In recent years, the holographic synthetic aperture radar (SAR) has attracted an increasing interest because of its potential ability of full three-dimensional (3-D) reconstructions at very high resolution over 360°azimuth angle variation. The traditional Fourier-based focusing methods are susceptible to the problem of irregular sampling which is unavoidable in practical multicircular SAR data acquired by the airborne systems. In this paper, we propose a holographic SAR tomographic processing method based on the time domain back projection (BP) algorith $\mathbf{m}$, which can cope with the irregular sampling. Both the coherent and incoherent imaging methods are adopted to investigate the anisotropic behavior of the backscattering. The public GOTCHA data is processed by the proposed method and the results are shown to verify the validity of the proposed method.