# Altimetry - Explore the Science & Experts | ideXlab

## Altimetry

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### Pierre Prandi – One of the best experts on this subject based on the ideXlab platform.

• ##### Arctic Sea Level During the Satellite Altimetry Era
Surveys in Geophysics, 2017
Co-Authors: A. Carret, Jon-arild Johannessen, O. B. Andersen, Michael Ablain, Pierre Prandi, Ana Blázquez, Anny Cazenave

Abstract:

Results of the sea-level budget in the high latitudes (up to 80°N) and the Arctic Ocean during the satellite Altimetry era. We investigate the closure of the sea-level budget since 2002 using two Altimetry sea-level datasets based on the Envisat waveform retracking: temperature and salinity data from the ORAP5 reanalysis, and Gravity Recovery And Climate Experiment (GRACE) space gravimetry data to estimate the steric and mass components. Regional sea-level trends seen in the Altimetry map, in particular over the Beaufort Gyre and along the eastern coast of Greenland, are of halosteric origin. However, in terms of regional average over the region ranging from 66°N to 80°N, the steric component contributes little to the observed sea-level trend, suggesting a dominant mass contribution in the Arctic region. This is confirmed by GRACE-based ocean mass time series that agree well with the Altimetry-based sea-level time series. Direct estimate of the mass component is not possible prior to GRACE. Thus, we estimated the mass contribution from the difference between the Altimetry-based sea level and the steric component. We also investigate the coastal sea level with tide gauge records. Twenty coupled climate models from the CMIP5 project are also used. The models lead us to the same conclusions concerning the halosteric origin of the trend patterns.

• ##### Monitoring Sea Level in the Coastal Zone with Satellite Altimetry and Tide Gauges
Surveys in Geophysics, 2017
Co-Authors: Paolo Cipollini, Francisco M. Calafat, Svetlana Jevrejeva, Angelique Melet, Pierre Prandi

Abstract:

We examine the issue of sustained measurements of sea level in the coastal zone, first by summarizing the long-term observations from tide gauges, then showing how those are now complemented by improved satellite Altimetry products in the coastal ocean. We present some of the progresses in coastal Altimetry, both from dedicated reprocessing of the radar waveforms and from the development of improved corrections for the atmospheric effects. This trend towards better altimetric data at the coast comes also from technological innovations such as Ka-band Altimetry and SAR Altimetry, and we discuss the advantages deriving from the AltiKa Ka-band altimeter and the SIRAL altimeter on CryoSat-2 that can be operated in SAR mode. A case study along the UK coast demonstrates the good agreement between coastal Altimetry and tide gauge observations, with root mean square differences as low as 4 cm at many stations, allowing the characterization of the annual cycle of sea level along the UK coasts. Finally, we examine the evolution of the sea level trend from the open to the coastal ocean along the western coast of Africa, comparing standard and coastally improved products. Different products give different sea level trend profiles, so the recommendation is that additional efforts are needed to study sea level trends in the coastal zone from past and present satellite altimeters. Further improvements are expected from more refined processing and screening of data, but in particular from the constant improvements in the geophysical corrections.

• ##### Sea level variability in the Arctic Ocean observed by satellite Altimetry
Ocean Science Discussions, 2012
Co-Authors: Pierre Prandi, Anny Cazenave, Michael Ablain, Nicolas Picot

Abstract:

Abstract. We investigate sea level variability in the Arctic Ocean from observations. Variability estimates are derived both at the basin scale and on smaller local spatial scales. The periods of the signals studied vary from high frequency (intra-annual) to long term trends. We also investigate the mechanisms responsible for the observed variability. Different data types are used, the main one being a recent reprocessing of satellite Altimetry data in the Arctic Ocean. Satellite Altimetry data is compared to tide gauges measurements, steric sea level derived from temperature and salinity fields and GRACE ocean mass estimates. We establish a consistent regional sea level budget over the GRACE availability era (2003–2009) showing that the sea level drop observed by Altimetry over this period is driven by ocean mass loss rather than steric effects. The comparison of Altimetry and tide gauges time series show that the two techniques are in good agreement regarding sea level trends. Coastal areas of high variability in the Altimetry record are also consistent with tide gauges records. An EOF analysis of September mean Altimetry fields allows identifying two regions of wind driven variability in the Arctic Ocean: the Beaufort Gyre region and the coastal European and Russian Arctic. Such patterns are related to atmospheric regimes through the Arctic Oscillation and Dipole Anomaly.

### Anny Cazenave – One of the best experts on this subject based on the ideXlab platform.

• ##### Arctic Sea Level During the Satellite Altimetry Era
Surveys in Geophysics, 2017
Co-Authors: A. Carret, Jon-arild Johannessen, O. B. Andersen, Michael Ablain, Pierre Prandi, Ana Blázquez, Anny Cazenave

Abstract:

Results of the sea-level budget in the high latitudes (up to 80°N) and the Arctic Ocean during the satellite Altimetry era. We investigate the closure of the sea-level budget since 2002 using two Altimetry sea-level datasets based on the Envisat waveform retracking: temperature and salinity data from the ORAP5 reanalysis, and Gravity Recovery And Climate Experiment (GRACE) space gravimetry data to estimate the steric and mass components. Regional sea-level trends seen in the Altimetry map, in particular over the Beaufort Gyre and along the eastern coast of Greenland, are of halosteric origin. However, in terms of regional average over the region ranging from 66°N to 80°N, the steric component contributes little to the observed sea-level trend, suggesting a dominant mass contribution in the Arctic region. This is confirmed by GRACE-based ocean mass time series that agree well with the Altimetry-based sea-level time series. Direct estimate of the mass component is not possible prior to GRACE. Thus, we estimated the mass contribution from the difference between the Altimetry-based sea level and the steric component. We also investigate the coastal sea level with tide gauge records. Twenty coupled climate models from the CMIP5 project are also used. The models lead us to the same conclusions concerning the halosteric origin of the trend patterns.

