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Robinson, B. F.

Publications and source records attributed to Robinson, B. F..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Integrating sphere transmissometer for field measurement of leaf transmittance

A simple field-rated transmissometer is described for rapidly determining the normal hemispherical transmittance T(0 deg, 2 pi) of leaves measured in situ in the four Landsat wavelength bands. The transmissometer requires direct solar illumination of the leaf sample. It collects the transmitted light with an integrating sphere and measures the collected light using a commercially available radiometer. The transmittances determined by the transmissometer are comparable with those measured by a labortory spectrophotometer with an integrating sphere attachment.

Vanderbilt, V. C.↗
NASA NTRS1985

Specular, diffuse, and polarized light scattered by two wheat canopies

Using polarization measurements, the reflectance factor of two wheat canopies is divided into components due to specularly and diffusely reflected light. The data show that two key angles may be predicted, the angle of the polarizer for minimum flux and the angle of incidence of sunlight specularly reflected by a leaf to a sensor. The results show that specular reflection is a key aspect to radiation transfer by two canopies. Results suggest that the advent of heading in wheat may be remotely sensed from polarization measurements of the canopy reflectance.

Vanderbilt, V. C.↗
NASA NTRS1983

Overview of remote sensing field research - Requirements and status

The history of the development of remote sensing is briefly discussed, taking into account the study of the optical spectral properties of plants in the early 1950s, the concept of 'spectral signature', the multispectral scanner, and the Thematic Mapper scanner. The present state of development of remote sensing is examined. It is found that the requirements for field measurements for remote sensing field research are the same as the requirements envisioned in the 1960s. However, improved models for predicting scene reflectance and considerable field experience have clarified the aims and procedures. Information related to the status of optical measurements for crops and soils research is presented.

Robinson, B. F.↗
NASA NTRS1983

Data acquisition and preprocessing techniques for remote sensing field research

A crops and soils data base has been developed at Purdue University's Laboratory for Applications of Remote Sensing using spectral and agronomic measurements made by several government and university researchers. The data are being used to (1) quantitatively determine the relationships of spectral and agronomic characteristics of crops and soils, (2) define future sensor systems, and (3) develop advanced data analysis techniques. Researchers follow defined data acquisition and preprocessing techniques to provide fully annotated and calibrated sets of spectral, agronomic, and meteorological data. These procedures enable the researcher to combine his data with that acquired by other researchers for remote sensing research. The key elements or requirements for developing a field research data base of spectral data that can be transported across sites and years are appropriate experiment design, accurate spectral data calibration, defined field procedures, and through experiment documentation.

Biehl, L. L.↗
NASA NTRS1982

Performance evaluation and calibration of a modular multiband radiometer for remote sensing field research

A multiband radiometer suitable for operation from helicopter, small plane, truck, or tripod platforms was developed. The standard unit is equipped with the seven thematic mapper spectral bands with an added band from 1.5 to 1.30 microns; however, up to eight user specified bands from 0.4 to 15 microns may be installed under clean field conditions. Results of prototype tests of the spectral responsivity of the detectors, the transmittance of the optical filters as a function of wavelength, the fields of view, and the system linearity, temperature stability, noise performance, and dynamic range were evaluated. Minor modifications were made to the instrument and the results of final testing are reported.

Robinson, B. F.↗
NASA NTRS1982

Extension of laboratory-measured soil spectra to field conditions

Spectral responses of two glaciated soils, Chalmers silty clay loam and Fincastle silt loam, formed under prairie grass and forest vegetation, respectively, were measured in the laboratory under controlled moisture equilibria using an Exotech Model 20C spectroradiometer to obtain spectral data in the laboratory under artificial illumination. The same spectroradiometer was used outdoors under solar illumination to obtain spectral response from dry and moistened field plots with and without corn residue cover, representing the two different soils. Results indicate that laboratory-measured spectra of moist soil are directly proportional to the spectral response of that same field-measured moist bare soil over the 0.52 micrometer to 1.75 micrometer wavelength range. The magnitudes of difference in spectral response between identically treated Chalmers and Fincastle soils are greatest in the 0.6 micrometers to 0.8 micrometer transition region between the visible and near infrared, regardless of field condition or laboratory preparation studied.

Stoner, E. R.↗
NASA NTRS1982

Soybean canopy reflectance as a function of view and illumination geometry

The results of an experiment designed to characterize a soybean field by its reflectance at various view and illumination angles and by its physical and agronomic attributes are presented. Reflectances were calculated from measurements at four wavelength bands through eight view azimuth and seven view zenith directions for various solar zenith and azimuth angles during portions of three days. An ancillary data set consisting of the agronomic and physical characteristics of the soybean field is described. The results indicate that the distribution of reflectance from a soybean field is a function of the solar illumination and viewing geometry, wavelength and row direction, as well as the state of development of the canopy. Shadows between rows greatly affected the reflectance in the visible wavelength bands and to a lesser extent in the near infrared wavelengths. A model is proposed that describes the reflectance variation as a function of projected solar and projected viewing angles. The model appears to approximate the reflectance variations in the visible wavelength bands from a canopy with well defined row structure.

