Apparatus and a method utilizing correlation interferometer direction finding for determining the
azimuth and elevation to an aircraft at long range and flying at low altitudes above water with a transmitting
radar while resolving multipath signals. The signals from the
radar are received both directly and reflected from the surface of the water using horizontally polarized and vertically polarized antenna arrays, are digitized and are stored in separate covariant matrices. Eigenvalues for the eigenvectors of the matrices processed on
signal samples recorded on horizontally polarized X arrays are compared to the eigenvalues for the eigenvectors of the
covariance matrices processed on
signal samples recorded on vertically polarized X arrays.
Incident field polarization is associated with the
antenna array measurements that yield the strongest eigenvalue. The eigenvector and eigenvalues for the strongest
signal are selected and used for subsequent
signal processing. An initial global search assuming mirror sea-state reflection conditions using the signal eigenvector having the strongest eigenvalue is performed to yield an approximate elevation α and
azimuth β to the aircraft. The approximate values are then used as the starting point for a subsequent conjugate gradient search to determine accurate elevation α and
azimuth β to the aircraft.