Radar measurements of Martian topography and surface properties: The 1971 and 1973 oppositions

The Goldstone radar system was used at a wavelength of 12.6 cm to probe the Martian surface during the 1973 opposition. Measurements of range and reflected power were made at least weekly between July 12 and November 24. Surface cells isolated by the radar system were 8 km E-W × 110 km N-S. Altitudes were calculated from signal time delays measured relative to a triaxial ellipsoid and were combined with altitudes measured during the 1971 opposition. Contours of constant altitude were calculated at 200 m intervals between latitudes ?14° and ?22°. These contours are presented in conjunction with Mars charts derived from Mariner 9 television pictures. Reflected power was measured at angles of incidence between ?5° and +5°. These measurements were combined with those obtained during the 1971 opposition. Predictions of the reflected power versus the angle of incidence were calculated from the exponential surface model of Hagfors. The predictions were fit to the data in a least-squares sense, using a nonlinear iterative procedure, to yield estimates of surface roughness and reflectivity. The smoother regions exhibit a typical reflectivity of 8.2%. A tendency for the reflectivity to decrease with increasing roughness was observed.     

Monochromatic intensity measurements of selected areas of lunar surface for possible investigations

Absolute photoelectric intensity measurements of 104 selected lunar regions are given in five interference filters 4035 Å, 4765 Å, 5538 Å, 6692 Å and 7922 Å. Among these regions, eighteen lunar regions have been measured repeatedly for several phase angles between +86° and ?43°. They include observations made very close to the full Moon. A catalogue has been compiled to serve as a basin for possible investigations of colour contrasts of lunar grounds, variation of the ratio of reflectivity with wavelengths and phase angles for morphological studies. The study can be extended for the brightness phase variation, opposition effect and radiance factors at zero phase in five colours.     

Characteristics of the surface and features of the propagation of radio waves in the atmosphere of Venus from data of bistatic radiolocation experiments using Venera 9 and 10 satellites

The results of the investigation of two regions of Venus by bistatic radiolocation are presented. The experiments were carried out at wavelength λ₀ = 32 cm. Maps of the distribution of reflectivity were obtained and characteristics of the relief, dielectric permittivity, soil density, and refraction attenuation in the atmosphere were measured. The value of the dispersion of small-scale slopes in the observed regions, γ, varies between 0.4 and 2.2°. There are some features on the reflectivity maps. Some of these features may correspond to mountain slopes with values in the range 2 to 8°. Corresponding changes of relief heights are contained in the interval 0.8 to 2.6 km. The features are found within the region (in the venerocentric IAU system): ?26.5 to 25.0° latitude and 220.0?239.2° longitude. One area was revealed with large values of permittivity in the range 6.5–7.5, and soil density between 2.7 and 2.9 g/cm³. The center of this area is located at ?23.5° latitude and 230.4° longitude. The extent of this region is 80 km. The results of measurements of the refraction angle and the refraction attenuation of radio waves are in good agreement with the parameters of the atmosphere of Venus received from the Soviet landers.     

Radar studies of the Martian surface at centimeter wavelengths: The 1975 opposition

The Goldstone radar system was operated at wavelengths of 3.5 and 12.6 cm to probe the Martian surface during the 1975 opposition. Regions studied in detail by range-Doppler techniques are Syrtis Major, Sinus Meridiani, and the crater Schiaparelli. Average rms slopes of 1.6° and 1.1° were measured in Syrtis Major at 3.5 and 12.6 cm, respectively, while the average reflectivity was 0.064 ± 0.02 at both wavelengths. No wavelength dependence of surface roughness was seen in Sinus Meridiani, where rms surface slopes averaged 1.8° and the reflectivity was 0.08 ± 0.02. The regions around Schiaparelli were probed at a 12.6-cm wavelength. The echo from the bottom of the crater was undetectable. Hence _ρ0C < 25, where _ρ0 is the reflectivity and C is the Hagfors roughness parameter. Operating at 3.5 cm during May and June of 1976, 149 continous-wave echo spectra were obtained near latitude 18°, sampling most longitudes including the early Viking landing sites A1 and A2. The average total radar cross section is 4.8% of the geometrical cross section. The diffuse component was estimated to be 1.9%, leaving 2.9% to the average quasi-specular component. The average rms slope is 4.1°. Six spectra obtained at site A1 indicate that rms slopes are 5 to 9° between latitudes 17 and 19°. Three spectra obtained at s site A2 indicate an rms slope of 3.9°.     

