i just finished reading Sleeping Island by PG Downs.its about a 1936 canoe trip to a Hudson Bay tradeing post on the then unmapped Nueltin Lake ..even the bush planes had a very hard time finding it.in a nutshell Downs gets to the post which is out of everything and waiting for a long overdue re-supply by air.when the plane is finally spotted it's far to the west and going in big circles tryng to find the post--a fire is lit and brush tossed on,the pilot sees that and lands.. OK..the point of this post--Downs said that the thin ribbon of smoke against the dark background of trees had saved the day.the pilot made for the smudge and did not see the buildings untill he was over them..so maybe simple,easy and available is just as good if not better that "high tech"