scholarly journals Dual Frequency Radar Ice and Snow Signatures

1983 ◽  
Vol 29 (102) ◽  
pp. 286-295
Author(s):  
R. D. Ketchum
Keyword(s):  
Sea Ice ◽  
Sea Water ◽  
Open Water ◽  
Good Choice ◽  
Signal Loss ◽  
Dual Frequency ◽  
X Band ◽  
Radar Imagery ◽  
High Backscatter ◽  
L Band

AbstractDual frequency (X-band and L-band) synthetic-aperture radar imagery of sea ice is examined to show the differences between the bands and their complementary nature for resolving ambiguities in interpretation. High backscatter at X-band from visibly smooth thin ice is not observed at L-band. One hypothesis is that the high X-band backscatter may be caused by a reflective layer at the snow/ice interface. A second hypothesis is that the high X-band backscatter may be caused by moisture in the snow. A third hypothesis states that the phenomenon may be due to snow flowers. High backscatter at L-band is observed for slush on open water. The return is very weak at X-band, thus allowing distinction of slush by comparing L-band and X-band images. High intensity, but only partial returns from icebergs at L-band have been observed. The hypothesis is that internal iceberg/sea-water reflections are occurring. Some signals are directed away from the antenna, other reinforced signals are returned, producing very bright images. Occasionally, time-delayed signals are returned causing a false image at far range from the iceberg. The conclusion is that L-band is a poor choice for studies of iceberg distribution and size, but a good choice for iceberg detection because of the high reinforced returns from many icebergs and the low return from the adjacent sea ice. The penetration and subsequent signal loss of L-band in glacial ice, when compared to high X-band returns, may be useful to map glacierized land masses.

scholarly journals Dual Frequency Radar Ice and Snow Signatures

1983 ◽  
Vol 29 (102) ◽  
pp. 286-295 ◽  
Author(s):  
R. D. Ketchum
Keyword(s):  
Sea Ice ◽  
Sea Water ◽  
Open Water ◽  
Good Choice ◽  
Signal Loss ◽  
Dual Frequency ◽  
X Band ◽  
Radar Imagery ◽  
High Backscatter ◽  
L Band

Abstract Dual frequency (X-band and L-band) synthetic-aperture radar imagery of sea ice is examined to show the differences between the bands and their complementary nature for resolving ambiguities in interpretation. High backscatter at X-band from visibly smooth thin ice is not observed at L-band. One hypothesis is that the high X-band backscatter may be caused by a reflective layer at the snow/ice interface. A second hypothesis is that the high X-band backscatter may be caused by moisture in the snow. A third hypothesis states that the phenomenon may be due to snow flowers. High backscatter at L-band is observed for slush on open water. The return is very weak at X-band, thus allowing distinction of slush by comparing L-band and X-band images. High intensity, but only partial returns from icebergs at L-band have been observed. The hypothesis is that internal iceberg/sea-water reflections are occurring. Some signals are directed away from the antenna, other reinforced signals are returned, producing very bright images. Occasionally, time-delayed signals are returned causing a false image at far range from the iceberg. The conclusion is that L-band is a poor choice for studies of iceberg distribution and size, but a good choice for iceberg detection because of the high reinforced returns from many icebergs and the low return from the adjacent sea ice. The penetration and subsequent signal loss of L-band in glacial ice, when compared to high X-band returns, may be useful to map glacierized land masses.

scholarly journals Deriving sea-ice thickness and ice types in the Sea of Okhotsk using dual-frequency airborne SAR (Pi-SAR) data

2002 ◽  
Vol 34 ◽  
pp. 429-434 ◽  
Author(s):  
Takeshi Matsuoka ◽  
Seiho Uratsuka ◽  
Makoto Satake ◽  
Akitsugu Nadai ◽  
Toshihiko Umehara ◽  
...  
Keyword(s):  
Sea Ice ◽  
Acoustic Doppler Current Profiler ◽  
Open Water ◽  
Ice Thickness ◽  
Dual Frequency ◽  
Backscattering Coefficient ◽  
Sea Ice Thickness ◽  
National Space ◽  
L Band ◽  
Airborne Sar

