Comparing the ocean color measurements between MOS and SeaWiFS: A vicarious intercalibration approach for MOS

The modular optoelectronic scanner (MOS) is a German instrument that was la unched in the spring of 1996 on the Indian IRS-P3 satellite. With the succe ssful launch of NASA's Sea-viewing Wide Field-of-view Sensor (SeaWiFS) in t he summer of 1997, there are non two ocean color missions in concurrent ope ration, and there is interest within the scientific community to compare da ta from these two sensors. In this paper, we describe our efforts to retrie ve ocean-optical properties from both SeaWiFS and MOS using consistent meth ods. We first briefly review the atmospheric correction, which removes more than 90% of the observed radiances in the visible, and then we describe ho w the atmospheric-correction algorithm used for the SeaWiFS data can be mod ified for application to other ocean color sensors. Next, since the retriev ed water-leaving radiances in the visible between MOS and SeaWiFS are signi ficantly different, we developed a vicarious intercalibration method to rec alibrate the MOS spectral bands based on the optical properties of the ocea n and atmosphere derived from the coincident SeaWiFS measurements. Furtherm ore, because of the strange calibration behavior of the MOS 750 nm band, we modified the atmospheric correction such that the MOS 685 and 868 nm bands can also be used. We present and discuss the MOS-retrieved, ocean-optical properties before and after the vicarious calibration using both the MOS 68 5 and 750 nm coupled with 868 nm bands in comparison with results from SeaW iFS and demonstrate the efficacy of this approach. We show that it is possi ble and efficient to vicariously intercalibrate sensors between one and ano ther.