Radar observations of Itokawa in 2004 and improved shape estimation

Abstract— We present June 2004 radar images of asteroid 25143 Itokawa (1998 SF36) that improve upon the longitude‐latitude coverage of images obtained in 2001 by Ostro et al. (2004) and use the 2001–2004 data to refine that paper's constraints on Itokawa's shape. The 2004 images, the first of the asteroid's southern side, look distinctly different from the 2001 images, revealing leading edges that are much more curved and rugged than the nearly convex leading edges seen at northern latitudes in 2001. Itokawa is shaped like a slightly asymmetrical, bent, lumpy ellipsoid with dimensions along the principal axes within 10% of 594 times 320 times 288 m. To illustrate the uncertainty space associated with shape reconstruction from images with suboptimal orientational coverage, we present two alternative three‐dimensional models of the object.     

Radar observations of asteroid 1580 Betulia

Radar observations of the asteroid 1580 Betulia, made at a wavelength of 12.6 cm, show a mean radar cross section of 2.2 ± 0.8 km² and a total spectral bandwidth of 26.5 ± 1.5 Hz. Combining our bandwidth measurements with the optically determined rotation period sets a lower limit to the asteroid's radius of 2.9 ± 0.2 km.     

Galilean satellites: 1976 radar results

Radar observations of the Galilean satellites, made in late 1976 using the 12.6-cm radar system of the Arecibo Observatory, have yielded mean geometric albedos of 0.04 ± , 0.69 ± 0.17, 0.37 ± 0.09, and 0.15 ± 0.04, for Io, Europa, Ganymede, and Callisto, respectively. The albedo for Io is about 40% smaller than that obtained approximately a year earlier, while the albedos for the outer three satellites average about 70% larger than the values previously reported for late 1975, raising the possibility of temporal variation. Very little dependence on orbital phase is noted; however, some regional scattering inhomogeneities are seen on the outer three satellites. For Europa, Ganymede, and Callisto, the ratios of the echo received in one mode of circular polarization to that received in the other were: 1.61 ± 0.20 1.48 ± 0.27, and 1.24 ± 0.19, respectively, with the dominant component having the same sence of circularity as that transmitted. This behavior has not previously been encountered in radar studies of solar system objects, whereas the corresponding observations with linear polarization are “normal.” Radii determined from the 1976 radar data for Europa and Ganymede are: 1530 ± 30 and 2670 ± 50 km, in fair agreement with the results from the 1975 radar observations and the best recent optical determinations. Doppler shifts of the radar echoes, useful for the improvement of the orbits of Jupiter and some of the Galilean satellites, are given for 12 nights in 1976 and 10 nights in 1975.     

Radar Observations of Asteroid 3908 Nyx

We report Doppler-only (cw) radar observations of basaltic near-Earth asteroid 3908 Nyx obtained at Arecibo and Goldstone in September and October of 1988. The circular polarization ratio of 0.75±0.03 exceeds ∼90% of those reported among radar-detected near-Earth asteroids and it implies an extremely rough near-surface at centimeter-to-decimeter spatial scales. Echo power spectra over narrow longitudinal intervals show a central dip indicative of at least one significant concavity. Inversion of cw spectra yields two statistically indistinguishable shape models that have similar shapes and dimensions but pole directions that differ by ∼100°. We adopt one as our working model and explore its implications. It has an effective diameter of 1.0±0.15 km and radar and visual geometric albedos of 0.15±0.075 and 0.16^+0.08_−0.05. The visual albedo supports the interpretation by D. P. Cruikshank et al. (1991, Icarus89, 1-13) that Nyx has a thermal inertia consistent with that of bare rock. The model is irregular, modestly asymmetric, and topographically rugged.     

A review of the assessments of the major fisheries resources in South Africa

The waters off South Africa's coastline boast a rich mix of commercially fished species. Quantitative assessments of these marine resources have developed from simple methods first applied in the 1970s, to models that encompass a wide range of methodologies. The more valuable resources have undergone regular assessments in recent decades, with frequencies closely related to the management approach employed for each fishery. Many of these assessments form the operating models used to simulation-test candidate management procedures. This paper provides a comprehensive review of the assessments of 11 of the most important fisheries resources in South Africa. Some assessments use simple biomass dynamics models, whereas others are a hybrid of age- and length-based models, each designed to model the specific characteristics of the resource and fishery concerned. Many of the assessments have been disaggregated by species/stock and/or area as related multispecies/stock/ distribution hypotheses have arisen. This paper explores the similarities and differences in the data available and the methods applied. The review indicates that, whereas the status of three of these resources cannot be estimated reliably at present, the status of six resources is considered to be reasonable to good, whereas that of abalone Haliotis midae and West Coast rock lobster Jasus lalandii remains poor.     

Arecibo radar observations of Phobos and Deimos

In November 2005, we observed the moons of Mars using the Arecibo 2380-MHz (13-cm) radar, obtaining a result for the OC radar albedo of Phobos (0.056±0.014) consistent with its previously reported radar albedo and implying an upper bound on its near-surface bulk density of . We detected Deimos by radar for the first time, finding its OC radar albedo to be 0.021±0.006, implying an upper bound on its near-surface density of , consistent with a high-porosity regolith. We briefly discuss reasons for these low radar albedos, Deimos' being possibly the lowest of any Solar System body yet observed by radar.     

Radar and photoelectric observations of asteroid 2100 Ra-Shalom

Results of 13-cm-wavelength radar observations and V-filter photoelectric observations of Ra- Shalom during its 1981 Aug–Sep apparition are reported. The radar data yid detections of echoes in the same sense of circular polarization as transmitted (i.e., the SC sense) as well as in the opposite (OC) sense. The estimate of the ratio of SC to OC echo power, μ_c = 0.14 ± 0.02, indicates that most, but certainly not all, of the backscattering is due to single reflections from surface elements that are fairly smooth at decimeter scales. The value obtained for the OC radar cross section on Aug 26 (1.2 ± 0.3 km²) is about three times larger than those obtained on Aug 23, 24, and 25. The echo bandwidth appears to be within about 1.5 Hz of 5.0 Hz on each date. The photoelectric data suggest a value, P_syn = 19.79 hr, for the synodic rotation period, and yield a composite lightcurve with two pairs of extrema. Combining this value for P_syn with a firm lower bound (4 Hz) on the maximum echo bandwidth yields a lower bound of 1.4 km on the maximum distance between Ra-Shalom's spin axis and any point on its surface.     

Proposal to Use MAGDAS/CPMN to Study the Equatorial Electrojet: A Philippine Contribution to the International Heliophysical Year

As a Philippine contribution to the International Heliophysical Year, we propose to use the MAGnetic Data Acquisition System/Circum Pan-Pacific Magnetometer Network (MAGDAS/CPMN), installed by the Space Environment Research Center (SERC), Kyushu University along the 210° magnetic meridian and the magnetic equator, to study the equatorial electrojet (EEJ) and counter electrojet (CEJ). Through this installation, it is made possible to observe geomagnetic field variations in real time. By utilizing this network of ground-based instruments, we hope to elucidate their regular day-to-day and seasonal variabilities and variations during magnetic storms and substorms. We also want to study the behavior of this ionospheric current system before, during, and after the occurrence of an earthquake.