Green corona emission,calcium plage activity and solar sector magnetism

The relationship between coronal green line emission and solar sector magnetism has been studied statistically for the years 1965–1969. This period includes the rising portion and the maximum phase of solar cycle no. 20. In the years around solar maximum the results suggest the existence of longitudinal magnetic arcades at the solar sector boundaries. The arcades extend from at least 50°N to 50°S and are flanked by north-south oriented coronal holes about 90° apart. In the rising portion of the cycle the general picture consists of a high green line intensity structure to the west of the boundary and a region of low intensity several days wide to the east of it.Analyses of the calcium plage distribution in the years 1962–1969 show that, on the average, there is a tendency for the plage activity to peak near the sector boundaries. It is further concluded that the activity distribution suggested by Wilcox (1971a, b) is not typical of the behaviour of solar activity relative to the sector boundaries.     

Variations in air density,satellite drag coefficient and atmospheric rotation rate from analysis of the orbit of 1966-92D

Variations in air density, the satellite drag coefficient, and the atmospheric rotation rate at 60°S lat and 120–130 km height during the period September 1968–June 1969 have been determined from analysis of the high-eccentricity orbit of the 4th Molyniya 1 upper-stage rocket body, 1966-92D. The results show good correlation between density increases and strong geomagnetic activity, although solar flares of equal geomagnetic index value do not consistently produce density changes of equal magnitude. A 30 per cent semi-annual variation was observed, but there was no indication of the 50 per cent lower thermosphere seasonal-latitudinal variation that was predicted from the CIRA 1972 atmosphere. The satellite drag coefficient was observed to begin decreasing with height at an altitude where the molecular mean free path, λ, was twice the satellite's length. The coefficient decreased to a value approaching 1.0 as the satellite's perigee height fell below the altitude where λ was one-half the length. A mean atmospheric rotation rate of 1.1 ± 0.1 Earth rot/day was obtained for the last 20 days of decay. However, variations were observed with west-to-east wind speeds of ?100 m/sec measured for a local time of 13 hr.     

Mariner 9 ultraviolet spectrometer experiment: Observations of ozone on Mars

The Mariner 9 Ultraviolet Spectrometer has observed the 2550 Å ozone spectral absorption feature on Mars. This absorption was previously detected in the south polar region by Mariner 7 in 1969. Mariner 9 did not observe ozone at any time in the equatorial region, nor at the south polar cap during its summer season. However, ozone was found in the north polar region beginning at a latitude of 45°N and extending northward. Ozone later appeared in the southern hemisphere southward of 50°S as the Mars autumnal equinox approached. The presence of ozone on Mars seems to be coupled to the water vapor content of its atmosphere.     

Electron temperature models of the thermosphere to 1100 km based on ESRO-4 measurements

Measurements of thermospheric electron temperatures at altitudes in the range 250–1100 km, made with a Langmuir probe carried on the polar-orbiting satellite ESRO-4, have been used to derive model functions of electron temperature in terms of altitude, magnetic latitude and local time for the periods November 1972 to June 1973 and March to October 1973. The technique used to compute the coefficients of the model functions is described, and the model electron temperatures are compared with those obtained from similar instruments on the Ariel-1 satellite in 1962 and the ESRO-1A satellite in 1968–1969, and from ground-based observatories. The models reproduce the major features of topside electron distributions viz. mid-day temperatures exceeding midnight temperatures by about 500 K, dawn enhancement leading to peak temperatures greater than mid-day values particularly around 50° magnetic latitude, and temperatures increasing with altitude at all latitudes and with latitude at all altitudes. The daytime mid-latitude temperature is used to complete a series of observations by various techniques over a solar cycle and thereby to confirm the sense and degree of solar cycle control on the thermospheric electron temperature predicted by theoretical considerations.     

Topography and radar scattering properties of Mars

High-resolution radar observations of Mars at a wavelength of 3.8 cm have been carried out at the Haystack Observatory for a period of about 6 months surrounding the 1971 opposition. The relative surface height variation with longitude over a band of Martian latitudes between about ?14° and ?22° has been derived from these observations with an error of about 75m in the most favorable cases. At ?14° latitude, the dielectric constant was found to increase steadily from about 1.7 at 70°W to about 5.0 at 110°W. Over the same interval the rms surface slopes vary from 2° to 1°. The mean equatorial radius of Mars as determined from the combined radar data of 1967, 1969 and 1971 was found to be 3394 ± 2km.     

