Geoscience Reference
In-Depth Information
This resulted in soil compaction (higher bulk density and moisture content) in the area and affected
the propagation velocity of the radar signals.
The conclusions of Boniak et al. (2002) were that GPR is very effective in locating and mapping
underground drainage tile beneath golf greens. One suggestion that they offered was that a high-
accuracy Global Positioning System (GPS) be used to geo-reference each location in the course of
doing the radar transects. In another publication, Chong et al. (2000) also used GPR to determine
the root zone of golf greens.
3.7 InCoRpoRAtIon of GpR And GpS Into GIS
In the last ten years, three-dimensional modeling of radar data has increased due in part to inex-
pensive, commercially available, and user-friendly software. Applications of geographic informa-
tion systems (GISs) have increased for the same reasons. Therefore, more users are employing the
technologies. But integrating all three—GPR, GPS, and GIS—has not been routinely appreciated.
One of the first to explore this opportunity was Tischler (2002).
As discussed in Tischler (2002) and Tischler et al. (2002), GIS provides a means of storing,
manipulating, analyzing, and displaying spatially distributed data in a two-dimensional or three-
dimensional view. Combining the efficiency and practicality of GPR with the visual appeal and
interpretive power of GIS is the next reasonable step in the development of both technologies. This
can be accomplished using GPS. However, few methods exist for combining geo-referenced GPR
data with GIS data sets, which would reduce time and costs while increasing the interpretive quality
of the information.
Four models were developed (Tischler, 2002). Model 1 consisted of categorical data that pre-
dict the presence of sand or an argillic horizon based on GPR amplitude readings. Model 2 was
a numerical raster model that predicted GPR amplitude values continuously throughout the field.
Models 3 and 4 were both numerical raster models that predict the depth to argillic horizon but
differ in their methods of generation. The GPR processing steps taken, specific objectives, and the
quantitative analysis performed on the data, differentiate all the models. Summarizing his results,
Tischler commented that Model 1 met the objectives initially defined but the statistical correlation
was not as strong as expected. Model 2 was much more visually appealing than Model 1, but the end
value of his predicted ∆A (change in amplitude) was not a good variable to model. Models 3 and 4
were similar in generation and display. Both models predicted the same variable, depth to argillic,
and are raster models. Figure 3.4 and Figure 3.5 are examples of Models 1 and 2, respectively.
3.8 ConClUSIonS
There is no doubt that geophysical techniques have an essential function in the agricultural research
world. Only GPR was discussed in detail in this chapter, but a similar chapter could be dedicated to EM
use for agricultural purposes, especially in regions where the soil conditions for GPR are limited.
Over the twenty plus years that GPR has been routinely used by agriculturists, many of the studies
have had direct or indirect applications to agriculture production and management. Some of the direct
applications include mapping bedrock depth in a glaciated landscape; conducting microanalyses of
soil and karst; high-resolution mapping soil and rock stratigraphy; interpreting a fragipan; improving
interpretation of water table depths and groundwater flow patterns; determining forest productivity
on a glacial drift soil; and assessing Bt horizons in sandy soils and ortstein. Indirect applications of
GPR include detection, identification, location, mapping, predicting, or estimating a buried feature
or object that may affect production or management in an incidental fashion. This has been a sig-
nificant and increasing use for GPR and includes many investigations in detecting and monitoring
groundwater and nutrients. Some of these are estimating soil water content during irrigation and
drainage; identifying subsurface flow pathways; approximating moisture contents in the vadose zone;
Search WWH ::




Custom Search