Traditionally, the emissivity spectrum of a material has been measured in the laboratory using a single pixel spectral measurement device, such as a Fourier Transform Infrared Radiometer (FTIR). This measurement technique is limited to a single spatial location on a target material at a time. The exact location of the measurement on the target material is difficult to control due to the nature of the single pixel measurement. Further, due to the measurement setup, target materials often have to be modified from their original form in order to conduct the single pixel measurements. For a complex target material consisting of multiple components, separate measurements are necessary to characterize the spectral variations of the target material across its spatial extent. For single pixel spectral measurement devices, spectral characterization of the target material as a function of spatial location on the target material is limited to the number of separate measurements that the operator has the time and patience to measure. Even if an operator has the time to make multiple single-pixel measurements that cover the entire surface of the target material, because of the difficulty of controlling the location of the pixel on the sample, the true spectral-spatial characterization of the target material is not possible.
In remote sensing applications, it is known to deploy multispectral or hyperspectral sensors. For example, the Spatially Enhanced Broadband Array Spectrograph System (SEBASS) created by The Aerospace Corporation of El Segundo, Calif. has a sensor which provides spectral capability in both the mid-wave infrared and long-wave infrared bands. See, e.g., Hackwell, J., Warren, D. W., Bongiovi, R. P., Hansel, S. J., Hayhurst, T. L., Mabry, D. J., Sivjee, M. G., Skinner, J. W., “LWIR/MWIR Imaging Hyperspectral Sensor for Airborne and Ground-based Remote Sensing,” Proc. SPIE Conf. Imaging Spectrometry III, vol. 2819, November 1996, pp. 102-107, which is incorporated by reference herein in its entirety.
It would be useful to be able to provide methods and systems for measuring spectral characteristics of materials more efficiently, e.g., with fewer measurements. It would be useful to be able to provide methods and systems for accurately measuring spectral characteristics in all areas of a sample, or in larger-sized areas of a sample. It would be useful to be able to provide methods and systems that are capable of providing true independent-of-temperature (i.e., independent of the temperature of the environment) measurements of emissivity, transmissivity, and/or reflectivity for a sample. It would be useful to be able to provide methods and systems that are capable of determining spatial variability in the spectral characteristics of a sample.