Engineering topics

Jordan, R. L.

Publications and source records attributed to Jordan, R. L..

31 records · Page 2

NASA NTRS1982

Spaceborne synthetic-aperture imaging radars - Applications, techniques, and technology

In June 1978, the Seasat satellite was placed into orbit around the earth with a synthetic-aperture imaging radar (SAR) as one of the payload sensors. The Seasat SAR provided, for the first time, synoptic radar images of the earth's surface with a resolution of 25 m. In November 1981, the second imaging radar was successfully operated from space on the Shuttle. The Shuttle Imaging Radar-A acquired images over a variety of regions around the world with an imaging geometry different from the one used by the Seasat SAR. The spaceborne SAR principle is discussed, taking into account ambiguities, orbital and environmental factors, range curvature and range walk, surface interaction mechanisms, thermal and speckle noise, key tradeoff parameters, and nonconventional SAR systems. Attention is also given to spaceborne SAR sensors, the digital processing of spaceborne SAR data, the optical processing of spaceborne SAR data, postimage formation processing, data interpretation techniques and applications, and the next decade.

Elachi, C.↗

NASA NTRS1980

The Seasat-A synthetic aperture radar system

The paper discusses the Seasat-A synthetic aperture radar system (SAR). The objective of this system was to detect ocean waves from orbital altitudes. A SAR system operating at 1275 MHz was designed to meet this objective; the choice of wavelength resulted from the imagery obtained by aircraft during 1972 to 1974 and the ease of implementation. The Seasat-A SAR system was turned-on in orbit on July 4, 1978, and gathered imagery until the spacecraft bus failed in orbit in Oct. 1978. The hardware including the antenna, the radar sensor, and data-link subsystem, and the SAR data processing subsystem are described; the radar performance including the SAR system error budget and various SAR imageries are presented, concluding that the performance of the Seasat-A SAR system met all of its parameters on at least some of the imagery.

Jordan, R. L.↗

NASA NTRS1979

SEASAT-A synthetic aperture radar performance

The SEASAT-A satellite synthetic aperture radar (SAR) is presented, and its performance since it began operation in July 1978, is examined. The imaging radar system, the first to be designed as an orbital scientific instrument, was intended to generate continuous imagery over a 100-km swath at 25-m resolution from an altitude of 800 km. SAR image quality is measured in terms of resolution, the range of detectable radar backscatter, and the contrast ratio, each of which is affected by antenna, sensor, data link, and recording/processor subsystem parameters. Microdensitometer scans of output image film of actual SEASAT-A SAR data reveal a range resolution of less than 25 m, an azimuth resolution of approximately 40 m, a noise equivalent dynamic range of from 9.6 to -21 + or - 5 dB, and an image contrast ratio of 7.5 dB. SEASAT-A SAR performance is concluded to have confirmed the utility of spaceborne radar sensing.

Jordan, R. L.↗

NASA NTRS1978

Orbital radar evidence for lunar subsurface layering in Maria Serenitatis and Crisium

Data from the lunar-orbiting Apollo 17 radar sounding experiment (60-m wavelength) have been examined in both digital and holographic formats, and it is concluded that there are two subsurface radar reflectors below the surface in Mare Serenitatis and one reflector below the surface in Mare Crisium. The mean apparent depths of the reflectors below the surface of the former Mare are 0.9 and 1.6 km, while the reflector below the surface of the latter Mare has a mean depth of 1.4 km. These reflectors represent basin-wide subsurface interfaces. Techniques for reducing surface backscatter (clutter) in the data are described, and reasons for thinking that the distinct alignments in radar returns represent subsurface reflecting horizons are explained

Peeples, W. J.↗

NASA NTRS1978

Synthetic Aperture Radar (SAR) data processing

The available and optimal methods for generating SAR imagery for NASA applications were identified. The SAR image quality and data processing requirements associated with these applications were studied. Mathematical operations and algorithms required to process sensor data into SAR imagery were defined. The architecture of SAR image formation processors was discussed, and technology necessary to implement the SAR data processors used in both general purpose and dedicated imaging systems was addressed.

Beckner, F. L.↗

NASA NTRS1978

The SEASAT-A synthetic aperture radar design and implementation

The SEASAT-A synthetic aperture imaging radar system is the first imaging radar system intended to be used as a scientific instrument designed for orbital use. The requirement of the radar system is to generate continuous radar imagery with a 100 kilometer swath with 25 meter resolution from an orbital altitude of 800 kilometers. These requirements impose unique system design problems and a description of the implementation is given. The end-to-end system is described, including interactions of the spacecraft, antenna, sensor, telemetry link, recording subsystem, and data processor. Some of the factors leading to the selection of critical system parameters are listed. The expected error sources leading to degradation of image quality are reported as well as estimate given of the expected performance from data obtained during a ground testing of the completed subsystems.

