Satellite Altimetry Observations of Large-Scale Internal Solitary Waves

Magalhaes, J.M.; Silva, J. C. B. da

doi:10.1109/lgrs.2017.2655621

Cited by 21 publications

(24 citation statements)

References 19 publications

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“…This makes the internal waves or oil slick appear darker than the surrounding area. and a similar phenomenon observed by satellite altimeter has also been reported in [25]. Obviously, there is an intensity boundary around ~5° incidence, as shown in Figure 11a.…”

Section: Discussionsupporting

confidence: 87%

“…When the modulated area gets smoother, the backscattered signal will decrease and the internal waves will appear as dark stripes, which coincides with the situation that occurred in the far range. While different from conventional SAR, the near-nadir incidence of InIRA determines its received signals are mainly from specular reflection, so internal waves are supposed to be bright stripes, which coincides with the near range situation, and a similar phenomenon observed by satellite altimeter has also been reported in [25]. Obviously, there is an intensity boundary around~5 • incidence, as shown in Figure 11a.…”

Section: Discussionsupporting

confidence: 53%

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Performance Analysis of Ocean Surface Topography Altimetry by Ku-Band Near-Nadir Interferometric SAR

2017

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Abstract:Interferometric imaging radar altimeter (InIRA) is the first spaceborne Ku-band interferometric synthetic aperture radar (InSAR) which is specially designed for ocean surface topography altimetry. It is on the Tiangong II space laboratory, which was launched on 15 September 2016. Different from any other spaceborne synthetic aperture radar (SAR), InIRA chooses a near-nadir incidence of 1 •~8• in order to increase the altimetric precision and swath width. Limited by the size of the Tiangong II capsule, the baseline length of InIRA is only 2.3 m. However, benefitting from the low orbit, the signal-to-noise ratio of InIRA-acquired data is above 10 dB in most of the swath, which, to a certain extent, compensates for the short baseline deficiency. The altimetric precision is simulated based on the system parameters of InIRA. Results show that it is better than 7 cm on a 5-km grid and improves to 3 cm on a 10-km grid when the incidence is below 7.4 • . The interferometric data of InIRA are processed to estimate the altimetric precision after a series of procedures (including image coregistration, flat-earth-phase removal, system parameters calibration and phase noise suppression). Results show that the estimated altimetric precision is close to but lower than the simulated precision among most of the swath. The intensity boundary phenomenon is first found between the near range and far range of the SAR images of InIRA. It can be explained by the modulation of ocean internal waves or oil slick, which smooths ocean surface roughness and causes the modulated area to appear either brighter or darker than its surroundings. This intensity boundary phenomenon indicates that the available swath of high altimetric precision will be narrower than expected.

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Section: Discussionsupporting

confidence: 87%

Section: Discussionsupporting

confidence: 53%

Performance Analysis of Ocean Surface Topography Altimetry by Ku-Band Near-Nadir Interferometric SAR

2017

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“…On the contrary, in the SRAL along-track altimeter records, radar backscatter from rougher sea surface patches appears attenuated in comparison to the unperturbed background, and the backscatter from a smooth sea surface patch appears enhanced in comparison to the unperturbed background. This is a reversed picture in comparison to imaging SARs [27] (see also Magalhaes and da Silva [14] and their Figure 2 comparing SAR imaging and conventional pulse-limited altimeter backscatter geometries).…”

Section: Discussionmentioning

confidence: 94%

“…As the along-track footprints of SRAL are much finer than conventional pulse-limited altimeters, the trailing edges of the SRAL echoes are much less affected by ISWs than pulse-limited altimetry echoes whose power shifts toward trailing edges as a consequence of ISW inhomogeneities in the illuminated area. Because the SRAL waveforms are more robust and stable, it implies that the retracked geophysical parameters such as SLA and SWH from the internal wave field are more realistic compared with the unrealistic estimates from Jason-2 that are affected by the ISW-like events and significantly biased in scales of 10 km [14].…”

Section: Discussionmentioning

confidence: 99%

“…Other factors limiting the capability of altimetry data for ISW detection include the relative orientation between the satellite ground-track and the ISW crests, particularly for altimeters that operate in SAR mode (see Figure 1c). Magalhaes and da Silva [14] (henceforth MdS) demonstrated that the Jason-2 altimetry data with a high sampling rate (i.e., 20 Hz) hold a variety of short-period signatures that are consistent with surface manifestations of ISWs in the ocean. Based on the synergetic observations from satellite imaging sensors, such as SAR and other high-resolution optical sensors (e.g., 250 m resolution MODIS images), MdS demonstrated that ISWs can be unambiguously recognized.…”

Section: Introductionmentioning

confidence: 99%

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SAR Mode Altimetry Observations of Internal Solitary Waves in the Tropical Ocean Part 1: Case Studies

2018

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It is well known that internal waves (IWs) of tidal frequency (i.e., internal tides) are successfully detected in sea surface height (SSH) by satellite altimetry. Shorter period internal solitary waves (ISWs), whose periods (and spatial scales) are an order of magnitude smaller than tidal internal waves, have been generally assumed too small to be detected with conventional altimeters. This is because conventional (pulse-limited) radar altimeter footprints are somewhat larger than or of similar size, at best, as the typical wavelengths of the ISWs. Here we demonstrate that the synthetic aperture radar altimeter (SRAL) on board the Sentinel-3A can detect short-period ISWs. A variety of signatures owing to the surface manifestations of the ISWs are apparent in the SRAL Level-2 products over the ocean. These signatures are identified in several geophysical parameters, such as radar backscatter (sigma0), sea level anomaly (SLA), and significant wave height (SWH). Radar backscatter is the primary parameter in which ISWs can be identified owing to the measurable sea surface roughness perturbations in the along-track sharpened SRAL footprint. The SRAL footprint is sufficiently small to capture radar power fluctuations over successive wave crests and troughs, which produce rough and slick surface patterns arrayed in parallel bands with scales of a few kilometers. The ISW signatures are unambiguously identified in the SRAL because of the exact synergy with OLCI (Ocean Land Colour Imager) images, which in cloud-free conditions allow clear identification of the ISWs in the sunglint OLCI images. We show that both sigma0 and SLA yield realistic estimates for routine observation of ISWs with the SRAL, which is a significant improvement from previous observations recently reported for conventional pulse-limited altimeters (Jason-2). Several case studies of ISW signatures are interpreted in light of our knowledge of radar backscatter in the internal wave field. An analysis is presented for the tropical Atlantic Ocean off the Amazon shelf to infer the frequency of the phenomena, being consistent with previous satellite observations in the study region.

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Experimental Study on the Variation of Optical Imaging Characteristics with Zenith Angle due to Internal Solitary Waves in Sunglint

Liu,

Sun,

Chang

et al. 2024

J. Ocean Univ. China

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Satellite Altimetry Observations of Large-Scale Internal Solitary Waves

Cited by 21 publications

References 19 publications

Performance Analysis of Ocean Surface Topography Altimetry by Ku-Band Near-Nadir Interferometric SAR

Performance Analysis of Ocean Surface Topography Altimetry by Ku-Band Near-Nadir Interferometric SAR

SAR Mode Altimetry Observations of Internal Solitary Waves in the Tropical Ocean Part 1: Case Studies

Experimental Study on the Variation of Optical Imaging Characteristics with Zenith Angle due to Internal Solitary Waves in Sunglint

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