Chemical composition measurements of the atmosphere of Jupiter with the Galileo Probe mass spectrometer.

The Galileo Probe entered the atmosphere of Jupiter on December 7, 1995. Measurements of the chemical and isotopic composition of the Jovian atmosphere were obtained by the mass spectrometer during the descent over the 0.5 to 21 bar pressure region over a time period of approximately 1 hour. The sampling was either of atmospheric gases directly introduced into the ion source of the mass spectrometer through capillary leaks or of gas, which had been chemically processed to enhance the sensitivity of the measurement to trace species or noble gases. The analysis of this data set continues to be refined based on supporting laboratory studies on an engineering unit. The mixing ratios of the major constituents of the atmosphere hydrogen and helium have been determined as well as mixing ratios or upper limits for several less abundant species including: methane, water, ammonia, ethane, ethylene, propane, hydrogen sulfide, neon, argon, krypton, and xenon. Analysis also suggests the presence of trace levels of other 3 and 4 carbon hydrocarbons, or carbon and nitrogen containing species, phosphine, hydrogen chloride, and of benzene. The data set also allows upper limits to be set for many species of interest which were not detected. Isotope ratios were measured for 3He/4He, D/H, 13C/12C, 20Ne/22Ne, 38Ar/36Ar and for isotopes of both Kr and Xe.     

CRISTA-NF measurements of water vapor during the SCOUT-O3 Tropical Aircraft Campaign

The new remote sensing experiment CRISTA-NF (Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere – New Frontiers) successfully participated in the SCOUT-O3 Tropical Aircraft Campaign in November and December 2005. CRISTA-NF operated aboard the high-altitude research aircraft M-55 Geophysica. Mid-infrared spectra (4–15 μm) were measured in the limb sounding geometry with high spatial resolution (250 m vertical sampling, 5–15 km along track sampling). Measurements were carried out during transfer flights between Oberpfaffenhofen, Germany, and Darwin, Australia, as well as during several local flights near Darwin. Water vapor volume mixing ratios in the upper troposphere and lower stratosphere were derived from the CRISTA-NF radiance measurements by utilizing a rapid radiative transfer forward model and the optimal estimation retrieval approach. CRISTA-NF water vapor measurements below the hygropause have a total retrieval error of 15–40% (i.e. root mean square of accuracy and precision). The systematic terms are dominating in the retrieval error budget. The contributions of a priori information to the retrieval results are less than 5–10%. The vertical resolution of the observations is about 250–500 m when permitted by instrument sampling. In this paper we present first results for three transfer flights of the campaign. Being generally in good agreement with corresponding ECMWF operational analyzes, the CRISTA-NF measurements show significantly higher variability and local structures in the upper tropospheric water vapor distributions.     

Derivation of OH concentrations from LIMS measurements

Stratospheric concentrations of OH have been derived from LIMS measurements of minor constituents. Two methods have been used. Assuming that HNO₃ and NO₂ are in photochemical steady state, LIMS measurements of these species, with knowledge of appropriate rate constants and a calculation of the HNO₃ photolysis rate, allow nearly global fields of OH to be derived. The derived profiles show satisfactory agreement with observations. As a check on our method, OH has also been derived by calculations of its sources and sinks using LIMS measurements of H₂O. The two methods agree extremely well in low latitudes. At higher latitudes the agreement is less satisfactory. This is discussed in terms of the diurnal behaviour of the species and the time constant of the HNO₃/NO₂ equilibrium.     

Analysis of precipitable water vapor from GPS measurements in Chengdu region: Distribution and evolution characteristics in autumn

The rainfall process of Chengdu region in autumn has obvious regional features. Especially, the night-time rain rate of this region in this season is very high in China. Studying the spatial distribution and temporal variation of regional atmospheric precipitable water vapor (PWV) is important for our understanding of water vapor related processes, such as rainfall, evaporation, convective activity, among others in this area. Since GPS detection technology has the unique characteristics, such as all-weather, high accuracy, high spatial and temporal resolution as well as low cost, tracking and monitoring techniques on water vapor has achieved rapid developments in recent years. With GPS–PWV data at 30-min interval gathered from six GPS observational stations in Chengdu region in two autumns (September 2007–December 2007 and September 2008–December 2008), it is revealed that negative correlations exist between seasonally averaged value of GPS–PWV as well as its variation amplitude and local terrain altitude. The variation of PWV in the upper atmosphere of this region results from the water vapor variation from surface to 850 hPa. With the help of Fast Fourier Transform (FFT), it is found that the autumn PWV in Chengdu region has a multi-scale feature, which includes a seasonal cycle, 22.5 days period (quasi-tri-weekly oscillation). The variation of the GPS–PWV is related to periodical change in the transmitting of the water vapor caused by zonal and meridional wind strengths’ change and to the East Asian monsoon system. According to seasonal variation characteristics, we concluded that the middle October is the critical turning point in PWV content. On a shorter time scale, the relationship between autumn PWV and ground meteorological elements was obtained using the composite analysis approach.     

