Search

We present new images and photometry of the massive star forming complex Cygnus X obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope. A combination of IRAC, MIPS, UKIRT Deep Infrared Sky Survey (UKIDSS), and Two Micron All Sky Survey (2MASS) data are used to identify and classify young stellar objects. Of the 8,231 sources detected exhibiting infrared excess in Cygnus X North, 670 are classified as Class I and 7,249 are classified as Class II. Using spectra from the FAST spectrograph at the Fred L. Whipple Observatory and Hectospec on the MMT, we spectrally typed 536 sources in the Cygnus X complex to identify the massive stars. We find that YSOs tend to be grouped in the neighborhoods of massive B stars (spectral types B0 to B9). We present a minimal spanning tree analysis of clusters in two regions in Cygnus X North. The fraction of infrared excess sources that belong to clusters with greater or equal to 10 members is found to be 50-70%. Most Class II objects lie in dense clusters within blown out H II regions, while Class I sources tend to reside in more filamentary structures along the bright-rimmed clouds, indicating possible triggered star formation., Accepted for publication in The Astrophysical Journal, v720 n1, Sep 2010. Sponsored in part by the National Science Foundation Research Experiences for Undergraduates (REU) and Department of Defense Awards to Stimulate and Support Undergraduate Research Experiences (ASSURE) programs under Grant no. 0754568 and by the Smithsonian Institution.

Aircraft and radar weather data recorded for support of the Minuteman PVM-5 test are presented. The link-offset mode was used successfully to obtain radar data for correlation with the aircraft data. The correlation data were quite good, and provided usable relations of reflectivity factor (Z) and water content (M) on five of nine passes. Application of the Z-M relations to the reflectivity data recorded along the re-entry trajectories provided estimates of the water content profile and the weather severity index (WSI) for each of the trajectories., Air Force surveys in geophysics.

An engineering analysis and development effort has been executed to design a superpressure airship, POBAL-S, capable of station keeping at an altitude of 21 kilometers for a duration of 7 days while supporting a payload weighing 890 newtons and requiring 500 watts of electrical power. A detailed parametric trade-off between various power sources and other design choices was performed. The computer program used to accomplish this analysis is described and many results are presented. The system concept which resulted was a fuel cell powered, propeller driven airship controlled by an on-board autopilot with basic commands telemetered from a ground control station. Design of the balloon, power train, gimbaled propeller assembly, and electronic/electrical systems is presented. Flight operations for launch and recovery are discussed.

A survey of the sky in the intermediate infrared spectral region is reported. The objective was to obtain the brightness and spatial distribution of a representative sample of the types of celestial objects that emit strongly in the infrared. Of primary concern was the determination of the positions of unusual sources of emission with sufficient accuracy to enable them to be acquired by ground based telescopes for further detailed investigation.

The characterization of ionospheric scintillations in terms of scintillation index is discussed. Scintillation index cannot be directly applied to the design of systems that use transionospheric propagation. The relationships of scintillation index to system design parameters, cumulative amplitude distributions, and fade levels, are shown. The determination of a spectral index is explained and its use for extrapolating the results of ionospheric scintillation measurements to a desired frequency is shown.

This publication, in conjunction with the main volume, AFCRL-TR-74- 0393, dated 21 August 1974, contains the papers presented at the Eighth AFCRL Scientific Balloon Symposium, 30 September to 3 October 1974, held at Hyannis, MA. The papers are grouped in accordance with the five symposium sessions: Powered Balloons, Tethered Balloons, Free Balloon Technology, Balloon-Borne Experiments, and Special Applications., See also AD-A003 398.

In this report, the author discusses the effect of slewing on the temporal frequency spectrum of the scintillations of a laser beam propagating through a turbulent medium. It is assumed that the turbulent medium is characterized by the index of refraction n(r,t) = 1 + (n sub 1)(r,t), where the fluctuation (n sub 1) is much < 1. It is further assumed that (n sub 1) varies sufficiently slowing in comparison with the time required for the signal transversal.

