RADARSAT-2 Imagery Research Articles

Deformation of the Arctic Ocean ice cover after the 2007 record minimum in summer ice extent

We examine the deformation of the Arctic Ocean sea ice cover after the record minimum in summer extent in 2007. The period spans ~ 2.5 months between September 15 and December 1. Ice drift and deformation inside the ice edge, within a domain that initially covers ~ 0.76 × 10 6 km 2 of the western Arctic, are derived from high-resolution RADARSAT imagery from the Alaska Satellite Facility. Poleward of 80°N, we find a net convergence of more than 14% over the period. This large convergence is associated with the strength, location, and persistence of the Beaufort high-pressure pattern that led to prevailing on-shore winds north of Ellesmere Island and Greenland. This can be contrasted to the nearly 25% divergence of the ice cover, accompanied by a large regional vorticity of − 0.93 (or a clockwise rotation of ~ 53°) south of 80°N. The same atmospheric pattern produced openings as the ice cover drifts southwest towards the unconstrained ice-free part of the southern Beaufort and Chukchi Seas. These sustained strain rates, especially convergence, impacts the area and thickness distribution of the sea ice cover in the Arctic Basin. If unaccounted for, this deformation-induced decrease in ice coverage (in this region with predominantly multiyear ice) could be incorrectly ascribed to ice export with a concurrent decrease in Arctic sea ice volume, when in fact the ice volume is conserved but with a local redistribution in thickness. ► Examined deformation of the Arctic sea ice cover after the record minimum in summer extent in 2007. ► Ice drift and deformation derived from high-resolution RADARSAT imagery. ► Poleward of 80°N, we find a net convergence of more than 14% over the period. ► South of 80°N, there is a 25% divergence, accompanied by a large regional vorticity of − 0.93 (or a clockwise rotation of ~ 53°). ► These sustained strain rates, impacts the area and thickness distribution of the sea ice cover in the Arctic Basin.

New Data Sources for Completing National Topographic Mapping of Northern Canada at 1:50,000

Complete topographic mapping coverage of Canada is essential as a basis for the sustainable development of its resources. In 2000, the unmapped areas at a scale of 1:50 000 in the Arctic islands in Nunavut and the Northwest Territories, amount to over 800 000 square kilometres, equivalent to approximately 1 500 map sheets. In 2003, a northern mapping project was launched to complete the topographic map coverage in Northern Canada. In order to explore all possible scenarios, the Centre for Topographic Information – Sherbrooke (CTIS) worked closely with the Canadian Space Agency and the private sector on various feasibility tests. After investigating multiple data sources, the combination of existing aerial photography, LANDSAT 7 ETM+, SPOT5/HRS imagery, interferometric pairs of ERS 1-2 tandem and RADARSAT-2 imagery were chosen for planimetric data and Canadian Digital Elevation Data (CDED) acquisition. In 2004, mapping contracts were carried out on a test site and positive results from these tests initiated the production of the unmapped areas of Canada. The planimetric vector data are available on the GeoGratis Web portal and the CDED data sets are available on the GeoBase Web portal.

Rice area mapping, yield, and production forecast for the province of Nueva Ecija using RADARSAT imagery

Monitoring rice production is an important tool for the Government of the Philippines’ objective to achieve rice sufficiency by 2013. For decision makers to ensure that the country has an adequate rice supply, it is imperative that timely and accurate information on rice area, yield forecasts, and production be regularly updated with little or no statistical response burden to producers; this study describes a process well suited for the integration and utilization of the methodologies for rice monitoring using radar data. Currently, the national and regional rice production in the Philippines is estimated through a complex and labor-intensive process using surveys of farmers and fields. Faster, reliable, and more efficient methods are needed to monitor production because rice production is affected by seasonal crop prices, climate, and daily weather.To accurately forecast rice production in near real time, remote sensing technology was used. A rice crop monitoring application using RADARSAT imagery was initially developed and tested in 2001. This application was modified and retested in the wet season of 2007 in Muñoz and Santo Domingo, Nueva Ecija, Philippines. This application demonstrated the capability to forecast rice production over an extended region. The program also offered flexibility in its ancillary data requirements, making it suitable for a practical and operational rice monitoring program.During the wet season of 2008, the rice area in the province of Nueva Ecija was mapped, and yield and production were forecast using the developed methodology. Data gathered from this project were compared with data obtained from the Philippines Bureau of Agricultural Statistics (BAS). The accuracy, at the provincial level, of the rice area and production estimates derived from remotely sensed data were 97.4% and 96.6%, respectively, when compared with the BAS statistical data.