Observations of Venus water vapor over the disk of Venus: The 1972–1974 data using the H2O lines at 8197 Å and 8176 Å

The Venus water vapor line at 8197.71 Å has been monitored at several positions on the disk of Venus and at phase angles between 21° and 162°. Variations in the abundance have been found with spatial location, phase angle and time. During the 1972–1974 period, the total two-way absorption has varied from less than 1 to 77 μm of water vapor. The dependence on phase angle indicates 20 to 50 μm over the disk between 30° and 110° and small, but detectable amounts present during the rest of the observations. The spatial distribution with respect to the intensity equator is uniform with no location on the disk having systematically a higher or lower abundance. Comparisons made between the water vapor abundandances and the CO₂ abundances determined from near-simultaneous observations of CO₂ bands at the same positions on the disk of Venus show no correlation for the majority of the samples.     

Beobachtungsergebnisse der Berliner Arbeitsgemeinschaft für veränderliche Sterne e.V. (BAV)

In this 10th compilation of BAV results of observations are given from the year 1972 and some from the year 1969 for 187 observed minima of 50 eclipsing binaries, 84 maxima of 18 RR Lyrae- and δ Cephei-stars, 123 results of 55 Mira stars and 85 results of 15 RV Tauri-stars and irregular variables.     

Ultraviolet observations of Mars made by the orbiting astronomical observatory

Ultraviolet albedos of Mars in the region γγ2000–3600 Å are discussed. When the reflectivity due to the known amount of CO₂ on Mars is accounted for, the remaining reflectivity may be used to set an upper limit for the surface albedo. The result disagrees qualitatively with published ultraviolet reflectivities of limonite and carbon suboxide. An alternate interpretation of the observations leads to the conclusion that CO₂ comprises at least 60% of the molecular atmosphere of Mars, assuming the remainder to be argon. A comparison of the OAO results with 1969 Mariner ultraviolet data reveals some important areas of conflict.Attempts to detect Mars at wavelengths less than γ2000 Å were unsuccessful, with only very high upper limits being set.     

Analysis of the orbit of 1970-97b (cosmos 378 rocket)

Cosmos 378 rocket, 1970-97B, entered orbit on 17 November 1970, with orbital inclination 74.0°, period 105 min and perigee height 230 km, and decayed on 30 September 1972 after 683 days in orbit. The RAE computer program PROP was used, with more than 1900 observations from 64 stations, to determine the orbit at 39 epochs between February 1971 and September 1972.The main aim of the analysis was to determine the atmospheric rotation rate from the decrease in orbital inclination, which was determined with a mean standard deviation of 0.0010° and a best standard deviation of 0.0003°. After removal of relevant perturbations, analysis of the variation in inclination between July 1971 and April 1972 yields the surprisingly low average atmospheric rotation rate of 0.75 ± 0.05 rev/day, at a mean height of 250 km. The local time at perigee is however strongly biassed towards daytime values (07–16 hr), so the results lend support to the picture of east-to-west winds by day and west-to-east winds by night.Values of scale height are obtained by analysis of the change in perigee height.     

The intensity variation of the atomic oxygen red line during morning and evening twilight on 9–10 April 1969

During the evening of 9 April and the morning of 10 April 1969, the twilight zenith intensity of the atomic oxygen red line OI(³P-¹D) at 6300 Å was measured at the Blue Hill Observatory (42°N, 17°W). At the same time incoherent scatter radar data were being obtained at the Millstone Hill radar site 50 km distant. We have used a diurnal model of the mid-latitude F-region to calculate the ionospheric structure over Millstone Hill conditions similar to 9–10 April 1969. The measured electron temperature, ion temperature, and electron density at 800 km are used as boundary conditions for the model calculations. The diurnal variation of neutral composition and temperature were obtained from the OGO-6 empirical model and the neutral winds were derived from a semiempirical three-dimensional dynamic model of the neutral thermosphere. The solar EUV flux was adjusted to yield reasonable agreement between the calculated and observed ionospheric properties.This paper presents the results of these model computations and calculations of the red line intensity. The 6300 Å emission includes contributions from photoelectron excitation, dissociative recombination, Schumann-Runge photodissociation and thermal electron impact. The variations of these four components for morning and evening twilight between 90–120° solar zenith angles, and their relative contributions to the total 6300 Å emission line intensity, are presented and the total is compared to the observations. For this particular day the Schumann-Runge photodissociation component, calculated using the solar fluxes tabulated by Ackermann (1970), is the dominant component of the morning twilight 6300 Å emission. During evening twilight it is necessary to utilize a lower O₂ density than for the morning twilight in order to bring the calculated and observed 6300 Å emission rates into agreement. The implication that there may be a diurnal variation in the O₂ density at the base of the thermosphere is discussed in the light of available experimental data and current theoretical ideas.     

