Coastal sea level from CryoSat-2 SARIn altimetry in Norway

Idžanović, Martina; Ophaug, Vegard; Andersen, Ole

doi:10.1016/j.asr.2017.07.043

Cited by 24 publications

(26 citation statements)

References 24 publications

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“…The 1 Hz CS2 data agree better with the tide-gauge time series than the 20 Hz data in terms of mean correlations. The agreement between the 20 Hz CS2 data and tide-gauge data from NMA (mean standard deviation of 12.1 cm and mean correlation of 0.77) represents encouraging improvements compared to the results in Idžanović et al [22]. For the same 20 tide gauges, they obtained a mean standard deviation of 14.7 cm and a mean correlation of 0.64 using standard CS2 corrections and the simple threshold retracker.…”

Section: Summary and Discussionsupporting

confidence: 57%

“…Next, we rejected all |SLA| > 1 m. To identify and eliminate outliers, we used the same approach as outlined in Idžanović et al [22]. With this method, the multiple Student's t test [23] was applied to the sea-level anomalies in each individual satellite pass.…”

Section: Cryosat-2 Sarin Data Processingmentioning

confidence: 99%

“…In the last step, we established 45 km × 45 km boxes around each tide gauge containing CS2 observations and formed "CS2 tide gauges", see Figures 1b and 2. The positions and dimension of the CS2 boxes are equivalent to those defined in Idžanović et al [22]. Using the 20 Hz CS2 data, we have significantly more CS2 observations available in our CS2 boxes (see Table 1), and can gain a few kilometers towards the tide gauges.…”

Section: Cryosat-2 Sarin Data Processingmentioning

confidence: 99%

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An Attempt to Observe Vertical Land Motion along the Norwegian Coast by CryoSat-2 and Tide Gauges

et al. 2019

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Present-day climate-change-related ice-melting induces elastic glacial isostatic adjustment (GIA) effects, while paleo-GIA effects describe the ongoing viscous response to the melting of late-Pleistocene ice sheets. The unloading initiated an uplift of the crust close to the centers of former ice sheets. Today, vertical land motion (VLM) rates in Fennoscandia reach values up to around 10 mm/year and are dominated by GIA. Uplift signals from GIA can be computed by solving the sea-level equation (SLE),Ṡ =Ṅ −U. All three quantities can also be determined from geodetic observations: relative sea-level variations (Ṡ) are observed by means of tide gauges, while rates of absolute sea-level change (Ṅ) can be observed by satellite altimetry; rates of VLM (U) can be determined by GPS (Global Positioning System). Based on the SLE,U can be derived by combining sea-surface measurements from satellite altimetry and relative sea-level records from tide gauges. In the present study, we have combined 7.5 years of CryoSat-2 satellite altimetry and tide-gauge data to estimate linear VLM rates at 20 tide gauges along the Norwegian coast. Thereby, we made use of monthly averaged tide-gauge data from PSMSL (Permanent Service for Mean Sea Level) and a high-frequency tide-gauge data set with 10-min sampling rate from NMA (Norwegian Mapping Authority). To validate our VLM estimates, we have compared them with the independent semi-empirical land-uplift model NKG2016LU_abs for the Nordic-Baltic region, which is based on GPS, levelling, and geodynamical modeling. Estimated VLM rates from 1 Hz CryoSat-2 and high-frequency tide-gauge data reflect well the amplitude of coastal VLM as provided by NKG2016LU_abs. We find a coastal average of 2.4 mm/year (average over all tide gauges), while NKG2016LU_abs suggests 2.8 mm/year; the spatial correlation is 0.58.

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Section: Summary and Discussionsupporting

confidence: 57%

Section: Cryosat-2 Sarin Data Processingmentioning

confidence: 99%

Section: Cryosat-2 Sarin Data Processingmentioning

confidence: 99%

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An Attempt to Observe Vertical Land Motion along the Norwegian Coast by CryoSat-2 and Tide Gauges

et al. 2019

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“…Consequently, we envisage that SAR-mode altimetry will generate more data right at the coast. The benefits of altimetry in SAR mode along the Norwegian coast were investigated by [49]. They demonstrated that a preliminary release of Cryosat-2 SIRAL (Synthetic Aperture Interferometric Radar Altimeter) data provides reliable and comprehensive sets of data in 45 × 45 km boxes around most Norwegian tide gauges, at least at tide gauges close to the open ocean.…”

