| 1. |
- Thierfelder, Tomas, et al.
(författare)
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Evaluating the effect of DEM resolution on performance of cartographic depth-to-water maps, for planning logging operations
- 2022
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Ingår i: International Journal of Applied Earth Observation and Geoinformation. - : Elsevier BV. - 0303-2434 .- 1569-8432. ; 108
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Tidskriftsartikel (refereegranskat)abstract
- Reliable and accurate soil moisture maps are needed to minimise the risk of soil disturbance during logging operations. Depth-to-water (DTW) maps extracted from digital elevation models have shown potential for identifying water flow paths and associated wet and moist areas, based on surface topography. We have examined whether DEMs from airborne LiDAR data with varying point density can improve performance of DTW maps in planning logging operations. Soil moisture content was estimated on eight sites after logging operations and compared to DTW maps created from DEMs with resolutions of 2 m, 1 m, and 0.5 m. Different threshold values for wet soil (1 m and 1.5 m depth to water) were also tested. The map performances, measured by accuracy (ACC) and Matthews Correlation Coefficient (MCC), changed slightly (79%, 81% and 82% and 0.33, 0.26 and 0.30 respectively) when DEM resolutions varied from 2 m to 1 m, and 0.5 m. The corresponding values when the DTW threshold value for wet/dry soil changed from 1 m to 1.5 m were 70%, 72%, 71% and 0.38, 0.41 and 0.39. LiDAR-based DEM resolutions of 1–2 m were found to be sufficient for extraction of DTW maps during planning of logging operations, when knowledge about soil hydrological features, associated wet and moist areas, and their connectivity is beneficial.
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| 2. |
- Bergström, Dan, et al.
(författare)
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Effects of Boom-Corridor and Selective Thinnings on Harvester Productivity in Dense Small Diameter Pyrenean Oak (Quercus pyrenaica Willd.) Coppices in Spain
- 2024
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Ingår i: Croatian Journal Of Forest Engineering. - 1845-5719. ; 45
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Tidskriftsartikel (refereegranskat)abstract
- Due to socioeconomic transformations in the 20th century, Quercus pyrenaica Willd. coppices in Spain, as well as other European coppices, have experimented an abandonment and lack of intervention leading to stagnant high density stands with fragile health due to competition. Thinnings are often required to ensure their stability and health, producing forest products such as firewood or biomass, which are key energy sources in a carbon-neutral economy. However, thinnings are seldom performed because they lack economic sustainability due to a low productivity, high costs and low biomass prices. In this study, two thin-ning methods, selective thinning (ST) and boom-corridor thinning (BCT), were tested car-rying out a time study in a high-density small-diameter Q. pyrenaica stand in the Leon province (Castilla y Leon, Spain) with a forest harvester base machine, on which an accumulating felling head Bracke C16c was mounted. The residual stands were significantly different regarding the final density (greater in BCT) and the final average DBH (bigger in ST), while thinning intensity (odt center dot ha-1) was the same. In most work elements, time per tree was not significantly different. BCT showed a significant 48.6% increase in harvester productivity when compared to ST, with averaging 4.43 and 2.99 odt center dot pmh-1, respectively, due mainly to the average weight per extracted tree, 42% greater in BCT. When considering the common range of unit tree weight, the productivity was 16-23% greater for BCT, far less than observed in the trials. These results show the potential of BCT over ST in the studied conditions, although there is room for improvement. Further studies could include the future evolution of the treated stands and perform a cost analysis.
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| 3. |
- Bergström, Dan, et al.
(författare)
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Effects of boom-corridor thinning on harvester productivity and residual stand structure
- 2022
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Ingår i: International Journal of Forest Engineering. - : Informa UK Limited. - 1494-2119 .- 1913-2220. ; 33, s. 226-242
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Tidskriftsartikel (refereegranskat)abstract
- Biomass derived from small-diameter, dense, thinning stands is largely underutilized within the European Union, mainly because of in-effective harvesting methods and cutting technology, leading to high supply costs. Therefore, the efficacy of boom-corridor thinning (BCT) and selective thinning (ST) on harvester felling and bunching productivity was compared for the first thinning of whole tree biomass in small-diameter, dense stands. BCT working method is when trees are cut with linear movements of the harvester's boom reach, along narrow corridors, instead of cutting each tree selectively (ST). Trials were performed in six forest stands, one in Sweden, two in Finland, and three in Slovenia, using the same harvester and operator. A time-and-motion study was carried out in 64 pre-marked study units (32 replications per method), across a variety of stand conditions. The biomass removal for both treatments averaged 40.2 dry t ha -1 and BCT productivity averaged 5.4 dry t PMh -1. For BCT, harvester work time consumption (sec tree -1) and productivity (dry t PMh -1) were on average 27% lower and 16% higher, respectively, compared with ST. The effectiveness of the accumulating felling head technology used could potentially be increased by implementing a feed-roller system when handling excessive tree lengths. Developing dedicated harvesting technology for BCT could further boost productivity, facilitating cost-effective and sustainable utilization of low-value small-diameter tree biomass and replacing fossil resources.
