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Keafer, L. S., Jr.

Publications and source records attributed to Keafer, L. S., Jr..

18 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Radiometer requirements for Earth-observation systems using large space antennas

Requirements are defined for Earth observation microwave radiometry for the decade of the 1990's by using large space antenna (LSA) systems with apertures in the range from 50 to 200 m. General Earth observation needs, specific measurement requirements, orbit mission guidelines and constraints, and general radiometer requirements are defined. General Earth observation needs are derived from NASA's basic space science program. Specific measurands include soil moisture, sea surface temperature, salinity, water roughness, ice boundaries, and water pollutants. Measurements are required with spatial resolution from 10 to 1 km and with temporal resolution from 3 days to 1 day. The primary orbit altitude and inclination ranges are 450 to 2200 km and 60 to 98 deg, respectively. Contiguous large scale coverage of several land and ocean areas over the globe dictates large (several hundred kilometers) swaths. Radiometer measurements are made in the bandwidth range from 1 to 37 GHz, preferably with dual polarization radiometers with a minimum of 90 percent beam efficiency. Reflector surface, root mean square deviation tolerances are in the wavelength range from 1/30 to 1/100.

Keafer, L. S., Jr.↗
NASA NTRS1983

Pushbroom radiometry and its potential using large space antennas

Electromagnetic radiation is emitted by matter which was heated to a temperature above absolute zero. The amount of blackbody radiation in the microwave frequency region of interest (10 to the 8th power f 10 to the 10th power Hz) emitted by matter can be determined from the Rayleigh-Jeans approximation to Planck's Radiation Law. The amount of electromagnetic radiation from matter which is not a blackbody is a function of the emissivity of the material. The emissivity is a factor less than unity and is a function of several parameters including chemical composition, temperature, frequency, surface characteristics, and viewing angle. A radiometer is an instrument which detects and provides a measure of the electromagnetic radiation being emitted by a material or surface area within the radiometer's antenna beamwidth. Microwave radiometers provide the capability for remote measurements from Earth orbits of geophysical parameters. These measurements will require the use of a microwave imaging radiometer using a large aperture deployable antenna with multiple beams in a pushbroom mode to achieve high spatial resolution and large swath width.

Harrington, R. F.↗
NASA NTRS1983

A summary of mission and system performance requirements for large space antennas

Mission definition studies and system analyses have been described for a number of potential civilian missions and a few military missions. In this paper, an attempt is made to summarize the most formidable mission and system performance requirements for large space antennas. The emphasis will be on the civilian systems; only those aspects of military mission and system requirements that are unclassified are included.

Keafer, L. S., Jr.↗
NASA NTRS1982

Tropospheric Passive Remote Sensing

The long term role of airborne/spaceborne passive remote sensing systems for tropospheric air quality research and the identification of technology advances required to improve the performance of passive remote sensing systems were discussed.

Keafer, L. S., Jr.↗
NASA NTRS1982

Radiometer mission requirements for large space antenna systems

Requirements are defined for Earth observational microwave radiometry using large space antenna systems with apertures in the 50 to 200 meter range. General Earth observational needs, specific measurement requirements, orbital mission guidelines and constraints, and general radiometric requirements are defined. Specific measurements include soil moisture, water surface temperature, water roughness, ice boundaries, salinity, and water pollutants. Measurements with 10 to 1 km spatial resolution and 3 to 1 day temporal resolution are required.

Keafer, L. S., Jr.↗
NASA NTRS1982

Results from the July 1981 Workshop on Passive Remote Sensing of the Troposphere

Potential roles of passive remote sensors in the study of the chemistry and related dynamics of the lower atmosphere were defined by a Tropospheric Passive Remote Sensing Workshop, and technology advances required to implement these roles were identified. A promising role is in making global-scale, multilayer measurements of the more abundant trace tropospheric gaseous species (e.g., O3, CO, CH4, HNO3) and of aerosol thickness and size distribution. It includes both nadirand limb-viewing measurements. Technology advances focus on both scanning- and fixed-spectra, nadir-viewing techniques with resolutions of 0.1 kaysers or better. Balloon- and Shuttle-borne experiments should be performed to study the effects of instrument noise and background fluctuations on data inversion and to determine the utility of simultaneously obtained nadir- and limb-viewing data.

Keafer, L. S., Jr.↗
NASA NTRS1982

Sensor technology for future atmospheric observation systems

The remote sensing instruments that will be needed for research in atmospheric environmental quality in the future are considered. The needs are determined on the basis of a model that incorporates scientific knowledge objectives, measurement needs, and potential space missions, spacecraft and instruments in order to discern the technology requirements. While emphasis is placed on global surveys that make full use of the synoptic observation capabilities of spaceborne sensors, the importance of airborne and ground-based sensors in this research is also recognized. Several of the instruments that are identified to fulfill the knowledge objectives are spectrometers and radiometers using such passive measurement techniques as interferometer correlation absorption radiometry, and heterodyne spectrometry. Lidar instruments are also seen as important future developments.