Use of Radarsat-2 ultra-fine images in horticulture–intensive farming: land use detection and crop discrimination

Horticulture is the study of herbaceous plants destined for human consumption that can be consumed with or without industrial processes. Because of the growing pattern of horticulture crops, remote sensing is a useful tool to monitor their seasonal production. The use of all-weather synthetic aperture radar (SAR) images allows global monitoring of these crops. Radar high-resolution satellite imagery is preferred because it is less expensive and more convenient than airborne imagery. The new Radarsat-2 platform with an ultra-fine beam 3 m resolution mode offers new possibilities in land use detection and land cover crop discrimination for plots of one acre or less. This study reviews the use of Radarsat-2 images and compares ultra-fine beam and quad-polarized Radarsat-2 imagery to evaluate the effectiveness of the ultra-fine mode versus the quad-polarized mode for small-plot crop discrimination.

Development of a water clear of sea ice detection algorithm from enhanced SeaWinds/QuikSCAT and AMSR-E measurements

We develop and evaluate water clear of sea ice (open water following ice cover) detection algorithms that make use of Scatterometer Image Reconstruction (SIR) SeaWinds/QuikSCAT (QuikSCAT) backscatter (σ°) and Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) brightness temperature (T B) measurements. Algorithm validation was performed within Canadian Arctic waters using the Canadian Ice Service Digital Archive (CISDA) ice charts, NASATeam ice concentration estimates, extended AVHRR Polar Pathfinder (APP-x) albedo data, RADARSAT-1 imagery, and MODIS imagery. Results indicate that the temporal evolution of QuikSCAT σ°, AMSR-E polarization ratio (PR18), and AMSR-E vertical spectral gradient ratio (GR3618) can detect water clear of sea ice events, however mean differences due to frequency dependent characteristics of the data (spatial resolution; sensitivity to open water) were apparent. All water clear of sea ice algorithms are in good agreement with the timing and clearing patterns given by the CISDA. The QuikSCAT algorithm provided a more representative ice edge and more details on the ice clearing process due to higher spatial resolution, however, transient clearing events were better represented by the AMSR-E PR(18) or (GR3618) algorithm. By exploiting the strengths of each sensor, we found that a QuikSCAT and AMSR-E fused algorithm provide improved open water area estimates by as much as 11%. The fusion of QuikSCAT and AMSR-E PR(18) yielded in the most spatially representative open water detection. The residual surface of the water clear of sea ice algorithms was found to provide another measure of the average September minimum pan-Arctic sea ice extent within 6% of the NASATeam algorithm estimates.

Monitoring lake ice during spring melt using RADARSAT-2 SAR

Multipolarized RADARSAT-2 SAR imagery is used to monitor lake ice during the spring melt period. The study area is Old Crow Flats, Yukon, in the Canadian Arctic. HH and HV backscatter from lake ice is shown to have significant temporal variability and interlake diversity. Backscatter thresholds are statistically estimated to discriminate decaying lake ice from open water. A classification methodology is described that uses a HH backscatter threshold to identify initial break-up and a HV backscatter threshold for the main period of break-up. Classification accuracies are >81% ( = 0.189) prior to initial break-up and 66%–97% ( = 0.353–0.868) during break-up. This study demonstrates the potential of RADARSAT-2 imagery and, by extension, other C-band SAR satellites, to provide lake ice break-up information in support of monitoring and reporting requirements, subsequent decision-making, and scientific tasks for the Government of Canada.

