Short baseline helicopter positioning radar for low visibility

A method for determining position of an aircraft with respect to a ground station, comprising:

• transmitting a signal from the ground station, the signal comprising a plurality of electromagnetic signals, each signal having a different selected frequency, wherein transmission of each frequency is followed by a time interval of no transmission such that multiple path signals have decreased in amplitude by a predetermined amount;
• detecting the signals at an array of sensors disposed on the aircraft in a selected pattern, the array including at least one reference sensor and at least three spaced apart phase difference determination sensors;
• determining a difference in arrival time of the signals between the reference sensor and each of the phase difference determination sensors by determining a relationship between frequency and phase difference between signals detected by the reference sensor and each time difference determination sensor at each of a plurality of frequencies without using a time reference between sensors;
• and
• determining a spatial position of the aircraft from the time differences.

A method for determining position of an aircraft with respect to a ground station, comprising:

• transmitting a signal from the aircraft, the signal comprising a plurality of electromagnetic signals, each signal having a different selected frequency;
• detecting the signals at an array of sensors disposed on the ground surface in a selected pattern, the array including at least one reference sensor and at least three spaced apart time difference determination sensors, the array deployed from the aircraft prior to landing;
• determining a difference in arrival time of the signals between the reference sensor and each of the time difference determination sensors;
• and
• determining a spatial position of the aircraft from the time differences.