OPTIS – A Satellite test of Special and General Relativity

OPTIS has been proposed as a small satellite platform in a high elliptical orbit (apogee 40,000 km, perigee 10,000 km) and is designed for high precision tests of foundations of Special and General Relativity. The experimental set-up consists of two ultrastable Nd:YAG lasers, three crossed optical resonators (monolithic cavities), an ensemble of atomic clocks, an optical comb generator, laser tracking devices and a drag-free control system. OPTIS enables improved tests of (1) the isotropy and (2) constancy of the speed of light, (3) special relativistic time dilation, (4) the universality of the gravitational redshift by comparison of various clocks, can measure (5) the absolute value of the gravitational redshift, (6) the Lense–Thirring effect and (7) the perigee advance and (8) can make a test of a hypothetical Yukawa part in the gravitational potential. To avoid any influence from atmospheric drag, solar radiation, or Earth albedo, the satellite needs drag-free control to depress the residual acceleration down to 10⁻¹⁴ m/s² in the frequency range between 10⁻² and 10⁻³ Hz. Precise thermal control must be used to stabilize the cavity temperature to within one part in 10⁷ at time scales of 100 s and to one part in 10⁵ on the orbit time scale.     

On the information contents and regularisation of lunar gravity field solutions

Till the present day the recovery of the lunar gravity field from satellite tracking data depends in a crucial way on the level and method of regularisation. With Earth-based tracking only, the spatial data coverage is limited to only slightly more than 50% and the inverse problem remains severely ill-posed. The development of global gravity models suitable for precise orbit modeling as well as geophysical studies therefore requires a significant level of regularisation, limiting the solution power over the far-side where no gravity information is available. Unconstrained solutions, within the framework of global harmonic base functions, are only possible for very low degrees (< 10). Any significant change to this situation is only to be expected when global satellite-to-satellite tracking data of high quality becomes available early in the next decade. Yet, a rigorous analysis of the impact of the chosen method and level of regularisation is lacking. Most gravity models employ a Kaula-type signal smoothness constraint of 15 × 10⁻⁵ /l², which allows a good overall data fit as well as a smooth field over the far-side. Furthermore, a geographical type of constraint has been suggested, where surface accelerations have been introduced in areas of no data coverage. Modern numerical methods, on the other hand, offer direct tools and search mechanisms for the optimal level of regularisation. This paper presents a study of Tikhonov-type regularisation of lunar gravity solutions, with emphasis on the so-called L-curve and quasi-optimality methods for regularisation parameter estimation. Furthermore, new quality measures of lunar gravity solutions are presented, which account for the bias introduced by the regularisation.     

Spin axis orientation of Ajisai determined from Graz 2 kHz SLR data

The Graz 2 kHz Satellite Laser Ranging (SLR) measurements allow determination of the spin axis orientation of the geodetic satellite Ajisai. The high repetition rate of the laser makes it possible to determine the epoch time when the laser is pointing directly between two corner cube reflector (CCR) rings of the satellite. Identification of many such events during a few (up to 3) consecutive passes allows to state the satellite orientation in the celestial coordinate system. Six years of 2 kHz SLR data (October 2003–October 2009) delivered 331 orientation values which clearly show precession of the axis along a cone centered at 14^h56^m2.8^s in right ascension and 88.512° in declination (J2000.0 celestial reference frame) and with an half-aperture angle θ of 1.405°. The spin axis precesses with a period of 117 days, which is equal to the period of the right ascension of the ascending node of Ajisai’s orbit. We present a model of the axis precession which allows prediction of the satellite orientation – necessary for the envisaged laser time transfer via Ajisai mirrors.     

The physical properties of the “local fluff”

Observations of interstellar gas in front of stars near the Sun are briefly reviewed to obtain for the properties of the local fluff: n−0.1 cm⁻³, n_e^≤ 0.003 cm⁻³, T−11, 500 °K, and B−3−5 μG. The velocity vector obtained from He° λ584 backscattered data (V, 1, b) = (−25 km s⁻¹, 3°, +17°) appears to adequately describe the heliocentric upwind velocity vector for the local fluff.     

