Correlation between Synthetic Aperture Radar Surface Winds and Deep Water Velocity in the Amundsen Sea, Antarctica (original) (raw)
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Spaceborne synthetic aperture radar observations of ocean waves traveling into sea ice
Journal of Geophysical Research, 2002
1] Damping of ocean waves by sea ice is studied using spaceborne synthetic aperture radar (SAR) images of the marginal ice zone (MIZ) acquired by the European Remote sensing satellite ERS-2. SAR imaging of waves damped by sea ice is analyzed theoretically. The impact of sea ice on the azimuthal cutoff is studied by simulation of the azimuthal SAR image autocorrelation function as well as the two-dimensional SAR image spectrum. Typical imaging artifacts like spiky wave crests and wave refraction seen on SAR scenes of the MIZ are reproduced by simulation. Sensitivity studies are performed using models for wind sea and swell systems. It is shown that the degradation of the azimuthal SAR image resolution is dominated by the orbital velocity variance of the waves, while the coherence time of the complex radar reflectivity has a minor impact. A first-order analysis of wave damping observed on SAR scenes is carried out using a technique that was originally developed for wind estimation by . The method does not require a priori information and is insensitive to real aperture modulation. The azimuthal SAR image cutoff wavelength is estimated and related to the orbital velocity variance of the sea surface by regression. The model is fitted on the basis of a global set of model ocean wave spectra. The technique is applied within the sea ice and in the open water in front of the ice boundary. On the basis of simple models for wind sea and swell, ocean wave attenuation rates are obtained from the observed orbital velocity decrease of waves entering the ice. The required wind information is derived from calibrated SAR data using the CMOD method. Two case studies showing examples from the Greenland and the Weddell Seas are given. It is shown that the estimated wave damping is consistent with damping parameters found in earlier field campaigns carried out in the Weddell Sea and the Bering Sea. An inversion technique providing estimates for the two-dimensional wave spectra behind and in front of the ice boundary as well as a two-dimensional filter function characterizing the sea ice impact is introduced. The technique is based on simultaneous inversion of the two-dimensional image spectra in the open water and within the ice using a priori information from an ocean wave model. It is shown that the technique gives results consistent with the first-order analysis based on the cutoff estimation.
2013
Ice shelves, which are mainly found in Antarctica consist of floating extensions of ice sheets.They provide an interface for the interactions between the ice sheet and the ocean. Althoughthey present their own flow dynamics, ice shelves remain attached to the grounded ice, thusregulate ice discharge of the ice sheet into the ocean. The control ice shelves exert on inlandice is called the Buttressing effect. A mass loss of ice shelves induces a loss of buttressing,which enables a greater discharge of ice into the ocean and contributes to the sea level rise.In a warming world, studying ice shelves and their dynamics become essential if we wantto quantify the Antarctic contribution to the future sea level rise.This thesis is a satellite-based SAR interferometry study of the ice shelves in the regionof Dronning Maud Land, Antarctica. SAR interferometry (InSAR) is an imaging techniquethat compares phase information from images taken at different times to measure surfacedisplacements betw...
