We present novel in-field vegetation fire observations, and the analyses used to process the data, using brightness temperatures recorded by longwave infrared camera and thermal image velocimetry. The brightness temperatures from a wind-driven stubble wheat fire were obtained in video format with a 60 frames per second (fps) acquisition rate. Multi-level sonic anemometers mounted on a 10m in-fire tower were used for in-situ measurements of turbulent velocity and air temperatures, while fuel level air and flame temperatures were collected by an array of thermocouples. The camera’s image pixel resolution was adequate to resolve dynamics and in accordance with the in-fire thermocouple spacing distances. The in-situ and remotely measured flaming zone dynamics were derived using two different methodologies, Thermal Image Velocimetry (TIV) and Image Segmentation (IS). The results highlight spatial and spectral information of coherent turbulent and mean velocity structures. The power spectra decomposition of the thermal image velocimetry showed similar spectral characteristics to the sonic velocity measurements during the fire passage under the tower with a similar inertial subrange slope. This result reveals plausible evidence of interaction between the flaming zone and wind turbulence for a prescribed rapidly moving stubble wheat fire. This research presents a new field measurement methodology for understanding fire-atmospheric interactions between the flaming zone and the immediate overlying atmospheric turbulent boundary layer.

WindNinja is a high-resolution diagnostic wind model developed for use by operational wildland fire management. The original version of WindNinja employed a numerical solver to enforce conservation of mass (COM). Because the COM solver is fast-running, requires little technical experience to run, and predicts ridgetop speed up and channeling effects well, it is widely used by the operational fire community. The COM solver has limitations, however, in regions where momentum effects dominate the flow, such as in regions of flow separation, which can occur on the lee-side of terrain obstacles. Recently, a second solver has been incorporated into WindNinja which enforces conservation of mass and momentum using computational fluid dynamics (CFD) techniques based on the Reynolds-Averaged Navier-Stokes (RANS) equations. In this work we compare simulations from the CFD solver to measurements made during three field campaigns (Askervein Hill, Bolund Hill, and Big Southern Butte) as well as to simulations from the COM solver and an LES model. Evaluations focus on near-surface winds during high-wind periods, which are of particular interest to wildland fire managers.