IR (Infrared) Sky Radiance Distributions in the Marine Boundary Layer
Abstract
Infrared optical properties of the marine boundary layer are basic in the performance of thermal imaging systems, such as forward looking infrared sensors, over the ocean. To aid in evaluating the performance of these sensors, spatial distributions of infrared sky radiance in the 3-5 micron mid-wavelength infrared and 8-12 micron long wavelength infrared spectral bands were measured simultaneously at low elevation angles above the sea surface. Calibrated AGA, Model 780, dual scanning systems functioned as imaging infrared radiometers. Radiosondes were released from at a range of 5 Km due west of the coastal sensor site a Naval Ocean Systems Center, San Diego, CA. Wind speed, direction, sea temperature, and cloud conditions were also recorded on board the ship. Sequential images of radiance distributions provided control data for monitoring the stability or variability of atmospheric conditions throughout the time for radiosonde ascent to about 6 km altitude. Measured IR sky radiance distributions were compared with corresponding clear sky radiance using the LOWTRAN 6 computer code. Cloud radiance and scattered solar radiation restricted the comparison to elevations close to the optical horizon where aerosol attenuation would be greatest. Infrared aerosol transmittance was inferred from the ratio of measured radiance to calculated clear-sky radiance along the horizon line of sight. Equivalent temperatures for blackbody radiance at the horizon were either less than or equal to the ambient air temperature near the sea surface, except when the MWIR band included scattered solar radiation; consequently, only the LWIR band could be used to infer aerosol transmittance reliably.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1988
- Accession Number
- ADA193683
Entities
People
- David B. Law
- William J. Schade