Analysis of coal fire dynamics in the Wuda syncline impacted by fire-fighting activities based on in-situ observations and Landsat-8 remote sensing data

Abstract Coal fires are a global catastrophe for valuable coal resources, the environment, human health and safety. Fire-fighting activities are the approach to limit these catastrophic influences and to extinguish active coal fires. The Wuda syncline in Inner Mongolia is one of the biggest coalfields suffering from coal fires in China, and is one of the coalfire areas globally, which has been analyzed most comprehensively. Massive fire-fighting activities have been undertaken to quench coal fires in the Wuda syncline. Particularly, activities such as blasting and excavation have accelerated since the year 2010. Influence of fire-fighting activities on coal fire dynamics is a significant topic but has rarely been reported yet. Although airborne and spaceborne earth observation data holds the potential to monitor extinguishing activities, this data is rarely applied for this purpose. Airborne thermal scanner data is cost intensive to fly, and spaceborne Landsat-7 scanner system with a thermal band at 60 m spatial resolution in 2003 led to a limited exploitation of this valuable data source. Just recently, Landsat-8 satellite data, with a thermal infrared band of 100 m spatial resolution is available since early 2013 and is able to fill this gap. We conducted in-depth in-situ surveys on coal fires and fire-fighting activities in the Wuda syncline in May 2014 after visiting the Wuda coalfield in 2012. We integrated our in-situ observations and thermal anomalies extracted from both Landsat-8 and Landsat-7 (SLC-on, acquired before the scanner failure) satellite data using an automated moving-window thermal anomaly extractor (regional anomaly extractor, RAE), and analyzed coal fire dynamics impacted by fire-fighting activities and the state of coal fires in the Wuda syncline. Results show that after over 4 years of efforts to fight against coal fires in the Wuda syncline, the Nos. 1–7, No. 9, No. 12, and No. 13 coal fire zones are extinct. However, the No. 8, No. 10, No. 11, and No. 14–No. 18 coal fire zones are still active, and furthermore three novel coal fire zones have evolved. In the light of in-situ surveys in the Wuda coalfield, these active and newly developed coal fires are mainly attributed to extinguishing related activities, such as the blasting and excavation in fire affected areas, which lead to the exposure of pure coal seams, weathered coal pillars, and coal waste piles to the outside air. The contact of this coal and coal remnants with oxygen triggers spontaneous combustion of coal and further develops to coal fires. Additionally, time-series analyses of extracted thermal anomalies suggest that coal fires propagate eastward according with the dip direction of coal seams in the Wuda coalfield. The regional thermal anomaly extraction tool (RAE) can delineate thermal anomalies with a high accuracy, which is confirmed by our in-situ surveys. This paper is the first investigation on dozens of Landsat satellite images to evaluate the state of coal fires within one year, which is more accurate compared to previous approaches analyzing merely one or several satellite images to assess the state of coal fires during one year period.