GRASP — A gamma-ray astronomy mission dedicated to the fine spectroscopy and positioning of celestial gamma-ray sources

The GRASP Mission - Gamma Ray Astronomy with Spectroscopy and Positioning - will be the first high resolution spectral imager to operate in the gamma-ray region of the spectrum. The instrument covers the photon energy range from approximately 15 keV to more than 100 MeV. A combination of discrete germanium solid state devices and scintillation counters form a position sensitive gamma-ray detection matrix which is operated in conjunction with a coded aperture mask to create arc minute images of the gamma-ray sky with a spectral resolution of typically λ/Δλ ∼1000. The use of a coded mask with a ‘zoom’ facility will permit the combination of field of view and angular resolution to be adjusted to suit the scientific aims of each observation. The respective continuum and line sensitivities will be typically 10⁻⁸ph cm⁻² s⁻¹ keV⁻¹ and 3 10⁻⁶ cm⁻² s⁻¹ for point sources of gamma-rays with photon energies close to 1 MeV.     

Preliminary study on migration pattern of the Tibetan antelope (Pantholops hodgsonii) based on satellite tracking

The spatial and temporal patterns of the endangered Tibetan antelope or chiru (Pantholops hodgsonii) have been studied using satellite-based ARGOS platform transmitter terminal (PTT) tracking data. The data was obtained from the satellite tracking of two female Tibetan antelopes that were collared with satellite transmitters and have been tracked from August 2007 to April 2009.     

EXOSAT observations of two gamma-ray burst sources

EXOSAT observations of the 19 Nov 1978 and 25 Mar 1979b gamma bursters are presented, for the 0.02–2.5 keV energy range. No source was detected in either case, leading to temperature upper limits for the neutron stars assumed to be present of 10⁵–10⁶ °K. Polar cap accretion rates are constrained to values of 10⁻¹²–10⁻¹⁸ M_⊙/y km². The EXOSAT non-detection of the source discovered by the Einstein satellite in the 19 Nov 1978 error box may be explained if the burster is more distant than about 1.5 kpc.     

Gamma-ray observations of explosive nucleosynthesis products

In this review I discuss the various γ-ray emission lines that can be expected and, in some cases have been observed, from radioactive explosive nucleosynthesis products. The most important γ-ray lines result from the decay chains of ⁵⁶Ni, ⁵⁷Ni, and ⁴⁴Ti. ⁵⁶Ni is the prime explosive nucleosynthesis product of Type Ia supernovae, and its decay determines to a large extent the Type Ia light curves. ⁵⁶Ni is also a product of core-collapse supernovae, and in fact, γ-ray line emission from its daughter product, ⁵⁶Co, has been detected from SN1987A by several instruments. The early occurrence of this emission was surprising and indicates that some fraction of ⁵⁶Ni, which is synthesized in the innermost supernova layers, must have mixed with the outermost supernova ejecta.Special attention is given to the γ-ray line emission of the decay chain of ⁴⁴Ti (⁴⁴Ti → ⁴⁴Sc → ⁴⁴Ca), which is accompanied by line emission at 68, 78, and 1157 keV. As the decay time of ⁴⁴Ti is ∼86 yr, one expects this line emission from young supernova remnants. Although the ⁴⁴Ti yield (typically 10⁻⁵–10⁻⁴M_⊙) is not very high, its production is very sensitive to the energetics and asymmetries of the supernova explosion, and to the mass cut, which defines the mass of the stellar remnant. This makes ⁴⁴Ti an ideal tool to study the inner layers of the supernova explosion. This is of particular interest in light of observational evidence for asymmetric supernova explosions.The γ-ray line emission from ⁴⁴Ti has so far only been detected from the supernova remnant Cas A. I discuss these detections, which were made by COMPTEL (the 1157 keV line) and BeppoSAX (the 68 and 78 keV lines), which, combined, give a flux of (2.6 ± 0.4 ± 0.5) × 10⁻⁵ ph cm⁻² s⁻¹ per line, suggesting a ⁴⁴Ti yield of (1.5 ± 1.0) × 10⁻⁴M_⊙. Moreover, I present some preliminary results of Cas A observations by INTEGRAL, which so far has yielded a 3σ detection of the 68 keV line with the ISGRI instrument with a flux that is consistent with the BeppoSAX detections. Future observations by INTEGRAL-ISGRI will be able to constrain the continuum flux above 90 keV, as the uncertainty about the continuum shape, is the main source of systematic error for the 68 and 78 keV line flux measurements. Moreover, with the INTEGRAL-SPI instrument it will be possible to measure or constrain the line broadening of the 1157 keV line. A preliminary analysis of the available data indicates that narrow line emission (i.e., Δv < 1000 km s⁻¹) can be almost excluded at the 2σ level, for an assumed line flux of 1.9 × 10⁻⁵ ph cm⁻² s⁻¹.     

