scholarly journals A Multi-Sensor Approach to the Interpretation of Radar Altimeter Wave Forms from Two Arctic Ice Caps

1987 ◽  
Vol 9 ◽  
pp. 60-68 ◽  
Author(s):  
Mark R. Drinkwater ◽  
Julian A. Dowdeswell
Keyword(s):  
Surface Roughness ◽  
Leading Edge ◽  
High Amplitude ◽  
Wave Form ◽  
Radar Altimeter ◽  
Ice Caps ◽  
Lower Amplitude ◽  
Wet Snow ◽  
Radio Echo Sounding ◽  
Wave Forms

Data collected over Svalbard on 28 June 1984 by a 13.81 GHz airborne radar altimeter enabled analysis of signals returned from two relatively large ice masses. Wave forms received over the ice caps of Austfonna and Vestfonna are analysed with the aid of existing aerial photography, radio echo-sounding data, and Landsat MSS images acquired close to the date of the altimeter flight. Results indicate that altimeter wave forms are controlled mainly by surface roughness and scattering characteristics. Wet snow surfaces have narrow 3 dB back-scatter half-angles and cause high-amplitude signals, in contrast to relatively dry snow surfaces with lower-amplitude diffuse signals. Metre-scale surface roughness primarily affects wave-form amplitude and leading-edge slope, this becoming apparent over ice streams on Vestfonna.

scholarly journals A Multi-Sensor Approach to the Interpretation of Radar Altimeter Wave Forms from Two Arctic Ice Caps

1987 ◽  
Vol 9 ◽  
pp. 60-68 ◽  
Author(s):  
Mark R. Drinkwater ◽  
Julian A. Dowdeswell
Keyword(s):  
Surface Roughness ◽  
Leading Edge ◽  
High Amplitude ◽  
Wave Form ◽  
Radar Altimeter ◽  
Ice Caps ◽  
Lower Amplitude ◽  
Wet Snow ◽  
Radio Echo Sounding ◽  
Wave Forms

Data collected over Svalbard on 28 June 1984 by a 13.81 GHz airborne radar altimeter enabled analysis of signals returned from two relatively large ice masses. Wave forms received over the ice caps of Austfonna and Vestfonna are analysed with the aid of existing aerial photography, radio echo-sounding data, and Landsat MSS images acquired close to the date of the altimeter flight. Results indicate that altimeter wave forms are controlled mainly by surface roughness and scattering characteristics. Wet snow surfaces have narrow 3 dB back-scatter half-angles and cause high-amplitude signals, in contrast to relatively dry snow surfaces with lower-amplitude diffuse signals. Metre-scale surface roughness primarily affects wave-form amplitude and leading-edge slope, this becoming apparent over ice streams on Vestfonna.

scholarly journals A Multi-Sensor Approach to the Interpretation of Radar Altimeter Wave Forms from Two Arctic Ice Caps

1987 ◽  
Vol 9 ◽  
pp. 60-68 ◽  
Author(s):  
Mark R. Drinkwater ◽  
Julian A. Dowdeswell
Keyword(s):  
Surface Roughness ◽  
Leading Edge ◽  
High Amplitude ◽  
Wave Form ◽  
Radar Altimeter ◽  
Ice Caps ◽  
Lower Amplitude ◽  
Wet Snow ◽  
Radio Echo Sounding ◽  
Wave Forms

Data collected over Svalbard on 28 June 1984 by a 13.81 GHz airborne radar altimeter enabled analysis of signals returned from two relatively large ice masses. Wave forms received over the ice caps of Austfonna and Vestfonna are analysed with the aid of existing aerial photography, radio echo-sounding data, and Landsat MSS images acquired close to the date of the altimeter flight. Results indicate that altimeter wave forms are controlled mainly by surface roughness and scattering characteristics. Wet snow surfaces have narrow 3 dB back-scatter half-angles and cause high-amplitude signals, in contrast to relatively dry snow surfaces with lower-amplitude diffuse signals. Metre-scale surface roughness primarily affects wave-form amplitude and leading-edge slope, this becoming apparent over ice streams on Vestfonna.

