arXiv:2610.34224v1 Announce Type: new Abstract: Frequency-selective Rayleigh fading in distributed acoustic sensing (DAS) based on phase-sensitive optical time-domain reflectometry (phi-OTDR) calls for effective diversity, but existing rotated-vector-sum (RVS) combining of nonoverlapping subbands incurs a spatial-resolution penalty. In this letter, we propose frequency-domain replica reconstruction and noise-whitened principal component combining (PCC) that combines a full-band replica and overlapping subbands using fixed weights estimated across probing periods after whitening correlated replica noise. This approach retains wider subbands and reduces reliance on noisy first-period alignment, balancing diversity with nominal spatial resolution. Experiments over approximately 7.1 km of fiber with 16-microsecond linear frequency-modulated (LFM) pulses recover 500-Hz vibrations with reduced background phase excursions and a 2.46-2.76-dB improvement in the vibration-to-background ratio (VBR) over the first-period RVS.