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| Instruments / CryoSat / Observing the Earth / Our Activities / ESA |
Space in Videos - 2015 - 12 - Earth’s shifting ice
Carrying an advanced radar altimeter, CryoSat orbits Earth at just over 700 km, reaching latitudes of 88° north and south to maximise its coverage of the poles.
The radar altimeter is not only able to detect tiny variations in the height of the ice but also measure sea level with unprecedented accuracy.
As the animation shows, the mission’s measurements of sea level incidentally also map the topography of the ocean floor, revealing thousands of previously unchartered ‘seamounts’, ridges and deep ocean structures.
This animation visualises the changes the satellite has seen on Earth since its launch in 2010.
Related/Background:
- Scagliola, M.; Fornari, M.; Tagliani, N., "Pitch Estimation for CryoSat by Analysis of Stacks of Single-Look Echoes," in Geoscience and Remote Sensing Letters, IEEE , vol.12, no.7, pp.1561-1565, July 2015
doi: 10.1109/LGRS.2015.2413135
Abstract: This letter describes a novel approach to retrieve the pitch of the CryoSat satellite by the analysis of Synthetic Interferometric Radar ALtimeter (SIRAL) acquisitions in synthetic aperture radar (SAR) or SAR-interferometric mode over ocean. The power distribution of the single-look echoes, which are gathered for each sample location on the Earth surface, has been verified to be modulated by the along-track antenna pattern. Thus, the actual antenna pointing direction can be retrieved by fitting the model of the along-track antenna pattern on the power distribution of a stack, which is a collection of single-look echoes referred to the same ground location but acquired from different look angles. With the pitch measurement being independent of the attitude information returned by the onboard star trackers, by comparison of the pitch measured from data and of the pitch from the star tracker, the existence of a bias on the pitch can be verified. Exploiting the proposed approach, the pitch returned by star trackers on CryoSat has been found to be biased by about 0.0533°, confirming similar results obtained by other methods proposed in the literature. It is worth noticing that the method for pitch estimation here described is not limited to CryoSat but can be applied to any SAR altimeter without loss of generality.
keywords: {antennas;cryostats;echo;oceanographic techniques;radar altimetry;synthetic aperture radar;CryoSat satellite;SAR-interferometric mode;along-track antenna pattern;antenna pointing direction;ocean;onboard star trackers;pitch estimation;pitch measurement;power distribution;single-look echoes;stacks analysis;synthetic aperture radar;synthetic interferometric radar altimeter acquisitions;Antennas;Radar tracking;Satellites;Sea measurements;Sea surface;Synthetic aperture radar;Altimetry;CryoSat;calibration;mispointing;synthetic aperture radar (SAR)},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7080848&isnumber=7067019
Patel, A.; Paden, J.; Leuschen, C.; Kwok, R.; Gomez-Garcia, D.; Panzer, B.; Davidson, M.W.J.; Gogineni, S., "Fine-Resolution Radar Altimeter Measurements on Land and Sea Ice," in Geoscience and Remote Sensing, IEEE Transactions on , vol.53, no.5, pp.2547-2564, May 2015
doi: 10.1109/TGRS.2014.2361641
Abstract: Satellite radar altimeter (RA) measurements are important for continued monitoring of rapidly changing polar regions. In 2010, the European Space Agency launched CryoSat-2 carrying SIRAL, a Ku-band RA with objectives of determining the thickness and extent of sea ice and the topography of the ice sheets. One difficulty with Ku-band radar surveys over snow and ice is unknown penetration of RA signal into snow cover. Improving our understanding of the interactions of RA signals with snow and ice is needed to produce accurate elevation products. To this end, we developed a low-power, ultrawideband (12-18 GHz) RA for airborne surveys to provide fine resolution measurements capable of detecting both scattering from the surface and layers within sea ice and ice sheets. These measurements provide a means of identifying the dominant scattering location of lower resolution RA measurements comparable to satellite-based instruments. We generated two products: a full-bandwidth waveform (FBW) to identify scattering targets at fine resolution and a reduced-bandwidth waveform (RBW) to represent conventional RA measurements. Retrackers are used to generate height estimates over various surface conditions for comparisons. Over ice sheets, the leading-edge tracker provided consistent ice-surface elevation measurements between the FBW and RBW results; however, there were significant differences between the results from the centroid tracker. Over sea ice, the location of the dominant return between the results from snow-covered sea ice is highly variable. This paper provides an overview of RA surveys in polar regions, a description of the CReSIS system, and a discussion of the results.