In this work elastic constants of some infrared window materials were calculated from ultrasonic measurements using a pulse overlap technique. Velocity measurements were determined in various directions in CVD zinc selenide and in hot forged KCl alloy windows. These measurements permitted the determination of Young's Modulus, the shear modulus, the bulk modulus, and Poisson's ratio. Some anistropy was found in the elastic properties of these fabricated or 'as-grown' infrared windows. For example, in the case of the chemically vapor deposited ZnSe which exhibits a small amount of elastic anistropy, the elastic properties were found to be isotropic in all directions normal to the growth direction. The modulus values observed for directions in the plane of the zinc selenide window were found to change by approximately two percent when measured in directions parallel to the plate growth direction. The experimental results obtained were, in some cases, compared with various calculation approximations which yield polycrystalline elasticity parameters from single crystal data.

The various types of large balloon systems in use today, or under development, are examined with regard to potential use in the SEEK STAR multi- mode transmission system. Tethered balloons are shown to satisfy many communications applications, but to lack the altitude capability needed by SEEK STAR. The powered free balloon is seen to offer the best potential. The AFCRL powered balloon system, POBAL, is described and test results are presented. Its successor system, POBAL-S, is also described and evaluated. The demise of the POBAL-S development at AFCRL and the reappearance of the concept under the Navy's HASPA program is discussed and the applicability of HASPA to the SEEK STAR mission is evaluated. It is shown that, although the HASPA can theoretically satisfy or exceed all SEEK STAR needs, a delay of about three years must be endured before definitive results are available. Free-flying (that is, unpowered) balloon systems, both zero-pressure and superpressure, are evaluated and the advantages of the ground-launched and air-launched systems are pointed out. A status report on the Air-Launched Balloon System (ALBS) development is given.

An analytical and numerical study was performed on a novel design scheme for an antenna for limited one-dimensional scan. The system has a number of control elements approximately equal to the minimum that are theoretically compatible with the aperture size and field of view (FOV). The radiating structure consists of a 'boot lace' lens with linear outer and circular inner profiles. This geometry plays a basic role in determining excellent scan performance over a moderate frequency band. A linear array whose size depends critically upon scan requirements and the lens focal length is located on the focal plane and is focussed onto the inner lens profile. The array is fed by a Hybrid Network (HN) performing a spatial Fourier transformation. The input ports of the HN are fed by the output ports of a Beam Forming Network (BFN) through a set of variable phase shifters. The BFN has separate input ports for the sum and difference patterns controlled independently. The system works as follows. The antenna illumination is synthesized as the weighted superposition of components illuminations or 'overlapping subarrays', each of which is due to the excitation of one of the ports of the HN. The amplitudes of the subarray excitations are fixed and determined by the power divisions provided by the BFN. Their phases are controlled by the set of variable phase shifters. A desirable feature of the scheme is that for fixed phase shifter settings, neither the beam scans nor the width changes for a moderate frequency variation.

The main purpose of the report is to establish certain structural properties of a peculiar class of Plane Wave Spectra (PWS) representing an aperture field (or, equivalently of radiation patterns) which make the aperture reactive power equal to zero. To achieve this objective the entire question of the representation of an aperture field through a PWS is reexamined from a novel viewpoint. The Fourier transform (FT) of the transverse electric field on the aperture is considered as a two-dimensional vector field on the wavenumber plane, represented through two scalar functions, which are its coordinates in a chosen vector basis (Section 3). The choice of the latter has an important physical significance since it corresponds to the decomposition of the PWS into two components having differently polarized radiation patterns and different reactive properties. In Section 4, it is shown that the conductance and the susceptance of an aperture can be expressed as integrals (extended over the visible and invisible space) of two quadratic forms (whose explicit expressions depend upon the basis chosen to represent the PWS).

Samples representative of most of the optical fibers presently available in lengths of 10 m or more were tested for their responses to energetic radiation. Glass fibers doped with three different levels of cesium were also prepared and tested. Permanent and transient x-radiation effects tests were performed. Neutron effects tests were performed. All of the fibers tested showed decreases in transmission when exposed to radiation. All of the fibers emitted fluorescent light pulses when exposed to intense x-ray pulses.

This is the seventh in a series of Reports on Research at the Air Force Cambridge Research Laboratories. This report covers a two-year interval. It was written primarily for Air Force and DOD managers of research and development and more particularly for officials in Headquarters Air Force Systems Command, for the Director of Science and Technology (DL), and for the Commanders of and the Laboratories within DL. The work of each of the laboratories is discussed as a separate chapter. Additionally, the report includes an introductory chapter on AFCRL management and logistic activities related to the reporting period.

