A Multi-Leading Edge and Multi-Threshold Waveform Retracker

Chang, Xiaotao; Li, Jian Cheng; Guo, J.; Hwang, Cheinway

doi:10.1002/cjg2.975

Cited by 10 publications

(4 citation statements)

References 14 publications

(7 reference statements)

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“…The threshold retracker was developed by Davis (1993) and this algorithm uses a prescribed threshold value with respect to the OCOG amplitude or the maximum waveform amplitude to determine the objective gate and improve the estimation of range. The improved threshold retracker has been developed in the case of complex waveforms to identify sub-waveforms within the measured waveform and select the best ranging gate (Hwang et al, 2006;Chang et al, 2006;Guo et al, 2010). The Beta-5 parameter retracker was developed by Martin et al (1983) to retrieve ranges from the single-ramp return waveforms by fitting a 5-parameter functional model.…”

Section: Retracker Selectionmentioning

confidence: 99%

Inversion of marine gravity anomalies over southeastern China seas from multi-satellite altimeter vertical deflections

Zhang

Sandwell

Jin

et al. 2017

Journal of Applied Geophysics

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The accuracy and resolution of marine gravity field derived from satellite altimetry mainly depends on the range precision and dense spatial distribution. This paper aims at modeling a regional marine gravity field with improved accuracy and higher resolution (1′×1′) over Southeastern China Seas using additional data from CryoSat-2 as well as new data from AltiKa. Three approaches are used to enhance the precision level of satellite-derived gravity anomalies. Firstly we evaluate a suite of published retracking algorithms and find the two-step retracker is optimal for open ocean waveforms. Secondly, we evaluate the filtering and resampling procedure used to reduce the full 20 or 40 Hz data to a lower rate having lower noise. We adopt a uniform low-pass filter for all altimeter missions and resample at 5 Hz and then perform a second editing based on sea surface slope estimates from previous models. Thirdly, we selected WHU12 model to update the corrections provided in geophysical data record. We finally calculated the 1'×1' marine gravity field model by using EGM2008 model as reference field during the remove/restore procedure. The root mean squares of the discrepancies between the new result and DTU10, DTU13, V23.1, EGM2008 are within the range of 1.8~3.9mGal, while the verification with respect to shipboard gravity data shows that the accuracy of the new result reached a comparable level with DTU13 and was slightly superior to V23.1, DTU10 and EGM2008 models. Moreover, the new result has a 2mGal better accuracy over open seas than coastal areas with shallow water depth.

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Section: Retracker Selectionmentioning

confidence: 99%

Inversion of marine gravity anomalies over southeastern China seas from multi-satellite altimeter vertical deflections

Zhang

Sandwell

Jin

et al. 2017

Journal of Applied Geophysics

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“…Waveform retracking methods can be classified into two types as the function fitting method and the statistical method [3,7,8], mainly including the β-parameter fitting model [9], the model of offset center of gravity (OCOG) [10], the threshold model [11], and the surface and volume scattering retracking algorithm (SVSR) [12]. Supposing that the returned pulse is Gaussian, the 5-/9-parameter function in the β-parameter fitting model is solved to fit the waveforms in the least squares sense.…”

mentioning

confidence: 99%

A multi-subwaveform parametric retracker of the radar satellite altimetric waveform and recovery of gravity anomalies over coastal oceans

Guo

Gao

Hwang³

et al. 2009

Sci. China Earth Sci.

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The quality of satellite radar altimetric data is very important in studies of geodesy, geophysics, and oceanography. Over coastal oceans, altimeter waveforms are contaminated by the terrain and physical environments so that the accuracy of altimeter data is lower than that over open oceans. Here we develop a new multi-subwaveform parametric retracker (MSPR) to improve the quality of altimeter data for the recovery of gravity anomaly in coastal oceans. The least squares collocation method is used to recover the residual gravity anomaly over the coastal water from altimetric data. The waveform data records from Geosat/GM around Taiwan Island are practically retracked with MSPR. When compared with the Taiwan geoid height, the results retracked by MSPR are more accurate than those retracked by the well-known β-5-parmeter method and from the geophysical data records (GDRs). The gravity anomalies over Taiwan coastal waters are calculated from the retracked altimeter data with the least squares collocation. When we compared gravity anomalies computed using altimeter GDRs with the ship-borne gravity data over Taiwan coastal ocean, we found that the results from retracked data are more accurate than those from GDRs. multi-subwaveform parametric retracker, waveform retracking for radar satellite altimetry, gravity anomaly, least squares collocation, Geosat/GM Citation:Guo J Y, Gao Y G, Hwang C W, et al. A multi-subwaveform parametric retracker of the radar satellite altimetric waveform and recovery of gravity anomalies over coastal oceans.

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“…Given the coastal land topography, the powers of the echoed waveforms fluctuate continuously. Therefore, AGC has to adjust successively according to the power of the preceding echoed waveforms (Remy et al, 1990;Chang et al, 2006). Consequently, SSHs derived from contaminated altimetric waveforms are relatively low in accuracy within 0 to 5 km from coasts.…”

Section: Resultsmentioning

confidence: 99%

“…(AGC) processes differ when satellite moves through coastlines from ocean to land and vice versa; thus, waveforms evolve differently and are totally irreversible (Chang et al, 2006). Because of the lag effect of AGC and different or mixed characteristics of the reflected surfaces in the coastal regions, the ordinate units are not consistent throughout all the subfigures in Figure 3.…”

Section: Study Area and Datamentioning

confidence: 99%

Improvement of Envisat Altimetric Measurements in Taiwan Coastal Oceans by a Developed Waveform Retracking System

Kuo¹,

Yang²,

Kao³

et al. 2015

J ENV INFORM

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A new waveform retracking system applied on 18-Hz Envisat RA-2 data (cycles 10 to 90) was successfully developed in this study and aimed to improve the accuracy of measuring sea surface heights (SSHs) in coastal oceans around Taiwan. The specialized retracking system comprised the CurveFit retracker of fitting altimetry subwaveforms to the Brown model along with Gaussian peak models and a technique of removing non-ocean waveforms. Therefore, our system can favorably retain ocean-reflected waveforms and effectively reduce the land contamination in reflected waveforms. Results demonstrated that the CurveFit retracker performed best within 0 to 5 km offshore in all the study areas, with improvement percentages (IMPs) reaching a maximum of 92%. Within 5 to 10 km from the coast, the CurveFit retracked SSHs considerably improved with an IMP of up to 93%. Given that most waveforms, particularly of ground tracks from ocean to land, conformed to a typical ocean model in the 5 to 10 km zone, all the used retrackers similarly achieved satisfactory and equivalent improvements. This study also manifested that the accuracy of retracked SSHs largely depends on both land topography and ground tracks approaching or leaving land. The amount and accuracy of valid retracked measurements along ground tracks from land to ocean were remarkably lower than those of ground tracks across the coastline reversely. Moreover, the altimetric waveforms were highly contaminated by coastal land topography when ground tracks approached coastal flat land from the ocean or passed through coastal undulating topography toward the ocean.

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A Multi-Leading Edge and Multi-Threshold Waveform Retracker

Cited by 10 publications

References 14 publications

Inversion of marine gravity anomalies over southeastern China seas from multi-satellite altimeter vertical deflections

Inversion of marine gravity anomalies over southeastern China seas from multi-satellite altimeter vertical deflections

A multi-subwaveform parametric retracker of the radar satellite altimetric waveform and recovery of gravity anomalies over coastal oceans

Improvement of Envisat Altimetric Measurements in Taiwan Coastal Oceans by a Developed Waveform Retracking System

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