NOAA Teacher at Sea
Yaara Crane
Aboard NOAA Ship Thomas Jefferson
June 22, 2013 – July 3, 2013
Mission: Hydrographic Survey
Geographical area of cruise: Mid-Atlantic
Date: Saturday, June 22, 2013
Latitude: 38.81°N
Longitude: 75.10°W
Weather Data from Bridge:
Wind Speed: 10.27 knots
Surface Water Temperature: 20.59°C
Air Temperature: 20.60°C
Relative Humidity: 79.00%
Barometric Pressure: 1023.18mb
Science and Technology Log
This morning I came aboard the Thomas Jefferson via small boat transfer from the pilot station dock in Lewes, Delaware. Since coming on board, I have been welcomed by so many people, toured the ship, had a safety training, cautiously drove the small boat around the Delaware Bay, and tried to learn some background about hydrographic surveys. That is quite a lot of new things to process in only 5 hours!
The major purpose of hydrography is to create a thorough imaging of the ocean floor, particularly to warn mariners of any obstructions or shallows. There is evidence that nautical charts showing depth have been in use since as early as the sixth century BCE, and can easily be created through the use of a lead weight and a string. These days, NOAA ships have much more high tech ways of surveying the ocean floor. The Thomas Jefferson spends most of its time at sea charting waterways and coastlines to ensure safe travels for both private and commercial mariners to be able to navigate safely. Priorities in a nautical charting mission are based on factors including: waterway usage rates, stakeholder requests, rates of change to the sea floor (both natural and anthropogenic), and age of the chart’s source. For example, a waterway to a port used by oil tankers would be very important to survey because the result of a tanker running headlong into an obstruction would be disastrous. After Hurricane Sandy hit the East Coast in October 2012, the Thomas Jefferson was assigned to survey the sea floor of New York City’s harbor in case of any new obstructions that might have been blown in undetected. No other ship was allowed to sail through the harbor until the Coast Guard received the new charts. So far this summer, the Thomas Jefferson has already spent countless hours surveying the area around Long Island Sound and the Delaware Bay.
To have a better grasp of the major scientific research that occurs on a hydrographic research vessel, I spent a portion of the afternoon speaking with Ensign Andrew Clos. Ensign Clos mentioned that the two most important tools for data collection are the side scan sonar (SSS) and the multi-beam echo sounder (MBES). These two tools work through the use of sound waves to collect both 2D and 3D data. The SSS and the MBES send sound waves which are reflected back to the ship and transformed into images analyzed by the scientists on board. The side scan sonar is towed by the ship in very carefully spaced horizontal lines to gather the initial data about the existence of any objects in the water. An acoustic image is created and analyzed for anything out of the ordinary, in which case the MBES is launched for further investigation. The MBES is hull-mounted to the ship and survey launches, and lets out sound waves in a 128° cone which much more accurately determines the depth and position of the object. The MBES can collect millions of data points in a day, which is converted into three-dimensional images.
The scientists aboard spend many hours sifting through the data, and correcting the data for differences in depth based on tidal flows and water data. Sound waves travel through water at approximately 1500 meters/second (m/s), much faster than the 340 m/s in air. However, differences in salinity and temperature can impact the accuracy of measurements. All of the branches of NOAA must work together to piece together the puzzle of the ocean floor.
Personal Log
This has been quite a busy week for me, which has culminated in this spectacular adventure. Monday was our last day of final exams, and today I feel like that was a lifetime ago! I spent most of yesterday morning driving to Delaware, and was rewarded with spending the afternoon relaxing on Rehoboth Beach. As it turns out, relaxing is on the table for tomorrow, too. The TJ is waiting on a repair to the MBES, and will need to stay anchored close to port for at least one more day. Commander Krepp has allowed some of the members of the crew to arrange for a day out paddling and kayaking around the beach. Still, there is work to be done and safety to consider aboard a NOAA vessel, so even that excursion has to be carefully managed into two shifts.
Weather-wise, it has been a beautiful weekend. There is a slight breeze, but not enough to make waves worth mentioning. The TJ is also anchored just behind a breakwater which helps to keep waves at bay. All of this adds up to a very calm shipboard experience, with barely any feeling of rocking or swaying while aboard the ship. I have rarely suffered from motion sickness and hope to continue my good record throughout this cruise. No seasickness means I can make my way over to the ice cream bar for a little afternoon snack…
Did You Know?
Fossil remains of horseshoe crabs have been found spanning approximately the last 450 million years. They are called living fossils because they are some of the rare species that have survived extinction with little genetic diversity.
