Engineering topics

Wellman, J. B.

Publications and source records attributed to Wellman, J. B..

At least 19 records

NASA NTRS1991

Tiltrotor Acoustic Flight Test: Terminal Area Operations

This paper provides a comprehensive description of an acoustic flight test of the XV- 15 Tiltrotor Aircraft with Advanced Technology Blades (ATB) conducted in August and September 1991 at Crows Landing, California. The purpose of this cooperative research effort of the NASA Langley and Ames Research Centers was to obtain a preliminary, high quality database of far-field acoustics for terminal area operations of the XV-15 at a takeoff gross weight of approximately 14,000 lbs for various glide slopes, airspeeds, rotor tip speeds, and nacelle tilt angles. The test also was used to assess the suitability of the Crows Landing complex for full scale far-field acoustic testing. This was the first acoustic flight test of the XV-15 aircraft equipped with ATB involving approach and level flyover operations. The test involved coordination of numerous personnel, facilities and equipment. Considerable effort was made to minimize potential extraneous noise sources unique to the region during the test. Acoustic data from the level flyovers were analyzed, then compared with data from a previous test of the XV-15 equipped with Standard Metal Blades

SantaMaria, O. L.↗

NASA NTRS1986

Hyperspectral Infrared Images of Terrain

Images at 128 wavelengths allow direct identification of many earth surface materials. Two reports describe advanced airborne spectrometer that creates images of terrain at many wavelengths. Airborne imaging spectrometer (AIS) produces two-dimensional images in 128 spectral bands in 1.2-to-2.4-micrometer wavelength region. Images created by 32-by-32 array of mercury cadmium telluride detector elements. Array views swath of Earth below moving aircraft. Used for agricultural, geological, and other surveys.

Vane, G.↗

NASA NTRS1986

Compact Imaging Spectrometer

Imaging spectrometer for use in crop and mineral resource-mapping experiments is scaled-down version. Compact imaging spectrometer uses Schmidt/Littrow optics with single spherical primary mirror. Radiation from scene strikes reflecting Schmidt corrector plate located near center of curvature of primary spherical mirror.

Wellman, J. B.↗

NASA NTRS1985

Optical remote sensing of the earth

In the present assessment of the contributions of optical earth resources remote sensing in the 0.4-15.0 micron region, attention is given to underlying principles, applications to scientific disciplines such as geology, hydrology and oceanography, the recent development history of the requisite sensors, and sensor development trends. Development status characterizations are given for thematic mapping, modular optoelectronic multispectral scanning, the telescope/CCD 'SPOT' program of France, the thermal IR multispectral scanner for mineral signature identification, airborne imaging spectrometry, and the Advanced Visible and IR Imaging Spectrometer that is nearing deployment. Technology development trends and the capabilities they portend are projected.

Goetz, A. F. H.↗

NASA NTRS1984

Airborne imaging spectrometer - A new tool for remote sensing

The first of a new class of remote sensing instruments is described. The Airborne Imaging Spectrometer represents the first use of two-dimensional integrated infrared area arrays in a scientific application. The instrument images 32 cross-track pixels simultaneously, each in 128 spectral bands in the 1.2- to 2.4-micron region. The IFOV of the instrument is 1.9 mrad/pixel and the spectral sampling interval is 9.6 nm. Plans include upgrading the detector from the current 32 x 32 element HgCdTe CCD array to a 64 x 64 element array in 1985. Science and engineering data are currently being actively gathered with the instrument.

Vane, G.↗

NASA NTRS1983

Airborne imaging spectrometer - A new tool for remote sensing

The first of a new class of remote sensing instruments is described. The Airborne Imaging Spectrometer represents the first use of two-dimensional area arrays in a scientific application. The instrument images 32 cross-track pixels simultaneously, each in 128 spectral bands in the 1.2 to 2.4 micro region. The IFOV of the instrument is 1.9 mrad and the spectral sampling interval is 9.6 nanometers. Plans include upgrading the detector from the current 32 x 32 element HgCdTe CCD array to a 64 x 64 element array in 1984. Science and engineering data are currently being actively gathered with the instrument.