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| 4. |
- Bergström, Dan, et al.
(författare)
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Environmental Impacts of Boom-Corridor and Selectively Thinned Small-Diameter-Tree Forests
- 2022
-
Ingår i: Sustainability. - : MDPI AG. - 2071-1050. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- European forest stands of small-diameter trees can provide industries with biomass as an alternative to fossil use. Small-tree harvesting is costly using conventional methods but using accumulating felling heads (AFH) in combination with a novel boom-corridor thinning (BCT) technique can increase harvester productivity and supply cost efficiency. This method has great potential to reduce costs, but its environmental impact compared with selective thinning (ST) needs to be determined. The objectives of this study were therefore to quantify and compare tree and soil damage as well as air, water and soil emissions for both BCT and ST in various European small-diameter-tree forests. Trials were performed in 84 study units (42 replications per thinning technique) across four countries. Damaged trees (with a diameter at breast height >= 7 cm) were measured after thinning and after forwarding. Harvesting emissions were calculated from a life cycle assessment. The percentage of remaining trees that had been damaged by the harvesting processes was 13% and 19% for BCT and ST, respectively, and the difference was significant. BCT exhibited the lowest emissions in all environmental impact categories considered, in all countries. Greenhouse gas emissions were on average 17% lower for BCT. BCT in small-diameter-tree stands therefore reduces the environmental impact of thinning operations compared with conventional methods, and results in less damage to the remaining trees.
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| 5. |
- Bohlin, Jonas, et al.
(författare)
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Remote measuring of the depth of wheel ruts in forest terrain using a drone
- 2021
-
Ingår i: International Journal of Forest Engineering. - : Informa UK Limited. - 1494-2119 .- 1913-2220. ; 32, s. 224-234
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Tidskriftsartikel (refereegranskat)abstract
- Even at a well-managed harvesting site, vehicle trafficking occurs on at least 12% of the area and might cause ruts and compaction. The use of drones for inventory and mapping in forestry is still a new method. The purpose of this study was to develop a method for measuring the size and depth of wheel ruts caused by forest machines in harvested areas, using drones and Structure from Motion photogrammetry. In order to investigate the accuracy of drone photogrammetry, measurements from flight altitudes of 60 m and 120 m above ground level were compared with manual measurements. The same methods were used at a control site on farm land, taking into account the rut depth and the location of the sample surface (close to trees or in a fully open area). No statistically significant differences were found between manual measurements and remote measurements from 60 m or 120 m altitude at the harvesting site (R-2 0.77-0.83). At the control site, an underestimation of 2.2 cm of the rut depth was found for remote measurements made from 120 m altitude. The data derived from drone images were able to reproduce the 3D model of surface features, such as bulges and ruts; these measurements were considered to be equivalent to manual measurements. For practical applications, a post-harvest survey using drones could contribute to verifying compliance with international forest certification standards or by private contractors to evaluate rut formation on their harvest sites.
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| 6. |
- Edlund, Björn, et al.
