Ocean surface topography measured by the Geosat radar altimeter during the Frontal Air-Sea Interaction Experiment

1991 ◽  
Vol 96 (C12) ◽  
pp. 22087 ◽  
Author(s):  
James J. Bisagni
Keyword(s):  
Surface Topography ◽  
Ocean Surface ◽  
Radar Altimeter ◽  
Interaction Experiment

scholarly journals Ocean Surface Topography Altimetry by Large Baseline Cross-Interferometry from Satellite Formation

2020 ◽  
Vol 12 (21) ◽  
pp. 3519
Author(s):  
Weiya Kong ◽  
Bo Liu ◽  
Xiaohong Sui ◽  
Running Zhang ◽  
Jinping Sun
Keyword(s):  
Surface Topography ◽  
Ocean Surface ◽  
Baseline Length ◽  
Radar Altimeter ◽  
Satellite Formation ◽  
Satellite Platform ◽  
Marine Gravity ◽  
Development Tendency ◽  
Cross Track ◽  
Along Track

Imaging Radar Altimeter (IRA) is the current development tendency for ocean surface topography (OST) altimetry, which utilizes Synthetic Aperture Radar (SAR) and interferometry to improve the spatial resolution of OST to several kilometers or even better. Meanwhile, centimetric altimetry accuracy should be guaranteed for applications such as geostrophic currents or marine gravity anomaly inversion. However, the baseline length of IRA which determines the altimetric sensitivity is confined by the satellite platform, in consideration of baseline vibration and payload capability. Therefore, the baseline length from a single satellite can extend to only tens of meters, making it difficult to achieve centimetric accuracy. Referring to the successful experience from TerraSAR-X/TanDEM-X, satellite formation can easily extend the baseline length to hundreds or thousands of meters, depending on the helix orbit. Therefore, we propose the large baseline IRA (LB-IRA) from satellite formation for OST altimetry: the carrier frequency shift (CFS) is brought in to compensate for the severe baseline decorrelation, and the helix orbit is carefully selected to prevent severe time decorrelation from along-track baseline. The numerical results indicate that the LB-IRA, whose cross-track baseline ranges between 629~1000 m and along-tack baseline ranges between 0~40 m, can achieve ~1 cm relative accuracy at 1 km resolution.

scholarly journals Effects of Interferometric Radar Altimeter Errors on Marine Gravity Field Inversion

Sensors ◽  
2020 ◽  
Vol 20 (9) ◽  
pp. 2465
Author(s):  
Xiaoyun Wan ◽  
Shuanggen Jin ◽  
Bo Liu ◽  
Song Tian ◽  
Weiya Kong ◽  
...  
Keyword(s):  
Gravity Field ◽  
Gravity Anomalies ◽  
Ocean Surface ◽  
Radar Altimeter ◽  
The North ◽  
Phase Errors ◽  
Marine Gravity ◽  
East Component ◽  
The Impact ◽  
Field Inversion

The traditional altimetry satellite, which is based on pulse-limited radar altimeter, only measures ocean surface heights along tracks; hence, leads to poorer accuracy in the east component of the vertical deflections compared to the north component, which in turn limits the final accuracy of the marine gravity field inversion. Wide-swath altimetry using radar interferometry can measure ocean surface heights in two dimensions and, thus, can be used to compute vertical deflections in an arbitrary direction with the same accuracy. This paper aims to investigate the impact of Interferometric Radar Altimeter (InRA) errors on gravity field inversion. The error propagation between gravity anomalies and InRA measurements is analyzed, and formulas of their relationship are given. By giving a group of possible InRA parameters, numerical simulations are conducted to analyze the accuracy of gravity anomaly inversion. The results show that the accuracy of the gravity anomalies is mainly influenced by the phase errors of InRA; and the errors of gravity anomalies have a linear approximation relationship with the phase errors. The results also show that the east component of the vertical deflections has almost the same accuracy as the north component.

