ROH is "Ruling Operational Height". See the term used on this link, search for R.O.H.
http://www.bbrclub.org/BATTLE%20ORDE...0SQUADRONS.htm
Dog and Cat (and also ROH) reference here:
https://www.google.com/books/edition...sec=frontcover
"Each flight of balloons was given a different name, such as 'Dog', 'Cat' and 'Hen'".
So it would appear that the "Dogs" were the balloons that made up the "Dog Flight", etc.
Reading through more of the above link, it appears the ROH would change based on weather/wind conditions and the alert level (white, yellow, red etc.).