Kenneth C. Jezek

Automated extraction of coastline from satellite imagery by integrating Canny edge detection and locally adaptive thresholding methods

This paper presents a comprehensive approach to effectively and accurately extract coastlines from satellite imagery. It consists of a sequence of image processing algorithms, in which the key component is image segmentation based on a locally adaptive thresholding technique. Several technical innovations have been made to improve the accuracy and efficiency for determining the land/water boundaries. The use of the Levenberg-Marquardt method and the Canny edge detector speeds up the convergence of iterative Gaussian curve fitting process and improves the accuracy of the bimodal Gaussian parameters. The result is increased reliability of local thresholds for image segmentation. A series of further image processing steps are applied to the segmented images. Particularly, grouping and labelling contiguous image regions into individual image objects enables us to utilize heuristic human knowledge about the size and continuity of the land and ocean masses to discriminate the true coastline from other object boundaries. The final product of our processing chain is a vector-based line coverage of the coastline, which can be readily incorporated into a GIS database. Our method has been applied to both radar and optical satellite images, and the positional precision of the resulting coastline is measured at the pixel level.

Development of an Antarctic digital elevation model by integrating cartographic and remotely sensed data : A geographic information system based approach

We present a high-resolution digital elevation model (DEM) of the Antarctic. It was created in a geographic information system (GIS) environment by integrating the best available topographic data from a variety of sources. Extensive GIS-based error detection and correction operations ensured that our DEM is free of gross errors. The carefully designed interpolation algorithms for different types of source data and incorporation of surface morphologic information preserved and enhanced the fine surface structures present in the source data. The effective control of adverse edge effects and the use of the Hermite blending weight function in data merging minimized the discontinuities between different types of data, leading to a seamless and topographically consistent DEM throughout the Antarctic. This new DEM provides exceptional topographical details and represents a substantial improvement in horizontal resolution and vertical accuracy over the earlier, continental-scale renditions, particularly in mountainous and coastal regions. It has a horizontal resolution of 200 m over the rugged mountains, 400 m in the coastal regions, and approximately 5 km in the interior. The vertical accuracy of the DEM is estimated at about 100–130 m over the rugged mountainous area, better than 2 m for the ice shelves, better than 15 m for the interior ice sheet, and about 35 m for the steeper ice sheet perimeter. The Antarctic DEM can be obtained from the authors.

Jakobshavn Glacier, west Greenland: 30 years of spaceborne observations

Early 1960s reconnaissance satellite images are compared to more recent image and map data in an inter- annual and seasonal study of West Central Greenland margin fluctuations. From 1962 to 1992, ice sheet margins to the north and south of Jakobshavn Glacier retreated despite a decline in average summer temperatures. The retreat may be reversing along the southern flank of the ice stream where regional mass balance estimates are positive. From 1950 to fluctuated -2.5 km around its annual mean position. The total calving flux during the summer is more than six times that during winter. We identified that summer melting and the break-up of sea ice and icebergs in the fjord are important in controlling the rate of iceberg production. If correct, calving rates may be expected to increase should climate become warmer in the near future.

An improved coherent radar depth sounder

The University of Kansas developed a coherent radar depth sounder during the 1980s. This system was originally developed for glacial ice-thickness measurements in the Antarctic. During the field tests in the Antarctic and Greenland, we found the system performance to be less than optimum. The field tests in Greenland were performed in 1993, as a part of the NASA Program for Arctic Climate Assessment (PARCA). We redesigned and rebuilt this system to improve the performance. The radar uses pulse compression and coherent signal processing to obtain high sensitivity and fine along-track resolution. It operates at a center frequency of 150 MHz with a radio frequency bandwidth of about 17 MHz, which gives a range resolution of about 5 m in ice. We have been operating it from a NASA P-3 aircraft for collecting ice-thickness data in conjunction with laser surface-elevation measurements over the Greenland ice sheet during the last 4 years. We have demonstrated that this radar can measure the thickness of more than 3 km of cold ice and can obtain ice-thickness information over outlet glaciers and ice margins. In this paper we provide a brief survey of radar sounding of glacial ice, followed by a description of the system and subsystem design and performance. We also show sample results from the field experiments over the Greenland ice sheet and its outlet glacicrs.

