IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 48, NO. 5, MAY 2010 2343 Dry–Wet Bedrock Interface Detection by Radio Echo Sounding Measurements Achille Zirizzotti, Lili Cafarella, James Arokasami Baskaradas, Ignazio Ezio Tabacco, Stefano Urbini, Morena Mangialetti, and Cesidio Bianchi Abstract—In this paper, a method to distinguish a wet or dry bedrock–ice interface is proposed. It is based on the analysis of radio echo sounding (RES) measurements, a widely employed method for determining bedrock topography in Antarctica. In par- ticular, the RES system has played an important role in subglacial lake exploration and hydrogeological studies at the bedrock–ice interface. Recently, bedrock characterization has been improved through the analysis of the power of radar echoes. Signal power depends on bedrock reflectivity and its specific physical condition. In this paper, a linear model describing the loss term (internal ice absorption) is proposed. This model, together with other known quantities, contributes toward an assessment of power variation of bedrock reflectivity in order to determinate wet and dry bedrock interfaces in the Dome C region in Antarctica. Index Terms—Bedrock reflectivity, ice absorption, internal ice layers, radio echo sounding (RES) systems. I. I NTRODUCTION T HE RADIO echo sounding (RES) system is an active remote-sensing technique that utilizes electromagnetic waves that are capable of penetrating ice. This technique is used to obtain information about the electromagnetic properties of different interfaces that reflect the incoming signal back to the acquisition system [14]. RES surveys have been widely employed in Antarctica ice-sheet exploration and are still an indispensable tool for mapping bedrock morphologies and properties of the last unknown continent on Earth. Year after year, polar research becomes increasingly important because of global warming. In addition, the discovery of numerous subglacial lake areas (entrapped in the ice sheet) has attracted scientific interest to the possible existence of water circulation between lakes or beneath the ice [1], [15], [21]. While differ- ences between rock and lake surfaces are often well identifiable in radargrams, this is not always true for wet and dry rock surfaces. To this end, the assessment of the physical condition of the ice bottom interface by studying the power of radar echoes could complete the significance of a RES data set and enhance its final interpretation [12]. The analysis is based on the received power of the echo signal from the base of the ice sheet. Geometrical spreading, medium focusing, ice absorption, Manuscript received December 12, 2008; revised September 2, 2009. First published February 17, 2010; current version published April 21, 2010. A. Zirizzotti, L. Cafarella, J. A. Baskaradas, S. Urbini, and C. Bianchi are with the Istituto Nazionale di Geofisica e Vulcanologia, 00143 Rome, Italy (e-mail: achille.zirizzotti@ingv.it). I. E. Tabacco and M. Mangialetti are with the Sezione Geofisica, Università di Milano, 20129 Milano, Italy. Digital Object Identifier 10.1109/TGRS.2009.2038900 Fig. 1. General case that illustrates power-loss difference passing from an ice- rock to ice-water surface reflector. A net gain of ΔR =7.7 dB in reflected signal, switching from dry to wet reflector, is clearly visible. and reflectivity are factors considered for the returned power of the echo signal. The study of the power of radar echoes could become a powerful tool to investigate and highlight the differences between water and wet or dry bedrock that play an important role in some advanced polar research, including hydrological connections between lakes under the Antarctic ice sheet. II. I NTERFACE REFLECTING SURFACES In order to distinguish the different reflecting properties of reflecting surfaces, reference will be made here to homo- geneous and horizontal surfaces. Fig. 1 shows a schematic view of an ideal plane in which ice layers lie partially over rock and partially over water. In this case, the electromagnetic power reflected by the subglacial interface depends only on the reflection coefficients, i.e., on the physical nature of the subglacial surfaces. In Table I, the media, with their related symbols, real and imaginary parts of the dielectric permittivity ε r =(ε ′ - jε ′′ ), and conductivity are reported. The reflection coefficient ρ at the surface separating media 1 and 2 (in the case of vertical incidence) is ρ = √ ε r1 - √ ε r2 √ ε r1 + √ ε r2 . (1) The power loss R due to reflection is equal to |ρ| 2 when expressed in decibels. The power loss T due to transmission is equal to 1 -|ρ| 2 when expressed in decibels [20]. 0196-2892/$26.00 © 2010 IEEE