## 4 Discussion  
The GPR sections enhanced the delineation of the uppermost horizons (blue line in Figure 2b) within the scanned distance. The phase attributes enhanced the identification of the soil layers based on both vertical and lateral distortions on the continuity of horizontal patterns in the sections. Integration of the enhancement with the amplitude reflections (Figure 2a) in the processed data facilitated the recognition of the soil layers. A better soil horizon architecture was made possible by the GPR signal phase attributes. The identified soil layers included the topmost horizon, which is thought to be composed of high organic contents, particularly from the field observations. Based on literature records, the adjacent layer is considered loam sandy soil. The concealing nature of the adjacent layer and the dearth of exposed soil profile in the area did not allow us to substantiate this assertion. In addition, the depth to the horizons is also determinable from the GPR sections, which may provide fair information about the thickness of the layers. The zone identified as the low matric potential is marked with a cyan dotted line (Figure 3b). It is suggestive of the zone of water movement direction after the water infiltration, indicating lower potential that triggers the water movement. The phase attribute also enhanced the delineation of adjacent soil horizons suspected to have higher matric potential (white dotted line in Figure 3b). Moreover, the increase in the magnitude of the instantaneous phase computed for the GPR signals is thought to be the effect of the infiltration that informed the affinity of the zone to water. Furthermore, the discrepancy in the magnitude of the lower spectra at the different zones of consideration may indicate the influence of water content variations in the two scenarios. Noticeable power peak shifts from high frequency to low frequency in the high matric potential zone may also be an indication of variations in the volumetric contents of the two zones. In addition, changes observed from the time-frequency plots of the recorded GPR EM signals from the test site may also explain the tendency of movement  
Figure 6: Centroid frequency plot from the GPR datasets showing variations in matric potential within the subsoil.  
of infiltrated water towards the low matric potential rather than the high potential zone. Finally, the centroid frequency plot analysis also gave credence to the soil characteristic variations identified from other results analyses. Nevertheless, it is worth pointing out that the non-uniqueness characteristics of geophysical data interpretations may also inform the possible explanation of the obtained results to be stratigraphical changes in the vadose zone. The results of the frequency analysis may also be related to changes in near-surface material and antenna coupling. It should be noted that the GPR technology application in subsurface evaluation is largely site-specific. The soil conditions (clay contents, levels of water saturation, and accessibility) need to be considered before the use of the method. This is to ensure high resolution, accuracy, and depth of penetration of the EM pulse energy due to attenuation.