Bauer, M. E.↗
NASA NTRS1982

A crops and soils data base for scene radiation research

Management and planning activities with respect to food production require accurate and timely information on crops and soils on a global basis. The needed information can be obtained with the aid of satellite-borne sensors, if the relations between the spectral properties and the important biological-physical parameters of crops and soils are known. In order to obtain this knowledge, the development of a crops and soils scene radiation research data base was initiated. Work related to the development of this data base is discussed, taking into account details regarding the conducted experiments, the performed measurements, the calibration of spectral data, questions of data base access, and the expansion of the crops and soils scene radiation data base for 1982.

Biehl, L. L.↗
NASA NTRS1982

Calibration procedures for measurement of reflectance factor in remote sensing field research

A means by which measurements of the optical properties of crops and soils can be knowledgeably compared from site to site and instrument to instrument is presented in detail. The definition of bidirectional reflectance factor is reviewed and discussed. Procedures for field implementation are illustrated and discussed. Spectral and goniometric properties of laboratory and field reference surfaces are given. It is concluded that intelligent use of the bidirectional reflectance factor technique is an accurate and practical means to obtain the spectral, optical properties of crops and soils needed for advancements in agricultural remote sensing.

Robinson, B. F.↗
NASA NTRS1981

A multiband radiometer and data acquisition system for remote sensing field research

Specifications are described for a recently developed prototype multispectral data acquisition system which consists of multiband radiometer with 8 bands between 0.4 and 12.5 micrometers and a data recording module to record data from the radometer and ancillary sources. The systems is adaptable to helicopter, truck, or tripod platforms, as well as hand-held operation. The general characteristics are: (1) comparatively inexpensive to acquire, maintain and operate; (2) simple to operate and calibrate; (3) complete with data hardware and software; and (4) well documented for use by researchers. The instrument system is to be commercially available and can be utilized by many researchers to obtain large numbers of accurate, calibrated spectral measurements. It can be a key element in improving and advancing the capability for field research in remote sensing.

Bauer, M. E.↗
NASA NTRS1981

Simulated response of a multispectral scanner over wheat as a function of wavelength and view/illumination direction

The reflectance response with view angle of wheat, was analyzed. The analyses, which assumes there are no atmospheric effects, and otherwise simulates the response of a multispectral scanner, is based upon spectra taken continuously in wavelength from 0.45 to 2.4 micrometers at more than 1200 view/illumination directions using an Exotech model 20C spectra radiometer. Data were acquired six meters above four wheat canopies, each at a different growth stage. The analysis shows that the canopy reflective response is a pronounced function of illumination angle, scanner view angle and wavelength. The variation is greater at low solar elevations compared to high solar elevations.

Bauer, M. E.↗
NASA NTRS1981

Diurnal changes in reflectance factor due to Sun-row direction interactions

Over a two year period, data were collected regarding the canopies of soybeans grown in rows in planter boxes placed on a turntable in an effort to investigate changes in the spectral reflectance factor related to row direction, Sun direction, soil background, and crop development stage. Results demonstrate that the direction of rows in a soybean canopy can affect the reflectance factor of the canopy by as much as 230%. The results for the red spectral region tend to support the validity of canopy reflectance models; results for the infrared region do not.

Bauer, M. E.↗
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

Soybean canopy reflectance as a function of view and illumination geometry

Reflectances were calculated from measurements at four wavelength bands through eight view azimuth and seven view zenith directions, for various solar zenith and azimuth angles over portions of three days, in an experimental characterization of a soybean field by means of its reflectances and physical and agronomic attributes. Results indicate that the distribution of reflectance from a soybean field is a function of the solar illumination and viewing geometry, wavelength, and row direction, as well as the state of canopy development. Shadows between rows were found to affect visible wavelength band reflectance to a greater extent than near-IR reflectance. A model describing reflectance variation as a function of projected solar and viewing angles is proposed, which approximates the visible wavelength band reflectance variations of a canopy with a well-defined row structure.

Ranson, K. J.↗
NASA NTRS1980

Field research on the spectral properties of crops and soils, volume 1

The experiment design, data acquisition and preprocessing, data base management, analysis results and development of instrumentation for the AgRISTARS Supporting Research Project, Field Research task are described. Results of several investigations on the spectral reflectance of corn and soybean canopies as influenced by cultural practices, development stage and nitrogen nutrition are reported as well as results of analyses of the spectral properties of crop canopies as a function of canopy geometry, row orientation, sensor view angle and solar illumination angle are presented. The objectives, experiment designs and data acquired in 1980 for field research experiments are described. The development and performance characteristics of a prototype multiband radiometer, data logger, and aerial tower for field research are discussed.

Bauer, M. E.↗
NASA NTRS1980

Spectral properties of agricultural crops and soils measured from space, aerial, field and laboratory sensors

It is pointed out that in order to develop the full potential of multispectral measurements acquired from satellite or aircraft sensors to monitor, map, and inventory agricultural resources, increased knowledge and understanding of the spectral properties of crops and soils are needed. The present state of knowledge is reviewed, emphasizing current investigations of the multispectral reflectance characteristics of crops and soils as measured from laboratory, field, aerial, and satellite sensor systems. The relationships of important biological and physical characteristics to their spectral properties of crops and soils are discussed. Future research needs are also indicated.

Bauer, M. E.↗