Radar measurements of melt zones on the Greenland Ice Sheet

Surface-based microwave radar measurements were performed at a location on the western flank of the Greenland Ice Sheet. Here, firn metamorphosis is dominated by seasonal melt, which leads to marked contrasts in the vertical structure of winter and summer firn. This snow regime is also one of the brightest radar targets on Earth with an average backscatter coefficient of 0 dB at 5.3 GHz and an incidence angle of 25°. By combining detailed observations of firn physical properties with ranging radar measurements we find that the glaciological mechanism associated with this strong electromagnetic response is summer ice lens formation within the previous winters snow pack. This observation has important implications for monitoring and understanding changes in ice sheet volume using space-borne microwave sensors.

RADARSAT-1 Antarctic Mapping Project: change-detection and surface velocity campaign

Abstract The RADARSAT-1 Antarctic Mapping Project (RAMP) is a collaboration between NASA and the Canadian Space Agency to map Antarctica using synthetic aperture radar (SAR). The first Antarctic Mapping Mission (AMM-1) was successfully completed in October 1997. Data from the acquisition phase of the 1997 campaign have been used to achieve the primary goal of producing the first high-resolution SAR image map of Antarctica. The Modified Antarctic Mapping Mission (MAMM) occurred during the fall of 2000. The acquisition strategy concentrated on collecting highest- resolution RADARSAT-1 data of Antarctica’s fast glaciers for change detection and feature-retracking estimates of surface velocity. Additionally, extensive data were acquired for interferometric analysis over the entire viewable region, which extends north of 80.1˚ S latitude. This paper summarizes the goals and strategy behind MAMM. It goes on to discuss ice-sheet margin changes observed on several ice shelves around the continent. Margin changes are documented by comparing AMM-1 and MAMM data with earlier datasets including European Remote-sensing Satellite-1 SAR imagery, Landsat imagery, the Antarctic Digital Database (version 1) coastline and Declassified Intelligence Satellite Photography. Analysis reveals a complex pattern of ice-margin advance and retreat without indicating any systematic behavior in ice-sheet extent about the ice-sheet perimeter.

Field Studies of Bottom Crevasses in the Ross Ice Shelf, Antarctica

Analyse des crevasses observees par sondages radar aeriens et terrestres, localisation de leurs points de formation

A Complete High-Resolution Coastline of Antarctica Extracted from Orthorectified Radarsat SAR Imagery

A complete, high-resolution coastline of Antarctica, extracted from an orthorectified mosaic of Radarsat-1 synthetic aperture radar (SAR) images through a sequence of automated image processing algorithms, is presented. A locally adaptive thresholding method is used to segment the orthorectified SAR images, while image-object formation and labeling, and edgetracing techniques are used to process the segmented images into vector-based cartographic products of coastline, defined here as the boundary between continental ice or rock exposures and sea ice covered ocean. The absolute accuracy of planimetric positioning of the resultant coastline is estimated to better than 130 m, and its spatial resolution (25 m) is adequate for supporting cartographic and scientific applications at 1:50,000 scale. This radar-image-derived coastline gives an accurate description of geometric shape and glaciological characteristics of the Antarctic coasts and also provides a precise benchmark for future change-detection studies.

On the recent calving of icebergs from the Ross ice shelf

Abstract The year 2000 has witnessed the calving of several remarkably large icebergs in the Ross and Weddell seas of Antarctica, including the calving of B-l 5, possibly the largest iceberg yet to be observed. Here we present satellite imagery that records the calving, and precursor events leading up to the detachment of B-l 5 from the Ross Ice Shelf in late March 2000. These images suggest that the evolution of a network of large rifts on the ice shelf over the decade prior to calving has controlled both the time of calving and the giant size of B-15. What controls this evolution in turn remains a mystery.

Evolution of electromagnetic signatures of sea ice from initial formation to the establishment of thick first-year ice

The spatial and temporal distribution of new and young sea ice types are of particular interest because of the influence this can exert on the heat and mass balance of the polar sea ice. The objective of the present work is to characterize the temporal evolution of the electromagnetic (EM) signatures of sea ice from initial formation through the development of first-year (FY) ice on the basis of the temporal variations in the physical properties of the ice. The time series of young sea ice signatures, including microwave emissivity, radar backscatter, and visible and infrared spectral albedo, has been measured at successive stages in the growth and development of sea ice, both under laboratory and field conditions. These observations have been accompanied by studies of the physical properties that influence the interaction between radiation and the ice. This has resulted in a consistent data set of concurrent multispectral observations that covers essentially all phases of the development of the different types of sea ice from initial formation to thick FY ice. Mutually consistent theoretical models covering the entire wavelength range of the observations are applied to selected cases and successfully match the observations. Principal component analysis (PCA) of the data set suggests combinations of the set of frequencies to effectively distinguish among different stages in the temporal evolution of the sea ice.