Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2005
Publication Date: 7/1/2005
Citation: Grift, T.E., Tekeste, M.Z., Raper, R.L. 2005. Acoustic compaction layer detection. Transactions of the ASAE. 48(5):1-8. Interpretive Summary: Developing new measurement technologies for on-the-go sensing of soil compaction will open up new opportunities for producers to eliminate compacted soil layers which severely impede root growth. A new approach to sensing soil compaction with acoustics was tested in the soil bins of the USDA-ARS-National Soil Dynamics Laboratory. Results indicated that this technology was able to detect different depths of a compacted soil layer and also could distinguish between various levels of soil compaction. Further research using this technology could enable on-the-go sensing of soil compaction and lead to management systems where tillage depth is adjusted with the changing depth of compaction.
Technical Abstract: The ASAE standardized cone penetrometer method is traditionally used to determine the depth and strength of compacted layers in the field. Several methods have been investigated to replace this point-to-point method by an on-the-fly equivalent employing force measurement using a wedge tip mounted on a shank, strain gages measuring the deflection of a tine, air permeability measurements, as well as ground-penetrating radar and microwaves. The on-the-fly system as described here, attempts to locate the compaction layer depth by measuring the sound produced by a cone while being drawn through the soil. It is an empirical, passive method based on the correlation of the amplitude of sound waves in a certain frequency range with soil parameters such as strength and bulk density. Experiments were performed in the soil bins of the USDA-ARS National Soil Dynamics Laborator in Auburn, AL. Constant depth experiments were carried out at two depths and three varying compaction levels. Also, variable depth (slope) experiments were carried out at three different compaction levels. The data were analyzed using the Short Time Fourier Transform and the results showed that indeed, the acoustic signal amplitudes are well correlated with depth and compaction levels of the soil. Also, the data revealed that the hardpan is detectable in the highest range of the frequency spectrum. This phenomenon gave rise to the hypothesis that the soil-cone interface behaves like a low pass filtering mechanism, where the cutoff frequency increases in the compaction layer due to a more intimate contact between sensor and medium.