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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Soil, water, and vegetation conditions in South Texas

The author has identified the following significant results. Reflectance measurements with a field spectroradiometer on nine dates (between December 9 and April 8) during the growing season of two wheat varieties, Milam and Penjamo, showed that the reflectance curves had the characteristic shape of vegetated surfaces by 4 weeks after the emergence. Green light (0.55 micron) reflectance was maximal and between water absorption bands (1.65 and 2.2 microns) reflectance was minimal when green vegetation development was greatest. Computer classification was accomplished for 81,000 hectare coastal rangeland area for October 13 and December 10, 1975, overpass dates. A hard freeze occurred between these two dates and many of the deciduous woody species defoliated so that more light penetrated to the herbaceous understory in December than in October.

Wiegand, C. L.↗
NASA NTRS1977

Field measurements of the spectral response of natural waters

The spectral response (air-water interface reflectance and water-volume scattering) of turbid river water (99 mg/liter suspended solids) and relatively clear lake water (10 mg/liter suspended solids) was measured in situ with a field spectroradiometer. The influence of the river bottom on the spectral response of the water also was determined by using a modified Secchi disc approach. The results indicated that turbid river water had a higher spectral response than clear lake water (about 6 percent) in the red (0.6-0.7 micron) and near-infrared (0.7-0.9 micron) portions of the spectrum. Also, the reflectance characteristics of the river bottom did not influence the spectral response of the turbid river water when the water was deeper than 30 cm

Bartolucci, L. A.↗
NASA NTRS1977

Further tests of the suits reflectance model

Experiments performed by stacking cotton leaves in the port of a spectroradiometer indicate that single leaf reflectance ceases to vary with more than two leaves in the visible region and eight leaves in the infrared region. Chance and LeMaster have shown that the Suits spectral reflectance model predicts an asymptotic dependence of crop reflectance on leaf area index (LAI) with crop reflectance static for leaf area indices in excess of two in the visible regions and six in the infrared regions of the spectrum. These results are experimentally verified in the field for Milam and Penjamo spring wheat, and a theoretical relationship is discussed that relates crop reflectance at 650 nm to crop canopy LAI. Experimental data are given that relate observer zenith angle to crop reflectance for wheat. The Suits reflectance model calculations for wheat fail to agree with this data.

Lemaster, E. W.↗
NASA NTRS1978

Results of the 1974 through 1977 NASA/JPL balloon flight solar cell calibration program

From 1974 through 1977, seven solar cell calibration flights and two R&D flights with a spectroradiometer as a payload were attempted. There were two R&D flights, and one calibration flight that failed. Each calibration flight balloon was designed to carry its payload to an altitude of 36.6 km (120 kft). The R&D flight balloons were designed for a payload altitude of 47.5 km (150 kft). At the end of the flight period, the upper (solar cell calibration system) and lower (consolidated instrument package (DIP) payloads were separated from the balloon and descend via parachutes. The calibrated solar cells recovered in this manner were used as primary intensity reference standards during solar simulator testing of solar cells and solar arrays with similar spectral response characteristics. This method of calibration has become the most widely accepted technique for developing space standard solar cells.

Sidwell, L. B.↗
NASA NTRS1977

Calibration analysis for a multi-channel infrared scanning radiometer

A procedure for calibrating an infrared scanning spectroradiometer by a computerized parametric error analysis technique was developed. The uncertainties in the radiometric measurements of scene radiance and (for the case of a blackbody scene) temperature due to possible uncertainties in the calibration target temperature, calibration target emissivity, and instrument temperature were calculated for a range of uncertainty levels in the parameters, as well as for a gamut of scent temperatures corresponding to a given spectral channel. This technique is applicable to the radiometric calibration of any infrared radiometer. It was applied specifically to the Cloud-Top Scanning (C.T.S) Radiometer, a three-channel instrument designed for aircraftborne cloud radiance measurements in the 6.75 and 11.5 micron thermal emission spectral regions.

Walden, H.↗
NASA NTRS1978

Effects of systemic and non-systemic stresses on the thermal characteristics of corn

Experiments were conducted on corn plants using a calibrated spectroradiometer under field conditions in the indium antimonide channel (InSb, 2.8 to 5.6 mm) and the mercury cadmium telluride channel (HgCdTe, 7 to 14 mm). A ground cover experiment, an experiment on nonsystemic corn plants, and an experiment on systemic-stressed corn plants were included. The average spectral radiance temperature of corn plant populations was found (1) to be statistically significantly different for four healthy corn plant populations, (2) to increase with increased blight severity, and (3) to be statistically significantly different for varying rates of nitrogen applications.

