The authors would like to acknowledge Benjamin Sommerkorn, Gabriel Dupont, Jake Eggan and Chirawat Sanpakit who assisted with the experiments presented here. Jeanette Cobian I&#241;iguez acknowledges support by NASA MUREP Institutional Research Opportunity (MIRO) grant number NNX15AP99A. This work was also funded by the USDA/USDI National Fire Plan through an agreement between USDA Forest Service, PSW Research Station and the University of California - Riverside.

Caution: As several steps in the following protocol involve activities that have the potential to cause injury, ensure that the proper personal protective equipment (PPE) is used following established safety protocols including fire resistant clothing and protective eyewear.
1. Crown Fuel Bed Load Cell Instrumentation Setup
<ol>
	<li>Modify 4 C-clamps by attaching dual spring gate carabiners (see Table of Materials) through the pin hole at the clamp&#39;s screw end (see Figure 2). Use the carabiners to suspend the crown fuel bed.</li>
	<li>Using a different set of C-clamps, affix each load strain gauge cell to the top portion of the wind tunnel frame (see Figure 2).</li>
	<li>Attach modified C-clamps to the free end of the strain gauge cells, with the carabiners hanging down. Attach chains to the platform for the crown fuel bed.</li>
	<li>To suspend the crown fuel bed platform from the wind tunnel frame, connect each of the crown fuel bed chains to a carabiner.</li>
	<li>Once each of the four load cells are fully mounted and connected to the fuel bed, connect their wires to the Wheatstone bridge which will be used for data acquisition. Cover the load cells with fire insulating material, such as the kind used for fire shelters.</li>
</ol>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56591/56591fig2.jpg" /> 
Figure 2: Wind tunnel crown fuel bed load cell instrumentation. (a) Wind tunnel front view (b) Modified C-clamp with carabiner and crown fuel bed chain which supports the crown fuel bed. (c) Load cell attached to the wind tunnel frame using a C-clamp. <a href="//cloudfront.jove.com/files/ftp_upload/56591/56591fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
2. Load Cell Calibration
NOTE: The signal produced by the load cells is converted to an equivalent mass through: 
<img alt="Equation 2" src="/files/ftp_upload/56591/56591eq2.jpg" /> 
where V is the signal, typically in millivolts, A and B are constants to be determined through calibration, and m represents the mass in grams. All the parameters in equation (2) are obtained through the custom instrument control interface developed for the crown mass instrumentation in this protocol. When first using the system, precision weights are used to calibrate the load cell signal. Calibration constants A and B will be obtained based on the signal produced when measuring the load of these precision weights. The constant A is calculated from: 
<img alt="Equation 3" src="/files/ftp_upload/56591/56591eq3.jpg" /> 
where mt is a the mass of trial precision weight, aw is the signal produced with the weight loaded on the load cell, whereas aw,o corresponds to the signal produced when no weight is applied on the load cell.
<ol>
	<li>To obtain the calibration constant A, hook precision weights (a good range would be 200 - 500 g) to the first load cell. Use the mass of the precision weights as parameter mt in equation (3).</li>
	<li>Set the load cell gain to 128 using the Input # field as shown in Figure 3b, i.1. This corresponds to the maximum value allowed by the device.</li>
	<li>Read the signal output at Output 0 from the instrument interface (See Figure 3b, i2). This is parameter aw in equation (3).</li>
	<li>Unhook the weight and read the new value displayed in the instrument interface ( Figure 3b, i2). This is parameter aw,o.</li>
	<li>Calculate A based on the parameters (mt, aw, aw,o) obtained in steps 2.1 to 2.4 and the equations presented.</li>
	<li>In the controller interface, fill in the Ch 0-M value for each sensor with the A value obtained in the previous step.</li>
	<li>To find the offset value, B, remove all weights, read the value in the &#39;Outputs Calibrated (g)&#39; box (See Figure 3c, i2), multiply this value by -1. The resulting number is constant B, type this number in the &#34;Addition&#34; Ch 0-A box (See Figure 3c, i.3).</li>
	<li>Repeat steps 2.3 - 2.8 for each load cell (0, 1, 2, 3), the system is now completely calibrated; proceed to load the fuel beds with the fuels.</li>
</ol>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56591/56591fig3.jpg" /> 
Figure 3: Instrument control interface data input steps for load cell calibration. (a) Bridge initial setup window with gain setup and enable box (b) Window for first stage of load cell calibration (c) Window for second stage of load cell calibration (d) Window for last stage of load cell calibration, file is saved here and data logging was started. <a href="//cloudfront.jove.com/files/ftp_upload/56591/56591fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
3. Preparation of Chaparral and Excelsior Fuel Beds
NOTE: Each experiment uses 2 kg of live chamise and 0.5 kg of excelsior (shredded aspen wood).
<ol>
	<li>From the pile of fuel collected for burning, collect several 1-pint bottles of fuel (3 - 4 bottles).
	<ol>
		<li>Follow the procedures delineated by Countryman and Dean to oven dry samples and obtain fuel moisture content30.</li>
	</ol>
	</li>
	<li>Trim individual branches from a bundle of recently harvested chamise to remove dead material and branch material greater than &#188; inch diameter. Place the remaining live fuel material in the container for weighing.</li>
