Radiometric Characterization and Absolute Calibration of the Marine Optical System (MOS) Bench Unit

Published

March 1, 2003

Author(s)

C Habauzit, Steven W. Brown, Keith R. Lykke, B. Carol Johnson, M Feinholz, M Yarbrough, D K. Clark

Abstract

The Marine Optical Spectrograph (MOS) is a dual CCD-based spectrograph system developed for in-water measurements of down-welling solar irradiance, Ε_d, and up-welling radiance, L_u. These measurements are currently used in the calibration and validation of satellite ocean color instruments such as MODIS and SeaWiFS. MOS was designed to be deployed from a ship for single measurements and also integrated into the Marine Optical Buoy (MOBY) for longer time series data sets. Measurements with the two spectrographs in the MOS systems can be compared in the spectral interval from about 580 nm to 630 nm. In this spectral range, they give different values for L_u or Ε_d at a common wavelength. To better understand the origin of this observation and the sources of uncertainty in the calibration of MOBY, a MOS bench unit was developed for detailed radiometric characterization and calibration measurements in a laboratory setting. In the work reported here, we describe a novel calibration approach using a tunable-laser-based, monochromatic, uniform, Lambertian, large area integrating sphere sources (ISS). Results are compared with those obtained by a conventional approach using a lamp-illuminated ISS. Differences in the MOS bench unit responsivity between the two calibration approaches were observed and attributed to stray light. A simple correction algorithm was developed for the broadband source that greatly improves the agreement between the two techniques. Implications for water-leaving radiance measurements by MOS are discussed.

Citation

Journal of Atmospheric and Oceanic Technology

Volume

20

Issue

no. 3

Pub Type

Journals

Keywords

CCD, ocean color, radiance responsivity, spectrograph, stray light

Citation

Habauzit, C. , Brown, S. , Lykke, K. , Johnson, B. , Feinholz, M. , Yarbrough, M. and Clark, D. (2003), Radiometric Characterization and Absolute Calibration of the Marine Optical System (MOS) Bench Unit, Journal of Atmospheric and Oceanic Technology (Accessed October 7, 2025)