D. C. Finnegan

Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland ice sheet

Significance Meltwater runoff from the Greenland ice sheet is a key contributor to global sea level rise and is expected to increase in the future, but it has received little observational study. We used satellite and in situ technologies to assess surface drainage conditions on the southwestern ablation surface after an extreme 2012 melting event. We conclude that the ice sheet surface is efficiently drained under optimal conditions, that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater release from the ice sheet. Thermally incised meltwater channels that flow each summer across melt-prone surfaces of the Greenland ice sheet have received little direct study. We use high-resolution WorldView-1/2 satellite mapping and in situ measurements to characterize supraglacial water storage, drainage pattern, and discharge across 6,812 km2 of southwest Greenland in July 2012, after a record melt event. Efficient surface drainage was routed through 523 high-order stream/river channel networks, all of which terminated in moulins before reaching the ice edge. Low surface water storage (3.6 ± 0.9 cm), negligible impoundment by supraglacial lakes or topographic depressions, and high discharge to moulins (2.54–2.81 cm⋅d−1) indicate that the surface drainage system conveyed its own storage volume every <2 d to the bed. Moulin discharges mapped inside ∼52% of the source ice watershed for Isortoq, a major proglacial river, totaled ∼41–98% of observed proglacial discharge, highlighting the importance of supraglacial river drainage to true outflow from the ice edge. However, Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056–0.112 km3⋅d−1 vs. ∼0.103 km3⋅d−1), and when integrated over the melt season, totaled just 37–75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean.

Empirical Waveform Decomposition and Radiometric Calibration of a Terrestrial Full-Waveform Laser Scanner

The parametric models used in Light Detection And Ranging (LiDAR) waveform decomposition routines are inherently estimates of the sensors system response to backscattered laser pulse power. This estimation can be improved with an empirical system response model, yielding reduced waveform decomposition residuals and more precise echo ranging. We develop an empirical system response model for a Riegl VZ-400 terrestrial laser scanner, from a series of observations to calibrated reflectance targets, and present a numerical least squares method for decomposing waveforms with the model. The target observations are also used to create an empirical radiometric calibration model that accommodates a nonlinear relationship between received optical power and echo peak amplitude, and to examine the temporal stability of the instrument. We find that the least squares waveform decomposition based on the empirical system response model decreases decomposition fitting errors by an order of magnitude for high-amplitude returns and reduces range estimation errors on planar surfaces by 17% over a Gaussian model. The empirical radiometric calibration produces reflectance values self-consistent to within 5% for several materials observed at multiple ranges, and analysis of multiple calibration data sets collected over a one-year period indicates that echo peak amplitude values are stable to within ±3% for target ranges up to 125 m.

Glaciological and marine geological controls on terminus dynamics of Hubbard Glacier, southeast Alaska

Hubbard Glacier, located in southeast Alaska, is the worlds largest nonpolar tidewater glacier. It has been steadily advancing since it was first mapped in 1895; occasionally, the advance creates an ice or sediment dam that blocks a tributary fjord (Russell Fiord). The sustained advance raises the probability of long-term closure in the near future, which will strongly impact the ecosystem of Russell Fiord and the nearby community of Yakutat. Here, we examine a 43 year record of flow speeds and terminus position to understand the large-scale dynamics of Hubbard Glacier. Our long-term record shows that the rate of terminus advance has increased slightly since 1895, with the exception of a slowed advance between approximately 1972 and 1984. The short-lived closure events in 1986 and 2002 were not initiated by perturbations in ice velocity or environmental forcings but were likely due to fluctuations in sedimentation patterns at the terminus. This study points to the significance of a coupled system where short-term velocity fluctuations and morainal shoal development control tidewater glacier terminus position.

Analyzing Glacier Surface Motion Using LiDAR Data

Understanding glacier motion is key to understanding how glaciers are growing, shrinking, and responding to changing environmental conditions. In situ observations are often difficult to collect and offer an analysis of glacier surface motion only at a few discrete points. Using light detection and ranging (LiDAR) data collected from surveys over six glaciers in Greenland and Antarctica, particle image velocimetry (PIV) was applied to temporally-spaced point clouds to detect and measure surface motion. The type and distribution of surface features, surface roughness, and spatial and temporal resolution of the data were all found to be important factors, which limited the use of PIV to four of the original six glaciers. The PIV results were found to be in good agreement with other, widely accepted, measurement techniques, including manual tracking and GPS, and offered a comprehensive distribution of velocity data points across glacier surfaces. For three glaciers in Taylor Valley, Antarctica, average velocities ranged from 0.8–2.1 m/year. For one glacier in Greenland, the average velocity was 22.1 m/day (8067 m/year).