	<li>Select 2 kg of the trimmed chamise and 0.5 kg of excelsior using an electronic scale. Place 0.5 kg of excelsior onto the surface fuel bed platform on the wind tunnel floor, ensuring that the bulk density is as uniform as possible. Do this by placing a known amount of excelsior over a known area depth.</li>
	<li>Pull apart (fluff) the compacted excelsior to decrease its bulk density so it will burn readily. &#160;Load 2 kg of trimmed chamise onto the platform hanging from the load cells to create the elevated fuel bed. Evenly spread the chamise branches over the entire platform to produce a uniform fuel bed.</li>
</ol>
4. Thermocouple Arrangement
NOTE: K-Type thermocouples are used to measure temperature of both fuel beds. Data is collected through a data acquisition system controlled with a custom graphical user interface (see table of materials for controller design software). The thermocouples recommended for use are 24 AWG thermocouples with a response time of 0.9 s.
<ol>
	<li>Connect an array of sixteen 24 AWG thermocouples (conductor diameter: 0.51054 mm) to a data logger (response time: 0.9 s).</li>
	<li>Insert 6 thermocouples into the crown fuel layer. Place these thermocouples 20 cm apart and avoid contact of thermocouples with branches. Insert 10 thermocouples into the surface fuel layer. Place these surface fuel thermocouples 10 cm apart and avoid contact of thermocouples with branches (See Figure 4).</li>
	<li>Activate data logging by clicking the &#34;Start&#34; button in the thermocouple control software interface.</li>
</ol>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56591/56591fig4.jpg" /> 
Figure 4: Diagram of surface and crown fuel beds with thermocouple array location. Here 6 thermocouples were inserted into the crown fuel layer 20 cm apart from each other. 10 thermocouples were inserted into the surface fuel layer 10 cm apart. <a href="//cloudfront.jove.com/files/ftp_upload/56591/56591fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
5. Image Acquisition Setup
<ol>
	<li>Mount the visual reference target that has red marks at 10-cm-intervals above the wind tunnel window. Use this target as a reference to determine flame height from the experiment video. 
	NOTE: Sample flame heights are presented in Figure 5.</li>
	<li>Setup photographic data collection. Focusing on the wind tunnel test area, adjust the camera focus so as to capture the entire vertical reference target as well as the fuel bed area.</li>
	<li>Setup video camera data collection. Mount the video camera with a universal camera wall mount on the wall to provide a full view of the wind tunnel test section.</li>
</ol>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56591/56591fig5.jpg" /> 
Figure 5: Photograph of sample flame heights from a typical experiment. The blue visual target with red marking serves as a reference to determine flame height from the experiment video. <a href="//cloudfront.jove.com/files/ftp_upload/56591/56591fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
6. Flow Setup
NOTE: The wind tunnel is equipped with a variable speed fan. The air flow in the wind tunnel has been previously calibrated to the fan speed. To achieve the desired wind velocity, the fan rotational speed (in Hz) is selected. In the present experiments, no wind and 1 m/s wind flow cases were studied.
<ol>
	<li>Set the fan speed to 1 m/s on the speed controller. Turn on the fan to ensure that it is functioning properly.</li>
	<li>Turn off the fan. It is now ready for use. 
	NOTE: The burn building is designed to conduct fire experiments safely while evacuating smoke from the working space. Notify local fire authorities that experiments are being conducted to eliminate the occurrence of false alarms.</li>
	<li>Close all doors in the building to ensure that the roof vents are the only possible exit for smoke evacuation.</li>
	<li>Turn on the air supply fans to bring in fresh air from outside the building at floor level. Turn on the exhaust fans to evacuate smoke through the roof vents. 
	NOTE: This will establish a low velocity, high volume air flow from outside the building that rises vertically due to the slight pressure difference and the roof openings.</li>
	<li>Prior to each experiment, use a wet-bulb hygrometer to measure the relative humidity and temperature of the ambient air.</li>
</ol>
7. Ignition (Implement Simultaneously with Step 8)
NOTE: The ignition process should be conducted as follows by the ignition crew member. For increased safety, it is recommended that a second crew member remain near the test area during ignition.
<ol>
	<li>When instructed to &#39;ignite&#39;, soak the leading edge of the excelsior surface fuel bed with denatured ethyl alcohol. Place the alcohol bottle away from the ignition zone and using a butane torch, ignite the end of the surface fuel bed in a line parallel to leading edge of the fuel bed. Be observant as the alcohol-soaked fuel will readily ignite.</li>
	<li>Once the fuel bed has been ignited, step out of the test section and close the tunnel door. If wind is required for the experiment, turn on the wind tunnel fan.</li>
</ol>
8. Initiate Experimental Run
NOTE: Upon verifying the experiment is correctly setup, the cameras should be started.
<ol>
	<li>Turn on the video camera to record.</li>
	<li>Speak aloud the experiment number/code, the date, and experimental configuration so the microphone on the video camera records this information.</li>
	<li>Instruct the computer crew to begin data logging by ticking the &#34;Enable data logging&#34; option in the instrument control interface (see Figure 3d, i.1). Instruct the ignition person to ignite the fuel. Once the ignition crew member exits the wind tunnel, instruct the wind crew member to start the wind tunnel fan. This will be the start of the experiment where time is zero (t = 0).</li>
</ol>

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The authors have nothing to disclose.