Kumar, R.↗
NASA NTRS1979

Waveguide arc study

Research on waveguide arcs is presented as well as an evaluation on an arc detector. Ways of improving the radio frequency arc generation include methods of generating RF arcs inside the resonator. Dc nitrogen arcs were used to study a spectroradiometer. The spectral strucutres obtained provide a general sketch of spectral distribution and their relative magnitude. The upgrading of a transmitter test light and the simulation of an LED array are reported.

Yen, H. C.↗
NASA NTRS1978

The application of smart sensor techniques to a solid-state array multispectral sensor

The solid-state array spectroradiometer (SAS) developed at JSC for remote sensing applications is a multispectral sensor which has no moving parts, is virtually maintenance-free, and has the ability to provide data which requires a minimum of processing. The instrument is based on the 42 x 342 element charge injection device (CID) detector. This system allows the combination of spectral scanning and across-track spatial scanning along with its associated digitization electronics into a single detector.

Mcfadin, L. W.↗
NASA NTRS1978

Advanced systems requirements for ocean observations via microwave radiometers

A future microwave spectroradiometer operating in several frequency bands will have the capability to step or sweep frequencies on an adaptable or programmable basis. The on-board adaptable frequency shifting can make the systems immune from radio interference. Programmable frequency sweeping with on-board data inversion by high speed computers would provide for instantaneous synoptic measurements or sea surface temperature and salinity, water surface and volume pollution, ice thickness, ocean surface winds, snow depth, and soil moisture. Large structure satellites will allow an order of magnitude improvement in the present radiometric measurement spacial resolution.

Blume, H.-J. C.↗
NASA NTRS1979

Signature evaluation of natural targets using high spectral resolution techniques

The concept of 'spectral signature' identification has been applied to LANDSAT and other broad-band multi-spectral scanner data to classify various materials on the earth's surface. A large amount of the spectral information available is invisible, however, to the broad-band sensors. Although the natural targets of interest in remote sensing do not exhibit fine line features such as those associated with gaseous media, there is significant information to be extracted from smoothly varying spectral reflection functions of most natural targets. Subtle variations observed recently in the high resolution 'spectral signatures' of vegetation targets, in particular, promise to open new avenues of application using higher spectral and radiometric resolution techniques. This research was accomplished using a 500-band spectroradiometer system specially adapted to rapid airborne operations

Collins, W.↗
NASA NTRS1981

Linear polarization of light by two wheat canopies measured at many view angles

The linear polarization and reflection of visible light by wheat as a function of sun-view directions, crop development stage, and wavelength were examined. Two-hundred spectra were taken continuously in wave-lengths from 0.45 to 0.72 Micron in 33 view directions using an Exotech model 20C spectroradiometer six meters above two wheat canopies in the boot and fully headed maturity stages. The analysis results show that the amount of linearly polarized light from the wheat canopies is greatest in the blue spectral region and decreases gradually with increasing wavelength. The results also show that the linearly polarized light from the canopies is generally greatest in the azimuth direction of the Sun and tends toward zero as the view direction tends toward the direction of the hot spot or anti-solar point. It is demonstrated that the single, angle of incidence of sunlight on the leaf, explains almost all of the variation of the amount of polarized light with Sun-view direction.

Bauer, M. E.↗
NASA NTRS1981

Mapping of submerged vegetation using remote sensing technology

Techniques for mapping submerged sea grasses using aircraft supported remote sensors are described. The 21 channel solid state array spectroradiometer was successfully used as a remote sensor in the experiment in that the system operated without problem and obtained data. The environmental conditions of clear water, bright sandy bottom and monospecific vegetation (Thalassia) were ideal.