keywords: {glaciology;radar altimetry;remote sensing by radar;sea ice;snow;topography (Earth);AD 2010;CReSIS system;ESA CryoSat-2;European Space Agency;SIRAL instrument;airborne surveys;fine resolution radar altimeter measurement;full bandwidth waveform;ice sheet topography;polar region monitoring;reduced bandwidth waveform;sea ice;snow;Radar;Satellites;Sea ice;Sea measurements;Sea surface;Snow;Airborne radar;frequency-modulated continuous wave (FMCW);radar altimetry review;sea ice;snow;ultrawideband radar},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6936928&isnumber=7001732
Dusseaux, R.; Afifi, S.; Dechambre, M.; Legresy, B., "Simulations of the altimetric signal intensity from 3D-layered air/snow/sea-ice rough interfaces," in General Assembly and Scientific Symposium (URSI GASS), 2014 XXXIth URSI , vol., no., pp.1-2, 16-23 Aug. 2014
doi: 10.1109/URSIGASS.2014.6929595
Abstract: Remote sensing of the sea-ice thickness is one of the main objectives of the Ku-band radar altimeter SIRAL-CRYOSAT II mission. On the one hand, sea-ice thickness is derived from the measurement of the height of the freeboard of the floes, and based on isostasy, assuming that the density of the water, the ice, as well as the snow, are known. On the other hand even if the snow load is known, the penetration of the electromagnetic waves into the snow strongly depends on the electrical and geophysical characteristics of the snow layer (density, temperature, permittivity, roughness). The remote sensing of the snow layer thickness (SLT) remains a real challenge and will be useful to correct the snow load for converting freeboard measurements from satellite altimetry into sea-ice thickness. If the dual frequency radar altimetry data show a good potential for remote sensing of snow and more generally of penetrating media [1], providing the SLT from Ku band data alone is highly motivated by the orbit of CRYOSAT designed to cover the entire Arctic. In this framework, a theoretical study, based on a 3D modelling of the scattering of electromagnetic waves by a stratified medium at normal incidence has been carried out in order to investigate and quantify the capacity of snow and ice penetration of Ku-band waves. The stratified medium is modelled as a snow layer considered as a stack of 2 sub-layers and the boundary layer at the bottom represented by a semi-infinite layer of ice-sea as shown on the figure 1. The roughness of each interface is taken into account and the small slope approximation (SSA) is used to determine the coherent and incoherent components of the scattered intensity [2-4]. It is demonstrated that the coherent intensity is the the specular direction but it depends on the rms-roughness heights and does not depends on the shape of the correlation function. The incoherent intensity depends even on the rms-roughness heights, but also on the shape of the correlati- n function. Several simulations have been conducted by varying the permittivity, thickness and roughness of each interface [5-6]. The 3 interfaces are random processes with Gaussian autocorrelation functions with zero mean values. The main conclusion is that the backscattered signal from the stratified medium is strongly related to the dielectric characteristics. It can vary significantly even if the variations of the stratified medium are small. This is an important result to be kept in mind when attempting the signal inversion. In addition, another similar study based on a 2D modelling of the scattering of electromagnetic waves by the same stratified medium at normal incidence and simulations in the same conditions have been previously conducted [7]. The roughness of each interface was also taken into account and the first-order small perturbation method (SPM) was used to determine the coherent and incoherent components of the scattered intensity. Results from those two studies are also compared at the end.
keywords: {air;electromagnetic wave scattering;geophysical signal processing;height measurement;oceanographic techniques;remote sensing;sea ice;snow;3D layered air-snow-sea ice rough interfaces;Gaussian autocorrelation function;SIRAL-CRYOSAT II mission;altimetric signal intensity;dielectric characteristics;electromagnetic waves scattering;freeboard measurements;remote sensing;sea ice thickness;signal inversion;small perturbation method;small slope approximation;water density;Electromagnetic scattering;Radar remote sensing;Remote sensing;Sea ice;Snow;Spaceborne radar},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6929595&isnumber=6928981
Fornari, M.; Scagliola, M.; Tagliani, N.; Parrinello, T.; Garcia Mondejar, A., "CryoSat: Siral calibration and performance," in Geoscience and Remote Sensing Symposium (IGARSS), 2014 IEEE International , vol., no., pp.702-705, 13-18 July 2014
doi: 10.1109/IGARSS.2014.6946520
Abstract: CryoSat's Synthetic Interferometric Radar Altimeter (SIRAL) [1] is a Ku-band pulsewidth limited radar altimeter that transmits pulses at a high pulse repetition frequency thus making the received echoes phase coherent and suitable for De-lay/Doppler processing [2]. Moreover SIRAL takes advantage of two antennas mounted across-track for interferometric capability, in order to determine the across-track direction from which the echo is received [3]. The calibration strategy for SIRAL includes both internal calibrations and external calibration [1]. Due to the fact that SIRAL is an interferometric phase coherent pulse-width limited radar altimeter, a proper calibration approach has been developed. In this paper we will describe as first the internal calibration strategy and then the different calibration corrections that are applied to science data. The internal calibration results over more than three years of mission will be presented, analysing their temporal evolution in order to highlight the stability of the instrument over its life. Finally, the external calibration measurements for SIRAL will be presented.
