Observation of the z = 2.46 quasar SDSS1615. Left: acquisition camera field image during observations of SDSS1615, showing successful acquisition and deiection of the quasar. Middle: average total flux: spectrum (red) over all four telescopes showing the detection of the broad Hα line at 2.228 μm consistent with, a redshift of z = 2.46. In blue is the average coherent flux spectrum using the UT4-UT1 and UT3-UT1 baseline and the post-processing explained in the text. Coherent flux is significantly defected across the entire spectrum. Right: average differential phase spectrum using the UT4-UT1 and UT3-UT1 baselines overlaid on the normalized total flux spectrum. With an RMS of ≈1–2° within the FWHM of the line (gray shaded region), we tentatively detect the rotating disk signal of the BLR.