Validation of satellite-derived atmospheric temperature and water vapor concentration using radiosonde and rocketsonde measurements

Measurements of the spectral radiance of the earth's atmosphere from satellites can be related to the vertical structures of temperature and humidity. Derived profiles of these quantities are compared with radiosonde and rocketsonde observations, as well as with horizontal and vertical cross-sections of the atmosphere. In some regions of the atmosphere, particularly where large gradients are found, significant differences occur. A method for overcoming these by use of Typical Shape Functions is discussed. Transmittances computed from theory require modifications which are not well defined, and radiances measured from some satellite instruments disagree with computed values in ways which suggest calibration or instrument problems.     

Gamma-ray measurements from the space shuttle during a solar flare.

An X2/2B level solar flare occurred on 12 August, 1989, during the last day of the flight of the Space Shuttle Columbia (STS-28). Detectors on the GOES 7 satellite observed increased X-ray fluxes at approximately 1400 GMT and a solar particle event (SPE) at approximately 1600 GMT. Measurements with the bismuth germanate (BGO) detector of the Shuttle Activation Monitor (SAM) experiment on STS-28 showed factors of two to three increases in count rates at high latitudes comparable to those seen during South Atlantic Anomaly (SAA) passages beginning at about 1100 GMT. That increased activity was observed at both north and south high latitudes in the 57 degrees, 300 kilometer orbit and continued until the detector was turned off at 1800 GMT. Measurements made earlier in the flight over the same geographic coordinates did not produce the same levels of activity. This increase in activity may not be entirely accounted for by observed geomagnetic phenomena which were not related to the solar flare.     

Determination of wind vectors from METEOSAT water vapor channel data

After applying special edge detection techniques to METEOSAT water vapor images midtropospheric wind vectors have been derived in cloudfree areas by using the single point tracking method. A comparison of derived wind vectors with radiosonde winds gave rms-differences of 5ms^?1 for wind velocity and 16° for wind direction.     

Towards accurate atmospheric mass density determination Using precise positional information of space objects

This paper presents a new method of deriving atmospheric mass densities with a high temporal resolution from precise orbit data of low earth orbiting (LEO) space objects. This method is based on the drag perturbation equation of the semi-major axis of the orbit of LEO space objects which relates the change rate of the semi-major axis to the atmospheric mass density. The effectiveness of the new method is evaluated using the GFZ-ISDC GPS rapid science orbit (RSO) products of the CHAMP satellite over a time period of 3 months. The densities derived using this new method and obtained from accelerometer data are compared and good agreements are achieved. An example of using the derived density to generate good orbit prediction for CHAMP is presented.     

Apparent rotation properties of space debris extracted from photometric measurements

Knowledge about the rotation properties of space debris objects is essential for the active debris removal missions, accurate re-entry predictions and to investigate the long-term effects of the space environment on the attitude motion change. Different orbital regions and object’s physical properties lead to different attitude states and their change over time.Since 2007 the Astronomical Institute of the University of Bern (AIUB) performs photometric measurements of space debris objects. To June 2016 almost 2000 light curves of more than 400 individual objects have been acquired and processed. These objects are situated in all orbital regions, from low Earth orbit (LEO), via global navigation systems orbits and high eccentricity orbit (HEO), to geosynchronous Earth orbit (GEO). All types of objects were observed including the non-functional spacecraft, rocket bodies, fragmentation debris and uncorrelated objects discovered during dedicated surveys. For data acquisition, we used the 1-meter Zimmerwald Laser and Astrometry Telescope (ZIMLAT) at the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald, Switzerland. We applied our own method of phase-diagram reconstruction to extract the apparent rotation period from the light curve. Presented is the AIUB’s light curve database and the obtained rotation properties of space debris as a function of object type and orbit.     

