Validating the TET-1 satellite sensing system in detecting and characterizing active fire 'hotspots'

Wildfires, or bushfires as they are known in Australia, are a natural occurrence in nearly every country over the globe, which take place during the hotter months of the year. Wildfires can be triggered through natural events, such as lightning strikes, which account for half of all wildfires in Australia, or through human induced methods, for example deliberately lit or through failure of infrastructure or equipment. In Australia, fires are a major natural hazard affecting over 25,000 km2 of land annually. Historically, fire detection has been performed by fire spotters, usually in towers or spotter aircraft, but in countries such as Australia, with a large extent of land that needs to be monitored, leads remote sensing techniques to be the obvious choice in providing resources in gathering this information when compared to other methods. Remote sensing technologies provide efficient and economical means of acquiring fire and fire-related information over large areas at regional to global scale on a routine basis, allowing for the early detection and monitoring of active fire fronts, which is essential for emergency services in responding timely to outbreaks of wildfires.<br><br>The objective of this study is to investigate the hotspot (fires and other thermal anomalies) detection and characterization product from the TET-1 satellite sensing system from the German Aerospace Centre (DLR). The satellite is envisioned, as part of a constellation of satellites, to provide detection and characterization of fires at a higher spatial resolution when compared to the current standard global coverage from the MODIS fire products. This study aims to validate the output from the detection and characterization algorithm, to provide a guide for the sensitivity of the system, especially for low power (small area and low temperature) fires. This consisted of conducting a simulation study into the limits of detection for the system, as well as performing a case study.<br><br>A simulation study was conducted in order to determine the sensitivity of the TET-1 satellite sensing system in detecting hotspots, for the purpose of determining limits of operation and as an aid in developing tests to assess the accuracy of the algorithm in detecting and characterizing fires. Determining the sensitivity involved ascertaining the minimum area and temperatures (in combination the total energy emitted by a fire) of a fire that would be able to be detected by the algorithm. The study found that under ideal conditions, the TET-1 detection and characterization algorithm is theoretically able to detect a fire of only 1m², albeit for temperatures of 1000K (approx. 727°C) and over. As the area of the fire increases, the required temperature decreases rapidly, for instance a 9m² fire is detectable from 650K (377°C). Once a fire becomes significantly large, for example 100m², the detectable temperatures falls to 500K (227°C), which is considered a smouldering temperature.<br><br>The characterization portion of the algorithm was found to accurately estimate the fire characteristics with low systematic errors (area ±12% and temperature ±3%). Adjusting the background temperature was found to not significantly influence either the detection or the estimation of the fire characteristics.<br><br>A case study was performed to validate the results from the simulation study, which was conducted near the town of Kangaroo Ground on 31st July 2015. This was an example of a low power fire with an effective fire area of 15.1m² and an average fire temperature at satellite overpass of 63°C (336K). Upon investigating the output from the camera system, although the fire could be seen in the MIR image in two adjoining pixels, the fire did not possess enough power to trigger the automatic detection threshold of the algorithm, and as such was not classified as a legitimate fire. Although not detected, a comparison was made of the energy emitted by the fire (measured in radiance to directly compare with the camera) to the amount detected by the satellite. The energy from the fire was determined to be; = 0.302 W/sr.m²µm and = 7.612 W/sr.m².µm, while the radiances captured by the sensors was; for pixel 1 = 0.3102 W/sr.m².µm and = 6.835 W/sr.m².µm, and for pixel 2 = 0.3102 W/sr.m².µm and = 6.817 W/sr.m².µm. These results show that the MIR radiances were comparable, but that the TIR radiances were not, although no definitive reason for this discrepancy could be determined. Other errors with the output from the satellite camera system were found, most serious being the geo-location of the pixels. The reported position of the test site by the camera system differed by over 12km from the actual location of the test site.