# Illegal Logging Detection Based on Acoustic Surveillance of Forest
## 1 Introduction  
Forests have an imperative role in the maintenance of the earth's global biodiversity and preservation of the ecological balance. In general, forest covers across the globe are crucial and are a vital indicator of the overall health levels of the planet. It is well pointed out that forests properly purify air, preserve watersheds, prevent erosion, improve the quality of the water, and provide natural resources. In addition, forests assist in the face of global warming and they absorb a lot of carbon dioxide which is the major greenhouse gas, and thus assist in protection of the globe from climate change. According to various studies, it has been indicated that approximately 1.6 billion people across the globe rely on forests environments for their livelihoods and also that approximately 60 million indigenous people greatly rely on forests for their life and subsistence [1]. Many factors affect the existence and the sustainability of the forests. A main threat is illegal logging which can cause unmanaged and irreparable deforestation. Additionally, illegal logging is considered to be the greatest threat to biodiversity, since forests support almost 90% of terrestrial biodiversity [2]. Moreover, illegal logging poses a great threat to the sustainability of forest ecosystems and can result in extensive deforestation which has a substantial negative effect on the atmosphere. The main results of illegal logging are flash floods, landslides, drought, and also climate change and global warming [2]. Illegal logging also results in losses of government revenues and may also contribute to the rise of poverty [3]. Illegal logging activities affect the counties that are forest rich and also many countries that import and utilize various wood-based products from wood-producing countries [4]. In many cases, the range or scale of illegal logging is impossible to accurately calculate, mainly due to the nature of the activity. Illegal forest activities across the globe are estimated to result in approximately USD 10-15 billion losses of annual government revenue [3,5]. Illegal trade irregularities were specified in the mid-1990s as accounting for almost 15% of global trade [6]. In addition, it has been pointed out that, in the most vulnerable forest regions, more than half of all the logging activities have been performed illegally [7] Despite the recent work of the ecological initiatives and the formulation of various monitoring tools for export timber products, it is necessary, more than ever before, to employ systems for detecting illegal logging [8]. Many authorities in charge of forest management have taken actions for surveillance and information collection of forest environments aimed at confronting illegal logging and deforestation. In general, surveillance is conducted mainly by ground-based methods that use sensor-based monitoring approaches and that exploit the advancement of existing technologies [2]. The ground-based methods include on-site monitoring by staff and patrols for the surveillance of the forest [9]. In addition, observation towers are often used by specialized personnel for visual detection of illegal activities and fires. However, these approaches are very expensive, time-consuming, and in most cases, require a lot of resources. Therefore, technology-based methods and solutions need to be exploited. During the last decades, developments in remote sensing technologies, as well as advancements in information and communication technologies (ICT) have enabled the utilization of automated or semi-automated surveillance solutions in broad areas such as forests. Technologies such as video surveillance, wireless surveillance systems, aerial photographs and satellite imagery, and communications are used. Satellite imagery is a costly solution for monitoring any illegal activities in forest areas such as illegal logging, trespassing, and deforestation, and these activities cannot always be detected by satellite photos.