scholarly journals Analysis of Simulated Radar Altimetric Wave Forms for Polar Ice and Snow Surfaces (Abstract)

1987 ◽  
Vol 9 ◽  
pp. 241-241
Author(s):  
Eva Novotny
Keyword(s):  
Sea Ice ◽  
Leading Edge ◽  
Wave Form ◽  
Polar Regions ◽  
Radar Altimeter ◽  
Single Wave ◽  
Height Determination ◽  
Wave Forms ◽  
Imaging Instrument ◽  
Ice Floes

The radar altimeter of the satellite Seasat has proved that ice and snow surfaces in the polar regions can return meaningful signals if the terrain is not excessively rugged or sloping. Because the use of the leading edge of the wave forms for height determination entails inherent uncertainties and, at best, provides only a single datum per wave form, the entire wave forms should be studied. Excesses or deficiencies in amplitude at various ranges within a single wave form, and the changes that occur in successive wave forms, can be analysed to yield information on the geometric and scattering properties of features observed by the altimeter.Results from computer simulations are presented, showing how (1) a margin of sea ice (sinusoidal in the model) can be mapped, (2) the boundaries of two isolated ice floes can be outlined, (3) sea-ice concentrations can be derived within annuli about the nadir of an individual footprint, and (4) for land ice, the elevations of topographic features, together with the general slope of the ground, can be determined if an imaging instrument that operates simultaneously with the altimeter provides the outlines of these features. In examples (1) and (2), it is assumed that the ice is contiguous wherever that is possible, to permit the analytical reconstruction of the ice margin or individual ice floes in the presence of the inevitable ambiguity in the position of any feature with respect to the two sides of the satellite track. Example (4) requires that the altimeter record correctly records the strongest signals returned by ice-packs. This condition is not fulfilled by any existing radar altimeter, but it may be achieved in the next generation of these instruments. In additional examples of information from entire wave forms, the effects of crevasses and sastrugi in reducing or re-distributing the energy of the returned signals are also illustrated.Full details of these analyses and results will be published at a later date.

scholarly journals Analysis of Simulated Radar Altimetric Wave Forms for Polar Ice and Snow Surfaces (Abstract)

1987 ◽  
Vol 9 ◽  
pp. 241
Author(s):  
Eva Novotny
Keyword(s):  
Sea Ice ◽  
Leading Edge ◽  
Wave Form ◽  
Polar Regions ◽  
Radar Altimeter ◽  
Single Wave ◽  
Height Determination ◽  
Wave Forms ◽  
Imaging Instrument ◽  
Ice Floes

The radar altimeter of the satellite Seasat has proved that ice and snow surfaces in the polar regions can return meaningful signals if the terrain is not excessively rugged or sloping. Because the use of the leading edge of the wave forms for height determination entails inherent uncertainties and, at best, provides only a single datum per wave form, the entire wave forms should be studied. Excesses or deficiencies in amplitude at various ranges within a single wave form, and the changes that occur in successive wave forms, can be analysed to yield information on the geometric and scattering properties of features observed by the altimeter. Results from computer simulations are presented, showing how (1) a margin of sea ice (sinusoidal in the model) can be mapped, (2) the boundaries of two isolated ice floes can be outlined, (3) sea-ice concentrations can be derived within annuli about the nadir of an individual footprint, and (4) for land ice, the elevations of topographic features, together with the general slope of the ground, can be determined if an imaging instrument that operates simultaneously with the altimeter provides the outlines of these features. In examples (1) and (2), it is assumed that the ice is contiguous wherever that is possible, to permit the analytical reconstruction of the ice margin or individual ice floes in the presence of the inevitable ambiguity in the position of any feature with respect to the two sides of the satellite track. Example (4) requires that the altimeter record correctly records the strongest signals returned by ice-packs. This condition is not fulfilled by any existing radar altimeter, but it may be achieved in the next generation of these instruments. In additional examples of information from entire wave forms, the effects of crevasses and sastrugi in reducing or re-distributing the energy of the returned signals are also illustrated. Full details of these analyses and results will be published at a later date.

