Contains reports on one research project.Joint Services Electronics Program (Contract DAAB07-71-C-0300)National Aeronautics and Space Administration (Grant NGR 22-009-526

Muehlner, Dirk J.

Weiss, Rainer

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VI. GRAVITATION RESEARCHAcademic and Research StaffProf. Rainer WeissProf. Dirk J. MuehlnerRichard L. BenfordGraduate StudentsMargaret A. FrerkingD. Kingston OwensA. PRELIMINARY RESULTS OF A MEASUREMENT OF THE JSISOTROPY OF THE COSMIC BACKGROUND RADIATIONIN THE FAR INFRAREDJoint Services Electronics Program (Contract DAAB07-71-C-0300)National Aeronautics and Space Administration (Grant NGR 22-009-526)Dirk J. Muehlner, Rainer WeissWe report preliminary results of a balloon flight, on January 28, 1974, from thescientific balloon facility of the National Center for Atmospheric Research (NCAR), inPalestine, Texas. The flight reached an altitude of 39 km and produced useful data at floataltitude for 1 1/3 hours. The instrument was described in Quarterly Progress ReportNo. 112 (pp. 23-26).Figure VI-1 shows the output of the differential radiometer as a function of azimuthangle for both high-frequency (10-20 cm-1) and low-frequency (3-10 cm- ) channels.The angular sampling interval is 11. 50, the full beamwidth at half maximum is 200 andthe rotation rate is 4 rpm.The uppermost pair of curves is an average over 30 rotations early in the flightwhile the moon was still in the field of view. The lunar signal is bipolar as it entersfirst one horn and then the other.The middle curves are an average over 430 rotations; no corrections were appliedto the data. The large sinusoidal term in the high-frequency channel is caused by theatmosphere, since the balloon gondola had a .250 wobble in zenith angle as it rotated. Thewobble was caused by a sticky universal joint which has since been replaced.The lowest curves are the same averages as the middle ones with correctionsapplied. The corrections are made in the following manner. Several times during theflight one horn is moved 100 in zenith angle, and the change in differential radiometeroutput is measured and used to determine the zenith angle sensitivity. In this flightATRJ = 0. 0290 K/degHF JSQPR No. 1141.0 i-JS0.60.20.0.20.61.00.60.200.20.61.00.60.200.20.61.0LF 00 mOOV= I ATR =3.52xIO20K- HF 500mV=I A TR =.I 16xl(2 OK,--HF I00mV=1 ATR =2.3xlO 3 KLF 10 mV= I ATJ = 3.52xO 30HFIOmV=l I TR =2.3xIO 4 KLFIOmV= 1 IATRJ=3.52xio oK2 6 10 14 18 22 26 30S EFig. VI- 1.COSINE0.35 1.26 k-10 0 +10 mV-018 1.24+0.49 ±0.8-1.3 1 0.64QPR No. 114Averaged differential radiometer output as afunction of azimuth.SINE0.66±0.81-10 0 +10 mV-0.66± 1.252w3w +0.62±0.511+0.82±0.54w 0LFig. VI-2. Fourier amplitudes of the low-frequency signal.(VI. GRAVITATION RESEARCH)RJsSATRJ 0. 007 0K/deg.A0zBy using these coefficients and the output of an instrumented bubble level mounted onthe apparatus, the signals in both channels are corrected for wobble. Finally, the low-frequency signal is corrected for atmospheric inhomogeneity by subtracting a times thehigh-frequency signal. The a is the ratio of the atmospheric signal in the two channels;in this experiment a was determined to be1 V(HF)- = 53. 25.a V(LF) atmIt turned out that no other corrections were needed. One of our major worries hadbeen that stratospheric wind shear would cause temperature gradients across theradiometer. To our surprise, the differential temperature variation of the horns and-2,mirrors was less than 10-2 K throughout a rotation. The emissivities of both horns andmirrors were measured during the flight by heating and the result was less than 5 X 10- 2Figure VI-2 shows results of a Fourier analysis of the low-frequency data, taken in30 rotation blocks, at the rotation frequency and 3 harmonics. For the W componentthe cosine coefficient is positive if South is hot and the sine coefficient is positive if Eastis hot. The data are given in millivolts of radiometer output,-31 mV m 1.76 X0 3 OKR.The noise in the experiment is caused entirely by the detector and is Gaussian. Fora flight planned in June 1974, we have improved the detector by a factor of 3.The velocity of the Earth in the co-moving frame determined by the expansion of theuniverse would be detected as an anisotropy with a period equal to the rotation periodof the gondola. If P is the velocity divided by c and 0 is the angle between the zenithand the velocity, the relation between the radiometer output and p sin 0 is given by,.T (AI/AT)RJ .ATRJp sin 0 = 2 AV AV( ) = 1.5 AV(p).o (AI/AT)PL RJThe preliminary results of this flight are-3(p sin 0 )E- W = (0.92± 1. 12) X 10--3(p sin )N_S = (0. 49 ± 1. 74) X 10 .N-SCQPR No. 114

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