Savastano, K. J.↗
NASA NTRS1982

Characteristic variations in reflectance of surface soils

Surface soil samples from a wide range of naturally occurring soils were obtained for the purpose of studying the characteristic variations in soil reflectance as these variations relate to other soil properties and soil classification. A total 485 soil samples from the U.S. and Brazil representing 30 suborders of the 10 orders of 'Soil Taxonomy' was examined. The spectral bidirectional reflectance factor was measured on uniformly moist soils over the 0.52 to 2.32 micron wavelength range with a spectroradiometer adapted for indoor use. Five distinct soil spectral reflectance curve forms were identified according to curve shape, the presence or absence of absorption bands, and the predominance of soil organic matter and iron oxide composition. These curve forms were further characterized according to generically homogeneous soil properties in a manner similar to the subdivisions at the suborder level of 'Soil Taxonomy'. Results indicate that spectroradiometric measurements of soil spectral bidirectional reflectance factor can be used to characterize soil reflectance in terms that are meaningful to soil classification, genesis, and survey.

Stoner, E. R.↗
NASA NTRS1981

High spectral resolution airborne spectrometry

An airborne spectroradiometer system developed at Columbia University has been providing new spectral data for use in remote sensing for natural resources. The system has been improved by addition of a solid state silicon detector array, and has been extended into the infrared by addition of a 64 element lead sulfide detector array. The infrared data in the 2000 to 2500 nm region especially holds large potential for mineral and oil exploration.

Collins, W.↗
NASA NTRS1981

Field measurement of spectral reflectance

It is pointed out that success in acquiring remote sensing data for describing a given target, such as vegetation, is contingent upon an understanding of the reflectance properties of the target and its surroundings. Field measurements of a target's spectral reflectance are in most cases made with single-beam instruments by sequentially viewing the target and a white standard reflector, which is assumed to be Lambertian. Since variation in atmospheric transmission can occur between the times of measuring the target and the standard reflector, substantial errors in reflectance calculated from these measurements may result. To preclude this possibility the irradiance on, and the radiance reflected from, the target must be measured simultaneously. Measurements of the spectral hemispherical-conical reflectance of a target are made by simultaneously measuring irradiance and radiance with pairs of portable spectroradiometers. The techniques for calibrating the instruments and for collecting and analyzing spectral reflectance data on vegetative canopies are described. Significant instrumental sources of error and their magnitude are discussed, together with problems involved in making such measurements.

Duggin, M. J.↗
NASA NTRS1982

Field measurement of reflectance - Some major considerations

The simultaneous use of two portable spectroradiometers to measure radiance and irradiance from crop fields is reported. Two sensors were employed to assess the crop cover radiance reflectance, while a third instrument measured irradiance from a white Lambertian reflectance target, with all radiometers being equipped with optic fiber probes. Calibration procedures for the instruments are outlined, including the usage of laboratory standards and recalibration before every test by exposing all sensors to the Lambertian reflector. Calculation of the angular geometry between the sun, target, and sensor was found to be necessary to determine the angle dependence for each wave band and the surface variability. It is recommended that suitable portable equipment be fabricated with calibration procedures and manuals that can be used by the nonelectrical engineer in order to standardize measurements for comparison between two instruments.

Duggin, M. J.↗
NASA NTRS1983

Remote Sensing Program

Field spectroradiometric and airborne multispectral scanner data were related to vineyard yield and other agronomic variables in an attempt to determine the optimum wavelengths for yield prediction modeling. Reflections between vine canopy reflectance and several management practices were also considered. Spectral analysis of test vines found that, although some correlations with vine yield were significant, they were inadequate for producing a yield prediction model. The findings also indicate that the vines examined through the field spectroradiometers were not truly representative. Geologic linears identified from aerial photographys, LANDSAT images, and maps were compared to gas well locations in three New York' counties. Correlations were found between the dominant trends in regional liners and gas field boundaries and trends. Other projects being conducted under the grant include determining vegetable acreage in mucklands, site selection for windmills, spectral effects of sulfur dioxide, and screening tomato seedlings for salt tolerance.

Philipson, W. R.↗
NASA NTRS1982

Airborne infrared mineral mapping survey of Marysvale, Utah

Infrared spectroradiometer survey results from flights over the Marysvale, Utah district show that hydrothermal alteration mineralogy can be mapped using very rapid and effective airborne techniques. The system detects alteration mineral absorption band intensities in the infrared spectral region with high sensitivity. The higher resolution spectral features and high spectral differences characteristic of the various clay and carbonate minerals are also readily identified by the instrument allowing the mineralogy to be mapped as well as the mineralization intensity.

Collins, W.↗