(författare)
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The effect of rollover protection systems and trailers on quad bike stability
- 2020
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Ingår i: International Journal of Forest Engineering. - : Informa UK Limited. - 1494-2119 .- 1913-2220. ; 31, s. 95-105
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Tidskriftsartikel (refereegranskat)abstract
- Quad bikes are light-weight vehicles which are used for transportation of personnel, equipment, and material in forestry operations such as planning, logging, planting, and fire-fighting. With increased quad bike usage, serious injuries have become an increasing concern. The most common forms of severe incidents occur when a quad bike loses stability, causing injuries as it rolls over the rider trapped beneath. The risk of injuries during a rollover incident can be decreased by equipping the vehicle with rollover protection systems (ROPS), but since ROPS tend to decrease the stability of quad bikes, their use can be a trade-off between the risk of overturning and the outcome of any such incident. In this study, we examine the effects of approach angle, trailer load, ROPS and different hardware configurations on a quad bike’s static stability. We found that approach angle and trailer configurations influenced the vehicle’s stability, although the effect was difficult to quantify in a static environment. Furthermore, the quad bike’s stability was negatively influenced by equipping it with a heavy (44 kg) ROPS. It reduced the static stability by an average of 5.1°, while a light (14.7 kg) prototype ROPS only reduced the vehicle’s static stability by an average of 1.0°. The negative impact a ROPS has on a quad bike’s lateral stability could be effectively counteracted by increasing the quad bike’s track width. Increasing track width by less than 2% (20 mm) compensated for any negative impact that the light prototype ROPS had on the quad bike’s lateral stability.
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| 7. |
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| 8. |
- Kronholm, Thomas, et al.
(författare)
-
Implementering av skyddsbågar på fyrhjulingar : en utvärdering av användares erfarenheter av ett vältskydd
- 2023
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Intresset för fyrhjulingar har ökat under de senaste åren och fyrhjulingen är idag ett frekvent använt arbets- och nöjesfordon i Sverige. Enbart under år 2021 registrerades 12 000 nya fyrhjulingar i Sverige. Med en mer utbredd användning av fyrhjulingar så har också antalet allvarliga olyckor och dödsfall i samband med fyrhjulingskörning ökat. Trafikverket, försäkringsbolag, skogsföretag, forskare och en del branschorganisationer har under de senaste åren därför initierat flera projekt och insatser i syfte att öka säkerheten och minska antalet omkomna och skadade fyrhjulingsanvändare. En säkerhetshöjande åtgärd som återkommande lyfts fram i forskningen är att utrusta fyrhjulingen med ett vältskydd, en så kallad skyddsbåge, som skyddar föraren vid vältningsolyckor. Vid en vältningsolycka riskerar föraren att hamna i kläm under maskinen, men med ett vältskydd som hindrar maskinen från att rulla runt så minskar denna risk betydligt. I vissa länder, t.ex. Australien, finns idag krav på att fyrhjulingar skall vara utrustade med någon typ av vältskydd. I Sverige har intresset för att utrusta fyrhjulingen med vältskydd hittills varit begränsat. En del studier har pekat på att det både bland förare och tillverkare har funnits ett motstånd mot implementering av vältskydd, bl.a. på grund av en oro för att det skulle vara hindrande för normal användning.Det övergripande syftet med detta projekt har varit att kartlägga och beskriva erfarenheterna från en stor grupp med användare av fyrhjuling med vältskydd och därigenom öka säkerheten och det allmänna medvetandet om nyttan med vältskydd på fyrhjulingar. En målsättning är att detta arbete kan skynda på utvecklingen av säkerheten för fyrhjulingar och på sikt leda till en storskalig implementering av vältskydd i Sverige, i likhet med den utveckling som redan skett i andra länder.För kunna samla in erfarenheter från fyrhjulingsanvändare med vältskydd så importerades vältskydd av märket Quadbar från Australien och distribuerades till ca 50 personer som hade anmält intresse att montera ett vältskydd på sin fyrhjuling och därefter dela med sig av sina synpunkter och erfarenheter. Dessa synpunkter samlades in vid tre olika enkättillfällen. Den första enkäten gjordes inför monteringen av vältskyddet, den andra efter en kortare tids användning och den sista drygt ett år efter att vältskyddet hade monterats. Den första enkäten besvarades av 50 deltagare, den andra av 38, och den sista enkäten besvarades av 37 deltagare.De vanligaste farhågorna inför projektet var att vältskyddet skulle påverka körningen och framkomligheten, eller att det skulle vara hindrande för transporter. Exempelvis att det kan fastna i låg hängande grenar eller liknande och därmed orsaka en olycka. Andra farhågor var att det skulle vara hindrande för användningen av vissa redskap, så som vinsch eller släp. Ur ett säkerhetsperspektiv var deltagarna generellt positivt inställda till vältskyddet.En stor majoritet av deltagarna använde normalt sin fyrhjuling till transporter av material, person och utrustning i skogsbruket, eller till transporter på gården. Färre än hälften använde den normalt till nöjesåkning. De vanligaste terrängtyperna som fyrhjulingen framfördes i var skogsmark, enskild väg, traktorväg och jordbruksmark. En mindre andel av deltagarna framförde i normala fall fyrhjulingen på allmän väg. Det var mycket vanligt att fyrhjulingen kördes tillsammans med ett tillkopplat släp som saknade bromsar. Drygt hälften av deltagarna transporterade även last på fyrhjulingens bakre eller främre lastbåge.Under