Engineering topics

Gray, T. I.

Publications and source records attributed to Gray, T. I..

4 records

NASA NTRS1982

Effect of subpixel-sized cloud on target discrimination from satellite data

The paper reports results of a study of the effects of subpixel-sized clouds on remotely sensed radiance; the NOAA-7 Advanced Very High Resolution Radiometer was used in the study. It is noted that it is quite possible that clouds could exist with dimensions of less than 1 x 1 km, which will not be resolvable as discrete pixels filled only by cloud, but which will be recorded as pixels with radiance values not characteristic of the ground target. It is shown that for a clear atmosphere the presence of even 20% cloud produces a fivefold decrease or worse in vegetative index at all scan angles for both pure and mixed targets. These effects are large and show that undetected cloud can produce drastic changes in combinations of recorded radiance used for vegetative assessment.

Duggin, M. J.↗

NASA NTRS1982

Advanced Very High Resolution Radiometer (AVHRR) data evaluation for use in monitoring vegetation. Volume 1: Channels 1 and 2

Data from the National Oceanic and Atmospheric Administration satellite system (NOAA-6 satellite) were analyzed to study their nonmeteorological uses. A file of charts, graphs, and tables was created form the products generated. It was found that the most useful data lie between pixel numbers 400 and 2000 on a given scan line. The analysis of the generated products indicates that the Gray-McCrary Index can discern vegetation and associated daily and seasonal changes. The solar zenith-angle correction used in previous studies was found to be a useful adjustment to the index. The METSAT system seems best suited for providing large-area analyses of surface features on a daily basis.

Horvath, N. C.↗

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

Utilization of Meteorological Satellite Imagery for World-Wide Environmental Monitoring the Lower Mississippi River Flood of 1979 - Case 1

The 1979 Lower Mississippi River flood was selected as a test case of environmental disaster monitoring utilizing NOAA-n imagery. A small scale study of the St. Louis Missouri area comparing ERTS-1 (LANDSAT) and NOAA-2 imagery and flood studies using only LANDSAT imagery for mapping the Rad River of the North, and Nimbus-5 imagery for East Australia show the nonmeteorological applications of NOAA satellites. While the level of NOAA-n imagery detail is not that of a LANDSAT image, for operational environmental monitoring users the NOAA-n imagery may provide acceptable linear resolution and spectral isolation.

Helfert, M. R.↗