Snow Property Controls on Modeled Ku-Band Altimeter Estimates of First-Year Sea Ice Thickness: Case Studies From the Canadian and Norwegian Arctic

Nandan, Vishnu; Scharien, Randall K.; Geldsetzer, Torsten; Kwok, R.; Yackel, John J.; Mahmud, Mallik; Rösel, Anja; Tonboe, Rasmus; Granskog, Mats A.; Willatt, Rosemary; Stroeve, Julienne; Nomura, Daïki; Frey, M. M.

doi:10.1109/jstars.2020.2966432

Cited by 25 publications

(44 citation statements)

References 66 publications

(109 reference statements)

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“…Kroisleitner et al, 2018), but usage of satellite altimetry in this context remains unexplored. Signal interaction with vegetation limits the applicability of Ku-and Ka-bands for soil observations regarding freeze and thaw status (Park et al, 2011) as well as surface height. Wider use of altimetry for snow and permafrost applications requires higher spatial resolution and temporal coverage than what is available to Figure 2.…”

Section: Snow On Land and Permafrostmentioning

confidence: 99%

The Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) high-priority candidate mission

et al. 2020

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Abstract. The Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) mission is one of six high-priority candidate missions (HPCMs) under consideration by the European Commission to enlarge the Copernicus Space Component. Together, the high-priority candidate missions fill gaps in the measurement capability of the existing Copernicus Space Component to address emerging and urgent user requirements in relation to monitoring anthropogenic CO2 emissions, polar environments, and land surfaces. The ambition is to enlarge the Copernicus Space Component with the high-priority candidate missions in the mid-2020s to provide enhanced continuity of services in synergy with the next generation of the existing Copernicus Sentinel missions. CRISTAL will carry a dual-frequency synthetic-aperture radar altimeter as its primary payload for measuring surface height and a passive microwave radiometer to support atmospheric corrections and surface-type classification. The altimeter will have interferometric capabilities at Ku-band for improved ground resolution and a second (non-interferometric) Ka-band frequency to provide information on snow layer properties. This paper outlines the user consultations that have supported expansion of the Copernicus Space Component to include the high-priority candidate missions, describes the primary and secondary objectives of the CRISTAL mission, identifies the key contributions the CRISTAL mission will make, and presents a concept – as far as it is already defined – for the mission payload.

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Section: Snow On Land and Permafrostmentioning

confidence: 99%

The Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) high-priority candidate mission

et al. 2020

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“…due to ice lenses/crusts), radar signals undergo absorption within the snow volume (e.g., Kwok and Maksym, 2014;Ricker et al, 2015). Recent studies suggest reduced signal penetration into the snow pack, with a more diffuse snow/sea ice interface, on both Arctic and Antarctic sea ice (Gerland et al, 2013;Kwok and Kacimi, 2018), especially if the snow pack is saline (Nandan et al, 2020;Nandan et al, 2017) or very deep with ice lenses present (King et al, 2018). In addition, deep snow pushes the ice surface below the water level, leading to negative freeboard and induces flooding and slushy, snow-ice formation in the basal layers of the snow pack, which, when measured with a radar altimeter system, can result in a dominant scattering horizon above the true snow/ice interface (Nandan et al, 2020), and hence an overestimation of ice freeboard and thus sea ice thickness, and an underestimate of total snow thickness.…”

Section: Discussionmentioning

confidence: 99%

“…On FYI, overlying snow also wicks brine upwards from the sea ice surface during freeze-up, producing saline snow layers, predominately observed in the bottom-most 0.06-0.08 m of the snow pack (Drinkwater and Crocker, 1988;Geldsetzer et al, 2009;Nandan et al, 2016Nandan et al, , 2017Nandan et al, , 2020. Sea ice salinity observations from the 1-m thick FYI floe, collected on 5 and 23…”

Section: Discussionmentioning

confidence: 99%

“…Previous studies (Barber et al, 1998;Barber and Nghiem, 1999;Nghiem et al, 1995;Geldsetzer et al, 2009;Nandan et al, 2017;Nandan et al, 2020) have reported the impact of saline snow on FYI, which alters the geophysical, thermodynamic, dielectric and radar scattering properties of the snow cover, thereby impacting radar signal penetration through the snow pack. Nandan et al (2017) and (2020) showed that a saline snow cover on a FYI setting, induced by upward brine wicking from the sea ice surface, shifted the main radar scattering horizon away from the snow/sea ice interface by up to 0.07 m, and weakened the signal arising from the saline scattering horizon.…”

Section: Discussionmentioning

confidence: 99%

“…In recent years, a significant change towards thinner ice with thicker snow cover (Renner et al, 2014;Rösel et al, 2018) has been observed in this region, caused by an increase in intense storm events and associated precipitation in this area (Woods and Caballero, 2016;Graham et al, 2017;Rinke et al, 2017). In addition, previous studies indicate that radar signal penetration through the snow pack might be lower under certain geophysical snow-ice conditions in this area (Gerland et al, 2013;King et al, 2018;Nandan et al, 2020) and also in the Weddell Sea ice in the Antarctic (Kwok and Kacimi, 2018). Snow and ice conditions in this region differ to those in the Canada Basin and central Arctic (e.g., Webster et al, 2014;2018), and they have been found to induce substantial negative freeboards with subsequent flooding of the snow pack, more akin to the conditions in the seasonal ice pack of the Southern Ocean (Massom et al, 2001).…”

