Space-based Platforms Research Articles

Monte Carlo computer simulations of ground-based and space-based coherent DIAL water vapor profiling

Ground-based and space-based coherent DIAL water vapor measurement performance at the 2.1-microm Ho:YAG wavelength is presented using a Monte Carlo computer simulation. The stochastic simulation allowed improved modeling of lidar system, platform, atmospheric, and data processing parameter effects on performance and better understanding of their interrelationships. Results indicate that accurate water vapor measurements in the lower troposphere are potentially achievable from both ground- and space-based platforms.

Radiative Transfer to Space through a Precipitating Cloud at Multiple Microwave Frequencies. Part I: Model Description

Abstract In a two-part study we investigate the impact of time-dependent cloud microphysical structure on the transfer to space of passive microwave radiation at several frequencies across the EHF and lower SHF portions of the microwave spectrum in order to explore the feasibility of using multichannel passive-microwave retrieval techniques for the estimation of precipitation from space-based platforms. A series of numerical sensitivity experiments have been conducted that were designed to quantify the impact of an evolving cumulus cloud in conjunction with a superimposed rain layer on the transfer to space of microwave radiation emitted and scattered from the cloud layers, rain layer and the underlying surface. The specification of cloud microphysics has been based on the results of a time-dependent two-dimensional numerical cumulus model developed by Hall (1980). An assortment of vertically homogeneous rain layers, described by the Marshall-Palmer rain drop distribution, has been inserted in the model a...

On the feasibility of correlation tracking at moderate resolution

The SOUP experiment demonstrated that photospheric surface flows can be measured by correlation tracking of white-light intensity features at high resolution (November et al., 1987). In order to assess the feasibility of this technique with observations made at lower resolution, we have applied it to the same SOUP data artificially degraded, but still free of seeing distortion. Comparison with the velocity structures inferred from the original data shows generally good agreement when the resolution is better than about 2″. The radial outflow from a sunspot penumbra, however, can only be seen with resolution of better than 1″. With resolution of worse than 2″, the inferred velocity fields rapidly lose coherence, while resolution of better than 1″ yields little improvement. We conclude that apertures as small as 10–14 cm on a space-based platform will be useful for the measurement of large-scale horizontal motions.

Whole-Field Measurement of Ice Displacement and Strain Rates

The flow of glacier ice is mapped using high-resolution photography and noncoherent light speckle interferometry. Time-lapse, double-exposures of a straining surface yield Young’s fringes when the resulting image is interrogated by a narrow beam of coherent light. Such fringe patterns, when corrected for camera motion, are indicative of the surface displacement occurring between exposures. Results of glacier field experiments are consistent with those garnered by conventional methods at the Nisqually Glacier, Washington. The interferometric method seems amenable to other geophysical applications, such as mapping sea ice flow, using terrestrial or space-based camera platforms.

The Ethics of Space-Based Ballistic Missile Defense

In 1967 the United States and the Soviet Union signed the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies, commonly known as the Outer Space Treaty. The treaty went into effect on October 10, 1967 and prohibits the stationing of weapons of mass destruction in space or on celestial bodies. Both nations apparently perceived benefits in preventing escalation of the arms race into space. Space exploration could concentrate upon nonmilitary missions such as medical research, or military missions designed to guarantee peace, such as orbiting spy satellites. The weapons-of-mass-destruction clause in the treaty is officially inter preted as including only nuclear weapons. In 1981, the Soviets proposed a treaty at the United Nations calling for a ban on the stationing of weapons of any kind in space and, in 1983, they presented a resolution seeking the prohibition of space based antisatellite weapons (ASATs).1 Of course, Soviet proposals are always met with a great deal of skepticism. Colin Gray, for instance, warns us that Soviet calls for negotiations to prevent the militarization of space are part of a Soviet plan to untrack the Strategic Defense Initiative (SDI). Gray remarks that SDI will need ASATs to defend against Soviet satellites whose mission will be to destroy SDI tracking in stallations on space-based platforms.2 Regardless of what the real intentions of the Soviets are, it is fair to say that the U.S. has undertaken a new orientation toward space-based weapons under President Reagan. In his now famous speech, Peace and National Security, delivered on March 23, 1983, Reagan urged the development of a defensive system which would make nuclear weapons ob solete. The speech presented a vision of a population defense which would free citizens from the threat of nuclear destruction and allow the United States to abandon reliance upon the immoral policy of mutual assured destruction (MAD) for deterrence.3 SDI will be a layered system with many space-based components. The version envisaged by James C. Fletcher, head of the Reagan-commissioned Defense Technologies Study and current director of NASA, involves four defensive layers correlated to the phases of a ballistic missile's flight: boost, post-boost, midcourse, and terminal.4 Three of these layers rely upon space-based weapons. It is doubtful that any of the layers would involve

The Characterization of an Air Pollution Episode Using Satellite Total Ozone Measurements

A case study is presented which demonstrates that measurements of total ozone from a space-based platform can be used to study a widespread air pollution episode over the southeastern U.S. In particular, the synoptic-scale distribution of surface-level ozone obtained from an independent analysis of ground-based monitoring stations appears to be captured by the synoptic-scale distribution of total ozone, even though about 90 percent of the total ozone is in the stratosphere. Additional analyses of upper air meteorological data, other satellite imagery, and in situ aircraft measurements of ozone likewise support the fact that synoptic-scale variability of tropospheric ozone is primarily responsible for the observed variability in total ozone under certain conditions. The use of the type of analysis discussed in this study may provide an important technique for understanding the global budget of tropospheric ozone.

The evolution of a serviceable EURECA

Within the European space platform program the EURECA is being established as a ground-based platform for short microgravity missions. The development towards a serviceable platform for longer, scientific missions is described. The plan of an advanced space-based platform for increasing payload demands is outlined. The platform design and the adaptation to scientific missions and servicing operations are investigated. The cost-effective utilization of the different platform types using new operational concepts is analyzed in parametric life cycle cost calculations for different payloads and mission scenarios.

Submillimeter-wave heterodyne spectroscopy with a compact solid state radiometer

A compact, solid state submillimeter-wave heterodyne radiometer has been developed and was used to measure spectral characteristics of a water vapor jet in a space simulation chamber. Features of the 557 GHz water vapor line profile were observed in significantly greater detail than in previous experiments through an increased sensitivity and improved frequency resolution (600 kHz). The local oscillator of the radiometer consisted of a frequency multiplication chain which was driven by an InP Gunn oscillator at 92.6 GHz, and which contained a frequency tripler and harmonic mixer in cascade. The front end of the receiver had a noise temperature of 4500 K (DSB) at 555 GHz, consumed 3 W and weighed 3 kg. This advance in technology is particularly relevant to submillimeter-wave radiometry from a space-based platform.

The Zeeman broadening of high n solar recombination lines

The Zeeman broadening of high n lines is derived. While in areas of the quiet Sun with field strengths of ≈1 G the upper boundary of the observable frequency region of recombination lines is defined by electron impact broadening, in active regions with field strengths ≳25 G the Zeeman broadening will shift this boundary to higher frequencies. The frequency region most favourable for observations is derived and the corresponding Doppler, electron impact and Zeeman broadening are discussed. The strengths of the recombination lines obtained in earlier calculations is reduced when one considers besides the Doppler broadening the electron impact and Zeeman broadening also. The frequency region favourable for observations is compared with the atmospheric transparency of the microwave region; it is found that observations require at least high altitude stations or space-based platforms. Details of using the Zeeman broadening of high n recombination lines for mapping (coronal) magnetic fields are given.