GNSS-Derived Path Delay: An Approach to Compute the Wet Tropospheric Correction for Coastal Altimetry

Fernandes, Joana; Lázaro, Clara; Nunes, Alexandra L.; Pires, Nelson; Bastos, L.; Mendes, V. B.

doi:10.1109/lgrs.2010.2042425

Cited by 48 publications

(30 citation statements)

References 13 publications

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“…In these regions, alternative sources must be used. For regions possessing permanent GNSS stations, GNSS-derived wet path delays can be derived with an accuracy close to 1 cm, the same accuracy as MWR-derived WTC (e.g., [55]). This approach is particularly favorable for small lakes and reservoirs, where the measurements at a single location can be representative of the whole lake, the approach followed by, e.g., [7].…”

Section: Wtc Estimationmentioning

confidence: 97%

“…The problems associated with the computation of the wet tropospheric correction in the coastal regions, where the MWR measurements also become invalid, in the context of missions possessing an on-board MWR, has been addressed by several authors [53][54][55][56]. These authors have derived algorithms for improving the WTC in the coastal regions, but these algorithms have not been customized for inland water regions.…”

Section: Wtc Estimationmentioning

confidence: 99%

“…This approach is particularly favorable for small lakes and reservoirs, where the measurements at a single location can be representative of the whole lake, the approach followed by, e.g., [7]. However, unlike the coastal regions, where GNSS data have been used in combination with other available wet path delay sources (valid MWR measurements in the vicinity of the point and model values) [55], so far, this procedure has not been exploited over inland water regions.…”

Section: Wtc Estimationmentioning

confidence: 99%

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Atmospheric Corrections for Altimetry Studies over Inland Water

et al. 2014

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Originally designed for applications over the ocean, satellite altimetry has been proven to be a useful tool for hydrologic studies. Altimeter products, mainly conceived for oceanographic studies, often fail to provide atmospheric corrections suitable for inland water studies. The focus of this paper is the analysis of the main issues related with the atmospheric corrections that need to be applied to the altimeter range to get precise water level heights. Using the corrections provided on the Radar Altimeter Database System, the main errors present in the dry and wet tropospheric corrections and in the ionospheric correction of the various satellites are reported. It has been shown that the model-based tropospheric corrections are not modeled properly and in a consistent way in the various altimetric products. While over the ocean, the dry tropospheric correction (DTC) is one of the most precise range corrections, in some of the present altimeter products, it is the correction with the largest errors over continental water regions, causing large biases of several decimeters, and along-track interpolation errors up to several centimeters, both with small temporal variations. The wet tropospheric correction (WTC) from the on-board microwave radiometers is hampered by the contamination on the radiometer measurements of the surrounding lands, making it usable only in the central parts of large lakes. In addition, the WTC from atmospheric models may also have large errors when it is OPEN ACCESSRemote Sens. 2014, 6 4953 provided at sea level instead of surface height. These errors cannot be corrected by the user, since no accurate expression exists for the height variation of the WTC. Alternative and accurate corrections can be computed from in situ data, e.g., DTC from surface pressure at barometric stations and WTC from Global Navigation Satellite System permanent stations. The latter approach is particularly favorable for small lakes and reservoirs, where GNSS-derived WTC at a single location can be representative of the whole lake. For non-timely critical studies, for consistency and stability, model-derived tropospheric corrections from European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis ERA Interim, properly computed at surface height, are recommended. The instrument-based dual-frequency ionospheric correction may have errors related with the land contamination in the Ku and C/S bands, making it more suitable to use a model-based correction. The most suitable model-based ionospheric correction is the Jet Propulsion Laboratory (JPL) global ionosphere map (GIM) model, available after 1998, properly scaled to the altimeter height. Most altimeter products provide the GIM correction unreduced for the total electron content extending above the altitude of these satellites, thus overestimating the ionospheric correction by about 8%. Prior to 1998, the NIC09 (NOAA Ionosphere Climatology 2009) climatology provides the best accuracy.