keywords: {Doppler effect;calibration;geophysical techniques;radar altimetry;radar cross-sections;radar interferometry;CryoSat synthetic interferometric radar altimeter;Doppler processing;Ku-band pulsewidth limited radar altimeter;SIRAL calibration;SIRAL calibration strategy;SIRAL performance;across-track direction;delay processing;external calibration;high pulse repetition frequency;interferometric capability;interferometric phase coherent pulse-width limited radar altimeter;internal calibrations;received echoes;temporal evolution;Calibration;Delays;Gain;Gain control;Instruments;Radar;Transponders;Altimetry;CryoSat;calibration},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6946520&isnumber=6946328
Villladsen, H.; Andersen, O.B.; Stenseng, L., "Annual cycle in lakes and rivers from CryoSat-2 altimetry — The Brahmaputra river," in Geoscience and Remote Sensing Symposium (IGARSS), 2014 IEEE International , vol., no., pp.894-897, 13-18 July 2014
doi: 10.1109/IGARSS.2014.6946569
Abstract: A key concern of the CryoSat-2 orbit has been its long repeat period of 369 days, which is usually undesirable for river and lake monitoring. However, the results of this study show that CryoSat-2 data can indeed be used for such monitoring by utilizing the high spatial coverage and the sub-cycle period of 30 days. The performance of CryoSat-2/SIRAL altimetry for river level monitoring is investigated by studying river levels retrieved from Ganges and Brahmaputra. An evaluation of CryoSat-2 river levels from LRM, SAR and SARIn data is performed by comparing with Envisat data from the period in which the two missions overlapped (2010-2012). Time series constructed using simple linear interpolation are fitted with a model to compare the captured annual signals and amplitudes. The annual cycles seen in CryoSat-2 and Envisat altimetry data agree very well and provide confidence in using CryoSat-2 data to continue river level archives from satellite radar altimetry.
keywords: {lakes;remote sensing by radar;rivers;AD 2010 to 2012;Brahmaputra river;CryoSAT-2 altimetry;CryoSat-2 altimetry data;CryoSat-2 data;CryoSat-2 orbit;CryoSat-2 river levels;CryoSat-2-SIRAL altimetry;Envisat altimetry data;Envisat data;LRM data;SARIn data;lake annual cycle;lake monitoring;river annual cycle;river level archives;river level monitoring;river monitoring;satellite radar altimetry;Altimetry;Lakes;Monitoring;Radar tracking;Rivers;Satellites;Time series analysis;Brahmaputra;CryoSat;Envisat;hydrology;inland waters;satellite altimetry},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6946569&isnumber=6946328
Galin, N.; Wingham, D.J.; Cullen, R.; Francis, R.; Lawrence, I., "Measuring the Pitch of CryoSat-2 Using the SAR Mode of the SIRAL Altimeter," in Geoscience and Remote Sensing Letters, IEEE , vol.11, no.8, pp.1399-1403, Aug. 2014
doi: 10.1109/LGRS.2013.2293960
Abstract: This letter describes the retrieval of the pitch of the CryoSat-2 satellite from the full bit rate (FBR) SAR mode data that are collected over the ocean by the SAR/Interferometric Radar Altimeter (SIRAL). Starting with the FBR SAR mode data, we form beams at the forward and backward look angles with respect to the nadir direction. If the satellite is flying pitched, the asymmetrical weighting of the echo power in the forward-looking and backward-looking beams that resulted from the along-track antenna gain pattern is used to measure the pitch of the satellite. The method depends on accurate knowledge of the orbit and the altimeter echoes only. In consequence, we are able to compare the results with the contemporaneous pitch value that is measured by the onboard star trackers, and particularly, we are able to determine a bias in the star tracker pitch measurements. We find that the star trackers' pitch measurements are biased, with a constant offset of 0.055 ° ± 0.0073 °. Because the star tracker attitude is used to inform the onboard control system, this bias implies that CryoSat-2 is flying nose up, with an average pitch of about 0.055 °.
keywords: {radar altimetry;radar antennas;remote sensing by radar;synthetic aperture radar;CryoSat-2 pitch;CryoSat-2 satellite;FBR SAR mode data;SAR-Interferometric Radar Altimeter;SIRAL altimeter;along-track antenna gain pattern;altimeter echoes;backward look angle;echo power asymmetrical weighting;forward look angle;full bit rate;onboard control system;star tracker pitch measurements;synthetic aperture radar;Extraterrestrial measurements;Oceans;Power distribution;Satellites;Sea measurements;Synthetic aperture radar;Vectors;Altimetry;CryoSat-2;calibration;mispointing;pitch;synthetic aperture radar (SAR)},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6709791&isnumber=6763141
Galin, N.; Wingham, D.J.; Cullen, R.; Fornari, M.; Smith, W.H.F.; Abdalla, S., "Calibration of the CryoSat-2 Interferometer and Measurement of Across-Track Ocean Slope," in Geoscience and Remote Sensing, IEEE Transactions on , vol.51, no.1, pp.57-72, Jan. 2013
doi: 10.1109/TGRS.2012.2200298
Abstract: This paper describes the calibration of the CryoSat-2 interferometer, whose principal purpose is to accurately measure the height of the Antarctic and Greenland ice sheets. A sequence of CryoSat-2 data acquisitions over the tropical and midlatitude oceans were obtained between June and September 2010, from the SIRAL “A” and redundant SIRAL “B” radars operating in their “SARIN” mode, during a sequence of satellite rolls between -0.6° and 0.4°. Using the arrival angle of the echo relative to the interferometer baseline, the attitude of the satellite determined by the star trackers, and estimates of the ocean surface across-track slope from the EGM08 geoid, we determined the errors in the interferometer estimate of surface slope as functions of the roll angle and ocean surface waveheight. These were found to be in close agreement with the theoretical description. The scale factor of the interferometric measurement of angle was determined to be 0.973 ± 0.002. We estimate the accuracy of the across-track slope measurement of the interferometer by applying this scale factor to the measured phase. In applying this scale factor to the measurements, the across-track slope of the marine geoid was obtained with an accuracy of 26 μrad at 10 km and 10 μrad at 1000 km. We conclude that the instrument performance considerably exceeds that needed for the accurate determination of height over the sloping surfaces of the continental ice sheets. The results also demonstrate that CryoSat-2 provides the first observations of the instantaneous vector gradient of the ocean surface, and that the normal-incidence interferometric configuration has a greater potential for the measurement of the ocean across-track slope than has been previously recognized.