scholarly journals Using airborne Ku-band altimeter waveforms to investigate winter accumulation and glacier facies on Austfonna, Svalbard

2013 ◽  
Vol 59 (217) ◽  
pp. 893-899 ◽  
Author(s):  
Robert L. Hawley ◽  
Ola Brandt ◽  
Thorben Dunse ◽  
Jon Ove Hagen ◽  
Veit Helm ◽  
...  
Keyword(s):  
Snow Depth ◽  
European Space Agency ◽  
Synthetic Aperture Radar Image ◽  
Altimeter Data ◽  
Radar Altimeter ◽  
Ice Caps ◽  
Ice Cap ◽  
Space Agency ◽  
Wet Snow ◽  
Airborne Sar

AbstractWinter balance is an important metric for assessing the change on glaciers and ice caps, yet measuring it using ground-based techniques can be challenging. We use the European Space Agency prototype Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) to extract snow depths from the received altimeter waveforms over Austfonna ice cap, Svalbard. Additionally, we attempt to distinguish the long-term firn area from other glacier facies. We validate our results using snow depth and glacier facies characterizations determined from ground-based radar profiles, snow pits and a multi-look satellite synthetic aperture radar image. We show that the depth of the winter snowpack can be extracted from the altimeter data over most of the accumulation zone, comprising wet snow zone and a superimposed ice zone. The method struggles at lower elevations where internal reflections within the winter snowpack are strong and the winter snow depth is less than ∼1 m. We use the abruptness of the reflection from the last summer surface (LSS) to attempt to distinguish glacier facies. While there is a general correlation between LSS abruptness and glacier facies, we do not find a relationship that warrants a distinct classification based on ASIRAS waveforms alone.

scholarly journals Analysis of satellite-altimeter height measurements above continental ice sheets

1993 ◽  
Vol 39 (133) ◽  
pp. 591-600
Author(s):  
P. Femenias ◽  
F. Remy ◽  
R. Raizonville ◽  
J. F. Minster
Keyword(s):  
Large Scale ◽  
Ice Sheets ◽  
Leading Edge ◽  
Wave Form ◽  
Large Set ◽  
Satellite Altimeter ◽  
Wave Forms ◽  
Continental Ice Sheets ◽  
Radar Wave ◽  
Snow Temperature

AbstractIn order to estimate the accuracy of altimetric height measurements over ice sheets, an altimeter wave-form simulator has been developed, and different tracking methods have been tested. A large range of surface features, including large-scale and medium-scale features and micro-roughness have been taken into account for modeling of either surface-or volume-scattering. A large set of parameters affects the trailing edge of the radar wave form, so that re-tracking algorithms based on the detection of its leading edge provide better retrievals of the surface height than those based on the analysis of the whole wave form. A volume component is clearly present in the radar wave forms; its effect on the leading edge depends mostly on the snow grain-size (and therefore on the snow temperature) and on the pointing angle. However, on average, the induced error on the snow-surface height estimation should only be around 25 cm.

scholarly journals Analysis of satellite-altimeter height measurements above continental ice sheets

1993 ◽  
Vol 39 (133) ◽  
pp. 591-600 ◽  
Author(s):  
P. Femenias ◽  
F. Remy ◽  
R. Raizonville ◽  
J. F. Minster
Keyword(s):  
Large Scale ◽  
Ice Sheets ◽  
Leading Edge ◽  
Wave Form ◽  
Large Set ◽  
Satellite Altimeter ◽  
Wave Forms ◽  
Continental Ice Sheets ◽  
Radar Wave ◽  
Snow Temperature