• ##### Effect of the processing methodology on satellite Altimetry-based global mean sea level rise over the Jason-1 operating period
Journal of Geodesy, 2014
Co-Authors: Olivier Henry, Anny Cazenave, Michael Ablain, Benoit Meyssignac, Dallas Masters, Steve Nerem, Gilles Garric

Abstract:

Determining how the global mean sea level (GMSL) evolves with time is of primary importance to understand one of the main consequences of global warming and its potential impact on populations living near coasts or in low-lying islands. Five groups are routinely providing satellite Altimetry-based estimates of the GMSL over the Altimetry era (since late 1992). Because each group developed its own approach to compute the GMSL time series, this leads to some differences in the GMSL interannual variability and linear trend. While over the whole high-precision Altimetry time span (1993–2012), good agreement is noticed for the computed GMSL linear trend (of $$3.1\pm 0.4$$ 3.1 ± 0.4  mm/year), on shorter time spans (e.g., {

• ##### Sea level variability in the Arctic Ocean observed by satellite Altimetry
Ocean Science Discussions, 2012
Co-Authors: Pierre Prandi, Anny Cazenave, Michael Ablain, Nicolas Picot

Abstract:

Abstract. We investigate sea level variability in the Arctic Ocean from observations. Variability estimates are derived both at the basin scale and on smaller local spatial scales. The periods of the signals studied vary from high frequency (intra-annual) to long term trends. We also investigate the mechanisms responsible for the observed variability. Different data types are used, the main one being a recent reprocessing of satellite Altimetry data in the Arctic Ocean. Satellite Altimetry data is compared to tide gauges measurements, steric sea level derived from temperature and salinity fields and GRACE ocean mass estimates. We establish a consistent regional sea level budget over the GRACE availability era (2003–2009) showing that the sea level drop observed by Altimetry over this period is driven by ocean mass loss rather than steric effects. The comparison of Altimetry and tide gauges time series show that the two techniques are in good agreement regarding sea level trends. Coastal areas of high variability in the Altimetry record are also consistent with tide gauges records. An EOF analysis of September mean Altimetry fields allows identifying two regions of wind driven variability in the Arctic Ocean: the Beaufort Gyre region and the coastal European and Russian Arctic. Such patterns are related to atmospheric regimes through the Arctic Oscillation and Dipole Anomaly.

### M. Becker – One of the best experts on this subject based on the ideXlab platform.

• ##### is coastal mean sea level rising faster than the global mean a comparison between tide gauges and satellite Altimetry over 1993 2007
Geophysical Research Letters, 2009
Co-Authors: Pierre Prandi, Anny Cazenave, M. Becker

Abstract:

[1] Based on a careful selection of tide gauges records from the Global Sea Level Observing System network, we investigate whether coastal mean sea level is rising faster than the global mean derived from satellite Altimetry over the January 1993–December 2007 time span. Over this 15-year time span, mean coastal rate of sea level rise is found to be +3.3 ± 0.5 mm/yr, in good agreement with the Altimetry-derived rate of +3.4 ± 0.1 mm/yr. Tests indicate that the trends are statistically significant, hence coastal sea level does not rise faster than the global mean. Although trends agree well, tide gauges-based mean sea level exhibits much larger interannual variability than Altimetry-based global mean. Interannual variability in coastal sea level appears related to the regional variability in sea level rates reported by satellite Altimetry. When global mean sea level is considered (as allowed by satellite Altimetry coverage), interannual variability is largely smoothed out.

• ##### Is coastal mean sea level rising faster than the global mean? A comparison between tide gauges and satellite Altimetry over 1993-2007
Geophysical Research Letters, 2009
Co-Authors: Pierre Prandi, Anny Cazenave, M. Becker

Abstract:

Based on a careful selection of tide gauges records from the Global Sea Level Observing System network, we investigate whether coastal mean sea level is rising faster than the global mean derived from satellite Altimetry over the January 1993-December 2007 time span. Over this 15-year time span, mean coastal rate of sea level rise is found to be + 3.3 +/- 0.5 mm/yr, in good agreement with the Altimetry-derived rate of + 3.4 +/- 0.1 mm/yr. Tests indicate that the trends are statistically significant, hence coastal sea level does not rise faster than the global mean. Although trends agree well, tide gauges-based mean sea level exhibits much larger interannual variability than Altimetry-based global mean. Interannual variability in coastal sea level appears related to the regional variability in sea level rates reported by satellite Altimetry. When global mean sea level is considered (as allowed by satellite Altimetry coverage), interannual variability is largely smoothed out. Citation: Prandi, P., A. Cazenave, and M. Becker (2009), Is coastal mean sea level rising faster than the global mean? A comparison between tide gauges and satellite Altimetry over 1993-2007, Geophys. Res. Lett., 36, L05602, doi:10.1029/2008GL036564.