keywords: {calibration;geophysical equipment;glaciology;AD 2010 06 to 09;Antarctic ice sheet;CryoSat-2 Interferometer;EGM08 geoid;Greenland ice sheet;SARIN mode;SIRAL A radar;SIRAL B radar;across track ocean slope;calibration;data acquisitions;ocean surface waveheight;roll angle;scale factor;Radar tracking;Satellites;Sea measurements;Sea surface;Surface waves;Calibration;CryoSat-2;interferometry;radar altimetry},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6227346&isnumber=6387651
Meloni, M.; Vingione, G.; Ferrazzoli, P.; Parrinello, T., "Recent developments in radar altimetry over land and applications to future altimetric missions," in Geoscience and Remote Sensing Symposium (IGARSS), 2012 IEEE International , vol., no., pp.4594-4597, 22-27 July 2012
doi: 10.1109/IGARSS.2012.6350445
Abstract: Satellite radar altimetry, which was initially designed for accurate measurements of sea surface height, has been demonstrated to be suitable for land surfaces as well. In this paper, a simplified expression of the flat surface impulse response (PFS), which enters in the computation of the radar Impulse Response (IR), has been found which is valid for a nadir pointing system as well as for small mis-pointing angles. On the basis of this model, simulations have been performed taking into account the system characteristics of the new sensor SIRAL (Cryosat-2), considered operating in LRM (Low Resolution Mode) varying some key parameters such as backscattering coefficient, off-nadir angle, surface RMS height in order to investigate the performance of the model itself. The outputs of the simulations show consistent and expected results in the various simulated scenarios. The simulated IRs were compared with real altimetric data from ENVISAT RA-2 and Cryosat-2 SIRAL for different types of targets such as Desert, Ocean, Ice.
keywords: {altimeters;backscatter;geophysical techniques;remote sensing by radar;synthetic aperture radar;transient response;Cryosat-2 SIRAL;ENVISAT RA-2;IR simulations;SAR mode;SIRAL sensor;altimetric missions;backscattering coefficient;desert surfaces;flat surface impulse response;land surfaces;low resolution mode;nadir pointing system;off-nadir angle;radar impulse response;real altimetric data;satellite radar altimetry;sea surface height measurements;small mis-pointing angles;Antarctica;Australia;Ice surface;Radar applications;Surface fitting;Surface topography;Altimetry;Cryosat-2;IR;LRM},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6350445&isnumber=6350328
Wingham, D.J.; Wallis, D.W., "The Rough Surface Impulse Response of a Pulse-Limited Altimeter With an Elliptical Antenna Pattern," in Antennas and Wireless Propagation Letters, IEEE , vol.9, no., pp.232-235, 2010
doi: 10.1109/LAWP.2010.2046471
Abstract: This letter describes the impulse response of a pulse-limited altimeter with an elliptical antenna pattern from a uniformly rough surface inclined at an angle to a sphere or, equivalently, from spherical surface and mispointed antenna. An integral for the impulse response is given, and analytic forms for the special cases of a mispointed circular antenna and a nadir-pointed elliptical antenna are derived. An analytic approximation for the case of small ellipticity and small surface gradient (or mispointing) are also given. The letter is illustrated with numerical examples that show the general effect of ellipticity on the impulse response. It also shows that in the practical case of the elliptical CryoSat-2 satellite SIRAL antenna, the analytic approximation is sufficiently accurate to provide a correction for the ellipticity for CryoSat-2 echoes from the ocean surface.
keywords: {antenna radiation patterns;radioaltimeters;remote sensing by radar;satellite antennas;transient response;CryoSat-2 echoes;analytic approximation;elliptical CryoSat-2 satellite SIRAL antenna;elliptical antenna pattern;ellipticity;mispointed circular antenna;nadir-pointed elliptical antenna;ocean surface;pulse-limited altimeter;rough surface impulse response;spherical surface;surface gradient;Altimetry;antennas;remote sensing},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5438773&isnumber=5423326
D'Aria, D.; Guccione, P.; Rosich, B.; Cullen, R., "Delay/Doppler altimeter data processing," in Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International , vol., no., pp.137-140, 23-28 July 2007
doi: 10.1109/IGARSS.2007.4422748
Abstract: The ESA Cryosat-2 mission will mount a de- lay/Doppler radar altimeter (DDA), named SIRAL, for the study of the trends in Earth's continental and marine ice fields. A DDA has many advantages over a conventional altimeter, retrieving a better resolution in the along track direction as a result of coherent processing of the backscattering energy. This permits the extension of applications to ice sheet monitoring as well as coastal studies, maintaining necessary precision for the open ocean. Operational SIRAL data processing for the Cryosat-2 mission is based on the precise wavenumber domain approach, following the strategy developed and verified for the Cryosat-1 mission [1]. A novel way of processing, supported by the chirp zeta transform (CZT) is here presented. Basically the CZT allows the Doppler beam formation to be directed toward the output surface samples in a single stage, increasing the computational efficiency of the processing at the expense of a slightly lower accuracy. The more precise wavenumber domain approach can be used to validate the method. The SIRAL sensor parameters and simulated scenarios will be taken as models to derive experimental results.