testperioden var ca 20 % av deltagarna med om en olycka eller incident med sin fyrhjuling. Totalt inrapporterades tio olyckor eller incidenter. Vid de vältningsolyckor som inträffat hade vältskyddet fungerat som det var tänkt och haft en positiv inverkan på utfallet, enligt de beskrivningar som deltagarna har lämnat. Vid några av de mindre allvarliga incidenterna hade förarna av ovana eller oaktsamhet missbedömt den nya höjden på ekipaget eller glömt bort att de Sammanfattning hade vältskyddet bakom ryggen, vilket hade lett till att vältskyddet hade tagit i när de kört under låga passager (t.ex. en klädlina). Inga personskador har inrapporterats i samband med incidenterna.Deltagarna var generellt nöjda med den vältskydd de hade haft, vilket framgår av att en stor andel uttryckte att det var troligt eller mycket troligt att de skulle rekommendera Quadbar till sina bekanta. Resultaten visar också att deltagarnas säkerhetskänsla ökade med vältskyddet monterad på fyrhjulingen. Detta gällde både för deras egen och för andra förares säkerhet. Deras trygghetskänsla ökade över tid.De mest vanliga bekymren som en del deltagare hade upplevt var att det aktuella vältskyddets infästning försämrade möjligheten att koppla till släpp på fyrhjulingen, samt att det försvårade användningen av vinsch. Den medföljande dragkroksförlängaren ansågs i vissa fall ha för dålig hållfasthet. Några deltagare hade därför gjort modifieringar på vältskyddet, dess infästning, eller något tillbehör till denna för att kunna nyttja fyrhjulingen enligt sina egna behov. Att vältskyddet gjorde ekipaget högre försvårade också transport av fyrhjulingen på släp med kåpa. Flera deltagare efterlyste därför en smidigare lösning för att tillfälligt kunna plocka av eller vika ner vältskyddet. Liknande önskemål hade de som ville kunna använda vinsch eller för att komma åt förvaringsutrymmen som annars blockerades av vältskyddet.En av studiens slutsatser är att vältskyddet generellt verkar ha fungerat bra för de flesta av deltagarna, och användningen av vältskydd kan öka både den upplevda och den faktiska säkerheten vid fyrhjulingsanvändning. Deltagarnas positiva inställning till att rekommendera vältskyddet till bekanta kan antas bidra till ett ökat intresse hos fler att införskaffa denna eller liknande vältskydd. Projektet har också synliggjort vad som särskilt behöver utvecklas för att just Quadbar ska bli ännu bättre lämpad för fyrhjulingsanvändare som främst nyttjar den i skogsbruket.
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| 9. |
- Li, Songyu, 1994-
(författare)
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Vision based perception systems for unmanned forestry machines
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- After years of continuous development in the past decades, the field of forest production has achieved a notable degree of mechanization. Nonetheless, the unceasing demand for increased productivity in forestry operations continues to drive the rapid expansion of forestry automation. Critical aspects of forest production, including activities such as harvesting, forwarding, seedling planting, and soil preparation, hold significant potential for improved automation. These advancements promise numerous advantages, such as heightened production efficiency, reduced environmental impact, reduced operational costs, and the creation of a more favourable work environment. Beyond fostering industrial progress, such innovations could also make a positive contribution to the sustainable development of forestry.Forestry operations take place in intricate natural forest environments, rendering the automation of these processes complex and challenging. To realize full automation of forest machines, it is imperative to equip them with environmental awareness and cognitive capabilities. This can be achieved by integrating advanced imaging sensors with sophisticated algorithms, thereby enabling forest machinery to possess a vision system. By utilizing both novel and existing solutions for object detection, positioning, categorization, and status analysis within the machine's surroundings, combined with intelligent decision-making and control mechanisms, forest machinery can attain a higher degree of operational automation.This thesis primarily focuses on the development, deployment, and validation of vision systems on an unmanned forestry machine platform, with a special emphasis on the prototype development of essential features that are still manually executed in contemporary forestry operations. These features include forest terrain obstacle detection, roundwood pose estimation, automated selection of seedling planting locations, and autonomous obstacle avoidance for mounders.In this thesis, vision systems rooted in color and stereo camera sensing are designed and deployed on an unmanned forest machinery platform. These systems encompass the following key functionalities:• A precise positioning system for detecting forest terrain obstacles, such as stones and stumps, using stereo camera data in conjunction with deep learning techniques.• Localization and pose estimation capabilities for ground logs, leveraging stereo cameras and deep learning.• An analysis of the planning area for obstacle detection, along with the extraction of feasible planting zones for establishing seedling planting locations.• The development of an automated obstacle avoidance system for forestry mounders, powered by visual solutions.Through rigorous testing in real-world scenarios spanning logging, loading, planting, and site preparation, this paper demonstrates the feasibility and practicality of enhancing the level of automation in forest machinery operations through the integration of vision systems. It culminates in the creation of tangible and efficient functional prototypes, leading towards a new era of automation in the field of forestry.