In the report Rayleigh scattering for a short wire is examined for two simple motions, rotation and vibration. Rotation of the wire causes an amplitude modulation and vibration causes a phase modulation. Each of these modulations influences the backscattered spectra so that the characteristic frequency of the periodic motion appears. For the rotating wire, it is twice the rotation frequency. From the spectra it is possible to recognize the type of motion responsible. The study therefore serves as a first step in the development of models for complicated motions of actual objects such as tanks and trucks, thereby leading to possible vehicle signature classification schemes. The appendices include: a brief discussion of the formalism of polarization scattering matrices; a short examination of the relation between the scattered spectra due to periodic motions and the conventional Doppler effect; and an examination of the analogy between the rotating and vibrating wires and molecules as conventional Raman scatters, including a brief section on the energetics of the scattering process.

NAVSTAR is a triservice satellite navigation system designed to provide the means for military aircraft, ships, and ground users throughout the world to obtain precise position and velocity information at any time of day, in any kind of weather. Since the user's position is measured by the time delays between his location and several satellites, the additional delay due to tropospheric refraction must be taken into account. For angles above 5 degrees the time delay, or corresponding range error, can be estimated from the local surface refractivity, if known. The worldwide statistics of surface refractivity analyzed in this report show that refractivity is correlated with site latitude, height above sea level, and season, all of which should be readily known. Regression lines for range error corrections based on these parameters are derived, and the accuracy of the corrections are estimated. At 5 degrees, the minimum elevation angle at which NAVSTAR is intended to be used, the range error is about 80 ft.

Results of radiometer measurements of infrared Hydroxyl (OH) emissions from five rocket flights are presented. Two of the rocket payloads were flown from Poker Flat Rocket Range, Alaska and three were flown from White Sands Missile Range, Nex Mexico. Four of the flights were flown during nighttime conditions and one (at WSMR) was flown during twilight (CHI = 99 deg). Each rocket payload was instrumented with liquid nitrogen cooled dual-channel radiometers to measure infrared OH emissions from the vibration-rotation bands 2-0 through 5-3 (1.56 micrometer channel) and the 7-5 through 9-7 (1.99 micrometer channel). The rocket data shows that the principle OH emissions in the bands cited occurs in a thin layer 8 to 10 km thick with peak emission near an altitude of 89 km. The ratio of nighttime 1.56 micrometer to 1.99 micrometer radiance is constant, at a value of 1.4, up to an altitude of 80 km regardless of latitude. At twilight, this ratio is larger at low altitudes (60 km) and diminishes with increasing altitude. Estimated nighttime peak volume emission rates at WSMR are 1 megaphotons per cm per sec per micrometer in the 1.56 micrometer band and 0.7 megaphotons per cu cm per sec per micrometer in the 1.99 micrometer band.

An investigation was made of the use of Transverse Electric (TE) Modes of propagation rather than the conventional Transverse Magnetic (TM) Modes at Very Low Frequencies. Theoretical comparisons show that TE waves should propagate better then TM waves in the earth-ionosphere waveguide under both normal and disturbed ionospheric conditions. Electromagnetic boundary conditions at the surface of the earth prevent efficient excitation and reception of radio waves generated in the TE Mode, but at higher altitudes, air-to-air communications is a practical reality., Presented at the Science and Engineering Symposium, Kirtland AFB, Albuquerque, N. Mex.

This is one of a series of reports on the Trailblazer II program. The particular aspect treated here involves the unmodified expansion-region plasma and its effect on an antenna located on the vehicle shoulder. This report describes some of the theoretical approaches used, discusses the levels of approximation involved, and shows the agreement between these various methods and the test data. The failure of a single set of assumptions to yield consistent agreement over a range of altitudes confirms the need to adopt flow models appropriate to the changing regimes encountered during reentry. One significant conclusion is that performance characteristics such as reflection and interantenna coupling which depend mostly on the level of peak electron density can be represented by simple plane wave, as well as by the more sophisticated slot antenna models. The latter approach, however, is necessary to describe propagation across the entire plasma sheath.

The surfaces of polished KCl samples, prepared by different mechanical polishing techniques, were examined using a scanning electron microscope and electron microprobe. An evaluation of the general quality of the polish and of the chemical composition of foreign matter found on the surface was completed. A qualitative analysis using an energy dispersive system was performed on all samples. Quantitative microanalysis was also completed. The results of these analyses and their implications are discussed in this report. The need for laser window materials with good optical and mechanical properties motivated this study.

