Report Date - November 6th to November 12th, 2023

Prepared By: Summer Manestar & Andrew Kamerosky

For the week of November 6th, 2023, the estimated median chlorophyll-A (ChlA) continued to be low across the Indian River Lagoon (IRL). Imagery collected the previous week on November 5th was compared against November 11th due to the other available scene of the week being collected on November 9th (Table 1). 

The Southern Mosquito Lagoon (SML), Northern-North IRL (N-NIRL), Central-North IRL (C-NIRL), Central Banana River Lagoon (C-BRL), Northern Banana River Lagoon (N-BRL), Southern Banana River Lagoon (S-BRL), Southern-North IRL (S-NIRL) and the North-Central IRL (N-CIRL) ended the week below the 6 µg/L threshold for healthy levels of ChlA. 

There were two (2) Sentinel-2 scenes usable during this period, with only the November 9th scene providing full coverage of the IRL. There were two (2) usable Sentinel-3 scenes during this period.

Table 1 - Sentinel-3 estimated median ChlA in µg/L and percent change between November 5th and November 11th, 2023, by IRL Basin.

There was only one (1) S2 scene with full coverage of the IRL during the week which was collected on November 9th. There did not appear to be any areas within the IRL experiencing bloom conditions. Due to cloud cover, several areas of elevated ChlA are likely overestimated. 

Figure 1 - Processed Sentinel-2 imagery for November 9, 2023.

Sentinel 3

There were two (2) scenes from Sentinel 3 that were usable for detection of bloom activity the week of November 6th (Figure 2, Figure 3). Due to the scenes being only two (2) days apart, the following analysis focuses on the November 5th scene from the previous week and then November 11th (Figure 4, Figure 5). 

Figure 2 - Processed Sentinel-3 imagery for November 5, 2023.

Figure 3 - Processed Sentinel-3 imagery for November 11, 2023.

Figure 4 - Sentinel 3 estimated Chlorophyll A (ChlA) Levels in Micrograms/Liter (µg/L) for November 5th and November 11th, 2023, over sections of the Southern Mosquito Lagoon (SML) and North Indian River Lagoon (NIRL). The box plots represent the range of estimated ChlA values for each Basin, with the boxes showing the second quartile, median, and third quartile, and the whiskers representing the first and fourth quartiles.

Figure 5 - Sentinel 3 estimated Chlorophyll A (ChlA) Levels in Micrograms/Liter (µg/L) November 5th and November 11th, 2023, over sections of the Banana River Lagoon (BRL) and Central Indian River Lagoon (CIRL). The box plots represent the range of estimated ChlA values for each Basin, with the boxes showing the second quartile, median, and third quartile, and the whiskers representing the first and fourth quartiles.

SJRWMD IRL Continuous Monitoring Stations

There is no analysis of the SJRWMD Continuous Monitoring stations due to a data service outage from the SJRWMD.

The availability and usability of satellite imagery is contingent upon both the satellite being overhead and low cloud cover. The orbits of the Sentinel satellites will on occasion cover a portion versus all of the Indian River Lagoon. Likewise, cloud cover can also result in only portions of the Indian River Lagoon (IRL) being visible. Table 2 below lists the availability of Sentinel imagery and its usability for Harmful Algal Bloom (HAB) analysis.

Table 2 - Sentinel 2 and 3 imagery availability for the week of November 6th, 2023

N - Imagery Not Available

Y - C - Imagery Available, Cannot Use Due to Cloud Cover

Y - P - Imagery Available, Only Partial Imagery of IRL

Y - G - Imagery Available, No Issues Over the IRL

Methods

HAB’s observed by this project are defined as over 80 Micrograms/Liter (µg/L) Chlorophyll A (ChlA) (as estimated by a calibrated Normalized Difference Chlorophyll Index (NDCI)) and persistent across the week in review. The algorithms that transform the NDCI index value to estimated ChlA concentrations were developed using a second-order polynomial equation. The Sentinel 2 (S2) equation has a Root Square (R2) of 0.81 with a Root Mean Square Error (RMSE) of 14.14 ug/L of ChlA. The Sentinel 3 (S3) equation has an R2 of 0.92 and an RMSE of 9.92 ug/L ChlA. The RMSE is a measure of the accuracy of a model in estimating values, ChlA in this instance, where a lower value is indicative of higher accuracy. It does not identify if the model consistently over or underestimates the modeled values. The equations are below:

• S2 Estimated ChlA = 297.36(NDCI)2 + 313.98(NDCI) + 36.152

• S3 Estimated ChlA = 437.07(NDCI)2 + 348.98(NDCI) + 33.928

   Figure 6 - SJRWMD Continuous Monitoring stations and IRL Basins used for S2 and S3 analysis. 

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