Synthetic Aperture Radar Imaging of Upper Ocean Circulation Features and Wind Fronts
Journal of Geophysical Research, 1991
Airborne C band synthetic aperture radar (SAR) data were collected during the Norwegian Continental Shelf Experiment (NORCSEX) carried out in March 1988. Unique signature variations in the SAR backscatter due to upper ocean circulation features and wind fronts were found. It is documented that a current jet of 0.3 m s -• with a shear of about 0.3 x 10 -3 s -• is correlated with a narrow, bright curved line in the backscatter. In comparison a rapid wind shift of 9 m s-• resulted in a sharp transition from dark to brighter backscatter regions. The corresponding profiles of backscatter modulation across these features are expressed by a peak of about 2 dB in contrast to a steplike increase of 5-8 dB. This suggests that SAR image expressions of upper ocean circulation features and wind fronts can be distinguished and classified. On the basis of this classification, we attempt to quantify the dominating marine geophysical variables. This method for systematic interpretation of SAR images should be further validated with the use of airborne or satellite data such as from the first European Space Agency remote sensing satellite, ERS 1. 1. [1981]; see also the Seasat II collection of papers in the Journal of Geophysical Research, volume 88, number C3, 1983). In order to simulate and evaluate the ERS 1 detection capability, the pre-launch ERS 1 Norwegian Continental Shelf Experiment (NORCSEX '88) was carried out off the west coast of Norway, centered at 64øN, in March 1988. The NORCSEX program was selected by ESA under the Announcement of Opportunity and will continue with two post-launch validation experiments in summer and fall 1991. The sampling strategy of NORCSEX '88 was to measure simultaneously near-surface wind, waves, and current and their interaction by coordinated use of remote sensing and in situ data [Johannessen, this issue]. In particular, C band SAR measurements were acquired using the Canadian Convair-580 aircraft with the aim of investigating the feasibility of classifying and quantifying variations in SAR backscatter due to upper ocean circulation features and wind fronts. Synthetic aperture radar imaging of the ocean surface at incidence angles from 20 ø to 70 ø is principally caused by resonant Bragg scattering, whereby the transmitted radar waves are scattered by short gravity waves of approximately the radar wavelength [Wright, 1978; Hasselmann et al., Paper number 91JC00301. 0148-0227/91/91JC-00301 $05.00 1985]. These waves are formed in response to the wind stress. Variations of these short waves are usually induced by long gravity waves, variable wind speed and stratification in the marine atmospheric boundary layer, and variable currents associated with upper ocean circulation features such as fronts, eddies, and internal waves as well as bottom topography [Beal et al., 1981]. Expressions of these surface roughness variations have been seen in numerous spaceborne and airborne SAR images. For example, off the east coast of the United States, surface roughness patterns associated with warm water Gulf Stream rings were detected and tracked by the Seasat SAR [Lichy et al., 1981; Vesecky and Stewart, 1982]. Lichy et al. and Vesecky and Stewart also reported on SAR image manifestations of surface roughness changes reflecting mesoscale wind field patterns. Moreover, Rufenach et al. [1983] proposed to utilize the Doppler shifts induced by the radial velocities of the scatterer to obtain an estimate of the ocean surface current component perpendicular to the SAR flight track. Recently, Barnett et al. [1989] introduced an inverse method to convert SAR data to estimates of current shear, provided that a well-defined swell as well as an ocean circulation feature exist within the illuminated area. When 10,411 10,412 JOHANNESSEN ET AL.'-SYNTHETIC APERTURE RADAR IMAGING OF CURRENTS AND WIND
Remote Sensing
The Ross Sea region, including three main polynya areas in McMurdo Sound, Terra Nova Bay, and in front of the Ross Ice Shelf, has experienced a significant increase in sea ice extent in the first four decades of satellite observations. Here, we use Co-Registration of Optically Sensed Images and Correlation (COSI-Corr) to estimate 894 high-resolution sea ice motion fields of the Western Ross Sea in order to explore ice-atmosphere interactions based on sequential high-resolution Advanced Synthetic Aperture Radar (ASAR) images from the Envisat satellite acquired between 2002–2012. Validation of output motion vectors with manually drawn vectors for 24 image pairs show Pearson correlation coefficients of 0.92 ± 0.09 with a mean deviation in direction of −3.17 ± 6.48 degrees. The high-resolution vectors were also validated against the Environment and Climate Change Canada sea ice motion tracking algorithm, resulting in correlation coefficients of 0.84 ± 0.20 and the mean deviation in the ...
