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Duggin, M. J.

Publications and source records attributed to Duggin, M. J..

23 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Evaluation of NOAA-AVHRR data for crop assessment

A study has been carried out in order to determine the angular limits which should be imposed upon NOAA06 and -7 satellite advanced very high-resolution radiometer (AVHRR) data used in vegetation assessment. The study involved simulations of anticipated sensor output over a wheat crop and empirical investigation of sensor data over vegetated areas. The conclusion drawn from both approaches is that less than 10% variation in the simulated vegetative index may be anticipated across the swath of imagery used if only the central 512 pixels are utilized.

Duggin, M. J.↗
NASA NTRS1982

Effect of sub-pixel sized cloud on vegetation assessment from satellite data

The visible and reflected infrared channels of the NOAA-7 Advanced Very High Resolution Radiometer (AVHRR) are used for environmental monitoring, including agricultural crop assessment. An index consisting of a combination of digital data from these channels is used to screen the AVHRR data for cloud. The effects on spectral signature of sub-pixel sized cloud, which does not fill the entire IFOV of the instrument, are considered. It is shown that, for two different targets, for clear and turbid atmospheric conditions and for various scan angles, cloud which would not be detected during the screening process will cause substantial effects (up to a five-fold decrease) in the data.

Duggin, M. J.↗
NASA NTRS1981

Ground level reflectance measurement techniques - An evaluation with emphasis on the importance of spectral calibration

The bandpasses, overflight conditions, and sensor geometry that will provide optimum target discrimination in remote-sensing studies can be determined only from spectral reflectance measurements made for various sun-target-sensor geometries, supplemented by model calculations which can be checked against field data. The accurate measurement of ground reflectance properties is critical to the design of future sensors and to the determination of imaging conditions. The current investigation has the objective to review typical methods of measuring spectral reflectance, to point out some of the problems inherent to reflectance measuring techniques, and to present a method of checking measurement accuracy.

Duggin, M. J.↗
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.↗