Using multi-beam RADARSAT-1 imagery to augment mapping surficial geology in northwest Alberta, Canada

This paper evaluates the applicability of multi-beam RADARSAT-1 satellite imagery for mapping surficial sediments in northwest Alberta, Canada, using simple arithmetic algorithms. The goal is to make the RADARSAT-1 imagery acquired by the Alberta Geological Survey (AGS) usable to common users who have no access to complex image classification software and (or) expertise. Unlike the Canadian Shield, northern Alberta is mantled with much thicker glacial deposits that are covered by the Northern Boreal Forest. This limits the use of conventional image classification techniques, as there is not a one-to-one relationship between vegetation and the underlying surficial sediments. The RADARSAT-1 data utilized consists of RADARSAT-1 imagery acquired using Standard Beam 1 and 7 in both ascending and descending passes. Moisture and surface roughness information can be extracted by applying algorithms that calculate the differences between images acquired from different incidence angles and look directions (ascending versus descending looks). The image created using different incidence angles highlights flat surfaces, including wetlands, agricultural areas, and forest fire scars. The image generated using opposing look directions enhances geomorphologic features, including ice flow features, meltwater channels, till hummocks, and sand dune ridges. In addition, the enhanced RADARSAT-1 imagery (includes integration of topographic information provided by a digital elevation model (DEM)) provides an additional level of confidence to the air photo interpretation conducted in regions with little or no ground access and also provides a regional perspective on large-scale subtle surface morphological elements (e.g., ice flow patterns) that might be overlooked in individual aerial photographs.

Evidence of past fluctuations on Stancomb-Wills Ice Tongue, Antarctica, preserved by relict flow stripes

AbstractThis paper presents a newly derived velocity field of the Brunt Ice Shelf and Stancomb-Wills Ice Tongue in East Antarctica. Velocity is derived using automated feature-tracking techniques on RADARSAT-1 imagery from the 1997 Antarctic Mapping Mission-1 (AMM-1) and 2000 Modified Antarctic Mapping Mission (MAMM). We measure velocities up to 1350 m a−1 at the ice front. Closer investigation of the velocity field and radar images reveals an obvious divergence of contemporary flowlines from relict flow stripes along a portion of Stancomb-Wills Ice Tongue. Analysis of relict flow stripes can reveal glacial events in the past. Assuming relatively steady flow since the event occurred, we utilize the current velocity field to reconstruct former stripe configuration. We believe the flowline deviation points to a change in dynamics that occurred approximately 140 years ago, perhaps due to thinning and an associated shift in grounding-line position. This seems to be supported by historic observations and bottom topography data.

A semi-automated tool for surface water mapping with RADARSAT-1

Fresh water is arguably the most vital resource for all aspects of a healthy and stable environment and society. Monitoring the extent of surface water enables resource managers to detect perturbations and long-term trends in water availability and set consumption guidelines accordingly. Radar in general, and RADARSAT-1 in particular, is very good at detecting open surface water and has been used operationally for flood monitoring in many countries. Significant radar data archives now exist to analyse seasonal, annual, and decadal trends in surface water availability. A software tool (Forest non-Forest Class Extraction or FnFCE), based on software initially designed for deforestation classification with RADARSAT-1 data and later modified to include a flood mapping capability, has been adapted for this surface water application. Three test sites have been selected to demonstrate this surface water mapping tool, including Fort Mackay, Alberta, a tar sands area with water used for industrial purposes; Cache Lake in Tuktut Nogait National Park, Northwest Territories, where the many park lakes are currently poorly monitored and understood; and Old Crow Flats, Yukon Territory, a large area of ponds and lakes thought to be at risk from permafrost degradation and important to caribou migration and oil and gas development. This paper describes the software tool and demonstrates preliminary results of monitoring seasonal and annual changes in surface water distribution using RADARSAT-1 imagery for the three test sites. An overview of the successes and limitations of the approach is given, as well as a summary of the current state of evolution of the method and the envisioned software development plan.