AbstractDual-frequency, multi-polarization airborne synthetic aperture radar (Pi-SAR; developed by the Communications Research Laboratory and National Space Development Agency of Japan) observations of the seasonal sea-ice region off the Okhotsk coast of Hokkaido, Japan, were carried out in February 1999 using X- and L-band radar frequencies with a resolution of 1.5 and 3.0 m. In conjunction with the SAR observations, the sea-ice thickness (draft) and velocity were measured by a moored Ice Profiling Sonar (IPS) and an Acoustic Doppler Current Profiler (ADCP). Tracks of the sea ice passing over the IPS were estimated from the time series of the ADCP ice-velocity and -direction data. Along these tracks, the SAR backscattering coefficient profiles were compared with the IPS ice-draft profiles. The results showed that the L-band SAR backs cattering profiles correlated well with the IPS ice-draft data, particularly in the thicker part (a few meters thick) of the rim of first-year ice, which had a large backscattering coefficient. Although the X-band SAR backscattering profiles did not correlate well with the IPS data, thin ice (<10 cm thick) showed a large backscattering coefficient. The L-band SAR and IPS data did not distinguish thin ice from open water.

scholarly journals The Separation of Sea-Ice Types in Radar Imagery (Abstract)

1987 ◽  
Vol 9 ◽  
pp. 247-247
Author(s):  
Benjamin Holt ◽  
F.D. Carsey
Keyword(s):  
Surface Morphology ◽  
Sea Ice ◽  
Open Water ◽  
Classification Algorithm ◽  
First Year ◽  
Volume Scattering ◽  
Radar Imagery ◽  
L Band ◽  
Sar Imagery ◽  
Scale Surface

The ability to distinguish the several major types of sea ice with active radar instruments has been well studied in recent years. The separation of sea-ice types by radar results principally from variations in radar back-scatter due to characteristic differences of these ice types in surface morphology and brine content. When sea ice is viewed with an active radar at angles greater than about 20° from nadir, undeformed ice reflects radar waves and results in a low return, while ridges, hummocks, and small-scale surface features scatter the radar waves and produce a high return. The presence of salt increases the dielectric constant of ice; penetration by radar into the ice is then negligible, and the return is essentially determined by surface morphology. The absence of salt reduces the dielectric properties of ice; radar waves can then penetrate the ice to some depth and are scattered by air bubbles and brine-drainage channels (called volume scattering), thereby enhancing the return even for roughened surfaces. All these properties vary significantly with radar frequency and polarization as well as seasonally. For example, higher radar frequencies respond to smaller-scale surface features, while lower radar frequencies penetrate further into the ice with resulting volume scattering.The high-resolution imagery from synthetic aperture radars (SAR), mounted on aircraft, shuttle, or satellite platforms, is very effective for many sea-ice studies, including the separation of ice types. An aircraft-mounted X-band (9 GHz) SAR, for example, can discriminate smooth first-year ice, rough first-year ice, multi-year ice, and open water by the intensity (tone) of the radar returns and floe geometry. The preferred SARs to date for satellites and shuttle platforms have been L-band (1–2 GHz) systems. SAR imagery of sea ice was extensively acquired by Seasat in 1978 over the Beaufort Sea, with limited quantities obtained by the Shuttle Imaging Radar (SIR-B) over the Weddell Sea in 1984. While L-band SAR can discriminate rough and smooth ice along with roughened open water based on image intensity and floe geometry, the returns from thick first-year ice and multi-year ice are not clearly distinguishable. The fact that there is volume scattering from multi-year ice suggests that there may be textural or spatial frequency variations that could be used to separate these two major ice types in radar imagery. In order to investigate the separation of sea-ice types in the large amount of L-band SAR imagery available, image-analysis techniques including filtering and classification programs have been utilized, pointing towards an automatic classification algorithm for use in future SAR sea-ice data sets, especially from space.An important characteristic of all SAR imagery is the presence of image speckle, a coherent form of noise caused by the random variability of scatterers across even a uniform surface. Most SAR processors reduce this effect by averaging multiple independent samples but this is done at the cost of reducing resolution. Speckle reduction can also be accomplished by filtering. Several filters have been tested including median, box, and adaptive edge filters. Each filter has different characteristics in terms of smoothing speckle and in the response to sharp gradients or edges, such as ridge or lead openings, as well as computational requirements. Optimization of each filter’s parameters has been determined by the quality of classification of each ice type.The classification programs that have been tested are based on tone and texture image characteristics. The programs are supervised; that is, a small training area for each class is pre-selected for statistical analysis. From these statistics, the remainder of the imagery is subjected to the particular classification algorithm. The tone program separates classes based on the mean, standard deviation, and number of standard deviations of each class, and includes a Bayesian maximum-likelihood classifier for ambiguous elements. The texture program determines the statistical homogeneity of each class and the optimal segmentation of each small area into the various classes.