keywords: {Doppler radar;geophysical techniques;radioaltimeters;Doppler beam formation;ESA Cryosat-2 mission;SIRAL instrument;chirp zeta transform;delay/Doppler altimeter data processing;wavenumber domain approach;Backscatter;Data processing;Delay;Doppler radar;Earth;Energy resolution;Ice;Monitoring;Radar tracking;Sea measurements},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4422748&isnumber=4422708
Le Gallou, N.; Ludwig, M.; Mavrocordatos, C.; Balestra, L.; Battisti, A.; Regan, P.; Weston, R.; Seymour, D.; Darbandi, A.; Lavielle, F.; Touchais, J.Y., "50W L-band and 25W Ku-band SSPA for European Space Programs," in Microwave Conference, 2005 European , vol.2, no., pp.4 pp.-, 4-6 Oct. 2005
doi: 10.1109/EUMC.2005.1610106
Abstract: This paper describes state of art solid state power amplifiers developed in the frame of two major European Space Programs (Galileo and Cryosat), using the most advanced technologies fully qualified for space applications. Three types of 50W SSPA have been developed in L-band for Galileo, and one 25W SSPA in Ku-band has been developed for the SIRAL instrument on board Cryosat. Highly reliable technologies have been used to meet the very stringent space standards. In the next few years, GaN technologies may offer substantial improvements for spaceborne SSPA.
keywords: {III-V semiconductors;gallium compounds;microwave power amplifiers;space vehicle electronics;wide band gap semiconductors;25 W;50 W;Cryosat space program;European Space Programs;GaN;Galileo space program;Ku-Band SSPA;L-band SSPA;SIRAL instrument;solid state power amplifiers;space applications;Aerospace electronics;Art;Gallium nitride;L-band;Power generation;Radio frequency;Solid state circuits;Space exploration;Space technology;Temperature},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1610106&isnumber=33799
Mavrocordatos, C.; Attema, E.; Davidson, M.; Lentz, H.; Nixdorf, U., "Development of ASIRAS (Airborne SAR/Interferometric Altimeter System)," in Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004 IEEE International , vol.4, no., pp.2465-2467 vol.4, 20-24 Sept. 2004
doi: 10.1109/IGARSS.2004.1369792
Abstract: ASIRAS is an airborne system designed for sea-ice and ice sheet monitoring. It has been developed by ESA under a Technology Research Program contract. The main sensor of this system is a high resolution Ku-band radar altimeter with 1GHz bandwidth. The observation concept is based on a scaled configuration of SIRAL sensor on board CryoSat. The principle of the measurements is based on a combination of ranging, SAR and Interferometric techniques. The development and the validation of ASIRAS are now completed. The system will be extensively used during the Calibration and Validation campaigns of CryoSat mission. This paper describes the key design drivers and the main features of the system. The key operational parameters of the instrument are discussed, with particular focus on the link between the space-based and the airborne configuration. Finally, the performance of the instrument is presented, based on the results obtained from technical flights and a validation campaign.
keywords: {airborne radar;hydrological equipment;oceanographic equipment;radiowave interferometers;radiowave interferometry;remote sensing by radar;sea ice;synthetic aperture radar;1 GHz;ASIRAS;CryoSat mission;ESA;Ku-band radar altimeter;SAR techniques;SIRAL sensor;Technology Research Program contract;airborne SAR/interferometric altimeter system;airborne configuration;airborne system;ice sheet monitoring;interferometric techniques;sea-ice monitoring;Aircraft;Antenna measurements;Bandwidth;Contracts;Instruments;Laser radar;Radar antennas;Sensor systems;Surface topography;Telephony},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1369792&isnumber=29947
Rey, L.; de Chateau-Thierry, P.; Phalippou, L.; Calvary, P.; Mavrocordatos, C., "SIRAL the radar altimeter for the CryoSat mission, pre-launch performances," in Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004 IEEE International , vol.1, no., pp.671, 20-24 Sept. 2004
doi: 10.1109/IGARSS.2004.1369118
Abstract: The development phase of the SAR Interferometer Radar Altimeter (SIRAL) is in the final stage in Alcatel Space and during year 2004 the Engineering and the Flight Models is tested before delivery to the Mission Prime ASTRIUM GmbH. This ESA mission will be used to estimate - on a global scale - the fluctuations in mass of sea-ice and land-ice. This paper gives a detailed presentation of the microwave and processing units developed, followed by a survey of the pre-launch performances.
