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Coherently related S (2.3 GHz) and X band (8.4 GHz) signals transmitted from Voyager 1 and 2 have been used to probe the Jovian atmosphere during occultations of the spacecraft by Jupiter. The observations have yielded profiles in height of the gas refractivity, molecular number density, pressure, temperature, and microwave absorption in the troposphere and stratosphere of Jupiter at latitudes ranging from 0° to about 70°S. The data cover a pressure range from 1000 to 1 mbar over a height interval of 160 km. At the 1000‐mbar level, the temperature was 165±5 K, and the lapse rate was equal to the adiabatic value of 2.1 K/km, within the resolution of the measurements. The ammonia abundance in this region of the atmosphere was about 0.022±0.008%, in approximate agreement with the value derived from cosmic abundance considerations. The tropopause, which was detected near the 140‐mbar level, had a temperature of 110 K. Above the tropopause, the temperature increased with increasing altitude, reaching 160±20 K in the 10‐ to 1‐mbar region of the stratosphere. Significant horizontal density variations were detected in the stratosphere. This may imply a nonuniform temperature and aerosol distribution across the Jovian disk or high‐ and low‐pressure regions due to local atmospheric dynamics. The zenoid or gravity equipotential surface which best fits the 100‐mbar isobaric surface has an equatorial radius of 71,541±4 km and a polar radius of 66,896±4 km.

The S (2.3 GHz) and Xband (8.4 GHz) tracking links with the Viking orbiters have been used to study the atmosphere and topography of Mars at latitudes ranging from 74øS to 73øN. Data acquired in the troposphere show large meteorological changes with near-surface temperatures ranging from 150 ø to 250øK. Inversion layers were observed above the polar caps and in areas engulfed by dust storms. At other locations the temperature was found to decrease with increasing height at a rate equal to the dry adiabatic lapse rate. Seasonal pressure variations, presumably caused by changes in the polar frost deposits, were observed. At the 5-km altitude level the atmospheric pressure ranged from about 3.5 to 4.8 mbar during the Martian year. The measurements in the upper atmosphere yielded double-and single-layered electron density profiles on the sunlit and dark sides of the planet, respectively. A comparison of the Viking occultation data with earlier Mariner measurements has revealed that the temperature and plasma scale height of the ionosphere appear to be functions of solar activity. The topographic occultation data agree well with the elevation contours that are shown on U.S. Geological Survey map M 25M 3 RMC except in a few areas such as the south polar region and the Alba Patera region of Mars. In the south polar region the occultation measurements yielded surface elevations ranging from 3 to 6 km relative to the reference gravity equipotential surface or reference areoid. The terrain around Alba Patera was found to be 6 to 7 km high.• G. F. L. has officially changed his family name from Fjeldbo (as it appears in the reference list) to Lindal.When the spacecraft receiver lost phase lock during occultation by Mars, the downlink carrier frequencies were derived from a free-running crystal oscillator on board the vehicle. This operating mode was used during egress measurements and is called one-way tracking. Two-way ingress measurements provided the best occultation data, since all carrier frequencies in that tracking mode were derived from a stable earth-based reference oscillator. Both spacecraft revolved in their orbits around Mars in the same direction that the planet turned about its spin axis. At equatorial and intermediate latitudes the ingress and egressdata were therefore always acquired on the evening and morning side of the planet, respectively.The prime tracking stations involved in recording the signals from the Viking orbiters were the NASA deep space stations 14, 43, and 63, located in California, Australia, and Spain, respectively. A more detailed description of the radio instrumentation has been given in an earlier report [Michael et al., 1972]. DATA ANALYSISDuring the occultation of the Viking orbiters by the Martian atmosphere the carrier frequencies of the radio tracking links were perturbed due to refraction. As is described in our primary mission report, we utilize these frequency perturbations to determine the vertical distribution of the tropospheric gas refractivity and the ionospheric electron d...

During the flyby of Saturn by Pioneer 11 on September 1, 1979, radio occultation measurements of the ionosphere and upper neutral atmosphere were made near the terminator at latitudes 9.7 ø south and 11.6 ø south. The principal electron density peak of the ionosphere occurs at an altitude of about 1,800 km and has a magnitude of 11,400 cm -3, with a sharp lower peak of about 9,000 cm -3 at about 1,200 kin. The scale height above the main peak corresponds to an exosphere temperature of about 1150 K for an H + ionosphere. Ionization appears to extend to 30,000 kin, with a broad peak of magnitude 7,000 cm -3 at an altitude of about 14,500 kin, corresponding to the inner edge of the C ring. The low density of the lower portion of the ionosphere can probably be explained by ring shadowing and equatorial anomaly, and the relatively high densities about 30,000 kin, if real, could be explained if densities of ~ 103 e•ist at higher latitudes that are connected to the site of measurement by field lines and by plasmaspheric heating by the rings. In the neutral atmosphere, measurements were made to a pressure level of about 180 mbar, showing a temperature inversion region with a triple minimum. The temperature at the principal minimum at 60,344 km is 88 + 4 K at a pressure of 74 mbar, and there is a prominent minimum about 80 km above the principal one. Comparisons with the temperature structure derived from the infrared radiometer data (Ingersoll et al., this issue) suggest that the helium fraction in the Saturnian atmosphere is 10 + 4%. • to the spacecraft designers of the Pioneer project at NASA Ames Research Center and NASA/JPL (Jet Propulsion Laboratory) Deep Space Network, which made improvements in the ground receiving station radio systems that were more than sufficient to overcome the increased communication distanc•.A close flyby of Saturn necessarily brings the spacecraft into occultation by the planet and therefore provides an opportunity to probe its ionosphere and atmosphere with the signal from the spacecraft's communications link. The purpose of our experiment was to learn as much as possible about the structure of the electron density in the ionosphere and the temperature and pressure in the top layers of the neutral atmosphere within the limitations imposed by Pioneer's radio system and by the earth-Saturn-sun geometry at the time of encounter. The Pioneer 11 radio system employs a single S band (2.293 GHz) radio link for communication with the earth. Since only one frequency is available, the effects of charged particles cannot be isolated by means of the differen-tial Doppler technique, and so the frequency fluctuations caused by the ionosphere must be laboriously separated from the effects of oscillator drift, drifts introduced by orbital uncertainty, and the effects of interplanetary plasma fluctuations, which at the time of encounter were quite formidable because of the proximity of the earth-Saturn line to the sun. Spacecraft solar conjunction occurred only 10 days after encounter, and on encounter da...

Radio occultation measurements at S band (2.293 gigahertz) of the ionosphere and upper neutral atmosphere of Saturn were obtained during the flyby of the Pioneer 11 Saturn spacecraft on 5 September 1979. Preliminary analysis of the occultation exit data taken at a latitude of 9.5 degrees S and a solar zenith angle of 90.6 degrees revealed the presence of a rather thin ionosphere, having a main peak electron density of about 9.4 x 10/(3) per cubic centimeter at an altitude of about 2800 above the level of a neutral number density of 10(19) per cubic centimeter and a lower peak of about 7 x 10(3) per cubic centimeter at 2200 kilometers. Data in the neutral atmosphere were obtained to a pressure level of about 120 millibars. The temperature structure derived from these data is consistent with the results of the Pioneer 11 Saturn infrared radiometer experiment (for a helium fraction of 15 percent) and with models derived from Earth-based observations for a helium fraction by number of about 4 to 10 percent. The helium fraction will be further defined by mutual iteration with the infrared radiometer team.