Vane, G.↗

NASA NTRS1983

An imaging spectrometer experiment for the Shuttle

An imaging spectrometer experiment concept for earth remote sensing, developed as part of NASA's Multispectral Linear Array program, will map a series of test sites at high spatial and spectral resolution from the vantage point of the Shuttle payload bay. The instrument covers the spectral range from 0.4 to 2.5 micrometers with a sampling interval of 10 nanometers in the visible and near infrared (to 1.0 micrometer) and 20 nanometers in the short wavelength infrared (1.0 to 2.5 micrometers). Resolution corresponding to a ground instantaneous field of view (pixel size) of 30 meters is provided over a swath width of 12 kilometers. On-board data editing is utilized to select a subset of the data stream for transmission to the ground. The instrument utilizes silicon and mercury cadmium telluride area array detectors. Pointing mirrors are included to permit specific test sites to be imaged from the Shuttle orbit.

Wellman, J. B.↗

NASA NTRS1983

A Shuttle Imaging Spectrometer Experiment for the late 1980's

The Shuttle Imaging Spectrometer Experiment (SISEX), proposed as a next experimental step in the development of advanced earth remote sensing technology, is capable of imaging the earth's surface simultaneously in 128 spectral bands covering the range from 0.4 to 2.5 micrometers. Laboratory and field measurements have suggested the utility of high-spectral-resolution remote sensing, and an aircraft-borne precursor to the SISEX has demonstrated the ability to distinguish among differing vegetation and rock types - in certain cases making unique identifications. The SISEX instrument utilizes an area-array focal plane, populated by visual- and infrared-sensitive detectors, to acquire simultaneous spatial and spectral information on a line-by-line basis. The spectrum is dispersed by means of a prism spectrometer. The performance analysis indicates that the scientific requirements for radiometric precision can be achieved using optics with an effective circular aperture of 11 cm.

Wellman, J. B.↗

NASA NTRS1982

The imaging spectrometer approach

Two important sensor design drivers are the requirement for spatial registration of the spectral components and the implementation of the advanced multispectral capability, including spectral band width, number of bands and programmability. The dispersive approach, fundamental to the imaging spectrometer concept, achieves these capabilities by utilizing a spectrometer to disperse the spectral content while preserving the spatial identity of the information in the cross-track direction. Area array detectors in the spectrometer focal plane detect and store the spatial and multispectral content for each line of the image. The choice of spectral bands, image IFOV and swath width is implemented by programmed readout of the focal plane. These choices in conjunction with data compression are used to match the output data rate with the telemetry link capability. Progress in the key technologies of optics, focal plane detector arrays, onboard processing, and focal plane cooling supports the viability of the imaging spectrometer approach.

Wellman, J. B.↗

NASA NTRS1982

Imaging spectrometer technologies for advanced Earth remote sensing

A major requirement of multispectral imaging systems for advanced Earth remote sensing is the provision for greater spectral resolution and more versatile spectral band selection. The imaging spectrometer instrument concept provides this versatility by the combination of pushbroom imaging and spectrally dispersing optics using area array detectors in the focal plane. The shuttle imaging spectrometer concept achieves 10- and 20-meter ground instantaneous fields of view with 20-nanometer spectral resolution from Earth Orbit. Onboard processing allows the selection of spectral bands during flight; this, in turn, permits the sensor parameters to be tailored to the experiment objectives. Advances in optical design, infrared detector arrays, and focal plane cooling indicate the feasibility of the instrument concept and support the practicability of a validation flight experiment for the shuttle in the late 1980s.

Wellman, J. B.↗

NASA NTRS1982

Imaging spectrometer - An advanced multispectral imaging concept

The concept of an imaging spectrometer, which is being studied as a potential Space Shuttle experiment, is evaluated as a 'push-broom' imager that includes a spectrometer to disperse each line of imaging information into its spectral components. Using this instrument, the dispersed energy falls upon a two-dimensional focal plane array that detects both spatial and spectral information. As the line field of view is advanced over the earth by the motion of the spacecraft, the focal plane is read out constantly, which produces 'push-broom' images at multiple wavelengths. Ground instantaneous fields of view of 10 m in the visual and 20 m in the infrared are provided by the system, at a spectral resolution of 20 nm over the range from 0.4-2.5 microns. The system utilizes a triple-pass Schmidt optical system with a mosaic focal plane. A subset of the data stream is selected and encoded for transmission by the use of onboard processing.

