Snow melting bias in microwave mapping of Antarctic snow accumulation

Magand, Olivier; Picard, Ghislain; Brucker, Ludovic; Fily, Michel; Genthon, C.

doi:10.5194/tc-2-109-2008

Cited by 26 publications

(20 citation statements)

References 24 publications

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“…Even though the L-band radiation emanates from deep in the ice sheet, surface reflection is an important process of the radiative transfer. It has been demonstrated that regions where melt occurs can bias snow accumulation retrievals using microwave TB (Magand et al, 2008), Fig. 4 shows that similar bias can be expected using L-band observations.…”

Section: The Greenland Ice Sheet (Gis)mentioning

confidence: 49%

Weekly gridded Aquarius L-band radiometer/scatterometer observations and salinity retrievals over the polar regions – Part 2: Initial product analysis

2014

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Abstract.Following the development and availability of Aquarius weekly polar-gridded products, this study presents the spatial and temporal radiometer and scatterometer observations at L band (frequency ∼ 1.4 GHz) over the cryosphere including the Greenland and Antarctic ice sheets, sea ice in both hemispheres, and over sub-Arctic land for monitoring the soil freeze/thaw state. We provide multiple examples of scientific applications for the L-band data over the cryosphere. For example, we show that over the Greenland Ice Sheet, the unusual 2012 melt event lead to an L-band brightness temperature (TB) sustained decrease of ∼ 5 K at horizontal polarization. Over the Antarctic ice sheet, normalized radar cross section (NRCS) observations recorded during ascending and descending orbits are significantly different, highlighting the anisotropy of the ice cover. Over sub-Arctic land, both passive and active observations show distinct values depending on the soil physical state (freeze/thaw). Aquarius sea surface salinity (SSS) retrievals in the polar waters are also presented. SSS variations could serve as an indicator of fresh water input to the ocean from the cryosphere, however the presence of sea ice often contaminates the SSS retrievals, hindering the analysis. The weekly grided Aquarius L-band products used are distributed by the US Snow and Ice Data Center at http: //nsidc.org/data/aquarius/index.html, and show potential for cryospheric studies.

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Section: The Greenland Ice Sheet (Gis)mentioning

confidence: 49%

Weekly gridded Aquarius L-band radiometer/scatterometer observations and salinity retrievals over the polar regions – Part 2: Initial product analysis

2014

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“…Furthermore, Magand et al . [] show that regions potentially affected by melting should be completely masked‐out from the microwave‐based interpolation schemes. It is clear that surface melting occurs on FIS in the present climate [ Schlosser et al ., ; Kaczmarska et al ., ], which may be responsible for the large discrepancies between our results and those of Arthern et al .…”

Section: Spatiotemporal Patterns Of Surface Mass Balancementioning

confidence: 99%

Surface mass balance on Fimbul ice shelf, East Antarctica: Comparison of field measurements and large‐scale studies

et al. 2013

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[1] Many challenges remain for estimating the Antarctic ice sheet surface mass balance (SMB), which represents a major uncertainty in predictions of future sea-level rise. Validating continental scale studies is hampered by the sparse distribution of in situ data. Here we present a 26 year mean SMB of the Fimbul ice shelf in East Antarctica between 1983-2009, and recent interannual variability since 2010. We compare these data to the results of large-scale SMB studies for similar time periods, obtained from regional atmospheric modeling and remote sensing. Our in situ data include ground penetrating radar, firn cores, and mass balance stakes and provide information on both temporal and spatial scales. The 26 year mean SMB on the Fimbul ice shelf varies between 170 and 620 kg m À2 a À1 giving a regional average value of 310 ± 70 kg m À2 a À1 . Our measurements indicate higher long-term accumulation over large parts of the ice shelf compared to the large-scale studies. We also show that the variability of the mean annual SMB, which can be up to 90%, can be a dominant factor in short-term estimates. The results emphasize the importance of using a combination of ground-based validation data, regional climate models, and remote sensing over a relevant time period in order to achieve a reliable SMB for Antarctica.

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“…Glazed surfaces (Frezzotti et al, 2002a;Scambos et al, 2012), thermal cracks and irregular patches of hoar on the surface (Gow, 1969;Courville et al, 2007) can also be found at some specific points. These features affect the distribution of snow accumulation and represent one of the challenges in scaling up local surface mass balance measurements to the continent scale (Goodwin, 1990;Magand et al, 2008;Das et al, 2013). Although the size of these features is much smaller than the microwave radiometer footprint, they have an influence on the signal.…”

Section: Introductionmentioning

confidence: 99%

Influence of meter-scale wind-formed features on the variability of the microwave brightness temperature around Dome C in Antarctica

et al. 2014

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Abstract. Space-borne passive microwave radiometers are widely used to retrieve information in snowy regions by exploiting the high sensitivity of microwave emission to snow properties. For the Antarctic Plateau, many studies presenting retrieval algorithms or numerical simulations have assumed, explicitly or not, that the subpixel-scale heterogeneity is negligible and that the retrieved properties were representative of whole pixels. In this paper, we investigate the spatial variations of brightness temperature over a range of a few kilometers in the Dome C area. Using ground-based radiometers towed by a vehicle, we collected brightness temperature at 11, 19 and 37 GHz at horizontal and vertical polarizations along transects with meter resolution. The most remarkable observation was a series of regular undulations of the signal with a significant amplitude reaching 10 K at 37 GHz and a quasi-period of 30-50 m. In contrast, the variability at longer length scales seemed to be weak in the investigated area, and the mean brightness temperature was close to SSM/I and WindSat satellite observations for all the frequencies and polarizations. To establish a link between the snow characteristics and the microwave emission undulations, we collected detailed snow grain size and density profiles at two points where opposite extrema of brightness temperature were observed. Numerical simulations with the DMRT-ML microwave emission model revealed that the difference in density in the upper first meter explained most of the brightness temperature variations. In addition, we found that these variations of density near the surface were linked to snow hardness. Patches of hard snow -probably formed by wind compaction -were clearly visible and covered as much as 39 % of the investigated area. Their brightness temperature was higher than in normal areas. This result implies that the microwave emission measured by satellites over Dome C is more complex than expected and very likely depends on the year-to-year areal proportion of the two different types of snow.

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Snow melting bias in microwave mapping of Antarctic snow accumulation

Cited by 26 publications

References 24 publications

Weekly gridded Aquarius L-band radiometer/scatterometer observations and salinity retrievals over the polar regions – Part 2: Initial product analysis

Weekly gridded Aquarius L-band radiometer/scatterometer observations and salinity retrievals over the polar regions – Part 2: Initial product analysis

Surface mass balance on Fimbul ice shelf, East Antarctica: Comparison of field measurements and large‐scale studies

Influence of meter-scale wind-formed features on the variability of the microwave brightness temperature around Dome C in Antarctica

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