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NJF Seminar 438: Evaluation of ground penetration radar (GPR) for characterization of silage stack compaction

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Syddansk Universitet
NJF Seminar 438: Evaluation of ground penetration radar (GPR) for characterization of
silage stack compaction
Green, Ole; Lindstrøm, Johanne; Jørgensen, Rasmus Nyholm; Sørensen, Claus Aage Grøn
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NJF Report
Publication date:
2010
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Green, O., Lindstrøm, J., Jørgensen, R. N., & Sørensen, C. A. G. (2010). NJF Seminar 438: Evaluation of
ground penetration radar (GPR) for characterization of silage stack compaction. NJF Report, 6(7), 50-52.
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NJF Report • Vol 6 • No 7 • Year 2010
NJF Seminar 438
Sensors for soil and plant mapping
and terrain analysis
Skara, Sweden, 27-28 October 2010
Nordic Association
of Agricultural Scientists
45
Evaluation of Ground Penetration Radar (GPR) for
characterization of silage stack compaction
Ole Green1*, Johanne Lindstrøm1, Rasmus Nyholm Jørgensen2 and Claus Grøn
Sørensen1
1) Department of Biosystems Engineering, University of Aarhus
2) Institute of Chemical Engineering, Biotechnology and Environmental Technology,
University of Southern Denmark
*) Corresponding author: Ole Green, email:Ole.Green@agrsci.au.dk, Research Centre
Foulum, Blichers Allé 20, DK-8830 Tjele
Introduction
The compaction process in a silage stack is a key process in the overall silage
production as it relates to obtaining an optimal quality of the feeding silage (Williams
et al., 1997, Shao et al. 2005). Also, the costs of the silage production are affected
by the silage compaction. The basic principles of the compaction procedure have
been known for many years (Buckmaster et al., 1990) and several analyses have
been carried out to describe how the resulting silage density is affected by a number
of factors. Muck et al. (2004) and Savoie et al. (2004) described how the silage
density is dependent on the compaction methods and Muck & Holmes (2000),
Bernier-Roy et al. (2001) and Muck & Holmes (2004) analyzed and found a
significant influence from different storage methods.
Neal (2004) reports that geologists and soil scientists have used ground penetrating
radar (GPR) as a method in sedimentology for many years. The GPR system functions
by sending a high frequency electric impulse into the soil and measuring the
reflectance time (Daniels et al., 1988). In terms of specific usage, the method has
been used for characterizing soil structure, compaction and type (Petersen et al.
2005), determining water contents (Lunt et al. 2005, Doolittle et al., 2006) and
localizing objects in the soil (Freeland et.al., 1998). Also, GPR has been used in
agriculture as an on-line sensor in precision agriculture applications (Adamchuk et
al., 2004).
The structural composition of silage has many similarities with a humus soil. Hence,
the idea and objective of the presented pilot experiment were to evaluate a GPR-
system for the characterization of silage stack compaction.
Results
Five profiles from a silage stack were characterized with a GPR-system and with a CP
as a reference method. The profile that was located 12.5 meters from the end wall of
the silage stack showed significant similarities regarding the illustrated structure of
the top of the silage stack. Both of the measuring methods showed that the centre
bottom of the measured area has a higher material density, and when comparing the
results, the phase shifts in the GPR measurements to fit with the areas in the CP
measurement where there is a distinct higher PR.
The measurements revealed that the centre of the stack is more compact in the sub
part of the stack compared to the top-layers, and this is in agreement with studies
made by D'Amours & Savoie (2004) which showed the same density distribution.
Along the walls of the silage stack and within a distance of 1 m from the wall, the
density is also lower. D'Amours & Savoie (2005) reported a similar density
distribution in a silage stack confined to a concrete silo.
Based on experiences with GPR measurements, the penetration depths were
estimated to a maximum range from 0.60 to 0.80 m, which is similar to the
measuring depth with the CP. The reduced penetration depths are possibly caused by
46
high water content combined with a high salinity, while salt in the silage water
increases the conductivity of the material.
In order to acquire additional knowledge about the factors affecting the radar
penetration depths, it would be relevant to carry out experiments as a way to
measure the dielectric resistance of various silage types. Also, measurements of the
water contents and density as a function of depths may reveal how changes in these
parameters would affect the radar waves.
The visual data interpretation of the two methods has shown that a GPR scan of the
top layer of a silage stack is likely to give the same information as a measurement
made with a high resolution penetration measure, but the advantage of the former is
that the time required to perform a radar scan is substantially reduced.
References
Adamchuk, V.I., Hummel, J.W., Morgan, M.T. & Upadhyaya, S.K. (2004): On-the-go
soil sensors for precision agriculture. Computers and Electronics in Agriculture, vol.
44 (2004) p. 71-91
Buckmaster, D.R., C.A. Rotz and J.R. Black. 1990. Value of alfalfa losses on dairy
farms. Trans. of the ASAE. 33(2):351-360
Bernier-Roy, Tremblay, Pormerleau & Savoie (2001): Compaction and Density of
Forage in Bunker Silos, ASAE meeting presentation, nr. 11089, 2001
Daniels, J.J., Grumman, D.L. & Vendi, M.A. (1997): Coincident Antenna Three-
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