The ability to measure the elevated fuel mass throughout the experiment was one of the main advantages of the technique presented here. Previous studies addressing chaparral fire have focused on either only crown fire initiation or only on surface spread, but not both. Such studies have quantified the possibility of ignition in the crown layer and have left study of spread for future work23. Our methodology allows for measurement of mass loss, temperature distribution, and flame geometry for both ...

In 2016, the state of California experienced a total of 6,986 wildland fires, consuming 564,835 acres1, costing millions of dollars in damage, and risking the wellness of hundreds of people. Because of the regional Mediterranean climate, a major fuel source for these fires are chaparral vegetation communities2. Fire spread in chaparral can be considered a crown fire since the main fuel that burns is elevated3. Co-existing with the predominantly live crown layer, is the dead surface fuel layer, which consists of cast foliage, branches, and herbaceous plants which grow under and between the individual shrubs. Fire will more easily initiate in the dead surface fuel layer. Once the surface fire ignites, the fire may transition to the crown layer where the energy released by the fire increases dramatically. While chaparral fires have typically been modelled as a fire spreading in deep surface fuels4, there has been limited study of chaparral fires as crown fires.

Crown characteristics in chaparral, including foliage particle shape, differ from boreal coniferous forest, where most of the research has occurred. Numerous laboratory and field scale studies have investigated various aspects of wildfire dynamics6,5,7,3,8,9,10,11,12. Within the realm of laboratory experiments, several studies have examined the influence of parameters such as wind and fuel properties on chaparral crown fire behavior. Lozano7 examined characteristics of crown fire initiation in the presence of two discrete crown fuel beds. In Tachajapong et al.3, discrete surface and crown layers were burned inside a wind tunnel and the surface fire was characterized. Only crown fire initiation was fully described leaving full analysis of spread for future work. Li et al.11 reported on the propagation of a flame though single chaparral shrubs. In related work, Cruz et al.10,9 developed a model to predict the ignition of coniferous foliage above a spreading surface fire. Burn characteristics of chaparral fuels have been explored in experimental studies of bulk fuels and individual leaves13,14,15,16. Dupuy et al.13 studied the burning characteristics of Pinus pinaster needles and excelsior by burning the fuels in cylindrical baskets. They observed that in these fuels, flame height was related to heat release rate via a two-fifths power law as has been reported previously in the literature17,18. Sun et al.14 burned chaparral fuels in similar cylindrical baskets to analyze the burning characteristics of three chaparral fuels: chamise (Adenostoma fasciculatum), ceanothus (Ceanothus crassifolius), and manzanita (Arctostaphylos glandulosa).
Motivated by results from the aforementioned laboratory studies, our purpose here is to present a methodology to characterize spread in both surface and shrub crown layers. Furthermore, we aim to clarify some of the key characteristics that dictate the degree of surface-crown layer interaction. To this purpose, we developed an experimental laboratory methodology to study the vertical transition of a fire burning in a wildland surface fuel to a fire spreading in an elevated shrub fuel. In these types of fires, translation of the fire to the shrub crown, known as crowning, may be followed by sustained spread under the right conditions. In general, chaparral fire behavior is dictated by topography, weather, and fuel19. It has been shown that wind affects energy release rate in the fuels5,3,8,20.
Fire spread in porous fuels can be viewed as a series of transitions or thresholds that must be crossed to be successful21. Energetically, a fuel particle ignites if the amount of heat that it receives results in a mixture of gases that successfully react with oxygen. The resulting flame spreads if the heat from the burning particle ignites an adjacent fuel particle. The fire spreads across the ground if it is able to cross gaps between combustible fuel elements. If the flame of a surface fire is able to propagate vertically into the crown of shrubs and trees, a significant change in fire behavior, including increased heat release rates, is often observed due to a greater availability of fuel. Thermal energy dynamics in wildland fires encompass several scales, from the very large scale, such in mega-fires which often require climatological modeling, to the small scale requiring chemical scale kinetic modeling. Here, we deal with laboratory wind tunnel scale behavior modeling; for chemical scale cellulose combustion studies, the reader is referred to works such as Sullivan et al.22
Since 2001, we have conducted a variety of experiments examining some of the laboratory scale energy thresholds23,8,24,25,26,27, with an emphasis on live fuels associated with chaparral. While outdoors measurements of fire may provide more lifelike results, the controlled environment of the wind tunnel allow for delineation of the impact of various parameters. Controlling wind, for example, is especially important for chaparral crown fires occurring in regions such as Southern California where foehn type winds, known as Santa Ana winds, are typical drivers of fire events. Because a major motivator for the methodology described here is to study the effect of wind and other controlled parameters on chaparral fire spread, this study was performed in a laboratory scale wind tunnel. The reader is directed to the work by Silvani et al.28 for field measurements of temperature in chaparral fires similar to the ones presented here. For field measurements on the effect of wind on fire spread, please see Morandi et al.29
