Multifrequency Microwave Emission Fromthe Dome-C Area on the East Antarctic Plateau: Temporal and Spatial Variability

Macelloni, Giovanni; Brogioni, Marco; Pampaloni, P.; Cagnati, Anselmo

doi:10.1109/tgrs.2007.890805

Cited by 53 publications

(44 citation statements)

References 25 publications

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“…A detailed analysis of the spatial and temporal variability of passive microwave data close to Dome C was given by Long and Drinkwater (2000); Macelloni et al (2007);Brucker et al (2011). These studies included the effects of viewing azimuth angle and acquisition time on the satellite observations.…”

Section: Passive Microwave Satellite Observationsmentioning

confidence: 99%

“…Brightness temperatures are mainly sensitive to the snowpack while the atmosphere is negligible at the frequencies of 19 and 37 GHz used here Brucker et al, 2011). Despite the penetration depth which is of the order of metres at these frequencies (Surdyk, 2002a;Macelloni et al, 2007), using a combination of T B at different polarisations can emphasise the sensitivity to the properties of the air-snow interface. computed two indexes, the T B ratio of vertical over horizontal polarisations, and the T B difference of both polarisations.…”

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confidence: 99%

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Hoar crystal development and disappearance at Dome C, Antarctica: observation by near-infrared photography and passive microwave satellite

et al. 2013

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Abstract. Hoar crystals episodically cover the snow surface in Antarctica and affect the roughness and reflective properties of the air-snow interface. However, little is known about their evolution and the processes responsible for their development and disappearance despite a probable influence on the surface mass balance and energy budget. To investigate hoar evolution, we use continuous observations of the surface by in situ near-infrared photography and by passive microwave remote sensing at Dome C in Antarctica. From the photography data, we retrieved a daily indicator of the presence/absence of hoar crystals using a texture analysis algorithm. The analysis of this 2 yr long time series shows that Dome C surface is covered almost half of the time by hoar. The development of hoar crystals takes a few days and seems to occur whatever the meteorological conditions. In contrast, the disappearance of hoar is rapid (a few hours) and coincident with either strong winds or with moderate winds associated with a change in wind direction from southwest (the prevailing direction) to southeast. From the microwave satellite data, we computed the polarisation ratio (i.e. horizontal over vertical polarised brightness temperatures), an indicator known to be sensitive to hoar in Greenland. Photography data and microwave polarisation ratio are correlated, i.e. high values of polarisation ratio which theoretically correspond to low snow density values near the surface are associated with the presence of hoar crystals in the photography data. Satellite data over nearly ten years (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011) confirm that a strong decrease of the polarisation ratio (i.e. signature of hoar disappearance) is associated with an increase of wind speed or a change in wind direction from the prevailing direction. The photography data provides, in addition, evidence of interactions between hoar and snowfall. Further adding the combined influence of wind speed and wind direction results in a complex picture of the snow-atmosphere interactions in Antarctica which deserves further quantification and modelling.

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Section: Passive Microwave Satellite Observationsmentioning

confidence: 99%

mentioning

confidence: 99%

Hoar crystal development and disappearance at Dome C, Antarctica: observation by near-infrared photography and passive microwave satellite

et al. 2013

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“…This suggests that the snowpack from one pixel to a neighbor is generally similar. A particularly homogeneous area was identified on the ice divide near Dome C (Macelloni et al, 2007), which might be suitable for the calibration of passive microwave satellites (Macelloni et al, 2006).…”

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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“…One such method is a scatter plot; by analyzing the shape, we can determine if the variables are linearly correlated or not. We also examined the values of the trailing edge and the backscatter between the leading edge width and the elevation difference in each scatter plot to determine whether we could separate the influence of surface undulations from the subsurface scattering [28][29][30]. The backscatter is influenced by the penetration via the snowpack properties but also by the surface properties.…”

Section: Focus On Four Specific Locationsmentioning

confidence: 99%

Study of the Penetration Bias of ENVISAT Altimeter Observations over Antarctica in Comparison to ICESat Observations

2014

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Abstract:The aim of this article is to characterize the penetration bias of the ENVIronmental SATellite (ENVISAT) radar altimeter over the Antarctic ice sheet through comparison with the more accurate measurements of the Ice, Cloud and land Elevation Satellite (ICESat) altimeter at crossover points. We studied the difference between ENVISAT and ICESat fluctuations over six years. We observed the same patterns between the leading edge width and the elevation difference. Both parameters are linked, and the major bias is due to the lengthening of the leading edge width due to the radar penetration. We show that the elevation difference between both altimeters and the leading edge width are linearly well-linked with a 0.8 Pearson correlation coefficient, whereas the slope effect over the coasts is difficult to analyze. When we analyze each crossover point temporal evolution locally, the linear correlation between the leading edge width and the elevation difference is between −0.6 and −1. Fitting a linear model between them, we find a reliability index greater than 0.7 for the Antarctic Plateau and Dronning Maud Land, which confirms that the penetration effect has a linear influence on the retrieved height. Moreover, we present results from SARAL/AltiKa (launched in February 2013) that confirm SARAL/AltiKa accuracy and the promising information it will provide.

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Multifrequency Microwave Emission Fromthe Dome-C Area on the East Antarctic Plateau: Temporal and Spatial Variability

Cited by 53 publications

References 25 publications

Hoar crystal development and disappearance at Dome C, Antarctica: observation by near-infrared photography and passive microwave satellite

Hoar crystal development and disappearance at Dome C, Antarctica: observation by near-infrared photography and passive microwave satellite

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

Study of the Penetration Bias of ENVISAT Altimeter Observations over Antarctica in Comparison to ICESat Observations

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