The phase ratios of the color index: Mapping of two regions of the near side of the Moon

From the ground-based colorimetry performed for two surface regions of the near side of the Moon, images of the phase ratio of the color index C(600 nm/470 nm) have been built for the phase angles between 2° and 95°. It has been found that for phase angles smaller than α ∼ 40°–50°, the color index of the highlands grows with the phase quicker than that of the mare regions. For larger phase angles, α > 50°, a reverse situation is observed. The laboratory data on the spectrophotometry of the lunar samples confirm the peculiarities found in the phase dependence of color. The influence of multiple scattering on the phase dependence of the color of the mare and highland regions of the Moon are discussed.     

Analysis of the orbit of Cosmos 72 (1965-53B) near 15th-order resonance

Cosmos 72 (1965-53B) was launched on 16 April 1965 into a near-circular orbit with an average height of 570 km and inclination 56°. Over the years, the orbit has contracted slowly under the influence of air drag, and On 27 June 1972 passed through exact 15th-order resonance, when successive equator crossings are 24° apart in longitude and the ground track repeats after 15 rev. The orbit has been determined at seven epochs between April 1972 and February 1973, using the RAE orbit refinement program PROP, with 544 optical and radar observations: the average orbital accuracy is about 50 m in height and 0.0008° in inclination.For Cosmos 72 the change in inclination at 15th-order resonance, due to perturbations by 15th-order harmonics in the geopotential, is greater than for any satellite previously analysed— nearly 0.07°—and analysis of the change, using the seven PROP orbits and 45 U.S. Navy orbits, yields equations accurate to 4 per cent for the geopotential coefficients of order 15 and odd degree (15, 17, 19 …). A similar analysis of the variation in eccentricity gives less accurate equations for coefficients of order 15 and even degree (16, 18 …). The variations in right ascension of the node and argument of perigee have also been analysed.     

Pluto: New photometry and a determination of the axis of rotation

New photoelectric observations of Pluto, made in 1971, 1972, and 1973, show that the amplitude of the 6-day rotational light variation is larger (about 0.22 mag) and the mean magnitude is fainter $\text{(}\text{V}{}_0\text{= 15.1)}$ than during earlier periods of observation. The change is interpreted as due to a large obliquity of the rotational axis (probably larger than 50°). The phase coefficient of Pluto is about 0.05 mag/deg at 1° solar phase angle.     

Observation of sectored structure in the outer solar corona: Correlation with interplanetary magnetic field

Daily images of the white light corona between 3 and 10 R _? have been recorded by a coronagraph aboard the OSO-7 unmanned satellite since October 3, 1971. Images for the years 1972 and 1973 have been examined for persistent coronal forms. For most of 1972 there passed over the Sun's east limb a regular alternation of northern and southern streamers separated frequently by equatorial fans. The alternation suggested the rotation of a stable four-sectored coronal structure produced by two northern streamers, 180° apart in longitude and a similar pair of southern streamers shifted 90° in longitude. Toward the end of 1972 this structure evolved into a two-sectored structure produced by a single northern streamer and a single southern streamer separated by 180° in longitude. This structure remained stable during most of 1973. Transition from a northern to southern streamer, converted to Earth passage dates, correlated with the passage of a -/+ sector boundary in the interplanetary magnetic field. Conversely, the transition from a southern to northern streamer was associated with a +/-boundary passage. These correlations support the recent observations of Hansen et al. (1973).     

The orbit of 1972-05b in its final phase,with geophysical inferences

The polar orbit of HEOS 2 second-stage rocket, 1972-05B, has been determined on each of the final 16 days before its decay in September 1978, using the RAE orbit refinement program, PROP 6, with about 1360 observations. An accuracy of 30–70 m, both radial and across track, was achieved.Eleven values of density scale height have been determined from the decrease in perigee height, with a 2% error; seven of these values are within 6% of the CIRA 1972 reference-atmosphere values, the rms value being 4% higher than CIRA.The rotation rate of the upper atmosphere, A, was determined from the decrease in orbital inclination as Λ = 1.40 ± 0.05 rev day^?1; i.e. a strong west-to-east zonal wind of 160 ± 20m s^?1, at a mean height of about 240 km. The local time was 01–02 h; solar activity was high; and the latitude of perigee moved steadily from 10°N to 67°S.     

High-dispersion spectroscopic observations of Venus near superior conjunction: I. The carbon dioxide band at 7820 Å

Nine plates of the 7820 Å CO₂ band were taken in 1971. A curve-of-growth analysis of the CO₂ lines indicates a rotational temperature of 241 ± 2°K, with an average slope to the curve of growth of 0.60 ± 0.03. The Venus phase angle ranged from 7.2 to 10.7°. The equivalent widths of the 1971 data fall on a smooth curve fit through the 1969 data for this band; there does not appear to be any discontinuity in the phase curve at small phase angles.