Ocean tides from satellite altimetry and GRACE

Mayer‐Gürr, Torsten; Savcenko, R; Bösch, Wolfgang; Daras, Ilias; Flechtner, Frank; Dahle, Christoph

doi:10.1016/j.jog.2011.10.009

Cited by 54 publications

(36 citation statements)

References 18 publications

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“…GRACE allows for measurements of the Earth’s gravity field, producing measurements with greater magnitudes. These measurements can be used in monitoring changes in water and ice around the globe, ocean surface and deep currents, as well as provides vital information in the measurement of surface and groundwater changes [91,92,93]. Changes in the TWSA over the lake area has a direct influence on the hydrological and the ecological dynamics around the lake [49].…”

Section: Resultsmentioning

confidence: 99%

Recent Surface Water Extent of Lake Chad from Multispectral Sensors and GRACE

Buma

Seo

2018

Sensors

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Consistent observations of lakes and reservoirs that comprise the majority of surface freshwater globally are limited, especially in Africa where water bodies are exposed to unfavorable climatic conditions and human interactions. Publicly available satellite imagery has increased the ability to monitor water bodies of various sizes without much financial hassle. Landsat 7 and 8 images were used in this study to estimate area changes around Lake Chad. The Automated Water Extraction Index (AWEI), Normalized Difference Water Index (NDWI), Modified Normalized Difference Water Index (MNDWI) and Normalized Difference Vegetation Index (NDVI) were compared for the remote sensing retrieval process of surface water. Otsu threshold method was used to separate water from non-water features. With an overall accuracy of ~96% and an inter-rater agreement (kappa coefficient) of 0.91, the MNDWI was a better indicator for mapping recent area changes in Lake Chad and was used to estimate the lake’s area changes from 2003–2016. Extracted monthly areas showed an increasing trend and ranged between ~1242 km2 and 2231 km2 indicating high variability within the 13-year period, 2003–2016. In addition, we combined Landsat measurements with Total Water Storage Anomaly (TWSA) data from the Gravity Recovery and Climate Experiment (GRACE) satellites. This combination is well matched with our estimated surface area trends. This work not only demonstrates the importance of remote sensing in sparsely gauged developing countries, it also suggests the use of freely available high-quality imagery data to address existing lake crisis.

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Section: Resultsmentioning

confidence: 99%

Recent Surface Water Extent of Lake Chad from Multispectral Sensors and GRACE

Buma

Seo

2018

Sensors

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“…Applying the EOT11a global empirical ocean tide model EOT11a [35] instead of the EOT10a model [26] for orbit determination of the altimetry satellites studied by us has also minor impact on the residuals. Thus, the mean values of SLR RMS fits decrease by 0.14% for Envisat and by 0.04% for Jason-1, but increase by 0.04% for ERS-1 and 0.19% for ERS-2 over the whole duration of each mission and do not change notably for TOPEX/Poseidon.…”

Section: Determinationmentioning

confidence: 99%

Improvements in Precise Orbits of Altimetry Satellites and Their Impact on Mean Sea Level Monitoring

Rudenko

Neumayer

Dettmering

et al. 2017

IEEE Trans. Geosci. Remote Sensing

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Abstract-New, precise, consistent orbits (VER11) of altimetry satellites ERS-1, ERS-2, TOPEX/Poseidon, Envisat, Jason-1 and Jason-2 have been recently derived at GFZ German Research Centre for Geosciences in the extended ITRF2008 terrestrial reference frame using improved models and covering the time span 1991-2015. These orbits show improved quality, as compared to GFZ previous (VER6) orbits derived in 2013. Improved macromodels reduce root mean square (RMS) fits of satellite laser ranging (SLR) observations by 2.6, 6.9 and 7.0% for TOPEX/Poseidon, Jason-1 and Jason-2, respectively. Applying Vienna Mapping Functions 1 instead of Hopfield model for tropospheric correction of Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) observations reduces RMS fits of SLR observations by 2.0-2.4% and those of DORIS observations by 2.6% for Envisat and Jason satellites. Using satellite true attitude instead of models improves Jason-1 SLR RMS fits by 41% from July 2012 until July 2013. The VER11 orbits indicate the mean values of the SLR RMS fits between 1.2 and 2.1 cm for the different missions. The internal orbit consistency in the radial direction is between 0.5 and 1.9 cm. The global mean sea level trend for the period 1993 to 2014 from TOPEX, Jason-1 and Jason-2 is increased by 0.2 mm/year to 3.0 mm/year from the GFZ VER6 to VER11 orbits. Regionally, the decadal trends from GFZ VER11 and external orbits vary in the order of 1 mm/year.

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“…[2] For about one decade now, time variations in the Earth's gravity field have been monitored by the Gravity Recovery and Climate Experiment (GRACE) [Tapley et al, 2004] satellite mission. This novel data set provides valuable insight into a number of mass redistribution phenomena on Earth that include ice-mass changes and their relation to global atmospheric circulation patterns [Sasgen et al, 2010] and contribution to sea level [Jacob et al, 2012], terrestrial water storage variations and groundwater depletion [Rodell et al, 2009], coseismic displacements associated with major earthquakes [Han et al, 2006], ocean tides in ice-covered seas [Mayer-G€ urr et al, 2012], or large-scale ocean bottom pressure variations and their relation to the time-varying winds [Boening et al, 2011].…”

Section: Introductionmentioning

confidence: 99%

Simulating high-frequency atmosphere-ocean mass variability for dealiasing of satellite gravity observations: AOD1B RL05

Dobslaw

Flechtner

Bergmann-Wolf

et al. 2013

J. Geophys. Res. Oceans

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118

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[1] An improved version of the OMCT ocean model with 1 spatial resolution provides bottom pressure anomalies for the new release 05 of the GRACE Atmosphere and Ocean Dealiasing Level 1B (AOD1B) product. For high-frequency signals with periods below 30 days, this model explains up to 10 cm 2 of the residual sea level variance seen by ENVISAT in large parts of the Southern Ocean, corresponding to about 40% of the observed sea level residuals in many open ocean regions away from the tropics. Comparable amounts of variance are also explained by AOD1B RL05 for colocated in situ ocean bottom pressure recorders. Although secular trends contained in AOD1B RL05 cause GRACE KBRR residuals to increase in shallow water regions, we find a reduction of those residuals over all open ocean areas, indicating that AOD1B RL05 is much better suited to remove nontidal high-frequency mass variability from satellite gravity observations than previous versions of AOD1B.Citation: Dobslaw, H., F. Flechtner, I. Bergmann-Wolf, C. Dahle, R. Dill, S. Esselborn, I. Sasgen, and M. Thomas (2013), Simulating high-frequency atmosphere-ocean mass variability for dealiasing of satellite gravity observations: AOD1B RL05,

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Ocean tides from satellite altimetry and GRACE

Cited by 54 publications

References 18 publications

Recent Surface Water Extent of Lake Chad from Multispectral Sensors and GRACE

Recent Surface Water Extent of Lake Chad from Multispectral Sensors and GRACE

Improvements in Precise Orbits of Altimetry Satellites and Their Impact on Mean Sea Level Monitoring

Simulating high-frequency atmosphere-ocean mass variability for dealiasing of satellite gravity observations: AOD1B RL05

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