scholarly journals Ensemble matching of repeat satellite images applied to measure fast-changing ice flow, verified with mountain climber trajectories on Khumbu icefall, Mount Everest

2020 ◽  
Vol 66 (260) ◽  
pp. 905-915
Author(s):  
Bas Altena ◽  
Andreas Kääb
Keyword(s):  
Velocity Field ◽  
Image Matching ◽  
Satellite Images ◽  
Optical Data ◽  
Single Pair ◽  
Complex Flow ◽  
Mount Everest ◽  
Glacier System ◽  
Mountain Climbers ◽  
Fast Flow

AbstractVelocities within an icefall are typically the fastest within a glacier system and experience complex flow. The combination of convergent and fast flow, and steep slope generate a quickly changing and intensely fractured surface. This complicates velocity extraction from repeat satellite images, especially when common pattern matching procedures are used. In this study, we exploit the high temporal revisit of medium-resolution satellite images using a novel image matching technique, ensemble matching, making it possible to generate a high-resolution (30 m) velocity field from high-repeat image sequences despite challenging image conditions. We demonstrate this technique for the first time in the glaciology domain using repeat Sentinel-2 optical data over the famous Khumbu icefall, situated on the southern slopes of Mount Everest. Estimates of velocity go just over 1 m d−1, which is slower than summer velocities from noisy single pair image matching. This icefall is frequently crossed by high-altitude mountaineers who use a route confined by fixed ropes and ladders set out every season. The mountain climbers typically record their trajectory on their personal satellite navigation device. We use such volunteered geographic information to verify our velocity estimates, confirming our underestimation with ensemble matching. Besides unprecedented remotely sensed surface velocities over the icefall, we also note that the generated velocity field can aid with the planning of a safe passage through this icefall.

scholarly journals ACCURACY IMPROVEMENT BY THE LEAST SQUARES IMAGE MATCHING EVALUATED ON THE CARTOSAT-1

2015 ◽  
Vol XL-1-W5 ◽  
pp. 11-14 ◽  
Author(s):  
H. Afsharnia ◽  
A. Azizi ◽  
H. Arefi
Keyword(s):  
High Resolution ◽  
Least Squares ◽  
Optical Sensors ◽  
Image Matching ◽  
Satellite Images ◽  
Functional Model ◽  
Stereo Image ◽  
Optical Data ◽  
High Resolution Satellite Images ◽  
Matching Techniques

Generating accurate elevation data from satellite images is a prerequisite step for applications that involve disaster forecasting and management using GIS platforms. In this respect, the high resolution satellite optical sensors may be regarded as one of the prime and valuable sources for generating accurate and updated elevation information. However, one of the main drawbacks of conventional approaches for automatic elevation generation from these satellite optical data using image matching techniques is the lack of flexibility in the image matching functional models to take dynamically into account the geometric and radiometric dissimilarities between the homologue stereo image points. The classical least squares image matching (LSM) method, on the other hand, is quite flexible in incorporating the geometric and radiometric variations of image pairs into its functional model. The main objective of this paper is to evaluate and compare the potential of the LSM technique for generating disparity maps from high resolution satellite images to achieve sub pixel precision. To evaluate the rate of success of the LSM, the size of the y-disparities between the homologous points is taken as the precision criteria. The evaluation is performed on the Cartosat-1 stereo along track images over a highly mountainous terrain. The precision improvement is judged based on the standard deviation and the scatter pattern of the y-disparity data. The analysis of the results indicate that, the LSM has achieved the matching precision of about 0.18 pixels which is clearly superior to the manual pointing that yielded the precision of 0.37 pixels.

scholarly journals New velocity map and mass-balance estimate of Mertz Glacier, East Antarctica, derived from Landsat sequential imagery

2003 ◽  
Vol 49 (167) ◽  
pp. 503-511 ◽  
Author(s):  
Etienne Berthier ◽  
Bruce Raup ◽  
Ted Scambos
Keyword(s):  
Velocity Field ◽  
Drainage Basin ◽  
Flow Speed ◽  
East Antarctica ◽  
Landsat Images ◽  
Mean Velocity ◽  
Speed Increase ◽  
Glacier System ◽  
Show Evidence ◽  
Basal Melting

AbstractAutomatic feature tracking on two Landsat images (acquired inJanuary 2000 and December 2001) generates a complete and accurate velocity field of Mertz Glacier, East Antarctica. This velocity field shows two main tributaries to the ice stream. Between the tributaries, a likely obstruction feature in the bedrock results in a slow-down of the flow. A third Landsat image, acquired in 1989 and combined with the 2000 image, permits the determination of the glacier mean velocity during the 1990s. Although some parts of the Mertz Glacier system show evidence of slight speed increase, we conclude that the Mertz flow speed is constant within our uncertainty (35 m a−1). Using this complete velocity field, new estimates of the ice discharge flux, 17.8 km3 a−1 (16.4 Gt a−1), and of the basal melting of the tongue, 11 m a−1 of ice, are given. Our results lead to an apparent imbalance of the drainage basin (ice discharge 3.5 km3 a−1 lower than the accumulation). Considering previous studies in the Mertz Glacier area, we then discuss the uncertainty of this imbalance and the problems with accumulation mapping for this region.

