Free periodical satellite/aerial imagery There is a company called Planet Labs which sells daily satellite imagery covering the whole globe that can be used for various research  like agriculture, forestry etc. I wonder if there is a free equivalent of Planet Labs that offers periodically captured satellite or aerial imagery with decent resolution possibly on global scale or at least on regional scale (whole country). Do maybe NASA or ESA offer something periodical with decent coverage and resolution?
There are a wide ranging of publically available satellite images with different spatial and temporal resolutions. Notably Landsat (https://earthexplorer.usgs.gov/) and Sentinel (https://scihub.copernicus.eu/dhus/#/home) come to mind.
If you are interested in analysing remote sensing products at a global or regional scale, Google Earth Engine (https://developers.google.com/earth-engine) may be a useful tool for you. GEE can directly access Landsat and Sentinel products at no cost to the user.
I hope this information is of use to you.