Arctic epishelf lakes as sentinel ecosystems: Past, present and future

Ice shelves are a prominent but diminishing feature of the northern coastline of Ellesmere Island in the Canadian High Arctic (latitude 82–83°N). By blocking embayments and fiords, this thick coastal ice can create epishelf lakes, which are characterized by a perennially ice‐capped water column of freshwater overlying seawater. The goal of this study was to synthesize new, archived, and published data on Arctic epishelf lakes in the context of climate change. Long‐term changes along this coastline were evaluated using historical reports, cartographic analysis, RADARSAT imagery, and field measurements. These data, including salinity‐temperature profiling records from Disraeli Fiord spanning 54 years, show the rapid decline and near disappearance of this lake type in the Arctic. Salinity‐temperature profiling of Milne Fiord, currently blocked by the Milne Ice Shelf, confirmed that it contained an epishelf lake composed of a 16‐m thick freshwater layer overlying seawater. A profiling survey along the coast showed that there was a continuum of ice‐dammed lakes from shallow systems dammed by multiyear landfast sea ice to deep epishelf lakes behind ice shelves. The climate warming recently observed in this region likely contributed to the decline of epishelf lakes over the last century, and the air temperature trend predicted for the Arctic over the next several decades implies the imminent loss of this ecosystem type. Our results underscore the distinctive properties of coastal ice‐dammed lakes and their value as sentinel ecosystems for the monitoring of regional and global climate change.

Radar imaging of winter seismic survey activity in the National Petroleum Reserve-Alaska

ABSTRACTDuring the spring of 2006, Radarsat-1 synthetic aperture radar (SAR) imagery was acquired on a continual basis for the Teshekpuk Lake Special Area (TLSA), in the northeast portion of the National Petroleum Reserve, Alaska (NPR-A) in order to monitor lake ice melting processes. During data processing, it was discovered that the Radarsat-1 imagery detected features associated with winter seismic survey activity. Focused analysis of the image time series revealed various aspects of the exploration process such as the grid profile associated with the seismic line surveys as well as trails and campsites associated with the mobile survey crews. Due to the high temporal resolution of the dataset it was possible to track the progress of activities over a one month period. Spaceborne SAR imagery can provide information on the location of winter seismic activity and could be used as a monitoring tool for land and resource managers as increased petroleum-based activity occurs in the TLSA and NPR-A.

Monitoring the 2004 Flood in the Meghna River Basin in Bangladesh Using Ground Data, RADARSAT Imagery and GIS

Monitoring the 2004 Flood in the Meghna River Basin in Bangladesh Using Ground Data, RADARSAT Imagery and GIS

The evolution of surface flow stripes and stratigraphic folds within Kamb Ice Stream: why don’t they match?

AbstractFlow stripes seen in satellite imagery of ice streams and ice shelves are caused by surface undulations with kilometer-scale spacing and meter-scale relief and generally indicate current or recent fast ice flow. On a similar scale, folding of internal ice stratigraphy depicted in cross-flow ice-penetrating radar profiles is also a common occurrence in ice streams, suggesting a possible relationship between the two sets of features. We have traced surface flow stripes in RADARSAT and MODIS imagery on Kamb Ice Stream, West Antarctica, from the onset of streaming flow into the near-stagnant trunk. We compare the morphology and evolution of the surface flow stripes to the folds seen in the internal stratigraphy in cross-ice-stream radar profiles. We find essentially no correspondence in the observed locations or spacings between the radar internal layer folds at depths greater than 100 m and the flow stripes on the surface. The gap in the radar data and the surface mappings in the top 100 m of firn prevents a precise depiction of how the flow stripes and fold patterns at depth diverge. We explore hypotheses about how flow stripes and internal stratigraphic folds can originate and evolve differently as ice flows downstream. We suggest that flow stripes are subject to surface processes that can modify their morphology independently of the internal stratigraphy, leading to changes in the pattern of flow stripes relative to the internal layers below.

