Depth profiling of peat deposits with impulse radar

Abstract

With the growing interest in peat as an energy fuel, the need for better inventories of this resource becomes increasingly important. Although conventional imaging sensors can provide information on the areal extent of peatlands, depth measurements must still be taken in the field in order to estimate the volume of material present. A recently completed program conducted in eastern Newfoundland suggests that impuse radar systems can provide depth information and volume estimates comparable to those obtained with manual measurement techniques. Ground-based data were acquired using 80- and 400-MHz radar systems and airborne data were collected using 80- and 120-MHz systems. For ground-based profiles, peat thickness of up to 8.1 m was clearly measureable. The airborne profile data were generally poorer in quality; however, depths of up to 4.8 m were successfully profiled from an altitude of 1.5 m. No significant seasonal variations were observed. Impulse radar techniques seem to be particularly useful for reconnaissance level surveys. Additional research is needed in order to develop a system suitable for airborne profiling. Key words: impulse radar, peat resources, peatlands, Newfoundland, depth, volume, profiling, airborne profiling, radar propagation.

Determining the number of manual measurements required to improve peat thickness estimations by ground penetrating radar

“…Part of the MAE can be explained by the degree of heterogeneity of the peat profile related to variations in peat moisture content and bulk density (Welsby, 1988), as well as by surface and subsurface irregularities of the profiles (Warner et al, 1990). The MAE found in this study is slightly larger than values reported in literature (Worsfold et al, 1986;Hänninen, 1992;Theimer et al, 1994;Slater and Reeve, 2002;Bradford et al, 2005). It is also larger than the GPR theoretical vertical resolution.…”

“…The mean maximum difference between peat thicknesses estimated from repeated coring on 1 m 2 was 0·19 m at Lanoraie and 0·32 m at Covey Hill. This is in the same range as the uncertainties on manual measurements obtained by Worsfold et al (1986). The composite EMW velocities estimated using the complete datasets are 0·040 m ns -1 (SD = 0·008 m ns -1 ) for Lanoraie and 0·039 m ns -1 (SD = 0·013 m ns -1 ) for Covey Hill.…”

“…Although manual peat thickness can be taken as the true value, it is clear that these measurements contain a certain margin of uncertainty. According to Worsfold et al (1986), this uncertainty can come from non-vertical soundings, irregularities in the deposit base and visual rounding off of the sampler depth. At both sites, the measurement uncertainty was assessed by performing ten repeated measurements within 1 m 2 zones at five randomly selected locations on the transects.…”

“…Ground-penetrating radar has been used to study peat thickness or volume for more than two decades (e.g. Bjelm, 1980;Worsfold et al, 1986;Hänninen, 1992;Warner et al, 1990;Lapen et al, 1996). More recently, GPR applications have extended to peatland stratigraphy and morphology (Warner et al, 1990;Comas et al, 2004Comas et al, , 2005, peat moisture and bulk density (Warner et al, 1990), thaw depth (Bradford et al, 2005) and subsurface piping in peat (Holden et al, 2002;Holden, 2004Holden, , 2005Holden, , 2006.…”

“…Theimer et al, 1994). The simplest and most direct approach to estimate EMW velocity is to use a depth-to-target calibration with manual sampling points (Bjelm, 1980;Worsfold et al, 1986;Welsby, 1988;Theimer et al, 1994;Slater and Reeve, 2002;Bradford et al, 2005;Comas et al, 2005). Using a small number of calibration points could underestimate the spatial variability of the EMW velocity and therefore limit the accuracy of GPR peat thickness estimates.…”