Journal of Geophysical Research, 1991
Quasi-simultaneous measurements of the ocean surface by the Canada Centre for Remote Sensing (CCRS) Convair-580 (CV-580) synthetic aperture radar (SAR) were acquired on March 20, 1988, along an ascending pass of the Geosat radar altimeter as part of the prelaunch ERS-1 Norwegian Continental Shelf Experiment (NORCSEX '88). Over a region where the SAR look direction is parallel to the wind vector, a relationship between the ocean scattering cross sections measured by the Geosat altimeter and the SAR is obtained. In the regions where the wind direction is changing, an estimate of the wind direction is derived from the differences measured between the altimeter and the SAR scattering cross sections. Wavelength and wave directions derived from the SAR wave spectra are in good agreement with the sea truth data obtained with the wave directional buoys and with the altimeter-derived swell estimates. Significant wave height measured by the Geosat altimeter is compared with the buoy measurements and is used to assess the validity of the significant wave height deduced from the SAR. 1. INTRODUCTION On March 20, 1988, as part of the Norwegian Continental Shelf Experiment (NORCSEX '88) prelaunch ERS-1 windwave-current investigation [NORCSEX '88 Group, 1989], the Canada Centre for Remote Sensing (CCRS) Convair-580 (CV-580) synthetic aperture radar (SAR) flew a data acquisition pattern over the Haltenbanken region of the Norwegian continental shelf. The purpose of this flight was to provide near-simultaneous supporting data for ocean surface measurements made during an ascending pass of the Geosat altimeter. To our knowledge, this is the first time that coincident observations of the ocean surface from satellite radar altimeter and airborne SAR have been acquired quasi-simultaneously along a track several hundred kilometers long (Figure 1). Sea state parameters such as wind speed, significant wave height (SWH), and wavelength are inferred from the radar observations and are compared with corresponding parameters from surface observations. The measurements from one radar are used to improve and complement the capabilities of the
ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 2019
Antarctica and Greenland are two major Earth's continental ice shelves which play an important role in influencing Earth's energy balance through their high albedo. The ice sheets comprise of grounded ice or the continental glaciers and their associated ice shelves. Surface velocity is an important parameter that needs to be monitored to understand the glacier dynamics. Marine terminating glaciers have higher velocity than land terminating glaciers. Therefore, ice shelves are generally observed to have higher velocity as compared to continental glaciers. The focus of this study is Amery ice shelf (AIS) which is the third largest ice shelf located in east Antarctica terminating into the Prydz Bay on the eastern Antarctica. The surface ice-flow velocity of AIS is very high compared to its surrounding glaciers which flows at a rate of 1400 ma-1 and drains about 8% of the Antarctic ice sheet. AIS is fed by different glaciers and ice streams at the head, as well as from the western and eastern side of the ice shelf before it terminates into the ocean. The primary objective of this study was to compute velocity of the eastern tributary glaciers of AIS using SAR from Sentinel-1 data. The secondary objective was to compare the winter and summer velocities of the glaciers for 2017-2018. The offset tracking method has been applied to the ground range detected (GRD) product obtained from Sentinel-1 satellite. This method is suitable for regions with higher glacier velocity where interferometry is generally affected by the loss of coherence. The offset tracking method works by tracking the features on the basis of another feature and calculates the offset between the two features in the images. Two tributary glaciers near the Clemence massif and another glacier near the Pickering Nunatak feed into this ice shelf from the eastern glacial basin region that drains ice from the American Highland, east Antarctica. The glaciers near the Clemence massif showed low annual velocity which ranged from 100 ma-1at the head to ~300 ma-1 near the end of the glacier, where it merges with AIS. The glaciers flowing near the Pickering Nunatak exhibited moderate velocity ranging from 150 ma-1 at its head and reaching up to 450 ma-1 near the tongue. The summer velocity (March 2018) was observed to be higher than the velocity in winter (July 2017) and the difference between the summer and the winter velocities was found to be between 50 ma-1 and 130 ma-1. The results for the velocity were obtained at 120 m resolution and were compared with the previous MEaSUREs (Making Earth System Data Records for Use in Research Environments) yearly velocity at 450 m and 1 km resolution provided by National Snow and Ice Data Center portal. The results were evaluated using statistical measure-bias and the accuracy was derived using the root mean square error. The bias did not exceed 20 ma-1for the three glaciers and the accuracy was observed to be more than 85% for most of the regions. The accuracy of the results suggests that the offset tracking technique is useful for future velocity estimation in the regions of high glacier velocity.