keywords: {ice;interferometry;radar altimetry;remote sensing by radar;sea ice;synthetic aperture radar;AD 2004;Alcatel Space;CryoSat payload;ESA mission;European Space Agency;Mission Prime ASTRIUM GmbH;SAR Interferometer Radar Altimeter;SIRAL pre-launch performance;Synthetic Aperture Radar;engineering/flight model;microwave/processing unit;sea-ice/land-ice mass fluctuation;Demodulation;Instruments;Pulse measurements;Radar measurements;Radar tracking;Reflector antennas;Sea ice;Spaceborne radar;Telephony;Transmitting antennas},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1369118&isnumber=29944
Raney, R.K.; Leuschen, C.J., "Simultaneous laser and radar altimeter measurements over land and sea ice," in Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004 IEEE International , vol.1, no., pp.678, 20-24 Sept. 2004
doi: 10.1109/IGARSS.2004.1369120
Abstract: Elevation data derived from space-based altimeter measurements over landand sea-ice are key to understanding the Earth's ice mass balance. This importance is recognized by both NASA, as expressed in the laser altimeter GLAS on ICESat, and ESA, as expressed in the radar altimeter SIRAL on CryoSat. The JHU/APL Delay-Doppler Phase-monopulse (D2P) radar altimeter has shown its value as a scientific/calibration/validation instrument, and has participated in two airborne field campaigns sponsored by NASA and ESA to collect simultaneous radar and laser altimeter measurements over land and sea ice. These measurements are unique; they provide colocated, cross-calibrated, and high-precision altimetry data over a variety of geophysical ice conditions in two very different frequency regimes. In this paper, we give an overview of the CryoVEx field campaign in 2003 including basic system parameters, flight tracks, and sample waveforms from the airborne experiment.
keywords: {Doppler radar;airborne radar;height measurement;ice;interferometry;radar altimetry;remote sensing by laser beam;remote sensing by radar;sea ice;synthetic aperture radar;AD 2003;CryoSat;CryoVEx field campaign;Delay-Doppler phase-monopulse radar altimeter;ESA;Earth ice mass balance;GLAS;Geoscience Laser Altimeter System;ICESat;NASA;SAR Interferometer Radar Altimeter;SIRAL;airborne experiment;geophysical ice condition;high-precision JHU/APL D2P radar altimeter;land/sea ice;space-based altimeter measurement;Airborne radar;Calibration;Delay;Earth;Geophysical measurements;Laser radar;NASA;Radar measurements;Sea ice;Sea measurements},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1369120&isnumber=29944
Rey, L.; de Chateau-Thierry, P.; Phalippou, L.; Mavrocordatos, C., "Siral the radar altimeter for the cryosat mission, pre-launch performances," in Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International , vol.5, no., pp.2974-2976, 2003
doi: 10.1109/IGARSS.2003.1294652
Abstract: Not Available
keywords: {Demodulation;Instruments;Laser radar;Performance evaluation;Radar tracking;Reflector antennas;Sea ice;Spaceborne radar;Telephony;Transmitting antennas},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1294652&isnumber=28605
Wingham, D.J., "CryoSat: a mission to determine fluctuations in the Earth's ice fields," in Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International , vol.3, no., pp.1750-1752 vol.3, 24-28 June 2002
doi: 10.1109/IGARSS.2002.1026242
Abstract: This paper provides an overview of the CryoSat satellite mission, the first of the European Space Agency 'Opportunity' Missions. It is aimed at measuring fluctuations in Earth's land and marine ice fields. The mission objectives, instrument system and measurement principles, mission operation and the approach to the calibration and validation of the measurements are described.
keywords: {glaciology;hydrological techniques;oceanographic techniques;remote sensing by radar;sea ice;spaceborne radar;CryoSat;ESA;European Space Agency;Ku-band;SHF;SIRAL;calibration;fluctuations;glacier;glaciology;hydrology;ice fields;ice sheet;instrument system;land ice;measurement technique;mission objectives;ocean;radar altimetry experiment;radar remote sensing;satellite mission;satellite remote sensing;sea ice;spaceborne radar;validation;Arctic;Earth;Extraterrestrial measurements;Fluctuations;Ice thickness;Satellites;Sea ice;Sea level;Sea measurements;Uncertainty},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1026242&isnumber=22038
Haas, C., "Validation of CryoSat sea-ice products: instruments and methods," in Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International , vol.3, no., pp.1753-1755 vol.3, 24-28 June 2002
doi: 10.1109/IGARSS.2002.1026243
Abstract: Sea-ice properties like ice and snow density, freeboard, thickness, roughness, and their measurement are described in the context of ground-truth studies for the validation of CryoSat measurements. Both ground-based and airborne methods are presented.
