scholarly journals A New Method of Satellite Radar Altimeter Waveform Retracking Based on Waveform Derivative

2020 ◽  
Vol 36 ◽  
Author(s):  
Z. Li ◽  
X. Liu ◽  
G. Jinyun ◽  
J. Yuan ◽  
Y. Niu ◽  
...  
Keyword(s):  
New Method ◽  
Radar Altimeter ◽  
Waveform Retracking ◽  
Satellite Radar

scholarly journals Seasonal variation in the apparent height of the East Antarctic ice sheet

1997 ◽  
Vol 24 ◽  
pp. 191-198 ◽  
Author(s):  
D. Yi ◽  
C. R. Bentley ◽  
M. D. Stenoien
Keyword(s):  
Seasonal Variation ◽  
Accumulation Rate ◽  
Surface Elevation ◽  
Secular Change ◽  
Radar Signal ◽  
Real Surface ◽  
Radar Altimeter ◽  
Depth Of Penetration ◽  
Orbit Error ◽  
Satellite Radar

A satellite radar altimeter can be used to monitor surface elevation change over polar ice sheets. Thirty-five months of Geosat Exact Repeat Mission (ERM) data from November 1986 to September 1989 over a section of East Antarctica (69–72.1 ∘S, 80–140∘ E) have been used in this study. A model that considers both surface and volume scattering was used to retrack the altimeter waveforms. Surface elevations for each month after the first three were compared to the average elevations for the first 3 months through a crossover method. The averaged crossover elevation difference changed with time in a way that suggests a yearly cycle in surface elevation. The average amplitude of the cycle is about 0.6 m. We have been unable to find any satisfactory explanation for the observed changes, in terms of either sources of error or contributors to real surface-height changes. We strongly suspect that orbit error plays a major role in producing the variations, although we know of no quantitatively satisfactory source of a quasi-seasonal variation in orbit error. Other possible contributors include a real seasonal variation in accumulation rate, seasonal changes in the delay of the radar signal as it propagates through the atmosphere, unmodeled variations in the depth of penetration of the radar pulse into the firn, changes in the thickness of the ice and the firn zone in response to seasonal variations in pressure and temperature, and the inverted barometer effect. Even though we do not know the cause of the variations, the results show the importance of comparing elevations at the same time of year for observations that are not continuous, while at the same time showing that even annually spaced measurements may not be free of substantial errors associated with interannual variability. The quasi-periodic variations obscure any evidence of a moderate secular change in surface height, if there is one, but a dramatic lowering at rates approaching 1 ma–1, such as are known elsewhere in Antarctica, can definitely be ruled out.

scholarly journals Using the temporal variability of satellite radar altimetric observations to map surface properties of the Antarctic ice sheet

1998 ◽  
Vol 44 (147) ◽  
pp. 197-206 ◽  
Author(s):  
Benoît Legrésy ◽  
Frédérique Rémy
Keyword(s):  
Ice Sheet ◽  
Temporal Variations ◽  
Radar Altimeter ◽  
Height Measurement ◽  
Radar Echoes ◽  
Measuring Surface ◽  
Antarctic Continent ◽  
Ice Sheet Mass Balance ◽  
Satellite Radar ◽  
The Antarctic

AbstractThe problem of measuring surface height and snowpack characteristics from satellite radar altimeter echoes is investigated. In this paper, we perform an analysis of the ERS1 altimeter dataset acquired during a 3 day repeat orbit. The analysis reveals that there are temporal variations in shapes of the radar altimeter echo and that these variations are linked to meteorological phenomena. The time- and space-scales over which these variations apply are a few to tens of days and a few hundred kilometres, respectively. This phenomenon, if not accounted for, can create error in the height measurement. A numerical echo model is used to recover snowpack characteristics by taking advantage of the temporal variations of the radar echoes. A map of penetration depth of the radar waves in the Ku band over the Antarctic continent is obtained and suggests that grain-size produces the dominant effect on radar extinction in the snowpack at this frequency. Finally, a procedure is proposed to correct the height measurement within the context of ice-sheet mass-balance survey.

scholarly journals Geostatistical methods for mapping Antarctic ice surfaces at continental and regional scales

2000 ◽  
Vol 30 ◽  
pp. 76-82 ◽  
Author(s):  
Ute Christina Herzfeld ◽  
Ralf Stosius ◽  
Marcus Schneider
Keyword(s):  
Surface Elevation ◽  
Altimeter Data ◽  
Radar Altimeter ◽  
Sea Level Changes ◽  
Ice Streams ◽  
Geostatistical Methods ◽  
Ice Surface ◽  
Geophysical Study ◽  
Satellite Radar ◽  
The Antarctic

AbstractThe Antarctic ice sheet plays a major role in the global system and the large ice streams discharging into the circumpolar sea represent its gateways to the world’s oceans. Satellite radar-altimeter data provide an opportunity for mapping surface elevation at kilometer resolution with meter accuracy. Geostatistical methods have been developed to accomplish this. We distinguish two goals in mapping the Antarctic ice surface: (a) construction of a continent-wide atlas of maps and digital terrain models, and (b) calculation of maps and models suitable for the study of individual glaciers, ice streams and ice shelves. The atlases consist of accurate maps of ice-surface elevation compiled from Seasat, Geosat and ERS-1 altimeter data, covering all of Antarctica surveyed by Geosat (to 72.1° S) and by ERS-1 (to 81.5° S). With a 3 km grid they are the highest-resolution maps available today with continent-wide coverage. The resolution permits geophysical study and facilitates monitoring of changes in ice-surface elevation and changes in flux across the ice-ocean boundary, which is essential for monitoring sea-level changes.

scholarly journals Modeling the signature of a transponder in altimeter return data and determination of the reflection surface of the ice cap near the GRIP camp, Greenland

1998 ◽  
Vol 44 (148) ◽  
pp. 625-633
Author(s):  
G. Haardenog-Pedersen ◽  
K. Keller ◽  
C. C. Tscherning ◽  
N. Gundestrup
Keyword(s):  
Global Positioning System ◽  
Propagation Delay ◽  
Radar Altimeter ◽  
Reflection Point ◽  
Ice Cap ◽  
Global Positioning ◽  
Satellite Radar ◽  
The Difference ◽  
Satellite Radar Altimetry

AbstractUsing an active transponder with the ERS-I and ERS-2 radar altimeters, the distance to the satellite was measured at a location close to the GRIP site, Greenland, at an altitude of 3.2 km. The measurement was executed while the transponder was in the “ice-tracking mode”. It includes a bias due to the propagation delay. The location of the transponder was determined using the global positioning system.The transponder signal was modeled and the distance from the altimeter to the effective reflection point of the transponder was determined. Since the transponder was located within 1 km of the ground tracks, the measurement was corrected for this offset. A correction was also done for the surface slope, resulting in the distance (plus bias) to the closest sub-satellite point on the surface of the (compact) snow.The transponder signal was then removed from the radar altimeter waveform, enabling the determination of the distance (plus bias from the altimeter to the first reflective surface within the snow. The différence between this distance and that obtained using the transponder was < 2 m. This shows that the surface which gives rise to the first return of the reflection agrees with the surface of the (compact, dry) snow at this high-altitude location. This is an important result to be used when studying ice-cap topography using satellite radar altimetry.

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