KU-Band radar altimeter for surface elevation measurements in polar regions using a wideband chirp generator with improved linearity

2012 ◽  
Author(s):  
D. Gomez-Garcia ◽  
F. Rodriguez-Morales ◽  
C. Leuschen ◽  
S. Gogineni
Keyword(s):  
Surface Elevation ◽  
Polar Regions ◽  
Radar Altimeter ◽  
Ku Band

scholarly journals Seasonal variations of the backscattering coefficient measured by radar altimeters over the Antarctica Ice Sheet

2017 ◽  
Author(s):  
Fifi I. Adodo ◽  
Frédérique Remy ◽  
Ghislain Picard
Keyword(s):  
Seasonal Variations ◽  
Seasonal Cycle ◽  
Ice Sheet ◽  
Sensitivity Study ◽  
Surface Elevation ◽  
Radar Altimeter ◽  
Backscattering Coefficient ◽  
Electromagnetic Model ◽  
Snow Temperature ◽  
Ku Band

Abstract. Spaceborne radar altimeter is a valuable tool for observing the Antarctica Ice Sheet. The radar wave penetration into the snow provides information both on the surface and the subsurface of the snowpack due to its dependence on the snow properties. However this penetration also induces a negative bias on the estimated surface elevation. Empirical corrections of this space and time-varying bias are usually based on the backscattering coefficient variability. We investigate the spatial and seasonal variations of the backscattering coefficient at the S (3.2 GHz), Ku (13.6 GHz) and Ka (37 GHz) bands. We identified two clearly marked zones over the continent, one with the maximum of Ku band backscattering coefficient in the winter and another with the maximum in the summer. To explain this, we performed a sensitivity study of the backscattering coefficient at the S, Ku and Ka bands to surface snow density, snow temperature and snow grain size using an electromagnetic model. The results show that the seasonal cycle of the backscattering coefficient at the Ka band, is dominated by the volume echo and is mainly explained by snow temperature. In contrast, the cycle is dominated by the surface echo at the S band. At Ku band, which intermediate in terms of wavelength between S and Ka bands, the seasonal cycle is in the first zone dominated by the volume echo and by the surface echo in the second one. Such seasonal and spatial variations of the backscattering coefficient at different radar frequencies should be taken into account the for more precise estimation of the surface elevation changes.

First results from the e Copernicus Sentinel-6 satellite mission 

2021 ◽  
Author(s):  
Craig Donlon ◽  
Robert Cullen ◽  
Luisella Giulicchi ◽  
Marco Fonari
Keyword(s):  
Sea Level ◽  
Microwave Radiometer ◽  
Precise Orbit Determination ◽  
Well Being ◽  
The European Union ◽  
Radar Altimeter ◽  
Satellite Mission ◽  
International Partnership ◽  
Satellite Missions ◽  
Ku Band

<p>The threat of sea level rise to coastal communities is an area of significant concern to the well-being and security of future generations. Environmental policy actions and decisions affecting coastal states are being made now.  Given the considerable range of applications, sustained altimetry satellite missions are required to address operational, science and societal needs. This article describes the Copernicus Sentinel-6 mission that is designed to address the needs of the European Copernicus programme for precision sea level, near-real-time measurements of sea surface height, significant wave height, and other products tailored to operational services in the climate, ocean, meteorology and hydrology domains. It is designed to provide enhanced continuity to the very stable time series of mean sea level measurements and ocean sea state started in 1992 by the TOPEX/Poseidon (T/P) mission and follow-on Jason-1, Jason-2 and Jason-3 satellite missions. The mission is implemented through a unique international partnership with contributions from NASA, NOAA, ESA, EUMETSAT, and the European Union (EU).  It includes two satellites that will fly sequentially (separated in time by 5 years). The first satellite, named Sentinel-6 Michael Freilich, launched from Vandenburg Air Force Base, USA on 21<sup>st</sup> November 2020. The main payload is the Poseidon-4 dual frequency (C/Ku-band) nadir-pointing radar altimeter providing synthetic aperture radar (SAR) processing in Ku-band to improve the signal through better along-track sampling and reduced measurement noise. The altimeter has an innovative interleaved mode enabling radar data processing on two parallel chains, one with the SAR enhancements and the other furnishing a "Low Resolution Mode" that is fully backward-compatible with the historical T/P and Jason measurements, so that complete inter-calibration between the state-of-the-art data and the historical record can be assured. A three-channel Advanced Microwave Radiometer for Climate (AMR-C) developed by NASA JPL provides measurements of atmospheric water vapour that would otherwise degrade the radar altimeter measurements. An experimental High Resolution Microwave Radiometer (HRMR) is also included in the AMR-C design to support improved performance in coastal areas. Additional sensors are included in the payload to provide Precise Orbit Determination, atmospheric sounding via GNSS-Radio Occultation and radiation monitoring around the spacecraft.</p><p>Early in-orbit performance data are presented.</p>

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 CryoSat-2 delivers monthly and inter-annual surface elevation change for Arctic ice caps

2015 ◽  
Vol 9 (3) ◽  
pp. 2821-2865 ◽  
Author(s):  
L. Gray ◽  
D. Burgess ◽  
L. Copland ◽  
M. N. Demuth ◽  
T. Dunse ◽  
...  
Keyword(s):  
Snow Accumulation ◽  
Surface Elevation ◽  
Radar Altimeter ◽  
Elevation Change ◽  
Ice Caps ◽  
Ice Cap ◽  
Winter Snow ◽  
Surface Elevation Change ◽  
Devon Ice Cap ◽  
Arctic Ice

