The Eyes and Ears of the Coast: A 360-Degree View of the Gulf of Mexico
By Christine Wendling
Having accurate, accessible, real-time oceanic and atmospheric information available prior to, during, and following catastrophic events has a significant impact on a community’s ability to save lives, property, and ecosystem function. Two LSU College of the Coast and Environment labs are experts at acquiring this information: The Earth Scan Laboratory (ESL) and the Wave-Current Information System (WAVCIS) provide a wealth of critical environmental measurements both above and below the Gulf of Mexico’s surface.
ESL uses three antennas on the roof of LSU’s Howe-Russell Building to capture satellite measurements and imagery of the Gulf Region. The lab uses polar orbiting and geostationary satellites that detect a variety of wavelengths (such as infrared radiation) to quantify water surface temperature, circulation changes, water quality, sediment distribution and transport. They can also identify areas of flooding and algal blooms that occur in Louisiana’s lakes and bays and along the coast.
While ESL observes the Gulf from above, WAVCIS looks at what lies beneath the surface of the water. WAVCIS is a monitoring program that provides real-time data for meteorology (wind, air pressure, humidity, etc.), water level (tide and storm surge), water velocity profiles, and waves or sea state which include wave height and period (or duration) off the Louisiana coast.
The information collected from these two labs has a variety of real-world uses. One example is that ESL can detect chlorophyll a which enables the tracking of algal (phytoplankton) blooms (sometimes toxic to humans and shellfish) in the imagery collected from the Moderate-resolution Imaging Spectroradiometer (MODIS)-equipped satellites. MODIS acquires information in 36 spectral bands, including infrared for temperature and blue and green channels that detect chlorophyll. High concentrations of chlorophyll a in phytoplankton can lead to hypoxia in bottom waters, a phenomenon in which the concentration of dissolved oxygen in water decreases until it can no longer support living aquatic organisms. In fact, the second largest hypoxia zone in the world is in the Northern Gulf of Mexico on the Louisiana/Texas continental shelf.
ESL also monitors deepwater currents, such as the Loop Current that flows northward from Cuba toward the Bird-foot delta in the northern Gulf of Mexico. High-velocity currents within eddies from the Loop Current can disrupt oil collection on deepwater platforms in the Gulf. Monitoring and predicting these currents can help oil and gas companies to better protect their people and equipment. In addition, cyclonic frontal eddies along the Loop Current’s margin create upwellings of nutrient-rich waters that attract pelagic fish, such as tuna and swordfish, to spawn—valuable information for the fishing industry.
While ESL collects deepwater current information, WAVCIS investigates subsurface coastal currents vital to protecting the Louisiana coastline from unexpected storm surges. Unlike ESL satellites, which monitor a large swath of the Gulf above the surface, WAVCIS stations use Acoustic Doppler Current Profilers (ADCPs) to take vertical profiles of fixed points in the water and measure water flow velocity. This information is transmitted back to the lab and relayed through the internet to Gulf of Mexico Coastal Ocean Observing System every hour.
ADCPs send out an acoustic signal through the water column and receive a reflective signal back to the receiving sensor. The length of time it takes for the sound to reach the sensor indicates its depth in the water. The longer it takes, the further away it is from the sensor.
“In addition, with the calculation of what we call a Doppler shift in frequency, the velocity of the water can be estimated. By these calculations, the ADCPs can give you a profile of the velocity of the water,” said Chunyan Li, program director of WAVCIS.
These point measurements can be used as standalone data for analyses, or used for numerical models to predict conditions throughout the entire area. This information can be used by National Oceanic and Atmospheric Administration and other researchers to predict the behavior of tides, waves, and storm surges from an oncoming hurricane, important information for communities along the coast to determine when to evacuate and to anticipate the extent of property damage.
WAVCIS data and model results can be used to help determine the direction of ocean currents, important for search-and-rescue missions. If someone on a vessel goes overboard, the data and models could help rescuers pinpoint their search area and ultimately help locate the individual faster.
“Using a computer, we can punch in our data and generate models that show, five hours later, where this person would most likely be. It could tell rescuers to search to the west rather than the east. [Knowing the direction of the current] is critical to finding them in time,” said Li.
April 2018 marks the eight-year anniversary of the 2010 Deepwater Horizon Gulf of Mexico oil spill, the largest oil spill to ever occur in U.S. waters since 1969. Tracking the oil was a critical part of disaster response efforts, and ESL and WAVCIS played a pivotal role in the immediate aftermath.
