The Mars flyby of ROSETTA will provide a valuable opportunity for sounding, at high spatial resolution, the Mars atmosphere and surface in the infrared and microwave range. The VIRTIS infrared ...imaging spectrometer should be able to determine the surface mineralogy and temperature of the observed areas, the abundances of minor constituents (H
2O, CO), and possibly to study the atmospheric thermal profile. VIRTIS will complement the OMEGA and PFS infrared spectrometers on-board the Mars Express mission, expected to operate in Mars orbit at the time of the ROSETTA flyby. The MIRO microwave spectrometer is expected to provide information on the thermal profile, the H
2O vertical distribution, the temperature of the subsurface, and possibly the atmospheric winds. In addition, the Mars flyby of ROSETTA will provide the first opportunity for testing the VIRTIS and MIRO instruments, in particular for wavelength/frequency and photometry/radiometry calibration.
The high obliquity (~50°) of comet 67P/Churyumov-Gerasimenko (67P) is responsible for a long-lasting winter polar night in the southern regions of the nucleus. We report observations made with the ...submillimeter and millimeter continuum channels of the Microwave Instrument onboard the Rosetta Orbiter (MIRO) of the thermal emission from these regions during the period August-October 2014. Before these observations, the southern polar regions had been in darkness for approximately five years. Subsurface temperatures in the range 25−50 K are measured. Thermal model calculations of the nucleus near-surface temperatures carried out over the orbit of 67P, coupled with radiative transfer calculations of the MIRO channels brightness temperatures, suggest that these regions have a thermal inertia within the range 10−60 J m-2 K-1 s-0.5. Such low thermal inertia values are consistent with a highly porous, loose, regolith-like surface. These values are similar to those derived elsewhere on the nucleus. A large difference in the brightness temperatures measured by the two MIRO continuum channels is tentatively attributed to dielectric properties that differ significantly from the sunlit side, within the first few tens of centimeters. This is suggestive of the presence of ice(s) within the MIRO depths of investigation in the southern polar regions. These regions started to receive sunlight in May of 2015, and refinements of the shape model in these regions, as well as continuing MIRO observations of 67P, will allow refining these results and reveal the thermal properties and potential ice content of the southern regions in more detail.
Sub-millimeter spectra recorded by the MIRO sounder aboard the Rosetta spacecraft have been used at the time of an Earth flyby (November 2007) to check the consistency and validity of the ...instrumental data. High-resolution spectroscopic data were recorded in 8 channels in the vicinity of the strong water line at 557GHz, and in a broad band continuum channel at 570GHz. An atmospheric radiative transfer code (ARTS) and standard terrestrial atmospheres have been used to simulate the expected observational results. Differences with the MIRO spectra suggest an anomaly in the behavior of four spectroscopic channels. Further technical investigations have shown that a large part of the anomalies are associated with an instability of one of the amplifiers. The quality of the MIRO data has been further tested by inverting the spectra with an atmospheric inversion tool (Qpack) in order to derive a mesospheric temperature profile. The retrieved profile is in good agreement with the one inferred from the Earth Observing System Microwave Limb Sounder (EOS-MLS). This work illustrates the interest of validating instruments aboard planetary or cometary spacecraft by using data acquired during Earth flybys.
•Expected atmospheric observational results of a MIRO Earth flyby have been simulated.•Differences with the MIRO recorded spectra suggest an anomaly in 4 channels.•The instrument anomalies have been associated with an instable amplifier.•The MIRO spectra have been further tested by retrieving an atmospheric temperature profile.•The retrieved profile is in good agreement with the temperature inferred from EOSMLS.
