Abstract:

This dataset contains Moderate Resolution Imaging Spectroradiometer (MODIS)-derived color index (CI), frontal density, and sea surface temperature (SST) in the Gulf of Mexico, at 1,1, and 4-km spatial resolutions, respectively, at monthly temporal resolution. These products were processed and distributed by Optical Oceanography Lab (https://optics.marine.usf.edu/) at University of South Florida. The original data have been sub-setted to the Gulf of Mexico region (18N to 31N and 98W to 79W) to calculate the monthly mean CI distributions, frontal index, and SST over the 2016-2018 period. Figures illustrating the CI distributions, frontal density, and SST for the Gulf of Mexico region are included for all data.

Suggested Citation:

Hu, Chuanimin and Oscar Garcia-Pineda. 2020. Moderate Resolution Imaging Spectroradiometer (MODIS)-derived color index (CI), frontal density, and sea surface temperature (SST) in the Gulf of Mexico between 2016-01-01 and 2018-12-31. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-dhqm-9q43

Purpose:

The systematic documentation of CI distributions in the Gulf of Mexico between 2016 and 2018 using MODIS satellite ocean color measurements. CI provides a relative index to measure the color changes due to phytoplankton, colored dissolved organic matter, and suspended particles. Different from the NASA standard chlorophyll-a data product, CI is designed to provide more data coverage regardless of sun glint, thin clouds, and thick aerosols. Because of the much-improved coverage, CI is a better product in examining relative ocean color patterns rather than the absolute chlorophyll-a concentration, especially from daily snapshot images. The systematic documentation of frontal density distributions in the Gulf of Mexico between 2016 and 2018 using MODIS satellite ocean color measurements. The frontal density is a measure of how often an ocean front appears in a certain location for a given period. The systematic documentation of SST distributions in the Gulf of Mexico between 2016 and 2018 using MODIS satellite ocean color measurements.

Data Parameters and Units:

Monthly distributions: monthly_CI_composite (Color Index, unitless); Lat (latitude, [degrees N]); Lon (longitude, [degrees E]); palette (rgb values, [0-255]). Monthly distributions: frontal_density_real (frontal density, [%]); Lat (latitude, [degrees N]); Lon (longitude, [degrees E]); palette (rgb values, [0-255]). Monthly distributions: sst (sea surface temperature, [oC]); lat (latitude, [degrees N]); lon (longitude, [degrees E]); palette (rgb values, [0-255]).

Methods:

This ocean color data products generated from satellite measurements using the Moderate Resolution Imaging Spectroradiometer. Data products are accessible at https://optics.marine.usf.edu/. The monthly mean data products are gridded to 1-km resolution for the region of 18N to 31N and 98W to 79W. For each image pixel, the CI value is calculated as the difference between Rrc(555) and a linear baseline between Rrc(469) and Rrc(645), where the numbers in the parenthesis indicate MODIS wavelengths and Rrs refers to Rayleigh corrected reflectance generated by the NASA standard processing software, SeaDAS (http://seadas.gsfc.nasa.gov). Additional corrections for sun glint contributions are made through the shortwave infrared (SWIR) wavelengths. Cloud masking is through an empirical threshold determined from several near-infrared (NIR) and SWIR bands. More details can be found in the following publications: Canny, John F., 1986. A computational approach to edge detection. IEEE Transactions on Pattern Analysis and Machine Intelligence 8 (6), 679–698; and Hu, Chuanimin. 2011. An empirical approach to derive MODIS ocean color patterns under severe sun glint. Geophysical Research Letters, 38, L01603. doi:10.1029/2010GL045422. This ocean color data product is generated from satellite measurements using the Moderate Resolution Imaging Spectroradiometer. There are three steps used in generating the front density data product. One, MODIS CI images are created first from daily measurements, using the methods described in Hu (2011), where the images are accessible at https://optics.marine.usf.edu/. As described in the README file for the CI data product, CI is designed to derive relative ocean color changes, even in the presence of sun glint, thin clouds, and thick aerosols. Therefore, the CI images show much more improved coverage than NASA standard chlorophyll-a images, thus suitable for delineation of oceanic fronts. Two, the front lines are determined through an edge detection method, described in Canny (1986). The method is based on pixel gradient, combined with a statistically determined threshold. Three, the front lines derived from individual MODIS CI images are weighted by the front strength, and then aggregated in time to derive frontal density maps. These are standard Level 3 NASA data products, generated from satellite measurements using the Moderate Resolution Imaging Spectroradiometer. All data collection, algorithms, and product uncertainties can be found on the NASA Algorithm Theoretical Basis Document (ATBD) website at https://oceancolor.gsfc.nasa.gov/atbd/sst/. The monthly mean data products are gridded to 4-km resolution. This dataset is associated with the publication: Hu, Chuanimin. 2011. An empirical approach to derive MODIS ocean color patterns under severe sun glint. Geophysical Research Letters, 38, L01603. doi:10.1029/2010GL045422.

Provenance and Historical References:

Canny, John F., 1986. A computational approach to edge detection. IEEE Transactions on Pattern Analysis and Machine Intelligence 8 (6), 679–698. Hu, Chuanimin. 2011. An empirical approach to derive MODIS ocean color patterns under severe sun glint. Geophysical Research Letters, 38, L01603. doi:10.1029/2010GL045422.

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