scholarly journals Detection of Archaeological Looting from Space: Methods, Achievements and Challenges

2019 ◽  
Vol 11 (20) ◽  
pp. 2389 ◽  
Author(s):  
Deodato Tapete ◽  
Francesca Cigna
Keyword(s):  
Remote Sensing ◽  
Image Processing ◽  
High Resolution ◽  
Satellite Data ◽  
Satellite Images ◽  
Google Earth ◽  
Optical Data ◽  
Mena Region ◽  
Processing Methods ◽  
Optical Imagery

Illegal excavations in archaeological heritage sites (namely “looting”) are a global phenomenon. Satellite images are nowadays massively used by archaeologists to systematically document sites affected by looting. In parallel, remote sensing scientists are increasingly developing processing methods with a certain degree of automation to quantify looting using satellite imagery. To capture the state-of-the-art of this growing field of remote sensing, in this work 47 peer-reviewed research publications and grey literature are reviewed, accounting for: (i) the type of satellite data used, i.e., optical and synthetic aperture radar (SAR); (ii) properties of looting features utilized as proxies for damage assessment (e.g., shape, morphology, spectral signature); (iii) image processing workflows; and (iv) rationale for validation. Several scholars studied looting even prior to the conflicts recently affecting the Middle East and North Africa (MENA) region. Regardless of the method used for looting feature identification (either visual/manual, or with the aid of image processing), they preferred very high resolution (VHR) optical imagery, mainly black-and-white panchromatic, or pansharpened multispectral, whereas SAR is being used more recently by specialist image analysts only. Yet the full potential of VHR and high resolution (HR) multispectral information in optical imagery is to be exploited, with limited research studies testing spectral indices. To fill this gap, a range of looted sites across the MENA region are presented in this work, i.e., Lisht, Dashur, and Abusir el Malik (Egypt), and Tell Qarqur, Tell Jifar, Sergiopolis, Apamea, Dura Europos, and Tell Hizareen (Syria). The aim is to highlight: (i) the complementarity of HR multispectral data and VHR SAR with VHR optical imagery, (ii) usefulness of spectral profiles in the visible and near-infrared bands, and (iii) applicability of methods for multi-temporal change detection. Satellite data used for the demonstration include: HR multispectral imagery from the Copernicus Sentinel-2 constellation, VHR X-band SAR data from the COSMO-SkyMed mission, VHR panchromatic and multispectral WorldView-2 imagery, and further VHR optical data acquired by GeoEye-1, IKONOS-2, QuickBird-2, and WorldView-3, available through Google Earth. Commonalities between the different image processing methods are examined, alongside a critical discussion about automation in looting assessment, current lack of common practices in image processing, achievements in managing the uncertainty in looting feature interpretation, and current needs for more dissemination and user uptake. Directions toward sharing and harmonization of methodologies are outlined, and some proposals are made with regard to the aspects that the community working with satellite images should consider, in order to define best practices of satellite-based looting assessment.

Measurements of Flow Modification by Particle Deposition Inside a Packed Bed Using Time-Resolved PIV

2008 ◽  
Author(s):  
Elvis E. Dominguez-Ontiveros ◽  
Carlos Estrada-Perez ◽  
Yassin A. Hassan
Keyword(s):  
Heat Transfer ◽  
Velocity Field ◽  
Flow Structure ◽  
Particle Deposition ◽  
Packed Bed ◽  
Packed Bed Reactor ◽  
Temperature Fields ◽  
Complex Flow ◽  
Flow Modification ◽  
Complex Flow Structure

In the Advanced Gas Cooled Pebble Bed Reactors for nuclear power generation, the fuel is spherical coated particles. The energy transfer phenomenon requires detailed understanding of the flow and temperature fields around the spherical fuel pebbles. Detailed information of the complex flow structure within the bed is needed. Generally, for computing the flow through a packed bed reactor or column, the porous media approach is usually used with lumped parameters for hydrodynamic calculations and heat transfer. While this approach can be reasonable for calculating integral flow quantities, it may not provide all the detailed information of the heat transfer and complex flow structure within the bed. The present experimental study presents the full velocity field using particle image velocity technique (PTV) in a conjunction with matched refractive index fluid with the pebbles to achieve optical access. Velocity field measurements are presented delineating the complex flow structure.

scholarly journals Exploiting High Geopositioning Accuracy of SAR Data to Obtain Accurate Geometric Orientation of Optical Satellite Images

