They may be marks left from the soil analysis & testing for the proposed 20th London Airport at Cliffe Marshes. (after LHR, LGW, Stansted, Luton, Prestwick, Lydd, Manston, John Lennon/Beatles international, Unst/Billy Connolly/London Airport et al)
Any local could have told them that Cliffe
Marshes, will be fairly soggy, and subject to fog on quite a few days of the year!