scholarly journals The Separation of Sea-Ice Types in Radar Imagery (Abstract)

1987 ◽  
Vol 9 ◽  
pp. 247
Author(s):  
Benjamin Holt ◽  
F.D. Carsey
Keyword(s):  
Surface Morphology ◽  
Sea Ice ◽  
Open Water ◽  
Classification Algorithm ◽  
First Year ◽  
Volume Scattering ◽  
Radar Imagery ◽  
L Band ◽  
Sar Imagery ◽  
Scale Surface

The ability to distinguish the several major types of sea ice with active radar instruments has been well studied in recent years. The separation of sea-ice types by radar results principally from variations in radar back-scatter due to characteristic differences of these ice types in surface morphology and brine content. When sea ice is viewed with an active radar at angles greater than about 20° from nadir, undeformed ice reflects radar waves and results in a low return, while ridges, hummocks, and small-scale surface features scatter the radar waves and produce a high return. The presence of salt increases the dielectric constant of ice; penetration by radar into the ice is then negligible, and the return is essentially determined by surface morphology. The absence of salt reduces the dielectric properties of ice; radar waves can then penetrate the ice to some depth and are scattered by air bubbles and brine-drainage channels (called volume scattering), thereby enhancing the return even for roughened surfaces. All these properties vary significantly with radar frequency and polarization as well as seasonally. For example, higher radar frequencies respond to smaller-scale surface features, while lower radar frequencies penetrate further into the ice with resulting volume scattering. The high-resolution imagery from synthetic aperture radars (SAR), mounted on aircraft, shuttle, or satellite platforms, is very effective for many sea-ice studies, including the separation of ice types. An aircraft-mounted X-band (9 GHz) SAR, for example, can discriminate smooth first-year ice, rough first-year ice, multi-year ice, and open water by the intensity (tone) of the radar returns and floe geometry. The preferred SARs to date for satellites and shuttle platforms have been L-band (1–2 GHz) systems. SAR imagery of sea ice was extensively acquired by Seasat in 1978 over the Beaufort Sea, with limited quantities obtained by the Shuttle Imaging Radar (SIR-B) over the Weddell Sea in 1984. While L-band SAR can discriminate rough and smooth ice along with roughened open water based on image intensity and floe geometry, the returns from thick first-year ice and multi-year ice are not clearly distinguishable. The fact that there is volume scattering from multi-year ice suggests that there may be textural or spatial frequency variations that could be used to separate these two major ice types in radar imagery. In order to investigate the separation of sea-ice types in the large amount of L-band SAR imagery available, image-analysis techniques including filtering and classification programs have been utilized, pointing towards an automatic classification algorithm for use in future SAR sea-ice data sets, especially from space. An important characteristic of all SAR imagery is the presence of image speckle, a coherent form of noise caused by the random variability of scatterers across even a uniform surface. Most SAR processors reduce this effect by averaging multiple independent samples but this is done at the cost of reducing resolution. Speckle reduction can also be accomplished by filtering. Several filters have been tested including median, box, and adaptive edge filters. Each filter has different characteristics in terms of smoothing speckle and in the response to sharp gradients or edges, such as ridge or lead openings, as well as computational requirements. Optimization of each filter’s parameters has been determined by the quality of classification of each ice type. The classification programs that have been tested are based on tone and texture image characteristics. The programs are supervised; that is, a small training area for each class is pre-selected for statistical analysis. From these statistics, the remainder of the imagery is subjected to the particular classification algorithm. The tone program separates classes based on the mean, standard deviation, and number of standard deviations of each class, and includes a Bayesian maximum-likelihood classifier for ambiguous elements. The texture program determines the statistical homogeneity of each class and the optimal segmentation of each small area into the various classes.