Several parameters influencing the spread in chaparral fuels have been experimentally analyzed by quantifying the probability of fire spread success in elevated fuel beds8. The current experimental study involves a methodology developed to study chaparral crown fire spread by modeling surface fuels and crown fuels inside the test section of a low speed wind tunnel. The surface fuel is modeled with excelsior (dried shredded wood). The surface fuel bed is placed on the ground level of the wind tunnel over a standard scale (see Figure 1). Representing the crown fuel bed, a fuel bed with chamise was placed over the surface fuel bed by suspending the fuel from a platform mounted on the wind tunnel frame (see Figure 1). Both fuel beds are instrumented for temperature and mass loss measurements; flame geometry is obtained from video recordings of experiments. Parameters measured include mass loss rate, fuel moisture content and the relative humidity of the air. Parameters controlled were wind presence, distance between surface fuel bed and crown fuel bed, and the presence of surface fuel. The measured mass loss rate can be used to calculate the heat release rate, which is defined as: 
<img alt="Equation 1" src="/files/ftp_upload/56591/56591eq1.jpg" /> 
where h is the heat of fuel combustion, m is the fuel mass, and t is time.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56591/56591fig1.jpg" /> 
Figure 1: Wind tunnel experimental setup. Locations of the crown fuel bed, the surface fuel bed, and the tunnel fan have been labeled for convenience. The surface fuel bed is placed on the ground level of the wind tunnel over a standard scale. Representing the crown fuel bed, a fuel bed with chamise was placed over the surface fuel bed by suspending the fuel from a platform mounted on the wind tunnel frame. <a href="//cloudflare.jove.com/files/ftp_upload/56591/56591fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Experiments have focused on understanding the behavior of chaparral crown fires, particularly ignition, mechanisms of flame propagation and spread, flame front velocities, and fuel consumption rates.To study the interaction between a surface fire and a crown fire, six configurations of surface and crown fuel beds with and without applied wind flow, have been burned in the wind tunnel: crown fuel only with and without wind (2), crown and surface fuel beds separated by two distances with and without wind (4). Table 1 summarizes the experimental configurations with the 6 experimental classes. In the table, the surface fuel bed parameter denotes whether surface fuel was present during the experiment, the wind parameter refers to the presence of wind and crown height refers to the distance between the bottom of the crown fuel bed and the bottom of the surface fuel bed. Fuel moisture was measured for each experiment but not controlled, average fuel moisture content was 48%, whereas the minimum and maximum values were 18% to 68%, respectively.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Class</td>
			<td>Surface Fuel Bed</td>
			<td>Wind</td>
			<td>Crown Height</td>
		</tr>
		<tr>
			<td>A</td>
			<td>Absent</td>
			<td>No wind</td>
			<td>60 or 70 cm</td>
		</tr>
		<tr>
			<td>B</td>
			<td>Absent</td>
			<td>1 ms-1</td>
			<td>60 or 70 cm</td>
		</tr>
		<tr>
			<td>C</td>
			<td>Present</td>
			<td>No wind</td>
			<td>60 cm</td>
		</tr>
		<tr>
			<td>D</td>
			<td>Present</td>
			<td>No wind</td>
			<td>70 cm</td>
		</tr>
		<tr>
			<td>E</td>
			<td>Present</td>
			<td>1 ms-1</td>
			<td>60 cm</td>
		</tr>
		<tr>
			<td>F</td>
			<td>Present</td>
			<td>1 ms-1</td>
			<td>70 cm</td>
		</tr>
	</tbody>
</table>
Table 1: Experiment configurations. Here the surface fuel bed parameter denotes whether surface fuel was present during the experiment, the wind parameter refers to the presence of wind and crown height refers to the distance between the bottom of the crown fuel bed and the bottom of the surface fuel bed.
An electronic scale measured surface fuel mass and we developed a custom mass loss system for the crown layer. The system consisted of individual load cells connected to each corner of the suspended fuel bed. Consumer-grade video cameras recorded the visual flames; image processing of the visual data using a custom script generated flame characteristics including height and angle. A program was developed to convert video frames from RGB (red/green/blue) coding to black and white through a process of light intensity thresholding. The edge of the flame was obtained from the black and white video frames. Maximum flame height was defined as the highest point of the flame edge, instantaneous flame heights were also obtained. In an image, flame height was measured from the base of the fuel bed to the maximum vertical point of the flame. All processing codes as well as the instrument control interface designed for this protocol have been made available by the authors here through their software access site. Harvesting the live fuel locally and conducting the experimental burns within 24 h minimized moisture loss. A thermocouple array recorded fuel bed temperature in the wind stream-wise direction enabling the calculation of spread rate. Figure 1 shows a diagram of the fuel bed setup along with the thermocouple arrangement. Details of the experimental protocol follow.

