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Drinkwater, Mark R.

Publications and source records attributed to Drinkwater, Mark R..

29 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Multifrequency polarimetric synthetic aperture radar observations of sea ice

The present study introduces a fully polarimetric airborne SAR data set of sea ice. Images were acquired in the Beaufort, Bering, and Chukchi seas in March 1988. Statistics of the magnitude, phase, and polarization of complex backscattered signals recorded by three-frequency SAR are examined for various scenes with different ice characteristics. Results indicate that combinations of frequency and polarization enhance current capability to distinguish ice of different properties using single-frequency fixed-polarization-microwave radar. A specific example is the polarimetric identification of new ice formation which may not be easily distinguished in ERS-1 5.3-GHz VV polarization of SAR data. Such findings are consistent with theoretical model simulations of scattering characteristics of sea ice.

Drinkwater, Mark R.↗
NASA NTRS1991

Ku band airborne radar altimeter observations of marginal sea ice during the 1984 Marginal Ice Zone Experiment

Pulse-limited, airborne radar data taken in June and July 1984 with a 13.8-GHz altimeter over the Fram Strait marginal ice zone are analyzed with the aid of large-format aerial photography, airborne synthetic aperture radar data, and surface observations. Variations in the radar return pulse waveforms are quantified and correlated with ice properties recorded during the Marginal Ice Zone Experiment. Results indicate that the wide-beam altimeter is a flexible instrument, capable of identifying the ice edge with a high degree of accuracy, calculating the ice concentration, and discriminating a number of different ice classes. This suggests that microwave radar altimeters have a sensitivity to sea ice which has not yet been fully exploited. When fused with SSM/I, AVHRR and ERS-1 synthetic aperture radar imagery, future ERS-1 altimeter data are expected to provide some missing pieces to the sea ice geophysics puzzle.

Drinkwater, Mark R.↗
NASA NTRS1991

Multi-frequency, multi-polarization SAR and radiometer sea ice classification

Microwave remotely sensed data were acquired simultaneously in March 1988 over Beaufort, Chukchi, and Bering Sea ice using the JPL multifrequency, polarimetric synthetic aperture radar (SAR), and multifrequency dual-polarization GSFC radiometer. The experiment was conducted as a series of coordinated underflights of the DMSP SSM/I satellite radiometer to validate ice products derived from its radiance values. Concurrent flights by an NRL P-3 aircraft enabled overlapping high-resolution, single-frequency images to be acquired over the same surfaces using a Ka-band scanning microwave radiometer. Precise coregistration to an accuracy of 100 m, +/- 25 m enables comparison of temporally and spatially coincident active and passive microwave datasets. Three-channel polarimetric SAR data are compared with dual-polarized radiometer data at several SSM/I frequencies, showing backscatter signatures to be highly correlated with radiometric temperatures. Further comparisons are used to evaluate ice concentration retrievals and to show how multiparameter datasets can be used to resolve ambiguities present in identifying certain sea ice forms with a single microwave instrument.

Drinkwater, Mark R.↗
NASA NTRS1991

Observations of the late-summer to fall sea ice transition with the 14.6 GHz Seasat scatterometer

Seasat 14.6-GHz scatterometer data are used to investigate variations in the large area-averaged backscatter signature during the late summer to fall transition. The temporal evolution in the backscatter coefficient indicates general changes in the surface properties of the sea ice which are attributed to the seasonal cycle. Notable events in this typical cycle are the meltpond maximum, rapid drainage or disappearance of the meltponds, fall cooling and freeze-up, and ultimately snowfall. All are manifested in the signature record, and a simple empirical scattering model is used to infer the mean snow and ice properties and their temporal variation.

Drinkwater, Mark R.↗
NASA NTRS1989

LIMEX '87 ice surface characteristics - Implications for C-band SAR backscatter signatures

Ice surface characterization data collected in 1987, during the Labrador Sea Ice Margin Experiment, are analyzed to estimate the changes in snow and ice properties at the onset of melt. Surface measurements were made from an ice research vessel on several days (some of which had coincident remote-sensing flights) at a number of locations in the marginal ice zone. These data are used as input parameters in a simple scattering model to simulate the effects of variations in material properties upon C-band scattering signatures. Snow moisture and large-scale surface roughness are demonstrated to have the largest effect upon HH polarization scattering cross-section sigma(HH)(O) and large differences are predicted between undeformed floe surfaces and deformed or undulating rough ice surfaces. Using a parametric approach, an approximate picture of rough and smooth ice signatures and their relative contrast are provided. The models reproduce a trend observed in synthetic aperture radar (SAR) images of increasing backscatter contrast between deformed and underformed ice over an early period of warning: such observations are consistent with the results of analysis of SAR images to date. The model also reproduces a calibrated SAR-derived signature with a reasonable degree of accuracy.

Drinkwater, Mark R.↗
NASA NTRS1989

C-band SAR observations of marginal ice zone rheology in the Labrador Sea

Synthetic-aperture radar (SAR) imagery collected during the LIMEX'87 field program in the Labrador Sea is used to qualitatively interpret the deformational modes in play throughout the experiment. The ice cover exhibited two distinct rheologies separated by a clear line of shear: a nonlinear viscous outer regime, and a quasi-brittle inner regime. A single constitutive relation capable of effectively modeling both is unlikely within a plastic rate-independent formulation. Rate-dependent effects are discussed in relation to favoring brittle fraction in an otherwise ductile material.

Drinkwater, Mark R.↗
NASA NTRS1989

Limex'87 ice surface characteristics and their effect upon C-band SAR sigantures

Ice surface characterization data were recorded during March 1987 in the Labrador Sea marginal ice zone, at the onset of spring melt. Measured data are used as input parameters in a simple scattering model to simulate the effects of temporal variations in material properties upon C-band scattering signatures. Snow moisture and surface roughness have a significant effect upon sigma(0)HH and large differences are predicted between undeformed floe surfaces and deformed or rubbled ice areas. The model reproduces a calibrated synthetic-aperture-radar (SAR)-derived signature obtained during the experiment with a reasonable degree of certainty. Predictions also simulate a trend observed in SAR images of increasing backscatter contrast between deformed and undeformed ice over period of surface warming.

Drinkwater, Mark R.↗
NASA NTRS1989

Preliminary observations of Labrador Sea marginal ice zone rheology using C-band SAR

SAR imagery collected in the Labrador Sea during Limex '87 are used to interpret modes of sea-ice deformation. The ice canopy exhibited two distinct rheologies separated by a clear line of shear; a quasi-brittle inner regime and a nonlinear viscous outer regime. A single constitutive relation capable of modeling both is unlikely within a plastic rate-independent formulation. Rate dependent effects are discussed as an explanation for brittle fracture in ductile materials.

Drinkwater, Mark R.↗
NASA NTRS1988

Modelling changes in the dielectric and scattering properties of young snow-covered sea ice at GHz frequencies

Observations of the physical properties of the snow cover and underlying young fast ice in Resolute Passage, Canada, were made during the winter of 1982. Detailed measurements of snow density and ice and snow temperatures, salinities, and brine volumes were made over a period of 46 d, beginning when the ice was 0.4 m thick and about 9 d old. The recorded values are used in a theoretical mixture model to predict the dielectric properties of the snow cover over the microwave frequency range. The results of this analysis are then used to investigate the effects of the snow properties on the radar backscatter signatures of young sea ice. The results show that backscatter is a function of the incidence angle and can change significantly over short periods of time during the early evolutionary phase of ice and snow-cover development. This has important consequences for the identification of young ice forms from SAR or SLAR images.

Drinkwater, Mark R.↗