scholarly journals Comparison of Sea-ice Type Identification Between Airborne Dual Frequency Passive Microwave Radiometry and Standard Laser/Infrared Techniques

1975 ◽  
Vol 15 (73) ◽  
pp. 225-239
Author(s):  
S. G. Tooma ◽  
R. A. Mennella ◽  
J. P. Hollinger ◽  
R. D. Ketchum
Keyword(s):  
Sea Ice ◽  
Ground Truth ◽  
Open Water ◽  
Weather Conditions ◽  
Passive Microwave ◽  
Single Frequency ◽  
Naval Research ◽  
First Year ◽  
Dual Frequency ◽  
Brightness Temperatures

AbstractDuring December 1973, the Naval Oceanographie Offirc (NAVOCKANO) and the Naval Research Laboratory (NRL) conducted a joint remote-sensing experiment over the sea-ice fields off Scoresby Sound on the east coast of Greenland using NAVOCEANO’s RP3-A Birdseye aircraft, laser profiler, and infrared scanner, and NRL’s 19.34 and 31.0 GHz nadir-looking radiometers. The objectives of this mission were: (1) to develop skills for interpreting sea-ice passive microwave data. (2) to expand, if possible, the two-category capability (multi-year ice and first-year ice) of passive microwave sensors over sea ice, (3) to compare two frequencies (19 and 31 GHz) to determine which may be more useful in a scanning radiometer now under development at NRL, and (4) to determine the value of multi-frequency as compared to single-frequency study of sea ice.Since, because of darkness and remoteness, no photography or in situ ground truth were possible for this mission, it was necessary to rely on the interpretations of the laser and infrared (IR) data to evaluate the performance of the microwave radiometers. Fortunately, excellent laser and IR data were collected, and a confident description of the ice overflown was possible.Five ice conditions: (1) open water/new ice, (2) smooth first-year ice, (3) ridged first-year ice, (4) multi-year ice, and (5) a higher brightness temperature form of multi-year ice interpreted as second-year ice were identifiable, regardless of weather conditions, by comparing the average of the two microwave brightness temperatures at the two frequencies with their difference.

Comparison of Sea-ice Type Identification Between Airborne Dual Frequency Passive Microwave Radiometry and Standard Laser/Infrared Techniques

1975 ◽  
Vol 15 (73) ◽  
pp. 225-239 ◽  
Author(s):  
S. G. Tooma ◽  
R. A. Mennella ◽  
J. P. Hollinger ◽  
R. D. Ketchum
Keyword(s):  
Sea Ice ◽  
Ground Truth ◽  
Open Water ◽  
Weather Conditions ◽  
Passive Microwave ◽  
Single Frequency ◽  
Naval Research ◽  
First Year ◽  
Dual Frequency ◽  
Brightness Temperatures

Abstract During December 1973, the Naval Oceanographie Offirc (NAVOCKANO) and the Naval Research Laboratory (NRL) conducted a joint remote-sensing experiment over the sea-ice fields off Scoresby Sound on the east coast of Greenland using NAVOCEANO’s RP3-A Birdseye aircraft, laser profiler, and infrared scanner, and NRL’s 19.34 and 31.0 GHz nadir-looking radiometers. The objectives of this mission were: (1) to develop skills for interpreting sea-ice passive microwave data. (2) to expand, if possible, the two-category capability (multi-year ice and first-year ice) of passive microwave sensors over sea ice, (3) to compare two frequencies (19 and 31 GHz) to determine which may be more useful in a scanning radiometer now under development at NRL, and (4) to determine the value of multi-frequency as compared to single-frequency study of sea ice. Since, because of darkness and remoteness, no photography or in situ ground truth were possible for this mission, it was necessary to rely on the interpretations of the laser and infrared (IR) data to evaluate the performance of the microwave radiometers. Fortunately, excellent laser and IR data were collected, and a confident description of the ice overflown was possible. Five ice conditions: (1) open water/new ice, (2) smooth first-year ice, (3) ridged first-year ice, (4) multi-year ice, and (5) a higher brightness temperature form of multi-year ice interpreted as second-year ice were identifiable, regardless of weather conditions, by comparing the average of the two microwave brightness temperatures at the two frequencies with their difference.

