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A wide variety of remote sensing and ground-based (proximal sensing) methods have been developed to describe soil physical properties and their lateral variations. Remote sensing enables the estimation of soil properties over large areas, but the information is often limited to the soil surface. Ground-based methods enable the derivation of soil properties for the whole soil column thickness, although these methods cannot be conducted over large areas. The aim of the present study is to contribute to the assessment of the efficacy of airborne thermal prospection over bare soils in soil mapping. This study focuses on a comparison between this technique, which can investigate over the whole soil column thickness after a sufficiently long transient heat exchange period, and pedological and electrical resistivity data that were recorded for three different depths of investigation. The study area is located in the Beauce region, where the soils (haplic Calcisol or calcaric Cambisol) consist of a loamy–clay layer that is 0.3 m–1.4 m thick and overlies Tertiary Beauce limestone. Thermal measurements were recorded by ARIES radiometer in December after six days of heat loss from the ground. The investigation depth could thus be considered to be larger than the thickness of the ploughed layer. Comparisons using statistical analyses between the thermal measurements, electrical resistivity, and pedological data demonstrated that: (i) the spatial organization of the thermal inertia map is similar to the spatial organization of the 0-m to 1.7-m resistivity map; and (ii) the thermal apparent inertia values are significantly different between the haplic Calcisols and the calcaric Cambisols and can thus be mapped with a high spatial resolution over large areas. The applicability of thermal prospecting in soil mapping opens up many possibilities considering the present advances in light-infrared radiometers. Beside agronomical concerns, this methodology will also facilitate progress in engineering applications, including the cross estimation of electrical and thermal properties.

International audience; If field applications of the electrostatic method are limited to roughly the first ten metres due to the necessity of staying in a low-induction number domain, the possibilities it opens in urban area surveying, dry hole resistivity logging, non-destructive testing and laboratory studies of the complex resistivity justify the design of a new multi-frequency resistivity meter presenting a very low-input capacitance and high-phase sensitivity. After a first series of sample measurements in the laboratory, the new resistivity meter was tested in two different field contexts: the mapping of building remains in a Gallo-Roman archaeological site under a flat meadow and the assessment of the thickness of anthropogenic layers in a town. The first test allowed a direct comparison with previous galvanic resistivity measurements and proved a very good agreement between the magnitude and spatial distribution of electrical resistivity. The second test established its reliable measuring abilities in a disturbed environment.

Soil magnetic properties are significantly modified by pedogenesis and human activity; consequently their study is an important source of information about soil structure and history. In addition to measurements of magnetic susceptibility, now commonly practised, magnetic viscosity measurements can be undertaken as a routine survey method if well-matched instruments that are easy to use in the field and that offer a sufficient depth of investigation, exist. A theoretical study, supported by field tests of a prototype, demonstrates that a Slingram perpendicular coil configuration with a one-metre inter-coil spacing allows the required one-metre depth of investigation to be reached for both 1D and 3D models. The sensitivity of the instrument response to the viscosity is also very high over the whole measurement range (10μs to 1ms), while the sensitivity to electrical conductivity is reduced to a minimum. A first experiment at the Roman site of Vieil-Evreux illustrates how viscosity measurements can complement magnetic field and susceptibility measurements for a more accurate identification of an archaeological feature.