Retracking CryoSat-2, Envisat and Jason-1 radar altimetry waveforms for improved gravity field recovery

Garcia, E. S. M.; Sandwell, David T.; Smith, Walter H. F.

doi:10.1093/gji/ggt469

Cited by 108 publications

(101 citation statements)

References 38 publications

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“…2a). We chose the grav.img.23.1 model (http://topex.ucsd.edu/ marine_grav/mar_grav.html) (Sandwell and Smith 2009;Garcia et al 2014;Sandwell et al 2013Sandwell et al , 2014 simply because it is accompanied by error estimates as a function of location, which are readily used in the error propagation (Sect. 3).…”

Section: Gravity Datamentioning

confidence: 99%

“…Figure 7 shows the differences between the gravity anomalies used in AGQG2017 and AGQG2009 and the difference between AGQG2017 and AGQG2009 quasigeoid heights. Notable features are: (1) the differences in gravity anomalies offshore between grav.img.23.1 (Sandwell and Smith 2009;Garcia et al 2014;Sandwell et al 2013Sandwell et al , 2014 and DTU08GRAV (Andersen et al 2010), particularly in the coastal zone (Fig. 7a); and (2) differences in quasigeoid heights in the mountains along the Great Dividing Range in south-eastern Australia (Fig.…”

Section: Modified Stokes Parameter Sweepsmentioning

confidence: 99%

“…Though the geometric component of AUSGeoid09 could be remodelled for AUSGeoid2020 using AGQG2009 and the co-located GNSS-AHD heights now available over Australia, we would also like to profit from the following new data: (i) an additional ∼280,000 land gravity observations; (ii) retracked satellite altimeter-derived marine gravity anomalies that include Jason-1 and CryoSat-2 data (Sandwell and Smith 2009;Garcia et al 2014;Sandwell et al 2013Sandwell et al , 2014; (iii) the 1 × 1 (∼30 m) resolution DEM-H digital elevation model (Gallant et al 2011) derived from the Shuttle Radar Topography Mission (STRM; Farr et al 2007); and (iv) improved numerical integration routines in the 1D-FFT implementation of Stokes's integral (Haagmans et al 1993).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The first Australian gravimetric quasigeoid model with location-specific uncertainty estimates

Featherstone

McCubbine

Brown

et al. 2017

J Geod

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We describe the computation of the first Australian quasigeoid model to include error estimates as a function of location that have been propagated from uncertainties in the EGM2008 global model, land and altimeterderived gravity anomalies and terrain corrections. The model has been extended to include Australia's offshore territories and maritime boundaries using newer datasets comprising an additional ∼280,000 land gravity observations, a newer altimeter-derived marine gravity anomaly grid, and terrain corrections at 1 × 1 resolution. The error propagation uses a remove-restore approach, where the EGM2008 quasigeoid and gravity anomaly error grids are augmented by errors propagated through a modified Stokes integral from the errors in the altimeter gravity anomalies, land gravity observations and terrain corrections. The gravimetric quasigeoid errors (one sigma) are 50-60 mm across most of the Australian landmass, increasing to ∼100 mm in regions of steep horizontal gravity gradients or the mountains, and are commensurate with external estimates.

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Section: Gravity Datamentioning

confidence: 99%

Section: Modified Stokes Parameter Sweepsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The first Australian gravimetric quasigeoid model with location-specific uncertainty estimates

Featherstone

McCubbine

Brown

et al. 2017

J Geod

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“…Trench axis data were from Bassett and Watts, (, ). The background bathymetry data were from Sandwell et al () and Garcia et al () and were processed with the Generic Mapping Tools (GMT) (Wessel & Smith, ; Wessel et al, ). This work was supported by National Science Foundation (NSF) [10.13039/100000001](EAR‐1620251) at Scripps Institution of Oceanography, UC San Diego.…”