scholarly journals Estimation of sea-ice physical parameters using polarimetric SAR: results from Okhotsk and Lake Saroma campaign

2001 ◽  
Vol 33 ◽  
pp. 120-124 ◽  
Author(s):  
Hiroyuki Wakabayashi ◽  
Takeshi Matsuoka ◽  
Kazuki Nakamura ◽  
Fumihiko Nishio
Keyword(s):  
Sea Ice ◽  
Correlation Coefficient ◽  
Ground Truth ◽  
Open Water ◽  
Physical Parameters ◽  
Dual Frequency ◽  
Ground Truth Data ◽  
National Space ◽  
Airborne Sar ◽  
Interferometric Sar

AbstractWe have acquired ground-truth data at Lake Saroma, northeast Hokkaido, Japan, and the surrounding area since 1993 in order to collect data on regional sea ice in the Sea of Okhotsk. The data were acquired in 1999 by polarimetric and interferometric SAR (Pi-SAR), the dual-frequency, fully polarimetric airborne SAR system jointly developed by the National Space Development Agency of Japan (NASDA) and the Communications Research Laboratory (CRL), simultaneously with ground experiments. This paper describes the results of polarimetric data analysis of typical sea ice observed in the offshore region near Lake Saroma. The polarimetric parameters used were correlation coefficient and phase difference. Based on the analysis of these parameters, we found that the correlation coefficient between RR and LL polarizations can discriminate four categories including three types of ice and open water.

scholarly journals Winter Sea-ice mapping from multi-parameter synthetic-aperture radar data

1994 ◽  
Vol 40 (134) ◽  
pp. 31-45 ◽  
Author(s):  
Eric Rignot ◽  
Mark R. Drinkwater
Keyword(s):  
Sea Ice ◽  
Classification Accuracy ◽  
Open Water ◽  
Radar Data ◽  
Single Frequency ◽  
First Year ◽  
Synthetic Aperture Radar Data ◽  
Ice Conditions ◽  
L Band ◽  
Single Polarization

AbstractThe limitations of current and immediate future single-frequency, single-polarization, space-borne SARs for winter sea-ice mapping are quantitatively examined, and improvements are suggested by combining frequencies and polarizations. Ice-type maps are generated using multi-channel, air-borne SAR observations of winter sea ice in the Beaufort Sea to identify six ice conditions: (1) multi-year sea ice; (2) compressed first-year ice; (3) first-year rubble and ridges; (4) first-year rough ice; (5) first-year smooth ice; and (6) first-year thin ice. At a single polarization, C- (λ = 5.6 cm) and L- (λ = 24 cm) band frequencies yield a classification accuracy of 67 and 71%, because C-band confuses multi-year ice and compressed, rough, thick first-year ice surrounding multi-year ice floes, and L-band confuses multi-year ice and deformed first-year ice. Combining C- and L-band improves classification accuracy by 20%. Adding a second polarization at one frequency only improves classification accuracy by 10–14% and separates thin ice and calm open water. Under similar winter-ice conditions, ERS-1 (Cvv) and Radarsat (CHH) would overestimate the multi-year ice fraction by 15% but correctly map the spatial variability of ice thickness; J-ERS-1 (LHH) would perform poorly;and J-ERS-1 combined with ERS-1 or Radarsat would yield reliable estimates of the old, thick, first-year and thin-ice fractions, and of the spatial distribution of ridges. With two polarizations, future single-frequency space-borne SARs could improve our current capability to discriminate thinner ice types.

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