## 1 Introduction  
Currently, there is no reliable and cost-effective method available in the United States (U.S.) for detecting and monitoring subsurface smoldering events (SSEs) and related thermal imbalances at U.S.  
landfills [1]. Such a method is needed as a timely warning tool for the identification of the location and spatiotemporal extent of subsurface \"hotspots,\" while also aiding in the prevention or minimization of costly subsurface fires and thermal damage to liners and gas/leachate handling systems. The space borne remote sensing of landfill surface temperatures by thermal infrared sensing offers a promising approach. As discussed below, interpretation of the publicly available Landsat data archive enables the monitoring of large areas, such as landfills. The nondestructive, noninvasive methods described in this paper allow for the observation of multiple locations quickly and at low-to-no cost and the assembly of a satellite image archive that indicates changes in the thermal state of landfill surfaces over time. Further algorithmic interpretations of these thermal-areal time series can be used to isolate persistent hotspot signatures by filtering externally forced thermal variations (e.g., from seasonal thermal trends) and short-term thermal excursions [2]. Moreover, with further development, the algorithms presented herein can serve as a basis for an automated monitoring/warning method. For example, the application of machine learning to sudden-change detection could ultimately reduce the burden associated with human-in-the-loop monitoring and facilitate expert event verification and the pursuit of remedial action. Using this algorithmic approach, we present our case study and the obtained preliminary simple stationary statistical metrics (e.g., mean and standard deviation) for the data collected during the study period, with the results indicating that accumulated subsurface heat can be detected by satellite images. We identified the 2010 onset and migration of an SSE in the Bridgeton Sanitary Landfill, with the remote sensing results comparing favorably to ground observations during the same time period. Previously researchers have examined four landfills located in North America (Michigan, New Mexico, Alaska, and British Columbia) to investigate the thermal states of municipal solid waste (MSW) landfills as a function of usual operational conditions and climatic regions [3]. A comprehensive study has also been conducted to assess the physical and thermal properties of wastes affecting heat transfer and fire ignition [4; 5]. In accordance with many other studies, this work showed that in landfills with no SSE or other long-term thermal anomalies, the usual heat generated in MSW landfills is largely the byproduct of the biological decomposition of organic waste along with leachate and gas [6; 7; 8; 9; 10; 11; 12; 13]. Under these conditions, the landfill temperature remains close to the air temperature at shallow depths and near the edges of the landfill and reaches maximum values relative to the air and ground temperatures near the areal center and at intermediate depths. Observations indicated that a baseline \"healthy\" landfill thermal state can be observed by satellite-based remote sensing [3]. Indeed, this technology has been used previously to map and monitor landfills. For example, Landsat Thematic Mapper (TM) images were used to monitor the Al-Qurain landfill in Kuwait and observed a 1-4 \({}^{\circ}\)C temperature elevation for the surface of the landfill site relative to the surrounding desert area [14]. A similar study at the Trail Road landfill site near Ottawa, Canada observed an average 9 \({}^{\circ}\)C temperature elevation from 1985 to 2009 [15]. These studies demonstrate that satellite-based remote sensing applications that use time series analysis and appropriate image processing techniques can identify and map landfill sites based on differences between baseline surface temperatures and their surroundings.