Table 2. Advantages of using Earth observation images in the estimation of environmental and climatic determinants and risk mapping of climate-related infectious diseases.

Advantage	Description
Accurate, regular measurements at different spatial and temporal resolutions	Compared with data acquired on the ground, the homogeneity and regularity of observations made using Earth observation images permit more accurate measurement of changes occurring over time, such as environmental and climatic changes. These measurements are made at different spatial and temporal resolutions which allow for the observation of phenomena (e.g. vector habitats, microclimatic conditions) and their changes according to a varied spectrum of measurement scales ranging from 0.31 m to over 75 km, and temporal observation frequencies ranging from 5 minutes to 16 days. This multi-scale observation capacity offered by Earth observation images is unique and makes it possible to estimate ECD and to map risk on local, regional and global scales according to the public health objectives.
High spatial density of observations, combined with coverage of vast territories, remote regions and areas difficult to access	The measurements made using Earth observation images are continuous data covering the entire geographic area covered by the sensor. ECDs can be estimated and low-risk or high-risk areas identified for any part of the territory. Earth observation image cover immense territories that cannot be sampled with ground data. Most Earth observation satellites can pick up images covering the entire planet, including remote regions and geographic areas difficult to access. This is very useful in supporting public health initiatives that target remote communities.
Recurrence of observations over a long period	Earth observation images have been acquired recurrently for nearly 40 years. The observation capacity for any given territory over long periods offers a great opportunity to study and predict the impact of climate change on the emergence and re-emergence of climate-related diseases.
Ready-to-use Earth observation image derivatives	Many ready-to-use products have been developed from Earth observation images to make these data accessible to a broader community of persons not expert in the processing and analysis of Earth observation images. These products relate to both environmental determinants and climatic determinants.
Low-cost access to vast amounts of data	There are over 1,700 Earth observation satellites in operation (74). Earth observation images from many of these satellites are accessible free of charge via open data platforms, as are the majority of Earth observation image derivatives. The majority of commercial Earth observation images involve data with very high spatial resolution (less than 2 m). Costs associated with these data are dropping quickly with the increase in Earth observation systems and the improvement of their performance.
Speed of mobilization of many satellites to support emergency operations	Under the International Charter on Space and Major Disasters (72), satellites and services can be rapidly mobilized by numerous space agencies to support the management of emergencies in major disaster zones. They offer the ability to quickly assess risks of epidemics in these zones in a context where the number of major disasters is rising with climate change. The Charter has been operational since the year 2000. It was activated to support responses related to the outbreak of the Ebola virus in West Africa in 2014 (73). This marked the first time the Charter was activated for the management of an infectious disease.

Abbreviation: ECD, environmental and climatic determinants