<table>
	<tbody>
		<tr>
			<td>Wind Tunnel Instrumentation</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>cDAQ-9178 CompactDAQ Chassis</td>
			<td>National Instruments</td>
			<td>781156-01</td>
			<td></td>
		</tr>
		<tr>
			<td>NI-9213 C Series Temperature Input Module</td>
			<td>National Instruments</td>
			<td>785185-01</td>
			<td></td>
		</tr>
		<tr>
			<td>NI SignalExpress for Windows</td>
			<td>National Instruments</td>
			<td>779037-35&#160;</td>
			<td>Newest version, older version used for experiment</td>
		</tr>
		<tr>
			<td>High Temperature Nextel Insulated Thermocouple Elements</td>
			<td>Omega</td>
			<td>XC-24-K-18</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermocouple Extension Wire with Polyvinyl Coated Wire and Tinned Copper Overbraid</td>
			<td>Omega</td>
			<td>EXPP-K-24S-TCB-P</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultra High Temperature Miniature Connectors</td>
			<td>Omega</td>
			<td>SHX-K-M</td>
			<td></td>
		</tr>
		<tr>
			<td>CompuTrac MAX 2000XL&#160;</td>
			<td>Arizona Instruments</td>
			<td>MAX-2000XL</td>
			<td>Discontinued, Newer Model Out</td>
		</tr>
		<tr>
			<td>Kestrel 3000 Pocket Weather Meter</td>
			<td>Nielsen-Kellerman</td>
			<td>0830</td>
			<td></td>
		</tr>
		<tr>
			<td>Satorius CPA 34001S&#160;</td>
			<td>Sartorius</td>
			<td>25850314</td>
			<td>Discontinued Model</td>
		</tr>
		<tr>
			<td>5 Kg Micro Load Cell (X4)</td>
			<td>Robotshop.com</td>
			<td>RB-Phi-118</td>
			<td>Strain Gauge Load Cell</td>
		</tr>
		<tr>
			<td>Phidget PhidgetBridge Wheatstone Bridge Sensor Interface</td>
			<td>Robotshop.com</td>
			<td>RB-Phi-107</td>
			<td>Interfaces with 4 load cells, performs signal amplification</td>
		</tr>
		<tr>
			<td>#2 Stainless S-Biner (X4)</td>
			<td>Home Depot</td>
			<td>SB2-03-11</td>
			<td>Dual spring gate carabiners used to mount load cells</td>
		</tr>
		<tr>
			<td>2 in. Malleable Iron C-Clamp</td>
			<td>Home Depot</td>
			<td># 4011</td>
			<td>Used to mount load cells</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Personal Protective Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Wildland Firefighter Nomex Shirt</td>
			<td>GSA Advantage</td>
			<td>SH35-5648</td>
			<td></td>
		</tr>
		<tr>
			<td>Fireline 6 oz Wildland Fire Pants</td>
			<td>GSA Advantage</td>
			<td>139702MR SEV16</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Fuels</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Chamise</td>
			<td>Collected in situ</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Natural Shredded Wood Excelsior &#8211; Natural Coarse 50 lbs bail</td>
			<td>Paper Mart</td>
			<td>21-711-88</td>
			<td></td>
		</tr>
		<tr>
			<td>Bernzomatic UL100 Basic Propane Torch Kit</td>
			<td>Home Depot</td>
			<td>UL100KC</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropyl alcohol</td>
			<td>Convenience store</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Video and Photography</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Nikon D3000 10.2-MP DSLR camera with DX-format sensor and 3x 18x55mm Zoon-NIKKOR VR Image Stabilization Lens</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sony Handycam Camcorder DCR-SX85</td>
			<td>Amazon.com</td>
			<td>DCR-SX85</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Software</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NI LabView</td>
			<td>National Instruments</td>
			<td>Student Version</td>
			<td>Used for instrument control and interfacing</td>
		</tr>
		<tr>
			<td>MATLAB Student Version (MATLAB_R2014a)</td>
			<td>Mathworks</td>
			<td>Student Version&#160;</td>
			<td>Used for data post-processing including image processing</td>
		</tr>
	</tbody>
</table>

wind tunnel experiments to study chaparral crown fires

The present protocol presents a laboratory technique designed to study chaparral crown fire ignition and spread. Experiments were conducted in a low velocity fire wind tunnel where two distinct layers of fuel were constructed to represent surface and crown fuels in chaparral. Chamise, a common chaparral shrub, comprised the live crown layer. The dead fuel surface layer was constructed with excelsior (shredded wood). We developed a methodology to measure mass loss, temperature, and flame height for both fuel layers. Thermocouples placed in each layer estimated temperature. A video camera captured the visible flame. Post-processing of digital imagery yielded flame characteristics including height and flame tilt. A custom crown mass loss instrument developed in-house measured the evolution of the mass of the crown layer during the burn. Mass loss and temperature trends obtained using the technique matched theory and other empirical studies. In this study, we present detailed experimental procedures and information about the instrumentation used. The representative results for the fuel mass loss rate and temperature filed within the fuel bed are also included and discussed.

Crown and surface flame height data were obtained from the video data. Typical flame height trends for experiments is presented in Figure 6. Flame height behavior followed that found in Sun et al.14
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/56591/56591fig6.jpg" /> 
Figure 6: Estimated crown flame height. Here U = 1 m/s,...

Watch this Scientific Journal Video about Wind Tunnel Experiments to Study Chaparral Crown Fires at JoVE.com

Wind Tunnel Experiments to Study Chaparral Crown Fires

This protocol describes wind tunnel experiments designed to study the transition of a fire from the ground to the canopy of chaparral shrubs.

The present protocol presents a laboratory technique designed to study chaparral crown fire ignition and spread. Experiments were conducted in a low ...

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9.6K Views.  University of California, Riverside. This protocol describes wind tunnel experiments designed to study the transition of a fire from the ground to the canopy of chaparral shrubs.

