Engineering topics

Walthall, Charles L.

Publications and source records attributed to Walthall, Charles L..

10 records

NASA NTRS2000

BOREAS RSS-3 Atmospheric Measurements from a Helicopter-Mounted Sunphotometer

The BOREAS RSS-3 team collected and processed helicopter-based measurements of atmospheric conditions to estimates of aerosol optical thickness and atmospheric water vapor. The automatic sun-tracking photometer for helicopters was deployed during all three 1994 IFCs at numerous tower and auxiliary sites in both the NSA and the SSA. Six spectral channels (440, 540, 613, 670, 870, and 1030 nm) were chosen to span the visible and NIR wavelengths and to avoid gaseous absorption. One additional channel, 940 nm, was selected to measure the water column abundance above the helicopter platform. The data are stored in tabular ASCII files.

Hall, Forrest G.↗

NASA NTRS2000

BOREAS RSS-3 Imagery and Snapshots from a Helicopter-Mounted Video Camera

The BOREAS RSS-3 team collected helicopter-based video coverage of forested sites acquired during BOREAS as well as single-frame "snapshots" processed to still images. Helicopter data used in this analysis were collected during all three 1994 IFCs (24-May to 16-Jun, 19-Jul to 10-Aug, and 30-Aug to 19-Sep), at numerous tower and auxiliary sites in both the NSA and the SSA. The VHS-camera observations correspond to other coincident helicopter measurements. The field of view of the camera is unknown. The video tapes are in both VHS and Beta format. The still images are stored in JPEG format.

Walthall, Charles L.↗

NASA NTRS2000

BOREAS RSS-3 Reflectance Measured from a Helicopter-Mounted Barnes MMR

The BOREAS RSS-3 team acquired helicopter-based radiometric measurements of forested sites with a Barnes MMR. The data were collected in 1994 during the three BOREAS IFCs at numerous tower and auxiliary sites in both the NSA and SSA. The 15-degree FOV of the MMR yielded approximately 79-m ground resolution from an altitude of 300 m. The MMR has seven spectral bands that are similar to the Landsat TM bands, ranging from the blue region to the thermal. The data are stored in tabular ASCII files. The data are stored in tabular ASCII files.

Hall, Forrest G.↗

NASA NTRS2000

BOREAS RSS-3 Reflectance Measured from a Helicopter-Mounted SE-590

The BOREAS RSS-3 team collected multiple remotely sensed data sets from the NASA UH-1 helicopter. This data set includes helicopter-based radiometric measurements of forested sites acquired during BOREAS made with an SE-590 processed to reflectance factors. The data used in this analysis were collected in 1994 during the three BOREAS IFCs at numerous tower and auxiliary sites in both the NSA and the SSA. The 15-degree FOV of the SE-590 yielded a ground resolution of approximately 79 m at the 300-m nominal altitude. The data are provided in tabular ASCII files.

Hall, Forrest G.↗

NASA NTRS1993

Advanced solid-state array spectroradiometer data collection during HAPEX-2 Sahel

Data collection using the Advanced Solid-state Array Spectroradiometer (ASAS) during the Hydrologic Atmospheric Pilot Experiment in the Sahel (HAPEX-II Sahel) field campaign in the Republic of Niger, West Central Africa from 22 Aug. to 19 Sep. 1992 is documented. Details on the ASAS system such as the hardware, data collection methods, information on system calibration, and data processing procedures are included. The ASAS configuration deployed for HAPEX-II Sahel contains several new components, including a new sensor array and pointing system. Because of this, new calibration procedures are being developed at the same time that the first ASAS images from HAPEX-II Sahel are being processed. These new calibration procedures will be documented in a future publication.

Walthall, Charles L.↗

NASA NTRS1992

Assessing spatial and seasonal variations in grasslands with spectral reflectances from a helicopter platform

The helicopter system data acquisition technique has shown to be a viable means of gathering surface data with spectral detail adequate for intersite, intrasite, and temporal characterizations and for assessing temporal and spatial variability throughout the FIFE 1987 IFCs. The successful employment of nadir measurements for grassland assessments is notable given the reflectance anisotropy (Middleton, 1992). Though only five sites were repetitively observed, the conclusions reached from this particular sample of sites agree well with assessments from other data sources (Sellars et al., 1990 and Kittel et al., 1990).

Walthall, Charles L.↗

NASA NTRS1992

Multispectral, multialtitude observations of the KUREX-91 experiment site from a helicopter platform

An eight-channel modular multiband radiometer, a 252-channel SE-590 spectroradiometer, and a single-channel infrared thermometer were mounted in a nadir-looking attitude on a Soviet MI-8 helicopter to collect visible, infrared, and thermal measurements of the KUREX-91 study area. These measurements were coincident with surface, other airborne, and spaceborne measurements collected during the July 1991 field campaign. The helicopter missions included both hovers and slow-flight transects over specific sites. Multiple altitude flights over several of the study sites were also made. Study sites included grasslands, forest stands, and agricultural fields. Data collection was executed so that observations from the multispectral devices could be compared with multispectral and biophysical observations made on the surface as well as with multispectral observations from other airborne and spaceborne systems. A preliminary analysis of multispectral and multialtitude data of several study sites is presented.

Walthall, Charles L.↗

NASA NTRS1991

Estimation of shortwave hemispherical reflectance (albedo) from bidirectionally reflected radiance data

An equation for estimating albedo from bidirectional reflectance data is proposed. The estimates of albedo are found to be greater than values obtained with simultaneous pyranometer measurements. Particular attention is given to potential sources of systematic errors including extrapolation of bidirectional reflectance data out to a view zenith angle of 90 deg, the use of inappropriate weighting coefficients in the numerator of the albedo equation, surface shadowing caused by the A-frame instrumentation used to measure the incoming and outgoing radiation fluxes, errors in estimates of the denominator of the proposed albedo equation, and a 'hot spot' contribution in bidirectional data measured by a modular multiband radiometer.

Starks, Patrick J.↗

NASA NTRS1991

Advanced Solid-State Array Spectrometer (ASAS) data sets from the 1990 field season: A unique look at two forested ecosystems

The Advanced Solid-state Array Spectrometer (ASAS) is a pointable imaging spectrometer which uses a solid-state array to acquire imagery of terrestrial targets in 29 spectral bands from .4 to .8 microns. Performance and calibration of the instrument are described. The ASAS data sets obtained in 1990 provide a unique look at forest canopies from two different forest regions of the North America continent under varying temporal, spectral, and bidirectional conditions. These data sets will be used to study such parameters as the albedo of forest canopies, the dynamics of scene radiation due to factors such as canopy architecture, moisture stress, leaf chemistry, topography, and understory composition.

Walthall, Charles L.↗

NASA NTRS1991

A pointable, helicopter-based remote sensing data acquisition system for collecting bidirectional reflectance data

Discussed here is a new configuration of a helicopter-borne remote sensing system to support field measurements programs such as studies of forest decline damage associated with atmospheric deposition and the Forest Ecosystems Dynamics project. In this new configuration, the sensor payload is mounted externally on a hinged pallet located on the starboard side of the Bell Iroquois UH-1B (HUEY) helicopter. The sensor payload includes a set of bore-sighted instruments consisting of a Barnes Modular Multiband Radiometer (MMR), a Spectron Engineering (SE) 590 spectroradiometer, an Everest infrared temperature sensor, and a Sony CCD video camera with a 10x zoom lens. The system was tested and excellent data was acquired in 1990.

Williams, Darrel L.↗