A computational technique has been developed in one dimension for prediction of radiation-induced electrical currents and electrostatic fields in metal-dielectric slab structures. High energy radiation transport effects produce divergent electron currents, time-dependent electrostatic fields, and time-dependent conduction electron currents. These effects are considered and the computational technique predicts electric fields approaching breakdown intensity and time-dependent electrode currents which may even change sign. Brief comments on application of the technique to field effect electronic devices are included. Results are given for several metal-dielectric slab combinations under 200 keV and 1.25 MeV photon irradiations.

Re-entry weather encountered by Minuteman tests PVM-4 and PVM-3 is described in this report. Documentation was accomplished by WC-135B and WB-57F aircraft, by radar, and by lidar. Weather was essentially clear for each mission except for high thin cirrus layer clouds (water content less than 0.003 gm/cum) encountered by PVM-4. Low level clouds were present on each day. Data from all sources are presented, and operational problems of the weather documentation plan are discussed.

Reentry weather measurements conducted under the Minuteman Natural Hazards Program are described. The missions described are the SAC OT-45, the Minuteman PVM-8, and the ABRES RVTO. Documentation was accomplished primarily by instrumented C-130E and Cessna Citation aircraft, by high-power radar, and by satellite. All of these missions were postured to reenter in 'minimum weather' and the analysis shows that the weather objectives were met in all cases. One of the OT-45 RV's passed through clouds below 6 km, but the values of Weather Severity Index (WSI) were less than 0.1 for all the trajectories. The PVM-8 RV's passed through clouds at 14 km, 8 to 12 km, and below 6 km with maximum water content of 0.0015, 0.005, and 0.03 gm cu m respectively. WSI was 0.1 for RV1 and 0.2 for RV2. The RVTO reentry weather was clear except for thin scattered cirrus above 10 km altitude (water content less than 0.001 gm cu m). Simultaneous weather measurements were performed by aircraft and radar in the link-offset mode, in which the radar weather data were recorded at a fixed distance ahead of the aircraft.

A first-order model algorithm designed to reduce ionospheric time- delay errors by approximately 50% rms on a world-wide basis for single frequency users of the Global Positioning System/NAVSTAR is described. The algorithm was designed for greatest accuracy during times of day when ionospheric time-delay errors are expected to be largest. The algorithm is available in several options from one which requires only a monthly mean solar-flux value to one which requires 9 daily or monthly update coefficients. Several approximations also are made in the geometry calculations to further reduce operational user computer storage and running time requirements.

Design of certain Air Force systems intended for world-wide usage requires knowledge of the possible joint extremes of high temperatures with high humidity. Previous studies have addressed themselves to this problem, but the statistics reported therein were not presented in terms of joint occurrence frequencies. This study presents joint values of temperature (to 120F) and dew point (to 93F) equalled or exceeded from 0.1 to 80% of the time (hours) in the world's severest joint high-temperature, high-humidity environment (Abadan, Iran). These values are compared with the joint high-temperature, high-humidity criteria presented in Military Specification MIL-E-38453A. This comparison indicates that the use of MIL-E-38453A can lead to overdesign at temperatures above 120F and to underdesign at lower temperatures.

This report describes the construction and operation of a vacuum hot- pressing apparatus and details of a technique for hot-forging pure and doped alkali halide single crystals to produce high-strength IR windows without degrading optical absorption.

Reflector antennas designed with the aid of a technique by which the caustics of the subreflector are matched to those of the main reflector are shown to have the improved limited-sector-scanning capabilities. The matching is achieved over angular scanning sectors of interest by positioning and shaping subreflectors for parabolic cylinder and paraboloidal antennas. The important applications are in the traffic control radars and satellite communications where a small-aperture subreflector can be illuminated by a plane-wave source such as a small phased array, resulting in high-grain limited-scan beam-steering on a large-aperture reflector.

