Inverse Electromagnetic Scattering Models for Sea Ice
Inverse scattering algorithms for reconstructing the physical properties of sea ice from scattered electromagnetic field data are developed.
Electromagnetic↗
Engineering topics
Onstott, R. G.
Publications and source records attributed to Onstott, R. G..
Evolution of Electromagnetic-Signatures of Sea Ice From Initial Formation Through the Establishment of Thick First-Year Ice
The objective of the present work is to characterize the temporal evolution of the electromagnetic signatures of sea ice from initial formation through the development of first-year ice on the basis of the temporal variations in the physical properties of the ice.
Electromagnetic↗
The Role of Snow on Microwave Emission and Scattering Over First-Year Sea Ice.
Projections for global warming indicate that the polar regions will likely provide both a larger magnitude and earlier indiation of climate variability and change that will the more temperate regions of the planet.
microwave↗
Arctic coastal polynya observations with ERS-1 SAR and DMSP SSM/I
Work to improve the characterization of the distribution of new and young sea ice types and open water amount within Arctic coastal polynyas through the combined use of ERS-1 SAR (Synthetic Aperture Radar) and DMSP SSM/I (Defense Meteorological Satellite Program Special Sensor Microwave/Imager) data is described. Two St. Lawrence Island polynya events are studied using low resolution, geocoded SAR images and coincident SSM/I data. The SAR images are analyzed in terms of polarization and spectral gradient ratios. Results of the combined analysis show that the SAR ice type classification is consistent with that from SSM/I and that the combined use of SAR and SSM/I can improve the characterization of thin ice better than either data set can do alone.
Cavalieri, D. J.↗
Microwave and physical properties of sea ice in the winter marginal ice zone
Surface-based active and passive microwave measurements were made in conjunction with ice property measurements for several distinct ice types in the Fram Strait during March and April 1987. Synthesis aperture radar imagery downlinked from an aircraft was used to select study sites. The surface-based radar scattering cross section and emissivity spectra generally support previously inferred qualitative relationships between ice types, exhibiting expected separation between young, first-year and multiyear ice. Gradient ratios, calculated for both active and passive data, appear to allow clear separation of ice types when used jointly. Surface flooding of multiyear floes, resulting from excessive loading and perhaps wave action, causes both active and passive signatures to resemble those of first-year ice. This effect could possibly cause estimates of ice type percentages in the marginal ice zone to be in error when derived from aircraft- or satellite-born sensors.
Tucker, W. B., III↗
Multi-frequency SAR, SSM/I and AVHRR derived geophysical information of the marginal ice zone
A description is given of the fusion of synthetic aperture radar (SAR), special sensor microwave imager (SSM/I), and NOAA Advanced Very High Resolution Radiometer (AVHRR) data to study arctic processes. These data were collected during the SIZEX/CEAREX experiments that occurred in the Greenland Sea in March of 1989. Detailed comparisons between the SAR, AVHRR, and SSM/I indicated: (1) The ice edge position was in agreement to within 25 km, (2) The SSM/I SAR total ice concentration compared favorably, however, the SSM/I significantly underpredicted the multiyear fraction, (3) Combining high resolution SAR with SSM/I can potentially map open water and new ice features in the marginal ice zone (MIZ) which cannot be mapped by the single sensors, and (4) The combination of all three sensors provides accurate ice information as well as sea surface temperature and wind speeds.
Shuchman, R. A.↗
NASA, Navy, and AES/York sea ice concentration comparison of SSM/I algorithms with SAR derived values
Previous research studies have focused on producing algorithms for extracting geophysical information from passive microwave data regarding ice floe size, sea ice concentration, open water lead locations, and sea ice extent. These studies have resulted in four separate algorithms for extracting these geophysical parameters. Sea ice concentration estimates generated from each of these algorithms (i.e., NASA/Team, NASA/Comiso, AES/York, and Navy) are compared to ice concentration estimates produced from coincident high-resolution synthetic aperture radar (SAR) data. The SAR concentration estimates are produced from data collected in both the Beaufort Sea and the Greenland Sea in March 1988 and March 1989, respectively. The SAR data are coincident to the passive microwave data generated by the Special Sensor Microwave/Imager (SSM/I).
