scholarly journals Bed topography of Jakobshavn Isbræ, Greenland, and Byrd Glacier, Antarctica

2014 ◽  
Vol 60 (223) ◽  
pp. 813-833 ◽  
Author(s):  
S. Gogineni ◽  
J.-B. Yan ◽  
J. Paden ◽  
C. Leuschen ◽  
J. Li ◽  
...  
Keyword(s):  
High Sensitivity ◽  
Radar Data ◽  
Unmanned Aerial Systems ◽  
Music Algorithm ◽  
Bed Topography ◽  
Ice Surface ◽  
Elevation Data ◽  
Track Surface ◽  
Cross Track ◽  
Aerial Systems

AbstractThis paper presents the bed topography of Jakobshavn Isbræ, Greenland, and Byrd Glacier, Antarctica, derived from sounding these glaciers with high-sensitivity radars. To understand the processes causing the speed-up and retreat of outlet glaciers, and to enable the development of next-generation ice-sheet models, we need information on bed topography and basal conditions. To this end, we performed measurements with the progressively improved Multichannel Coherent Radar Depth Sounder/Imager (MCoRDS/I). We processed the data from each antenna-array element using synthetic aperture radar algorithms to improve radar sensitivity and reduce along-track surface clutter. We then applied array and image-processing algorithms to extract the weak bed echoes buried in off-vertical scatter (cross-track surface clutter). At Jakobshavn Isbræ, we observed 2.7 km thick ice ~30 km upstream of the calving front and ~850 m thick ice at the calving front. We also observed echoes from multiple interfaces near the bed. We applied the MUSIC algorithm to the data to derive the direction of arrival of the signals. This analysis revealed that clutter is dominated by the ice surface at Jakobshavn Isbræ. At Byrd Glacier, we found ~3.62 km thick ice, as well as a subglacial trench ~3.05 km below sea level. We used ice thickness information derived from radar data in conjunction with surface elevation data to generate bed maps for these two critical glaciers. The performance of current radars must be improved further by ~15 dB to fully sound the deepest part of Byrd Glacier. Unmanned aerial systems equipped with radars that can be flown over lines spaced as close as 5 m apart in the cross-track direction to synthesize a two-dimensional aperture would be ideal for collecting fine-resolution data over glaciers like Jakobshavn near their grounding lines.

scholarly journals Cavity Ring-Down Methane Sensor for Small Unmanned Aerial Systems

Sensors ◽  
2020 ◽  
Vol 20 (2) ◽  
pp. 454 ◽  
Author(s):  
Benjamin Martinez ◽  
Thomas W. Miller ◽  
Azer P. Yalin
Keyword(s):  
Near Infrared ◽  
High Sensitivity ◽  
Unmanned Aerial Systems ◽  
Test Results ◽  
Methane Sensor ◽  
Open Path ◽  
Low Mass ◽  
Aerial Systems ◽  
High Finesse ◽  
Cavity Ring Down

We present the development, integration, and testing of an open-path cavity ring-down spectroscopy (CRDS) methane sensor for deployment on small unmanned aerial systems (sUAS). The open-path configuration used here (without pump or flow-cell) enables a low mass (4 kg) and low power (12 W) instrument that can be readily integrated to sUAS, defined here as having all-up mass of <25 kg. The instrument uses a compact telecom style laser at 1651 nm (near-infrared) and a linear 2-mirror high-finesse cavity. We show test results of flying the sensor on a DJI Matrice 600 hexacopter sUAS. The high sensitivity of the CRDS method allows sensitive methane detection with a precision of ~10–30 ppb demonstrated for actual flight conditions. A controlled release setup, where known mass flows are delivered, was used to simulate point-source methane emissions. Examples of methane plume detection from flight tests suggest that isolated plumes from sources with a mass flow as low as ~0.005 g/s can be detected. The sUAS sensor should have utility for emissions monitoring and quantification from natural gas infrastructure. To the best of our knowledge, it is also the first CRDS sensor directly deployed onboard an sUAS.

scholarly journals Regional Assessments of Surface Ice Elevations from Swath-Processed CryoSat-2 SARIn Data

