Averaged 10° azimuth slices for RSNR of cross-correlation functions from conventional (first row), one-bit (second row) and RAM (third row) preprocessing for entire CI OBS array records in March 2012. Frequency band: 0.115–0.145 Hz (first column) and 0.2–0.3 Hz (second column). Cross-correlation functions shown are restricted to those with RSNR larger than 3 dB on both sides. 821, 833, 860, 856, 860 and 856 out of 861 station-pairs are chosen in (a) to (f), respectively. The contours are the same as in Fig. 7. The most important stations are enclosed by the red frame. Note that the first row have different colour scales.