Ground to Air signals are a reliable visual means of signaling rescuers during a back-country emergency. Typically one finds an open space with a contrasting/neutral background (grass, sand, etc.) and lays out a pattern of symbols and letters that convey a message most Search and Rescue (SAR) members recognize as part of an international SAR language.
In order to be seen from even a slow-moving aircraft several hundred feet above the ground, each emergency symbol needs to be at least 12 feet wide and formed by lines at least three feet wide and 15 feet long (a standard 5:1 ratio of length to width).
As important as size is high contrast between the symbols and the background. Light backgrounds work well with evergreen boughs and foliage, dark branches and even ashes from a fire. Dark backgrounds favor lighter colored rocks/boulders and perhaps items of clothing or gear. High contrast is the key for high visibility.
What happens if you need to make a high visibility signal in a snow field where there are no evergreens, no fire ash, nothing of contrast to make your signal visible from above?
Trampling down snow with snowshoes or boots can work but that may not provide much contrast depending upon where the sun is (high in the sky or lower towards the horizon?). Using shadows cast by the sun can create wider areas of darkness if you create both a trench and a raised ridge of snow immediate adjacent to the trench.
Digging a North-South aligned deep-walled trench creates sides that will cast shadows at different times of day. If snow is lined up alongside the trench, it creates even more height from which a shadow can be cast. Together, a white base of snow might project a 2’-3’ band of dark shadow along each edge of the trenched symbol. That slight difference in contrast may be enough to be seen from above.
Most any conspicuous symbol with get the attention of a SAR observer but knowing the correct signals will enable you to communicate more efficiently with the rescuers. Remember critical signs if you can ( “I” – Require Doctor; “II” – Require Medical Supplies; “X” – Unable to proceed, etc.).
An easy way to have these symbols handy in the field is to use an indelible marker to record these signals on a piece of gear you’ll always have with you (inscribed on an inner panel of a life jacket; inside of a stuff sack; flap of survival kit, etc.).
The most critical aspect of a Ground-to-Air signal is making it big and make sure it’s in stark contrast to the background upon which it’s laid out.
Be Smart; Be Safe; Have Fun!