The authors consider some concerns regarding a technique of narrowband synthetic aperture radar imaging (N-SAR), called coherent Doppler tomography (CDT), which may be a good candidate spaceborne applications. Using a single frequency signal, resolution of two tenths of a wavelength can be achieved in the point spread function if the radar platform circles the ground patch to be imaged. However, the high sidelobe level of -8 dB in the point spread function results in an unacceptable dynamic range. To reduce the sidelobe level, two approaches are presented: coherent processing using multiple discrete frequencies and noncoherent subaperture processing. Simulation results demonstrate that the sidelobe level is substantially reduced by both methods. However, the resolution is degraded and the computational overhead is greatly increased for noncoherent subaperture processing. A possible satellite geometry configuration which could utilize N-SAR processing to provide high-resolution global mapping capability is presented.
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