Detection of large-scale ocean circulation and tides

1983 ◽  
Vol 309 (1508) ◽  
pp. 361-370 ◽  
Keyword(s):  
Heat Flux ◽  
Surface Topography ◽  
Ocean Circulation ◽  
Satellite Altimetry ◽  
Large Scale ◽  
Precise Measurement ◽  
Ocean Surface ◽  
Ocean Topography ◽  
Tidal Signal ◽  
Nearly Continuous

As emphasized recently by Munk & Wunsch, the traditional methods of monitoring the ocean circulation give data too hopelessly aliased in space and time to permit a proper assessment of basin-wide dynamics and heat flux on climatic timescales. The prospect of nearly continuous recording of ocean-surface topography by satellite altimetry with suitable supporting measurements might make such assessments possible. The associated identification of the geocentric oceanic tidal signal in the data would be an additional bonus. The few weeks of altimetry recorded by Seasat gave a glimpse of the possibilities, but also clarified the areas where better precision and knowledge are needed. Further experience will be gained from currently projected multi-purpose satellites carrying altimeters, but serious knowledge of ocean circulation will result only from missions that are entirely dedicated to the precise measurement of ocean topography.

CryoSat SIRAL: calibration and achievable performance after ten years of operations

2020 ◽  
Author(s):  
Michele Scagliola ◽  
Marco Fornari ◽  
Marco Meloni ◽  
Jerome Bouffard ◽  
Tommaso Parrinello
Keyword(s):  
Transfer Function ◽  
Phase Difference ◽  
Ocean Surface ◽  
Calibration Data ◽  
Path Delay ◽  
Radar Altimeter ◽  
Angle Of Arrival ◽  
True Value ◽  
Wide Range

<p>The main payload of CryoSat is a Ku-band pulsewidth limited radar altimeter, called SIRAL (Synthetic interferometric radar altimeter), that is equipped with two antennas for single-pass interferometric capability.</p><p>Due to the unique characteristics of SIRAL, a proper calibration approach was developed. In fact, not only corrections for transfer function, gain and instrument path delay have to be computed (as in previous altimeters), but also corrections for phase (SAR/SARIn) and phase difference between the two receiving chains (SARIN only). To summarize, SIRAL performs regularly four types of internal calibrations:</p><p>-           CAL1 in order to calibrate the internal path delay and long-term power drift.</p><p>-           CAL2 in order to compensate for the instrument IF transfer function.</p><p>-           CAL4 to calibrate the interferometer.</p><p>-           AutoCal, a specific sequence used to calibrate the gain and phase difference for each AGC setting.</p><p>After about 10 years of operational activity of the CryoSat satellite, the performance of the SIRAL instrument are revealed to be in line or better than the expected one.</p><p>In fact the calibration products, that have been designed to model a wide range of imperfections of the instrument, can be analyzed to highlight whether and how the instrument is changing over the time also as function of its thermal status. It is worth underlining here that each variation of the instrument measured by the calibration data is compensated in the Level1 processing. Inspecting the temporal evolution of the calibration data, SIRAL has been verified to be stable during its life. The performance of the SIRAL will be presented together with the outcomes of the stability analysis on the calibration data, in order to verify that the instrument has reached the requirements and that it is maintaining the performance over its life.</p><p> </p><p>In order to monitor the performance of the CryoSat interferometer along the mission, in orbit calibration campaigns have been periodically performed about once a year. The end-to-end calibration strategy for the CryoSat interferometer uses the ocean surface as the known external target. In fact, the interferometer can be used to determine the across-track slope of the overflown surface and the slope of the ocean surface can be considered as known starting from the geoid. Denoting by β the across-track slope of the ocean and assuming that the knowledge error of the geoid slope is negligibly small, β can be compared with the across-track slope derived from CryoSat SARin Level1b products which results in β'=η(θ-χ) where η is a geometric factor, θ is the angle of earliest arrival measured by the CryoSat interferometer and χ is the baseline roll angle. By comparison of the expected across-track slope β and the measured across-track slope β', the accuracy and the precision of the angle of arrival θ measured by the CryoSat interferometer can be assessed.</p><p>In our analysis, the long-term accuracy (i.e. the closeness of the measurement to the true value) and the long-term precision (i.e. the closeness of agreement among a set of measurements) of the CryoSat interferometer have been assessed.</p>

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