Fig. 2

Topic modelling with LDA. Topic model of 13,057 titles and abstracts found from the search string 1. Topic modelling is performed using a LDA model with 12 topics: a intertopic distance showing the marginal topic distribution of each topic, b–d top 30 most relevant terms for Topic 1, 2 and 8 respectively, along with its estimated term frequencies. Topic 1 and 2 have terms related to sensor and data, but Topic 1 is more focused on systems and applications whereas Topic 2 is associated with methods and algorithms. Topic 8 consists mostly of keywords related to imaging and satellite imaging