Integrated dataset for red tide (Karenia brevis bloom) patterns on the west Florida shelf
Description
This dataset contains integrated red tide (Karenia brevis harmful algal blooms) maps for the West Florida Shelf (24N – 31N, 87W – 81W) every month between 2003 and 2019. The integration is over in situ water sample analysis (which provides K. brevis cell concentration) and satellite data (which provides more frequent and spatial coverage than in situ data) using a practical approach. In situ cell counts data were obtained from a database maintained by the Florida Fish & Wildlife Conservation Commission (https://myfwc.com/research/redtide/monitoring/database/), and satellite data were collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite, available through NASA’s OB.DAAC (https://oceancolor.gsfc.nasa.gov). They were integrated to generate monthly maps of K. brevis bloom spatial extent and frequency. Specifically, the maps are expressed as bloom occurrence frequency (BOF) and bloom intensity (BI). The boundary of bloom locations represents the bloom footprint. Both maps are in imagery format (color coded in png files, MODIS_KB_bloom_WFS_images.zip) and binary format (floating point Geotiff files, MODIS_KB_bloom_WFS_binary.zip).
Files
Steps to reproduce
MODIS/Aqua satellite Level-0 data were obtained from NASA Goddard Space Flight Center, and processed to generate georeferenced spectral Remote Sensing Reflectance (Rrs, sr-1) data products using the standard NASA processing software (SeaDAS version 7.5) as well as calibration and algorithms embedded in SeaDAS. These products were further used to calculate normalized fluorescence line height (nFLH, Hu and Feng, 2017), red band difference (RBD, Amin et al., 2009), and to compose enhanced Red-Green-Blue (ERGB) images. The daily images were overlaid with FWC K. brevis cell counts data collected 7 days of the image acquisition date. The following steps were used to generate the integrated dataset: 1) For the study region of west Florida shelf (WFS), each of the RBD (after masking out pixels contaminated by stray lights and other artifacts) anomaly patches was roughly delineated if field data indicate high K. brevis counts; 2) The K. brevis bloom footprint within the delineated RBD anomaly patch was objectively delineated using a pre-defined RBD threshold (0.015 mW cm-2 m-1 sr-1, corresponding to about 105 cells/L K. brevis) according to the literature, and a corresponding binary flag file (1 indicates bloom, 0 indicates non-bloom, NaN (not a number) indicates no valid observation) was recorded; 3) Weekly, biweekly, and monthly bloom statistics (maps) were generated in two ways. One, bloom occurrence frequency (BOF, 0% - 100%) at each location was calculated as a ratio of number of bloom occurrences to number of valid observations. Two, average RBD value was calculated from all valid pixels at each location, representing bloom intensity (BI). These were stored in digital files. 4) K. brevis bloom (i.e., red tide) footprints at weekly, biweekly, monthly intervals were derived from their corresponding bloom occurrence frequency maps, and exported to digital files. All images and digital data have been recorded in Geotiff files (floating point values) and converted to png images to facilitate visualization. Amin, R., et al. (2009). Novel optical techniques for detecting and classifying toxic dinoflagellate Karenia brevis blooms using satellite imagery. Opt. Express 17(11), 9126–9144. Hu, C., and L. Feng (2017). Modified MODIS fluorescence line height data product to improve image interpretation for red tide monitoring in the eastern Gulf of Mexico. J. Appl. Remote Sens. 11(1), 012003 (2016), doi: 10.1117/1.JRS.11.012003.