This chapter contains sections titled: Introduction Conclusion

The Air Force Research Laboratory has developed the Demonstration and Science Experiments (DSX) to research technologies needed to significantly advance the capability to operate spacecraft in the harsh radiation environment of medium-earth orbits (MEO). The ability to operate effectively in the MEO environment significantly increases the capability to field space systems that provide high-speed satellite-based communication, lower-cost GPS navigation, and protection for satellites from space weather effects. The one of DSX's physics based research areas is the Space Weather Experiment (SWx), characterizing and modeling the space radiation environment in MEO, an orbital regime attractive for future space missions.

A mechanical housing design is developed to ensure the survival of electronics and optimize the performance of solid state detectors orbiting through the Van Allen radiation belts. This design is part of the Loss Cone Imager on board the AFRL's DSX satellite and consists of three mechanically separate units: Fixed Sensor Head; High Sensitivity Telescope; and Central Electronics Unit. These units need to withstand the vibrations and shocks associated with launch as well as provide shielding to highly energetic radiation and micrometeorite impacts. To obtain optimal performance from the detectors and high reliability from the electronics thermal restrictions are incorporated into the mechanical designs.

Polarization effects are typically assumed to be negligible in semi-conductor photo-detectors. However, effects on the order of a few percent or less have occasionally been reported. Such reports have been difficult to assess because they are typically at or near measurement limits. Because remote sensing technology currently under consideration requires calibration precision of 3 % or less, these effects can no longer be ignored. We have recently carried out a set of high-quality polarimetric measurements of semi-conductor photo-detector materials across appropriate wavelength ranges in order to develop a better understanding of polarization effects on photo-detector response. Samples studied include GaAs and Si. The wavelength range was chosen to encompass the transition between strongly absorbing and non-absorbing for these materials. In addition, GaAs was compared with Si in order to better understand the contribution of bi-refringence effects in the regime of high optical absorption as required for efficient photo-detection. Mueller matrix data were obtained in order to allow prediction of photo-detectors over a wide range of angles of incidence under polarized illumination. This understanding is of interest for applications that require very fast optics, which is often the case for systems that operate in “photon-starved” environments.

An initial tranche of results from day-to-day use of a robotic system for setting up 100 nl-scale vapour-diffusion sitting-drop protein crystallizations has been surveyed. The database of over 50 unrelated samples represents a snapshot of projects currently at the stage of crystallization trials in Oxford research groups and as such encompasses a broad range of proteins. The results indicate that the nanolitre-scale methodology consistently identifies more crystallization conditions than traditional hand-pipetting-style methods; however, in a number of cases successful scale-up is then problematic. Crystals grown in the initial 100 nl-scale drops have in the majority of cases allowed useful characterization of X-ray diffraction, either in-house or at synchrotron beamlines. For a significant number of projects, full X-ray diffraction data sets have been collected to 3 Å resolution or better (either in-house or at the synchrotron) from crystals grown at the 100 nl scale. To date, five structures have been determined by molecular replacement directly from such data and a further three from scale-up of conditions established at the nanolitre scale.

We present the results of efforts to understand the polarimetric characterization properties of gold- and silver-coated mirrors, furthering our abilities for design and calibration of optical sensors. A FT spectropolarimeter was used to determine the experimental Mueller Matrix for both the gold- and silver-coated mirrors, thus fully characterizing the polarization altering properties of each sample. Presented is the total, linear and circular polarizance for incident angles ranging from 15degrees to 60degrees and between 0.7 and 1.1 mum.

This paper is primarily concerned with the causes of the large density and temperature enhancements that are often observed during magnetically quiet periods on winter nights at mid‐latitudes in the North American sector. Measurements from a network of Digisondes and an incoherent scatter radar are compared with the field line interhemispheric plasma (FLIP) model for January 6–12, 1997, in order to examine the temporal evolution and geographical extent of the enhancements in eastern North America. Postsunset measurements at Millstone Hill show high electron temperatures accompanied by rapid density decay until midnight followed by a rapid temperature decay accompanied by a pronounced density enhancement in the early morning hours. The FLIP model reproduces the nighttime density enhancement well, provided the model is constrained to follow the topside electron temperature and also that the overlying plasmaspheric flux tube is full. The dramatic reduction in plasmaspheric heat flux near midnight results in a sharp decrease in ionospheric temperature, inducing a large downward flow of plasmaspheric ions which creates the nighttime enhancement in ionospheric density. We find that the nighttime plasmaspheric heat flux variation drives the nighttime ionospheric density variation, which is opposite to conclusions in previously published work. Although the plasmaspheric heat flux variation can explain the ionospheric density variation, the reasons for this heat flux variation are not understood. Convection of plasma from higher magnetic latitudes is now included in the FLIP model but is not needed to produce the observed nighttime density maximum. We have found that the fraction of light ions in the topside ionosphere at 500 km altitude in the model is very close to that obtained from chemical equilibrium and agrees well with the measured fraction. The model generally reproduces the daytime electron density very well at all stations except Bermuda, where the difference is as much as 50%.