AbstractIn order to estimate the accuracy of altimetric height measurements over ice sheets, an altimeter wave-form simulator has been developed, and different tracking methods have been tested. A large range of surface features, including large-scale and medium-scale features and micro-roughness have been taken into account for modeling of either surface-or volume-scattering. A large set of parameters affects the trailing edge of the radar wave form, so that re-tracking algorithms based on the detection of its leading edge provide better retrievals of the surface height than those based on the analysis of the whole wave form. A volume component is clearly present in the radar wave forms; its effect on the leading edge depends mostly on the snow grain-size (and therefore on the snow temperature) and on the pointing angle. However, on average, the induced error on the snow-surface height estimation should only be around 25 cm.

scholarly journals Satellite-Altimeter Measurements of Surface Height in Sea-Ice Areas (Abstract)

1987 ◽  
Vol 9 ◽  
pp. 240-240
Author(s):  
S.W. Laxon ◽  
C.G. Rapley
Keyword(s):  
Sea Ice ◽  
Open Ocean ◽  
Sea Surface ◽  
Wave Form ◽  
Radar Altimeter ◽  
Satellite Altimeter ◽  
Height Estimates ◽  
Wave Forms ◽  
Mean Sea Surface

The Seasat radar altimeter was designed to operate over the open ocean and encountered problems over sea ice. In particular, the on-board measurements of surface height were noisy and unreliable. As a consequence, published mean sea-surface and geoid maps based on the Seasat on-board height estimates either omit sea-ice-covered areas or include suspect data. We have identified and investigated the problems encountered by the Seasat altimeter over sea ice and have developed a technique for extracting accurate surface-height values from the sea-ice echo wave-form data. The retracking method is based upon fitting real wave forms to a library of model returns.

scholarly journals Satellite-Altimeter Measurements of Surface Height in Sea-Ice Areas (Abstract)

1987 ◽  
Vol 9 ◽  
pp. 240
Author(s):  
S.W. Laxon ◽  
C.G. Rapley
Keyword(s):  
Sea Ice ◽  
Open Ocean ◽  
Sea Surface ◽  
Wave Form ◽  
Radar Altimeter ◽  
Satellite Altimeter ◽  
Height Estimates ◽  
Wave Forms ◽  
Mean Sea Surface

The Seasat radar altimeter was designed to operate over the open ocean and encountered problems over sea ice. In particular, the on-board measurements of surface height were noisy and unreliable. As a consequence, published mean sea-surface and geoid maps based on the Seasat on-board height estimates either omit sea-ice-covered areas or include suspect data. We have identified and investigated the problems encountered by the Seasat altimeter over sea ice and have developed a technique for extracting accurate surface-height values from the sea-ice echo wave-form data. The retracking method is based upon fitting real wave forms to a library of model returns.

scholarly journals Interpretation of Radio-Echo Returns from Internal Water Bodies in Variegated Glacier, Alaska, U.S.A.

1987 ◽  
Vol 33 (115) ◽  
pp. 319-323 ◽  
Author(s):  
Robert W. Jacobel ◽  
Stefan K. Anderson
Keyword(s):  
Spectral Analysis ◽  
Thin Layer ◽  
Computer Simulations ◽  
Simplified Model ◽  
Wave Form ◽  
Cavity Size ◽  
Additional Information ◽  
Dielectric Contrast ◽  
Radio Echo Sounding ◽  
Wave Forms

AbstractRadio echo-sounding studies were used to detect water-filled cavities on Variegated Glacier, Alaska, during its surge in 1983. Cavity locations were determined by spatial surveys, and changes in cavity size and water content over a 5 week period were inferred from phase and amplitude changes in the echo wave form. Data were taken at both 4 and 8 MHz central frequencies of the impulse transmitter. These bi-frequency results, together with spectral analysis of the digitized wave forms, were used to provide additional information about the cavity dimensions. Cavity response is interpreted in terms of a simplified model of a thin layer of strong dielectric contrast. Computer simulations of radar pulses encountering such layers reproduce the main features of the data.

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