Measuring Biomass Using LiDAR, Lasers, and Lucky guesses

Justin Long Kevin Boston

Oregon State University College of Forestry

PresenterPresentation NotesAs a part of the Northwest Advanced Renewables Alliance, or NARA we evaluated 3 measurement methods to estimate the volume of piled logging residue with the idea of biomass utilization. One of the methods which estimates the volume of the piles based on their geometric shape, is widely used in the industry to estimate residual fuels, and smoke output. Our objective was to identify an accurate and efficient method to measure pile volume. We found that each method produces a reliable estimate of pile volume, with different degrees of confidence. As a result, the most appropriate measurement method depends on the degree of accuracy that is desired.

Northwest Advanced Renewables Alliance (NARA)

• NARA- From wood to Wing • 5 main areas of focus:

– Education – Sustainability measurement – Feedstocks – Conversion – Outreach

http://www.nararenewables.org/

PresenterPresentation NotesFirst, here is a quick overview of NARA which can be found online at nara renewables.orgFeaturing a broad alliance of private industry and educational institutions, the Northwest Advanced Renewables Alliance (NARA) takes a holistic approach to building a supply chain for aviation biofuel with the goal of increasing efficiency in everything from forestry operations to conversion processes. Using a large variety of feedstocks, from construction waste to forest residues, the project aims to create a sustainable industry to produce aviation biofuels and important co-products.

NARA is divided into 5 main areas of focus. Dr. Kevin Boston and myself are focusing on the feedstock logistics associated with the project. This project encompasses a small portion of Dr. Boston’s work which includes methods of measuring the recoverability of piled logging residue.

• Overview of Forest Biomass

• Measuring post harvest logging residue

• Evaluating the methods • Conclusions and

recommendations

Measuring Biomass Using LiDAR, Lasers, and Lucky guesses

PresenterPresentation NotesThis presentation will be divided into 4 segments. First, we will briefly provide an overview of forest biomass, methods of estimating the amount of forest biomass, and how it is defined in terms of this project.

Next, we will discuss the field measurement techniques used to estimate the volume of piled logging residue.

Following a the discussion of field measurements we will evaluate the performance of each method and conclude with recommendations for each method and examples of situations where each method may be appropriate.

Forest residues for bioenergy production

• Sources – Mill residues

• Used for a variety of alternative products.

– Logging residue • Often burned • Utilization limited by high

costs.

Photo source: www.weiku.com

Photo source: www.123rf.com

PresenterPresentation NotesOne potential source of biomass is from forest residues. These can come from one of two sources. One is logging residues generated from harvest operations. The second is mill residues generated from various manufacturing processes. Mill residues are generated from lumber, pulpwood, and plywood manufacturing. The products include bark, sawmill trimmings, pieces too small for any other solid wood use, sawdust, and veneer shavings. However, much of these mill residues are currently consumed by other manufacturing products that offer much higher returns to the mill than being sold for energy production. For example, Douglas-fir bark is sold in large quantities in the Pacific Northwest for a variety of products including soil amendments and decorative landscaping products. Coarse residues such as trimmings, slabs, and veneer clippings may be used as raw material for pulp, and a variety of engineered wood products. Planar shavings are popular for animal bedding and used widely in the commercial livestock and pet industries.

Logging residue is the material left on site following harvest. This material consists of tops, limbs, needles, stumps, and low-grade wood from breakage or defects. It is considered the lowest value material and is often burned on site to facilitate more efficient reforestation. The high cost to collect, process, and transport this material can limit its utilization as a viable fuel source. Managers hoping to use this material as fuel will need to efficiently manage the logging residue supply chain if they want to generate competitive energy rates. Thus, the first step that is needed for efficient management of the supply chain is to accurately measure the supply to plan the most efficient operations for the collection, processing, and transportation of this material.

• Allometric Models

Why measure supply?

http://oklahomasummer2010.pbworks.com/w/page/27173263/WHS%20TREES

PresenterPresentation NotesLogging residue supply can be estimated from standing volume using allometric models, or by measuring the volume of piled residue following harvest. Allometric models can estimate the volume in various components of standing trees. The sum of these individual components produces the total potential volume of biomass available. However, a portion of the potential biomass available from standing trees is utilized for higher value products, lost during collection, or left on site for erosion control and soil maintenance. As a result, the actual logging residue volume that ultimately resides in piles and is accessible for biomass collection and processing operations will need to be determined.

This study considers biomass as a by-product of harvest and compares techniques that directly measure the volume in the piles following harvest. The volume in these piles is an important component in the forest biomass supply chain to inform the choice of the logistical system used to collect, process, and transport biomass. For example, if the volume of material is large, but the current road is too narrow for the largest of chip vans, the volume in the piles is a significant element in the economic analysis to determine whether to modify the road and allow for larger trucks that have lower hauling costs. Misapplication of these logistical choices can result in unprofitable operations. Thus, reliable techniques to measure pile volumes need to be developed.