2021 ◽  
Vol 13 (17) ◽  
pp. 3535
Author(s):  
Zhongli Fan ◽  
Li Zhang ◽  
Yuxuan Liu ◽  
Qingdong Wang ◽  
Sisi Zlatanova
Keyword(s):  
Satellite Imagery ◽  
Image Matching ◽  
Satellite Images ◽  
Three Dimensional ◽  
Phase Correlation ◽  
Feature Descriptor ◽  
Matching Method ◽  
Reference Images ◽  
Sar Data ◽  
Optical Satellite Images

Accurate geopositioning of optical satellite imagery is a fundamental step for many photogrammetric applications. Considering the imaging principle and data processing manner, SAR satellites can achieve high geopositioning accuracy. Therefore, SAR data can be a reliable source for providing control information in the orientation of optical satellite images. This paper proposes a practical solution for an accurate orientation of optical satellite images using SAR reference images to take advantage of the merits of SAR data. Firstly, we propose an accurate and robust multimodal image matching method to match the SAR and optical satellite images. This approach includes the development of a new structural-based multimodal applicable feature descriptor that employs angle-weighted oriented gradients (AWOGs) and the utilization of a three-dimensional phase correlation similarity measure. Secondly, we put forward a general optical satellite imagery orientation framework based on multiple SAR reference images, which uses the matches of the SAR and optical satellite images as virtual control points. A large number of experiments not only demonstrate the superiority of the proposed matching method compared to the state-of-the-art methods but also prove the effectiveness of the proposed orientation framework. In particular, the matching performance is improved by about 17% compared with the latest multimodal image matching method, namely, CFOG, and the geopositioning accuracy of optical satellite images is improved, from more than 200 to around 8 m.

Winter Flow Dynamics of an On-Stream Stormwater Management Pond

2000 ◽  
Vol 35 (3) ◽  
pp. 505-524 ◽  
Author(s):  
P.M. Marsalek ◽  
W.E. Watt ◽  
J. Marsalek ◽  
B.C. Anderson
Keyword(s):  
Velocity Field ◽  
Stormwater Management ◽  
Dead Zone ◽  
Flow Region ◽  
Ice Cover ◽  
Ice Thickness ◽  
Winter Period ◽  
The North ◽  
Winter Operation ◽  
Fast Flow

Abstract The winter operation of an on-stream Stormwater management pond, located in Kingston, Ontario, Canada, was studied with respect to ice cover formation and breakup, density stratification, velocity field under the ice cover, and the risk of sediment washout The pond freezes over in late November, with the ice thickness reaching up to 0.5 m. During the first half of the winter period, the ice thickness was well described by Stefan’s formula with empirical coefficients appropriate for shallow water bodies. The pond was chemically stratified, with total dissolved solids concentrations up to 1200 mg L-1 observed close to the bottom. The meromictic stability of this stratification was calculated as 882 g . cm.cm-2. Measurements of the velocity field under the ice cover indicated a flow pattern comprising a fast flow region, a small dead zone and a large recirculation zone to the north and south of the fast flow trajectory, respectively. Such a pattern agreed well with that simulated by a CFD model (PHOENICS_). During a snowmelt event, the near-bottom velocities reached up to 0.05 m . S-1, but were not sufficient to scour the bottom sediment.

scholarly journals Surge dynamics on Bering Glacier, Alaska, in 2008–2011

2012 ◽  
Vol 6 (6) ◽  
pp. 1251-1262 ◽  
Author(s):  
E. W. Burgess ◽  
R. R. Forster ◽  
C. F. Larsen ◽  
M. Braun
Keyword(s):  
Surface Velocity ◽  
Small Scale ◽  
Glacier System ◽  
Bering Glacier ◽  
Elevation Data ◽  
Fast Flow ◽  
Two Stages ◽  
The University ◽  
Accelerated Flow ◽  
Offset Tracking

Abstract. A surge cycle of the Bering Glacier system, Alaska, is examined using observations of surface velocity obtained using synthetic aperture radar (SAR) offset tracking, and elevation data obtained from the University of Alaska Fairbanks LiDAR altimetry program. After 13 yr of quiescence, the Bering Glacier system began to surge in May 2008 and had two stages of accelerated flow. During the first stage, flow accelerated progressively for at least 10 months and reached peak observed velocities of ~ 7 m d−1. The second stage likely began in 2010. By 2011 velocities exceeded 9 m d−1 or ~ 18 times quiescent velocities. Fast flow continued into July 2011. Surface morphology indicated slowing by fall 2011; however, it is not entirely clear if the surge is yet over. The quiescent phase was characterized by small-scale acceleration events that increased driving stresses up to 70%. When the surge initiated, synchronous acceleration occurred throughout much of the glacier length. Results suggest that downstream propagation of the surge is closely linked to the evolution of the driving stress during the surge, because driving stress appears to be tied to the amount of resistive stress provided by the bed. In contrast, upstream acceleration and upstream surge propagation is not dependent on driving stress evolution.

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