New geophysical methods of investigating the nature and distribution of mountain permafrost with special reference to radiometry techniques

A series of geophysical surveys were undertaken within the PACE geophysical work package. Various methods were applied including refraction seismics, DC resistivity, ground penetrating radar (GPR), electromagnetic induction, radiometry and bottom temperature of snow cover (BTS). The focus of the surveys was to determine the internal structures and distribution of mountain permafrost. This paper gives a preliminary overview of progress. The two-dimensional DC resistivity tomography combines the geoelectrical sounding and mapping and makes it possible to model internal structures. This method was applied at all PACE drill sites. Electromagnetic induction methods showed good results, in particular the EM-31 for determining the permafrost distribution and the PROTEM to assess the overall permafrost thickness. A major new development discussed here is the use of passive microwave (11.4 GHz) for airborne remote measurement of the bottom temperature of snow cover (BTS). Manual BTS measurements agreed very well with the BTS determined by radiometry. To reduce ambiguity, several geophysical methods should be deployed at the same locality. As a further step, such measurements could be interpreted using joint inversions. Copyright © 2001 John Wiley & Sons, Ltd. RESUME Une serie de leves geophysiques a ete realise dans le cadre des travaux de PACE. Differentes methodes ont ete utilisees y compris la seismique refraction, la resistivite DC, le radar penetrant le sol (GPR), l'induction electro-magnetique, la radiometrie et la temperature a la base de la couverture nelgeuse (BTS). Le but de ces leves etait de determiner les structures internes et la distribution du pergelisol de montagne. Le present article donne une vue generale preliminaire des progres realises. La tomographie en deux dimensionns par resistivite. DC qui combine le sondage geoelectrique et la cartographie, rend possible la reconnaissance des structures internes. Cette methode a ete appliquee dans tous les sites de sondage. Les methodes par induction electromagnetique ont donne de bons resultats, en particulier la methode par EM-31 pour determiner la distribution du pergellisol, tandis que la methode PROTEM a ete utile pour estimer l'epaisseur totale du pergelisol. Un imporant nouveau developpement discute ici est l'emploi de micro-ondes passives (11.4 GHz) dans des mesures aeroportees de la temperature de la base de la converture de neige (BTS). Des mesures manuelles BTS se sont revelees bien en accord avec les donnees BTS obtenues par radiometrie. Pour diminuer les ambiguites, plusieurs methodes geophysiques devraient toujours etre utilisees. Copyright © 2001 John Wiley & Sons, Ltd.