Sea and Sky Infrared Radiances Near the Horizon
Abstract
Atmospheric infrared (8-12-microns)radiances over the ocean were measured from a shore station by using a calibrated thermal imaging system (AGA THERMOVISION Mod. 780). The Thermal Video Processor System (THERMOTEKNIX) available with the AGA allowed the mean equivalent blackbody temperatures corresponding to an area 1 deg above and 1 deg below the horizon in the scenes imaged to be determined during different meteorological and surface-wind-speed conditions. For this data set (18 thermograms), the mean sea temperatures differed the most from the mean cloud-free sky temperatures during low wind speed conditions. The differences were found to decrease with increasing wind speed. In contrast, the mean sea and sky temperatures measured during stratus cloud conditions were the same. The cloud-free data are used to evaluate background radiance algorithms, which must be used in the absence of radiometric measurements, to predict the performance of passive surveillance systems operating against airborne targets close to the horizon. Airborne measurements were made of the vertical profiles of metrological parameters and sea surface temperatures determined during 12 of the AGA measurements. From these measurements, LOWTRAN 6 calculations of the mean sky temperatures were found to be in close agreement with the measured values. Calculated mean sea temperatures showed slightly more variations than the measurements. These data are also used in a multiple regression analysis to derive an empirical relationship between the apparent mean sea and apparent mean sky temperatures which includes the measured wind speed and actual sea surface temperature. Infrared background; Optical propagation; Atmospheric physics.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1989
- Accession Number
- ADA209520
Entities
People
- Herbert G. Hughes