## 4 Results and Discussion
### General Information and Applications  
Landsat change detection research is published in journals of various fields, from remote sensing to ecology, demonstrating the relevance of Landsat change detection to many different scientific communities. In several of these studies, Landsat change detection results are considered a reliable source of data for comparing and evaluating non-remote sensing data. These products are also useful to demonstrate land use changes and their related impacts on the environment. Of 490 papers and 129 journals, _Remote Sensing of Environment_ and _Remote Sensing_ journal have the largest number of publications that applied Landsat data for change detection, featuring a total of 107 and 70 articles, respectively (Figure 6).  
Figure 5: A general workflow used in Landsat change detection studies.  
As shown in Figure 7, since 2008, there is an increasing number of Landsat change detection articles, largely because of the Landsat free-data policy. The availability of free data and improvements in data storage capacity significantly contributed to the exponential increase in the average number of Landsat images used in the articles reviewed (see Figure 7). Most recently, online repository and APIs with cloud computing platforms enabled researchers to easily use thousands of Landsat images. For example, [PERSON] et al. (2020) used 3.4 million Landsat images for mapping inland water dynamics through GEE [64].  
Landsat change detection studies cover a range of geographical scales, from small-to global-scale applications. Four of the reviewed studies produced global results using Landsat data [64; 65; 66; 67], while several other studies produced continental and country-wide results for Africa [68], Australia, China, the United States [69], Eastern Europe, and Russia [70], for example. Most large-area studies were implemented in the GEE platform, which is capable of handling a massive amount of data. Figure 8 shows by continent the total number of study areas and the total number of Landsat images used. As illustrated, studies in Asia applied Landsat data to map large study areas, whereas studies in North America incorporated more Landsat images in their analysis compared to other continents (through the inclusion of a temporal element).  
Figure 6: The number of Landsat change detection articles in each journal meeting the search criteria.  
Landsat change detection has various applications, from environmental monitoring to capturing the dynamics of human life. Figure 9 shows the major domains of Landsat change detection studies in different countries. Based on this meta-analysis, forests are the most studied domain using Landsat change detection. Urban expansion is the main focus in China, whereas agriculture and food security are the most common concerns in North Africa.  
Figure 8: The total number of study areas and images used in Landsat change detection studies on different continents (5 global studies excluded).  
Figure 7: The total number of Landsat change detection journal articles published since 1994.  
To better understand drivers of land cover change in the reviewed studies, the most common change agents are summarized in Table 2, categorized as caused by natural or anthropogenic means. Deforestation, urban expansion, human activities, and agriculture expansion are the most common agents of change in the reviewed articles. However, it should be noted that change is more often driven by multiple agents, and different change agents have direct or indirect impacts on each other. For example, deforestation impacts the environment and climate, and climate changes can trigger natural disasters.