Video: Wind Tunnel Experiments to Study Chaparral Crown Fires

Characterization of Surface Modifications by White Light Interferometry: Applications in Ion Sputtering, Laser Ablation, and Tribology Experiments

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. From the measured surface, 3D topographic maps can be subsequently analyzed using a variety of software packages to extract the information that is needed.
In this article we describe how white light interferometry, and optical profilometry (OP) in general, combined with generic surface analysis software, can be used for materials science and engineering tasks. In this article, a number of applications of white light interferometry for investigation of surface modifications in mass spectrometry, and wear phenomena in tribology and lubrication are demonstrated. We characterize the products of the interaction of semiconductors and metals with energetic ions (sputtering), and laser irradiation (ablation), as well as ex situ measurements of wear of tribological test specimens.
Specifically, we will discuss:
<ol class="lroman">
	<li>Aspects of traditional ion sputtering-based mass spectrometry such as sputtering rates/yields measurements on Si and Cu and subsequent time-to-depth conversion.</li>
	<li>Results of quantitative characterization of the interaction of femtosecond laser irradiation with a semiconductor surface. These results are important for applications such as ablation mass spectrometry, where the quantities of evaporated material can be studied and controlled via pulse duration and energy per pulse. Thus, by determining the crater geometry one can define depth and lateral resolution versus experimental setup conditions.</li>
	<li>Measurements of surface roughness parameters in two dimensions, and quantitative measurements of the surface wear that occur as a result of friction and wear tests.</li>
</ol>
Some inherent drawbacks, possible artifacts, and uncertainty assessments of the white light interferometry approach will be discussed and explained.

White light microscope interferometry is an optical, noncontact and quick method for measuring the topography of surfaces. It is shown how the method can be applied toward mechanical wear analysis, where wear scars on tribological test samples are analyzed; and in materials science to determine ion beam sputtering or laser ablation volumes and depths.

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. ...

Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for detailed observation, scenarios that make it challenging to observe with conventional imaging systems. One of these is the drop impact of liquids, which usually happens within one tenth of millisecond. To tackle this challenge, a fast imaging technique is introduced that combines a high-speed camera (capable of up to one million frames per second) with a macro lens with long working distance to bring the spatial resolution of the image down to 10 &#181;m/pixel. The imaging technique enables precise measurement of relevant fluid dynamic quantities, such as the flow field, the spreading distance and the splashing speed, from analysis of the recorded video. To demonstrate the capabilities of this visualization system, the impact dynamics when droplets of non-Newtonian fluids impinge on a flat hard surface are characterized. Two situations are considered: for oxidized liquid metal droplets we focus on the spreading behavior, and for densely packed suspensions we determine the onset of splashing. More generally, the combination of high temporal and spatial imaging resolution introduced here offers advantages for studying fast dynamics across a wide range of microscale phenomena.

Drop impact of non-Newtonian fluids is a complex process since different physical parameters influence the dynamics over a very short time (less than one tenth of a millisecond). A fast imaging technique is introduced in order to characterize the impact behaviors of different non-Newtonian fluids.

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for ...

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics Beamline of the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory1-4. This video demonstrates how the complex chemical structures of laboratory-based model flames are analyzed using flame-sampling mass spectrometry with tunable synchrotron-generated vacuum-ultraviolet (VUV) radiation. This experimental approach combines isomer-resolving capabilities with high sensitivity and a large dynamic range5,6. The first part of the video describes experiments involving burner-stabilized, reduced-pressure (20-80 mbar) laminar premixed flames. A small hydrocarbon fuel was used for the selected flame to demonstrate the general experimental approach. It is shown how species&#8217; profiles are acquired as a function of distance from the burner surface and how the tunability of the VUV photon energy is used advantageously to identify many combustion intermediates based on their ionization energies. For example, this technique has been used to study gas-phase aspects of the soot-formation processes, and the video shows how the resonance-stabilized radicals, such as C3H3, C3H5, and i-C4H5, are identified as important intermediates7. The work has been focused on soot formation processes, and, from the chemical point of view, this process is very intriguing because chemical structures containing millions of carbon atoms are assembled from a fuel molecule possessing only a few carbon atoms in just milliseconds. The second part of the video highlights a new experiment, in which an opposed-flow diffusion flame and synchrotron-based aerosol mass spectrometry are used to study the chemical composition of the combustion-generated soot particles4. The experimental results indicate that the widely accepted H-abstraction-C2H2-addition (HACA) mechanism is not the sole molecular growth process responsible for the formation of the observed large polycyclic aromatic hydrocarbons (PAHs).

Gas sampling from laboratory-scale flames with online analysis of all species by mass spectrometry is a powerful method to investigate the complex mixture of chemical compounds occurring during combustion processes. Coupled with tunable soft ionization via synchrotron-generated vacuum-ultraviolet radiation, this technique provides isomer-resolved information and potentially fragment-free mass spectra.

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics ...

Using Microwave and Macroscopic Samples of Dielectric Solids to Study the Photonic Properties of Disordered Photonic Bandgap Materials

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). In this article we will describe the methods for constructing and characterizing macroscopic disordered photonic structures using microwaves. The microwave regime offers the most convenient experimental sample size to build and test PBG media. Easily manipulated dielectric lattice components extend flexibility in building various 2D structures on top of pre-printed plastic templates. Once built, the structures could be quickly modified with point and line defects to make freeform waveguides and filters. Testing is done using a widely available Vector Network Analyzer and pairs of microwave horn antennas. Due to the scale invariance property of electromagnetic fields, the results we obtained in the microwave region can be directly applied to infrared and optical regions. Our approach is simple but delivers exciting new insight into the nature of light and disordered matter interaction.