2021 ◽  
Vol 13 (11) ◽  
pp. 2213
Author(s):  
Natalia Havelund Andersen ◽  
Sebastian Bjerregaard Simonsen ◽  
Mai Winstrup ◽  
Johan Nilsson ◽  
Louise Sandberg Sørensen
Keyword(s):  
Radar Data ◽  
The Arctic ◽  
Validation Data ◽  
Sea Levels ◽  
Ice Surface ◽  
Spatial Coverage ◽  
Elevation Data ◽  
The Stability ◽  
Surface Ice ◽  
The Cost

The Arctic responds rapidly to climate change, and the melting of land ice is a major contributor to the observed present-day sea-level rise. The coastal regions of these ice-covered areas are showing the most dramatic changes in the form of widespread thinning. Therefore, it is vital to improve the monitoring of these areas to help us better understand their contribution to present-day sea levels. In this study, we derive ice-surface elevations from the swath processing of CryoSat-2 SARIn data, and evaluate the results in several Arctic regions. In contrast to the conventional retracking of radar data, swath processing greatly enhances spatial coverage as it uses the majority of information in the radar waveform to create a swath of elevation measurements. However, detailed validation procedures for swath-processed data are important to assess the performance of the method. Therefore, a range of validation activities were carried out to evaluate the performance of the swath processor in four different regions in the Arctic. We assessed accuracy by investigating both intramission crossover elevation differences, and comparisons to independent elevation data. The validation data consisted of both air- and spaceborne laser altimetry, and airborne X-band radar data. There were varying elevation biases between CryoSat-2 and the validation datasets. The best agreement was found for CryoSat-2 and ICESat-2 over the Helheim region in June 2019. To test the stability of the swath processor, we applied two different coherence thresholds. The number of data points was increased by approximately 25% when decreasing the coherence threshold in the processor from 0.8 to 0.6. However, depending on the region, this came with the cost of an increase of 33–65% in standard deviation of the intramission differences. Our study highlights the importance of selecting an appropriate coherence threshold for the swath processor. Coherence threshold should be chosen on a case-specific basis depending on the need for enhanced spatial coverage or accuracy.

scholarly journals Interferometric discrimination of cross-track bed clutter in ice-penetrating radar sounding data

2020 ◽  
Vol 61 (81) ◽  
pp. 68-73 ◽  
Author(s):  
Kirk M. Scanlan ◽  
Anja Rutishauser ◽  
Duncan A. Young ◽  
Donald D. Blankenship
Keyword(s):  
Center Frequency ◽  
Adjacent Area ◽  
Bed Topography ◽  
Ice Cap ◽  
Digital Elevation ◽  
Interferometric Phase ◽  
Devon Ice Cap ◽  
Track Surface ◽  
Cross Track ◽  
Climate Studies

AbstractThe interpretations of relevant interfaces (i.e. the surface and bed) in radar sounding datasets over glaciers and ice sheets are primary boundary conditions in a variety of climate studies and particularly subglacial water routing models. It is therefore necessary to ensure these interpretations are consistent and not affected by cross-track clutter. For the surface interface, interferometry and a family of methods relying on digital elevation models have been used to successfully discriminate cross-track surface clutter. Here we present how interferometry can be applied to the problem of basal clutter from cross-track bed topography. Our approach is based on a comparison of the differential phases of ambiguous reflectors that may represent bed clutter and the differential phase of a reflector in an adjacent area that appears unaffected by basal clutter. The reflector yielding the smallest interferometric phase difference relative to the unambiguous bed reflector is considered to represent its consistent continuation. We successfully demonstrate our approach using 60 MHz center frequency MARFA data collected over Devon Ice Cap in the Canadian Arctic. Finally, we investigate the effects of clutter-affected and interferometry-corrected bed interpretations on ice layer thickness estimates, basal hydraulic head gradients and the potential extent of inferred subglacial water bodies.

scholarly journals Basal control of supraglacial meltwater catchments on the Greenland Ice Sheet

2018 ◽  
Author(s):  
Josh Crozier ◽  
Leif Karlstrom ◽  
Kang Yang
Keyword(s):  
Surface Topography ◽  
Transfer Functions ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Spatial Density ◽  
Bed Topography ◽  
Subglacial Environment ◽  
Ice Surface ◽  
Basal Sliding ◽  
Elevation Data

