GNGTS 2017 - 36° Convegno Nazionale

678 GNGTS 2017 S essione 3.2 Romero-Conde, A., Kusakabe, A., & Melgar, J. C. (2014). Physiological responses of citrus to partial rootzone drying irrigation. Scientia Horticulturae, 169, 234-238 Rossi, R. Amato, M., Bitella, G., Bochicchio, R., Ferreira Gomes, J., J., Lovelli, S., Martorella, E., Favale, P., (2011). Electrical resistivity tomography as a non-destructive method for mapping root biomass in an orchard. European Journal of Soil Science, 62 (2), 206–215 Satriani, A., Loperte, A., Soldovieri, F., (2015). Integrated geophysical techniques for sustainable management of water resource. A case study of local dry bean versus commercial common bean cultivars, Agricultural Water Management, 162, 57-66 Full-waveform inversion of IP data by means of a local and a global optimisation algorithm: preliminary results on synthetic data A. Vinciguerra, P. Costantini, M. Aleardi Earth Sciences Department, University of Pisa, Italy Introduction. Induced Polarisation (IP) is a geophysical method widely used in mining exploration and, recently, in hydrogeophysics. This technique can be applied in both frequency and time domain, and exploits the dispersive response of the half-space to the application of a time-varying electric field, for retrieving some relevantmineralogical and textural characteristics. A square current wave is injected into the ground by a transmitter and the potential is recorded by a receiver. In the standard IP time domain technique, the current wave is not recorded and it is assumed to be a theoretical square wave, whereas the voltage waveform is sampled at discrete intervals during the decay. The amount of polarisability of the half-space is then estimated by computing the area below the decay curve. The polarisation response can be better described by analysing the dispersion in the frequency domain; a common approach is to fit the observed resistivity spectrum with a variant of the Cole-Cole empirical equation (Pelton et al., 1978), a complex function of frequency whose parameters can be related to the petrophysical properties of the medium: (1) where m i is the chargeability, τ i is the time constant, c i is the frequency dependence, ρ 0 is the d.c resistivity and ω is the angular frequency. The index i varies from 1 (single dispersion model) to 2 (double dispersion model). It has been recently shown (Olsson, 2015) that taking into account the full I(t) and V(t) waveforms would theoretically allow to extend the useful bandwidth in the estimation of the magnitude and phase of the impedance spectral function. By assuming that the ground is a linear system, the complex resistivity spectrum (i.e. the system transfer function) can be computed by a simple spectral division between the voltage V(ω ) (output of the system) and current I(ω) (input of the system). The Cole-Cole parameters (CCP) can then be obtained by inversion of the retrieved spectrum. Given the presence of noise, the inversion of the spectra over an extended range of frequencies requires several preliminary steps of robust processing to increase the signal to noise (S/N) ratio. Besides this, inversion of the IP spectrum is very challenging, being Eq. (1) non-linear and affected by equivalence regions in the model space (Martinez et al ., 2012).