Jentz, R. R.↗
Intercomparison of synthetic- and real-aperture radar observations of Arctic sea ice during winter MIZEX '87
Active microwave measurements were made of various sea ice forms in March and April 1987 during the Marginal Ice Zone Experiment, at 1, 5, 10, 18, and 35 GHz using a synthetic aperture radar (SAR) and helicopter and ship-based scatterometers. The X-band (9.8 GHz) SAR data were compared to the scatterometer data and it was determined that for 5 GHz and higher frequencies both the SAR and scatterometers can differentiate open water, new ice (5 to 30 cm), first-year ice with rubble (0.60 -1.5 m), and multiyear ice. The analysis further confirmed that the C-band (5 GHz) SAR's flying on ESA ERS-1 and Radarsat will differentiate the mentioned ice types.
Schuchmann, R. A.↗
Active microwave measurements of artificial sea ice
A 5 m x 15 m outdoor tank of 1.2 m depth was filled with sea water, and polarimetric radar backscatter data were collected at 1.8, 5, and 10 GHz for incidence angles 0 to 60 deg. Observations commenced with open water and continued until 30 cm of sea ice formed. The roughness of the ice surface is important in determining the general backscatter level for first-year ice. Experiments were performed to study the change in backscatter with various roughness scales. Effects of freeze and thaw conditions were also examined. Absolute backscatter levels for new to gray ice are small, except for the large, coherent returns at vertical. The backscatter responses of new, gray, rough grey, and desalinated first-year ice at linear polarization are dissimilar. This is confirmed by examining their polarization signatures.
Onstott, R. G.↗
Radar backscatter of sea ice during winter
Active microwave measurements were made during the 1987 Marginal Ice Zone Experiment. Backscatter data were acquired at frequencies from 1.25 to 35 GHz, at incidence angles from 0 to 80 deg, and with linear antenna polarizations. The objective was to describe the scattering coefficients of the major ice types in the region and to study the winter conditions and their influence on the microwave response. Results show that multiyear and pancake ice produce strong backscatter, while returns from open water between floes and new ice are weak. First-year ice has a wide range of returns; when the surface is smooth returns are weak, and if roughened, i.e., like pancake ice, the returns increase substantially.
Onstott, R. G.↗
Evolution of microwave sea ice signatures during early summer and midsummer in the marginal ice zone
Emissivities at frequencies from 5 to 94 GHz and backscatter at frequencies from 1 to 17 GHz were measured from sea ice in Fram Strait during the marginal Ice Zone Experiment in June and July of 1983 and 1984. The ice observed was primarily multiyear; the remainder, first-year ice, was often deformed. Results from this active and passive microwave study include the description of the evolution of the sea ice during early summer and midsummer; the absorption properties of summer snow; the interrelationship between ice thickness and the state and thickness of snow; and the modulation of the microwave signature, especially at the highest frequencies, by the freezing of the upper few centimeters of the ice.
Onstott, R. G.↗
An inter-sensor comparison of the microwave signatures of Arctic sea ice
Active and passive microwave and physical properties of Arctic sea ice in the marginal ice zone were measured during the summer. Results of an intercomparison of data acquired by an aircraft synthetic aperture radar, a passive microwave imager and a helicopter-mounted scatterometer indicate that early-to-mid summer sea ice microwave signatures are dominated by snowpack characteristics. Measurements show that the greatest contrast between thin first-year and multiyear sea ice occurs when operating actively between 5 and 10 GHz. Significant information about the state of melt of snow and ice is contained in the active and passive microwave signatures.
