Adam LeWinter

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.

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.