Three single-frequency GPS receivers (G12 and DG12 made by ASHTECH) installed at Kototabang, Indonesia. Mutual distances between the GPS antennas are 116, 127, and 152 m. Two of the three antennas (E and W) are aligned in the zonal direction. The other (S) is located to the south of the others. Signal intensity of the GPS L1 frequency (1.57542 GHz) is sampled at a rate of 20 Hz, and amplitude scintillation index S4 is measured. Drift velocities of irregularities are derived using cross-correlation analysis with the time series of the signal intensity obtained from the three receivers. Details are described by Otsuka et al. (2006). Otsuka, Y., K. Shiokawa, and T. Ogawa, Equatorial ionospheric scintillations and zonal irregularity drifts observed with closely-spaced GPS receivers in Indonesia, J. Meteor. Soc. Japan, 84A, 343-351, 2006.