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Abstract
The Operational Land Imager (OLI) is a multispectral radiometer hosted on the recently launched Landsat8 satellite. OLI includes a suite of relatively narrow spectral bands at 30 m spatial resolution in the visible to shortwave infrared, which makes it a potential tool for ocean color radiometry: measurement of the reflected spectral radiance upwelling from beneath the ocean surface that carries information on the biogeochemical constituents of the upper ocean euphotic zone. To evaluate the potential of OLI to measure ocean color, processing support was implemented in Sea-viewing Wide Field-of-View Sensor (SeaWiFS) Data Analysis System (SeaDAS), which is an open-source software package distributed by NASA for processing, analysis, and display of ocean remote sensing measurements from a variety of spaceborne multispectral radiometers. Here we describe the implementation of OLI processing capabilities within SeaDAS, including support for various methods of atmospheric correction to remove the effects of atmospheric scattering and absorption and retrieve the spectral remote sensing reflectance (Rrs; sr−1). The quality of the retrieved Rrs imagery will be assessed, as will the derived water column constituents, such as the concentration of the phytoplankton pigment chlorophyll a.
Highlights
We define ocean color as the spectral distribution of reflected visible solar radiation upwelling from beneath the ocean surface
The numbers suggest that the NIR and shortwave IR (SWIR) bands of ETMþ are effectively unusable for the atmospheric correction approach that we propose here for Operational Land Imager (OLI), as noise in the NIR channel is equivalent to 10% of the signal and noise in the longest SWIR spectral band exceeds the typical radiance over oceans
Assuming MODISA is correct, this would suggest that the Rrs(443) or Rrs(482) retrievals are too high relative to Rrs(561), i.e., the spectral dependence is biased toward the blue, which may be due to uncertainty in the vicarious calibration or error in the aerosol retrieval
Summary
We define ocean color as the spectral distribution of reflected visible solar radiation upwelling from beneath the ocean surface. Prelaunch simulations based on radiometric performance specifications demonstrated that the sensor, while primarily designed for land applications, has the potential to provide useful measurements of aquatic environments, including the separation and quantification of Ca, CDOM, and suspended sediments in the water column.[4,5] A significant advantage of OLI over existing global ocean color capable missions is the 30 m spatial resolution, which is more than an order of magnitude higher than NASA’s Moderate Resolution Imaging Spectroradiometer[6] (MODIS) currently operating from the Aqua spacecraft (MODISA) and the Sea-viewing Wide Field-of-View Sensor[7] (SeaWiFS) that operated from 1997 to 2010. 90% of the visible radiation observed by Earth-viewing satellite sensors is sunlight reflected by air molecules and aerosols in the atmosphere The removal of this atmospheric signal to retrieve RrsðλÞ is referred to as atmospheric correction. We show some results of ocean color retrieval over the coastal and inland waters of Chesapeake Bay and compare them with coincident MODISA retrievals and in situ measurements
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