Measurement of the turbulence in the free atmosphere above Mt. Maidanak

Stellar scintillations were: measured at Mt. Maidanak during 42 nights in 1 998-1999 in order to estimate the contribution of the free atmosphere to th e seeing. The atmosphere above 1-2 km provides a median seeing of 0".39, wh ich is about one-third of the total seeing (0".70). The characteristic alti tudes of turbulent layers are from 3 to 11 km above the summit, and the app earance of layers at altitudes of 3-4 km is accompanied by a degradation of the Free-atmosphere seeing. The median isoplanatic angle is theta (0) = 2" .30 (lambda = 500 nm, at the zenith). This is the first time that such data have been obtained for Maidanak. The instruments used for these measurements-a modified four-channel photome ter and a prototype of a double-aperture scintillation sensor-are described in detail. The data reduction was based on accurate corrections for photon -counting statistics and the use of theoretical weighting functions relatin g scintillation indicts to the altitudes and intensities of turbulent layer s. Simultaneous or quasi-simultaneous measurements of scintillation indices using apertures of different sizes having significantly different weightin g Functions enable estimation of the altitude and intensity of the equivale nt turbulent layer. Despite the simplicity of this one-layer model, it prov ides fairly robust estimates of the integrated parameters of the real free atmosphere. (C) 2001 MAIK "Nauka/Interperiodica".