Photoload Sampling Technique
The first part of my semester work started with the Photoload Sampling Technique. The technique is a way to quickly and relatively accurately estimate an area fuel loading. Or how much fuel is available for a possible wildland fire. It is often measured before and after a fuel treatment in order to identify critical areas needing immediate treatment and then as a way to quantify a treatments successes. By using examples you can estimate the fuel loading of a small 1x1 meter plot (left) base on 4 fuel categories: 1 hour fuels (>1/4 inch), 10 hour fuels (1/4>1 inch), 100 hour fuels (1>3 inches), Live woody, and herbaceous. You estimate each category one at a time using a reference sheet (bottom left) and then add each category them together to get a plots fuel loading in either kilograms per meter squared (kg/m^2) or Imperial Tons per Acre (t/acre). The 'hour' reference in fuel sizes represents the amount of time that fuel size takes on average to reach a moisture content equilibrium with the surrounding relative humidity. Multiple micro plots are taken in a stand to be averaged along with another set of 10 square meter sub plots to measure 1000 hour fuels which are downed logs of 3 inches or greater diameter. 1000 hour values are found by measuring the total length of logs in a sub plot and their quadratic mean diameter to then plug into a table that gives you a fuel loading value. The power of the photo load technique is the ability to do a plot in under 5 min with experience and it only requiring a reference sheet a tape to measure fuel sizes and some way of marking a plot.
My photoload work curtailed with a hands on use of the Photoload Technique around the U-32 woods the ultimate goal being to compare fuel ladings effects on fire behavior. I split the school grounds into 5 'plots'. Plot locations were limited due to the post-christmas ice storm salvage logging but each plot was chosen to have fuel loading whether that be a complete difference in ecological composition or understory density. The experience not only really pushed to strengthen my ability's around the photoload technique it also served as a relief for me being ably to spend a class period alone outside in the woods away from the schools confines that I had been in for going on six years. All this data was first put into a paper data sheet found with the online publication of the technique and its reference sheets and then transferred into an excel sheet with my other fire behavior data (this sheet is on my Final Project page).
Rothermel's Surface Fire Model
In order to effectively carry out my fuel loading fire behavior investigation I first had to learn about how a fire spreads. To do this I focus me work on the Rothermel's Surface Fire Spread Model. Despite being developed in 1972 it is the most comprehensive way to model a fires spread. All information is either measurable like wind speed and moisture or can be found in a set of fuel models of various stand and fuel compositions. The model is split into two parts the Heat Source or the numerator and the Heat Sink as the denominator. As fire spread is considered a quasi-rate of spread it really defines the transfer of energy in BTUs from a burning fuel source to another. The Heat sink represents how much thermal energy is required for the fire to spread basked on oven dry fuel density or the density of fuels with 0% moisture, the effective heating number witch is distribution of energy based on the surface area to volume ratio of the fuel, and the heat of preignition witch is the total heat required to ignite the fuel and to evaporate any water in the fuel.
Heat source is based on the reaction intensity which is the amount of heat released by the fire and the propigationg flux ratio witch is the propogation ratio of how much energy is directed towards nearby fuels. The ratio is reliant on wind speeds and slopes since wind and upslopes can make the flames closer to the fuels resulting in higher energy transfer.
Heat source is based on the reaction intensity which is the amount of heat released by the fire and the propigationg flux ratio witch is the propogation ratio of how much energy is directed towards nearby fuels. The ratio is reliant on wind speeds and slopes since wind and upslopes can make the flames closer to the fuels resulting in higher energy transfer.
Before I used a commuter program called BehavePlus6 to calculate fire behavior of the fue plots form my photo loading, I first did a set of hand calculations to better understand how the model worked. Since each variable has its own set of variables and equations along with significant error from rounding large decimal places, this process took about 2-4 weeks depending on inclusion of a week plus of fixing decimal errors and the time spent learning about each equation and its variables since I didn't want to blindly solve this equation. I wanted to really learn it. Since the proofs of each variables equations require calculus, I hope to look back at the Rothermel model later in the year once my calculus skills are more developed to grow my understanding even further.