Validation of RADARSAT-1 vessel signatures with AISLive data

Automatic identification system (AIS) data have the potential to contribute significantly to the development of automated algorithms for ship signature identification in remotely sensed imagery. Datasets composed of RADARSAT-1 imagery collected over a 3-month period and the corresponding AIS data from AISLive were compiled. SAR-derived ship length and radar cross section features were validated against AIS data, thus demonstrating the utility of AIS as a source of ground truth.

Assessment of the AMSR-E Sea Ice-Concentration Product at the Ice Edge Using RADARSAT-1 and MODIS Imagery

Imagery from the C-band synthetic aperture radar (SAR) aboard RADARSAT-1 and the Moderate Resolution Imaging Spectroradiometer (MODIS) was used to evaluate the performance of the Advanced Microwave Scanning Radiometer-EOS (AMSR-E) ice-concentration product near the sea ice edge in the Bering Sea for four days during March 2003, which is concurrent with the AMSRIce03 field/aircraft campaign. The AMSR-E products were observed to perform very well in identifying open-water and pack-ice areas, although the AMSR-E products occasionally underestimate ice concentration in areas with thin ice. The position of the ice edge determined from AMSR-E data using a 15% concentration threshold was found to be, on average, within one AMSR-E grid square (12.5 km) of the ice edge determined from the SAR data, with the AMSR-E edge tending to be outside the SAR-derived edge

ICESat over Arctic sea ice: Interpretation of altimetric and reflectivity profiles

We provide an assessment of the ICESat altimeter for studying the Arctic Ocean and examine the magnitude of the large‐ and small‐scale expressions of geophysical processes embedded in the elevation profiles. This analysis includes data from six surveys. At the large scale the response of the ice‐covered ocean to atmospheric loading is near ideal (i.e., approximately −1 cm/hPa). After removal of the inverted barometer effects and best available geoid the elevation signal is still dominated by unresolved geoid residuals (∼0.4 m) that can be seen in the similarity of the remaining spatial patterns. Seasonal differences in elevations over multiyear ice are consistent with snow depth climatology; the broad differential spatial patterns are indicative of interannual differences in multiyear ice coverage associated with advection. Patterns in the derived surface roughness fields correspond to the seasonal and perennial ice zones seen in QuikSCAT data. At the small scale, near‐coincident RADARSAT imagery provides a spatial context for understanding the signature of the observed elevations, waveforms, and reflectivity, in particular, those associated with thin ice, open water, multiyear ice, and ridges. The precision of the elevation estimates measured over relatively flat sea ice, identified in synthetic aperture radar (SAR) imagery, is ∼2 cm. The unambiguous identification of ridged areas in coupled ICESat/RADARSAT analysis could be used to enhance the utility of SAR imagery for examining ridge distributions. Over a 20 day period we monitored the evolution of the reflectivity of a newly opened lead. The steep increase in reflectivity due to snow coverage suggests that dips in ICESat reflectivity are likely areas of thin ice and could serve as a basis for selection of tie points for use as sea level reference. Identification of these tie points is crucial for accurate estimation of sea ice freeboard.

A case Study of old-ice import and export through Peary and Sverdrup Channels in the Canadian Arctic Archipelago: 1998–2005

AbstractThis case Study attempts to quantify the amount and timing of the import, export and through-flow of old ice in the Peary Channel–sverdrup Channel area of the northern Canadian Arctic Archipelago during the period 1998–2005. The Study combines quantitative weekly area-averaged ice coverage evaluations from the Canadian Ice Service (CIS) Digital Archive with detailed analysis of Radarsat imagery and ice-motion results from the CIS ice-motion algorithm. The results Show that in 1998 more than 70% of the old ice in Peary–sverdrup was lost, half by melt and export to the South and the other half by export north into the Arctic Ocean, and that no Arctic Ocean old ice was imported into Peary–sverdrup. A net import of 10% old ice was Seen in 1999, with Some indication of through-flow into Southern channels. In 2000, no net import of old ice occurred in Peary–sverdrup, but there was Significant through-flow, with evidence of old ice reaching the Northwest Passage by November. Full recovery of the old-ice regime was complete by the end of 2001. More than two-thirds of the recovery was due to the in Situ formation of Second-year ice. Conditions in the following 3 years were near normal.

