New Concepts in Collision Avoidance Logic

Airborne collision avoidance logic is being developed to take advantage of the accurate bearing measurements provided by the Enhanced TCAS II system. This system issues horizontal and vertical resolution advisories, and should give fewer unnecessary alarms than earlier systems. Design tradeoffs and new techniques are described for threat detection, modeling of potential escape maneuvers, and the selection of resolution advisories. Plans for further development and evaluation are described.     

The interpretations of ultraviolet observations of comets

Summary Ultraviolet observations of comets from above the Earth's atmosphere have provided excellent new results and improved older ground based observations (OH) by an order of magnitude. Satellites are especially suitable because long integration times and observations during extended time intervals are possible.The existing cometary L observations have confirmed the relatively high overall gas production rates on the order of 10³⁰ molecule s^–1. The results strongly support the concept of an icy conglomerate solid cometary nucleus. Additional observations of hydroxyl and oxygen favor water to be one of the most abundant molecules in comets. The observations are in agreement with the predominent role of water in the evaporation process of the nuclear ices but are not proof in themselves.Water did not outnumber other consitutents by orders of magnitude in comets Bennett and Kohoutek. At least in these comets, carbon-containing molecules were possibly as numerous as water. Determination of the carbon scale length is necessary for a more quantitative statement.A hydrogen velocity of 7–9 km s^–1 was observed in comet Bennett as well as in comet Kohoutek for a variety of heliocentric distances and varying production rates. Determinations of the outflow velocity from L isophotes agree with line profile observations of L and H. Hydroxyl may constitute the main source for the hydrogen atoms with v _H - 8 km s^–1. The decay process, however, leading to this particular velocity is not yet known. Possibly a large portion of the OH radicals do not decay into hydrogen atoms or at least not into slow ones. If the high velocity component of 20 km s^–1 or more comprises a larger amount (up to 50%), most of the quoted hydrogen production rates must be revised upward.The intrinsic cometary brightness is only a very crude indicator of a comet's actual gas production rate as shown by comparison of comets Bennett and TSK. Comets can be successfully used as (extra ecliptic) space probes to measure interplanetary quantities, e.g., the curvature of the extended hydrogen clouds can be used for the absolute determination of the solar emission independent of instrumental calibration. Generally time dependent hydrogen density models must be used for the interpretation. The strength of the ultraviolet L emission favors its measurement as a standard procedure for the observation of comets (possibly together with OH (3090 Å)). These observations provide the most accurate results on the total cometary gas production rate and its variation with heliocentric distance.Dedicated to Professor L. Biermann in recognition of his inspiring guidance.On leave of absence from Max-Planck-Institut für Physik und Astrophysik, Munich.     

Synchronization of QAM Signals in the Presence of ISI

A data-aided carrier reconstruction method is described for quadrature amplitude modulation (QAM) data communications over narrow-band transmission channels. Previous analyses of this problem have assumed an "infinite" bandwidth of the communication link, so that negligible intersymbol interference (ISI) resulted. On the contrary, when ISI takes place, a different structure must be used which operates on sampled data. The performance of this structure is expressed analytically as a function of 1) the statistics of the message symbols, 2) the characteristics of the channel, and 3) the parameters of the tracking system. Excellent agreement has been found between the theory and the results of a computer simulation.     

Low-cost simulator for basic radar signals

Most modern radar simulators are costly and need cumbersome operations while used. Besides, they have many features not suitable for preliminary level. Basic training of radio monitoring personnel can be carried out with a simple and inexpensive system capable of producing both staggered and frequency hopping pulse radar signals with radiation pattern modulation. For operator convenience the system is programmed with basic programming language     

Global pictures of the ozone field,from high altitudes,from DE-I

Using the imaging instrumentation aboard the Dynamics Explorer spacecraft (DE-I), total column ozone densities are obtained in the sunlit hemisphere by measuring the intensities of backscattered solar ultraviolet radiation with multiple filters and multiple photometers. The high apogee altitude (23,000 km) of the eccentric polar orbit allows high resolution global-scale images of the terrestrial ozone field to be obtained within 12 minutes. Previous ozone-monitoring spacecraft have required much longer time periods for comparable spatial coverage because of their lower altitudes (<1200 km). The much higher altitude of DE-I also provides hours of continuous imaging of features compared to minutes or seconds with previous spacecraft. Near perigee, high resolution images can be gained with pixel size as small as 3 km to view mesoscale atmospheric variations. Utilizing these data, the effects of planetary-scale, synoptic-scale, and mesoscale dynamical processes, which control the distribution of ozone near the tropopause, can be studied. Preliminary results show short-term (less than one day) variations in the synoptic ozone field and these variations appear to be in accord with meteorological data. Spatial variations in the ozone field are found to be highly negatively correlated with tropopause altitude.     

A new spectrometric measurement of atmospheric 63 μm emission

Absolute zenith intensities of the atomic oxygen fine structure emission at 63 μm were measured above Kiruna, Sweden, on 9 December 1981 in the altitude regime of 85 km to 237 km. The measured data are compared with theoretical predictions for this emission. Both local thermodynamic equilibrium (LTE) and non-LTE conditions were assumed for the model intensity calculations. The importance of the 63 μm emission as a cooling mechanism of the thermosphere is briefly discussed.     

Daytime O/N<Subscript>2</Subscript> Retrieval Algorithm for the Ionospheric Connection Explorer (ICON)

The NASA Ionospheric Connection Explorer Far-Ultraviolet spectrometer, ICON FUV, will measure altitude profiles of the daytime far-ultraviolet (FUV) OI 135.6 nm and N₂ Lyman-Birge-Hopfield (LBH) band emissions that are used to determine thermospheric density profiles and state parameters related to thermospheric composition; specifically the thermospheric column O/N₂ ratio (symbolized as \(\Sigma\)O/N₂). This paper describes the algorithm concept that has been adapted and updated from one previously applied with success to limb data from the Global Ultraviolet Imager (GUVI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission. We also describe the requirements that are imposed on the ICON FUV to measure \(\Sigma\)O/N₂ over any 500-km sample in daytime with a precision of better than 8.7%. We present results from orbit-simulation testing that demonstrates that the ICON FUV and our thermospheric composition retrieval algorithm can meet these requirements and provide the measurements necessary to address ICON science objectives.