Remote Sensing of Environment
Measurements of wave heights in marginal ice zones are limited to very few in situ data. Here we revisit the linear and quasilinear theories of Synthetic Aperture Radar imaging of waves in the particular case of waves in sea ice. Instead of only working with spectra, we have developed an iterative nonlinear algorithm to estimate phase-resolved deterministic maps of wave-induced orbital velocities, from which elevation spectra can be derived. Application of this algorithm to Sentinel 1A wave mode images in the Southern Ocean shows that it produces reasonable results for swells in all directions except when they propagate at a few degrees off the range direction. The estimate of wave parameters is expected to work best when the shortest wave components, those which cause a pixel displacement of the order of the dominant wavelength in azimuth, can be neglected. Otherwise short waves produce a blurring of the image, increasing exponentially with the azimuthal wavenumber and reducing the estimated wave amplitude. Given the expected spatial attenuation of waves in ice-covered regions, our deterministic method should apply beyond a few tens of kilometers in the ice, without any correction for short wave effects. In situ data collected around the ice edge as part of the 2015 SeaState DRI cruise in the Beaufort confirm the progressive image blurring caused by such short waves, and the apparent reduction in the wave modulation. When short waves propagate from the open ocean towards the ice, this blurring can produce an unrealistic apparent increase of wave height, from the open ocean up to a few tens of kilometers inside the ice. Highlights ► An algorithm is proposed to obtain orbital velocity maps from SAR images over sea ice. ► The algorithm is validated in terms of ocean wave spectra using in situ measurements. ► Wave height retrieval works best in the absence of unresolved short waves.
Mapping the concentration of sea ice in the central Antarctic Peninsula with Sentinel 1 data
Revista Brasileira de Geografia Fisica, 2020
Sea ice acts as a thermal insulator between the ocean and the atmosphere and without it, the ocean will be free to emit heat to the atmosphere, influencing the formation of water bodies and ocean circulation. This article proposes the classification and identification of sea ice by means of Synthetic Aperture Radar (SAR) images in the C band, obtained by the Sentinel 1B satellite, Extra Wide Swath (EW) imaging mode under HH + HV polarizations, radiometrically calibrated and normalized to incidence angle at 30°. The study area covered the central oceanic region of the Antarctic Peninsula during the winter and early austral spring of 2018. Obtaining samples for the classification of SAR scenes was obtained through visual analysis of the target texture in Sentinel 2 optical images (Multispectral Instrument), falsecolor RGB compositions of the HH and HV polarizations (R-HH, G-HV, B-HV/HH and R-HH, G-HH, B-HV) and unsupervised classification through cluster analysis. Backscatter coefficients (σ°) were identified in the HH polarization of-8.0 to-12.6 dB for young ice and/or first-year ice,-2.1 to-7.3 dB for multiyear ice, and for the HV polarization of-19.3 to-24.2 dB for young ice and/or first-year ice and-6.8 to-13.4 dB for multiyear ice, making it possible to map the concentration of sea ice in the region of study by using these thresholds.
Estimation of Velocity of the Polar Record Glacier, Antarctica Using Synthetic Aperture Radar (SAR)
The 2nd International Electronic Conference on Remote Sensing, 2018
The ice flow velocity is a critical variable in understanding the glacier dynamics. The Synthetic Aperture Radar Interferometry (InSAR) is a robust technique to monitor Earth’s surface mainly to measure its topography and deformation. The phase information from two or more interferogram further helps to extract information about the height and displacement of the surface. We used this technique to derive glacier velocity for Polar Record Glacier (PRG), East Antarctica, using Sentinel-1 Single Look Complex images that were captured in Interferometric Wide mode. For velocity estimation, Persistent Scatterer interferometry (PS-InSAR) method was applied, which uses the time coherent of permanent pixel of master images and correlates to the same pixel of the slave image to get displacement by tracking the intensity of those pixels. C-band sensor of European Space Agency, Sentinel-1A, and 1B data were used in this study. Estimated average velocity of the PRG is found to be approximately ≈...
Satellite observations of upper-ocean currents in Terra Nova Bay, Antarctica
Annals of Glaciology, 2001
Ship and iceberg drifts, along with data from modern satellite-tracked drifting buoys, portray generally northward flow in the southwest Ross Sea. Less is known, however, about the ocean variability in this region. Here we use Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) imagery to describe a cyclonically rotating gyre inTerra Nova Bay, Antarctica (75" S, 165" E). The image sequence is taken from an exceptionally clear, calm, period during winter 1998. Surface currents, derived from trackin drifting ice with a maximum cross-correlation algorithm, were found 4 to be ~2 0 to 30 cm s . Based on scaling arguments, the observed currents appear to be best explained as an oceanic response to a rapidly changing, offshore, katabatic wind jet.