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| 10. |
- Lundbäck, Mikael, et al.
(författare)
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Global analysis of the slope of forest land
- 2021
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Ingår i: Forestry. - : Oxford University Press (OUP). - 0015-752X .- 1464-3626. ; 94, s. 54-69
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Tidskriftsartikel (refereegranskat)abstract
- Forests of the world constitute one-third of the total land area and are critical for e.g. carbon balance, biodiversity, water supply and as source for bio-based products. Although the terrain within forest land has a great impact on accessibility, there is a lack of knowledge about the distribution of its variation in slope. The aim was to address that knowledge gap and create a globally consistent dataset of the distribution and area of forest land within different slope classes. A Geographic Information System (GIS) analysis was performed using the open-source QGIS, GDAL and R software. The core of the analysis was a digital elevation model and a forest cover mask, both with a final resolution of 90 m. The total forest area according to the forest mask was 4.15 billion hectares whereof 82 per cent was on slope<15 degrees. The remaining 18 per cent was distributed over the following slope classes, with 6 per cent on a 15-20 degrees slope, 8 per cent on a 20-30 degrees slope and 4 per cent on a slope>30 degrees. Out of the major forestry countries, China had the largest proportion of forest steeper than 15 degrees followed by Chile and India. A sensitivity analysis with 20 m resolution resulted in increased steep areas by 1 per cent point in flat Sweden and by 11 per cent points in steep Austria. In addition to country-specific and aggregated results of slope distribution and forest area, a global raster dataset is also made freely available to cover user-specific areas that are not necessarily demarcated by country borders. Apart from predicting the regional possibilities for different harvesting equipment, which was the original idea behind this study, the results can be used to relate geographical forest variables to slope. The results could also be used in strategic forest fire fighting and large-scale planning of forest conservation and management.
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| 11. |
- Lundbäck, Mikael, et al.
(författare)
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New configurations of the tele-extraction concept
- 2023
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Ingår i: International Journal of Forest Engineering. - : Taylor & Francis. - 1494-2119 .- 1913-2220. ; 34:3, s. 397-407
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Tidskriftsartikel (refereegranskat)abstract
- Within cut-to-length forwarding, a theoretical semi-autonomous teleoperation concept called tele-extraction, with automation of crane work and teleoperation of driving, was modeled and simulated. Both configurations modeled had greater potential for cost reduction than a previously studied alternative where the driving was automated, and crane work was teleoperated. Teledrive with teleoperated driving empty, driving loaded, and driving between log piles while loading, showed a reduced cost of 10% for five operators on ten forwarders, whereas teledrive with both loading and driving while loading automated showed a reduced cost of 18% at four operators. In both configurations, the lowest cost was reached at about 10% lower productivity compared to standard forwarding. Increased extraction distance had a negative impact on potential for cost reduction since the driving was teleoperated while terminal activities were autonomous.
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| 12. |
- Lundbäck, Mikael, et al.
