# A Drone-Enabled Approach for Gas Leak Detection Using Optical Flow Analysis +
## 1 Introduction  
Gas leaks and emissions are challenges for various industries like petrochemical and oil and gas industries resulting in financial losses and possibly human injuries. Therefore, in recent years, significant efforts are dedicated to developing reliable gas leak detection techniques. Moreover, some studies are devoted to introducing techniques for detecting the origin of possible leaks for launching corrective measures. Gas leaks can be very dangerous to health and the environment. In confined spaces like buildings, even a small leak in pipelines can gradually build up to be an extremely lethal or even explosive amount of gas which can endanger staff. The release of some gases such as natural gas, propane, and isobutane into the atmosphere is harmful due to their effect on global warming or ozone depletion. Another area would be fugitive emissions which is the emission of gases from industrial equipment due to leaks or other sources of gas release which can lead to an increase in air pollution [1]. The analysis of gas emission can be very beneficial in many industries such as chemical manufacturing or oil and gas. The early detection of many hazardous gases, for instance, Volatile Organic Compounds (VOCs) or Methane can increase the functional safety of the system and prevent any health risk for the personnel. Unfortunately, there have been many incidents during previous years that show the importance of providing reliable gas leak detection techniques aspreventive measures. For instance, in July 2014, the occurrence of methane gas leak at Bhilai plant of Steel Authority Of India, caused the loss of six human lives [2]. The significance and consequences of gas leaks for the environment and human life motivated industries and governments to conduct regulated inspections as preventive measures to avoid such incidents. Gas leaks can cause financial losses for the companies and the end-users. For example, in the case of natural gas, possible gas leaks can cost companies and end-users significantly. The increase in the number of natural-gas consumers causes the rapid expansion and construction of gas pipelines and distribution centers [3]. Based on the report of the European Gas Pipeline Incident Data Group, the length of the gas transportation pipelines has grown more than 21% in the 1970-2016 period and the total length of natural gas distribution has almost reached 2,200,000 km in Europe [4]. The length and expansion rate in pipelines also increase the possibility of leaks and failures, making the necessity of regular and reliable inspection more significant and critical to avoid financial losses and dangerous incidents. These losses are not limited to companies and distribution systems; the possible leakages in buildings and industrial sites can cost end-users. Google Earth and Environmental Defense Fund collaborated by equipping Google Street View mapping cars with required sensors to map the methane gas leaks in various urban areas like Boston, Indianapolis, and New York City's Staten Island. The map shows methane seeping from thousands of aging pipes in the cities. Although the leaks were all low-level, end-users pay for the leaked gas [5]. To prevent gas leaks, many organizations and companies devoted a significant amount of efforts and investments to provide reliable and efficient gas leak detection techniques. Additionally, several surveys and studies were conducted on the gas leak related incidents by various organizations. One study stated that during the 1996-2006 period, eighty pipeline rupture incidents were reported in the Gulf of Mexico and Pacific areas. The report demonstrates that the probability of occurring an incident in this specific area is 0.43 incident per year [6; 7]. Another report focused on the risks of pipeline transportation states that around 1326 gas leaks were reported in Alberta, Canada between 2001 and 2005 [8].