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A ground‐penetrating radar (GPR) survey was conducted in May 1999 on the 1 km2 Circumpolar Active Layer Monitoring (CALM) grid 5 km east of Barrow, Alaska. Spatially continuous measurements were collected along established transects while the active layer remained frozen. The primary objectives were to determine the ‘long‐term’ position of the permafrost table, to recognize ice wedges and ice lenses, and to locate the organic–mineral soil interface. GPR signal and core collection were performed in tandem to verify signal interpretation, to calibrate the instrument, and to determine optimal GPR data‐collection parameters. Two‐way travel times from the antenna to subsurface reflectors were compared with measured depths obtained from soil cores to estimate an average pulse propagation velocity of 0.13 m/ns through the frozen soil. The most conspicuous subsurface reflectors were ice wedges, which gave high‐amplitude hyperbolic reflections. Owing to its higher ice content, the approximate long‐term position of the permafrost table could be traced laterally across the profile. Radar interpretations were obscured by the effects of cryoturbation, and because some horizons lack sufficient contrast in electrical properties. Highly detailed information can be obtained by collecting radar data at relatively slow speeds of advance, by using faster scanning rates (>32 scans/s), and by employing high‐frequency antennas (>400 MHz). Copyright © 2001 John Wiley & Sons, Ltd.RÉSUMÉUn levé réalisé avec un radar dont les ondes pénètrent dans le sol a été réalisé en mai 1999 sur un km2 appartenant à la grille établie pour suivre l'évolution de la couche active circumpolaire (CALM), 5 km a l'est de Barrow, Alaska. Des mesures ont été réalisées le long de transects alors que la couche active était gelée. Les premiers objectifs étaient de déterminer la position à long terme de la table du pergélisol, de reconnaître les coins et les lentilles de glace, et de localiser le contact entre les sols organiques et minéraux. Les données radar et des carottes de sondages ont été recueillies au même moment pour vérifier l'interprétation des données radar, calibrer l'instrument et déterminer les meilleurs paramètres d'enregistrement. Deux facons de calculer les temps de parcours depuis l'antenne jusqu'aux réflecteurs souterrains ont été comparés avec des mesures obtenues par sondages, pour estimer une vitesse moyenne de propagation de 0.13 m/ns à travers le sol gelé. Les réflecteurs les plus apparents ont été les coins de glace qui donnent des réflexions hyperboliques de grande amplitude. En raison de leur haute teneur en glace, la position approximative à long terme de la table du pergélisol a pu être reconnue le long des profils. Les interprétations sont obscurcies par les effects des cryoturbations et aussi, parce que certains horizons n'ont pas un contraste suffisant dans leurs propriétés électriques. Une information hautement détaillée peut être obtenue par la méthode radar en utilisant des vitesses lentes d'avancée, de rapides vitesses de scannages (>32 scans/s) et en utilisant des antennes de hautes fréquence (>400 MHz). Copyright © 2001 John Wiley & Sons, Ltd.

Hydrocarbon spills have occurred on Antarctic soils where fuel oils are utilized, moved or stored. We investigated the effects of hydrocarbon spills on soil temperature and moisture regimes by comparing the properties of existing oil contaminated sites with those of nearby, uncontaminated, control sites at Scott Base, the old Marble Point camp, and Bull Pass in the Wright Valley. Hydrocarbon levels were elevated in fuel-contaminated samples. Climate stations were installed at all three locations in both contaminated and control sites. In summer at Scott Base and Marble Point the mean weekly maximum near surface (2 cm and 5 cm depth) soil temperatures were warmer (P < 0.05), sometimes by more than 10°C, at the contaminated site than the control sites. At Bull Pass there were no statistically significant differences in near-surface soil temperatures between contaminated and control soils. At the Scott Base and Marble Point sites soil albedo was lower, and hydrophobicity was higher, in the contaminated soils than the controls. The higher temperatures at the Scott Base and Marble Point hydrocarbon contaminated sites are attributed to the decreased surface albedo due to soil surface darkening by hydrocarbons. There were no noteworthy differences in moisture retention between contaminated and control sites.

A tractor‐mounted pulsed nuclear magnetic resonance (NMR) moisture measurement instrument has been developed and fabricated for use in collecting ground truth data for calibrating and evaluating remotely sensed determinations. The measurement approach is based upon NMR which depends on the interaction between hydrogen nuclear magnetic moments and a magnetic field. The sensor unit, consisting of an electromagnet, detection coil, and tuning capacitor, is towed behind the tractor and provides continuous readout of the volumetric soil water content at selected depths to 63 mm. Preliminary laboratory measurements with this instrument on two soils, a clay and a loamy fine sand, correlate linearly with volumetric soil water content. Discrimination of water NMR signals from signals from other hydrogen‐bearing material is based on nuclear relaxation times, which reflect the molecular environment and structural bonding characteristics of the water molecules in the soil.

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