(författare)
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The economic potential of semi-automated tele-extraction of roundwood in Sweden
- 2022
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Ingår i: International Journal of Forest Engineering. - : Informa UK Limited. - 1494-2119 .- 1913-2220. ; 33, s. 271-288
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Tidskriftsartikel (refereegranskat)abstract
- The mechanization of roundwood harvesting in Sweden has historically cut costs rapidly. However, machinery and work methods have conceptually stayed the same since the introduction of the single-grip harvester. Current trends indicate that the next major wave of development will be based on automation, and that teleoperation is a step in this direction. This study aims to evaluate the economic potential of semi-automated tele-extraction compared to standard forwarding within the Nordic CTL two-machine harvesting system. The initial scenario examined autonomous terrain transportation with teleoperation during loading and unloading. A Discrete Event Simulation was implemented in the AnyLogic software. Input data included 1100 Swedish harvest sites, with in total 1.6 million m(3) and extraction distances from 20 to 1500 m. Scenarios with different numbers of teleoperators for a fleet of ten forwarders were tested. The optimum number of operators was seven per ten forwarders, resulting in a potential extraction cost reduction of 7% compared to standard forwarding. Extraction distances further than 500 m enabled use of five or six teleoperators, resulting in potential cost reductions of up to 15%. The highest potential cost reductions were linked to increased time used for autonomous driving, increasing the teleoperator availability for other machines. The simulation model provides a framework for further evaluation of new scenarios of automation and teleoperation of forwarders.
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| 13. |
- Lundbäck, Mikael, et al.
(författare)
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Traversability analysis using high-resolution laser-scans, simulation, and deep learning
- 2022
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Ingår i: Proceedings of the joint 44<sup>th</sup> annual meeting of Council on forestengineering (COFE), the 54<sup>th</sup> International symposiumon forest mechanization (FORMEC), and 2022 IUFRO ALL-division 3 meeting. - 9798985528213 ; , s. 119-120
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Traversability is of major importance in forestry, where heavy vehicles, weighing up to 40 tons whenfully loaded, traverse rough and sometimes soft terrain. Forest remote sensing is becoming available atresolutions where surface roughness and slope can be determined at length-scales smaller than the forestmachines. Using 3D multibody dynamics simulation of a forest machine driving in virtual terrain replications, the interaction can be captured in great detail. The observed traversability is then automaticallya function of the vehicle geometry, dynamics, and of the local terrain topography relative to heading. Weexpress traversability with three complementary measures: i) the ability to traverse the terrain at a target speed, ii) energy consumption, and iii) machine body acceleration. For high traversability, the lattertwo should be as small as possible while the first measure is at maximum. The simulations are, however,too slow for systematically probing the traversability over large areas. Instead, a deep neural networkis trained to predict the traversability measures from the local heightmap and target speed. The trainingdata comes from simulations of an articulated vehicle with wheeled bogie suspensions driving over procedurally generated terrains while observing the dynamics and local terrain topology. We evaluate themodel on laser-scanned forest terrains, previously unseen by the model. The model predicts traversability with an accuracy of 90% on terrains with 0.25 m resolution and it is 3000 times faster than the groundtruth realtime simulation and trivially parallelizable, making it well suited for traversability analysis andoptimal route planning over large areas. The trained model depends on the vehicle heading, target speed,and detailed features in the topography that a model based only on local slope and roughness cannotcapture. We explore traversability statistics over large areas of laser-scanned terrains and discuss howthe model can be used as a complement or in place of the currently used terrain classification scheme.
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| 14. |
- Lundbäck, Mikael, et al.
(författare)
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Worldwide trends in methods for harvesting and extracting industrial roundwood
- 2021
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Ingår i: International Journal of Forest Engineering. - : Informa UK Limited. - 1494-2119 .- 1913-2220. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Globally, almost 2 billion cubic meters of industrial roundwood are harvested yearly. Two of the most common methods of harvest and extraction are cut-to-length (CTL) and full-tree or tree-length (FT/TL). The aim of this study was to compile data on annual volumes of industrial roundwood harvested by the main methods in forestry countries. To quantify the effect of potential explanatory variables, the data were subjected to linear regression analysis, using shares of roundwood volumes harvested by fully mechanized CTL and/or FT/TL as response variables. Generally, high diesel price and Gross Domestic Product appear to favor CTL, while high shares of steep terrain (>20°) in forest land decrease the leve l of both mechanization and CTL, and low Social Security Rate (SSR) favor FT/TL. Two models were created for CTL, one with an R2 of 0.64 and another more complex with an R2 of 0.75. A separate model for mechanization (CTL and FT/TL together) showed an R2 0.57. The CTL models could potentially be used to predict shares of roundwood volumes harvested by CTL in countries not included in this study. Predictions for countries with large harvested volumes, e.g. China and India, are presented here, but they require validation, as does the model’s applicability for countries with small harvested volumes. Countries with less than 10% of steep slope forests are almost exclusively mechanized according to the model. For FT/TL, the proposed model is probably not sufficiently robust for prediction, but it highlights SSR as one important explanatory variable.
