Radiometric Modeling of Complex Cavernous Targets in Localized Microclimatic Conditions with Emphasis on Mechanical Draft Cooling Towers

Research Team: Matthew Montanaro (Ph.D. student), David Messinger, Scott Brown, and Carl Salvaggio

Sponsor: Department of Energy, Savannah River National Laboratory

Project Scope: RIT is providing support to the Department of Energy at the Savannah

River National Laboratory (SRNL) to gain insight into the phenomenology that influences the radiance field leaving the interior of a mechanical-draft cooling tower (MDCT). In order to accomplish this, existing DIRSIG modeling capabilities will be enhanced such that the simulations produced reflect, as accurately as possible, the actual data gathered with real airborne infrared imaging systems. These modeling efforts are focusing on the phenomenology associated with cavern-like targets composed of numerous internal material types. A cyclical approach is being followed where modeling approaches are continually modified based on newly discovered phenomenology observed in real image data. The desired outcome of the modeling will be accurate internal-element emissivities and temperatures for the components that comprise the cooling tower for use with an external process model developed by SRNL.

Project Status: These targets are complex in structure (see Figure 3.10-1) and are further complicated by the possible coating of water on some surfaces and the water laden localize atmosphere located immediately above the target area. Initial geometrical models have been assembled and initial image simulations carried out (see Figure 3.10-2) at this time. Much more work will be continuing on this step in the project during the coming year as further image collection experiments are carried out and material samples and optical properties are measured.

Figure 3.10-1: Schematic of the interior layout of a counter-flow tower	Figure 3.10-2: DIRSIG radiance image
Figure 3.10-3: SRS image (left) and DIRSIG image (right). Profiles indicated by solid white line
Figure 3.10-4: Apparent temperature profiles across the tower throat for the SRS image (left) and DIRSIG image (right).

Figure 3.10-3 and Figure 3.10-4 illustrate the current brightness temperature predictions from this effort for imagery actually gathered with a longwave infrared imager and the DIRSIG simulation. While the magnitudes for these predicted temperatures are different, the general shape of the profile across the opening of the tower is quite closely matched.

Magnitude differences currently are believed to originate from several sources of error. The most significant is believed to originate form the lack of bidirectional reflectance distribution data for the material surface resulting in an inaccurate contribution of sky radiance to the exiting radiance field. This affects both the reflected downwelling as well as the self-emitted energy. Currently, models for this bidirectional optical property are being investigated and implemented to determine if a close enough match of the temperature can be obtained by using a surrogate scattering description for these surfaces, as true measurements of the actual materials present will seldom be available. Additional errors are believed to be coming from the microclimate immediately above the tower due to increased water vapor column in this localized area. Further field experiments are being conducted in 2007 to ascertain the actual existence and extent of this source of error.