Field Measurement Techniques

• Geometric measurements

• Laser rangefinder

• LiDAR

PresenterPresentation NotesWe compared two different methods to predict piled slash volume against a control method. Since it was assumed that LiDAR was the best method to measure actual volume, and it was not a cost effective method of predicting pile volume, LiDAR was used as the control to compare the performance of the geometric and laser range-finder methods.

We measured 30 piles on recently harvested douglas-fir sites in western Oregon. The piles ranged from 29 – 1775 cubic meters in size with an average pile size of 157 cubic meters. However, in terms of biomass recoverability, these piles are very small. In fact, characteristic biomass piles often range from 500-4000 cubic meters.

Field Measurement Techniques: Geometric

Hardy 1996

PresenterPresentation NotesThe figure on the bottom left shows the types of piles that were encountered in this study. The first method we used was the geometric method. Geometric volume estimates were determined using two steps. First, each pile was visually classified as one of seven geometric shapes shown in the figure above. Then, the necessary dimensions were recorded to the nearest tenth of a foot to determine volume. In the case of irregular shaped piles the sum of the individual components was computed. Volumes were computed using the equations provided for the various shapes. For example, the pile in figure 1 was classified as a half sphere (Figure 3) and the parameters measured were height and width.

Field Measurement Techniques: Laser range-finder

Small Pile

Large Pile

PresenterPresentation NotesThe next method we used was the laser range-finder method which consists of a laser range-finder mounted on a tripod. The range-finder is equipped with an electronic compass and clinometer allowing it to take 3-dimensional coordinates of the surface of the pile. The range-finder has bluetooth capabilities allowing it to communicate with the handheld computer equipped with MapSmart software which is shown attached to the tripod.

Before data is collected, each traverse point is located and marked with an object. In this case we used traffic cones. A minimum of three traverse points must be used, however larger piles often require more to ensure adaquate overlap between each traverse point.

Field Measurement Techniques: Laser range-finder

Toe

Pile

Pile Shell

PresenterPresentation NotesData is collected by outlining the base or “Toe” of the pile from a beginning traverse point. Once the toe has been defined, the pile surface is then measured. Once a sufficient number of surface points have been collected a new traverse point is defined and the process is repeated until the entire pile has been mapped. For this project we used a minimum of 50 points per traverse station.

This method has been used to measure stockpile volumes of materials like pulp chips, coal, and gravel. However, slash piles are much more complex in shape making them more difficult to measure. For example, the overhanging branches on the pile to the right will give a misleading volume if they are measured. As a result, only the basic shell of the pile should be measured. This is where the laser range-finder method becomes more difficult as the user must determine what is the “basic shell” of the pile and what is just overhanging material. In most cases this is straightforward, however it becomes more difficult as pile shapes become more complex.

Field Measurement Techniques: Laser range-finder

PresenterPresentation NotesThe program calculates the volume of the pile by measuring the volume that is above the base, or “toe” of the pile and under the shell or surface of the pile.

The images above are 3d models of piles measured using the laser rage-finder. As you can see, none of the piles resemble a specific geometric shape. For example, the top two piles most closely resemble half spheres, but lack the convex slope. As a result the geometric method would likely overestimate the volume of these two piles.

The two piles on the bottom most closely resemble a half ellipsoid or half cylinder. Another option could be to divide the piles into two separate shapes. Consider the pile on the bottom left. Perhaps two half spheres would capture the void space in the center that a half ellipsoid would not.

Field Measurement Techniques: LiDAR

Small Pile

Large Pile

PresenterPresentation NotesThe LiDAR method consisted of a FARO Focus 3d Terrestrial Laser Scanner mounted on a tripod. The Scanner collects 3 dimensional coordinates of the pile surface at a scan rate of 700 thousand points per second. This method is similar to the laser range-finder method but instead of taking hundreds of measurements, the laser scanner takes millions.

Similar to the process used with the laser range-finder, a 3-dimensional model is created by taking measurements at multiple traverse stations to ensure adequate overlap between stations. Consecutive scans are tied together using tie points between each instrument setup which are shown as red triangles. We used a minimum of three tie points between each instrument setup which were, in this case ceramic spheres, mounted on an aluminum rod.

Field Measurement Techniques: LiDAR

PresenterPresentation NotesLiDAR volumes were calculated using a Cyclone software package. First, a Triangular Irregular Network (TIN) surface was fit to the smoothed pile surface. Overhanging logs and branches were modeled using a pipe fitting process and added to the volume of the TIN surface. These figures show the LiDAR produced models of the scanned piles. While the LiDAR data produce the most accurate volume estimates, the cost of equipment, and the technical skill required to process the data are high. As a result we assume that LiDAR is not an economically feasible method to measure biomass volume. Instead it is used as a means to compare the accuracy of the other two methods.

So a quick review of the modeling process. I would start by creating 3 separate layers. The first layer being all of the material that is not included in the pile. I would turn this layer off so I am looking at just the point cloud of the pile. Next I would create a layer of the overhanging material and turn this layer off. The result then should be a layer of the basic pile shell. I would fit a TIN surface to this layer, then add in the overhanging material which then would be modeled using the pipe fitting process.