The recent availability of the new EUVAC (Richards et al., 1994) and EUV94X (Tobiska, 1993b, 1994) solar flux models and new wavelength bin averaged photoionization and photoabsorption cross section sets led us to investigate how these new flux models and cross sections compare with each other and how well electron densities (Ne) calculated using them compare with actual measurements collected by the incoherent scatter radar at Millstone Hill (42.6°N, 288.5°E). In this study we use the Millstone Hill semiempirical ionospheric model, which has been developed from the photochemical model of Buonsanto et al. (1992). For the F2 region, this model uses determinations of the motion term in the Ne continuity equation obtained from nine‐position radar data. We also include two simulations from the field line interhemispheric plasma (FLIP) model. All the model results underestimate the measured Ne in the E region, except that the EUV94X model produces reasonable agreement with the data at the E region peak because of a large Lyman β (1026 Å) flux, but gives an unrealistically deep E‐F1 valley. The ionospheric models predict that the O2+ density is larger than the NO+ density in the E region, while numerous rocket measurements show a larger NO+ density. Thus the discrepancy between the ionospheric models and the radar data in the E region is most likely due to an incomplete understanding of the NO+ chemistry. In the F2 region, the photoionization rate given by EUV94X is significantly larger than that given by the EUVAC and earlier models. This is due to larger EUV fluxes in EUV94X compared to EUVAC over the entire 300‐1050 Å wavelength range, apart from some individual spectral lines. In the case of EUVAC, this is partly compensated for by larger photoelectron impact ionization due to the larger EUV fluxes below 250 Å. The differences between ionospheric model results for the different cross‐section sets are generally much smaller than the differences with the data.

We present a method to retrieve neutral thermospheric composition and the solar EUV flux from ground‐based twilight optical measurements of the O+(²P) 7320 Å and O(¹D) 6300 Å airglow emissions. The parameters retrieved are the neutral temperature, the O, O2, N2 density profiles, and a scaling factor for the solar EUV flux spectrum. The temperature, solar EUV flux scaling factor, and atomic oxygen density are first retrieved from the 7320‐Å emission, which are then used with the 6300‐Å emission to retrieve the O2 and N2 densities. The retrieval techniques have been verified by computer simulations. We have shown that the retrieval technique is able to statistically retrieve values, between 200 and 400 km, within an average error of 3.1 ± 0.6% for thermospheric temperature, 3.3 ± 2.0% for atomic oxygen, 2.3 ± 1.3% for molecular oxygen, and 2.4 ± 1.3% for molecular nitrogen. The solar EUV flux scaling factor was found to have a retrieval error of 5.1 ± 2.3%. All the above errors have a confidence level of 95%. The purpose of this paper is to prove the viability and usefulness of the retrieval technique by demonstrating the ability to retrieve known quantities under a realistic simulation of the measurement process, excluding systematic effects.

Optical constant determination of thin films is critical to the design of x-ray multilayers. In the x-ray region, surface roughness, interfacial roughness, interdiffusion, volume anisotropics, etc. all act to reduce the reflection. A method is described to include all imperfections that make a real film different from an ideal film into the `optical behavior' values for each individual layer and the multilayer as a whole. These `optical behavior' values can then be used to accurately predict the performance of the multilayer.

The Imaging Spectrometric Observatory (ISO) flown on the ATLAS 1 mission between 24 Mar 1992 and 2 Apr 1992, acquired a database designed to study several outstanding problems in the ionosphere, thermosphere and mesosphere. In this paper we discuss the goals and preliminary results from three of these studies. To support these studies, the ISO acquired a database of: 1) emissions for the retrieval of neutral and ion densities to test global models of the ionosphere and thermosphere; 2) emissions for the retrieval of mesospheric composition of major and minor constituents needed to test models of the oxygen-hydrogen photochemistry, 3) emissions of the bands of the metastable states of O2, and O(1S) produced by three-body recombination of O in the mesosphere.