Our representative results include the first experimental demonstration of the existence of a complete and isotropic PBG in a two-dimensional (2D) hyperuniform disordered dielectric structure. Additionally we demonstrate experimentally the ability of this novel photonic structure to guide electromagnetic waves (EM) through freeform waveguides of arbitrary shape.

Disordered structures offer new mechanisms for forming photonic bandgaps and unprecedented freedom in functional-defect designs. To circumvent the computational challenges of disordered systems, we construct modular macroscopic samples of the new class of PBG materials and use microwaves to characterize their scale-invariant photonic properties, in an easy and inexpensive manner.

Recently, disordered photonic materials have been suggested as an alternative to periodic crystals for the formation of a complete photonic bandgap (PBG). ...

Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at a frequency above the acoustic range (20 kHz). As a solid-state technology, ultrasonic lubrication can be used where conventional lubricants are unfeasible or undesirable. Further, ultrasonic lubrication allows for electrical modulation of the effective friction coefficient between two sliding surfaces. This property enables adaptive systems that modify their frictional state and associated dynamic response as the operating conditions change. Surface wear can also be reduced through ultrasonic lubrication. We developed a protocol to investigate the dependence of friction force reduction and wear reduction on the linear sliding velocity between ultrasonically lubricated surfaces. A pin-on-disc tribometer was built which differs from commercial units in that a piezoelectric stack is used to vibrate the pin at 22 kHz normal to the rotating disc surface. Friction and wear metrics including effective friction force, volume loss, and surface roughness are measured without and with ultrasonic vibrations at a constant pressure of 1 to 4 MPa and three different sliding velocities: 20.3, 40.6, and 87 mm/sec. An optical profilometer is utilized to characterize the wear surfaces. The effective friction force is reduced by 62% at 20.3 mm/sec. Consistently with existing theories for ultrasonic lubrication, the percent reduction in friction force diminishes with increasing speed, down to 29% friction force reduction at 87 mm/sec. Wear reduction remains essentially constant (49%) at the three speeds considered.

We present a protocol for using a piezoelectrically-assisted tribometer and optical profilometer to investigate the dependence of ultrasonic wear and friction reduction on linear velocity, contact pressure, and surface properties.

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at ...

Visualizing Hyporheic Flow Through Bedforms Using Dye Experiments and Simulation

Advective exchange between the pore space of sediments and the overlying water column, called hyporheic exchange in fluvial environments, drives solute transport in rivers and many important biogeochemical processes. To improve understanding of these processes through visual demonstration, we created a hyporheic flow simulation in the multi-agent computer modeling platform NetLogo. The simulation shows virtual tracer flowing through a streambed covered with two-dimensional bedforms. Sediment, flow, and bedform characteristics are used as input variables for the model. We illustrate how these simulations match experimental observations from laboratory flume experiments based on measured input parameters. Dye is injected into the flume sediments to visualize the porewater flow. For comparison virtual tracer particles are placed at the same locations in the simulation. This coupled simulation and lab experiment has been used successfully in undergraduate and graduate laboratories to directly visualize river-porewater interactions and show how physically-based flow simulations can reproduce environmental phenomena. Students took photographs of the bed through the transparent flume walls and compared them to shapes of the dye at the same times in the simulation. This resulted in very similar trends, which allowed the students to better understand both the flow patterns and the mathematical model. The simulations also allow the user to quickly visualize the impact of each input parameter by running multiple simulations. This process can also be used in research applications to illustrate basic processes, relate interfacial fluxes and porewater transport, and support quantitative process-based modeling.

This manuscript describes how to create regular bedforms in a flume, visualize flow through the bedforms, and use computer simulations to simulate the hyporheic flow. The computer simulations compare well with the experimental observations. This coupled simulation and experiment is well-suited for both research and educational purposes.

Advective exchange between the pore space of sediments and the overlying water column, called hyporheic exchange in fluvial environments, drives solute ...

A Robotic Platform to Study the Foreflipper of the California Sea Lion

The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most of their thrust with their large foreflippers. This protocol describes a robotic platform designed to study the hydrodynamic performance of the swimming California sea lion (Zalophus californianus). The robot is a model of the animal&#39;s foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the &#39;clap&#39;). The kinematics of the sea lion&#39;s propulsive stroke are extracted from video data of unmarked, non-research sea lions at the Smithsonian Zoological Park (SNZ). Those data form the basis of the actuation motion of the robotic flipper presented here. The geometry of the robotic flipper is based a on high-resolution laser scan of a foreflipper of an adult female sea lion, scaled to about 60% of the full-scale flipper. The articulated model has three joints, mimicking the elbow, wrist and knuckle joint of the sea lion foreflipper. The robotic platform matches dynamics properties&#8212;Reynolds number and tip speed&#8212;of the animal when accelerating from rest. The robotic flipper can be used to determine the performance (forces and torques) and resulting flowfields.

A robotic platform is described that will be used to study the hydrodynamic performance&#8212;forces and flowfields&#8212;of the swimming California sea lion. The robot is a model of the animal&#39;s foreflipper that is actuated by motors to replicate the motion of its propulsive stroke (the &#39;clap&#39;).