Ross Sea Ice Motion, Area Flux, and Deformation

Abstract The sea ice motion, area export, and deformation of the Ross Sea ice cover are examined with satellite passive microwave and RADARSAT observations. The record of high-resolution synthetic aperture radar (SAR) data, from 1998 and 2000, allows the estimation of the variability of ice deformation at the small scale (∼10 km) and to assess the quality of the longer record of passive microwave ice motion. Daily and subdaily deformation fields and RADARSAT imagery highlight the variability of motion and deformation in the Ross Sea. With the passive microwave ice motion, the area export at a flux gate positioned between Cape Adare and Land Bay is estimated. Between 1992 and 2003, a positive trend can be seen in the winter (March–November) ice area flux that has a mean of 990 × 103 km2 and ranges from a low of 600 × 103 km2 in 1992 to a peak of 1600 × 103 km2 in 2001. In the mean, the southern Ross Sea produces almost twice its own area of sea ice during the winter. Cross-gate sea level pressure (SLP) gradients explain ∼60% of the variance in the ice area flux. A positive trend in this gradient, from reanalysis products, suggests a “spinup” of the Ross Sea Gyre over the past 12 yr. In both the NCEP–NCAR and ERA-40 surface pressure fields, longer-term trends in this gradient and mean SLP between 1979 and 2002 are explored along with positive anomalies in the monthly cross-gate SLP gradient associated with the positive phase of the Southern Hemisphere annular mode and the extrapolar Southern Oscillation.

Assessing the accuracy of satellite derived global and national urban maps in Kenya

Ninety percent of projected global urbanization will be concentrated in low income countries. This will have considerable environmental, economic and public health implications for those populations. Objective and efficient methods of delineating urban extent are a cross-sectoral need complicated by a diversity of urban definition rubrics world-wide. Large-area maps of urban extents are becoming increasingly available in the public domain, as are a wide-range of medium spatial resolution satellite imagery. Here we describe the extension of a methodology based on Landsat ETM and Radarsat imagery to the production of a human settlement map of Kenya. This map was then compared with five satellite imagery-derived, global maps of urban extent at Kenya national-level, against an expert opinion coverage for accuracy assessment. The results showed the map produced using medium spatial resolution satellite imagery was of comparable accuracy to the expert opinion coverage. The five global urban maps exhibited a range of inaccuracies, emphasising that care should be taken with use of these maps at national and sub-national scale.

Monitoring the 1997 flood in the Red River Valley using hydrologic regimes and RADARSAT imagery

In this study, we attempt to relate hydrologic regimes of the 1997 flood in the Red River Valley to the areal extent of flooding, determined from RADARSAT imagery. We obtained ten scenes of RADARSAT imagery, from 27 April to 1 July, including bitmaps delineating flooded areas for each date, from the Manitoba Centre of Remote Sensing. These images were co‐registered using an image‐to‐image registration process. By overlaying these flood maps in chronological order, we compared the areal extent of flooding with the hydrologic regimes of the Red River, expressed as relative depths of flooding above the bankful stage at selected gauging stations. The results of the study indicated that the area of flooding on 4 May (1,984 km 2 ) corresponded well with the highest flood levels at several gauging stations. A previous scene on 27 April showed a larger area under water, but visual inspection of the processed imagery indicated a lack of conformity between flood level regimes and the areal extent of flooding on this date due to surface detention of pre‐flood storm runoff. Thus, the RADARSAT imagery represented the flood regimes adequately only when its interpretations were combined with hydrologic analysis and visual inspection of surface characteristics of the floodplain.