Comparison of OClO nadir measurements from SCIAMACHY and GOME

The scanning imaging absorption spectrometer for atmospheric chartography was launched successfully onboard ENVISAT on March 1, 2002. It observes the solar radiation transmitted and backscattered from the atmosphere and reflected from the ground in nadir, limb and occultation viewing modes. Chlorine dioxide (OClO), an important indicator for stratospheric chlorine activation, can be measured in the UV spectral range by differential optical absorption spectroscopy (DOAS).

First results of the DOAS retrieval of OClO slant column densities from the SCIAMACHY nadir measurements are presented and compared to measurements of the global ozone monitoring experiment (GOME), which has successfully measured OClO since 1995. While SCIAMACHY operates in the same orbit, it measures ≈30 min earlier than GOME and has an increased spatial resolution (30 × 60 km² compared to 40 × 320 km² for GOME).     

Temporal and spatial stochastic behaviour of high-frequency slant tropospheric delays from simulations and real GPS data

In this paper, a turbulence theory-based simulation procedure for slant tropospheric delay variations is presented. Based on this procedure tropospheric delay variations are simulated for three different geometric scenarios. The stochastic behaviour of the generated time series is assessed in terms of temporal structure functions. It is shown that the temporal structure functions – in general – follow a 5/3 to 2/3 power-law behaviour. Deviations from this behaviour due to the complex interaction between varying observation geometry and atmospheric/turbulent conditions are discussed.     

Reducing biological contamination by a space suited astronaut: Laboratory and field test results from Aouda.X

As part of the “PolAres” research programme, we are investigating techniques to detect and reduce forward contamination of the Mars regolith during human exploration. We report here on the development of a spacesuit simulator-prototype dubbed “Aouda.X,” document the inability of current technology to produce a static charge sufficient to minimize dust transport on the suit, and present preliminary results employing laser induced fluorescence emission (L.I.F.E.) techniques to monitor fluorescent microspherules as biological contamination proxies.     

Numerical modeling and optimization of bundled fiber optic FTIR probes for spectroscopy of small targets

Fiber optic probes coupled to a Fourier Transform Infrared (FTIR) spectrometer allow sample analysis without the need to place the sample directly into the instrument. This is particularly attractive for spacecraft lander/rover applications where the additional mechanics, mass and cost associated with excavating and placing a small sample in a sample bay is not desirable. This paper uses numerical modeling to analyze fiber bundle array configurations and fiber numerical apertures to determine their light gathering efficiency and sample size as a function of probe-to-sample distance. The model was validated against experimental measurements for a selection of off the shelf fiber optic probes. The collection efficiency of a probe can be optimized by using a hexagonal packing method, and by using fibers with high numerical apertures. By increasing the numerical aperture of the fibers used in our model probes from 0.2 to 0.5, we were able to increase the collection efficiency of a seven fiber probe from 4.5% to 9.5%, with the peak collection efficiency corresponding to a spot size of diameter 3 mm.     

Adaptive Phased-Array Tracking in ECM using Negative Information

Target tracking with adaptive phased-array radars in the presence of standoff jamming presents both challenges and opportunities to the track filter designer. A measurement likelihood function is derived for this situation which accounts for the effect of both positive and negative contact information. This likelihood function is approximated a? a weighted sum of Gaussian terms consisting of both positive and negative weights, accounting for the positive and negative contact information. Additionally, recent theoretical results have been reported which have derived an accurate measurement error covariance in the vicinity of the jammer when adaptive beamforming is used by the radar to null the effects of the jammer. We compare the impact of using a likelihood function that accounts for negative contact information and the corrected measurement error covariance by comparing five Kalman filter-based trackers in five different scenarios. We show that only those track filters which use both the negative contact information and the corrected measurement error covariance are effective in maintaining track on a maneuvering target as it passes through the jamming region. This approach can also be generalized to any target tracking problem where the sensor response is anisotropic.     