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Section: Wtc Estimationmentioning

confidence: 97%

Section: Wtc Estimationmentioning

confidence: 99%

Section: Wtc Estimationmentioning

confidence: 99%

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Atmospheric Corrections for Altimetry Studies over Inland Water

et al. 2014

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“…The DComb algorithm, based on the approaches followed by [2][3][4], estimates the WTC using objective analysis of several available data sources: Scanning MWR on board remote sensing (RS) satellites, Global Navigation Satellite Systems (GNSS), and the ECMWF ReAnalysis (ERA) Interim model. The purpose of the present study is the analysis and inter-calibration of some of the datasets used in the computation of the wet path delay of altimeter measurements over ocean, including open ocean, polar regions, and coastal zones, for their use in the DComb algorithm.…”

Section: Introductionmentioning

confidence: 99%

Analysis and Inter-Calibration of Wet Path Delay Datasets to Compute the Wet Tropospheric Correction for CryoSat-2 over Ocean

2013

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Unlike most altimetric missions, CryoSat-2 is not equipped with an onboard microwave radiometer (MWR) to provide wet tropospheric correction (WTC) to radar altimeter measurements, thus, relying on a model-based one provided by the European Center for Medium-range Weather Forecasts (ECMWF). In the ambit of ESA funded project CP4O, an improved WTC for CryoSat-2 data over ocean is under development, based on a data combination algorithm (DComb) through objective analysis of WTC values derived from all existing global-scale data types. The scope of this study is the analysis and inter-calibration of the large dataset of total column water vapor (TCWV) products from scanning MWR aboard Remote Sensing (RS) missions for use in the WTC computation for CryoSat-2. The main issues regarding the computation of the WTC from all TCWV products are discussed. The analysis of the orbital parameters of CryoSat-2 and all other considered RS missions, their sensor characteristics and inter-calibration is presented, providing an insight into the expected impact of these datasets on the WTC estimation. The most suitable approach for calculating the WTC from TCWV is investigated. For this type of application, after calibration with respect to an appropriate reference, two approaches were found to give very similar results, with root mean square differences of 2 mm.

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“…In recent years, GNSS was increasingly used to estimate regional wet troposphere delay [27,28], which can serve as basis to assess the delay derived from global climate models and improve altimetric measurements over land. Fernandes et al [29] reported that the means of differences between the zenith wet delays derived from GNSS and microwave radiometers onboard altimeters range between −11 mm to −5 mm with standard deviations (STDs) in the range of 17-22 mm.…”

Section: Introductionmentioning

confidence: 99%

Monitoring Vertical Land Motions in Southwestern Taiwan with Retracked Topex/Poseidon and Jason-2 Satellite Altimetry

et al. 2015

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This study successfully uses satellite altimetry, including Topex/Poseidon and Jason-2, retrieved by novel retrackers to monitor vertical land motions in Southwestern Taiwan. Satellite altimetry was originally designed to measure open oceans, so waveform retracking should be applied to overcome the complex waveforms reflected from lands. Modified threshold and improved subwaveform threshold retrackers were used in the study to improve the accuracy of altimetric land surface heights (LSHs) in Southwestern Taiwan. Results indicate that the vertical motion rates derived from both retrackers coincide with those calculated by 1843 precise leveling points, with a correlation coefficient of 0.96 and mean differences of 0.43 and 0.52 cm/yr (standard deviations: 0.61 and 0.69 cm/yr). In addition, wet troposphere delay by precise point positioning with the use of Global Navigation Satellite System data was employed to evaluate the impact of the delay on the estimates of vertical motion rates compared with that traditionally derived from the European Center for Medium-Range Weather Forecasts model when the microwave radiometer is non-functional over lands. The accuracies of retracked altimetric land motion rates corrected by wet troposphere delays derived from both models show no remarkable differences in the Tuku and Yuanchang areas because the accuracy of retracked altimetric LSHs is significantly worse than that of wet troposphere delays.

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GNSS-Derived Path Delay: An Approach to Compute the Wet Tropospheric Correction for Coastal Altimetry

Cited by 48 publications

References 13 publications

Atmospheric Corrections for Altimetry Studies over Inland Water

Atmospheric Corrections for Altimetry Studies over Inland Water

Analysis and Inter-Calibration of Wet Path Delay Datasets to Compute the Wet Tropospheric Correction for CryoSat-2 over Ocean

Monitoring Vertical Land Motions in Southwestern Taiwan with Retracked Topex/Poseidon and Jason-2 Satellite Altimetry

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