A global analysis of the temporal availability of PlanetScope high spatial resolution multi-spectral imagery

The PlanetScope CubeSat constellation is providing unprecedented global coverage, visible to near infrared, atmospherically corrected, 3 m imagery. The revisit interval between successive overpasses varies in space and time in a complex manner because of a variety of factors and particularly because of the different sensor orbits. The temporal availability of PlanetScope imagery is quantified in this study considering all of the publicly available images acquired globally for a 12 month period from December 1st 2019 to November 30th 2020. A total of 175.8 million images were acquired by the constellation that was composed of between 100 and 133 unique PlanetScope sensors each month and three sensor generations. The local morning overpass times of the three sensor generations were quantified and the most frequently occurring times were 10:16, 10:29, and 10:03 (to the nearest minute) with 90% of the images acquired with a range of morning overpass times of 2 h and 13 min, 1 h and 30 min, and 1 h and 50 min, for PlanetScope-0, PlanetScope-1, and PlanetScope-2, respectively. Maps, histograms and summary statistics of the total number of observations and revisit intervals are derived with respect to a global grid of 4.7 million land points spaced 5.6 km apart in the equal area sinusoidal projection. The annual and monthly number of PlanetScope observations and average revisit intervals did not vary in a geographically uniform manner. This is due to several factors including the different PlanetScope orbits, seasonal high latitude darkness at the time of sensor overpass, and because of the changing number of sensors on orbit as PlanetScope sensors were decommissioned and later generations became operational over the 12 month study period. In addition, the images in each frame of sensed data are not made available if they cannot be geolocated due to cloud and/or featureless or unstructured terrain precluding ground control matching. The PlanetScope constellation provided higher temporal resolution than provided by sensors such as Landsat-8 or Sentinel-2 although 9% of the global land grid locations, predominantly in the interior of Greenland and non-coastal Antarctica, had no observations. Considering the 12 months of global observations, the median average revisit interval was only 30.3 h, and 9.6%, 71.8%, and 88.4% of the land points had average revisit intervals