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| 15. |
- Nordfjell, Tomas
(författare)
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Control of Rough Terrain Vehicles Using Deep Reinforcement Learning
- 2022
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Ingår i: IEEE Robotics and Automation Letters. - 2377-3766. ; 7, s. 390-397
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Tidskriftsartikel (refereegranskat)abstract
- We explore the potential to control terrain vehicles using deep reinforcement in scenarios where human operators and traditional control methods are inadequate. This letter presents a controller that perceives, plans, and successfully controls a 16-tonne forestry vehicle with two frame articulation joints, six wheels, and their actively articulated suspensions to traverse rough terrain. The carefully shaped reward signal promotes safe, environmental, and efficient driving, which leads to the emergence of unprecedented driving skills. We test learned skills in a virtual environment, including terrains reconstructed from high-density laser scans of forest sites. The controller displays the ability to handle obstructing obstacles, slopes up to 27 degrees, and a variety of natural terrains, all with limited wheel slip, smooth, and upright traversal with intelligent use of the active suspensions. The results confirm that deep reinforcement learning has the potential to enhance control of vehicles with complex dynamics and high-dimensional observation data compared to human operators or traditional control methods, especially in rough terrain.
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| 16. |
- Nordfjell, Tomas
(författare)
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Impacts of wood extraction on soil: assessing rutting and soil compaction caused by skidding and forwarding by means of traditional and innovative methods
- 2022
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Ingår i: European Journal of Forest Research. - : Springer Science and Business Media LLC. - 1612-4669 .- 1612-4677. ; 141, s. 71-86
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Tidskriftsartikel (refereegranskat)abstract
- Intensive forestry operations may cause soil compaction, plastic soil disturbances and rutting, which are responsible for undesirable effects on soils, vegetation and water bodies. Despite the numerous studies aimed to identify the main factors affecting soil damages, it still remains unclear whether wood extraction methods and driving direction (uphill or downhill) may affect the impacts of forest machines. This research analyses soil compaction and soil penetration resistance as well as rutting from forwarding and skidding using the same farm tractor in up- and downhill wood extraction. Rutting was estimated by 3D soil reconstruction derived by portable laser scanning (PLS) and close-range photogrammetry using structure for motion (SfM). Our findings showed that the direction of extraction did not affect soil damage severity during forwarding on a 25% slope. On the contrary, in order to reduce soil compaction, downhill skidding is preferable to uphill skidding. The results showed that the pressure on the ground caused by vehicles can be distributed horizontally, thus affecting also the soil between the wheel tracks. The soil bulk density inside the tracks after 10 forwarding passes increased by 40% and with 23% between the wheel tracks. The soil displacement in skidding trails (7.36 m(3) per 100 m of trail) was significantly higher than in forwarding (1.68 m(3) per 100 m of trail). The rutting estimation showed no significant difference between the PLS and SfM methods, even comparing the two digital surface models (DSMs) obtained, even if photogrammetry was preferred for technical and practical reasons.
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| 17. |
- Nordfjell, Tomas
(författare)
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Skogsavverkning och markskador
- 2020
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Annan publikation (populärvet., debatt m.m.)abstract
- Forskning har visat att kombinationen av jordart och markfuktighet är starkt avgörande för om man fårstora markskador eller ej vid skogsavverkning. Grovkorniga jordarter har bra bärighet även vid högmarkfuktighet men för finkorniga jordarter försämras bärigheten kraftigt vid ökad markfukt. Viddrivningsplanering är det viktigt att bestämma jordart för att veta hur hög markfuktighet som kan tillåtasvid drivningstillfället. För steniga marker har det visat sig att en kombination av blockkvot ochmaximalt stickdjup med jordsond ger en god skattning av markens aktuella bärighet. En praktiskttillämpbar klassificering av skogsmarks bärighet utifrån enkelt mätbara variabler presenteras.
