## 5 Discussion and Conclusions  
Surprisingly, there are few published papers regarding the remote monitoring of landfill fires. To our knowledge, this is the first study to evaluate the performance of an interdisciplinary remote sensing method in monitoring and predicting fire events in the USA. Because of the closures of many landfills and other disposal facilities over the past 40 years [32], the number of neglected waste sites has increased along with the chance of subsurface events. These closed and abandoned waste sites around the USA must be monitored for subsurface activities that can lead to above-surface hazards. Remote sensing can be used to address this problem and locate hotspots by monitoring the thermal signature of  
Figure 12: Thermal states of the landfill in (**a**) February 2010 and (**b**) September 2011, and (**c**) thermal status difference. Figure 13: XBAR control chart showing violations, i.e., exceeding \(\pm 3\)\(\sigma\) (**a**) per observation and (**b**) per pixel. these waste sites. Hotspots can be an indication of the potential for fire that can threaten human health and the environment. In this paper, a noninvasive method is proposed for monitoring temperature by the collection of sufficient information to enable the timely detection of subsurface events. To reach this goal, in this study, temperature data contained in the Landsat satellite images (USGS Explorer archives) were converted into a more workable format and then analyzed. As presented in the results section, the location of hotspots at Bridgeton Sanitary Landfill, Missouri, were successfully detected and monitored. Multitemporal LST thermal maps were plotted for this case study, whereby a large difference between the LST and air temperature provided a warning of the need to investigate. We controlled for seasonality by measuring temperatures at different areas in the same landfill at the same time. This technique can effectively detect most hotspots and the results have been verified by the consultant report [21; 23]. The use of satellite remote sensing techniques for the detection of possible fires in landfills has great practical significance when there is no landfill data available or in the detection of illegal waste dumps. The 30-m spatial resolution of the thermal band can detect most of the substantial hotspots as these usually last for months and their generated heat propagates both vertically and horizontally for distances that are detectable by satellite infrared sensors. However; this technique is limited by the validity and availability of imagery because of cloud cover and the length of time between revisits of the satellite to the same place (every 16 days), respectively. The depth of the hotspot is also an important factor. For hotspots of the same size, the deeper the hotspot is, the smaller the increase in LST temperature. Given the availability of public data from the USGS Explorer satellite images database, the proposed method can be applied to any landfill in USA territory to predict subsurface thermal events. Future work should include the incorporation of this method into a formal satellite-based landfill monitoring system that uses thermal infrared observations from Landsat satellites to assess the thermal state of any landfill surface and identify anomalous thermal patterns and changes of any USA landfill. This information can also be used to issue warnings regarding the potential for landfill fires. The results generated by this study provide perfect data input for the monitoring system and includes algorithms for efficient satellite image classification and physically based land-surface temperature retrieval. Thermal remote sensing is an effective tool for monitoring the internal activities of landfills and provides a reliable method for predicting fire outbreaks and preventing possible environmental disasters. Investigation, H.A., M.G.R.F. and S.S.; Supervision, R.N. ; Writing--original draft, F.H., M.E.K., J.E. and N.B. ; Writing--review & editing, R.W.P.