The California sea lion (Zalophus californianus), is an agile and powerful swimmer. Unlike many successful swimmers (dolphins, tuna), they generate most ...

Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing

This manuscript describes an experimental procedure that allows obtaining diverse quantitative information on temporal and spatial evolution of water waves excited by time-dependent and steady wind forcing. Capacitance-type wave gauge and Laser Slope Gauge (LSG) are used to measure instantaneous water surface elevation and two components of the instantaneous surface slope at a number of locations along the test section of a wind-wave facility. The computer-controlled blower provides airflow over the water in the tank whose rate can vary in time. In the present experiments, the wind speed in the test section initially increases quickly from rest to the set value. It is then kept constant for the prescribed duration; finally, the airflow is shut down. At the beginning of each experimental run, the water surface is calm and there is no wind. Operation of the blower is initiated simultaneously with the acquisition of data provided by all sensors by a computer; data acquisition continues until the waves in the tank fully decay. Multiple independent runs performed under identical forcing conditions allow determining statistically reliable ensemble-averaged characteristic parameters that quantitatively describe wind-waves&#39; variation in time for the initial development stage as a function of fetch. The procedure also allows characterizing the spatial evolution of the wave field under steady wind forcing, as well as decay of waves in time, once the wind is shut down, as a function of fetch.

This manuscript describes a fully computer-controlled procedure that allows obtaining reliable statistical parameters from experiments of water waves excited by steady and unsteady wind forcing in a small-scale facility.

This manuscript describes an experimental procedure that allows obtaining diverse quantitative information on temporal and spatial evolution of water ...

Conducting Elevated Temperature Normal and Combined Pressure-Shear Plate Impact Experiments Via a Breech-end Sabot Heater System

A novel approach for conducting normal and/or combined pressure-shear plate impact experiments at test temperatures up to 1000 &#176;C is presented. The method enables elevated temperature plate-impact experiments aimed towards probing dynamic behavior of materials under thermomechanical extremes, while mitigating several special experimental challenges faced while performing similar experiments using the conventional plate impact approach. Custom adaptations are made to the breech-end of a single-stage gas-gun at Case Western Reserve University; these adaptations include a precision-machined extension piece made from SAE 4340 steel, which is strategically designed to mate the existing gun-barrel while providing a high tolerance match to the bore and keyway. The extension piece contains a vertical cylindrical heater-well, which houses a heater assembly. A resistive coil heater-head, capable of reaching temperatures of up 1200 &#176;C, is attached to a vertical stem with axial/rotational degrees of freedoms; this enables thin metal specimens held at the front-end of a heat-resistant sabot to be heated uniformly across the diameter to the desired test temperatures. By heating the flyer plate (in this case, the sample) at the breech-end of the gun-barrel instead of at the target-end, several critical experimental challenges can be averted. These include: 1) severe changes in the alignment of the target plate during heating due to the thermal expansion of the several constituents of the target holder assembly; 2) challenges that arise due to the diagnostics elements, (i.e., polymer holographic gratings, and optical probes) being too close to the heated target assembly; 3) challenges that arise for target plates with an optical window, where crucial tolerances between the sample, bond layer, and window become increasingly difficult to maintain at high temperatures; 4) in the case of combined compression-shear plate impact experiments, the need for high-temperature resistant diffraction gratings for the measurement of transverse particle velocity at the free surface of the target; and 5) limitations imposed on the impact velocity necessary for unambiguous interpretation of the measured free surface velocity versus time profile due to thermal softening and possibly yielding of the bounding target plates.By utilizing the adaptations mentioned above, we present results from a series of reverse geometry normal plate impact experiments on commercial purity aluminum at a range of sample temperatures. These experiments show decreasing particle velocities in the impacted state, which are indicative of material softening (decrease in post-yield flow stress) with increasing sample temperatures.

Here, we present a detailed protocol of a new approach for conducting elevated temperature reverse normal plate impact, and combined pressure-and-shear plate impact. The approach involves the use of a breech-end resistive coil heater to heat a sample held at the front-end of a heat-resistant sabot to the desired temperature.

A novel approach for conducting normal and/or combined pressure-shear plate impact experiments at test temperatures up to 1000 &#176;C is presented. The ...

Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous studies on flowing liquid films have neglected the contributions of spatial structures of waves to the impact outcome, while this has recently been shown to have a significant influence on the drop impact dynamics. In this report, we outline a step-by-step procedure to investigate the effect of periodic inlet forcing of a flowing liquid film leading to the production of spatiotemporally regular wave structures on drop impact dynamics. A function generator in connection with a solenoid valve is used to excite these spatiotemporally regular wave structures on the film surface while the impact dynamics of uniform-sized droplets are captured using a high-speed camera. Three distinct regions are then studied; viz. the capillary wave region preceding the large wave peak, the flat film region, and the wave hump region. The effects of important dimensionless quantities such as film Reynolds, drop Weber and Ohnesorge numbers parameterized by the film flow rate, drop speed, and drop size are also examined. Our results show interesting, hitherto undiscovered dynamics brought about by this application of film inlet forcing of the flowing film for both low and high inertia drops.

A protocol to study the contributions of waves to droplet impact dynamics on flowing liquid films is presented.

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous ...