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Sensitivity of glacier elevation analysis and numerical modeling to CryoSat-2 SIRAL retracking techniques (2021)

Trantow, Thomas ; Herzfeld, Ute C. ; Helm, Veit ; [et al.]

In: EPIC3Computers & Geosciences, 146, pp. 104610

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Publication Date: 2020-11-16

Description: The CryoSat-2 radar altimetry mission, launched in 2010, provides key measurements of Earth's cryosphere. CryoSat-2's primary instrument, the Synthetic Aperture Interferometric Radar Altimeter (SIRAL), allows accurate height measurements of sloped ice-surfaces including the highly crevassed Bering-Bagley Glacier System (BBGS) in southeast Alaska. The recent surge of the BBGS in 2011–2013, which resulted in large-scale elevation changes and wide-spread crevassing, presents an interesting challenge to the processing of the SIRAL measurements. Derivation of surface height is achieved by retracking the received waveform of the altimeter signal. Several such retracking methods have been developed. In this paper, we investigate the influence of six unique SIRAL retracking methods on (1) Digital Elevation Model (DEM) generation, (2) analysis of ice-surface topography, and (3) numerical modeling results of the BBGS during surge. First, we derive a surface DEM for each retracked dataset using kriging. The swath-processed dataset provides 100–250 times more points than the other datasets, which decreases DEM uncertainty associated with data coverage by a factor of 2–4. Differences between the six resulting DEMs imply that retracking methods can have significant effects on elevation and elevation-change analysis, but we find that lower-level processing has larger effects. Next, the sensitivity of the data-model connection is evaluated using a finite element model of the BBGS surge. We set up six modeling experiments, each initiated with a unique input surface DEM derived from the various retracking methods. While retracking choices effect estimation of unknown model parameters related to crevasse simulation, we have developed a procedure to limit these effects resulting in remarkably consistent parameter optimization across modeling experiments. Each model experiment yields an optimal friction coefficient in the sliding law of 10^-5 MPa*a/m, while estimates of the optimal von Mises stress threshold for crevasse initiation ranged between 230 and 240 kPa.

Repository Name: EPIC Alfred Wegener Institut

Type: Article , isiRev

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Monitoring Changes of Ice Streams Using Time Series of Satellite-Altimetry-Based Digital Terrain Models (1997)

Herzfeld, Ute C. ; Lingle, Craig S. ; Freeman, Cecily ; [et al.]

Springer

Mathematical geology 29 (1997), S. 859-890

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ISSN: 1573-8868

Keywords: Lambert Glacier/Amery Ice Shelf ; geostatistical evaluation ; Seasat ; Geosat ; grounding line ; elevation changes

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Mathematics

Notes: Abstract The Antarctic Ice Sheet plays a major role in the global system, and the large ice streams discharging into the circumpolar sea represent its gateways to the world's oceans. Satellite radar altimeter data provide an opportunity for mapping surface elevation at kilometer-resolution with meter-accuracy. Geostatistical methods have been developed for the analysis of these data. Applications to Seasat data and data from the Geosat Exact Repeat Mission indicate that the grounding line of Lambert Glacier/Amery Ice Shelf, the largest ice stream in East Antarctica, has advanced 10–12 km between 1978 and 1987–89. The objectives of this paper are to explore possibilities and limitations of satellite-altimetry-based mapping to capture changes for shorter time windows and for smaller areas, and to investigate some methodological aspects of the data analysis. We establish that one season of radar altimeter data is sufficient for constructing a map. This allows study of interannual variation and is the key for a time-series analysis approach to study changes in ice streams. Maps of the lower Lambert Glacier and the entire Amery Ice Shelf are presented for austral winters 1978, 1987, 1988, and 1989. As a first step toward understanding the dynamics of the ice-stream/ice-shelf system, elevation changes are calculated for grounded ice, the grounding zone, and floating ice. In the absence of (sufficient) surface gravity control for the Lambert Glacier/Amery Ice Shelf area, altimetry-based maps may facilitate improvement of geoid models as they provide constraints on the terrain correction in the inverse gravimetric problem.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1022381322872

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An Integrated Mapping Approach to Petroleum Exploration on the Pratt Anticline, Pratt County, Kansas (1999)

Merriam, Daniel F. ; Herzfeld, Ute C. ; Fuhr, Beth A.

Springer

Natural resources research 8 (1999), S. 69-86

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ISSN: 1573-8981

Keywords: Algebraic map comparison technique ; coincidence of similarity ; favorability maps ; geologic properties ; Midcontinent (USA)

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract A quantitative map comparison/integration technique to aid in petroleum exploration was applied to an area in south-central Kansas. The visual comparison and integration of maps has become increasingly difficult with the large number and different types of maps necessary to interpret the geology and assess the petroleum potential of an area; therefore, it is desirable to quantify these relationships. The algebraic algorithm used in this application is based on a point-by-point comparison of any number and type of spatial data represented in map form. Ten geological and geophysical maps were compared and integrated, utilizing data from 900 wells located in a nine-township area on the Pratt Anticline in Pratt County, Kansas. Five structure maps, including top of the Lansing Group (Pennsylvanian), Mississippian chert, Mississippian limestone, Viola Limestone (Ordovician), and Arbuckle Group (Cambro-Ordovician), two isopachous maps from top of Mississippian chert to Viola and Lansing to Arbuckle, a Mississippian chert porosity map, Bouguer gravity map, and an aeromagnetic map were processed and interpreted. Before processing, each map was standardized and assigned a relative degree of importance, depending on knowledge of the geology of the area. Once a combination of weights was obtained that most closely resembled the pattern of proved oil fields (target map), a favorability map was constructed based on a coincidence of similarity values and of geological properties of petroleum reservoirs. The resulting favorability maps for the study area indicate location of likely Mississippian chert and lower Paleozoic production.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1021685712467

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On the influence of kriging parameters on the cartographic output—A study in mapping subglacial topography (1993)

Herzfeld, Ute C. ; Eriksson, Mats G. ; Holmlund, Per

Springer

Mathematical geology 25 (1993), S. 881-900

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ISSN: 1573-8868

Keywords: universal kriging ; neighborhood search ; mapping ; subglacial topography ; ice thickness

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Mathematics

Notes: Abstract Geostatistics provides a suite of methods, summarized as kriging, to analyze a finite data set to describe a continuous property of the Earth. Kriging methods consist of moving window optimum estimation techniques, which are based on a least-squares principle and use a spatial structure function, usually the variogram. Applications of kriging techniques have become increasingly wide-spread, with ordinary kriging and universal kriging being the most popular ones. The dependence of the final map or model on the input, however, is not generally understood. Herein we demonstrate how changes in the kriging parameters and the neighborhood search affect the cartographic result. Principles are illustrated through a glaciological study. The objective is to map ice thickness and subglacial topography of Storglaciären, Kebnekaise Massif, northern Sweden, from several sets of radio-echo soundings and hot water drillings. New maps are presented.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00891049

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Optimization techniques for integrating spatial data (1995)

Herzfeld, Ute C. ; Merriam, Daniel F.

Springer

Mathematical geology 27 (1995), S. 559-588

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ISSN: 1573-8868

Keywords: map comparison ; Nelder-Mead downhill simplex method in multidimensions ; constrained estimation ; Kuhn-Tucker theory ; petroleum exploration

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Mathematics

Notes: Abstract Two optimization techniques ta predict a spatial variable from any number of related spatial variables are presented. The applicability of the two different methods for petroleum-resource assessment is tested in a mature oil province of the Midcontinent (USA). The information on petroleum productivity, usually not directly accessible, is related indirectly to geological, geophysical, petrographical, and other observable data. This paper presents two approaches based on construction of a multivariate spatial model from the available data to determine a relationship for prediction. In the first approach, the variables are combined into a spatial model by an algebraic map-comparison/integration technique. Optimal weights for the map comparison function are determined by the Nelder-Mead downhill simplex algorithm in multidimensions. Geologic knowledge is necessary to provide a first guess of weights to start the automatization, because the solution is not unique. In the second approach, active set optimization for linear prediction of the target under positivity constraints is applied. Here, the procedure seems to select one variable from each data type (structure, isopachous, and petrophysical) eliminating data redundancy. Automating the determination of optimum combinations of different variables by applying optimization techniques is a valuable extension of the algebraic map-comparison/integration approach to analyzing spatial data. Because of the capability of handling multivariate data sets and partial retention of geographical information, the approaches can be useful in mineral-resource exploration.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02093901

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Is the ocean floor a fractal? (1995)

Herzfeld, Ute C. ; Kim, Isaac I. ; Orcutt, John A.

Springer

Mathematical geology 27 (1995), S. 421-462

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ISSN: 1573-8868

Keywords: self-similarity ; self-affinity ; variogram-criterion ; inheritance of scaling properties ; geostatistics ; bathymetric data

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Mathematics

Notes: Abstract The topographic structure of the ocean bottom is investigated at different scales of resolution to answer the question: Can the seafloor be described as a fractal process? Methods from geostatistics, the theory of regionalized variables, are used to analyze the spatial structure of the ocean floor at different scales of resolution. The key to the analysis is the variogram criterion: Self-similarity of a stochastic process implies self-similarity of its variogram. The criterion is derived and proved here: it also is valid for special cases of self-affinity (in a sense adequate for topography). It has been proposed that seafloor topography can be simulated as a fractal (an object of Hausdorff dimension strictly larger than its topological dimension), having scaling properties (self-similarity or self-affinity). The objective of this study is to compare the implications of these concepts with observations of the seafloor. The analyses are based on SEABEAM bathymetric data from the East Pacific Rise at 13°N/104°W and at 9°N/104°W and use tracks that run both across the ridge crest and along the ridge flank. In the geostatistical evaluation, the data are considered as a stochastic process. The spatial continuity of this process is described by variograms that are calculated for different scales and directions. Applications of the variogram criterion to scale-dependent variogram models yields the following results: Although the seafloor may be a fractal in the sense of the definition involving the Hausdorff dimension, it is not self-similar, nor self-affine (in the given sense). Mathematical models of scale-dependent spatial structures are presented, and their relationship to geologic processes such as ridge evolution, crust formation, and sedimentation is discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02084611

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