The Design Climatology Branch of the Air Force Cambridge Research Laboratories had the scientific responsibility for leading a DoD Task Group effort to revise MIL-STD-210A 'Climatic Extremes for Military Equipment'. This document represents the fruition of the goals of the task group. It relates the background studies supporting the values in MIL-STD-210B, so that MIL-STD-210B users need to consult only this single document for an elaboration on the MIL- STD-210B extremes. In addition, the report contains information on the origin, necessity for and the events leading to a revision of MIL-STD-210A. Discussions of the major changes in the Standard's philosophy and its contents are also provided., See also PB-121 741.

A FORTRAN computer program, LOWTRAN 3, is described for calculating the transmittance of the atmosphere in the spectral region from 0.25 to 28.5 micrometers at a spectral resolution of 20/cm. The program provides a choice of six atmospheric models covering seasonal and latitudinal variations from sea level to 100 km, two haze models, and accounts for molecular absorption, molecular scattering, and aerosol extinction. Refraction and earth curvature effects are also included. This program provides some modifications to the molecular absorption and aerosol extinction data provided in an earlier LOWTRAN 2 report. In addition, input modifications have been made, making the LOWTRAN 3 program considerably more flexible in terms of the input of meteorological data.

A novel, simplified approach to particle transport in slabs is given. The number of particles transmitted and reflected by a slab of finite thickness is obtained as a function of the number of collisions the particles receive. This 'orders-of-scattering' solution is facilitated by an invariant imbedding approach which leads to a set of integral recursion relations between transmitted and reflected particle currents. Solutions are given for both one- dimensional and three-dimensional transport in slabs for an arbitrary anisotropic scattering law.

A general model of high-energy laser interactions with solid surfaces is presented. Fluid transport equations are used to describe the heating and vaporization of a solid surface irradiated by intense laser energy. The vaporized target material diffuses into an ambient gas. Both the target vapor and ambient gas can ionize. Separate transport equations are used for the ambient gas, the gas of atoms in an excited state, the electrons, the target vapor, the ionized ambient gas, and the ionized target vapor. Among the over 30 physical processes included in the model are: laser wave absorption, electron and ion gas heating, diffusion of each species, excitation collisions, recombination, radiation transport, photoionization, shock formation, cascade ionization, thermionic emission, neutral impact ionization and energy, and momentum transfer among all fluid species. a computer program has been developed to numerically integrate these transport equations. The ignition and propagation of laser-supported absorption waves (LAWs) are studied as a function of incident power level. Graphs are presented of the temperature and density profiles of each species at various instants in time as a function of the incident laser power level. (Author)

The purpose of the DAASM project is to investigate the effects and limitations caused by the auroral and polar ionosphere on over-the-horizon HF propagation using a backscatter sounding system. The technique measures and records the complex amplitude of incoming, forward or backscatter signals, including noise, at each of the 12 elements of a broadside antenna array. The data is subsequently processed using sophisticated software on a CDC-6600 computer at AFCRL. This process, using Fourier analysis techniques, provides output in the form of Doppler frequency vs arrival-angle maps as well as coherence maps.

One of the questions most frequently asked by scientists/ experimenters who design balloon payloads concerns the magnitude of the opening forces of the parachute recovery system. Existing theory and an analytical method recently developed for horizontal deployment are adapted to balloon systems requirements. Engineering methods are used to develop expressions which allow the assessment of the parachute opening forces.

Updating a review of the global morphology of ionospheric scintillations published in 1971, this study adds additional experimental studies on familiar topics to newer types of measurements of ionospheric irregularities, including in situ experiments and artificial heating of the F- layer., See also report dated 16 Oct 1970, AD717694.

To develop alternative solutions to Air Force problems relating to signal transmission in the presence of ionization, AFCRL undertook an extensive investigation of techniques for modifying reentry plasmas. The program included laboratory tests and a series of reentry flight experiments. This report describes the flight test of one successful technique, Teflon ablation, a passive approach that requires no internal support systems. A reentry vehicle fitted with a Teflon-coated nosecap was instrumented to measure antenna impedance mismatch, interantenna coupling, signal attenuation, and charged-particle density. The probe data showed that the local boundary-layer electron density decreased by as much as a factor of 200. The Teflon coating effected a 25-dB decrease in S-band signal attenuation. High-power antenna breakdown was modified by the presence of the ablation products. Details of the vehicle design, flight dynamics, and ablation, are presented, and the results of the Teflon-ablation technique are contrasted with those of a successful liquid-injection technique that was tested on a previous flight. (Author)

Semi-transient and transient radiation-effects tests were performed on a Corning low-loss, radiation-resistant optical fiber. The semi-transient tests, which involved measurement of the fiber transmission during and after irradiation with X-rays, show this fiber to be much more resistant to permanent damage by radiation than other available glass fibers. The transient radiation- effects tests, in which the response of the fiber was measured during and for short times after pulses of X-rays and neutrons, show that the fiber may not be applicable to systems that cannot tolerate operational lapses of a few microseconds duration. This is because the fiber emits fluorescent radiation and shows temporary transmission losses during and shortly after pulses of radiation.

