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Davisson, L. D.

Publications and source records attributed to Davisson, L. D..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The U.S. Sarsat geosynchronous experiment - Ground processor description and test results

The development of a specialized digital signal processor, the Geosynchronous Signal Processor (GSP), for short beacon burst signal detection and demodulation is described. The processing is based on fast Fourier Transform techniques for detection and message integration on the respective message bursts for demodulation. The GSP is based on array processor technology; it is designed to yield an ultimate capacity of 50-75 simultaneous beacon transmissions within the nominal 20 KHz bandwidth centered at 406.025 MHz.

Flikkema, P. G.↗
NASA NTRS1980

Search and rescue emergency locating transmitter detection/location procedure via TIROS satellite

A procedure is described which works effectively to detect and locate emergency locating transmitters (ELTs) and emergency position indicating radio beacons (EPIRBs) in a multisignal environment. Using data generated from several manufactured ELTs with diverse superimposed Doppler curves, as many as 9 simultaneous ELTs can be detected and located at a variety of signal strengths. It is noted that average position errors of 10 km are attainable today at signal power to noise spectral density ratios as low as 17 dB-Hz.

Wren, P. E.↗
NASA NTRS1977

Monte Carlo simulation of wave sensing with a short pulse radar

A Monte Carlo simulation is used to study the ocean wave sensing potential of a radar which scatters short pulses at small off-nadir angles. In the simulation, realizations of a random surface are created commensurate with an assigned probability density and power spectrum. Then the signal scattered back to the radar is computed for each realization using a physical optics analysis which takes wavefront curvature and finite radar-to-surface distance into account. In the case of a Pierson-Moskowitz spectrum and a normally distributed surface, reasonable assumptions for a fully developed sea, it has been found that the cumulative distribution of time intervals between peaks in the scattered power provides a measure of surface roughness. This observation is supported by experiments.

Levine, D. M.↗
NASA NTRS1977

Tornado detection data reduction and analysis

Data processing and analysis was provided in support of tornado detection by analysis of radio frequency interference in various frequency bands. Sea state determination data from short pulse radar measurements were also processed and analyzed. A backscatter simulation was implemented to predict radar performance as a function of wind velocity. Computer programs were developed for the various data processing and analysis goals of the effort.

Davisson, L. D.↗
NASA NTRS1976

Data processing/display design for the space shuttle/spacelab Electromagnetic Environment Experiment (EEE)

Methods for data analysis, data compression including universal coding, storage and retrieval on random access storage devices, and display were developed and implemented on the GSFC Interdata computer. The original 64 bit per frequency band representation was reduced to 10 bits through source coding/universal coding, a compression ratio of 6.4, prior to storage. Rapid encoding/decoding was achieved by the algorithms used so that rapid random access is retained.

Davisson, L. D.↗
NASA NTRS1976

Reduction and analysis of data collected during the electromagnetic tornado experiment

Techniques for data processing and analysis are described to support tornado detection by analysis of radio frequency interference in various frequency bands, and sea state determination from short pulse radar measurements. Activities include: strip chart recording of tornado data; the development and implementation of computer programs for digitalization and analysis of the data; data reduction techniques for short pulse radar data, and the simulation of radar returns from the sea surface by computer models.

Davisson, L. D.↗
NASA NTRS1976

Daily weather direct readout microprocessor study

The work completed included a study of the requirements and hardware and software implementation techniques for NIMBUS ESMR and TWERLE direct readout applications using microprocessors. Many microprocessors were studied for this application. Because of the available Interdata development capabilities, it was concluded that future implementations be on an Interdata microprocessor which was found adequate for the task.

Davisson, L. D.↗
NASA NTRS1975

On-board data management study for EOPAP

The requirements, implementation techniques, and mission analysis associated with on-board data management for EOPAP were studied. SEASAT-A was used as a baseline, and the storage requirements, data rates, and information extraction requirements were investigated for each of the following proposed SEASAT sensors: a short pulse 13.9 GHz radar, a long pulse 13.9 GHz radar, a synthetic aperture radar, a multispectral passive microwave radiometer facility, and an infrared/visible very high resolution radiometer (VHRR). Rate distortion theory was applied to determine theoretical minimum data rates and compared with the rates required by practical techniques. It was concluded that practical techniques can be used which approach the theoretically optimum based upon an empirically determined source random process model. The results of the preceding investigations were used to recommend an on-board data management system for (1) data compression through information extraction, optimal noiseless coding, source coding with distortion, data buffering, and data selection under command or as a function of data activity, (2) for command handling, (3) for spacecraft operation and control, and (4) for experiment operation and monitoring.