Onstott, R. G.↗
Microwave properties of sea ice in the marginal ice zone
Active microwave properties of summer sea ice were measured. Backscatter data were acquired at frequencies from 1 to 17 GHz, at angles from 0 to 70 deg from vertical, and with like and cross antenna polarizations. Results show that melt-water, snow thickness, snowpack morphology, snow surface roughness, ice surface roughness, and deformation characteristics are the fundamental scene parameters which govern the summer sea ice backscatter response. A thick, wet snow cover dominates the backscatter response and masks any ice sheet features below. However, snow and melt-water are not distributed uniformly and the stage of melt may also be quite variable. These nonuniformities related to ice type are not necessarily well understood and produce unique microwave signature characteristics.
Onstott, R. G.↗
Active microwave measurements of Arctic sea ice under summer conditions
Radar provides a valuable tool in the study of sea-ice conditions and the solution of sea-ice operational problems. For this reason, the U.S. and Canada have conducted studies to define a bilateral synthetic aperture radar (SAR) satellite program. The present paper is concerned with work which has been performed to explore the needs associated with the study of sea-ice-covered waters. The design of a suitable research or operational spaceborne SAR or real aperture radar must be based on an adequate knowledge of the backscatter coefficients of the ice features which are of interest. In order to obtain the needed information, studies involving the use of a helicopter were conducted. In these studies L-C-X-Ku-band calibrated radar data were acquired over areas of Arctic first-year and multiyear ice during the first half of the summer of 1982. The results show that the microwave response in the case of sea ice is greatly influenced by summer melt, which produces significant changes in the properties of the snowpack and ice sheet.
Onstott, R. G.↗
Mobile spectrometer measures radar backscatter
The present article is concerned with a helicopter-borne spectrometer (Heloscat), which has been developed to permit high-quality scattering measurements from a mobile platform at remote sites. The term 'spectrometer' referes to a class of scatterometers. The term 'scatterometer' is employed to denote a specialized radar for measuring scattering coefficients as a function of angle. A spectrometer, on the other hand, is a scatterometer which can measure backscatter at several frequencies. The Heloscat system is discussed, taking into account two antennas, RF hardware, and an externally mounted pendulum for angle encoding. A dual-antenna configuration is used for cross-polarized measurements, while a single-antenna system is used for like-polarized measurements. Attention is also given to oscillator characteristics, efficient data handling, and aspects of calibration.
Gogineni, S.↗
Active microwave measurements of sea ice under fall conditions: The RADARSAT/FIREX fall experiment
A series of measurements of the active microwave properties of sea ice under fall growing conditions was conducted. Ice in the inland waters of Mould Bay, Crozier Channel, and intrepid inlet and ice in the Arctic Ocean near Hardinge Bay was investigated. Active microwave data were acquired using a helicopter borne scatterometer. Results show that multiyear ice frozen in grey or first year ice is easily detected under cold fall conditions. Multiyear ice returns were dynamic due to response to two of its scene constituents. Floe boundaries between thick and thin ice are well defined. Multiyear pressure ridge returns are similar in level to background ice returns. Backscatter from homogeneous first year ice is seen to be primarily due to surface scattering. Operation at 9.6 GHz is more sensitive to the detailed changes in scene roughness, while operation at 5.6 GHz seems to track roughness changes less ably.
Onstott, R. G.↗
C-band measurements of radar backscatter from ice project summary report
The ability to measure the radar scattering coefficient of ice with a helicopter or surface spectrometer was extended into the 4-8 GHz spectral region. The scattering coefficient was measured at Mould Bay, N.W.T., over a frequency range from 4 to 18 GHz for both summer and fall conditions. Scatter from fresh water ice in the St. Lawrence River and from numerous seasonal sea-ice types along the coast of Newfoundland were also measured. The C-band (near 5 GHz) scattering cross section for different types of ice shows poorer contrast than the scattering coefficient at higher frequencies, but better contrast than the negligible value found at L-band (1.5 GHz). At frequencies above 4 GHz the contrast in scattering coefficient between the different ice types is much less in summer than in other seasons; at most times of year the scattering is much stronger from multiyear than from other ice types, but in early summer it is actually slightly weaker than that from first year ice.
Onstott, R. G.↗