Geoscience Reference
In-Depth Information
agricultural fields. They concluded that geo-referenced GPR data sets have great potential to locate
soil horizons that control subsurface water pathways. Gish et al. (2005) continued with their interest
in identifying subsurface flow pathways by studying such occurrences in a corn (
Zea mays
L.) field.
They measured subsoil water contents that supported the GPR-identified preferential flow pathways.
The impact of the subsurface water pathways was observed by the increase in corn yield during a
drought season. Their conclusion was that subsurface pathways exist and influence soil moisture
and corn grain yield patterns.
3.5 GpR ApplICAtIonS to StUdy plAntS
Literature on the use of GPR applications to study plants has been extremely limited. One of the
main limitations has been the wavelength and resolution associated with commercially available
antennae. Until recently, the antennae were not able to distinguish very small objects such as plant
roots. Truman et al. (1988b) used GPR to assess root concentrations. This may have been the earliest
research in the application of GPR to evaluate plant roots.
More recently, Butnor et al. (2003) reported they were able to measure loblolly pine (
Pinus
taeda
L.) root biomass to a depth of 30 cm with the aid of a digital signal processed GPR. Correla-
tion coefficients were highly significant (
r
= 0.86,
n
= 60,
p
< 0.0001) between the GPR estimates
and the measured root biomass. They concluded that GPR could decrease the number of cores
needed to determine tree root biomass and biomass distribution. Hruska et al. (1999) had done a
similar study in the Czech Republic. They looked at the three-dimensional distribution of oak trees
(
Quercus petraea
(Mattusch.) Liebl) with DBH = 14 to 35 cm to estimate the coarse root density.
The GPR unit employed in this study was able to give a resolution of approximately 3 cm in all
directions. They reported satisfactory results.
Wielopolski et al. (2002) were concerned with increased CO
2
in the atmosphere. They believed
that a considerable portion of CO
2
could be sequestered in plant roots. But a suitable means to mea-
sure the root morphology, distribution, and mass without destroying the roots' environment was not
available. From these root characteristics, they wanted to access below-ground rates and limits of
carbon accumulations. Thus, using a 1.5 GHz impulse GPR system and off-the-shelf software, they
were able to image root systems (morphology and dimensions) in situ
.
They concluded from their
study that GPR could image a 2.5 mm root twig buried in sand (under ideal conditions), but that fur-
ther work is required to improve the images of the plant root system. Also, they believed that with
future developments, it would be possible to routinely image roots 2 to 3 mm in diameter.
3.6 GpR Golf CoURSe StUdIeS
A golf course was the study site of a very interesting investigation performed by Boniak et al.
(2002)
.
A suitable playing surface on a golf course is important for play and aesthetics. Surface
watering and subsurface drainage are necessary. When the underground drainage system is not
properly working, substantial damage may be done to the golf course resulting in a loss of playing
time. The exact location of the underground tile drainage system is not known on many golf courses.
To correct a problem, considerable destruction may be done to the course. Thus, the objective of
their study was to locate and map the tile drainage system under a putting green using the radar. By
doing so, it was expected that less physical destruction would take place to repair the tile because
the exact locations of trouble areas could be accurately located with the GPR. Several intriguing
findings were a result of this study.
Initially, the 900 MHz antenna was used because of its ability to detect shallow features with
high resolution, but it was not successful because of a recent application of granular fertilizer. The
fertilizer (high salt content) created noise and distortion to the radar data. As a result, the 400 MHz
antenna was used for the study. A discontinuity was located where the golfers would exit the greens.
