Currently, SaWS covers the entire Intra-Americas Sea, western Tropic Atlantic, and Bermuda. To facilitate visualization and navigation, the imagery products are divided into different geographic regions, for example Central Atlantic, Eastern Caribbean, Western Gulf of Mexico, Bermuda, etc. The "SaWS Clickable Map" at top of this paragraph shows the current coverage, where any region can be clicked to open a separate page unique to that region. A user may then select a specific date on the calendar, or use the “animate” function to browse through the image sequence quickly to determine the date of interest. A screenshot of a typical web interface is presented below.
Currently, VBS covers selected regions in the Gulf of Mexico, Cape Code, and Persian Gulf. In the future other regions may be added, depending on user needs and processing capacity. The current regions include:
Florida Panhandle [each links to its own page in a popup window] Apalachicola Bay Offshore Apalachicola Bay Saint George Sound Offshore Saint George Sound Saint Joseph Bay Offshore Saint Joseph Bay Saint Andrew Bay Offshore Saint Andrew Bay Perdido Bay, Pensacola Bay Offshore Pensacola Bay Choctawhatchee Bay Offshore Choctawhatchee Bay Florida Big Bend Apalachee Bay Offshore Apalachee Bay Steinhatchee River Suwannee River Central West Florida Charlotte Harbor Sarasota Bay Tampa Bay West Florida Shelf Florida Keys Florida Reef Tract Florida Straits Southwest Florida Birght Cape Cod Northern Persian Gulf
Estuaries and coastal zones are under influence of both climate variability and human impacts, and it is desirable to assess their water quality state and anomaly events to facilitate coastal management. The virtual buoy system (VBS) is established here to meet such needs through satellite measurements, algorithm development, data product customization, and data sharing. The VBS is based on a virtual antenna system (VAS) that obtains low-level satellite data and generates higher-level data products using both NASA standard algorithms and regionally customized algorithms in near real-time. The VB stations are predefined and carefully chosen to cover water quality gradients in estuaries and coastal waters, where multi-year time series of a variety of water quality parameters at monthly and weekly intervals are extracted and displayed. Details can be found in Hu et al. (2014)
Three basic steps are used to implement the VBS.
The first is to prepare satellite data products from individual satellite passes. This is through the VAS. Low-level data are downloaded from NASA [link to oceancolor.gsfc.nasa.gov] every day in near real-time, and then processed using the software SeaDAS and software and algorithm written in house. The data products are stored in HDF files
.The second is to design the VBS locations. These are based on user needs, the processing capacity at Optical Oceanography Laboratory (OOL), and water quality gradients in a specific region. Typically, for a region of interest, there are several to several 10s of VBS locations. These locations are displayed on a “clickable” map, where a user can click on any of these pre-defined locations to visualize water quality data.
The third is to query the HDF files (step 1) for each of the locations (step 2) to extract and plot the water quality data, with results saved in ASCII data file and png image file. This step is performed once every week to update all the time series data.
Finally, depending on the region, the water quality data may include some or all the following parameters: sea surface temperature (SST, oC), chlorophyll-a concentration (Chla, mg m-3), turbidity (NTU), diffuse light attenuation at 490 nm (Kd(490), m-1) or secchi disk depth (SDD, m), absorption coefficient of colored dissolved organic matter (CDOM), and bottom available light (BAL, %). The description of each parameter can be found under its corresponding tab on the web page.
Examples
Go to “Where to Find VBS Data” tab above, select one of the predefined regions, which will lead to the following steps. Fig. 1 below shows an example of the “clickable map” where the VBS locations are annotated. A mouse click on a location will bring a summary water quality page for that station, as shown in Fig. 2. A mouse click on one of the water quality tabs will bring the time series data and graph, as shown in Fig. 3. Fig. 1. A sample “clickable map” showing the VBS locations for the Central West Florida. A mouse click on one of the stations will bring a summary water quality table for that station (Fig. 2). Fig. 2. A screenshot showing summary tab for one VBS station. In the menu each individual water quality parameter is listed as a separate tab than can be clicked on. A click on the “Kd” tab will display all time series Kd data in both ASCII and graphic formats, as shown in Fig. 3. Fig. 3: A sample screenshot showing light attenuation time series for a VBS station.
Currently, SaWS covers the entire Intra-Americas Sea, western Tropic Atlantic, and Bermuda. To facilitate visualization and navigation, the imagery products are divided into different geographic regions, for example Central Atlantic, Eastern Caribbean, Western Gulf of Mexico, Bermuda, etc. The "SaWS Clickable Map" at top of this paragraph shows the current coverage, where any region can be clicked to open a separate page unique to that region. A user may then select a specific date on the calendar, or use the “animate” function to browse through the image sequence quickly to determine the date of interest. A screenshot of a typical web interface is presented below.
Under each images icon in the VAS (previous tab) there is a small GE button in the lower right corner. When this is clicked, a KML file is generated for that image. In addition, surface currents from the Hybrid Coordinate Ocean Model (HYCOM — from the National Ocean Partnership Program (NOPP)) are obtained, updated nightly, and made available via the VAS as a layer within Google Earth. Thus, both the image and surface currents can be displayed in Google Earth with a simple mouse click (see example below), thereby facilitating visualization and navigation. Within Google Earth, once a Sargassum raft is identified with latitude and longitude, current speed and direction (available through a mouse click over the current vector) near the raft can be used to predict the movement of the raft and a possible beaching time, in essence, forming an early warning system.
Sargassum has impacted the Caribbean in so many ways. Here we show a few photographs that reveal the serious nature of the problem.
Smetacek, V., and A. Zingone (2013). Green and golden seaweed tides on the rise, Nature, 504:84-88.
Wang, M., and C. Hu (2016), Mapping and quantifying Sargassum distribution and coverage in the Central West Atlantic using MODIS observations, Remote Sens. Environ., in press.