NASA has a serious problem with ice that forms on the cryogenic-filled Space Shuttle External Tank (ET) that could
endanger the crew and vehicle. This problem has defied resolution in the past. To find a solution, a cooperative
agreement was developed between NASA-Kennedy Space Center (KSC) and the U.S. Army Tank-automotive and
Armaments Research, Development & Engineering Center (TARDEC). This paper describes the need, initial
investigation, solution methodology, and some results for a mobile near-infrared (IR) ice detection and measurement
system developed by MDA of Canada and jointly tested by the U.S. Army TARDEC and NASA. Performance results
achieved demonstrate that the pre-launch inspection system has the potential to become a critical tool in addressing
NASA's ice problem.
The Shuttle Inspection Lidar (SIL) system is a derivative of a scanning lidar system being developed by MD Robotics and Optech. It incorporates a lidar, a camera, lights and video communications systems. The SIL is designed to meet the specific requirements for the on-orbit inspection and measurement of the Space Shuttle leading edge Reinforced-Carbon Carbon (RCC) and Thermal Protection System (TPS). The SIL has a flexible electrical and mechanical interface that enables it to be mounted on different locations including the Shuttle Remote Manipulator System (SRMS, Canadarm), and the Space Station Remote Manipulator System (SSRMS) on the International Space Station (ISS).
This paper describes the SIL system and the specifications of the imaging lidar scanner system, and discusses the application of the SIL for on-orbit shuttle inspection using the on-orbit SRMS. Ground-based measurements of the shuttle TPS taken by a terrestrial version of the imager are also presented.
A new multiscale wavelet transform algorithm for dim target detection in forward looking infrared (FLIR) imagery is described. The algorithm was evaluated using a database of FLIR image sequences representing different target, sensor, and background clutter scenarios. Detection performance was quantified in terms of the receiver operating characteristics (ROC) for all sequences. The detection performance of the new algorithm was compared to the Holmes double-gated filter method and was found to be comparable or significantly better depending on the image sequence.
This paper describes a new wavelet-transform-based nonlinear spatial filter called the scale subtraction filter (SSF). The SSF enhances dim target signals relative to clutter in forward- looking infrared (FLIR) imagery using the scale characteristics of the target. The SSF was applied to a database of FLIR image sequences representing different target, sensor, and background clutter scenarios. Detection performance was quantified in terms of the receiver operating characteristics (ROC) for all sequences. The detection performance of the new algorithm was compared to the Holmes double-grated filter method and was found to be equivalent or significantly better depending on the image sequence.
Measurements are reported of the infrared sunglint clutter channel caused by the direct solar reflection from the wave-perturbed sea surface at near-grazing angles of incidence. Apparent radiance has been measured over Monterey Bay as a function of azimuth and elevation angles relative to the sun direction using an AGA Thermovision 780 dual-band radiometric imaging system in the wavebands 2 to 5.6 (SW) and 8 to 12 micrometers (LW) with 7 degree(s) FOV. Time averaged profiles from multiframe averages show near-Gaussian angular distributions with half widths in the range 3 to 20 degrees (depending on solar angle) for look-down angles of 1 to 10 degrees below the horizon. The p- and s- polarized components of sea surface radiance have been obtained using an external wire-grid polarizing filter and compared with unpolarized measurements. The degree of polarization within the glint is shown to be horizontal and variable in the range 1% to 30%, depending on solar elevation, the higher degrees of polarization being found in the SW band. Significant vertical sea radiance polarization has been observed outside the solar glint in the 8 to 12 micrometers band, and is attributed to sea surface emission polarization.
This paper presents a sea radiance polarization model and experimental measurements of near- horizon sea glint polarization in the 3 - 5 micrometers and 8 - 12 micrometers spectral bands. The experimental measurements include the effects of polarization on the glint statistics, the degree of linear polarization and the polarization signal-to-noise ratio (SNR) improvement factor for both spectral bands in the presence of sea glint. The results indicate that the polarization in the 3 - 5 micrometers spectral band is dominated by the reflected solar and sky radiance and is polarized in the s plane. The polarization of intense sea glint in the 8 - 12 micrometers region is low and s polarized due to the weak solar spectrum in this band. In little or no glint, the radiation is weakly p polarized. Experimental data indicate that a polarizing filter can produce a significantly larger SNR improvement for the 3 - 5 micrometers spectral band than for the 8 - 12 micrometers band. Theoretical calculations using the polarization model show good agreement with the experimental data.