keywords: {oceanographic techniques;remote sensing by radar;sea ice;spaceborne radar;CryoSat;Ku-band;SHF;SIRAL;data products;freeboard;ground truth;measurement technique;ocean;radar altimetry method;radar remote sensing;roughness;satellite remote sensing;sea ice;snow cover;snow density;snowcover;snowpack;spaceborne radar;thickness;validation;Density measurement;Dielectric measurements;Ice surface;Ice thickness;Instruments;Sea ice;Sea measurements;Snow;Spaceborne radar;Thickness measurement},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1026243&isnumber=22038
Darbandi, A.; Lavielle, F.; Naudy, G.; Touchais, J.Y., "Ku -Band Solid State Power Amplifier For Siral Altimeter," in Microwave Conference, 2002. 32nd European , vol., no., pp.1-4, 23-26 Sept. 2002
doi: 10.1109/EUMA.2002.339256
Abstract: A compact, high efficiency 25W Kuband SSPA has been developed for the Siral Altimeter, cryosat program. SSPAs have been used in radar application for many years. The main advantages of the pulsed SSPAs are the followings: - Low distortion of amplitude and phase during the pulse. - High reproducibility of identical pulses. - High quality of output spectrum: low harmonic contents and reduced group delay time. This SSPA combines the output of four 8W-hybrid PHEMT modules with an integral waveguide combiner. AM/PM conversion was measured at 0.5 degree / dB and the phase shift were measured less than 5 degree.
keywords: {Delay effects;Harmonic distortion;PHEMTs;Phase distortion;Phase measurement;Power amplifiers;Pulse amplifiers;Radar applications;Reproducibility of results;Solid state circuits},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4140336&isnumber=4140284
Francis, C.R., "Design of the CryoSat system," in Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International , vol.3, no., pp.1759-1761 vol.3, 24-28 June 2002
doi: 10.1109/IGARSS.2002.1026245
Abstract: CryoSat, as the first Earth Explorer Opportunity Mission, is characterised by a clear focus on science within a very limited financial budget and a short development time. CryoSat is now well into its development and will be launched in 2004. The entire mission is designed in support of specific scientific objectives and this has enabled very clear trade-offs to be made in all the key technical aspects. The selection of the orbit, the payload and the services provided by the satellite subsystems have all been optimised. The primary instrument is a state-of-the-art radar altimeter with additional SAR and interferometric capabilities to improve its spatial resolution. The CryoSat orbit has an inclination of 92 degrees, to optimise the satellite measurements over polar regions. A single ground station, at Kiruna, will be used for all operations. The CryoSat mission has the promise of addressing a well-formulated scientific question, affordably, and within a realistic timescale.
keywords: {artificial satellites;glaciology;hydrological equipment;hydrological techniques;oceanographic equipment;oceanographic techniques;remote sensing by radar;sea ice;spaceborne radar;synthetic aperture radar;CryoSat;InSAR;SAR;SIRAL;artificial satellite;avionics;geophysical measurement technique;glacier;glaciology;ground station;ice sheet;instrument;land ice;ocean;orbit;payload;radar altimetry method;radar remote sensing;satellite subsystems;sea ice;spaceborne radar;synthetic aperture radar;Extraterrestrial measurements;Ice;Instruments;Particle measurements;Payloads;Satellites;Sea measurements;Spaceborne radar;Spatial resolution;Velocity measurement},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1026245&isnumber=22038
Rey, L.; de Chateau-Thierry, P.; Phalippou, L.; Mavrocordatos, C.; Francis, R., "SIRAL: the radar altimeter for CryoSat mission, under development," in Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International , vol.3, no., pp.1768-1770 vol.3, 24-28 June 2002
doi: 10.1109/IGARSS.2002.1026248
Abstract: SIRAL (SAR Interferometer Radar Altimeter) is the new spaceborne altimeter designed for CryoSat mission. The instrument is currently in the development phase, in ALCATEL SPACE, which encompasses an Engineering Model and a Flight Model. This ESA mission, planned for 2004, will be used to estimate - on a global scale - the fluctuations in mass of sea-ice and land-ice. This paper discusses the flexibility of the instrument and in particular its capability to operate in various modes (conventional altimeter, SAR and interferometer modes), and gives main results from the pre-developments and breadboard activities.
keywords: {glaciology;hydrological equipment;hydrological techniques;oceanographic equipment;oceanographic techniques;remote sensing by radar;sea ice;spaceborne radar;synthetic aperture radar;13.575 GHz;ALCATEL SPACE;CryoSat;ESA mission;Ku-band;SAR;SAR Interferometer Radar Altimeter;SHF;SIRAL;glacier;glaciology;ice sheet;instrument;measurement technique;ocean;radar altimetry;radar remote sensing;sea ice;spaceborne altimeter;spaceborne radar;synthetic aperture radar;Frequency;Instruments;Pulse measurements;Reflector antennas;Sea ice;Space charge;Spaceborne radar;Synthetic aperture radar;Telephony;Transmitting antennas},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1026248&isnumber=22038
Cullen, R.A.; Wingham, D.J., "CryoSat level 1b processing algorithms and simulation results," in Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International , vol.3, no., pp.1762-1764 vol.3, 24-28 June 2002
doi: 10.1109/IGARSS.2002.1026246
Abstract: The CryoSat synthetic interferometric altimeter (SIRAL) has been designed to extend the coverage of conventional pulse-limited altimeters to allow the measurement of sea ice thickness and the elevation of the marginal regions of ice sheets. The science data acquired by the instrument is of a more complex nature than the conventional radar altimeter and is in one of three forms each of which are described in the paper. Examination of simulated echoes from each of these 3 modes provides a useful insight into how the CryoSat mission will tackle its primary objectives, and how an improvement in elevation measurement will be made over its conventional satellite borne counterpart.