The Attenuation of Retroreflective Signatures on Surface Soils

Abstract Soil parameters such as water potential, temperature, organic matter ( om ), and particle size distribution influence biological activity and collectively define the state of soils, yet these properties are typically described through time-intensive, ground-based sampling efforts. To improve our understanding of soils through stand-off sensing techniques, Light Detection and Ranging was used to monitor the signature of retroreflective beads embedded in polymeric agents on four soils. Our goal was to generate probability density functions (PDFs) for stochastic predictions of the persistence of this signature through time. Our findings showed that the PDFs of the reflected signal between target and background soils became nearly indistinguishable after five months and that OM, nitrogen content, cation exchange capacity, and pH related to signature decline. This approach, while developed using polymer-bound retroreflectors, will serve as a framework where a signature-emitter is left in or on soil and differentially influenced by terrain, weather, and soil processes.

Building envelope and infrastructure assessment using an integrated thermal imaging and lidar scanning system : Amundsen-Scott South Pole Station, Antarctica

We conducted a combined lidar and Thermal Infrared (TIR) survey at the Amundsen-Scott South Pole Station, Antarctica, in January 2017 to assess the building thermal envelope and infrastructure of the Elevated Station. These coregistered data produce a three-dimensional (3-D) model with assigned temperature values for target surfaces, useful in spatially identifying thermal anomalies and areas for potential improvements. In addition, the accuracy of the resulting 3-D point cloud is useful for assessing building infrastructure by locating and quantifying areas of building settlement and structural anomalies. The lidar/TIR data collection was conducted in tandem with interior and exterior temperature and atmospheric measurement logging, handheld electro-optical imagery collection, and Global Navigation Satellite System real-time kinematic surveys to place the collected data in a global coordinate system. By analyzing the resulting data products, we conclude that while some thermal deficiencies exist, the building design and the material have maintained thermal-envelope integrity and display no significant thermal deficiencies. However, comparing building base elevations shows that significant and unequal settlement across the building has occurred. We suggest mitigating the thermal deficiencies through exterior repairs and that the building settlement be addressed in future leveling procedures to include lidar surveys. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. ERDC/CRREL TR-18-10 iii

Unmanned aircraft system-based lidar survey of structures above and below the water surface: Hilo Deep Draft Harbor Breakwater, Hawaii

With recent advancements in unmanned aircraft system (UAS) technology, along with the miniaturization of airborne laser scanning systems, capabilities of unmanned laser scanning (ULS) systems have increased. Traditional terrestrial laser scanning surveys provide high density point clouds (hundreds - thousands of pts/m2) of a focus area, but have limited field-of-view and line-of-sight due to the constrained static nature of the system. While airborne and mobile laser scanning platforms relieve many of these limitations, lower point density (airborne), confined operation pathways (mobile), and higher operational costs become a factor. Here we present results from ULS data acquired over the Hilo Deep Draft Harbor Breakwater in Hawaii in June 2018. Inspecting the breakwater for failures and instabilities is of vital importance for Hilo. At three kilometers length and exposure to open ocean, a terrestrial laser scanning survey of the breakwater is not possible. Airborne and mobile laser scanning are not ideal due to reduced point densities and site access, respectively. In June 2018, using a RIEGL RiCOPTER with VUX laser system, the authors collected highresolution data over the above water breakwater extents. For below water surfaces, a Riegl BDF-1 bathymetric depth finder was operated from the same UAS, used to generate profiles of subaqueous surfaces of the breakwater. These bathymetric transects supplement the detailed topographic data collected above water on the breakwater. We discuss the operational concerns in both project planning and acquisition phases, as well as detailed analysis of the resulting data, used for a rigorous structure inspection program.

Terrestrial hyperspectral image shadow restoration through fusion with terrestrial lidar

Recent advances in remote sensing technology have expanded the acquisition and fusion of active lidar and passive hyperspectral imagery (HSI) from exclusively airborne observations to include terrestrial modalities. In contrast to airborne collection geometry, hyperspectral imagery captured from terrestrial cameras is prone to extensive solar shadowing on vertical surfaces leading to reductions in pixel classification accuracies or outright removal of shadowed areas from subsequent analysis tasks. We demonstrate the use of lidar spatial information for sub-pixel HSI shadow detection and the restoration of shadowed pixel spectra via empirical methods that utilize sunlit and shadowed pixels of similar material composition. We examine the effectiveness of radiometrically calibrated lidar intensity in identifying these similar materials in sun and shade conditions and further evaluate a restoration technique that leverages ratios derived from the overlapping lidar laser and HSI wavelengths. Simulations of multiple lidar wavelengths, i.e., multispectral lidar, indicate the potential for HSI spectral restoration that is independent of the complexity and costs associated with rigorous radiometric transfer models, which have yet to be developed for horizontal-viewing terrestrial HSI sensors. The spectral restoration performance of shadowed HSI pixels is quantified for imagery of a geologic outcrop through improvements in spectral shape, spectral scale, and HSI band correlation.