Jordan, R. L.↗

NASA NTRS1977

A survey of SAR image-formation processing for earth resources applications

Currently there is considerable interest in active microwave sensors for earth resources applications, such as the SEASAT-A radar. However, to obtain spatial resolutions comparable to optical sensors at radar frequencies, sophisticated image formation processing techniques must be applied to the raw data. Processing requirements for non-coherent optical and coherent radar imaging systems are compared. The image formation processing requirements for synthetic aperture radar (SAR) systems are discussed. Both optical and digital techniques are addressed, and examples of hardware and imagery for each processing technique are presented.

Bayma, R. W.↗

NASA NTRS1977

A survey of SAR image-formation processing for earth resources applications

Currently there is considerable interest in active microwave sensors for earth resources applications. A particular example is the Seasat-A radar. However, to obtain spatial resolutions comparable to optical sensors at radar frequencies, sophisticated image formation processing techniques must be applied to the raw data. This paper briefly compares processing requirements for non-coherent optical and coherent radar imaging systems, and then discusses the image formation processing requirements for synthetic aperture radar (SAR) systems. Both optical and digital techniques are addressed, and examples of hardware and imagery for each processing technique are presented.

Bayma, R. W.↗

NASA NTRS1976

A Seasat-A Synthetic Aperture Imaging Radar System

The Seasat-A Synthetic Aperture Imaging Radar System is the first radar system of its kind designed for the study of ocean wave patterns from orbit. The basic requirement of this system is to generate continuous radar imagery with a 100-km swath with 25 m resolution from an orbital altitude of 800 km. These requirements impose unique system design problems and their solutions will be stated. The end to end data system will be described including interactions of the spacecraft, antenna, sensor, telemetry link, and data processor. The synthetic aperture radar system generates a large quantity of data (110 megabits per second) requiring the use of a dedicated data link. The data link selected for use with the synthetic aperture radar is an analog link with stable local oscillator encoding. The problems associated in telemetering the radar information with sufficient fidelity to synthesize an image on the ground will be described as well as the selected solutions to the problems.

Jordan, R. L.↗

NASA NTRS1976

The Seasat-A Synthetic Aperture Imaging Radar System

The Seasat-A Synthetic Aperture Imaging Radar System is the first radar system of its kind designed for orbital use. The requirement of this system is to generate continuous radar imagery with a 100-km swath with 25 m resolution from an orbital altitude of 800 km. These requirements impose unique system design problems and a description of the implementation will be given. The end to end data system will be described including interactions of the spacecraft, antenna, sensor, telemetry link, and data processor. The synthetic aperture radar system generates a large quantity of data (110 megabits per second) requiring the use of a dedicated data link. The data link selected for use with the synthetic aperture radar is an analog link with stable local oscillator encoding. The problems associated in telemetering the radar information with sufficient fidelity to synthesize an image on the ground will be described as well as the selected solutions to the problems. The interactions between the antenna attitude control system, rotation of the earth and the data processor will be described as well as proposed solutions, both optical and digital, to generate final imagery with the required 25 m resolution.

Jordan, R. L.↗

NASA NTRS1975

A SEASAT-A synthetic aperture imaging radar system

The SEASAT, a synthetic aperture imaging radar system is the first radar system of its kind designed for the study of ocean wave patterns from orbit. The basic requirement of this system is to generate continuous radar imagery with a 100 km swath with 25m resolution from an orbital altitude of 800 km. These requirements impose unique system design problems. The end to end data system described including interactions of the spacecraft, antenna, sensor, telemetry link, and data processor. The synthetic aperture radar system generates a large quantity of data requiring the use of an analog link with stable local oscillator encoding. The problems associated in telemetering the radar information with sufficient fidelity to synthesize an image on the ground is described as well as the selected solutions to the problems.

Jordan, R. L.↗

NASA NTRS1975

An earth and ocean SAR for Space Shuttle - User requirements and data handling implications

A brief summary is presented of user requirements for the Shuttle synthetic aperture radar (SAR) to be flown on a sortie mission of 7 to 10 days in duration, based on information collected from survey of the literature and direct user contacts. This information suggests selection of a dual frequency (L and X band) dual polarization SAR capable of meeting most user requirements. Particular attention is given to the SAR system specifications and the data handling capability expected to be available during the 1980s for the tracking and data relay satellite system (TDRSS). The data link requirements of the majority of Shuttle experiments will eventually determine whether the necessary high-capacity Shuttle-TDRSS return link will be part of the intrinsic Shuttle capability or will be part of the SAR payload.

Cohen, E. A.↗

NASA NTRS1974

The Apollo Lunar Sounder radar system

The objectives of the Apollo 17 Lunar Sounder Experiment (ALSE) were to detect subsurface geologic structures, to generate a continuous lunar profile, and to image the moon at radar wavelengths. A three-wavelength synthetic-aperture radar (SAR) operating at 60, 20, and 2 m wavelengths was designed to attain these objectives. The design choices reflected a balance of scientific requirements versus Apollo mission and hardware constraints. The radar data from the lunar mission were recorded on photographic film in a conventional SAR format, and were returned to earth for processing. A combination of optical and digital processing and exploitation techniques was applied to the scientific interpretation of the data. Some preliminary results from the lunar mission have been obtained.

Porcello, L. J.↗