Alvarado, U. R.↗
NASA NTRS1981

Mission definition for a large-aperture microwave radiometer spacecraft

An Earth-observation measurements mission is defined for a large-aperture microwave radiometer spacecraft. This mission is defined without regard to any particular spacecraft design concept. Space data application needs, the measurement selection rationale, and broad spacecraft design requirements and constraints are described. The effects of orbital parameters and image quality requirements on the spacecraft and mission performance are discussed. Over the land the primary measurand is soil moisture; over the coastal zones and the oceans important measurands are salinity, surface temperature, surface winds, oil spill dimensions and ice boundaries; and specific measurement requirements have been selected for each. Near-all-weather operation and good spatial resolution are assured by operating at low microwave frequencies using an extremely large aperture antenna in a low-Earth-orbit contiguous mapping mode.

Keafer, L. S., Jr.↗
NASA NTRS1981

Radiometer design concepts for large aperture microwave radiometer spacecraft

Concepts involving active and passive microwave systems for soil-moisture monitoring are discussed. It is shown that the first major development efforts should be directed toward the simpler passive design concepts. Subsequently, five passive design concepts for a microwave radiometer spacecraft are outlined and compared. Some common technology needs, such as large space structures and controls, are shown to exist. Also, some peculiar technology needs are identified, such as complicated phasing networks, dielectric lenses, tapered illumination, and reflector-surface irregularity and distortion control techniques. More detailed studies to address these design concepts and assess the associated technology needs are recommended.

Keafer, L. S., Jr.↗
NASA NTRS1978

Remote sensing R&D planning

A NASA method is described for forecasting remote sensing needs in the last decade of this century and for planning the necessary space system technology R&D. Five- and ten-year plans for earth observations in various disciplines are extrapolated forward to circa 1995 via a scenario which envisions major advances in remote sensing and information management. Space system studies identify the 'technology drivers', and development programs are initiated to develop the enabling technology. An example is given for a multipurpose large-aperture microwave radiometer spacecraft.

Keafer, L. S., Jr.↗
NASA NTRS1977

Transmitting and reflecting diffuser

An ultraviolet grade fused silica substrate is coated with vaporized fused silica. The coating thickness is controlled, one thickness causing ultraviolet light to diffuse and another thickness causing ultraviolet light to reflect a near Lambertian pattern.

Keafer, L. S., Jr.↗
NASA NTRS1973

Transmitting and reflecting diffuser

A near-Lambertian diffuser is described which transmits and reflects ultraviolet light. An ultraviolet grade fused silica substrate is coated with vaporized fuse silica. The coating thickness is controlled, one thickness causing ultraviolet light to diffuse and another thickness causing ultraviolet light to reflect a near Lambertian pattern.

Keafer, L. S., Jr.↗
NASA NTRS1973

Development of flight experiments for remote measurement of pollution

The status as of February 1973 of several NASA-sponsored development projects is reported concerning flight experiments for remote measurement of pollution. Eight passive multispectral instruments for remotely sensing air and water pollutants are described, as well as two active (laser radar) measuring techniques. These techniques are expected to add some new dimensions to the remote sensing of water quality, oceanographic parameters, and earth resources. Multiple applications in these fields are generally possible. Successful completion of the flight demonstration tests and comparisons with simultaneously obtained surface truth measurements may establish these techniques as valid water quality monitoring tools.

Keafer, L. S., Jr.↗
NASA NTRS1972

Flow field measurements around a Mars lander model using hot film anemometers under simulated Mars surface conditions

Results are presented from a wind-tunnel investigation of the flow field around a 0.45-scale model of a Mars lander. The tests were conducted in air at values of Reynolds number equivalent to those anticipated on Mars. The effects of Reynolds number equivalent to those anticipated on Mars. The effects of Reynolds number, model orientation with respect to the airstream, and the position of a dish-type antenna on the flow field were determined. An appendix is included which describes the calibration and operational characteristics of hot-film anemometers under simulated Mars surface conditions.

Greene, G. C.↗
NASA NTRS1972

A transmitting and reflecting diffuser for ultraviolet light

Fabrication of ultraviolet radiation diffusing layer in configuration that uses ultraviolet properties of fused silica condensate is discussed. Construction and operation of the device are described. Diagram of reflecting diffuser to show construction and method of operation is included.

Keafer, L. S., Jr.↗