Fig. 9. Waveforms collected from a Trime T3 probe using a Tektronix 1502 C TDR cable tester connected to the coaxial cable at the Trime-FM measuring device. At each depth shown, a waveform was collected with the top end of the probe waveguides placed at that depth in an access tube placed in a uniform smectitic clay soil. Water content as measured with a neutron probe was uniform throughout the profile. Travel time analysis by intersection of tangent lines (red with a vertical red line indicating the intersections) showed that travel time was practically equal at all depths, indicating that conventional TDR would predict equal water contents throughout the profile, although the Trime-FM did not. The relative lengths of horizontal arrows drawn from the left y axis to the waveforms indicate the changes in transit time for different set-point voltages at which a comparator circuit would time the arrival of the reflected pulse. The transit times illustrated in this manner are greater for the waveforms from deeper within the profile even though water contents are the same. The differences in slope of the reflected pulse are due to differences in soil temperature and/or bulk electrical conductivity. Data courtesy of Jean-Paul Laurent, Chargé de Recherches au CNRS, Laboratoire d'étude des Transferts en Hydrologie et Environnement, Grenoble, France.