Diffractive integrals for bistatic remote sensing using GPS signals

Diffractive integrals use a reference signal to derive the field distribution from the radio holograms. The phase of reference signal coincides with phase of the Green function and can be found by solving the scalar wave equation. This property of the reference signal demonstrates a fundamental nature of the radio holographic focused synthetic aperture principle (RFSA) specifically in its application to the radio occultation (RO) data analysis. The RFSA method has been validated by direct observations of multi-beam propagation in the atmosphere and weak reflections from the terrestrial surface, its vertical resolution has been estimated early as about 70 m. To compare the Canonical Transform (CT), Back Propagation (BP) and RFSA methods a general inverse operator (GIO) is introduced. CT as a partial case of GIO method can resolve physical rays in multi-path situations under an assumption of the global spherical symmetry of the atmosphere and ionosphere. RFSA method can account for the multi-path in the case when the global spherical symmetry is absent by using the appropriate model of the refractivity and has a promise to be effective for operational data analysis.