R.A. Shuchman

Detection of surface current features with ERS-1 SAR

ERS-1 SAR image expressions of mesoscale coastal ocean circulation features are examined. The dominating geophysical quantities and processes that are participating in the formation of the image expression are discussed. An attempt to characterise dynamics of the current features is carried out employing a SAR simulation model. Preliminary results suggest that systematic combination of simulation models and SAR images can lead to better quantitative interpretation of SAR images.<<ETX>>

Characterization Of Intrinsic Optical Properties For Sea Ice And Snow

A narrow He1ium:Neon (633nm) laser was used to measure transmission loss and spreading in thin samples of sea ice and snow collected from the Beaufort Sea during LEADEX ’91 and from sites in the high Arctic during March 1987. The sea ice types sampled include first year, multiyear, melt pond, and various stages of young sea ice in the thickness range of 2 to 20 centimeters. Snow samples include old snow from multiyear floes as well as fresher snow from first year ice types. These data were analyzed to characterize intrinsic beam transmission and small angle scattering optical properties. In sea ice the latter scattering properties are highly dependent on the intricate structure of air bubbles, brine channels, and internal platelet boundaries and considered important to the estimation of the volume scattering function and visible radiative transfer through the Arctic sea ice cover. In this technique beam spreading is first used to derive the modulation transfer function (MTF) using a Fourier-Bessel transform. The spatial frequency decay function derived from the MTF can be used to estimate the volume scattering function for small angles. For thin snow and many sea ice samples the beam spread functions could be characterized as having Gaussian shape and therefore easily parameterized for the numerical transforms. Beam transmission measurements derived from snow and sea ice samples compared favorably with previously derived extinction estimates.

Study of the relationship between the scale of sea ice deformation and radar backscatter intensity using ERS-1 SAR

Knowledge of the relationship between the backscatter response and physical properties of deformed sea ice is important in documenting the information which may be retrieved using synthetic aperture radar (SAR). Investigations have been conducted in the use of SAR to assess the state of deformation of Arctic sea ice and the robustness of the inversion of the SAR signatures to estimates of deformation state, ice thickness, and ridge height. This paper presents relevant issues and illustrates SAR signatures for a variety of deformed ice cases.

Satellite remote sensing of the Beaufort Sea during LEADEX '92

Preliminary observations from ERS-1 SAR imagery of a lead system are presented. Radar cross section values extracted from the ERS-1 data show changes due to lead evolution from open water to new ice. Work is ongoing to compare these results to in situ measurements and other satellite-based imagery.<<ETX>>

A Doppler spectral method of identifying water and ice in marginal-ice-zone imagery

Complex synthetic aperture radar (SAR) imagery at C-band and X-band were acquired in and near the marginal-ice-zone on March 26 1989 in the Greenland Sea. The authors specially process this imagery to obtain Doppler spectra from two backscatter regions: (1) newly forming ice inside a tongue shaped region called the Odden and (2) open water adjacent to the Odden. They observe Doppler bandwidth broadening from the water imagery compared to the spectral width backscattered from the ice. A model is developed describing this broadening in terms of the platform motion, and the short and long ocean waves. They claim this broadening is primarily due to random sub-resolution velocities within a SAR resolution cell caused by the short ocean waves. The bandwidth broadening is extracted as /spl Delta/f/spl circsub aspl ap/40 Hz at C-band and /spl Delta/f/spl circsub aspl ap/55 Hz at X-band. The corresponding scene correlation times are 2/spl tausub cspl ap/22 ms at C-band and 16 ms at X-band. The measured ice bandwidth due to the platform motion (155 m/s) is approximately 118 Hz at both C-band and X-band.<<ETX>>

Quantitative Measurements Of C-band Image Modulation Caused By Ocean Gravity Waves Across An Atmospheric Front During Norcsex '88

Airborne synthetic aperture r adar (SAR) images of ocean gravity waves were selected for velocity smearing analysis during three days of March, 1988. The velocity smearing was calculated using a least square fit to the azimuth wavenumber attenuation. Furthermore, an atmospheric frontal boundary with wind speed changing from 6 m/sec to 12 m/sec over a few kms was also analyzed. The SAR extracted velocity smearing varied from U” = 0.4 m/sec - 0.7 m/sec. A velocity smearing model was developed which describes when ocean gravity waves can be imaged as a function of R/V, incidence angle and azimuth angle. We estimate a minimum azimuth traveling wavelength can be imaged by the ERS-1 spaceborne radar; varying from 130 m at U” = 0.4 m/sec to 260 m at U” = 0.7 m/sec.