Repeat-pass, interferometric, radar observations of tropical rain-forest collected by the Shuttle Imaging Radar C (SIR-C) in the state of Rondonia, Brazil, reveal signal coherence is destroyed at C-band (5.6-cm) in the forest, whereas L-band (24-cm) radar signals remain strongly coherent over the entire landscape. At L-band, the rms difference in inferred topographic height between the forest and adjacent clearings is 5 m, equivalent to the height noise. Atmospheric delays are large, however, forming kilometer-sized anomalies with a 1.2-cm rms one way. Radar interferometric studies of the humid tropics must therefore be conducted at long radar wavelengths, with kilometric baselines or with two antennas operating simultaneously.

Ice discharge from north and northeast Greenland glaciers was calculated at the grounding line using ERS radar interferometry data acquired during the tandem phase. The resulting estimates exceed the production of icebergs at the glacier fronts by a factor 3.5. This large decrease in ice flux is attributed to extensive melting at the underside of the floating sections. When compared to the predicted grounding line ice discharge of an ice sheet in balance, the results show an excess 28 km3/yr of ice lost to the ocean. The north and northeast sectors of the Greenland Ice Sheet are therefore thinning and contributing positively to sea-level rise.

A statistical image model is proposed for segmenting polarimetric synthetic aperture radar (SAR) data into regions of homogeneous and similar polarimetric backscatter characteristics. A model for the conditional distribution of the polarimetric complex data is combined with a Markov random field representation for the distribution of the region labels to obtain the posterior distribution. Optimal region labeling of the data is then defined as maximizing the posterior distribution of the region labels given the polarimetric SAR complex data (maximum a posteriori (MAP) estimate). Two procedures for selecting the characteristics of the regions are then discussed. Results using real multilook polarimetric SAR complex data are given to illustrate the potential of the two selection procedures and evaluate the performance of the MAP segmentation technique. It is also shown that dual polarization SAR data can yield segmentation resultS similar to those obtained with fully polarimetric SAR data.

We present the first comprehensive high-resolution mosaic of ice velocity of the Northern (NPI) and Southern Patagonian Icefields (SPI), from multiple synthetic aperture radar and optical data collected between 1984 and 2014. The results reveal that many of the outlet glaciers extend far into the central ice plateaus, which implies that changes in ice dynamics propagate far inside the accumulation area. We report pronounced seasonal to interannual variability of ice motion on Pío XI and Jorge Montt, a doubling in speed of Jorge Montt, a major slow down of O'Higgins, significant fluctuations of Upsala and a deceleration of San Rafael, which illustrate the need for sustained, continuous time series of ice motion to understand the long-term evolution of the rapidly thinning icefields. The velocity product also resolves major ambiguities in glacier drainage in areas of relatively flat topography illustrating the need to combine topography and flow direction to map drainage basins.

ERS images of the two ends of the ice front of the Filchner-Ronne Ice Shelf, Antarctica, were utilized interferometrically to study the deformation rate of the ice shelf in response to viscous creep. On the western flank of Berkner Island (BI), near Hemmen Ice Rise (HIR), a time series of ERS data acquired in Feb 1992, in both ascending and descending mode, and with a 3-day time interval, were utilized to map the ice velocity in two dimensions. Finite-element ice-shelf flow simulations are compared with the ERS interferograms to interpret the ice motion in terms of the physical constraints on ice-shelf flow. Our efforts to fit artificial interferograms generated with model velocity output suggest that the flow regime is strongly influenced by three processes. First, a void-creation process responsible for rifts at coastal margins tends to uncouple the ice shelf from the ice rise and neighboring coast of BI. Second, sea ice within the void space appears to act as a binding agent between discrete ice-shelf fragments, allowing rigid-body rotations of these fragments. Third, strain rates appear to be enhanced in a narrow zone adjacent to HIR, implying significant strain softening along the boundary. We believe that SAR interferogram/model intercomparison represents a powerful impetus toward the development of better, more physically realistic ice-shelf flow models.

A digital representation of ice surface velocity is essential for a variety of glaciological, geologic and geophysical analyses and modeling. Here, we present a new, reference, comprehensive, high-resolution, digital mosaic of ice motion in Greenland assembled from satellite radar interferometry data acquired during the International Polar Year 2008 to 2009 by the Envisat Advanced Synthetic-Aperture Radar (ASAR), the Advanced Land Observation System (ALOS)'s Phase-Array L-band SAR (PALSAR) and the RADARSAT-1 SAR that covers 99% of the ice sheet in area. The best mapping performance is obtained using ALOS PALSAR data due to higher levels of temporal coherence at the L-band frequency; but C-band frequency SAR data are less affected by the ionosphere. The ice motion map reveals various flow regimes, ranging from patterned enhanced flow into a few large glaciers in the cold, low precipitation areas of north Greenland; to diffuse, enhanced flow into numerous, narrow, fast-moving glaciers in the warmer, high precipitation sectors of northwest and southeast Greenland. We find that the 100 fastest glaciers (v > 800m/yr) drain 66% of the ice sheet in area, marine-terminating glaciers drain 88% of Greenland, and basal-sliding motion dominates internal deformation over more than 50% of the ice sheet. This view of ice sheet motion provides significant new constraints on ice flow modeling. Copyright 2012 by the American Geophysical Union.