Supernova remnant 1987A: The latest report from the Chandra X-ray Observatory

We continue monitoring supernova remnant (SNR) 1987A with the Chandra X-ray Observatory. As of 2004 January, bright X-ray spots in the northwest and the southwest are now evident in addition to the bright eastern ring. The overall X-ray spectrum, since 2002 December, can be described by a planar shock with an electron temperature of ∼2.1 keV. The soft X-ray flux is now 8 × 10⁻¹³ ergs cm⁻² s⁻¹, which is about five times higher than four years ago. This flux increase rate is consistent with our prediction based on an exponential density distribution along the radius of the SNR between the HII region and the inner ring. We still have no direct evidence of a central point source, and place an upper limit of L_X = 1.3 × 10³⁴ ergs s⁻¹ on the 3–10 keV band X-ray luminosity.     

Gamma-ray burst detection capabilities of comptel

The imaging gamma-ray telescope COMPTEL, capable of detecting gamma rays in the 1 to 30 MeV range, is one of four experiments onboard NASA's Gamma-Ray Observatory GRO. Besides its primary objectives COMPTEL will contribute to the understanding of cosmic gamma-ray bursts. Summarising, COMPTEL localises bursts (S (E > 1 MeV) ≥ 2.10⁻⁶ erg/cm²) within 1 sr FOV to better than 1° at medium gamma-ray energies, measures continuum energy spectra in the range 0.1 MeV to 20 MeV with fluence S ≥ 6.9 10⁻⁷ erg/cm² (5σ, E≥100 keV), measures gamma-ray lines with detector resolution 9.6% (at 0.5 MeV) and 7.0% (at 1.5 MeV) and determines time histories of both gamma-ray line and continuum emission with t ≥ 0.1 sec resolution.     

GDP spatialization in Ningbo City based on NPP/VIIRS night-time light and auxiliary data using random forest regression

Accurate spatial distribution information on gross domestic product (GDP) is of great importance for the analysis of economic development, industrial distribution and urbanization processes. Traditional administrative unit-based GDP statistics cannot depict the detailed spatial differences in GDP within each administrative unit. This paper presents a study of GDP spatialization in Ningbo City, China based on National Polar-orbiting Partnership (NPP)/Visible Infrared Imaging Radiometer Suite (VIIRS) night-time light (NTL) data and town-level GDP statistical data. The Landsat image, land cover, road network and topographic data were also employed as auxiliary data to derive independent variables for GDP modelling. Multivariate linear regression (MLR) and random forest (RF) regression were used to estimate GDP at the town scale and were assessed by cross-validation. The results show that the RF model achieved significantly higher accuracy, with a mean absolute error (MAE) of 109.46 million China Yuan (CNY)·km⁻² and a determinate coefficient (R² = 0.77) than the MLR model (MAE = 161.8 million CNY·km⁻², R² = 0.59). Meanwhile, by comparing with the estimated GDP data at the county level, the town-level estimated data showed a better performance in mapping GDP distribution (MAE decreased from 115.1 million CNY·km⁻² to 74.8 million CNY·km⁻²). Among all of the independent variables, NTL, land surface temperature (T_s) and plot ratio (PR) showed higher impacts on the GDP estimation accuracy than the other variables. The GDP density map generated by the RF model depicted the detailed spatial distribution of the economy in Ningbo City. By interpreting the spatial distribution of the GDP, we found that the GDP of Ningbo was high in the northeast and low in the southwest and formed continuous clusters in the north. In addition, the GDP of Ningbo also gradually decreased from the urban centre to its surrounding areas. The produced GDP map provides a good reference for the future urban planning and socio-economic development strategies.     