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| 18. |
- Nordfjell, Tomas
(författare)
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Trafficability Prediction Using Depth-to-Water Maps: the Status of Application in Northern and Central European Forestry
- 2022
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Ingår i: Current Forestry Reports. - : Springer Science and Business Media LLC. - 2198-6436. ; 8, s. 55-71
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Tidskriftsartikel (refereegranskat)abstract
- Purpose of Review Mechanized logging operations with ground-based equipment commonly represent European production forestry but are well-known to potentially cause soil impacts through various forms of soil disturbances, especially on wet soils with low bearing capacity. In times of changing climate, with shorter periods of frozen soils, heavy rain fall events in spring and autumn and frequent needs for salvage logging, forestry stakeholders face increasingly unfavourable conditions to conduct low-impact operations. Thus, more than ever, planning tools such as trafficability maps are required to ensure efficient forest operations at reduced environmental impact. This paper aims to describe the status quo of existence and implementation of such tools applied in forest operations across Europe. In addition, focus is given to the availability and accessibility of data relevant for such predictions.Recent Findings A commonly identified method to support the planning and execution of machine-based operations is given by the prediction of areas with low bearing capacity due to wet soil conditions. Both the topographic wetness index (TWI) and the depth-to-water algorithm (DTW) are used to identify wet areas and to produce trafficability maps, based on spatial information.Summary The required input data is commonly available among governmental institutions and in some countries already further processed to have topography-derived trafficability maps and respective enabling technologies at hand. Particularly the Nordic countries are ahead within this process and currently pave the way to further transfer static trafficability maps into dynamic ones, including additional site-specific information received from detailed forest inventories. Yet, it is hoped that a broader adoption of these information by forest managers throughout Europe will take place to enhance sustainable forest operations.
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| 19. |
- Wiberg, Viktor, et al.
(författare)
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Discrete element modelling of large soil deformations under heavy vehicles
- 2021
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Ingår i: Journal of terramechanics. - : Elsevier. - 0022-4898 .- 1879-1204. ; 93, s. 11-21
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the challenges of creating realistic models of soil for simulations of heavy vehicles on weak terrain. We modelled dense soils using the discrete element method with variable parameters for surface friction, normal cohesion, and rolling resistance. To find out what type of soils can be represented, we measured the internal friction and bulk cohesion of over 100 different virtual samples. To test the model, we simulated rut formation from a heavy vehicle with different loads and soil strengths. We conclude that the relevant space of dense frictional and frictional-cohesive soils can be represented and that the model is applicable for simulation of large deformations induced by heavy vehicles on weak terrain.
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| 20. |
- Wiberg, Viktor, 1988-
(författare)
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Terrain machine learning
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of heavy vehicles in rough terrain is vital in the industry but has negative implications for the climate and ecosystem. In addition, the demand for improved efficiency underscores the need to enhance these vehicles' navigation capabilities. Navigating rough terrain presents distinct challenges, including deformable soil, surface roughness, and spatial and temporal terrain variability. Focusing on forestry, this thesis aims to improve navigation using machine learning and physics simulations. Without considering the vehicle-terrain dynamics, methods for navigation can result in unsafe or unnecessarily challenging situations. Specifically, we address route planning, control for autonomous vehicles, and soilde formations. We simulate soil using the discrete element method and vehicles using multibody dynamics.To enhance route planning, we train a predictor model that uses a height map of the terrain to predict measures of traversability. The model has a directional dependency, couples geometric terrain features with vehicle design and dynamics, and allows for swift evaluations over large areas. The proposed method facilitates detailed route planning, using multiple objectives to yield efficient solutions.We address autonomy in rough terrain navigation by training a controller through deep reinforcement learning. The control policy uses a local height map for perception to plan and control a forwarder with actively articulated suspensions. The controller adapts to overcome various obstacles and demonstrates skilled driving in rough terrain.Extending beyond simulation, we address the simulation-to-reality gap of vehicles with complex hydraulic drivelines through system identification and domain randomization. The results show that having an accurate model of the actuators, modelling system delays, and preventing bang-bang control yields successful transfer. Controllers that train in simulation and transfer to reality are a step toward autonomous vehicles.While the previously mentioned studies assume rigid terrain, we also answer if the discrete element method can capture large soil deformations due to heavy traffic. The results show that the discrete element method can represent a wide variety of natural soil and that the resulting rut depths agree well with empirical models and experimental data, including multipass scenarios.
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