A method for the analysis of spatial statistics in multifrequency polarimetric Synthetic Aperture Radar (SAR) data is presented. The objective is to extract the intrinsic variability of the target by removing the variability from other sources. Three sources which contribute to the spatial variability in the returned power from a distributed target are modelled, they are (1) image speckle, (2) system noise, and (3) the intrinsic spatial variability of the target or texture. Speckle and system noise are modelled based on an understanding of the physics of the SAR imaging and processing systems. Texture is modelled as a random variable which modulates the mean returned power from a distributed target. An image model which accounts for all three sources of variability is presented. The presence of texture is shown to increase the image variance-to-mean square ratio and to introduce deviations of the image a u toco variance function from the expected SAR system response. Two textural parameters, the standard deviation of texture and its autocovariance coefficient, are examined. This statistical approach is illustrated using sea-ice SAR imagery acquired by the Jet Propulsion Laboratory three-frequency polarimetric airborne SAR. Textural modulation of the signal has been detected in the imagery. Results show that for different sea-ice types the spatial statistics seem to vary more across frequency than across polarization and the observed differences increase in magnitude with decreasing frequency. The results also suggest the potential of this approach for discrimination of various sea-ice types and open water in single frequency, single polarization SAR data. Correlation of the spatial statistics to field measurements will be important for the verification of these observations. © 1993 Taylor & Francis Group, LLC.

The floating ice shelf in front of Petermann Glacier, in northwest Greenland, experiences massive bottom melting that removes 80% of its ice before calving into the Arctic Ocean. Detailed surveys of the ice shelf reveal the presence of 1-2 km wide, 200-400 in deep, sub-ice shelf channels, aligned with the flow direction and spaced by 5 km. We attribute their formation to the bottom melting of ice from warm ocean waters underneath. Drilling at the center of one of channel, only 8 m above sea level, confirms the presence of ice-shelf melt water in the channel. These deep incisions in ice-shelf thickness imply a vulnerability to mechanical break up and climate warming of ice shelves that has not been considered previously. Copyright 2008 by the American Geophysical Union.

We present a maximum a posteriori (MAP) classifier for classifying multifrequency, multilook, single polariza­tion, synthetic aperture radar (SAR) intensity data into regions or ensembles of pixels of homogeneous and similar radar backscatter characteristics. A model for the prior joint distribution of the multifrequency SAR intensity data is combined with a Markov random field for representing the interactions between region labels to obtain an expression for the posterior distribution of the region labels given the multifrequency SAR observa­tions. The maximization of the posterior distribution yields Bayes’s optimum region labeling or classification of the SAR data or its MAP estimate. The performance of the MAP classifier is evaluated by using computer- simulated multilook SAR intensity data as a function of the parameters in the classification process. Multilook SAR intensity data are shown to yield higher classification accuracies than one-look SAR complex amplitude data. Examples using actual two-frequency, four-look, SAR intensity data acquired by the NASA/Jet Propul­sion Laboratory airborne polarimetric SAR are presented. The MAP classifier is extended to the case in which the radar backscatter from the remotely sensed surface varies within the SAR image because of incidence angle effects. The results obtained illustrate the practicality of the method for combining SAR intensity observations acquired at two different frequencies and for improving classification accuracy of SAR data. © 1993 Optical Society of America.

The disintegration of several Antarctic Peninsula ice shelves has focused attention on the state of the Larsen C Ice Shelf. Here, we use satellite observations to map ice shelf speed from the years 2000, 2006 and 2008 and apply inverse modeling to examine the spatial pattern of ice-shelf stiffness. Results show that the northern half of the ice shelf has been accelerating since 2000, speeding up by 15% between 2000 and 2006 alone. The distribution of ice stiffness exhibits large spatial variations that we link to tributary glacier flow and fractures. Our results reveal that ice down-flow from promontories is consistently softer, with the exception of Churchill Peninsula where we infer a stabilizing role for marine ice. We conclude that although Larsen C is not facing imminent collapse, it is undergoing significant change in the form of flow acceleration that is spatially related to thinning and fracture. Copyright © 2011 by the American Geophysical Union.