Arctic Ocean Sea Level Record from the Complete Radar Altimetry Era: 1991–2018

Abstract

In recent years, there has been a large focus on the Arctic due to the rapid changes of the region. Arctic sea level determination is challenging due to the seasonal to permanent sea-ice cover, lack of regional coverage of satellites, satellite instruments ability to measure ice, insufficient geophysical models, residual orbit errors, challenging retracking of satellite altimeter data. We present the European Space Agency (ESA) Climate Change Initiative (CCI) Technical University of Denmark (DTU)/Technischen Universität München (TUM) sea level anomaly (SLA) record based on radar satellite altimetry data in the Arctic Ocean from the European Remote Sensing satellite number 1 (ERS-1) (1991) to CryoSat-2 (2018). We use updated geophysical corrections and a combination of altimeter data: Reprocessing of Altimeter Product for ERS (REAPER) (ERS-1), ALES+ retracker (ERS-2, Envisat), combination of Radar Altimetry Database System (RADS) and DTUs in-house retracker LARS (CryoSat-2). Furthermore, this study focuses on the transition between conventional and Synthetic Aperture Radar (SAR) altimeter data to make a smooth time series regarding the measurement method. We find a sea level rise of 1.54 mm/year from September 1991 to September 2018 with a 95% confidence interval from 1.16 to 1.81 mm/year. ERS-1 data is troublesome and when ignoring this satellite the SLA trend becomes 2.22 mm/year with a 95% confidence interval within 1.67-2.54 mm/year. Evaluating the SLA trends in 5 year intervals show a clear steepening of the SLA trend around 2004. The sea level anomaly record is validated against tide gauges and show good results. Additionally, the time series is split and evaluated in space and time.sheet mass losses. Outlet glaciers are losing mass more rapidly [6,7], contributing to the sea level rise, changing the oceans freshwater flux, and influencing the ocean thermohaline circulation [8].The polar oceans are often not included in the global sea level estimations and can be seen as white spots on the global sea level maps. This is because of the challenging polar sea level determination due to; the seasonal to permanent sea-ice cover, the lack of regional coverage of satellites, satellite instruments ability to measure ice, insufficient geophysical models, residual orbit errors and retracking of satellite altimeter data.The sea-ice cover is in constant change. The sea-ice extent is the largest in March and the smallest in September. The Norwegian and Barents Sea are only seasonally covered by sea-ice while the central part up to the Canadian Archipelago and the North coast of Greenland are permanently ice covered (see Figure 1 for an Arctic Ocean overview). The older ice is pushed against these parts, and additionally, the Canadian Archipelago and the land-fast ice areas are also the part with the fewest leads and consequently the most inaccurate sea level determination [9].

Sea Ice Remote Sensing Using GNSS-R: A Review

“…Large-scale sea ice remote sensing data from satellites have been used intensively [8]. Sea ice conditions, such as the extent, drift, growth stage, concentration, and thickness can be estimated from data acquired by passive microwave sensors [9][10][11][12][13], scatterometer [14,15], radar altimeter [3,16,17], and synthetic aperture radar (SAR) [18][19][20]. However, passive microwave and scatterometer data are generally characterized by coarse resolutions (typically 25-50 km).…”

“…Take Cyclone GNSS (CYGNSS) system as an illustration: the achieved average revisit time is 4 h [44] and the spatial resolution can be about 10 km for cases of incoherent scattering and about 500 m for coherent cases [45]. Therefore, the spatial resolution of spaceborne GNSS-R is comparable or better than that of radar altimeters (with a nominal circular footprint of 2-10 km in diameter for Envisat or an along-track footprint of 1.65 km × 0.30 km for CryoSat-2 [17]). In addition, the distance between successive CYGNSS measurements is about 6 km.…”

Editorial for Special Issue “Advances in Satellite Altimetry and Its Application”

“…The contributions of this special issue are sorted along their application area: the first paper [1] handles method development applicable to various regions of the Earth. Afterward, oceans [2,3], polar regions [4,5], coastal areas [6,7] and inland waters [8] are addressed. The last paper [9] deals with the Moon's topography.…”

“…The last paper [9] deals with the Moon's topography. All relevant satellite radar altimetry measurement techniques are covered: from Low Resolution Mode (LRM) [4][5][6] to Synthetic Aperture Radar (SAR) [1,2,4,5,7,8] and SAR in mode [7] to SWOT [3] as well as laser altimetry [1]. In the following, each paper is briefly summarized.…”

“…Rose et al [4] presented a complete and precise overview of sea level change in the Arctic Ocean, which was obtained after evaluating 1.5 billion radar measurements of various altimetry satellites from ERS-1 to CryoSat-2. A major challenge for a comprehensive analysis is the presence of sea ice, which covers vast areas of the Arctic Ocean and obscures the ocean surface underneath.…”