An improved,near real time water vapor path delay correction of Cryosat-2 sea surface height measurements

This paper presents improvements of a method (Stum et al., 2011) aimed at computing the water vapor path delay correction of altimeter sea surface height, using total precipitable water measurements from scanning microwave radiometers. The main interest of this improved method is for the Cryosat-2 mission over the ocean. Focus is made on the applicability of the method in near real time. An experiment to produce an operational path delay correction for Jason-2 and Cryosat-2 Interim Geophysical Data Records (IGDR) has been set up. Results confirm that the new correction, although less accurate than the one attainable with an embarked radiometer, improves the Cryosat-2 sea surface height accuracy.     

A neutral gas mass spectrometer to measure the chemical composition of the stratosphere

The Polar Balloon Atmospheric Composition Experiment (P-BACE) is a new generation of neutral gas mass spectrometer based on the time-of-flight principle. P-BACE is the scientific experiment on the Mars Environment Analog Platform (MEAP) flown successfully on a balloon mission in summer 2008. The MEAP mission was flown with a 334,000 m³ helium balloon in the stratosphere on a semicircular trajectory from northern Sweden around the North Pole to Canada using the summer northern hemispheric wind current. The atmospheric conditions at an atmospheric altitude of 35–40 km are remarkably similar to those on the surface of Mars and thus the balloon mission was an ideal testbed for our mass spectrometer P-BACE. Originally this instrument was designed for in situ measurements of the chemical composition of the Martian atmosphere.P-BACE has a unique mass range from 0 to 1000 amu/q with a mass resolution m/Δm (FWHM) > 1000, and the dynamic range is at least six orders of magnitude. During this experiment, the acquisition of one mass spectrum is a sum of 65,535 single spectra, recorded in a time frame of 66 s.The balloon mission lasted 5 days and had successfully demonstrated the functionality of the P-BACE instrument during flight conditions. We had recorded more than 4500 mass spectra. With little modifications, P-BACE can be used on a planetary mission for Mars, but for example also for Venus or Mercury, if placed on a satellite.     

On the influence of rough water surfaces on polarimetric investigations of aerosols from space

The equation of radiative transfer is solved for the complete Stokes' vector in order to study the polarization of solar radiation on top of a turbid atmosphere.The surface characteristics (bidirectional anisotropy and polarization properties of randomly oriented water surface elements) are contained in the lower boundary condition of the integro-differential equation. Results of surface model calculations are compared with polarimeter measurements of a natural scenario.On top of the atmosphere the degree of polarization is found to depend generally on the turbidity of the atmosphere. The degree of polarization reaches its maximum in the vicinity of the angle of specular reflection on the water surface, if the sun's zenith distance is about the Brewster's angle.According to the model calculations observation angles can be found where the degree of polarization does not depend on the surface roughness. Apparently these angles have to be preferred for determination of the atmospheric turbidity.     

Variability and climatology of precipitable water vapor from 12-year GPS observations in Taiwan

Because of global warming, global sea levels have risen, the frequency of drought in Taiwan is much more frequent in winter and spring, and rainfall tends to concentrate in summer. The probability of disaster-type weather has also increased significantly. Estimating precipitable water vapor (PWV) through GPS signals, related studies and analyses of weather conditions, and the effective use of meteorological forecasts have been valued by many meteorological research organizations and officials. In this study, PWV data from 2006 to 2017 and rainfall data were used for long-term harmonic analysis. PWV data calculated by ECMWF (ECMWF-PWV) and PWV data calculated by GPS (GPS-PWV) were subjected to regression analysis to verify the reliability of the GPS-PWV data. The research results show that GPS-PWV and ECMWF-PWV have extremely high correlations; however, the climatic characteristics of some regions and the high spatial resolution of GPS-PWV are able to accurately calculate the high topographic relief of small areas. It is judged that the GPS-PWV is more accurate than the ECMWF-PWV. It is worth noting that the PWV trend of the regions during the 6-year-before period has not changed very much, but the rainfall trend has changed obviously. Except for the eastern region, most of the regions show a decreasing trend year by year. More long-term observations are still needed to prove whether this phenomenon relates to global warming. Long-term rainfall analysis showed that the topography blocked water vapor to the western, southern, and mountainous regions, making them distinctly wet or dry. The harmonic curve showed great consistency with the peaks of PWV and rainfall. However, in the northern and eastern parts of the windward side, the time when maximum rainfall occurred each year may be one month later than the time when the maximum PWV value occurred each year. The reason for this difference is likely to be a decrease in the number of autumn typhoons, resulting in a nearly one-month difference in PWV peaks and rainfall peaks. Finally, we analyzed the linear trend of GPS-PWV and temperature for all regions in Taiwan, and found that annual increasing rate of GPS-PWV and temperature of all regions are within 0.4–0.5 mm/year and 0.04–0.11 C°/year, respectively.     