Polishing techniques used by AFCRL for polishing alkali halides are described. A brief rationale is given for the techniques and materials required for low damage window polishing. Step-by-step procedures are outlined for use by technician or higher level individuals interested in window polishing. Particular attention is given to methods of rough cutting mechanical polishing and chemical polishing of KCl crystals.

A simplified analysis was performed as a preliminary to a more elaborate analysis of data from an FM/CW backscatter sounder experiment known as RECAP in the polar winter ionosphere. The results show that a reasonably accurate simulation of ionogram data can be achieved with the simple procedure and these results are of value in themselves. A brief survey of the morphology of the polar winter ionosphere is included as an aid to further data interpretation. Particular attention was paid to the question of clutter, and a model for the different kinds thereof is presented. The suggestion that active control of the antenna radiation pattern may be used to mitigate against clutter degradation in an OTH backscatter radar was examined and found to have merit. Finally, the question of the observed signal strength characteristics was addressed and a model for non-deviative absorption is presented.

This publication contains preprints of papers presented at the Eighth AFCRL Scientific Balloon Symposium, 30 September to 3 October 1974, held at Hyannis, Mass. The papers are grouped in accordance with the five symposium sessions: Powered balloons; tethered balloons; free balloon technology; balloon-borne experiments; and special applications., See also Symposium no. 7, AD767582.

A model is presented for the thickness of the electron density profile in the region above the F layer maximum. The model varies with time and solar conditions; it is specified by observations or predictions of the height of the F layer maximum; and it is independent of latitude. Results indicate that a mean thickness parameter can be estimated to within about 15 percent and that there is a useful reduction in the day to day variability.

Computations of the observed frequency distribution of the magnitudes of vertical shears of horizontal winds between 5 and 20 km altitude are reported. The probability distribution of turbulent layers for various values of vertical thickness is discussed. An effective vertical-diffusion coefficient, Ke, is estimated from a simple model using this empirical turbulence probability distribution. Specifically, the authors calculate the effect of clear-air turbulence (CAT) upon vertical transport, using a model consisting of a vertical column of thin, randomly-spaced mixing (turbulent) layers separated by thick non-mixing atmospheric layers.

The change in apparent range between an L-Band Radar System and a high flying target introduced by a traveling ionospheric disturbance (TID) is calculated. Using an ambient Chapman electron density profile perturbated by a realistic TID model, the excess propagation time delay is determined by the use of ray-tracing techniques. For a fixed frequency, the variable component of group delay due to these irregularities is dependent on the direction of TID travel relative to the propagation path and the elevation angle. Numerical results for a typical case are represented.

This report covers the organizational, operational, funding, and logistic portions of the DoD-DASA effort at the Nevada Test Site during Operations Nougat and Sun Beam. Operations included Shots Hard Hat, Marshmallow, Danny Boy, Johnie Boy, Small Boy, Little Feller I and II, and the Vela-Uniform Program. The field activities started in November 1961 and ended in September 1962. Appendixes A through G contain shot and meteorological data, copies of statements of authority and agreements, information on reporting procedures, and a list of all reports resulting from both the Nevada and Pacific test operations conducted during 1962. The reports on the Pacific tests are listed as a convenience to readers interested in related projects in Operation Dominic., Extracted version of report dated 27 Feb 64.

The results of an investigation of the feasibility/desirability of conducting a demonstration experiment of ELF/VLF radio transmissions from a satellite to ground are described. Major problem areas are identified, the limitations of available information are discussed, and approaches, involving both theoretical and experimental efforts, are suggested for obtaining the necessary quantitative engineering data to plan such an experiment. Some aspects of possible Air Force uses of an ELF/VLF satellite communications system are also discussed.