Modified region growing for stereo of slant and textureless surfaces

In this paper, we present an algorithm for estimating disparity for images containing large textureless regions. We propose a fast and efficient region growing algorithm for estimating the stereo disparity. Though we present results on ice images, the algorithm can be easily used for other applications. We modify the first-best region growing algorithm using relaxed uniqueness constraints and matching for sub-pixel values and slant surfaces. We provide an efficient method for matching multiple windows using a linear transform. We estimate the parameters required by the algorithm automatically based on initial correspondences. Our method was tested on synthetic, benchmark and real outdoor data. We quantitatively demonstrated that our method performs well in all three cases.

A study of dune change in Victoria Valley, Antarctica between 1959 and 2002

Evidence of global climate change is expected to be first seen in polar regions, where subtle changes in climate may have large impacts on fragile geomorphic systems. Polar dunes are one such system for which there is little precise information available. For example, the extent to which polar aeolian deposits are stabilized by ice-bonded sands is unknown. As a first step towards a better understanding of the response of polar desert aeolian systems, we have mapped the sand dunes in Victoria Valley, Antarctica over the past four decades. The dune field is located at the confluence of the Packard and Victoria Valleys and has been the focus of field measurement programs for more than 40 years. Previous studies indicate that dune mobility has been limited to the crests shifting over ice-cemented sand layers within the dune in response to the Valley’s bi-direction wind regime. This is believed to impede net migration of the dune field. Short-term field studies have shown erratic movement of the dunes with the range between –14 and 62 m. However, no study has been made of longer term change in the morphological character of the dune field. In this study we use vertical air photographs and LIDAR data to map dune change over a 43 year period. We assess change in dune position and morphology over time. We find that the dunes have migrated (up to 75 m), and that dune form has changed, principally by lateral coalescing and limb extension. Movement of the dunes suggests that migration is possible despite the presence of ice and snow within the dune core. In addition, these changes support earlier observations that indicate a net (westerly) migration driven by topographically channeled thermally generated easterlies and gradient southeasterly winds. We infer this to indicate that the region has not undergone significant change in weather patterns in the last four decades. This is in agreement with the findings of Ayling and McGowan (2006) who investigated dust deposits on the adjacent Victoria Lower Glacier. Accordingly, it would appear that neither change in weather or climate due to global warming has caused significant change to the meteorology of the Victoria Valley, Antarctica and in-turn its aeolian geomorphic system.Plant macrofossils from permafrost deposits at the Bolshoy Lyakhovsky Island, New Siberian Archipelago, in the Russian Arctic were studied aiming at the revelation of climatic similarities and distinctions between the last and the current interglacial. The plant remains revealed the existence of a shrubland dominated by Alnus fruticosa, Betula nana, and Ledum palustre and interspersed with lakes and grasslands during the last interglacial. The reconstructed vegetation differs fundamentally from the high arctic tundra that exists in this region today, but resembles an open variant of subarctic shrub tundra as occurring near the tree line about 350 km southwest of the study site. Such difference in the plant cover implies that, during the last interglacial, the mean summer temperature was considerably higher, the growing season was longer, and soils outside the range of thermokarst depressions were drier than today. Pollen-based climatic reconstructions using the best modern analogue (BMA) approach suggest a mean temperature of the warmest month (MTWA) range of 914.5 °C during the warmest interval of the last interglacial. Reconstructions from plant macrofossils based on thermal minimum needs of included plants, representing more local environments, gained MTWA values above 12.5 °C in contrast to todays 2.8 °C. We explain this contrast in summer temperature and moisture conditions with a combination of summer insolation higher than present and climatic continentality in arctic Yakutia stronger than present as result of a considerably less inundated Laptev Shelf during the last interglacial. The project was funded by the German Research Foundation (DFG).Over two-thirds of northern and central Britain has been glaciated during the Quaternary, and the present landscape is a relict of the glacial processes that have acted to erode and redistribute large quantities of geological material. The landscape of Southern Britain by contrast, which lay largely beyond the maximum ice extent, was not subjected to such processes. Instead the present form of the landscape reflects approximately 2.5 million years of subaerial weathering under a climate regime, characterized since the onset of the Middle Pleistocene, by a long-term trend of periglacial-Interglacial-periglacial cycles operating with 100ka cyclicty. The effect of this, as preserved with the geological record, has been the extensive in-situ weathering of bedrock materials and the development of thick regolith. Since the region became populated, deforestation and cultivation has progressively removed the vegetation that once acted to stabilize the regolith, and the regolith material is now highly susceptible to erosion by hillwash and solifluction processes. This represents a significant ground stability hazard especially in relation to the subsidence and collapse of roads and property. In addition, large valley accumulations of regolith material can liquefy under prolonged periods of intense