keywords: {geophysical signal processing;glaciology;hydrological techniques;oceanographic techniques;radar signal processing;radar theory;remote sensing by radar;sea ice;spaceborne radar;CryoSat;Ku-band;SHF;SIRAL;elevation;glacier;glaciology;ice sheet;level 1b;measurement technique;ocean;pulse-limited altimeters;radar altimetry;radar remote sensing;satellite remote sensing;sea ice;spaceborne radar;synthetic interferometric altimeter;thickness;topography;Ice thickness;Instruments;Pulse measurements;Radar tracking;Satellites;Sea ice;Sea measurements;Sea surface;Spaceborne radar;Thickness measurement},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1026246&isnumber=22038
Rostan, F.; Mallow, U., "The CryoSat space segment: definition, design and predicted performance," in Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International , vol.6, no., pp.3102-3104 vol.6, 2002
doi: 10.1109/IGARSS.2002.1027098
Abstract: CryoSat is the first of the ESA Earth Explorer Opportunity Missions. It will allow an accurate determination of the marine and land ice mass fluxes at a global scale. This paper gives a brief overview on the CryoSat space segment, which is currently under development by an industrial consortium with Astrium as prime contractor.
keywords: {glaciology;hydrological equipment;hydrological techniques;oceanographic equipment;oceanographic techniques;radar equipment;remote sensing by radar;sea ice;spaceborne radar;synthetic aperture radar;Astrium;CryoSat;InSAR;SAR;SIRAL;definition;design;equipment;glaciology;global scale;hydrology;ice sheet;instrument;interferometric SAR;land ice;land ice mass fluxes;measurement technique;ocean;performance;radar remote sensing;sea ice;space segment;spaceborne radar;synthetic aperture radar;Aerospace industry;Earth;Fluctuations;Ice;Instruments;Optical interferometry;Pulse modulation;Radar tracking;Sea measurements;Spaceborne radar},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1027098&isnumber=22041
Rey, L.; de Chateau-Thierry, P.; Phalippou, L.; Mavrocordatos, C.; Francis, R., "SIRAL, a high spatial resolution radar altimeter for the Cryosat mission," in Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International , vol.7, no., pp.3080-3082 vol.7, 2001
doi: 10.1109/IGARSS.2001.978261
Abstract: SIRAL (SAR Interferometer Radar Altimeter) is the new spaceborne altimeter designed for CryoSat mission. This ESA mission, planned for 2004, will be used to estimate-on a global scale- the fluctuations in mass of sea-ice and land-ice. The novelty of SIRAL concept with respect to conventional pulse-limited altimeter, is the implementation of Doppler processing for along-track resolution enhancement and also of interferometry, used to locate the echo in the across-track direction. The innovative technical features of SIRAL are presented hereafter with regards to the function requirements and also the expected performance
keywords: {hydrological equipment;ice;oceanographic equipment;radar altimetry;radar resolution;radiowave interferometers;remote sensing by radar;sea ice;synthetic aperture radar;CryoSat mission;Doppler processing;SAR interferometer radar altimeter;SIRAL;across-track direction;along-track resolution enhancement;conventional pulse-limited altimeter;interferometry;land ice;sea-ice;spaceborne altimeter;Frequency;Ice;Instruments;Interferometry;Receiving antennas;Sea measurements;Sea surface;Spaceborne radar;Spatial resolution;Synthetic aperture radar},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=978261&isnumber=21051
Phalippou, L.; Rey, L.; de Chateau-Thierry, P., "Overview of the performances and tracking design of the SIRAL altimeter for the CryoSat mission," in Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International , vol.5, no., pp.2025-2027 vol.5, 2001
doi: 10.1109/IGARSS.2001.977891
Abstract: This paper presents the principle of the measurements, the main system features and the basic ground processing of SIRAL. Simulations of the main performances in the different modes are also discussed including the bidimensional impulse response (range and azimuth). A major scientific requirement is to ensure the continuity of the measurements. This is particularly challenging for the on-board tracker over the steepest parts of the Antarctica. As a consequence a new tracking algorithm has been designed for SIRAL with the expertise of CNES. The algorithm has been derived from the analysis of simulated echoes using an Antarctica DEM and a radar echo simulator. The tracking design and performance are briefly described
keywords: {artificial satellites;glaciology;hydrological equipment;hydrological techniques;oceanographic equipment;oceanographic techniques;remote sensing by radar;spaceborne radar;synthetic aperture radar;CryoSat;InSAR;Ku-band;SAR;SHF;SIRAL;artificial satellite;bidimensional impulse response;data processing;glaciology;ground processing;measurement technique;ocean;on-board tracker;performance;polar ice sheet;radar altimetry;radar remote sensing;sea ice;signal processing;spaceborne radar;synthetic aperture radar;tracking algorithm;tracking design;Azimuth;Ice;Oceans;Pulse measurements;Radar tracking;Sea measurements;Sea surface;Spaceborne radar;Spatial resolution;Surface topography},
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=977891&isnumber=21049
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