Annu. Rev. Astron. Astrophys. 1992. 30: 653-703 Copyright © 1993 by Annual Reviews. All rights reserved

3.2.4 BALLOON-BORNE ANISOTROPY OBSERVATIONS In addition to the work of Meinhold and Lubin (1991) mentioned above, one other group, led by de Bernardis (1988, 1989, 1990) has carried out a number of experiments sensitive to these angular scales with a one-meter class telescope on a balloon. Their instrument consists of a 1.2 meter primary mirror and a wobbling secondary mirror which is used to beam switch with an amplitude of 1° on the sky. They used two bolometer detectors cooled to 0.3K; one operating in the band 126 GHz-165 GHz and the other very broad band and operating below 840 GHz. The beams on the sky of the telescope-feed combinations were 60' FWHM and 25' FWHM, respectively. The low-frequency channel was subject to internal RF interference so that this group has only reported on their high-frequency results thus far. During the balloon flight they performed ~ constant azimuth drift scans at an elevation of 45°. They report results from a high Galactic latitude (-50° < b < - 43°) region observed covering a 20° strip in right ascension at = 6°.61-7°.89. The single switching procedure produced difference measurements for 87 independent fields. Signals were clearly detected which the authors ascribe to Galactic dust emission. In addition they derive upper limits to the intrinsic anisotropy which are given in Table 3.

In a recent balloon experiment Alsop et al (1992) made observations with a 1-meter telescope, having a beamwidth of 0°.5 and switched sinusoidally in azimuth with an amplitude of 1°.3. Observations were made simultaneously at 180 GHz, 270 GHz, and 360 GHz, using a ³He-cooled bolometer receiver. Variance in excess of that expected from the noise alone was detected at the level of T/T = 5 x 10^-5. This signal could not be interpreted as uniquely cosmological in origin because of concerns about possible systematic errors. An upper limit on the anisotropy derived from the observations is given in Table 3.