The Suomi National Polar-orbiting Partnership (SNPP) was successfully launched on October 28, 2011. The Visible
Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi NPP, which has 22 spectral bands (from visible to
infrared) similar to the NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS), is a multi-disciplinary
sensor providing observations for the Earth’s atmosphere, land, and ocean properties. In this paper, we provide some
evaluations and assessments of VIIRS ocean color data products, or ocean color Environmental Data Records (EDR),
including normalized water-leaving radiance spectra nLw(λ) at VIIRS five spectral bands, chlorophyll-a (Chl-a)
concentration, and water diffuse attenuation coefficient at the wavelength of 490 nm Kd(490). Specifically, VIIRS ocean
color products derived from the NOAA Multi-Sensor Level-1 to Level-2 (NOAA-MSL12) ocean color data processing
system are evaluated and compared with MODIS ocean color products and in situ measurements. MSL12 is now
NOAA’s official ocean color data processing system for VIIRS. In addition, VIIRS Sensor Data Records (SDR or Level-
1B data) have been evaluated. In particular, VIIRS SDR and ocean color EDR have been compared with a series of in
situ data from the Marine Optical Buoy (MOBY) in the waters off Hawaii. A notable discrepancy of global deep water
Chl-a derived from MODIS and VIIRS between 2012 and 2013 is observed. This discrepancy is attributed to the SDR
(or Level-1B data) calibration issue and particularly related to VIIRS green band at 551 nm. To resolve this calibration
issue, we have worked on our own sensor calibration by combining the lunar calibration effect into the current
calibration method. The ocean color products derived from our new calibrated SDR in the South Pacific Gyre show that
the Chl-a differences between 2012 and 2013 are significantly reduced. Although there are still some issues, our results
show that VIIRS is capable of providing high-quality global ocean color products in support of science research and
operational applications. The VIIRS evaluation and monitoring results can be found at the website:
http://www.star.nesdis.noaa.gov/sod/mecb/color/index.html.
The first geostationary ocean color satellite sensor, Geostationary Ocean Color Imager (GOCI) onboard the Korean Communication, Ocean, and Meteorological Satellite (COMS), which was launched in June of 2010 and has eight spectral bands from the blue to the near-infrared (NIR) wavelengths in 412–865 nm, can monitor and measure ocean phenomenon over a local area of the western Pacific region centered at 36°N and 130°E and covering ~2500 × 2500 km2. Hourly measurements during daytime (i.e., eight images per day from local 9:00 to 16:00) are a unique capability of GOCI to be used for the short- and long-term regional ocean environmental monitoring.
A recent study from a collaboration between NOAA Center for Satellite Applications and Research (STAR) and Korean Institute of Ocean Science and Technology (KIOST) showed that the GOCI ocean color products such as normalized water-leaving radiance spectra, nLw(λ), for GOCI coverage region derived using an iterative NIR-corrected atmospheric correction algorithm (Wang et al., Opt. Express, vol. 20, 741–753, 2012) were significantly improved compared with the original GOCI data products and have a comparable data quality as from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua in this region (Wang et al., Opt. Express, vol. 21, 3835–3849, 2013). It is also shown that the GOCI-derived ocean color data can be used to effectively monitor ocean phenomenon in the region such as tide-induced re-suspension of sediments, diurnal variations of ocean optical and biogeochemical properties, and horizontal advection of river discharge.
In this paper, we show some more recent results of GOCI-measured ocean diurnal variations in various coastal regions of the Bohai Sea, Yellow Sea, and East China Sea. With possibly eight-time measurements daily, GOCI provides a unique capability to monitor the ocean environments in near real-time, and GOCI data can be used to address the diurnal variability in the ecosystem of the GOCI coverage region. In addition, more in situ data measured around the Korean coastal regions are used to validate the GOCI ocean color data quality, including evaluation of ocean diurnal variations in the region. The GOCI results demonstrate that GOCI can effectively provide real-time monitoring of water optical, biological, and biogeochemical variability of the ocean ecosystem in the region.
KEYWORDS: Data modeling, Water, MODIS, Coastal modeling, Signal attenuation, In situ metrology, Satellites, Imaging systems, Satellite imaging, Biological research
The first geostationary ocean color sensor, Geostationary Ocean Color Imager (GOCI), on board the Korean
Communication Ocean and Meteorological Satellite (COMS), was successfully launched on June 26 of 2010. GOCI
includes 8 spectral bands in visible and near-infrared wavelengths with a coverage area of 2,500×2,500 km2 centered at
36°N and 130°E over the Korean seas. GOCI will provide an important capability to monitor ocean phenomenon with
one hour temporal and 500 m spatial resolutions for a better understanding of biogeochemical processes in the Korean
seas. However, there are uncertainties in estimating bio-optical properties since water properties in large areas of
Koreans are optically characterized as Case-2 waters due to strong tidal mixing and large amount of river discharges.
The newly-developed semi-analytical algorithm of diffusion attenuation coefficient at the wavelength of 490 nm,
Kd(490), for the turbid coastal waters was assessed using in situ radiometric and Kd(490) measurement obtained from
clear and turbid waters over the global ocean. Results of the Kd(490) data using the new model is well correlated with the
in situ Kd(490) measurements. Synoptic maps of Kd(490) data from the Moderate Resolution Imaging Spectroradiometer
(MODIS) onboard the Aqua satellite using the new model were derived in the Yellow Sea and East China Sea. The
MODIS-derived Kd(490) data show significant increased values along the turbid coastal waters including the Bohai Sea
and the Yangtze River Estuary. In general, the highest Kd(490) appeared in winter and the lowest Kd(490) are presented
in summer over the all area. Interannual variability of Kd(490) in timing and magnitude is apparent, but there is no
consistent trend of interannual variability across all areas.
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