Which is a valid procedure for departing a non-towered airport under IFR?

Filing a flight plan with a briefer is a valid procedure for departing a non-towered airport under IFR. This process ensures that the necessary information about the intended flight, including the route and altitude, is documented and communicated to air traffic control. It helps in providing a flight plan that ATC can monitor for safety and provides the pilot with necessary updates and clearances pertinent to their specific flight.

When departing under IFR from a non-towered airport, pilots must comply with the regulations that require filing an IFR flight plan in advance. This filing can be done either through a briefer or electronically, but it is crucial to ensure that ATC is aware of the flight details prior to departure.

The other options involve communication or procedures that are not applicable at non-towered airports. For instance, calling a tower for clearance or contacting ground control is unnecessary, as these services are not available at non-towered locations. Visual signals to depart are also not a standard procedure under IFR and do not provide the necessary communication or clearance required for safe flight operations in controlled airspace.