This editorial describes a collection of eight papers related to the assimilation of nonlocal observations in complex systems (geosciences, life sciences). This is a non-trivial topic since the assimilation of nonlocal observations requires advanced mathematical tools. For instance, it is well known that the very popular local ensemble transform Kalman filter (LETKF) in geophysical data assimilation cannot rigorously assimilate radiance-like observations.

This collection of paper, led by Axel Hutt, with Lili Lei, Alberto Carrassi and myself as co-editors, and entitled Editorial: Data Assimilation of Nonlocal Observations in Complex Systems, is published (open access) in Frontiers Applied Mathematics and Statistics. This work has been supported by the IRSN.