It is well known that in addition to roughness control, the most critical factor in the fabrication of x-ray multilayers is the accuracy of film thickness monitoring. Thickness accuracy and reproducibility of the x-ray multilayer deposition process can be improved by compensating for the film thickness variations in subsequent layers. We report the design of the `Bremsstrahlung Optical Monitoring System' (BOMS) for in situ multilayer spectral reflectance measurements and individual film optical thickness monitoring. The designed monitoring system, BOMS, utilizes the bremsstrahlung that occur during an electron beam deposition as the x-ray source and two energy sensitive detectors for the reference and sample beam reflectance measurements. In addition, the BOMS will create a powerful tool for in situ multilayer design, thus providing fabricated x-ray coatings with ultimate spectral performance.

In six companion papers we discuss a capability for X-ray tomographic spectrophotometry at three energy ranges to observe defects (in a general sense) in various systems using a novel X- ray optical and photometric approach. We describe new types of thin-film X-ray reflecting filters to provide energy-specific optical trains, inserted into existing X-ray interrogation systems. That is complemented by performing tomographic imaging at a few, to several, energies in each case. That provides a full tomographic and spectrophotometric analysis. Defects and inclusions can then be detected, and localized, discriminated, and classified, so that they may be dealt with by excision, and replacement with benign system elements. We analyze the principles of the technique as it leads to the design of three systems: The first operates at X-ray energies of 1 - 10 KeV. It deals with defects in microelectronic integrated circuits, which destroy the devices' electronic functionality, while they are still at the wafer stage of microelectronic device manufacture. Repair techniques can then be directed to excise the defects in situ, restore the functionality of the I/C's, and bring the effective manufacturing wafer yield to 100%. The second operates at X-ray energies of 10 - 30 keV. It deals with the defects in human tissue called tumors, which destroy the biological functionality of the organs that they inhabit. The chemical specificity and image resolution of the system will allow identification, localization, and mensuration of tumors without the need of biopsy. Then all measures necessary to plan effective therapies for the tumors. The third operates at X-ray energies of 30 - 70 keV. It deals with the defects in transportation systems which are represented by the presence of lethal objects (i.e., explosive devices) and contraband materials and objects in luggage and cargo. Steps can then be taken, for the excision of those objects, from the transportation system to restore its full functionality, guaranteeing the safe and legal passage of only those objects expected (to support the normal functions of society).© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A Lidar system designed by the authors to detect and observe the tracks of effluents emitted by ships at sea under propulsion by combustion of fossil fuels could have many useful applications. A prototype system uses a frequency-doubled Nd:YAG laser as the transmitter, at wavelengths of 0.53 and 1.06 micrometers , and examine the return for Rayleigh, Mie, fluorescence, and Raman scattering (hence called Advanced Rayleigh-Raman-Mie, ARRM), to determine thermodynamic and chemical conditions out to a given distance surrounding the Lidar operating station. We discuss the business potential of the system, its application to a number of technical and environmental problems, the potential for job creation by the use of such systems, and their value to both the users and the rest of society. One such application is discussed to a limited extent: wide-area surveillance for fire detection, in both urban and rural applications. Conversations with the City of Huntsville's Fire Department have revealed that the system is a quantum leap in fire detection, reporting, and hence firefighting response. Constant motion through the sky of a beam of green light could be a public nuisance. Therefore in an urban setting use of a primary surveillance transmitter consisting of a frequency-doubled CO2 laser is necessary for initial detection of the thermodynamic and fluid-dynamic indications of the rising plume, from the Mie and Rayleigh scattering. After each detection of a new plume, the system switches to the Nd:YAG transmitter for detailed characterization of the plume from the measured ARRM parameters.

This paper presents a new solar EUV flux model for aeronomic calculations (EUVAC), which is based on the measured F74113 solar EUV reference spectrum. The model provides fluxes in the 37 wavelength bins that are in widespread use. This paper also presents cross sections to be used with the EUVAC flux model to calculate photoionization rates. The flux scaling for solar activity is accomplished using a proxy based on the F10.7 index and its 81‐day average together with the measured solar flux variation from the EUVS instrument on the Atmosphere Explorer E satellite. This new model produces 50‐575 Å integrated EUV fluxes in good agreement with rocket observations. The solar cycle variation of the chromospheric fluxes agrees well with the measured variation of the Lyman α flux between 1982 and 1988. In addition, the theoretical photoelectron fluxes, calculated using the new EUV flux model, are in good agreement with the solar minimum photoelectron fluxes from the Atmosphere Explorer E satellite and also with the solar maximum photoelectron fluxes from the Dynamics Explorer satellite. Its relative simplicity coupled with its ability to reproduce the 50‐575 Å solar EUV flux as well as the measured photoelectron spectrum makes the model well suited for aeronomic applications. However, EUVAC is not designed to accurately predict the solar flux variability for numerous individual lines.