In order to extract quantitative aerosol backscatter coefficients from raw lidar signals it is necessary to calibrate the responsivity of the lidar system. Typically such an operation is performed by directing the lidar beam onto a distant calibration target whose scattering properties have been well characterized in laboratory trials. The Group maintains a Lidar Target Calibration Facility which provides this critical information. Presently, the Facility can measure target materials across the CO2 laser spectrum (including isotopic variants) and also the 2.1-µm holmium laser wavelength. Sample target data, along with a description of the Facility, can be found in Haner and Menzies (1989).
A precision reflectance characterization facility has also been constructed specifically for measurement of the bidirectional reflectance properties of Spectralon panels planned for use as in-flight calibration standards for the NASA Multi-angle Imaging SpectroRadiometer (MISR) instrument. Linearly polarized incident radiation is provided at three laser wavelengths: 442 nm, 632.8 nm, and 859.9 nm. The reflected radiance signal is ratioed against a reference signal in order to minimize the influence of amplitude instability in the laser sources. This and other noise reduction measures make possible a bidirectional reflectance function (BRF) measurement precision of +0.002 at the single standard deviation confidence level. The angular positioning system which manipulates the test piece has millidegree repeatability and resolution.
References
D. A. Haner and R. T. Menzies: Reflectance Characteristics of Reference Materials Used in Lidar Hard Target Calibration. Appl. Opt., 28(5), 1989, 857-864.
B. T. McGuckin, D. A. Haner, R. T. Menzies, C. Esproles, and A. M. Brothers: Directional reflectance characterization facility and measurement methodology. Appl. Opt., 35(24), 1996, 4827-4834.
D. A. Haner, B. T. McGuckin, R. T. Menzies, C. J. Bruegge, and V. Duval: Directional-hemispherical reflectance for Spectralon by integration of its bidirectional reflectance. Appl. Opt., 37(18), 1998, 3996-3999.
D. A. Haner, B. T. McGuckin, and C. J. Bruegge: Polarization characteristics of Spectralon illuminated by coherent light. Appl. Opt., 38(30), 1999, 6350-6356.
C. Bruegge, N. Chrien, and D. Haner: A Spectralon BRF data base for MISR calibration applications. Remote Sens. Environ., 77(3), 2001, 354-366.