Stray Light Characterization for MOBY

Published

February 1, 2002

Author(s)

Bettye C. Johnson, Steven W. Brown, Keith R. Lykke, M Feinholz, M Yarbrough, S Flora, D K. Clark

Abstract

The Marine Optical Spectrograpli (MOS) system is used as a down-welling irradiance and up-welling in-water radiance profiler in two configurations: as the sensor for the Marine Optical Buoy (MOBY) and as a mobile, sliipboard-deployable sensor. Both systems are used for vicarious calibration of satellite ocean color sensors, e.g. MODIS, SeaWiFS, OCT'S, POLDER, and IRSI-MOS. Ocean color, instrument specific, band-averaged normalized water-leaving radiances, nL_w's, are reported by the MOBY team, corresponding to data sets from MOBY at the Lanai, Hawaii site and various cruise stations for the MOS profiler. For the vicarious calibration of MODIS and SeaWiFS, total band-averaged nL_w's are required for the spectral range from 412 nm to 670 nm.Stray light in the MOS spectrographs affects the radiometry in a complicated manner that depends upon the relative spectral shape of the measured fluxes and the spectral region of interest. Here we report on the results of a detailed radiometric characterization of the MOS and MOBY configurations. In this work, a rigorous study of the MOS profiler was performed using broadly tunable, narrow-band lasers at the NIST facility for Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS). These measurements enabled an accurate determination of the stray light contribution to the measured signals from MOS. A stray light correction algorithm was developed and assessed using MOS measurements of a laboratory standard of spectral radiance. In a second phase of the study, a mobile tunable laser system was developed and deployed at the MOBY field support site in Honolulu, Hawaii, and MOBY (MOBY218) was characterized for stray light performance.The stray light characterization procedures and the preliminary results are presented. The correction algorithm was applied to MOS profiler system responses and test data sets from the Marine Optical Characterization Experiment 5 (MOCE-5) cruise. Additionally, the algorithm was applied to MOS data sets for a series of laboratory color-filtered sources of known spectral radiance. The initial tests on MOCE-5 stations demonstrate that the stray light effect on the upwelling spectral radiance, L_u(z, γ) isless than 5 % at 412 nm and smaller at other ocean color bands. The characterizations on MOBY218 concentrated on the radiance input optic that is coupled directly to the MOS, as well as the top and middle arms, which are coupled to MOS using optical fibers, Improved values of L_u(Z,γ), with lower uncertainty, will be determined for all MOBY data sets. These results impact the Calibrations of all ocean color satellites that use MOBY and MOS data sets and will provide more accurate values of the retrieved nLw's, spectral radiance attenuation coefficients and bio-optical products, i.e. pigment concentrations.

Citation

Stray Light Characterization for MOBY

Volume

82 No. 47

Publisher Info

American Geophysical Union Book of Abstracts Fall Meeting 2001,

Pub Type

Books

Keywords

display measurement, projection displays, replica mask, resolution, small area contrast, stray light

Citation

Johnson, B. , Brown, S. , Lykke, K. , Feinholz, M. , Yarbrough, M. , Flora, S. and Clark, D. (2002), Stray Light Characterization for MOBY, American Geophysical Union Book of Abstracts Fall Meeting 2001, (Accessed October 31, 2024)