GNSS receiver clock modeling when using high-precision oscillators and its impact on PPP

Processing data from Global Navigation Satellite Systems (GNSS) always requires time synchronization between transmitter and receiver clocks. Due to the limited stability of the receiver’s internal oscillator, the offset of the receiver clock with respect to the system time has to be estimated for every observation epoch or eliminated by processing differences between simultaneous observations. If, in contrast, the internal oscillator of the receiver is replaced by a stable atomic clock one can try to model the receiver clock offset, instead of estimating it on an epoch-by-epoch basis. In view of the progress made in the field of high-precision frequency standards we will investigate the technical requirements for GNSS receiver clock modeling at the carrier phase level and analyze its impact on the precision of the position estimates.     

Presolar Grains in Meteorites and Their Compositions

Small amounts of pre-solar “stardust” grains have survived in the matrices of primitive meteorites and interplanetary dust particles. These grains—formed directly in the outflows of or from the ejecta of stars—include thermally and chemically refractory carbon materials such as diamond, graphite and silicon carbide; as well as refractory oxides and nitrides. Pre-solar silicates, which have only recently been identified, are the most abundant type except for possibly diamond. The detailed study with modern analytical tools, of isotopic signatures in particular, provides highly accurate and detailed information with regard to stellar nucleosynthesis and grain formation in stellar atmospheres. Important stellar sources are Red Giant (RG) and Asymptotic Giant Branch (AGB) stars, with supernova contributions apparently small. The survival of those grains puts constraints on conditions they were exposed to in the interstellar medium and in the early solar system.     

Simultaneous EXOSAT-IUE observations of NGC 4151

NGC 4151 was observed four times in Nov. 83. The results indicate that: a) there exists a correlation between the X-ray and UV fluxes on the long term; b) the soft X-ray excess between 0.1 and 1 keV is probably steeper than expected from the leaky absorber model by Holt et al (1980); c)the spectral fit to the ME data, after correction for a soft component, yields =1,73±0.27, N_H=(15.2±2.2)×10²² cm^–2, E.W.(Fe line)=0.208±0.084 keV, and does not require a strong overabundance of Fe in the absorber. The relationship between N_H and the strength of the broad emission lines is commented.     

3C 273: A review of recent results

3C 273 is the most extensively studied quasar both from the ground and from space. Recent satellite observations have given important information on the overall electromagnetic spectrum of 3C 273 in the -ray, X-ray, and UV ranges. The most salient results are: (i) the energy per decade of frequency emitted by 3C 273 is nearly constant between 6000 Å and 500 MeV and is 20 × 10⁴⁶ erg s^-1 for H = 50 km s^-1 Mpc^-1; (ii) there is no absorption in the soft X-ray range in contrast to the X-ray spectrum of Seyfert nuclei; (iii) the optical and UV spectra cannot be fitted by power-law spectra only, and the energy distribution in this range suggests that a substantial fraction of the energy in the UV is emitted as back-body radiation at 20 000 K. If the peculiar shape of the UV spectrum is indeed caused by black-body radiation, then an estimate of the energy emitted under this form is 2.5 × 10⁴⁶erg s^-1, corresponding to an optically thick disk of 10¹⁶ cm in diameter.The UV spectrum of 3C 273 shows absorption lines at zero redshift caused by interstellar matter in the disk and halo of our Galaxy. The strength of C iv 1550 in absorption indicates the presence of a hot outer region in the halo. Extragalactic objects with mostly continuous UV spectra, such as 3C 273, are very promising UV sources which allow us to observe the absorbing material over the entire line of sight throughout the galactic halo.     

The effect of microgravity on plasma-osteocalcin

The rapid loss of bone mass is one of the serious problems which have to be solved before long-lasting manned spaceflights may be considered. In this paper we describe investigations in which we have checked whether the bone loss in astronauts as well as in osteoporotic patients may be related to abnormalities in a recently discovered calcium-binding protein, named osteocalcin. It was observed that in all subjects of a limited number of osteoporotic patients, the amount of calcium-binding groups (Gla-residues) in the circulating osteocalcin was substantially reduced. The Gla-content could be normalized, however, by the oral administration of vitamin K (1 mg/day). We also analyzed the Gla-content of plasma-osteocalcin from 4 astronauts before and after the D-1 mission. The amount of Gla-residues was reduced by more than 50% in the post-flight samples. It seems probable, that an increased vitamin K-intake by the astronauts will correct the observed abnormality, but whether this will lead to a decrease of the microgravity-induced bone-loss remains to be seen.