Methods of surveying the thickness of humous horizons using ground penetrating radar (GPR): an example from the Garmisch-Partenkirchen area of the Northern Alps

Abstract

Ecological studies commonly demand elaborate knowledge of the distribution pattern of humous horizons, especially in forest ecosystems with high humus variability. Conventional investigative methods are timeconsuming and surface-destructive. Ground penetrating radar (GPR), in contrast, offers a fast and non-destructive method of portraying the shallow subsurface. Against this background, the reliability of GPR-derived metric data on terrestrial humous horizons was tested at a study site in the altimontane zone of the Bavarian Alps (1,260 m a.s.l.). The GPR survey, using a shielded bistatic antenna device at 800 MHz, is based on eight parallel lines within a 30 9 30 m plot. The metric interpretation of the GPR results is validated by a trench, which records the thickness of humous horizons at a 10-cm interval, and is compared to conventional sampling methods, represented by 18 soil monolith profiles of both random and grid-based distribution. The results show that it is not possible to resolve the borders of single humous horizons. The delineation of humous against non-humous horizons, however, shows correlation (R = 0.553) with the reference data and delivers reliable data on the average thickness and variation of humous horizons. The observed thickness deviations between GPR and the trench line range between -9.5 and 7.5 cm, with remarkably narrow deviations of -2 to 2 cm or less in 50% of the cases. In summary, supported by the high number of data records (n = 1,727), GPR creates a much better and none destructive image of the actual humus distribution pattern compared to conventional methods.

In situ characterization of forest litter using ground‐penetrating radar

“…The aforementioned discrepancies generally tend to attenuate for total litter thickness (Figures e and f) for which significant correlations between measurements and estimates are found, revealing that the overestimations and underestimations observed for h OF were partly associated with, respectively, underestimations and overestimations of h OL at the corresponding measurement locations. This would indicate inaccurate delineation of these two horizons from GPR signal inversion in these cases, as also reported by Winkelbauer et al []. Yet although significant, these correlations remain relatively weak with values of 0.44 and 0.52 for the complete and simplified model versions, respectively, due to some large h TOT overestimations that are still observed at some deciduous locations.…”

“…Nevertheless, although GPR has been widely used for more than two decades for the delineation of mineral and organomineral soil horizons and for the determination of their physical and hydrogeophysical properties [e.g., Huisman et al , ; Lambot et al , ; Gerber et al , , ; Minet et al , ; André et al , ; Jonard et al , ] as well as for the investigation of peatland stratigraphy [e.g., Proulx‐McInnis et al , ; Comas et al , ], the potential of this geophysical technique for forest humus characterization has been poorly examined so far. In a first study on this topic, Winkelbauer et al [] surveyed the thickness of forest litter horizons using a time domain GPR device equipped with a 800 MHz center frequency antenna. They successfully retrieved the total thickness of humus horizons and could reconstruct its spatial variability but failed to delineate the different humus horizons.…”

Soluble nitrogen forms in sand soil of Pallag: a quantitative report

“…Humus is a main fertility component of the soil, 65-75% of its structure being made up of organic matter 8,9 . We decided to include humus content in this N-related study as it represents a known indicator of soil quality 10 .…”

Accounting for Surface Roughness Scattering in the Characterization of Forest Litter with Ground-Penetrating Radar

“…Nevertheless, few studies have investigated the potentialities of GPR to characterize litter. In a first study, Winkelbauer et al [31] successfully retrieved the total thickness of humus horizons and could reconstruct its spatial variability using a time domain GPR system equipped with a 800 MHz centre-frequency antenna. However, these authors could not delineate the different humus horizons, presumably as a result of the rather low operating frequency combined with the limited dielectric contrast between horizons and their generally small thicknesses.…”