Comparison of ground reflectance measurement with satellite derived atmospherically corrected reflectance: A case study over semi-arid landscape

Atmospheric corrections to satellite data are important for comparing multitemporal data sets over tropical regions with variable aerosol loading. In this study, we evaluated the potential of 6S radiative transfer model for atmospheric corrections of IRS-P6 AWiFS satellite data sets, in a semi-arid landscape. Ground measurements of surface reflectance representing different land use/land cover categories were conducted to relate IRS-P6 AWiFS top of atmospheric reflectance. The 6S radiative transfer model was calibrated for local conditions using ground measurements for aerosol optical depth, water vapor and ozone with a sun photometer. Surface reflectance retrieved from 6S code was compared with top of atmosphere (TOA) reflectance and ground based spectroradiometer measurements. Accurate parameterization of the 6S model using measurements of aerosol optical depth, water vapor and ozone plays an important role while comparing ground and satellite derived reflectance measurements.     

A Pre-Landing Assessment of Regolith Properties at the InSight Landing Site

This article discusses relevant physical properties of the regolith at the Mars InSight landing site as understood prior to landing of the spacecraft. InSight will land in the northern lowland plains of Mars, close to the equator, where the regolith is estimated to be \(\geq3\mbox{--}5~\mbox{m}\) thick. These investigations of physical properties have relied on data collected from Mars orbital measurements, previously collected lander and rover data, results of studies of data and samples from Apollo lunar missions, laboratory measurements on regolith simulants, and theoretical studies. The investigations include changes in properties with depth and temperature. Mechanical properties investigated include density, grain-size distribution, cohesion, and angle of internal friction. Thermophysical properties include thermal inertia, surface emissivity and albedo, thermal conductivity and diffusivity, and specific heat. Regolith elastic properties not only include parameters that control seismic wave velocities in the immediate vicinity of the Insight lander but also coupling of the lander and other potential noise sources to the InSight broadband seismometer. The related properties include Poisson’s ratio, P- and S-wave velocities, Young’s modulus, and seismic attenuation. Finally, mass diffusivity was investigated to estimate gas movements in the regolith driven by atmospheric pressure changes. Physical properties presented here are all to some degree speculative. However, they form a basis for interpretation of the early data to be returned from the InSight mission.     

Viscous-type processes in the solar wind-magnetosphere interaction

A debate of long standing concerns the role viscous interactions play in magnetospheric dynamics. Is it minor or is it central to, e.g., drive the low latitude boundary layer on closed field lines and account for the substantial level of wave activity seen on the flanks? Newer data and theoretical considerations leave little doubt that viscous coupling is important. The Kelvin-Helmholtz instability is a major protagonist in fostering momentum transfer. Closer studies of the state of the flank magnetosphere will help to resolve the issue.     

The history of international space programmes

In reviewing the past 50 years of international space cooperation, much of it stunningly successful, some bedevilled by difficulties, the author notes that ‘space’ can now only be understood as a complex area of widely varied sectors, further complicated by different funding sources and dual-use activities. While scientists were the initial drivers of cooperation, their flourishing programmes risk losing government funding to the grandiose manned missions being envisaged. Such funding is strongly reliant on political will rather than on the merits of any particular programme, something that, until recently with the GEO, has been particularly evident in earth observations. A major problem has been countries’ efforts to secure some minor national advantage at the expense of the bigger picture. But for international space cooperation truly to benefit humanity, a greater acceptance of working for the common good and more efficient programme management (no duplication) will be required.     

Gravitational unloading effects on muscle fiber size, phenotype and myonuclear number.

The effects of gravitational unloading with or without intact neural activity and/or tension development on myosin heavy chain (MHC) composition, cross-sectional area (CSA), number of myonuclei, and myonuclear domain (cytoplasmic volume per myonucleus ratio) in single fibers of both slow and fast muscles of rat hindlimbs are reviewed briefly. The atrophic response to unloading is generally graded as follows: slow extensors > fast extensors > fast flexors. Reduction of CSA is usually greater in the most predominant fiber type of that muscle. The percentage of fibers expressing fast MHC isoforms increases in unloaded slow but not fast muscles. Myonuclear number per mm of fiber length and myonuclear domain is decreased in the fibers of the unloaded predominantly slow soleus muscle, but not in the predominantly fast plantaris. Decreases in myonuclear number and domain, however, are observed in plantaris fibers when tenotomy, denervation, or both are combined with hindlimb unloading. All of these results are consistent with the view that a major factor for fiber atrophy is an inhibition or reduction of loading of the hindlimbs. These data also indicate that predominantly slow muscles are more responsive to unloading than predominantly fast muscles.     

Chirp Waveform Generation Using Digital Samples

This paper describes two methods of generating an analog frequency-modulated waveform by the use of a small number of digital samples of the ?chirp? waveform. The number of digital samples required is a function of the time-bandwidth product. For certain values of time-bandwidth product, this type of signal generation becomes extremely efficient. Several proofs are offered which show how to select ?optimum? values of time-bandwidth products. Two hardware implementations are suggested. One is based on the use of modulo arithmetic and a small stored memory table. The second method utilizes the inherent signal symmetries available if ?optimum? time-bandwidth products are selected. The symmetrical signal patterns are stored in recirculating reversible shift registers which can be read out at high speeds.     

Dust acoustic dressed solitons in a four component dusty plasma with nonthermal electron

Nonlinear dust acoustic dressed soliton are studied in a four component dusty plasma. Nonthermal distributions for electrons are considered. The Korteweg–de Vries (KdV) equation is derived by using reductive perturbation technique. A higher order inhomogeneous differential equation is obtained for the higher order correction. The expression for dressed soliton is obtained by the renormalization method. The expressions for higher order correction are determined using a series solution technique.     

Europe's next move

Some time before the end of the first quarter of 1991 the Ministerial Council of the European Space Agency will be taking decisions about the development phases of the Columbus and Hermes programmes. The prospects for completing either programme within the originally approved costs are not bright, and operational costs will be three times the amount the ESA spends on its scientific programme. Are they good value for money? The author argues that Europe is in danger of yielding to others the lead in the next generation of space flight.