Section: Discussionmentioning

confidence: 99%

Observed Sea-Level Changes along the Norwegian Coast

Breili

Simpson

Nilsen

2017

JMSE

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Norway's national sea level observing system consists of an extensive array of tide gauges, permanent GNSS stations, and lines of repeated levelling. Here, we make use of this observation system to calculate relative sea-level rates and rates corrected for glacial isostatic adjustment (GIA) along the Norwegian coast for three different periods, i.e., 1960 to 2010, 1984 to 2014, and 1993 to 2016. For all periods, the relative sea-level rates show considerable spatial variations that are largely due to differences in vertical land motion due to GIA. The variation is reduced by applying corrections for vertical land motion and associated gravitational effects on sea level. For 1960 to 2010 and 1984 to 2014, the coastal average GIA-corrected rates for Norway are 2.0 ± 0.6 mm/year and 2.2 ± 0.6 mm/year, respectively. This is close to the rate of global sea-level rise for the same periods. For the most recent period, 1993 to 2016, the GIA-corrected coastal average is 3.5 ± 0.6 mm/year and 3.2 ± 0.6 mm/year with and without inverse barometer (IB) corrections, respectively, which is significantly higher than for the two earlier periods. For 1993 to 2016, the coastal average IB-corrected rates show broad agreement with two independent sets of altimetry. This suggests that there is no systematic error in the vertical land motion corrections applied to the tide-gauge data. At the same time, altimetry does not capture the spatial variation identified in the tide-gauge records. This could be an effect of using altimetry observations off the coast instead of directly at each tide gauge. Finally, we note that, owing to natural variability in the climate system, our estimates are highly sensitive to the selected study period. For example, using a 30-year moving window, we find that the estimated rates may change by up to 1 mm/year when shifting the start epoch by only one year.

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“…The present work has found that the CryoSat‐2 data can be used to estimate tides with a precision comparable to that available from other data sources, even if they were not found useful for identifying topography or water column thickness. Improvements may be anticipated from innovations in processing CryoSat‐2 waveforms over ice surfaces (Nilsson et al, ) and ocean surfaces (Boy et al, ; Idzanovic et al, ), and a new version of the entire CryoSat‐2 geophysical data record is being prepared (Bouffard et al, ). Future efforts should aim to utilize these data more widely for mapping tides in the polar oceans.…”

Section: Discussion and Summarymentioning

confidence: 99%

Simultaneous Estimation of Ocean Tides and Underwater Topography in the Weddell Sea

Zaron

2019

JGR Oceans

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A new model for the M2, S2, K1, and O1 tides in the Weddell Sea is developed by assimilating CryoSat‐2 data into a barotropic tide model. A variational approach is used, which explicitly allows for errors in the water depth, that is, the bottom topography in open water and the water column thickness under floating ice shelves, so that an optimized estimate of the topography is obtained together with the tidal fields. In preparation for assimilation, the sensitivity of the tidal elevation to the interfacial drag at the sea floor and the ice‐water interface (under the floating ice shelves) is investigated; this motivates the development of a new drag parameterization which is more accurate and physically plausible in comparison with the interfacial drag alone. The assimilation of CryoSat‐2 data into the model results in tidal elevations with essentially the same accuracy as previous estimates, which is demonstrated by comparisons with independent in situ data and withheld CryoSat‐2 data. The novelty of the present tidal estimates is that they are consistent with well‐defined dynamics based on the Laplace Tidal Equations—augmented with the new parameterization of drag—and modifications of the prior estimate of underwater topography and water column thickness. Analysis of the sensitivity to the topography finds that, at this level of precision, the topography is not uniquely determined by the observed data.

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Coastal sea level from CryoSat-2 SARIn altimetry in Norway

Cited by 24 publications

References 24 publications

An Attempt to Observe Vertical Land Motion along the Norwegian Coast by CryoSat-2 and Tide Gauges

An Attempt to Observe Vertical Land Motion along the Norwegian Coast by CryoSat-2 and Tide Gauges

Observed Sea-Level Changes along the Norwegian Coast

Simultaneous Estimation of Ocean Tides and Underwater Topography in the Weddell Sea

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