Section: Acknowledgementsmentioning

confidence: 99%

Investigation of Backprojection Uncertainties With M6 Earthquakes

Fan

Shearer

2017

JGR Solid Earth

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We investigate possible biasing effects of inaccurate timing corrections on teleseismic P wave backprojection imaging of large earthquake ruptures. These errors occur because empirically estimated time shifts based on aligning P wave first arrivals are exact only at the hypocenter and provide approximate corrections for other parts of the rupture. Using the Japan subduction zone as a test region, we analyze 46 M6–M7 earthquakes over a 10 year period, including many aftershocks of the 2011 M9 Tohoku earthquake, performing waveform cross correlation of their initial P wave arrivals to obtain hypocenter timing corrections to global seismic stations. We then compare backprojection images for each earthquake using its own timing corrections with those obtained using the time corrections from other earthquakes. This provides a measure of how well subevents can be resolved with backprojection of a large rupture as a function of distance from the hypocenter. Our results show that backprojection is generally very robust and that the median subevent location error is about 25 km across the entire study region (∼700 km). The backprojection coherence loss and location errors do not noticeably converge to zero even when the event pairs are very close (<20 km). This indicates that most of the timing differences are due to 3‐D structure close to each of the hypocenter regions, which limits the effectiveness of attempts to refine backprojection images using aftershock calibration, at least in this region.

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“…The expected range waveform for a specular echo can be approximated with a Gaussian function as follows (modified from Garcia et al [20], Equation (2)):…”

Section: Water Levelmentioning

confidence: 99%

Envisat RA-2 Individual Echoes: A Unique Dataset for a Better Understanding of Inland Water Altimetry Potentialities

Abileah¹,

Scozzari

Vignudelli

2017

Remote Sensing

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Abstract:The exploitation of synthetic aperture properties in nadir-looking radars is opening new scenarios in the framework of satellite radar altimetry. Both recent and upcoming missions including Cryosat-2, Sentinel-3, Sentinel-6 and SWOT take benefit from the coherent processing of radar data, aimed at improving range measurements in particular contexts, such as ice, open ocean, coastal zone, and even inland waters. This work investigates the possibilities offered by current and future satellite radar altimetry missions for the study of inland water bodies, probing into the peculiarities of the expected radar returns and their potential usage. In this regard, signals collected by the RA-2 instrument (Radar Altimeter 2) onboard the Envisat mission offer an unprecedented possibility, even with a relatively low pulse repetition frequency, to analyze the peculiarities of actual signals for detecting and ranging small water surfaces. In particular, the RA-2 instrument offers a global archive of Individual Echoes (IEs), collected at the native sampling rate of 1795 Hz, in addition to the 18 Hz data obtained by incoherent averaging, which are typically delivered to the users as standard products. RA-2 shares with future radar platforms such as Sentinel-6 a continuous and interleaved working modality, as was recommended by the scientific community in designing next missions' requirements. This is a further reason to consider the usage of RA-2 IEs as particularly attractive. Whilst only available for a small percentage of the earth's surface, sufficient IE data exist to study the height retrieval capability of these echoes, in particular for what concerns small water bodies, where we show that enough coherence is exhibited for focusing relatively narrow surfaces and range them correctly. A peculiar aspect of this work lies in the assumption that most of the returned echoes (in RA-2 IEs) are specular. A theoretical framework is developed according to this assumption, which is validated by investigating real RA-2 data and observing their related specular features. In particular, we discuss how specular echoes are expected to be very common in inland altimetry, and are most often associated with small to medium size lakes and rivers. This paper illustrates the expected electromagnetic behavior of specular water targets by exploiting the classical radar cross-section (RCS) theory for specular surfaces. Results from the model are compared with real IE data in three selected case studies, regarding two rivers of variable width and one flood plain, in order to check different hydrological regimes. The model very closely matches the data in all cases, making the results of this validation activity very promising. In particular, we demonstrate the feasibility of using satellite radar altimetry in rivers much smaller than what was considered possible until now.

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Retracking CryoSat-2, Envisat and Jason-1 radar altimetry waveforms for improved gravity field recovery

Cited by 108 publications

References 38 publications

The first Australian gravimetric quasigeoid model with location-specific uncertainty estimates

The first Australian gravimetric quasigeoid model with location-specific uncertainty estimates

Investigation of Backprojection Uncertainties With M6 Earthquakes

Envisat RA-2 Individual Echoes: A Unique Dataset for a Better Understanding of Inland Water Altimetry Potentialities

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