Comparing the Models: Visually

Pile Image Geometric Model

LiDAR Model Laser Range-finder Model

39.6

39.6 22.8

35.7

PresenterPresentation NotesThe four figures show a model created for a pile using each measurement technique. While it seems apparent that the LiDAR model produces the best representation of the original pile, the takeaway message from this slide is the difference between the laser range-finder and geometric models. The geometric model is not able to capture the complex shape of the pile.

For example if you were given just the model of a pile and asked to fit that model to an image of the pile you would likely have no problem fitting the LiDAR model to the original pile. It may be more difficult to fit the laser range-finder model to the original pile, since it captures the basic shape of the pile surface, however the geometric model could fit a variety of pile since most of the piles measured fit either half-spheres or half ellipsoids.

Finally we see the predicted volume of each pile included with its model which provides a godd insight into the performance of each method.

Comparing the Models: Quantitatively .

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PresenterPresentation NotesThese two graphs show the results of a concordance correlation test. Concordance correlation has been used in the medical field to test the ability of equipment to produce the same results. The idea being that if you have two measurement methods, one being high cost, and the other being low cost you would want to use the low cost method if it was able to produce results that were as reliable as the high cost method. In this case the high cost method being the LiDAR data. The line indicates LiDAR volumes while the points on the graph represent the estimated volumes for each method. For example, a point below the line represents an estimate that was less than the “true” volume, while a point above the line represents an estimate larger than the true volume.

The graph on the left shows the concordance correlation for the geometric measurements. The geometric measurements had a correlation coefficient of 0.73 and are moderately correlated with LiDAR measurements. You can see that geometric measurements tended to under estimate the volume of smaller piles and over estimate the volume of larger piles.

The graph on the right shows the concordance correlation for the laser range-finder measurements. The laser range-finder measurements had a correlation coefficient of 0.91 and are strongly correlated with LiDAR measurements.

So the results of the concordance correlation analysis indicate that the laser rangefinder would be a suitable replacement for the more expensive LiDAR method, while geometric measurements would not be a suitable replacement.

Comparing the Models: Quantitatively Percent Accuracy

Pile Size Geo Laser Range-finder 20-40 31% 8% 40-60 30% 14% 60-80 23% 10% 80-100 21% 8% 100-1775 43% 11%

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PresenterPresentation NotesThe graph on the top right shows the accuracy of each method as a function of pile size. The geometric method is able to measure within 21 – 43% of the actual pile volume while the laser rangefinder is able to get between 8% and 14% of the actual volume. However considering the cost of measuring piles, the laser range-finder takes about 10 times as long to measure the piles which is shown in the graph below.

Geometric measurements can take about 1-5 minutes to measure each pile depending on the size and complexity of the pile. Laser range-finder measurements range from 10 – 30 minutes per pile, and LiDAR measurements are significantly higher from 180- 240 minutes. As a result if an accuracy of 30% is acceptable the geometric method may be the most appropriate method to use. But if more accurate results are desired the laser range-finder would be the best route to take. While the LiDAR provides very good information regarding pile shape, piece size distribution, and particle arrangement, the high cost of the equipment, data collection, and processing make it an unfeasible method of estimating pile volume for biomass.

Recommendation- Geometric

Method Hours

Geometric 2-10

Laser Range-finder 22-65

PresenterPresentation NotesOur first example is a 25 acre shovel unit with 130 piles. In the case of a unit with a large amount of small piles the cost of using the laser range-finder method is much higher than the geometric method. In this case the geometric method would be appropriate for two reasons. The first being the cost of using the laser range-finder method is much higher. The second is that the average pile size on this unit was less than 50 cubic meters. The geometric method performs well on piles less than 70 cubic meters.

Recommendation- Laser range-finder

Method Hours

Geometric 0.3-1.3

Laser Range-finder 2.3-8

PresenterPresentation NotesThis is a 52 acre cable unit with 16 large piles. In this case the average pile size is over 500 cubic meters which is much larger than the piles used in our analysis. In this case I would suggest that the laser range-finder method would be the appropriate method to use.

Thank you!

Metrics

• 1 cubic meter = 307 pounds • 1 cubic yard = 235 pounds • 1 load = 20 tons • 1 load = 130 cubic meters • 1 acre = 25-50 green tons • 1 acre = 1.25 – 2.5 loads

Western Oregon Olympic Peninsula

• 1 cubic meter = 461 pounds • 1 cubic yard = 348 pounds • 1 load = 20 tons • 1 load = 86 cubic meters • 1 acre = 15-60 green tons • 1 acre = 0.75 – 3 loads

Measuring Biomass Using LiDAR, Lasers, and Lucky guessesNorthwest Advanced Renewables Alliance (NARA)Slide Number 3Forest residues for bioenergy productionWhy measure supply?Field Measurement TechniquesField Measurement Techniques: GeometricField Measurement Techniques:� Laser range-finderField Measurement Techniques:� Laser range-finderField Measurement Techniques:� Laser range-finderField Measurement Techniques:� LiDARField Measurement Techniques:� LiDARComparing the Models: VisuallyComparing the Models: QuantitativelyComparing the Models: QuantitativelyRecommendation- GeometricRecommendation- Laser range-finderThank you!Metrics