Origins of the term British Exploring Officer

Does have any idea where and when the term Exploring Officer / Observing Officer was first used? I have searched online and even in Wellington's Dispatches and have come up blank.

A review of the letters, memoirs, and journals of Gordon, Cocks, Light, and Leith Hay, who were one never uses the term. Nor do the letters of John Grant and Lewis Ruman.

Lionel Challis, who created the Peninsular Roll Call in the 1920s and 1930s, also did not use the term in his lists. For that matter, neither did Napier and Oman in their histories. 

The most common used term from the 19th Century was Scouting Officer.

Could  Exploring Officer / Observing Officer be a modern invention? Possibly from the 1970s or later?

Thanks!

Bob