Dome C as a Candidate Cal/Val Site for SMOS
Inputs by Frederique Remy and Mark Drinkwater

Dome Concordia (Dome C) is a broad topographic dome roughly centred at 75° 06'06"S, 123° 23'42"E on the polar plateau of East Antarctica (at 3233 m elevation a.s.l.), and is situated more than 700 km from the coast. This location is about 65 km south of the old U.S. Dome C camp, and has been selected as the optimal site for a new collaborative European (EPICA) deep ice core [Tabacco and others, J. Glac, 2000]. The chosen core site will allow recovery of a core to a depth of 3250m with a climate history of some 400,000 years. In conjunction, the French and Italians have agreed to cooperate in the establishment of a research programme, including construction and operation of a scientific base "Concordia". The use of this station for scientific research is open to the world-wide scientific community and is considered here as a candidate calibration site for SMOS.

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The objectives of a calibration/validation project at this site is twofold: This site is well suited for cal/val. activity for the following reasons: Cold, dry snow is relatively transparent to microwaves, ensuring relative stability of the emissivity. The penetration of microwaves in layered Antarctic firn has been estimated using Ku-band radar altimeter data [Legresy and Remy, 1998], and using a combination of C-band scatterometer data and empirical scattering models [Bingham and Drinkwater, 2000]. At Ku-band, the estimated penetration depth is of the order of 6-7 m, and at P-band is of the order of 4000 m. L-band extinction is dominated primarily by temperature-regulated absorption in the upper 10 m (dependent on imaginary part of complex permittivity of snow/air mixture). The resulting penetration depth is estimated to be of the order of 100-150 m. The near-surface layer (i.e. top 10m), although experiencing seasonal temperature variability is largely transparent at L-band, and so the emissivity variability should be reasonably small. The primary thermally-forced brightness temperature variability (caused by surface air temperature generated waves in the vertical temperature profile), and is known, provided in-situ data is available. The seasonal cycle in air temperature at Dome C is of the order of 30° K. Short time-scale diurnal variability caused during polar daylight hours is low-pass filtered by the thermal conductivity of the snow, and lagged response of bulk firn temperature. Below 10m the firn temperature does not exhibit any seasonal temperature variation.

Recent data analyses by Bingham and Drinkwater [2000] have identified long-term climate/calibration drifts of SSM/I over the ice sheet (when modeled seasonal variations are removed) at high frequencies. These imply a long-term drifts of the order of XX K on time scales of XX years, whilst exhibiting short-term anomalies in Tb which appear to result from precipitation events or changes in the snow interface. The present revisit of SMOS at high latitudes suggest N?? overlapping measurements with an accuracy of ?? Kelvins, OR alternatively XX-day mean Tbs with an accuracy of ±?? K

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The Dome C Site is well characterized, with: Further in-situ measurement activities are planned in the frame of the Concordia project.
 
Priority Objectives (for Science Definition Studies):
 
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