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NIR as a toll for determination of log/biomass quality index in mountain forests – SLOPE project approach

Anna Sandak 1 ; Jakub Sandak 1 ; Katharina Böhm 2
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Introduction
Current methods for logs grading are based on visual rating, which is operator-dependant, time-consuming, subjective and no precise. It is desired therefore that the efficient grading should be conducted by means of automatic measurement of selected wood properties that are essential for the foreseen final product. Several applications of NIR spectroscopy in the field of wood technology were previously developed and proved its potential in controlled laboratory conditions. However, up-to-data only few have been introduced to the real-world wood processing industries; mostly on-line sorting of wooden products and quality control of the production. The work presented here is a part of the SLOPE project, which is focused on development of the integrated surveying system for mountainous forest. The aim is to exploit the advantages of combined diagnostics techniques and multivariate data analysis for more reliable and rational assessment of the harvesting material. In this case usability of NIR spectroscopy for characterization of bio-resources along harvesting chain is investigated.
Experimental
Applicability of compact sensor (MicroNIRTM 1700 JDSU) has been tested. Each spectrum has been measured with frequency of 80Hz and 12.5ms integration time in the range of 10526-6060cm-1. Additionally samples were measured in the laboratory condition with FT-NIR spectrometer VECTOR 22-N produced by Bruker Optics GmbH. The spectral range measured was between 4000cm-1 and 12000cm-1, with a resolution of 8cm-1.
Results and discussion
Six different NIR quality indexes were computed along various harvesting stages.
In the preliminary phase characterization of tree(s) before the cutting operations on the base of satellite and UAV imaginary was evaluated. In this phase the NIR quality index #1 was estimated, which is related directly to the health status, stress status and to the productivity capabilities of the tree(s) foreseen for harvest.
Direct measurement of the NIR spectra by means of portable instruments was performed in parallel to the tree marking operation, providing NIR quality index #2. Operation of tree felling was another opportunity for NIR characterization of the resources and sample collection. Series of NIR spectra were measured after tree cutting along the radial direction in the cross section by means of portable instruments (NIR quality index #3).
NIR sensor was also integrated with the processor head and was used for the in-process spectra acquisition. The result of NIR scanning on the processor head (NIR quality index #4) were then associated with single log and will be forwarded to the Forest Information System database.
Logs are usually stored after processing and therefore its measurements was repeated periodically in order to monitor the quality depreciation. The result of measuring NIR spectra of logs stored in piles (quality index #5) was computed by using same software tools as for proceeding stages.
Finally samples collected in the forest were measured instantaneously after arrival in the laboratory (at the wet state and with rough surface and conditioned state with planed surface) by using the bench equipment (index #6). All the chemometric models were implemented to the portable systems to be used for direct in-field estimation of the logs quality.