Transient measurements of HV interaction with the ambient and perturbed space environment

Transient measurements of current collected by a rocket payload charged to several kilovolts negative with respect to the ambient plasma were made during the SPEAR-3 sounding rocket mission. The measurements were taken in short bursts at 1MHz, coincident with the application of the high voltage. The measured current is seen to rise approximately parabolically for approximately 15μs before rolling over into an exponential decay towards steady state current collection. The exponential time constant of 40 to 50μs is interpreted as the characteristic ion-collection sheath formation time for the SPEAR-3 payload.     

Retrieval of the change of precipitable water vapor with zenith tropospheric delay in the Chinese mainland

As a preliminary step for assessing the impact of global positioning system (GPS) refractive delay data in numerical weather prediction (NWP) models, the GPS zenith tropospheric delays (ZTD) are analyzed from 28 permanent GPS sites in the Chinese mainland. The objectives are to estimate the GPS ZTD and their variability in this area. The differences between radiosonde precipitable water vapor (PWV) and GPS PWV have a standard deviation of 4 mm in delay, a bias of 0.24 mm in delay, and a correlation coefficient of 0.94. The correlation between GPS ZTD and radiosonde PWV amounts to 0.89, indicating that the variety of tropospheric zenith delay can reflect the change of precipitable water vapor. The good agreement also guarantees that the information provided by GPS will benefit the NWP models. The time series of GPS ZTD, which were derived continuously from 2002 to 2004, are used to analyze the change of precipitable water vapor in Chinese mainland. It shows that the general trend of GPS ZTD is diminishing from the south-east coastland to the north-west inland, which is in accordance with the distribution of Chinese annual amount of rainfall. The temporal distribution of GPS ZTD in the Chinese mainland is that the GPS ZTD reaches maximum in summer, and it reaches minimum in winter. The long term differences between the observational data sources require further study before GPS derived data become useful for climate studies.     

Spin motion determination of the Envisat satellite through laser ranging measurements from a single pass measured by a single station

The Satellite Laser Ranging (SLR) technology is used to accurately determine the position of space objects equipped with so-called retro-reflectors or retro-reflector arrays (RRA). This type of measurement allows to measure the range to the spacecraft with high precision, which leads to determination of very accurate orbits for these targets. Non-active spacecraft, which are not attitude controlled any longer, tend to start to spin or tumble under influence of the external and internal torques and forces.If the return signal is measured for a non-spherical non-active rotating object, the signal in the range residuals with respect to the reference orbit is more complex. For rotating objects the return signal shows an oscillating pattern or patterns caused by the RRA moving around the satellite’s centre of mass. This behaviour is projected onto the radial component measured by the SLR.In our work, we demonstrate how the SLR ranging technique from one sensor to a satellite equipped with a RRA can be used to precisely determine its spin motion during one passage. Multiple SLR measurements of one target over time allow to accurately monitor spin motion changes which can be further used for attitude predictions. We show our solutions of the spin motion determined for the non-active ESA satellite Envisat obtained from measurements acquired during years 2013–2015 by the Zimmerwald SLR station, Switzerland. All the necessary parameters are defined for our own so-called point-like model which describes the motion of a point in space around the satellite centre of mass.     

Estimation of precipitable water vapour from GPS measurements in Argentina: Validation and qualitative analysis of results

This paper presents PWV estimates from GPS data computed at four continuously operated GPS stations in Argentina established at Buenos Aires, Córdoba, Rosario and Salta over a 1 year period (2006–2007). The objective is to analyze the behaviour of the GPS PWV estimation using mean tropospheric temperature (_Tm$T_m$) values from the Bevis model, Sapucci model and obtained by a numerical integration of variables provided by the operational analysis of the National Centre of Environmental Prediction (NCEP). The results are validated using PWV values from nearest radio soundings. Moreover, a comparison between PWV values determined from microwave sensors deployed on the NOAA-18 satellite and PWV from GPS observations is also presented.     

Time distribution of the precipitable water vapor in central Saudi Arabia and its relationship to solar activity

Water vapor is the most important greenhouse gas. It plays a major role in the dynamics of atmospheric circulation, radiation exchange within the atmosphere, and climate variability. Knowledge of the distribution of water vapor is important for understanding climate change and global warming.