High-density and high-temperature molecular gas around the AGN in M51

We investigated the physical properties of molecular gas in the nuclear region of M51 (Seyfert 2). We obtained an aperture synthesis ¹³CO(J = 1 − 0) image using the Nobeyama Millimeter Array (NMA), and compared it with NMA ¹²CO(J = 1 − 0) and HCN(J = 1 − 0) maps at similar spatial resolutions. Within a radius of 180 pc from the center, the ¹³CO(1 − 0) integrated intensity was found to be 3 times weaker than that of HCN(1 − 0). Large-Velocity-Gradient (LVG) calculations suggest that the observed high HCN(1 − 0)/¹³CO(1 − 0) intensity ratio would arise from dense (n_H2 ∼ 10⁵ cm⁻³) and hot (T_kin ≳ 300 K) molecular clouds in the nuclear molecular disk. We also observed in the ¹²CO(1 − 0), (3 − 2), ¹³CO(1 − 0), and (3 − 2) lines using the Nobeyama 45m and JCMT 15m telescopes. We detected weak ¹³CO lines as well as strong ¹²CO lines. The LVG calculations assuming a two-component model suggest that there is a large amount of low-density (n_H2 ∼ 3 − 6 × 10² cm⁻³), low-temperature (T_kin ∼ 20 – 50 K) gas, and a small amount of high-density (n_H2 ≳ 10⁴ cm⁻³), high-temperature (T_kin ≳ 500 K) gas. The existence of the high-density and high-temperature component, although having a quite small beam filling factor, supports the aperture synthesis observation results mentioned above. Since this dense, hot gas is located in the nuclear molecular disk around the Active Galactic Nucleus (AGN), it may be heated by the strong X-ray radiation and/or by the shock induced by the radio jet.     

Depth dose distribution measurement on the Foton-M2 bio-satellite by TLD technique

In the framework of “Biology and Physics in Space” project of the European Space Agency (ESA), a returning satellite, Foton-M2, carried an open-to-space sample holder outside of the satellite body, called as BIOPAN-5, loaded with exo-biological experiments and dosemeters for RAdiation DOsimetry (RADO). One of the RADO experiments (Teflon – TLD) was dedicated to dose distribution measurements of the cosmic radiation by thermo-luminescent (TL) technique. It was found that the maximum surface absorbed dose rate, averaged over the first ∼8 mg/cm² thickness, was ∼2 Gy/d and showed a location dependence due the shading effect of the satellite construction elements. The dose rate decreased nearly by 3 orders of magnitude below 500 mg/cm².     

Registration of wave disturbances over Yakutia

The results of investigations of wave processes with periods 2 hours on their influence and on the night sky airglow intensity are given. The observations were carried out by multichannel spectrometer for three seasons of 1985–1988 at the optical testing ground Maimaga (γ = 63°N; λ = 129, 5°E). The synchronous detection of two and sometimes of three emissions of night sky airglow yielded the oppotunity to track a vertical travel of waves and to estimate their parameters. In most cases the waves propagate upward, i.e. the sources of waves were below mesosphere. The estimated vertical velocity change within 0,9-3,3 m/s and vertical wave length - within 18–85 km. A horizontal velocity varies from 83 to 330 m/s. The wave activity (the occurence frequency) and their amplitude in winter is higher than in spring. The estimated energies transfered by waves to the upper atmosphere are in winter 3.8·10⁻³ W/m² and in spring 2.7·10⁻³ W/m².     

Some features of the interplanetary disturbances in the post-solar maximum year period

Features of strong interplanetary disturbances (including 14 shock waves) are considered by the solar wind plasma measurements onboard the PROGNOZ-8 satellite. Examination of large-scale structure of the plasma fluxes enabled us to discover extreme values of proton temperature (～10⁶K) and density (～10²cm^?3) in some cases.The energy transferred by the interplanetary shock waves (10³¹–10³² erg) and their deceleration are estimated. Determination of the plasma parameter jumps for protons and α-particles at the shock front made it possible to estimate the potential barrier (40–400V) depending on magnetosonic Mach number.     

Particle and Joule heating of the neutral polar thermosphere in cusp region using Atmosphere Explorer-C satellite measurements

Simultaneous measurements taken by instruments on the Atmosphere Explorer - C satellite were used to compare electron and proton particle energy deposition, Joule heating, and neutral density perturbations in the region of the cusp.Altitude profiles of Joule heating, electron energy deposition, and electron density are derived using measurements taken by the satellite as input to a computer model. Electric fields are calculated using ion drift measurements. Figures are presented for a representative orbital pass.A peak Joule heating rate of 0.059 Wm^?2 occurred in the cusp region with a peak of 0.025 Wm^?2 in the evening auroral electrojet. Peak volume heating rates corresponding to these regions were 1.4 × 10^?6Wm^?3 and 7.10^?7 Wm^?3, both occurring at an altitude of 115 km. Particle energy deposition was about an order of magnitude less than Joule heating. Large neutral density perturbations are related to regions of heating.     

