Iterative annotation of solar panel plants in sentinel-2 imagery

We explore an iterative annotation strategy adapted to recurrent multispectral imagery provided by constellations such as Sentinel-2 and applied to the monitoring of events that develop over time. Our key example is the tracking of the progress in the installation of solar power plants. This problem has four difficulties that seem hard to tackle with automatic methods: an unknown and variable spectrum for the solar panels, a variable background, a variable orientation of the panels causing variable cover of the ground, and a variability of lighting and atmosphere transparency due to cloud shadows and water vapor density. We found that each site is different and that only the interactive annotation of the time series can give an acceptable segmentation of the panels. At this point, we describe a weakly monitored interactive annotation tool that predicts the annotation of new paneled zones from an annotation at a previous date. In that way, the human operator intervention is aided and limited to a few corrections from date to date.