The aim of this project was to measure high-altitude wind velocities and diffusion coefficients in the altitude region between 60 and 150 km. The method involved the ejection of a sodium vapor trail from a Cajun rocket at dust or dawn twilight. The sodium was sunlit, and as a result of emission of resonance radiation, was visible against a darkened background for about 20 minutes. The trail was photographed simultaneously from four different sites, allowing for subsequent triangulation to determine the altitude of various parts of the cloud. A major application of these wind and diffusion data, taken at dusk and dawn following the high-altitude nuclear tests, was to aid in determining the disposition of the nuclear debris., Extracted version of report dated 5 Apr 1965.

The first experimental objective in support of the Fish Bowl Series was to make accurate measurements of the physical properties of the normal atmosphere (1) to provide information required for an accurate analysis of blast and shock wave data, (2) to provide density data permitting a more precise determination of the Thor reentry trajectory and (3) to provide data required for accurate determination of the functional relationship between the ionization produced by the detonation and the radiation that produced it. The second objective was to make measurements shortly after each nuclear detonation to measure heating and changes in atmospheric density and pressure in the vicinity of the fireball., Extracted version of report dated 26 Mar 1965.

Reentry weather measurements conducted under the Minuteman Natural Hazards Program are described. The missions described here are PVM-6 and PVM-7, which were postured to reenter through 'heavy weather'. Documentation was accomplished primarily by instrumented C-130E and Cessna Citation aircraft, by high-power radar, and by satellite. The weather objective was met in a qualitative sense, in that the vehicles reentered through a thick cloud mass that was remarkably uniform horizontally in the reentry corridor. The weather Severity Indices (WSI) for the PVM-6 trajectories were 4.3, 5.9, and 3.6 for RV's 1, 2, and 3. The weather system was weakening by the time of the PVM-7 reentry, so that the WSI was 2.0 and 1.6 for RV's 1 and 2.

The objective of this project was to improve the basic understanding of the physics of high altitude nuclear detonations by measuring the thermal radiation from the high-altitude Shots Yucca, Orange, and Teak. Spectral irradiances obtained by distant airborne instrumentation are presented as a function of time in four wavelength bands. The measurements are extrapolated to an assumed point source, and these generalized results are discussed. Simple scaling laws are not sufficient to predict the thermal radiation from a high-altitude nuclear detonation. In particular, the power radiated in the infrared exceeds by a large factor that expected from a black body of dimensions comparable with the visible fireball. This implies the existence of some mechanism that is producing a greater proportion of infrared radiation than would be obtained using the equilibrium black body theory. Keywords: Thermal Radiation; High Altitude Bursts; Radiation Measurements; Atmospheric Transmission.

A new visibility instrument, the forward scatter visibility meter, has been developed. This report describes the development of the instrument, including the various field tests. Some thirty instruments have been operationally deployed in a network of automatic weather stations near L.G. Hanscom Field in Bedford, Mass. Comparisons between field instruments and transmissometers yield differences of about plus or minus 19 percent. Comparisons with visual observations show differences of plus or minus 34 percent and greater. Analyses of individual cases uncovered difficulties with the response time of observers and with ability to diagnose spatially varying visibility. The accuracy of visibility measurements is assessed and the report concludes by looking at the future of visibility instruments. (Author)

High resolution atmospheric transmittance curves are presented for the spectral region 320 to 13,200/cm (0.7576 to 31.25 micrometers). These spectra are useful as a guide for selecting laser wavelengths for atmospheric propagation studies in this spectral region. In addition, this report provides attenuation coefficients for those lines of the CO, HF, DF, and CO2 laser systems which suffer the least atmospheric attenuation. A new aerosol model is introduced here, taking into account recent measurements of the complex index of refraction of aerosol particles.

The photoelectric emission from films of LiF and KCl and sheet N due to extreme ultraviolet radiation of 8 photon energies from 10 to 50 eV has been studied with a planar-potential retarding analyzer. Current-voltage diagrams which provide an analysis of the normal energy of the emitted electrons have been obtained. Photons of energies greater than twice the depth of the filled band below vacuum potential produce an effect which may be interpreted as twoelectron emission. The results suggest this is an Auger process rather than being due to strong electron scattering. The results also indicate that the emission from LiF and KCl is preferentially in the forward direction., Reprint from Physical Review, 132:4, pp. 15701575, 15 Nov 1963.