Wellman, J. B.↗

NASA NTRS1982

Imaging spectrometer technologies for advanced earth remote sensing

A major requirement of multispectral imaging systems for advanced earth remote sensing is the provision for greater spectral resolution and more versatile spectral band selection. The imaging spectrometer instrument concept provides this versatility by the combination of pushbroom imaging and spectrally dispersing optics using area array detectors in the focal plane. The shuttle imaging spectrometer concept achieves 10- and 20-meter ground instantaneous fields of view with 20-nanometer spectral resolution from earth orbit. Onboard processing allows the selection of spectral bands during flight; this, in turn, permits the sensor parameters to be tailored to the experiment objectives. Advances in optical design, infrared detector arrays, and focal plane cooling indicate the feasibility of the instrument concept and support the practicability of a validation flight experiment for the shuttle in the late 1980s. Previously announced in STAR as N83-28542

Wellman, J. B.↗

NASA NTRS1981

Technologies for the multispectral mapping of earth resources

The application of solid-state detector array imaging to the remote sensing of the earth as a follow-on to currently planned Landsat missions provides the opportunity to achieve significantly increased performance. First-order advantages to be anticipated are higher sensitivity resulting in greater radiometric accuracies and improved geometric fidelity. The Multispectral Mapper design concept is responsive to a broad range of user needs by incorporating in-flight selection of spectral bands, instantaneous fields of view, and swath width. This versatility is achieved by the use of an imaging spectrometer which permits both spatial and spectral sampling in the image plane using area array detectors. Other improvements over the current Landsat multispectral scanner and Thematic Mapper include higher spatial resolution and inherently precise registration of the spectral bands. The key technologies required in order to realize these improvements include short-wavelength infrared detectors, wide field of view, broad spectral coverage optics, focal plane cooling, and high-speed onboard signal processing. Significant development activities will be required if an advanced remote sensing capability is to be implemented.

Wellman, J. B.↗

NASA NTRS1981

Multispectral mapper - Imaging spectroscopy as applied to the mapping of earth resources

An instrument concept that uses solid-state array imaging has been developed for a future land observing system. The design concept is responsive to a variety of use needs and provides improved capabilities over the planned Landsat Thematic Mapper. A comparison of the differing approaches to the instrument design was made, resulting in the selection of a concept which uses a spectrograph coupled to a line-array imager to provide simultaneous spatial and spectral resolution. The design provides an inherent solution to the problem of achieving precise registration among the spectral bands. Data processing on the focal plane is used to select the spectral bands and their band widths. Onboard capabilities include radiometric correction, selection of instantaneous field-of-view and swath width, and data compression.

Wellman, J. B.↗

NASA NTRS1980

Experiments in infrared multispectral mapping of earth resources

Two evolutionary infrared remote sensing experiments provide the basis for the development of an operational mapping capability for geology exploration. A 10-band radiometer scheduled for an early Shuttle flight has completed an aircraft flight program which demonstrated the utility of a number of narrow spectral channels. A multispectral mapper utilizing an infrared area array detector to acquire simultaneous images in multiple wavelengths is being assembled. A design concept for an operational sensor which employs area arrays for registered multispectral image data acquisition is under study. The sensor would utilize onboard spectral band selection, radiometric correction, and data compression to satisfy the demanding requirements of the user community.

Wellman, J. B.↗

NASA NTRS1980

Optics for future solar system exploration

The optics technology necessary for future solar system exploration is discussed. To satisfy the various mission objectives, optical components need to be of low weight, provide adequate spatial resolution and mapping coverage, provide necessary spectral resolution, provide means to perform adaptable mapping spectrometry, operate under low light levels, provide color images of high fidelity and operate under high temperatures. Future near-infrared mapping spectrometers are examined, and the use of focal-plane detectors to improve their sensitivity is discussed.

Norris, D. D.↗

NASA NTRS1979

Processing multispectral signals from a discrete-sensor array

Technique encoding and decoding color-image signals from array of discrete sensors can simplify fabrication of remote-sensing imaging system. Imaging system projects output on charge-coupled-device array. Computerized matrix decoding scheme decodes image.

Wellman, J. B.↗

NASA NTRS1979

Infrared focal plane arrays for planetary missions

Requirements for infrared detector array focal planes suitable for a set of prospective planetary missions are developed. Using the Galileo mission to Jupiter as a starting point, objectives and constraints applicable to outer planet missions are developed. The concept for an advanced mapping spectrometer utilizing 128 x 128 element infrared detector arrays is described. Specific implementations for the Saturn Orbiter Dual Probe mission, a Mars Orbiter mission, and a Titan Orbiter mission are defined. The analysis indicates that within the 1 to 5 micron range, broad scientific objectives for these missions can be met using focal plane arrays with detectivities on the order of 10 to the 14th cm sq root of Hz per W. The realization of such high detectivities in a low background application will necessitate careful development of the method by which the detector signals are multiplexed and read out.

Wellman, J. B.↗