more negative mass balance and experienced accelerated mass loss since 2006 (x 2.7 in south west region, x 5.6 in central west region). Conversely, east Greenland glaciers have generally experienced a decrease in the rate of mass loss. Lake-terminating glaciers have experienced the most negative mass balance, exacerbated by the occurrence of debris cover. These findings quantify great spatial heterogeneity, give context to the recent history of mass loss from GICs, and suggest the importance of including local glacier properties within glacier evolution models.

APPROVAL OF THE NEED FOR THE RECONSTRUCTION OF ARENI PUMPING STATION

The Areni-Khachik pumping station raises the waters of the Arpa river from the 976 m mark to the pressure basin located at the 2012 m mark of the upper mountain pass of the Khachik village, from which the water was given to the Khachik community with a maximum output of 415 l/s and to the Amaghu village with a maximum of 41 l/s. with output. The pumping station has three stages, the engine rooms of which are located: First stage, on the right bank of the Arpa river at the mark of 975 m, with a geodetic pumping height of 318 m, pumping output of 582 l/s. Second stage: at the 1295 m mark of the site near the Areni-Khachik highway, with a geodetic elevation of 370 m, pumping output of 456 l/s . And the third stage: at the site of 1651 m near the Areni-Khachik highway, with a geodetic elevation of 361 m, pumping output of 456 l /v . All three stages of the pumping station belong to the class of high-pressure pumping stations, with a relatively small discharge output and high pressure, the specific power consumption of which is significantly higher. Analyzing the technical condition of the pumping station, a program is proposed to implement its reconstruction and reduce operating costs.

Applicability of an ultra-long-range terrestrial laser scanner to monitor the mass balance of Muz Taw Glacier, Sawir Mountains, China

Glacier mass balance is a key component of glacier monitoring programs. Information on the mass balance of Sawir Mountains is poor due to a dearth of in-situ measurements. This paper introduces the applicability of an ultra-long-range terrestrial laser scanner (TLS) to monitor the mass balance of Muz Taw Glacier, Sawir Mountains, China. The Riegl VZ ® -6000 TLS is exceptionally well-suited for measuring snowy and icy terrain. Here, we use TLS to create repeated high spatiotemporal resolution DEMs, focusing on the annual mass balance (June 2, 2015 to July 25, 2016). According to TLS-derived high spatial resolution point clouds, the front variation (glacier retreat) of Muz Taw Glacier was 9.3 m. The mean geodetic elevation change was 4.55 m at the ablation area. By comparing with glaciological measurements, the glaciological elevation change of individual stakes and the TLS-derived geodetic elevation change of corresponding points matched closely, and the calculated balance was −3.864±0.378 m w.e.. This data indicates that TLS provides accurate results and is therefore suitable to monitor mass balance evolution of Muz Taw Glacier.

Ice flow modelling to constrain the surface mass balance and ice discharge of San Rafael Glacier, Northern Patagonia Icefield

ABSTRACTWe simulate the ice dynamics of the San Rafael Glacier (SRG) in the Northern Patagonia Icefield (46.7°S, 73.5°W), using glacier geometry obtained by airborne gravity measurements. The full-Stokes ice flow model (Elmer/Ice) is initialized using an inverse method to infer the basal friction coefficient from a satellite-derived surface velocity mosaic. The high surface velocities (7.6 km a−1) near the glacier front are explained by low basal shear stresses (<25 kPa). The modelling results suggest that 98% of the surface velocities are due to basal sliding in the fast-flowing glacier tongue (>1 km a−1). We force the model using different surface mass-balance scenarios taken or adapted from previous studies and geodetic elevation changes between 2000 and 2012. Our results suggest that previous estimates of average surface mass balance over the entire glacier (Ḃ) were likely too high, mainly due to an overestimation in the accumulation area. We propose that most of SRG imbalance is due to the large ice discharge (−0.83 ± 0.08 Gt a−1) and a slightly positiveḂ(0.08 ± 0.06 Gt a−1). The committed mass-loss estimate over the next century is −0.34 ± 0.03 Gt a−1. This study demonstrates that surface mass-balance estimates and glacier wastage projections can be improved using a physically based ice flow model.

Using an ultra-long-range terrestrial laser scanner to monitor the net mass balance of Urumqi Glacier No. 1, eastern Tien Shan, China, at the monthly scale

ABSTRACTWe describe the use of a terrestrial laser scanner (TLS) to monitor the net mass balance of Urumqi Glacier No. 1, eastern Tien Shan. We used an ultra-long-range Riegl VZ®-6000 TLS, which is specially designed for surveying snow- and ice-covered terrain, to create repeated high spatiotemporal resolution DEMs, focusing on the monthly-scale (25 April–28 May 2015) net mass balance. According to the TLS-derived DEMs, the area of Urumqi Glacier No. 1 was 1.558 km2on 25 April 2015 and the average surface elevation change was 0.225 m. By comparing the results from the use of TLS with the conventional glaciological mass-balance method, the correlation coefficient (R2) between glaciological elevation changes of individual stakes and the TLS-derived geodetic elevation change of corresponding points was 0.85. Considering the uncertainty of both methods, this is a promising result. Using the in situ measured snow densities (snow pits) of the glacier surface, the geodetic net mass balance was 0.074 m w.e., which is slightly positive. The mean uncertainty in the TLS-derived monthly net mass balance was 0.018 m w.e., showing that the TLS surveying system presented accurate and relevant results and is therefore suitable to monitor mass-balance evolution of mountain glaciers.

The Potential Impact of Vertical Sampling Uncertainty on ICESat-2/ATLAS Terrain and Canopy Height Retrievals for Multiple Ecosystems

With a planned launch no later than September 2018, the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) will provide a global distribution of geodetic elevation measurements for both the terrain surface and relative canopy heights. The Advanced Topographic Laser Altimeter System (ATLAS) instrument on-board ICESat-2 is a LiDAR system sensitive to the photon level. The photon-counting technology has many advantages for space-based altimetry, but also has challenges, particularly with delineating the signal from background noise. As such, a current unknown facing the ecosystem community is the performance of ICESat-2 for terrain and canopy height retrievals. This paper aims to provide the science user community of ICESat-2 land/vegetation data products with a realistic understanding of the performance characteristics and potential uncertainties related to the vertical sampling error, which includes the error in the perceived height value and the measurement precision. Terrain and canopy heights from simulated ICESat-2 data are evaluated against the airborne LiDAR ground truth values to provide a baseline performance uncertainty for multiple ecosystems. Simulation results for wooded savanna and boreal forest result in a mean bias error and error uncertainty (precision) for terrain height retrievals at 0.06 m (0.24 m RMSE) and −0.13 m (0.77 m RMSE). In contrast, results over ecosystems with dense vegetation show terrain errors of 1.93 m (1.66 m RMSE) and 2.52 m (3.18 m RMSE), indicating problems extracting terrain height due to diminished ground returns. Simulated top of canopy heights from ICESat-2 underestimated true top of canopy returns for all types analyzed with errors ranging from 0.28 m (1.39 m RMSE) to 1.25 m (2.63 m RMSE). These results comprise a first step in a comprehensive evaluation of ICESat-2 anticipated performance. Future steps will include solar noise impact analysis and investigation into performance discrepancy between visible and near-infrared wavelengths.

The Coordinate Transformation Method and Accuracy Analysis in GPS Measurement

Abstract This paper introduced WGS-84 and BJ-54 coordinate transformation model and the influence comparison from geodetic elevation between seven-parameter model and three-parameter model, and finished transformation parameters calculation and accuracy analysis of BJ-54 coordinate system at home and the world 84 coordinate system by an example, which had some reference to other GPS measurement projects.

Estimating the long-term calving flux of Kronebreen, Svalbard, from geodetic elevation changes and mass-balance modeling

AbstractThis study independently quantifies geodetic elevation change and models surface mass balance to solve the continuity equation. The approach is tested on two dynamically different glaciers, Kongsvegen and Kronebreen in northwest Svalbard, through two time epochs, 1966-1990/95 (I) and 1990/95-2007 (II). On Kongsvegen, a dynamically inactive glacier, the residual term represents an error associated with determining elevation changes and surface mass balance. It is apparent that centerline mass-balance estimates are not representative of the entire glacier, which we relate to center-line accumulation being larger than the elevation bin average. On Kronebreen, a fast-flowing and actively calving glacier, a significant part of the residual is identified with the long-term calving flux. For both glaciers, the cumulative surface mass balance remained close to zero during the first epoch but became increasingly negative in the second epoch. The long-term calving flux of Kronebreen is estimated to be -0.14 ± 0.03 km3 w.e.a-1 during epoch I and-0.20 ± 0.05 km3 w.e.a-1 in epoch II.

ESTIMATION OF BENCHMARK'S STABILITY BY ADJUSTMENT OF FREE GEODETIC ELEVATION BASE NETWORK

The paper presents a procedure to estimate benchmark's stability by adjustment of free geodetic elevation base network. The changes of adjusted heigh by software " CBSCI" for free networks consisted 3,4,5 benchmarks are 0.1-0.2 mm when to compare this method with a method one benchmark is unchanged in height and method the mean of heigh for benchmark group is unchanged. So, we can use this method for estimation of benchmark's stability when to measure settlement for engineering constructions.

Coseismic folding, earthquake recurrence, and the 1987 source mechanism at Whittier Narrows, Los Angeles basin, California

Static deformation associated with the October 1, 1987, Whittier Narrows, California, M = 6.0 earthquake was detected by geodetic elevation changes. The earthquake uplifted a 1.5‐km‐high Quaternary fold (the Santa Monica Mountains anticlinorium) by 50 mm but caused no fault rupture at the ground surface. This suggests that folding and faulting of the Los Angeles basin sediments are coincident and continuing. After correction for surveying errors and nontectonic subsidence, we model the 214 geodetic observations with a simple dislocation in an elastic half‐space. A thrust fault with reverse slip of 1.1±0.3 m and dipping 30°±4°N, with an upper edge at a depth of 12±1 km and a lower edge at 17±1 km, fits the geodetic data best and is consistent with the main shock hypocenter, fault plane solution, and initial aftershock distribution. The upper limit on the static stress drop, Δσ, is 17.5±5.0 MPa (175±50 bar). The lower limit on the geodetic moment is 1.0±0.2 × 1025 dyne cm, in accord with seismic estimates, indicating that most of the slip took place during seismic rupture. If earthquakes of M ≤ 6 characterize the blind thrust fault on which the earthquake occurred, we estimate a 200 year repeat time at Whittier Narrows, and a 5–18 year rate of earthquake occurrence within a 150‐km‐long band in the northern Los Angeles basin and Santa Monica Bay to the west. The 25‐year rate of historical occurrence since 1860 is less than this prediction. The deficit in moment release implies that either vigorous aseismic slip or infrequent larger earthquakes occur here.

Slip distribution of the 1985 Central Chile earthquake

Geodetic elevation changes record the deformation associated with the M s = 7.8, March 3, 1985, Central Chile earthquake. By summing elemental point sources in a half-space and employing a gradient technique with positivity constraints, we resolve the slip distribution on the dislocation surface. Most of the fault slip is concentrated on two patches at a depth between 30 and 40 km on a plane dipping 18° E. The patch containing the maximum slip is oriented parallel to the coast and is closely located to the reported hypocenter of the mainshock. The overall region of maximum slip (slip >- 2 m) is more than 140 km long and oriented N-S. The dislocation model obtained from the static field is in remarkable agreement with the mainshock location and aftershock distribution, moment release pattern from analysis of body and surface waves, and location and fault geometry of the main aftershock. The total moment derived from the dislocation model for the coseismic period is 1.6 ×10 28 dyn cm. Comparison of coastal uplift predicted by the model and observations associated with the previous large event in the region (August, 1906, M T = 8.4) suggests a possible variable rupture mode of the region. Estimations of the future crustal readjustment due to restressing and viscoelastic relaxation indicate a general subsidence over a broader area than the coseismically uplifted region. However, the maximum amplitude of the predicted postseismic elevation change is less than 10% of the maximum coseismic uplift. The proximity of the two patches of maximum slip to the aftershock areas of intermediate size thrust earthquakes in the region since 1971 suggests that these compressional events may represent slip prior to failure in the “weaker” updip region of the main asperities.

Planar high‐angle faulting in the basin and range: Geodetic analysis of the 1983 Borah Peak, Idaho, earthquake

Geodetic elevation changes record the broad‐scale deformation associated with the M = 7.0 October 28, 1983, Borah Peak, Idaho, earthquake on the Lost River fault. The crest of the Lost River Range rose 0.2 m, and adjacent Thousand Springs Valley subsided 1.0 m, in relation to reference points 45 km from the main shock epicenter. The deformation was modeled by dislocations in an elastic half‐space. A planar fault with uniform dip slip of 2.05±0.10 m, dipping 47°±2°SW and extending to a vertical depth of 13.3±1.2 km, fits the geodetic data best and is also consistent with the main shock hypocenter and fault plane solution. The geodetic moment is 2.6±0.5×1019 N m (2.6±0.5×1026 dyn cm), and the estimated static stress drop is 2.9±0.4 MPa (29±4 bars). Tests for coseismic slip on listric faults (which flatten with depth) and on detachments (horizontal faults or shear zones) showed fits to the geodetic data that are inferior to those for planar high‐angle faults. No detectable coseismic slip occurred on the Mesozoic White Knob thrust fault, although the low‐angle thrust sheet intersects the south end of Lost River fault near the 1983 mainshock epicenter. If the high‐angle Lost River fault abuts a flat‐lying detachment fault or shear zone, such a structure must lie at depths of >12 km, near the brittle‐ductile transition, where stick‐slip behavior gives way to creep. The depth and geometry of faulting at Borah Peak is similar to that inferred from seismic and geodetic evidence for the 1954 M = 7.2 Fairview Peak, Nevada, and the 1959 M = 7.3 Hebgen Lake, Montana, events, suggesting that if detachments are active at these localities, they are deep and most likely slip by creep.

STABILITY CRITERIA FOR TIDAL BASINS

The contribution deals with the morphologic examinations and calculations for a deep-water harbour which is to be constructed in the tidal flats of the Elbe estuary near the North Sea islands of Scharhorn and Neuwerk. An attempt is made to examine the stability of tidal channels (gullies)and tidal flats which may be disturbed to a greater or lesser extent by the various proposals for the connecting dike between the industrial area near the harbour and the coastline. The underlying logic for the determination of the equilibrium of the flats and the quantitative solution for the sand-balance is as follows: It has been shown in several empirical investigations that the increase of the relative volume of the tidal basin (V/VM ), referenced to the gully volume for MLW, can be determined as a simple function to the base (a)logarithm of the geodetic elevation (z*) between MLW and any higher contour level up to MHW. Furthermore it can be shown that (VMT ) is also a function of the tidal drainage area (E). The base(a)has been related to the size of the tidal drainage area (E), because this area is subject to considerable modification by offshore structures such as dikes and causeways.