ESL helped to mitigate the environmental risks by providing rapid access to real-time satellite measurements from satellite sensors. AVHRR, MODIS and GOES-East sensors were all used to track the Deepwater Horizon oil spill and to better understand the role of wind, as well as coastal and offshore currents to its motion. Visible band images of the spill region were available four times each day from NASA’s Moderate Resolution Imaging Spectrodiometer (MODIS) sensor, data received with ESL’s five-meter high-speed antenna. GOES-East imagery, updated every 30 minutes, provided the best possible view of ocean temperature, allowing the tracking of surface flow related to coastal and deepwater currents.
During the spill, ESL also produced de-clouded nighttime composites of Gulf temperatures for a clearer picture of surface temperatures and, thus, coastal and deepwater currents. Clouds are prevalent in the Gulf and inhibit the satellite’s ability to detect ocean temperatures. However, ESL has developed specialized software that reduces cloud-cover by retaining ocean pixels from a nighttime sequence of images over ten hours. Because the clouds are cold and the ocean is warmer, ESL’s software can separate out the two and remove the clouds from the composite.
“Our software creates a more useful image as it retains the warmest pixels from that image sequence, and the result is almost magic, as the clouds have disappeared and the coastal and deepwater currents are now apparent in the new composite image,” said Nan Walker, director of the Earth Scan Laboratory.
ESL provided these satellite products to emergency responders to assist them in tracking surface oil, as well as the currents, and to better understand the causes of large-scale motions in the Loop Current during that time.
In mid-May 2010, oil began moving southward towards the Loop Current, and Walker was one of the first to report this motion to responders and the media. ESL satellite imagery revealed that three cold-core eddies along the edge of the Loop Current had merged into a much larger eddy, measuring 280 x 130 km. Oil motion was influenced during this time period mainly by ocean currents, not the wind, as it was entrained offshore between a warm core eddy and this large cold core eddy. The fact that this eddy did not move substantially for several months turned out to be beneficial in preventing the oil from spreading even further toward the Florida Keys or along the U.S. eastern seaboard.
“There was a general fear that the oil was going to get caught up in the Loop Current and end up on the Florida reef tract near Key West. But, it didn’t because it got trapped in this large cold core eddy, and it just stayed where it was and eventually dispersed,” Walker said.
WAVCIS also took readings from their state-of-the-art oceanographic sensors on oil platforms and on the sea floor and made them available to the local, state, and federal governments, as well as the general public, allowing for a more thorough understanding of where the oil was and where it was going. Coupled with post-hoc spill observations, WAVCIS’ real-time wave height, period, direction, and vertical profiles of horizontal current velocity in the water column were helpful in developing useful transport models for future events like this one.
The Value of Archives
ESL was collecting satellite data long before it was widely available on the internet. However, since the explosion in publicly available satellite imagery and weather radar online, ESL still finds benefit in its expansive archive.
“We have a much more extensive archive of image products than many other labs because we’ve been collecting satellite data and producing image products since 2000. We add dozens of new images to our web page daily from multiple satellites including individual Gulf temperature images, night-time composites, as well as three-day, seven-day, fifteen-day, and thirty-day image composites,” Walker said.
In addition, the ESL website contains curated image galleries of historic Gulf events, such as the Deepwater Horizon Oil Spill, Mississippi River floods, oceanic “cool wakes,” and animations of famous hurricanes. And recently, ESL has developed animation software that enables faster and easier access to their archived image products and even allows users to create their own animations.
WAVCIS also keeps up-to-date meteorological forecast models on their public website. Li maintains a large archive of data dating back to 2015 that is available upon request.
Both of these archives are invaluable as historical records of significant Gulf events as well as serving as an important teaching tool for professors to illustrate difficult concepts in a visual format.
Earth Scan’s satellite measurements and WAVCIS’s acoustic profiles serve as the eyes and the ears of the Gulf. They provide critical real-time information to disaster management agencies as well as valuable archival data to educate students, researchers, and the public about Louisiana’s pressing coastal issues.
For More Information:
To View ESL’s archives, galleries, and animation generator: https://www.esl.lsu.edu/imagery/#galleries
To View the “Best of The Earth Scan Laboratory” Web Page: https://www.esl.lsu.edu/imagery/best-of-esl/
To View Real-Time WAVCIS models: http://www.wavcis.lsu.edu/models.html