Abstract. Ice surface topography controls the primary routing of surface meltwater on ablation zones of glaciers and ice sheets. Meltwater routing is important for understanding and predicting ice sheet evolution because surface melt can be both a direct source of ice mass loss and an influence on basal sliding and ice advection. Although controls on ice sheet topography at long wavelengths are well known, smaller scale features relevant for meltwater routing are not well understood. Here we examine the effects of two processes that can influence ice sheet surface topography: bed topography transfer and thermal-fluvial incision by supraglacial streams. We implement 2D bed topography and basal sliding transfer functions in seven study regions of the western Greenland Ice Sheet (GIS) ablation zone to study the influence of basal conditions on ice surface topography. Although bed elevation data quality is spatially variable, we find that ∼ 1–10 km scale ice surface features under variable ice thickness, velocity, and surface slope are well predicted by these transfer functions. We then use flow-routing algorithms to extract supraglacial stream networks from 2–5 m resolution digital elevation models, and compare these with synthetic flow networks calculated on ice surfaces predicted by bed topography transfer. Quantitative comparison of these networks reveals that bed topography can explain ∼ 1–10 km surface meltwater routing patterns without significant contributions from thermal-fluvial erosion by streams. We predict how supraglacial internally drained catchment (IDC) patterns on the GIS would change under time-varying ice flow and/or basal sliding regimes. Basal sliding variations exert a significant influence on IDC spatial distribution, and suggest a potential positive feedback between subglacial hydrologic regime to surface IDC patterning. Increased basal sliding will increase IDC spatial density (by decreasing IDC sizes) and cause more disperse meltwater input to the englacial and subglacial environment. This could result in less efficient subglacial channelization and increased basal sliding that would then further increase IDC density.

LIGHTER-THAN-AIR (LTA) UNMANNED AERIAL SYSTEM (UAS) CARRIER CONCEPT FOR SURVAILLANCE AND DISASTER MANAGEMENT

2019 ◽  
Vol 3 ◽  
pp. 1255
Author(s):  
Ahmad Salahuddin Mohd Harithuddin ◽  
Mohd Fazri Sedan ◽  
Syaril Azrad Md Ali ◽  
Shattri Mansor ◽  
Hamid Reza Jifroudi ◽  
...  
Keyword(s):  
Unmanned Aerial Vehicles ◽  
Disaster Management ◽  
Unmanned Aerial Systems ◽  
Unmanned Aerial System ◽  
Border Control ◽  
Aerial Vehicles ◽  
Operational Safety ◽  
In Situ Methods ◽  
Aerial Systems

Unmanned aerial systems (UAS) has many advantages in the fields of SURVAILLANCE and disaster management compared to space-borne observation, manned missions and in situ methods. The reasons include cost effectiveness, operational safety, and mission efficiency. This has in turn underlined the importance of UAS technology and highlighted a growing need in a more robust and efficient unmanned aerial vehicles to serve specific needs in SURVAILLANCE and disaster management. This paper first gives an overview on the framework for SURVAILLANCE particularly in applications of border control and disaster management and lists several phases of SURVAILLANCE and service descriptions. Based on this overview and SURVAILLANCE phases descriptions, we show the areas and services in which UAS can have significant advantage over traditional methods.

Beach and dune impacts due to Hurricane Florence in Dare County, North Carolina

Shore & Beach ◽  
2019 ◽  
pp. 44-49 ◽  
Author(s):  
Elizabeth Sciaudone ◽  
Liliana Velasquez-Montoya
Keyword(s):  
North Carolina ◽  
Prior Knowledge ◽  
Unmanned Aerial Systems ◽  
State University ◽  
National Wildlife Refuge ◽  
Sediment Samples ◽  
Wildlife Refuge ◽  
Full Report ◽  
Aerial Systems

Less than two weeks after Hurricane Florence made landfall in North Carolina (NC), a team of researchers from NC State University traveled to Dare County to investigate the storm’s effects on beaches and dunes. Using available post-storm imagery and prior knowledge of vulnerabilities in the system, the team identified several locations to visit in the towns of Kitty Hawk, Nags Head, Rodanthe, Buxton, and Hatteras, as well as a number of locations within the Pea Island National Wildlife Refuge (Figure 1). Data collected included topographic profiles, still imagery and video from unmanned aerial systems, sediment samples, and geo-located photography. This Coastal Observations piece presents some of the data and photos collected; the full report is available online (Sciaudone et al. 2019), and data collected will be made available to interested researchers upon request.

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