9,779 research outputs found
Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4
Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences
Lunar contour mapping system /lucom/ final report, 5 aug. 1964 - 18 mar. 1965
Radar sensor system for acquisition of lunar surface data - Lunar contour mapping syste
MIMO Radar Target Localization and Performance Evaluation under SIRP Clutter
Multiple-input multiple-output (MIMO) radar has become a thriving subject of
research during the past decades. In the MIMO radar context, it is sometimes
more accurate to model the radar clutter as a non-Gaussian process, more
specifically, by using the spherically invariant random process (SIRP) model.
In this paper, we focus on the estimation and performance analysis of the
angular spacing between two targets for the MIMO radar under the SIRP clutter.
First, we propose an iterative maximum likelihood as well as an iterative
maximum a posteriori estimator, for the target's spacing parameter estimation
in the SIRP clutter context. Then we derive and compare various
Cram\'er-Rao-like bounds (CRLBs) for performance assessment. Finally, we
address the problem of target resolvability by using the concept of angular
resolution limit (ARL), and derive an analytical, closed-form expression of the
ARL based on Smith's criterion, between two closely spaced targets in a MIMO
radar context under SIRP clutter. For this aim we also obtain the non-matrix,
closed-form expressions for each of the CRLBs. Finally, we provide numerical
simulations to assess the performance of the proposed algorithms, the validity
of the derived ARL expression, and to reveal the ARL's insightful properties.Comment: 34 pages, 12 figure
Comparison of wind velocity in thunderstorms determined from measurements by a ground-based Doppler radar and an F-106B airplane
As a part of the NASA Storm Hazards Program, the wind velocity in several thunderstorms was measured by an F-106B instrumented airplane and a ground-based Doppler radar. The results of five airplane penetrations of two storms in 1980 and six penetrations of one storm in 1981 are given. Comparisons were made between the radial wind velocity components measured by the radar and the airplane. The correlation coefficients for the 1980 data and part of the 1981 data were 0.88 and 0.78, respectively. It is suggested that larger values for these coefficients may be obtained by improving the experimental technique and in particular by slaving the radar to track the airplane during such tests
Innovative observing strategy and orbit determination for Low Earth Orbit Space Debris
We present the results of a large scale simulation, reproducing the behavior
of a data center for the build-up and maintenance of a complete catalog of
space debris in the upper part of the low Earth orbits region (LEO). The
purpose is to determine the performances of a network of advanced optical
sensors, through the use of the newest orbit determination algorithms developed
by the Department of Mathematics of Pisa (DM). Such a network has been proposed
to ESA in the Space Situational Awareness (SSA) framework by Carlo Gavazzi
Space SpA (CGS), Istituto Nazionale di Astrofisica (INAF), DM, and Istituto di
Scienza e Tecnologie dell'Informazione (ISTI-CNR). The conclusion is that it is
possible to use a network of optical sensors to build up a catalog containing
more than 98% of the objects with perigee height between 1100 and 2000 km,
which would be observable by a reference radar system selected as comparison.
It is also possible to maintain such a catalog within the accuracy requirements
motivated by collision avoidance, and to detect catastrophic fragmentation
events. However, such results depend upon specific assumptions on the sensor
and on the software technologies
Investigation of continental drift, phase 1 effort Progress report, 1 Apr. - 30 Sep. 1968
Feasibility of using ultrashort pulse laser ranging and independent clock radio interferometry distance measurement methods to test for existence of continental drif
Ionospheric gravity wave measurements with the USU dynasonde
A method for the measurement of ionospheric Gravity Wave (GW) using the USU Dynasonde is outlined. This method consists of a series of individual procedures, which includes functions for data acquisition, adaptive scaling, polarization discrimination, interpolation and extrapolation, digital filtering, windowing, spectrum analysis, GW detection, and graphics display. Concepts of system theory are applied to treat the ionosphere as a system. An adaptive ionogram scaling method was developed for automatically extracting ionogram echo traces from noisy raw sounding data. The method uses the well known Least Mean Square (LMS) algorithm to form a stochastic optimal estimate of the echo trace which is then used to control a moving window. The window tracks the echo trace, simultaneously eliminating the noise and interference. Experimental results show that the proposed method functions as designed. Case studies which extract GW from ionosonde measurements were carried out using the techniques described. Geophysically significant events were detected and the resultant processed results are illustrated graphically. This method was also developed for real time implementation in mind
Multiple Target Tracking
Due to radar\u27s range measurement accuracy, Range Time plots are used to represent radar data. When objects\u27 tracks cross on a Range Time plot, it is uncertain which track belongs to which target. An analysis of the frequency and angle of these crossings was performed. Mathematical analysis concluded that in certain situations, only one type of crossing can result. Further Monte Carlo simulations were used to study these crossing statistics in other situations. In addition, it was examined how well targets could be tracked through an individual crossing. The probabilities of correct track association were calculated as a function of a variety of factors. Given our models and assumptions, sensor fusion of Range Time and Range Doppler analysis substantially improved crossing classification
Software Defined Radio Based Frequency Modulated Continuous Wave Ground Penetrating Radar
Frequency modulated continuous wave (FMCW) radar allows for a wide range of research applications. One primary use of this technology and what is explored in this thesis, is imaging in the form of ground penetrating radar. To generate proper results, spectral wide-band reconstruction has been developed to overcome hardware limitations allowing for high resolution radar. Requiring complex reconstruction algorithms, the proposed method benefits greatly in terms of performance and implementation compared to other radar systems.
This thesis develops a wideband linearly frequency modulated radar leveraging a software-defined radio (SDR). The modular system is capable of a tunable wideband bandwidth up to the maximum SDR ratings. This high-resolution system is further improved through implementation of grating side-lobe suppression filters that correct for the spectral discontinuities imposed by the reconstruction. These grating lobes are managed through multiple techniques to alleviate any ghost imaging or false positives associated with object detection. The solution provided allows for generally non-coherent devices to operate with synchronous phase giving accurate sample-level measurements. Various corrections are in place as mitigation of hardware transfer functions and system level noise. First the system was theorized and simulated, illuminating the performance of the radar. Following development of the radar, measurements were conducted to confirm proper and accurate object detection. Further experiments were performed ensuring Ground Penetrating Radar (GPR) performance as designed. Applications of this work include Synthetic Aperture Radar (SAR) imaging, innovative GPR, and unmanned aerial vehicle (UAV) systems
Multiple Target Tracking
Due to radar\u27s range measurement accuracy, Range Time plots are used to represent radar data. When objects\u27 tracks cross on a Range Time plot, it is uncertain which track belongs to which target. An analysis of the frequency and angle of these crossings was performed. Mathematical analysis concluded that in certain situations, only one type of crossing can result. Further Monte Carlo simulations were used to study these crossing statistics in other situations. In addition, it was examined how well targets could be tracked through an individual crossing. The probabilities of correct track association were calculated as a function of a variety of factors. Given our models and assumptions, sensor fusion of Range Time and Range Doppler analysis substantially improved crossing classification
- …