Table 3. Limitations associated with the use of Earth observation images and their derivatives.

Limitation	Description
Coarse spatial resolution	The spatial resolution expresses the size of the smallest detail that can be observed in the image. A spatial resolution less than 30 m is generally recommended for mapping applications on a local scale. Earth observation images and their derivatives relating to climatic and microclimatic determinants have generally a coarse spatial resolution (more than 1000 m).
Low temporal resolution	Temporal resolution expresses the temporal frequency at which a satellite acquires Earth observation images for a same area. Bimonthly temporal resolution (16 days) is appropriate for Earth observation images used to estimate land cover environmental determinants. For Earth observation images that are used to estimate microclimatic determinants, a temporal resolution that can serve to establish daily averages would be more appropriate. However, commonly used free-access Earth observation images with a high spatial resolution (e.g. Landsat-8 images) do not have this temporal resolution.
Unknown or low accuracy	Climate change projections indicate temperature increases of 1°C to over 5°C in high latitudes, from the 1950s (76,77). An uncertainty below 1°C would be appropriate for Earth observation images and their derivatives related to temperature. Metadata of numerous Earth observational image derivatives do not indicate their accuracy, and the accuracy within any given Earth observation image derivatives can be highly variable and is generally not available.
Incomplete land cover classes composition	An Earth observation image derivative of environmental determinants must contain all the land cover classes representing environmental determinants of interest. However, the composition of land cover classes of a given Earth observation image derivative depends on its producer and the objectives of creating it. And, there is not a specifically-developed Earth observation image derivative to estimate all the ECDs of every climate-related infectious disease.
Inappropriate temporal aggregation scale	Temporal aggregation scale is the time step that is used to aggregate multi-temporal data. The aggregation scales that are mostly used for Earth observation image derivatives are daily, weekly, monthly and annual averages. The temporal aggregation scale to be used will depend on the vectors of the disease. The lifecycle of MBD vectors is very short (a few days to a few months), compared with that of TBD vectors (several years). A weekly scale is more appropriate in the first case and an annual scale in the second. However, for some ECDs, there are no Earth observation image derivatives with the target temporal aggregation scales (e.g. annual accumulation of surface degree-days, derived from land surface temperature images).
Long periods between updates	An annual update frequency is generally appropriate for Earth observation image derivatives used to estimate environmental determinants. However, several of these products are not updated annually.
Short archiving period	A relatively long archiving period—more than 15 or 30 years—may be necessary to study the evolution of infectious disease risks in the context of climate change. However, the archiving period of several Earth observation images and their derivatives is not long enough to study the impact of climate change on infectious diseases.
Incomplete geographic coverage	Risk assessment and risk mapping of infectious disease at borders often requires data covering several different administrative areas (e.g. Quebec/Ontario; Canada/United States).
Traditional methods and tools not adapted for massive Earth observation image data	An Earth observation image dataset covering a huge country like Canada, with a high spatial resolution, a high temporal resolution, frequent updates, and a long archiving period, will generate massive data for whose traditional methods and tools for Earth observation image data processing and management are not appropriate.

Abbreviations: ECD, environmental and climatic determinants; MBD, mosquito-borne diseases; TBD, tick-borne diseases