Davisson, L. D.↗
NASA NTRS1975

ITOS VHRR on-board data compression study

Data compression methods for ITOS VHRR data were studied for a tape recorder record-and playback application. A playback period of 9 minutes was assumed with a nominal 18 minute record period for a 2-to-1 compression ratio. Both analog and digital methods were considered with the conclusion that digital methods should be used. Two system designs were prepared. One is a PCM system and the other is an entropy-coded predictive-quantization, sometimes called entropy-coded DPCM or just DPCM, system. Both systems use data management principles to transmit only the necessary data. Both systems use a medium capacity standard tape recorder from specifications provided by the technical officer. The 10 to the 9th power bit capacity of the recorder is the basic limitation on the compression ratio. Both systems achieve the minimum desired 2 to 1 compression ratio. A slower playback rate can be used with the DPCM system due to a higher compression factor for better link performance at a given CNR in terms of bandwidth utilization and error rate. The report is divided into two parts. The first part summarizes the theoretical conclusions of the second part and presents the system diagrams. The second part is a detailed analysis based upon an empirically derived random process model arrived at from specifications and measured data provided by the technical officer.

Gray, R. M.↗
NASA NTRS1975

Advances in data compression

A rigorous real-variables treatment of general data compression and encoding problems, centered on formulation and proof of relevant existence theorems and a unified formulation of source coding (both noiseless and with a fidelity criterion) in inaccurately or incompletely specified statistical environments. Difficulties in modeling of sources with unknown or imperfectly known statistical descriptions are analyzed and source codes (SC) are classified (variable-rate noiseless SC, fixed-rate noiseless SC) and analyzed, along with types of code sequences (weighted-universal, maximin-universal, strongly or weakly minimax-universal). Universal coding on video data, variable-rate coding with distortion, and distortion-rate functions are discussed. Design strategies for universal coding algorithms are suggested, but the article is not oriented to specific methods of synthesizing data compression systems.

Davisson, L. D.↗
NASA NTRS1975

An operational video data compression system for ATS and ITOS

An operational data compression system has been developed and implemented for transmission of digitized ATS and ITOS-VHRR satellite video data over the wideband communication link between the Wallops Island, Va. Command and Data Acquisition Station and the National Environmental Satellite Service at Suitland, Md. This system uses minicomputers for the coding and decoding of the data to achieve maximum flexibility together with specially designed interface equipment for greater efficiency. No loss in data quality occurs due to the compression, and, in certain cases, data is transmitted which would be otherwise unavailable due to the limited channel capacity. This paper describes the method of compression, the equipment used, and the compression results attained.

Kutz, R. L.↗
NASA NTRS1974

The ergodic decomposition of stationary discrete random processes

The ergodic decomposition is discussed, and a version focusing on the structure of individual sample functions of stationary processes is proved for the special case of discrete-time random processes with discrete alphabets. The result is stronger in this case than the usual theorem, and the proof is both intuitive and simple. Estimation-theoretic and information-theoretic interpretations are developed and applied to prove existence theorems for universal source codes, both noiseless and with a fidelity criterion.

Gray, R. M.↗
NASA NTRS1972

Advanced communications techniques

Research results obtained under the Advanced Communications Techniques grant are introduced through a list of lectures and papers.

Davisson, L. D.↗
NASA NTRS1972

An operational data compression system using minicomputers.

Functional description of the real-time programmable data compression system that has been developed for operation between the data acquisition and satellite service ground stations and the ATS 1 and 3 satellites. The source data consist of TV pictures from these satellites that are received, compressed, transmitted, and reconstructed in real-time. General purpose minicomputers and specially designed I/O channels are used for compression and reconstruction. The installed compression system has passed all system input-output tests. Because of the great flexibility of the minicomputers, it is possible to vary the compression and to perform auxiliary tasks, such as data formatting.

Davisson, L. D.↗
NASA NTRS1971

A real time programmable data compression system for video data.

Description of the implementation of a data compression system for the real-time operational transmission (through microwave links) of ATS satellite pictures between the command and data acquisition station and a central location for computer processing. The system features the use of general-purpose minicomputers for encoding and decoding; this makes it possible to vary the employed data compression technique and to make simultaneous statistical calculations on the data. Data compression and expansion is accomplished in a manner that does not lower data quality.

Kutz, R. L.↗