Observations of galactic gamma-radiation with the SMM spectrometer

Preliminary results from the SMM γ-ray spectrometer indicate the detection of a constant source of 0.511 MeV annihilation radiation from the Galaxy. This source was observed in each of 5 years as the region of the Galactic center passed through the instrument's ∼120° field of view. Any year-to-year variability appears to be less than 30%. The measured intensity of the source is model dependent: for a point source at the center the average flux is (1.6 - 2.9) × 10⁻³ γ cm⁻² s⁻¹; for a distributed source following the Galactic CO emission the flux is (1.4 - 2.7) × 10⁻³ γ cm⁻² s⁻¹ rad⁻¹ (uncertainty is due primarily to systematic errors). It is likely that the radiation comes from a diffuse source and is not associated with the reported compact source at the Galactic center. We have no new information to report on the distribution of ²⁶Al γ-rays. Upper limits of 1.5 × 10⁻³ γ cm⁻² s⁻¹ are placed on Doppler-shifted lines from SS433.     

Selenodetic experiments of SELENE: Relay subsatellite,differential VLBI,and laser altimeter

Since 1960s, the gravitational potential of the Moon has been extensively studied from Doppler tracking data between a ground station and spacecraft orbiting in front of the Moon (e. g., Lorell and Sjogren, 1968; Bills and Ferrari, 1980; Konopliv et al., 1993; Lemoine et al., 1997). Because direct radio communication is interrupted while spacecraft is orbiting behind the Moon, however, the coverage of tracking data has been limited mostly to the nearside of the Moon so far. In order to compensate for such lack of tracking data, we propose satellite-to-satellite Doppler measurement by using a relay subsatellite in Japanese mission to the Moon in 2003. A complete coverage of Doppler tracking from an orbiter at sufficiently low altitude will significantly improve lunar gravity model and will contribute for future geophysical study of interior and tectonics on the Moon. Further, we propose differential VLBI experiment between the subsatellite and a propulsion module landed on the surface of the Moon. The differential VLBI is about 10 times more accurate than conventional Doppler measurement for long-wavelength gravity field. Besides, differential VLBI is sensitive to the displacement perpendicular to the line of sight. Thus the VLBI experiment provides precise estimates of the lunar gravity potential at low degree. The last proposal for selenodetic experiments is a laser altimeter. Global topography model has been already developed from the analysis of Clementine LIDAR data (Zuber et al., 1994), but it is suggested that the model includes appreciable anisotropy between NS and E-W directions due to highly eccentric orbit of Clementine spacecraft (Bills and Lemoine, 1995). The laser altimeter experiment from an orbiter in nearly circular orbit will provide a new reference for the isotropic lunar topography model.     

Spectroscopic study of plasma parameters for solar active regions and flares

Results are given of the study of active regions and flares by a high resolution Mg XI ion spectra obtained aboard rockets and a satellite. It is shown that there is a noticable similarity in the physical conditions in the plasma of active regions and flares. Plasma of both sources consists okf a thermal component with the temperature T ～ 2.?3.10⁶K for active regions and T ～ 1.5?2.5.10⁷K for flares and in both cases of a relatively small number (～ 1–5%) of suprathermal electrons with an energy E ～ 3–6 kT.     

Satellite evidence of harmful algal blooms and related oceanographic features in the Bohai Sea during autumn 1998

Harmful algal blooms (HABs) are truly global marine phenomena of increasing significance. Some HAB occurrences are different to observe because of their high spatial and temporal variability and their advection, once formed, by surface currents. A serious HAB occurred in the Bohai Sea during autumn 1998, causing the largest fisheries economic loss. The present study analyzes the formation, distribution, and advection of HAB using satellite SeaWiFS ocean color data and other oceanographic data. The results show that the bloom originated in the western coastal waters of the Bohai Sea in early September, and developed southeastward when sea surface temperature (SST) increased to 25–26 °C. The bloom with a high Chl-a concentration (6.5 mg m⁻³) in center portion covered an area of 60 × 65 km². At the end of September, the bloom decayed when SST decreased to 22–23 °C. The HAB may have been initiated by a combination of the river discharge nutrients in the west coastal waters and the increase of SST; afterwards it may have been transported eastward by the local circulation that was enhanced by northwesterly winds in late September and early October.