Issue link: https://read.dmtmag.com/i/43993
Figure 2. Major steps and considerations are described for modeling wildfire ground-attack travel time. The three types of impedance are combined such that the minimum friction/cost value is assigned to each location. A null value is assigned to locations with absolute barriers. This composited friction (a "discrete cost surface") is used to calculate the effective distance for every location to the closest dispatch station. The procedure moves out from each station in time-step waves (like a stone tossed into a pond) that consider the relative impedance as they propagate to gener- ate an accumulated cost surface (TTime in minutes), identifying the minimum travel time from the closest initial dispatch location to every location in a project area (see "Author's Notes"). Best Attack The three separate travel-time surfaces can be com- pared to identify the attack mode with the minimum response time (see Figure 3) and the differential times for alternative attack modes. In operational situations, this information could be accessed for a fire's location and used in dispatch and tactical planning. In the "Rappel Country" project, the information is used to strategically arrange helibase locations with rappel initial-attack capabilities. Tabular summaries for travel time from existing helibases by terrain and land-cover conditions were generated. In addition, rearrangement of helibase location and capabilities could be simulated and evaluated. From a GIS perspective, the project represents a noteworthy endeavor involving advanced grid-based map-analysis procedures across a large geographic expanse from the Rocky Mountains to the Pacific Ocean that was completed in less than four months by a small team of domain experts and GIS special- ists. The prototype analysis originally developed was interactively refined, modified and enhanced by the team and then applied over the expansive area. As with most projects, database development and model specification/parameterization formed the largest hurdles—the grid-based map-analysis component proved to be a "piece of cake" compared to nailing down the requirements and slogging around in millions upon millions of geo-registered 30-meter cells … whew! Author's Notes: For more information on Fire Program Solu- tions LLC and its wildfire projects, contact Don Carlton at DCARLTON1@aol.com; for an in-depth discussion of travel-time calculation, see the online book, Beyond Modeling III, Topic 25, Calculating Effective Distance, at www.innovativegis.com/Basis/ MapAnalysis/Default.htm. Figure 3. A map of the "best" initial attack mode for a large area was draped over a Google 3D image. SEPTEMBER 2O11 / WWW . GEOPLA CE .C O M 11