Ground Surface Elevation Research Articles

Long‐term field measurements of climate‐induced thaw subsidence above ice wedges on hillslopes, western Arctic Canada

AbstractNear‐surface wedges of massive ice commonly outline polygons in tundra lowlands, but such polygons have been difficult to identify on hillslopes because soil movement flattens the ridges and infills the troughs that form beside and above the ice wedges. Over the past three decades, the active layer has thickened near the western Arctic coast of Canada and consequent thawing of ice wedges has been detected by remote sensing for flat terrain but not, generally, on hillslopes. Annual field surveys (1996–2018) at the Illisarvik field site of thaw depth and ground surface elevation show the mean subsidence rate above hillslope ice wedges has been up to 32 mm a−1 since thaw depth reached the ice‐wedge tops in 2007. Annual mean ground temperatures at the site are about −3.0°C beneath late‐winter snow depths characteristic of the ice‐wedge troughs but about −5.3°C under conditions of the intervening polygons. The rate of thaw subsidence is high for natural, subaerial disturbances because meltwater from the ice wedges runs off downslope. The rate is constant, because the thickness of seasonally thawed ground above the ice wedges and the ice content of the ground remain the same while the troughs develop. Observations of changes in surface elevation in northern Banks Island between the late 1970s and 2019 show troughs on hillslopes where none was previously visible. Development of these troughs creates regional thermokarst landscapes, distinct from the widely recognized results of thawing relict glacier ice, that are now widespread over Canada's western Arctic coastlands. Recognition of ice‐wedge occurrence and accelerated thaw subsidence on hillslopes is important in the design of infrastructure proposed for construction in rolling permafrost terrain.

A Digital Terrain Modeling Method in Urban Areas by the ICESat-2 (Generating precise terrain surface profiles from photon-counting technology)

The ICE, Cloud and land Elevation Satellite-2 (ICES at-2) can provide new measurements of the Earth's elevations through photon-counting technology. Most research has focused on extracting the ground and the canopy photons in vegetated areas. Yet the extraction of the ground photons from urban areas, where the vegetation is mixed with artificial constructions, has not been fully investigated. This article proposes a new method to estimate the ground surface elevations in urban areas. The ICES at-2 signal photons were detected by the improved Density-Based Spatial Clustering of Applications with Noise algorithm and the Advanced Topographic Laser Altimeter System algorithm. The Advanced Land Observing Satellite-1 PALSAR –derived digital surface model has been utilized to separate the terrain surface from the ICES at-2 data. A set of ground-truth data was used to evaluate the accuracy of these two methods, and the achieved accuracy was up to 2.7 cm, which makes our method effective and accurate in determining the ground elevation in urban scenes.

City planning of Hermanninranta – A combination of geotechnics, contamination, and climate change

The Hermanninranta area presents one of the most geotechnically challenging urban planning areas in the City of Helsinki. The area located on the shore of Vanhankaupunginlahti (Old City Bay) is approx. 50 ha in size. Most of the area is reclaimed from the sea and only Kyläsaari island is a natural formation. Land reclamation in the area was performed in various stages between the 1840s to the 1980s. Natural very soft clay layers encountered in the area extend to a depth of over 40 m below ground surface. Today, the proximity to the city centre makes Hermanninranta very attractive for residential and commercial construction. Thick fill containing contaminated soil, slag and ash on top of soft deep clay, are a challenging combination. Variable fills have caused the settlement of soft clays and the displacement of the embankment towards the bay. Changing current land use for residential purposes will require changing of current ground surface elevation to approximately 2 to 2,5 m upward. This will be an issue impacting geotechnical engineering. Rising sea level caused by global warming shall also be considered. Settlement calculations show that within the next hundred years almost half of the area will be under water in case of no pile slab or soil improvement. The draft city plan has been updated based on these geotechnical, environmental and climate change studies.

Mining noise data for monitoring Arctic permafrost by using GNSS interferometric reflectometry

Ground surface elevation changes are closely linked to the dynamics of the active layer and near-surface permafrost. GNSS interferometric reflectometry (GNSS-IR), a technique utilizing reflected signals regarded as noise in the GNSS applications, such as positioning and navigation, can measure surface elevation changes in permafrost areas. In this study, we screen seven major open-data GNSS networks to identify the sites which are suitable for using GNSS-IR to study the permafrost areas in the Arctic. We identify 23 usable sites and obtain their surface elevation changes. As for the unusable sites in the permafrost areas, 68% and 25% of them are due to undulated reflecting surface and obstructions (e.g., buildings and trees), respectively. And 7% of the unsuitable sites are due to insufficient usable observations, though open and relatively smooth areas can be found in their surroundings. This study provides usable sites in the Arctic permafrost areas, which can fill some spatial gaps of the existing permafrost monitoring programs and provide complementary measurements to active layer thickness and permafrost temperature. The GNSS-IR measurements can provide new perspectives into permafrost studies and contribute to assessing the potential hazards of permafrost degradation to infrastructures and residential communities.

A novel approach of evaluating favorable areas for shale gas exploration based on regional geological survey and remote sensing data

The periphery of the Huangling Massif is one of the principal prospecting regions of the Lower Cambrian shale gas resources in South China. The geological setting and ground surface conditions are complicated within this area, and the petroleum geological data is limited due to the low degree of exploration. A novel approach based on the regional geological survey and remote sensing data was proposed. The favorable areas for gas exploration targeting the Lower Cambrian Niutitang Shale within the periphery of the Huangling Massif were evaluated by using this approach. Seven key indicators, including the depositional facies and current burial state of the shale strata, density of the exposed faults, dip angle of exposed strata, elevation and slope of the current ground surface, and land utilization, were selected. An evaluation criterion of these indicators was established to facilitate the classification of the study area into four ratings: favorable, low-risk, high-risk, and unfavorable. The overall evaluation of the seven indicators suggested a favorable area of 386.02 km2, a low-risk area of 1784.81 km2, and a high-risk area of 1689.97 km2, accounting for 0.91%, 4.21%, and 3.99% of the whole area, respectively. These results achieved a high level of compliance with the actual exploration discoveries and eliminated over 90% of the total area unsuitable for exploration and production. It is demonstrated that this novel approach can be effectively adopted in the comprehensive evaluation of the favorable area for shale gas exploration with a low degree of prospecting.

Plant community composition patterns in relation to microtopography and distance to water bodies in a tropical forested wetland

Abstract Understanding the spatial variation of a plant community’s composition in response to key environmental variables is a fundamental task to identify and promote better conservation strategies. In forested wetlands, hydrological regimes have been identified as crucial factors that shape the community’s attributes and composition patterns. Therefore, the objective of this study was to analyze the response of a tropical forested wetland diversity and structural attributes, as well as its species composition to two types of environmental proxies related to flooding and salinity regimes: microtopography and distance to water bodies. The forest was characterized by sampling all the individuals with DBH ≥ 10 cm found inside twenty-five 25 × 50 m plots. Each plot’s microtopographic variables and distance to water bodies were extracted using a LiDAR point cloud. The response of the community’s attributes to the quantified environmental proxies was analyzed using an RDA ordination. Community composition was the only attribute where the ordination was significant, particularly only its first axis. Additional analysis showed that Rhizophora mangle was gradually substituted by Terminalia buceras as the most abundant species along the RDA first axis. This first axis was significantly correlated with two environmental proxies: distance to the lagoon’s edge and standard deviation of ground surface elevation. Moreover, linear regression analysis revealed that the abundance of three species was explained by these environmental proxies. R. mangle abundance showed a negative response to standard deviation of ground surface elevation, while T. buceras and Chrysobalanus icaco showed a positive response to distance to the lagoon’s edge.

Risk factors for the conservation of saltmarsh vegetation and blue carbon revealed by earthquake-induced sea-level rise

Vegetated coastal ecosystems (VCEs) are in global decline and sensitive to climate change; yet may also assist its mitigation through high rates of ‘blue’ carbon sequestration and storage. Alterations of relative sea-level (RSL) are pervasive drivers of change that reflect the interaction between tidal inundation regimes and ground surface elevation. Although many studies have investigated sediment accretion within VCEs, relatively few have addressed spatiotemporal patterns of resilience in response to RSL change. In this study, we used high resolution elevation models and field surveys to identify RSL changes and socio-ecological responses in a tidal lagoon system following earthquakes in New Zealand. We expected that vegetation changes would result from RSL effects caused by surface-elevation changes in intertidal zones. Elevation measurements showed a sequence of vertical displacements resulting from major earthquakes in 2011 and 2012, and additional surface-elevation loss since. VCE losses were recorded over an 8 year period post-2011 in response to high rates of RSL rise (up to 41 mm yr−1). Anthropogenic factors influenced the pattern of losses and illustrate opportunities for managing risks to other VCEs facing RSL rise. Four key principles for building VCE resilience were identified: i) anthropogenic encroachment results in resilience loss due to the need for landward migration when changes exceed the tolerance thresholds of VCEs at their lower elevational limits; ii) connectivity losses exacerbate encroachment effects, and conversely, are a practical focus for management; iii) landscape-scale risk exposure is disproportionately influenced by the largest wetland remnants illustrating the importance of site-specific vulnerabilities and their assessment; and iv) establishing new protected areas to accommodate the movement of VCEs is needed, and requires a combination of land tenure rearrangements and connectivity conservation. Embracing these concepts offers promise for improving whole-system resilience to help address the challenge of global climate change.

Effect of digital elevation models on monitoring slope displacements in open-pit mine by differential interferometry synthetic aperture radar

Abstract Displacement monitoring in open-pit mines is one of the important tasks for safe management of mining processes. Differential interferometric synthetic aperture radar (DInSAR), mounted on an artificial satellite, has the potential to be a cost-effective method for monitoring surface displacements over extensive areas, such as open-pit mines. DInSAR requires the ground surface elevation data in the process of its analysis as a digital elevation model (DEM). However, since the topography of the ground surface in open-pit mines changes largely due to excavations, measurement errors can occur due to insufficient information on the elevation of mining areas. In this paper, effect of different elevation models on the accuracy of the displacement monitoring results by DInSAR is investigated at a limestone quarry. In addition, validity of the DInSAR results using an appropriate DEM is examined by comparing them with the results obtained by global positioning system (GPS) monitoring conducted for three years at the same limestone quarry. It is found that the uncertainty of DEMs induces large errors in the displacement monitoring results if the baseline length of the satellites between the master and the slave data is longer than a few hundred meters. Comparing the monitoring results of DInSAR and GPS, the root mean square error (RMSE) of the discrepancy between the two sets of results is less than 10 mm if an appropriate DEM, considering the excavation processes, is used. It is proven that DInSAR can be applied for monitoring the displacements of mine slopes with centimeter-level accuracy.

Global Positioning System interferometric reflectometry (GPS-IR) measurements of ground surface elevation changes in permafrost areas in northern Canada

Abstract. Global Positioning System interferometric reflectometry (GPS-IR) is a relatively new technique which uses reflected GPS signals to measure surface elevation changes to study frozen-ground dynamics. At present, more than 200 GPS stations are operating continuously in the Northern Hemisphere permafrost areas, which were originally designed and maintained for tectonic and ionospheric studies. However, only one site in Utqiaġvik, Alaska (formerly Barrow), was assessed to be usable for studying permafrost by GPS-IR. Moreover, GPS-IR has high requirements on the ground surface condition, which needs to be open, flat, and homogeneous. In this study, we screen three major GPS networks in Canada and identify 12 out of 38 stations located in permafrost areas as useful ones where reliable GPS-IR measurements can be obtained. We focus on the five Canadian Active Control System stations and obtain their daily GPS-IR surface elevation changes. We find that the ground surface subsided in Alert, Resolute Bay, and Repulse Bay respectively by 0.61±0.04 cm yr−1 (2012–2018), 0.70±0.02 cm yr−1 (2003–2014), and 0.26±0.05 cm yr−1 (2014–2019). At the other two sites of Baker Lake and Iqaluit, the trends are not statistically significant. The linear trends of deformation were negatively correlated with those of thaw indices in Alert, Resolute Bay, and Repulse Bay. Furthermore, in Resolute Bay, we also find that the end-of-thaw elevations during 2003–2012 were highly negatively correlated with the square root of thaw indices. This study is the first one using multiple GPS stations to study permafrost by GPS-IR. It highlights the multiple useful GPS stations in northern Canada, offering multi-year, continuous, and daily GPS-IR surface deformation, which provides new insights into frozen-ground dynamics at various temporal scales and across a broad region.

Spatial analysis of groundwater flowing artesian condition using machine learning techniques

This study introduces a methodology for modeling the groundwater artesian condition (AC) in a specific arid region of southern Iraq using five machine learning techniques; the stochastic gradient boosting (SGB), classification and regression trees (CART), random forest (RF), support vector machine (SVM), and k nearest neighbor (kNN). To this aim, an inventory map of flowing and non-flowing groundwater wells along with six explanatory factors were used. The chosen factors were the distance to faults (FDIS), faults density (FDEN), lineament density (LDEN), aquifer saturated thickness (ST), well depths (WD), and ground surface elevation. Examining the spatial pattern of flowing wells using the average nearest neighbor approach showed that the distribution of these wells is a cluster (average nearest ratio = 0.48). Testing the powerful factors in building the models using the Boruta package indicated that all factors play a role in controlling the emergence of AC. Five statistical error measures were employed to examine the predictive capability of the models used namely, Accuracy, kappa, receiver operating characteristic curve (ROC), sensitivity, and specificity. Applying the ML models in the R statistical package and its related caret package showed that the competent model was RF, followed by SGB and kNN. The worst performance models were CART and SVM. Accordingly, RF was used as the reference model for the probability mapping of AC in the study area, indicating the 29% (618 km̏) of the study area included in the predicted high AC and this zone mainly distribute in the eastern part and a small spot in the north. The AC probability map developed in the study could be used for drilling successful artesian flowing wells with minimal efforts and cost and thus, for efficient managing of this important system.

Evaluating the impact of hydrodynamic flow on the hydrocarbon potentials of the Cretaceous Anambra basin, Southeastern Nigeria

Fluid pressure data from wells drilled in the Anambra basin were analysed in order to characterize the regional groundwater dynamics in the Cretaceous formations and to evaluate the possible impact of the hydrodynamic flow of groundwater on the hydrocarbon prospectivity of the basin. The results demonstrate a general northeast to southwest flow, with regions of relatively high topographic expression in the eastern part, where the Cretaceous formations outcrop. These areas correspond to regions characterized by hydrostatic pressure condition, high hydraulic head and high flow strength. Conversely, areas of comparatively lower ground surface elevation, located in the western part of the basin, are associated with regions of overpressure, low hydraulic head and low flux. Two hydrostratigraphic systems, an upper one comprising the Ajali and Nsukka Formations and a lower one comprising the Nkporo Group and Mamu Formation are present. The upper hydrostratigraphic system is prone to downward invasion of the formations by meteoric groundwater, a process that has probably resulted in the devaluation of trapped hydrocarbons into heavy oil and bitumen that occur in the basin. The lower hydrostratigraphic system whose aquifers exist as isolated hydraulic units is considered to be in good hydrodynamic framework conducive for the preservation of hydrocarbons trapped in place.

Structure from motion photogrammetry in ecology: Does the choice of software matter?

Image‐based modeling, and more precisely, Structure from Motion (SfM) and Multi‐View Stereo (MVS), is emerging as a flexible, self‐service, remote sensing tool for generating fine‐grained digital surface models (DSMs) in the Earth sciences and ecology. However, drone‐based SfM + MVS applications have developed at a rapid pace over the past decade and there are now many software options available for data processing. Consequently, understanding of reproducibility issues caused by variations in software choice and their influence on data quality is relatively poorly understood. This understanding is crucial for the development of SfM + MVS if it is to fulfill a role as a new quantitative remote sensing tool to inform management frameworks and species conservation schemes. To address this knowledge gap, a lightweight multirotor drone carrying a Ricoh GR II consumer‐grade camera was used to capture replicate, centimeter‐resolution image datasets of a temperate, intensively managed grassland ecosystem. These data allowed the exploration of method reproducibility and the impact of SfM + MVS software choice on derived vegetation canopy height measurement accuracy. The quality of DSM height measurements derived from four different, yet widely used SfM‐MVS software—Photoscan, Pix4D, 3DFlow Zephyr, and MICMAC, was compared with in situ data captured on the same day as image capture. We used both traditional agronomic techniques for measuring sward height, and a high accuracy and precision differential GPS survey to generate independent measurements of the underlying ground surface elevation. Using the same replicate image dataset (n = 3) as input, we demonstrate that there are 1.7, 2.0, and 2.5 cm differences in RMSE (excluding one outlier) between the outputs from different SfM + MVS software using High, Medium, and Low quality settings, respectively. Furthermore, we show that there can be a significant difference, although of small overall magnitude between replicate image datasets (n = 3) processed using the same SfM + MVS software, following the same workflow, with a variance in RMSE of up to 1.3, 1.5, and 2.7 cm (excluding one outlier) for “High,” “Medium,” and “Low” quality settings, respectively. We conclude that SfM + MVS software choice does matter, although the differences between products processed using “High” and “Medium” quality settings are of small overall magnitude.

Modelling discontinuous terrain from DSMs using segment labelling, outlier removal and thin-plate splines

Models of ground surface elevations are crucial to many applications of remotely sensed data, including estimates of the height relative to ground of non-ground objects, such as buildings and vegetation. In highly engineered regions, such as cities, there are many discontinuities in both the ground surface and the surface of non-ground objects. Sub-metre resolution elevation data for these regions are increasingly available. At these resolutions there is sufficient information and a growing need to improve model accuracies by incorporating discontinuities. Here we provide a new method for generating high resolution models of discontinuous ground surfaces from breakline data and digital surface models derived from remotely sensed data. The method uses segment based filtering, outlier removal and multiresolution thin-plate spline surface fitting. Breaklines are included in the fitted surface using partial derivatives and a breakline-aware method for transferring between different resolutions. We demonstrate our method using elevation data derived from photogrammetry for suburban regions of Perth, Western Australia, and Vaihingen, Germany. We produced ground surface models with noticeable qualitative and quantitative improvements when breaklines are included, at an increased computational cost of approximately 10% when all other parameters remained the same. For LiDAR derived elevations, we report our residual error against a number of other methods recorded using the ISPRS Ground Filtering Test Sites.

Synthesis of Leaf-on and Leaf-off Unmanned Aerial Vehicle (UAV) Stereo Imagery for the Inventory of Aboveground Biomass of Deciduous Forests

Applications of stereo imagery acquired by cameras onboard unmanned aerial vehicles (UAVs) as practical forest inventory tools are hindered by the unavailability of ground surface elevation. It is still a challenging issue to remove the elevation of ground surface in leaf-on stereo imagery to extract forest canopy height without the help of lidar data. This study proposed a method for the extraction of forest canopy height through the synthesis of UAV stereo imagery of leaf-on and leaf-off, and further demonstrated that the extracted forest canopy height could be used for the inventory of deciduous forest aboveground biomass (AGB). The points cloud of the leaf-on and leaf-off stereo imagery was firstly extracted by an algorithm of structure from motion (SFM) using the same ground control points (GCP). The digital surface model (DSM) was produced by rasterizing the point cloud of UAV leaf-on. The point cloud of UAV leaf-off was processed by iterative median filtering to remove vegetation points, and the digital terrain model (DTM) was generated by the rasterization of the filtered point cloud. The mean canopy height model (MCHM) was derived from the DSM subtracted by the DTM (i.e., DSM-DTM). Forest AGB maps were generated using models developed based on the MCHM and sampling plots of forest AGB and were evaluated by those of lidar. Results showed that forest AGB maps from UAV stereo imagery were highly correlated with those from lidar data with R2 higher than 0.94 and RMSE lower than 10.0 Mg/ha (i.e., relative RMSE 18.8%). These results demonstrated that UAV stereo imagery could be used as a practical inventory tool for deciduous forest AGB.

Delimitation of flood areas based on a calibrated a DEM and geoprocessing: case study on the Uruguay River, Itaqui, southern Brazil

Abstract. Flooding is a natural disaster which affects thousands of riverside, coastal, and urban communities causing severe damage. River flood mapping is the process of determining inundation extents and depth by comparing historical river water levels with ground surface elevation references. This paper aims to map flood hazard areas under the influence of the Uruguay River, Itaqui (southern Brazil), using a calibration digital elevation model (DEM), historic river level data and geoprocessing techniques. The temporal series of maximum annual level records of the Uruguay River, for the years 1942 to 2017, were linked to the Brazilian Geodetic System using geometric leveling and submitted for descriptive statistical analysis and probability. The DEM was calibrated with ground control points (GCPs) of high vertical accuracy based on post-processed high-precision Global Navigation Satellite System surveys. Using the temporal series statistical analysis results, the spatialization of flood hazard classes on the calibrated DEM was assessed and validated. Finally, the modeling of the simulated flood level was visually compared against the flood area on the satellite image, which were both registered on the same date. The free DEM calibration model indicated high correspondence with GCPs (R2=0.81; p<0.001). The calibrated DEM showed a 68.15 % improvement in vertical accuracy (RMSE = 1.00 m). Five classes of flood hazards were determined: extremely high flood hazard, high flood hazard, moderate flood hazard, low flood hazard, and non-floodable. The flood episodes, with a return time of 100 years, were modeled with a 57.24 m altimetric level. Altimetric levels above 51.66 m have a high potential of causing damage, mainly affecting properties and public facilities in the city's northern and western peripheries. Assessment of the areas that can potentially be flooded can help to reduce the negative impact of flood events by supporting the process of land use planning in areas exposed to flood hazard.

UAV–LiDAR accuracy in vegetated terrain

We examined the horizontal and vertical accuracy of LiDAR data acquired from an unmanned aerial vehicle (UAV) at a field site with six vegetation types: coniferous trees, deciduous trees, short grass (0–0.3 m height), tall grass (>0.3 m height), short shrubs (0–1 m height), and tall shrubs (>1 m height). The objective was to assess positional accuracy of the ground surface in the context of digital mapping standards, and to determine how different vegetation types affect vertical accuracy. The data were acquired from a single-rotor vertical takeoff and landing UAV equipped with a Riegl VUX-1UAV laser scanner, KVH Industries 1750 IMU, and dual NovAtel GNSS receivers. Reference measurements of ground surface elevation were acquired with conventional field surveying techniques. Accuracy was evaluated using methods in the 2015 American Society for Photogrammetry and Remote Sensing (ASPRS) Positional Accuracy Standards for Digital Geospatial Data. Results show that horizontal accuracy and vegetated vertical accuracy at the 95% confidence level were 0.05 and 0.24 m, respectively. Median vertical errors significantly differed among 10 of 15 vegetation type pairs, highlighting the need to account for variations of vegetation structure. According to the 2015 ASPRS standards, the reported errors fulfill the requirements for mapping at the 2 and 8 cm horizontal and vertical class levels, respectively.

Improved Building Treatment Approach for Urban Inundation Modeling: A Case Study in Wuhan, China

This paper describes an improved building treatment approach (IBTA) for use in urban inundation modeling. In this approach, the ground surface elevation was raised by the threshold (h) of the building entrance height to account for both the blockage and storage effect of areas with dense building coverage. A higher roughness coefficient was assigned to the areas where buildings were located to compensate for the resistance effects caused by the inner wall of the structure. The campus of Huazhong University of Science and Technology (HUST) in Wuhan City, China, was used as a case study. Comparison between IBTA and several traditional building treatment approaches suggested that the model results were sensitive to the building treatment method and the threshold used for terrain preprocessing in dense building regions. Furthermore, as the interaction between the surface water flow and dense buildings were adequately represented by using a new terrain preprocessing approach, the proposed IBTA provided better performance in terms of maximum inundation depth and the peak depth time than the traditional approaches in areas with dense building coverage, such as that of the campus.

Economical Design of Sewer Line in Flat Terrain: A Case Study of Rajapur Sewerage System

Design of sewer line in flat terrain is a great challenge due to high excavation depth involved in laying a sewer line required for maintaining minimum velocity, slope and clear cover. Sewer design presented in this paper is result of sewer modelling software Bentley SewerCAD V8i. Estimation and cost analysis of a sewer system shows cost is directly related to the excavation depth. For economically efficient design of sewer line in a flat terrain of Rajapur-Bardia, sewer is designed in the gentle slope and flushing tanks are provided at sections where velocities are less than the minimum value recommended by Codes. Design and cost estimation of sewer network of 4.554 km with and without use of flushing tank are presented in this paper and two major benefits - cost and low invert level of outfall from ground surface elevation are achieved with flushing tank provision.

Decadal changes of surface elevation over permafrost area estimated using reflected GPS signals

Abstract. Conventional benchmark-based survey and Global Positioning System (GPS) have been used to measure surface elevation changes over permafrost areas, usually once or a few times a year. Here we use reflected GPS signals to measure temporal changes of ground surface elevation due to dynamics of the active layer and near-surface permafrost. Applying the GPS interferometric reflectometry technique to the multipath signal-to-noise ratio data collected by a continuously operating GPS receiver mounted deep in permafrost in Barrow, Alaska, we can retrieve the vertical distance between the antenna and reflecting surface. Using this unique kind of observables, we obtain daily changes of surface elevation during July and August from 2004 to 2015. Our results show distinct temporal variations at three timescales: regular thaw settlement within each summer, strong interannual variability that is characterized by a sub-decadal subsidence trend followed by a brief uplift trend, and a secular subsidence trend of 0.26 ± 0.02 cm year−1 during 2004 and 2015. This method provides a new way to fully utilize data from continuously operating GPS sites in cold regions for studying dynamics of the frozen ground consistently and sustainably over a long time.

Effects of sea-level rise and freshwater management on long-term water levels and water quality in the Florida Coastal Everglades

Since the 1880s, hydrological modification of the Greater Florida Everglades has reduced water levels and flows in Everglades National Park (ENP). The Comprehensive Everglades Restoration Program (CERP) began in 2000 to restore pre-drainage flows and preserve the natural landscape of the Everglades. However, sea-level rise (SLR) was not considered in the development of CERP. We used long-term data (2001–2016) from the Florida Coastal Everglades-Long Term Ecological Research Program to quantify and model the spatial dynamics of water levels, salinity, and nutrients in response to changes in climate, freshwater management and SLR in the Shark River Slough (SRS), ENP. Results indicate that fresh-to-marine head difference (FMHD) was the single most important factor affecting marine-to-freshwater hydrologic connectivity and transport of salinity and phosphorous upstream from the Gulf of Mexico. Sea-level has increasingly exceeded ground surface elevation at the most downstream freshwater site in SRS, thereby reducing the FMHD. We showed a higher impact of SLR in the dry season when there was practically no freshwater inflow to raise FMHD. We also demonstrated effectiveness of inflow depends more on the monthly distribution than the total annual volume. Hence, the impact per unit volume of inflow is significantly higher in the dry season in preventing high salinity and marine-derived nutrient levels. We advocate that FMHD needs to be factored into water management decisions to reduce adverse and likely irreversible effects of SLR throughout the Everglades landscape.