Abstract. We show that the CryoSat-2 radar altimeter can provide useful estimates of surface elevation change on a variety of Arctic ice caps, on both monthly and yearly time scales. Changing conditions, however, can lead to a varying bias between the elevation estimated from the radar altimeter and the physical surface due to changes in the contribution of subsurface to surface backscatter. Under melting conditions the radar returns are predominantly from the surface so that if surface melt is extensive across the ice cap estimates of summer elevation loss can be made with the frequent coverage provided by CryoSat-2. For example, the average summer elevation decreases on the Barnes Ice Cap, Baffin Island, Canada were 2.05 ± 0.36 m (2011), 2.55 ± 0.32 m (2012), 1.38 ± 0.40 m (2013) and 1.44 ± 0.37 m (2014), losses which were not balanced by the winter snow accumulation. As winter-to-winter conditions were similar, the net elevation losses were 1.0 ± 0.2 m (winter 2010/2011 to winter 2011/2012), 1.39 ± 0.2 m (2011/2012 to 2012/2013) and 0.36 ± 0.2 m (2012/2013 to 2013/2014); for a total surface elevation loss of 2.75 ± 0.2 m over this 3 year period. In contrast, the uncertainty in height change results from Devon Ice Cap, Canada, and Austfonna, Svalbard, can be up to twice as large because of the presence of firn and the possibility of a varying bias between the true surface and the detected elevation due to changing year-to-year conditions. Nevertheless, the surface elevation change estimates from CryoSat for both ice caps are consistent with field and meteorological measurements. For example, the average 3 year elevation difference for footprints within 100 m of a repeated surface GPS track on Austfonna differed from the GPS change by 0.18 m.

scholarly journals The European Space Agency’s Earth Explorer Mission CryoSat: measuring variability in the cryosphere

2004 ◽  
Vol 39 ◽  
pp. 313-320 ◽  
Author(s):  
Mark R. Drinkwater ◽  
Richard Francis ◽  
Guy Ratier ◽  
Duncan J. Wingham
Keyword(s):  
European Space Agency ◽  
Ice Sheets ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Radar Altimeter ◽  
Operating Characteristics ◽  
Space Agency ◽  
Explorer Mission ◽  
Arctic Sea ◽  
Ku Band

AbstractCryoSat is currently being prepared for a 2005 launch as the first European Space Agency Earth Explorer Opportunity mission. It is a dedicated cryospheric mission equipped with a Ku-band SIRAL (SAR/Interferometric Radar ALtimeter), whose primary objectives are to measure the variability and trends in the mass of the Arctic sea-ice cover and large terrestrial ice sheets. In this paper, an overview is provided of the mission and of the measurement characteristics of the new SIRAL instrument. Examples of data acquired on recent preparatory campaigns are presented, illustrating the operating characteristics of the key SIRAL modes. Preparatory plans for calibration and validation of CryoSat data are described.

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 Seasonal variations of the backscattering coefficient measured by radar altimeters over the Antarctic Ice Sheet

2018 ◽  
Vol 12 (5) ◽  
pp. 1767-1778 ◽  
Author(s):  
Fifi Ibrahime Adodo ◽  
Frédérique Remy ◽  
Ghislain Picard
Keyword(s):  
Seasonal Variations ◽  
Seasonal Cycle ◽  
Ice Sheet ◽  
Surface Elevation ◽  
Backscattering Coefficient ◽  
Antarctic Ice Sheet ◽  
Radar Wave ◽  
The Antarctic ◽  
Snow Temperature ◽  
Ku Band

Abstract. Spaceborne radar altimeters are a valuable tool for observing the Antarctic Ice Sheet. The radar wave interaction with the snow provides information on both the surface and the subsurface of the snowpack due to its dependence on the snow properties. However, the penetration of the radar wave within the snowpack also induces a negative bias on the estimated surface elevation. Empirical corrections of this space- and time-varying bias are usually based on the backscattering coefficient variability. We investigate the spatial and seasonal variations of the backscattering coefficient at the S (3.2 GHz ∼ 9.4 cm), Ku (13.6 GHz ∼ 2.3 cm) and Ka (37 GHz ∼ 0.8 cm) bands. We identified that the backscattering coefficient at Ku band reaches a maximum in winter in part of the continent (Region 1) and in the summer in the remaining (Region 2), while the evolution at other frequencies is relatively uniform over the whole continent. To explain this contrasting behavior between frequencies and between regions, we studied the sensitivity of the backscattering coefficient at three frequencies to several parameters (surface snow density, snow temperature and snow grain size) using an electromagnetic model. The results show that the seasonal cycle of the backscattering coefficient at Ka frequency is dominated by the volume echo and is mainly driven by snow temperature evolution everywhere. In contrast, at S band, the cycle is dominated by the surface echo. At Ku band, the seasonal cycle is dominated by the volume echo in Region 1 and by the surface echo in Region 2. This investigation provides new information on the seasonal dynamics of the Antarctic Ice Sheet surface and provides new clues to build more accurate corrections of the radar altimeter surface elevation signal in the future.

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.

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