The Effect of Spectral Shape on Clutter Standard Deviation

Many radar systems now employ wideband waveforms and noncoherent averaging techniques to reduce the scintillation of the backscatter from ground clutter. The purpose of this paper is to quantify the effects of the wideband spectral shape on the clutter standard deviation after noncoherent averaging of the received signal. Relationships are developed which quantify the clutter standard deviation for any spectral shape and any ratio of transmitted band-width to processed bandwidth.     

A Modification to Improve the Inverse Filter of Senmoto and Childers

An inverse filter, contained in a recently published paper by Senmoto and Childers, is improved by the application of a shaping function derived by Turin in an earlier paper.     

A Practical Distribution-Free Detection Procedure for Multiple-Range-Bin Radars

A distribution-free detection procedure for a multiplerange-bin radar is described. This procedure is based on the ranks of observations, but does not require elaborate equipment for rapidly ranking large amounts of data. Proposed equipment is described and analysis and results are given comparing this new procedure with certain practical (nondistribution-free) procedures. Comparisons with some "best" theoretical procedures are also given.     

The X-ray/Gamma-ray Spectrometer on the Near Earth Asteroid Rendezvous Mission

An X-ray/gamma-ray spectrometer has been developed as part of a rendezvous mission with the near-Earth asteroid, 433 Eros, in an effort to answer fundamental questions about the nature and origin of asteroids and comets. During about 10 months of orbital operations commencing in early 1999, the X-ray/Gamma-ray Spectrometer will develop global maps of the elemental composition of the surface of Eros. The instrument remotely senses characteristic X-ray and gamma-ray emissions to determine composition. Solar excited X-ray fluorescence in the 1 to 10 keV range will be used to measure the surface abundances of Mg, Al, Si, Ca, Ti, and Fe with spatial resolutions down to 2 km. Gamma-ray emissions in the 0.1 to 10 MeV range will be used to measure cosmic-ray excited elements O, Si, Fe, H and naturally radioactive elements K, Th, U to surface depths on the order of 10 cm. The X-ray spectrometer consists of three gas-filled proportional counters with a collimated field of view of 5° and an energy resolution of 850 eV @ 5.9 keV. Two sunward looking X-ray detectors monitor the incident solar flux, one of which is the first flight of a new, miniature solid-state detector which achieves 600 eV resolution @ 5.9 keV. The gamma-ray spectrometer consists of a NaI(Tl) scintillator situated within a Bismuth Germanate (BGO) cup, which provides both active and passive shielding to confine the field of view and eliminate the need for a massive and costly boom. New coincidence techniques enable recovery of single and double escape events in the central detector. The NaI(Tl) and BGO detectors achieve energy resolutions of 8.7% and 14%, respectively @ 0.662 MeV. A data processing unit based on an RTX2010 microprocessor provides the spacecraft interface and produces 256-channel spectra for X-ray detectors and 1024-channel spectra for the raw, coincident, and anti-coincident gamma-ray modes. This paper presents a detailed overview of the X-ray/Gamma-ray Spectrometer and describes the science objectives, measurement objectives, instrument design, and shows some results from early in-flight data.     

An Enduring Partnership Professional, Cultural, Personat

20 years ago, in September 1987, an adventure began which was unique in aviation/aerospace publishing. That adventure led to a multimedia partnership which has grown stronger every year since 1987 and developed into a lasting friendship and global business alliance that continues today.     

Atmospheric Attenuation Models for Satellite-To-Earth Links

In an earlier paper by the authors1 it was mentioned that atmospheric attenuation effects could be included by assuming that the attenuation is directly proportional to number of air masses. While this assumption is valid for the optical region, it is not true in the microwave region (1 to 40 GHz). For a clear atmosphere, the two constituents which absorb microwaves are oxygen and water vapor. An analysis of the atmospheric attenuation data for the microwave region has been made and some rather simple expressions for computing the attenuation as a function of zenith angle are developed with an accuracy suitable for satellite antenna footprint calculations.     

Observations of 1–30 MeV gamma rays from the galactic center

Preliminary results are reported for gamma ray observations of the galactic center region made during a 15 hour balloon flight from Alice Springs, Australia on April 18, 1979. The observations were carried out with the UCR double-scatter gamma-ray telescope at energies of 1 to 30 MeV. The observations are compatible with a galactic source of approximately equal brightness along the region 300°<ℓII<60°. The energy distribution joins smoothly to previous spark chamber results at energies above 30 MeV and to scintillator results below 1 MeV. It appears to be a combination of nuclear gamma ray lines superimposed on a bremsstrahlung spectrum with a power law (1.3±.7) × 10⁻³ E⁻(^1.7±.2). The ¹²C* line at 4.4 MeV appears to be present with a significance of about 16σ. The flux in the line is (6±3) × 10⁻⁴photons cm⁻²s⁻¹rad⁻¹. The oxygen line at 6.1 MeV does not seem to appear significantly above background.     

行星际磁场与磁尾磁通量绳形成的关系

收集了Cluster卫星在2001-2005年间观测到的磁尾磁通量绳事件,并对磁通量绳(magnetic flux rope)形成及其内部磁场结构与行星际磁场(IMF)的关系作了统计研究.考虑磁通量绳被观测到时行星际磁场的条件,在所有73个磁通量绳事件中,行星际磁场By分量占有主导地位的事件有80%,且78%的事件具有与行星际磁场By分量相同方向的核心场.行星际磁场通过在磁层顶与地球磁场相互作用改变南北等离子体片内磁场相对方向,形成有利于磁通量绳形成的磁场位形,并且行星际磁场By分量的方向对磁通量绳内部核心场的方向具有决定性影响.从统计结果来看,磁通量绳的形成并不会依赖于行星际磁场Bz分量的方向.     

NASA Human Health and Performance Center: Open innovation successes and collaborative projects

In May 2007, what was then the Space Life Sciences Directorate published the 2007 Space Life Sciences Strategy for Human Space Exploration, setting the course for development and implementation of new business models and significant advances in external collaboration over the next five years. The strategy was updated on the basis of these accomplishments and reissued as the NASA Human Health and Performance Strategy in 2012, and continues to drive new approaches to innovation for the directorate. This short paper describes the successful execution of the strategy, driving organizational change through open innovation efforts and collaborative projects, including efforts of the NASA Human Health and Performance Center (NHHPC).