DEGRADATION OF IMAGERY FROM OPTICAL-MECHANICAL SCANNERS: MOISTURE CONDENSATION ON OPTICS.
Abstract
Moisture condensation on the optics of optical-mechanical scanners can be a major factor in the degradation of imagery acquired under humid tropical conditions and has been so demonstrated with thermal infrared imagery acquired under these conditions. Conditions favorable to formation of condensation usually occur when the survey aircraft descends from a higher to a lower altitude. An analogous situation occurs in aerial photography but condensation is obviated by blowing warm air across the optical window in the camera well. Diffuse scattering and absorption of incident energy will cause the recorded imagery to have a monotonic appearance. There are several solutions to the moisture condensation problem: (1) maintain the temperature of the optical elements above the dew-point temperature by heating; (2) blow dry air across the optics; (3) install an IRTRAN-2 window in the bottom of the scanner well and blow warm air across this window; and (4) properly plan the data collection missions -- always climb in altitude over the course of the mission, do not descend during imagery acquisition. Several examples of thermal IR imagery, collected at different altitudes and at different times of the day, are presented and analyzed. It was found that enlargements of higher altitude imagery may be superior to those of lower altitude imagery (as long as the imaged feature can be resolved at the higher altitude), because increase in detail (thermal and/or spatial) is more than offset by imagery degradation caused by moisture condensation on the scanning optics. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1967
- Accession Number
- AD0382730
Entities
People
- Richard S. Williams Jr.
- Robert W. Fenn
Organizations
- Air Force Cambridge Research Laboratories