Differential Microwave Radiometers (DMRs) at frequencies of 31.5, 53, and 90 GHz have been designed and built to map the large angular scale variations in the brightness temperature of the cosmic ...microwave background radiation. The instrument is being flown aboard NASA's Cosmic Background Explorer (COBE) satellite, launched on November 18, 1989. Each receiver input is switched between two antennas pointing 60 deg apart on the sky. The satellite is in near-polar orbit with the orbital plane precessing at 1 deg per day, causing the beams to scan the entire sky in 6 months. In 1 year of observation, the instruments are capable of mapping the sky to an rms sensitivity of 0.1 mK per 7 deg field of view. The mission and the instrument have been carefully designed to minimize the need for systematic corrections to the data.
Images of Jupiter's synchrotron emission give a global view of the inner Jovian magnetosphere: they are very useful to analyze both the Salammbô-3D results (a three-dimensional modeling of the Jovian ...radiation belts (Beutier and Boscher, 1995) and the relative importance of prominent physical processes occurring in this region. Here we present comparisons between model synchrotron emission images highlighting specific processes deduced from our 3-D simulation, and observations made with the VLA in May 1997 at 20 cm. Both realistic and unrealistic models are presented to judge of the importance of few physical processes.
The 183-GHz water vapor line was tentatively detected on Mars in January 1991, with the IRAM 30-m millimeter antenna, under extremely dry atmospheric conditions. The measurement refers to the whole ...disk. The spectral line, although marginally detected, can be fit with a constant H2O mixing ratio of 1.0 x 10(exp -5), which corresponds to a water abundance of 1 pr-microns; in any case, an upper limit of 3 pr-microns is inferred. This value is comparable to the very small abundances measured by Clancy (1992) 5 weeks before our observation and seems to imply both seasonal and long-term variations in the martian water cycle.
Observations of Solar Irradiance Variability Willson, R. C.; Gulkis, S.; Janssen, M. ...
Science (American Association for the Advancement of Science),
1981-Feb-13, Letnik:
211, Številka:
4483
Journal Article
Recenzirano
High-precision measurements of total solar irradiance, made by the active cavity radiometer irradiance monitor on the Solar Maximum Mission satellite, show the irradiance to have been variable ...throughout the first 153 days of observations. The corrected data resolve orbit-to-orbit variations with uncertainties as small as 0.001 percent. Irradiance fluctuations are typical of a band-limited noise spectrum with high-frequency cutoff near 0.15 day$^{-1}$; their amplitudes about the mean value of 1368.31 watts per square meter approach $\pm $ 0.05 percent. Two large decreases in irradiance of up to 0.2 percent lasting about 1 week are highly correlated with the development of sunspot groups. The magnitude and time scale of the irradiance variability suggest that considerable energy storage occurs within the convection zone in solar active regions.
High-resolution OH 1612-MHz spectra are presented of the supergiant OH–IR sources VY CMa, VX Sgr, IRC 10420 and NML Cyg. The spectra have a resolution of 300 Hz. Narrow components in the spectra have ...linewidths as small as 550 Hz (0.1 km s–1) but there is no evidence for components narrower than this. These results are in accord with present understanding of maser line-narrowing and of the physical conditions in the OH maser regions. Many of the narrow components have an appreciable degree of circular polarization which is not apparent at the lower frequency resolutions usually employed. The circular polarization indicates the presence of magnetic fields of $\sim{1}\text{mG}$ in the circumstellar envelopes, at distances of $\sim{3}\times {10}^{16}\text{cm}$ from the central stars. These fields are strong enough to influence the outflow from the stars, and may help to explain some of the asymmetries which are seen in their circumstellar envelopes.
The techniques available for the identification and subtraction of sources of dynamic uncertainty from data of the Differential Microwave Radiometer (DMR) instrument aboard COBE are discussed. ...Preliminary limits on the magnitude in the DMR 1 yr maps are presented. Residual uncertainties in the best DMR sky maps, after correcting the raw data for systematic effects, are less than 6 micro-K for the pixel rms variation, less than 3 micro-K for the rms quadruple amplitude of a spherical harmonic expansion, and less than 30 micro-(K-squared) for the correlation function.
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