|Optical Oceanography Laboratory College of Marine Science|
Virtual buoy system (VBS) to monitor coastal water quality
What is VBS?
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 our 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. The VBS is operated in two ways:
● It monitors, extracts, and integrates near real-time data into multi-year time series of a variety of water quality parameters which are displayed graphically at weekly and monthly intervals.
● It checks diffences between weekly and monthly data and compares them with long term climatology allowing it to determine and display varying degrees of positive (reds) and negative (blues) anomalies. These anomalies can be seen on the summary tab of each virtual buoy station, a sample of which is shown below.
Click the "How VBS Works" tab above to see how it works. Further details can also be found in Hu et al. (2014)
How VBS Works
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 U.S. NASA every day in near real-time, and then processed using SeaDAS software and software or 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 our 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 station locations. These locations are displayed on a “clickable” map (shown to the right), 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 and every month to update all the time series data and check for anomalies.
Finally, depending on the region, the water quality data may include some or all the following parameters: sea surface temperature (SST, Co), 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 each station's web page.
Go to “Access and Download VBS Data” tab above and select one of the predefined regions. This tab has each of the regions and sub-areas represented as clickable buttons. They highlight when you hover over them. When you click on a button you will be presented with a pop-up clickable map which has all the stations on it. You may click any one of the stations on the map and be taken to the data for that station.
You will first be presented the summary tab that you saw in the previous tab on this page. However, you may click on any other tab on the station page to see the water quality time series data displayed in graph format, with an brief explaination of the data as well. You may also click the links to see the data in ASCII format. Or, you may click on the “clickable map” button found next to each station name. From this clickable map, you can get to (at least) any other station within the sub-area.
In the example below, you see the Kd(488) tab contents of West Florida Shelf Station 04. You can click on the image to see a larger one.
Access and Download VBS Data
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. Each region may contain sub-areas as seen in the clickable links below. Note in each case an image map will open that contains the sub-area (some image maps have more than one sub-areas). The selections below may also be found in the menu to the left under "Virtual Buoy Products", however, these are sorted by the satellite data regions from which they were derived. The current regions include:
Central West Florida
Florida Big Bend
Northern Persian Gulf