Section: Introductionmentioning

confidence: 91%

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Implications of surface flooding on airborne thickness measurements of snow on sea ice

Rösel

Farrell

Nandan

et al. 2020

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Abstract. Snow thickness observations from airborne snow radars, such as the NASA’s Operation IceBridge (OIB) mission, have recently been used in altimeter-derived sea ice thickness estimates, as well as for model parameterization. A number of validation studies comparing airborne and in situ snow thickness measurements have been conducted in the western Arctic Ocean, demonstrating the utility of the airborne data. However, there have been no validation studies in the Atlantic sector of the Arctic. Recent observations in this region suggest a significant and predominant shift towards a snow-ice regime, caused by deep snow on thin sea ice. During the Norwegian young sea ICE expedition (N-ICE2015) in the area north of Svalbard, a validation study was conducted on March 19, 2015, during which ground truth data were collected during an OIB overflight. Snow and ice thickness measurements were obtained across a two dimensional (2-D) 400 m × 60 m grid. Additional snow and ice thickness measurements collected in situ from adjacent ice floes helped to place the measurements obtained at the gridded survey field site into a more regional context. Widespread negative freeboards and flooding of the snow pack were observed during the N-ICE2015 expedition, due to the general situation of thick snow on relatively thin sea ice. These conditions caused brine wicking and saturation into the basal snow layers, causing more diffuse scattering and influenced the airborne radar signal to detect the radar main scattering horizon well above the snow/sea ice interface, resulting in a subsequent underestimation of total snow thickness, if only radar-based information is used. The average airborne snow thickness was 0.16 m thinner than that measured in situ at the 2-D survey field. Regional data within 10 km of the 2-D survey field suggested however a smaller deviation between average airborne and in situ snow thickness, a 0.06 m underestimate in snow thickness by the airborne radar, which is close to the resolution limit of the OIB snow radar system. Our results also show a broad snow thickness distribution, indicating a large spatial variability in snow across the region. Differences between the airborne snow radar and in situ measurements fell within the standard deviation of the in situ data (0.15–0.18 m). Our results suggest that, with frequent flooding of the snow-ice interface in specific regions of the Arctic in the future, it may result in an underestimate of snow thickness or an overestimate of ice freeboard, measured from radar altimetry, thereby affecting the accuracy of sea ice thickness estimates.

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Changing State of the Climate System

2023

Climate Change 2021 – The Physical Science Basis

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Chapter 2 assesses observed large-scale changes in climate system drivers, key climate indicators and principal modes of variability. Chapter 3 considers model performance and detection/attribution, and Chapter 4 covers projections for a subset of these same indicators and modes of variability. Collectively, these chapters provide the basis for later chapters, which focus upon processes and regional changes. Within Chapter 2, changes are assessed from in situ and remotely sensed data and products and from indirect evidence of longer-term changes based upon a diverse range of climate proxies. The timeevolving availability of observations and proxy information dictate the periods that can be assessed. Wherever possible, recent changes are assessed for their significance in a longer-term context, including target proxy periods, both in terms of mean state and rates of change.The increase in GMST since the mid-19th century was preceded by a slow decrease that began in the mid-Holocene (around 6500 years ago) (medium confidence). {2.3.1.1, Cross-Chapter Box 2.1} Changes in GMST and global surface air temperature (GSAT) over time differ by at most 10% in either direction (high confidence), and the long-term changes in GMST and GSAT are presently assessed to be identical. There is expanded uncertainty in GSAT estimates, with the assessed change from 1850-1900 to 1995-2014 being 0.85 [0.67 to 0.98] °C. {Cross-Chapter Box 2.3} The troposphere has warmed since at least the 1950s, and it is virtually certain that the stratosphere has cooled. In the Tropics, the upper troposphere has warmed faster than the near-surface since at least 2001, the period over which new observational techniques permit more robust quantification (medium confidence). It is virtually certain that the tropopause height has risen globally over 1980-2018, but there is low confidence in the magnitude. {2.3.1.2} Changes in several components of the global hydrological cycle provide evidence for overall strengthening since at least 1980 (high confidence). However, there is low confidence in comparing recent changes with past variations due to limitations in paleoclimate records at continental and global scales. Global land precipitation has likely increased since 1950, with a faster increase since the 1980s (medium confidence). Nearsurface specific humidity has increased over both land (very likely) and the oceans (likely) since at least the 1970s. Relative humidity has very likely decreased over land areas since 2000. Global total column water vapour content has very likely increased during the satellite era. Observational uncertainty leads to low confidence in global trends in precipitation minus evaporation and river runoff. {2.3.1.3} Several aspects of the large-scale atmospheric circulation have likely changed since the mid-20th century, but limited proxy evidence yields low confidence in how these changes compare to longer-term climate. The Hadley circulation has likely widened since at least the 1980s, and extratropical storm tracks have likely shi...

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Snow Property Controls on Modeled Ku-Band Altimeter Estimates of First-Year Sea Ice Thickness: Case Studies From the Canadian and Norwegian Arctic

Abstract: Uncertainty in snow properties impacts the accuracy of Arctic sea ice thickness estimates from radar altimetry. On firstyear sea ice (FYI), spatiotemporal variations in snow properties

Cited by 25 publications

References 66 publications

The Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) high-priority candidate mission

The Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) high-priority candidate mission

Implications of surface flooding on airborne thickness measurements of snow on sea ice

Changing State of the Climate System

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