rainfall and can result in catastrophic flooding and landslide events, such as those that occurred in Lynmouth in 1952 and more recently, in Boscastle on the north Cornwall coast in 2004. This abstract reports the findings of research undertaken both to map the spatial extent of these regolith deposits, and also to understand what controls their local and regional distribution. The research, based upon field analysis and NEXTMAP digital terrain models from two test areas in southwest England, reveals that the spatial distribution of in-situ and soliflucted regolith material is largely controlled by lithological variability and structural complexity of the bedrock. It is hoped that these models will prove an invaluable to planners to enable informed decision making and the prediction of natural geohazards.QUAVIDA is a new project which aims to understand the interactions among vegetation structure and function, climate and fire regimes during the Late Quaternary. The project targets Australasia as a critical area in the development of a global picture of environmental change. Australasia has experienced major wet/dry, temperature and atmospheric CO2 fluctuations in the past; human arrival and occupation have also had a substantial environmental influence. Much of the vegetation within the region is fire-prone (and fire-adapted), with fire management long and widely practised. We need to understand the natural climate variability, disentangle the role of humans in past changes and investigate how plant types, vegetation and fire regimes will respond to future climate changes. QUAVIDA will do this by using state-of-the-art earth system models in hypothesis-testing mode, running simulations for specific times in the past but with different model components operative and using different scenarios of external and internal forcing. In order to evaluate and interpret these simulations, comprehensive data sets describing palaeoenvironmental conditions at key times in the past will be required. Thus, the first major focus of activity within QUAVIDA has been the creation of a comprehensive database of palaeoenvironmental information from Australasia, covering the last 70,000 years. The database contains radiometrically-dated pollen, phytolith, plant macrofossil, stickrat midden, carbon isotope and charcoal records. Interrogation of this database will yield benchmark reconstructions of vegetation patterns and fire regimes for the evaluation of the model simulations. Using more than one source of palaeoenvironmental information allows differences in the temporal and spatial scale of different kinds of observations to be taken into account in making reconstructions. It also allows for the fact that different sources record different aspects of climate and/or environmental changes. This presentation will introduce QUAVIDA, the methods and preliminary results of the palaeo-data synthesis, and discuss the project’s contribution to the international earth-modelling community.In February 2004, a 4 m core spanning the last ~ 40 ka was retrieved from Native Companion Lagoon (NCL), southeast Queensland, Australia using a Russian D-section corer. Analysis of the top 1 m of the core, which represents the Holocene, identified a pronounced increase in aeolian sedimentation commencing at ~5700 cal BP with peaks in the deposition of wind transported sediment of 12.5 g m−2a at 4690 cal BP and 10.8 g m−2a at 3890 cal BP before decreasing to 0.3 g m−2a at ~2000 cal BP. The increase in aeolian sedimentation ~5700 cal BP was coincident with a pronounced increase in charcoal content of the core, thereby indicating that fire was most likely a key agent in the destabilisation of the local dunes. Geochemical provenance of the long traveled dust component of the record identified western Queensland and southwestern New South Wales as the dominant source areas. Analysis of pollens from the core indicate a reduction in aquatics similar to that reported by Donders et al. (2006) for Lake Allom, Fraser Island, while there was also a reduction in rainforest and pteridophytes. As a result, we believe that this period of increased aeolian sedimentation was caused by prolonged and severe drought possibly linked to the onset of ENSO type conditions in the mid-Holocene as reported by Moy et al. (2002) and Gagan et al. (2004). Through analogy with contemporary ENSO events, precipitation bearing southeasterly trade winds would have been suppressed and replaced by more frequent and dry west to southwesterly winds as indicated by the provenance of far traveled dust to west and southwestern source areas. Importantly, the NCL record identifies southeast Queensland as a region susceptible to prolonged and severe drought as a consequence of more persistent ENSO type conditions. Recent modeling studies suggest that ENSO type conditions may transform from their current interannual variability into the mean climate as a consequence of global warming. Our results suggest that if this was to occur, then southeast Queensland may experience the onset of another arid phase.A high resolution pollen record from the ODP 820 marine core for the last million years is presented. It is chronologically controlled by marine stratigraphic data.This record provides a picture of substantial vegetation and environmental change for the humid tropics region of northeastern Australia. It is the first largely continuous record in Australia to cover this length of time in any detail, although sediment accumulation rates decrease with increasing age. The influence of orbital forcing (particularly eccentricity and obliquity) is clearly present in the record providing good support for the proposed age model based on the marine stratigraphy, but each isotope stage contains some distinctive features. Superimposed on these cyclical patterns are abrupt and sustained changes in the representation of many taxa and community types that may be explained by a combination of regional changes in oceanic and atmospheric circulation systems throughout this time period, along with the impacts of people in the later part of the record (i.e. last 45,000 years BP).