NOAA Teacher at Sea
Aboard NOAA Ship Rainier
October 4 – 17, 2014
Mission: Hydrographic Survey
Geographical area of cruise: Kodiak Island, Alaska
Date: Wednesday, October 15th, 2014
Weather Data from the Bridge
Air Temperature: 4.4 °C
Wind Speed: 5 knots
Latitude: 57°56.9′ N
Longitude: 153°05.8′ W
Science and Technology Log
Thank you all for the comments you all have made. It helps me decide what direction to go in for my next post. One question asked, “How long does it take to map a certain area of sea floor?” That answer, as I responded, is that it depends on a number of factors including, but not limited to, how deep the water is and how flat the floor is in that area.
To make things easier, the crew uses an Excel spreadsheet with mathematical equations already built-in to determine the approximate amount of time it will take to complete an area. That answer is a bit abstract though. I wanted an answer that I could wrap my head around. The area that we are currently surveying is approximately 25 sq nautical miles, and it will take an estimated 10 days to complete the surveying of this area not including a couple of days for setting up tidal stations. To put this in perspective, Jefferson City, TN is approximately 4.077 sq nautical miles. So the area we are currently surveying is more than 6 times bigger than Jefferson City! We can do a little math to determine it would take about 2 days to survey an area the size of Jefferson City, TN assuming the features are similar to those of the area we are currently surveying.
Try to do the math yourself! Were you able to figure out how I got 2 or 3 days?
Since we’re talking numbers, Rainier surveyed an area one half the size of Puerto Rico in 2012 and 2013! We can also look at linear miles. Linear miles is the distance they traveled while surveying. It takes into account all of the lines the ship has completed. In 2012 and 2013, Rainier surveyed the same amount of linear nautical miles that it would take to go from Newport, Oregon to the South Pole Station and back!
Monday, I went on a launch to collect sonar data. This is my first time to collect sonar data since I started this journey. Before we could get started, we had to cast a CTD (Conductivity, Temperature and Depth) instrument. Sound travels a different velocities in water depending on the salinity, temperature, and pressure (depth), so this instrument is slowly cast down from the boat and measures all of these aspects on its way to the ocean floor. Sound travels faster when there is higher salinity, temperature, and pressure. These factors can vary greatly from place to place and season to season.
Imagine how it might be different in the summertime versus the winter. In the summertime, the snow will be melting from the mountains and glaciers causing a increase in the amount of freshwater. Freshwater is less dense than saltwater, so it mainly stays on top. Also, that glacial runoff is often much colder than the water lower in the water column. Knowing all of this, where do you think sound will travel faster in the summertime? In the top layer of water or a lower layer of water? Now you understand why it is so important to cast a CTD to make sure that our sonar data is accurate. To learn more about how sound travels in water, click here.
After casting our CTD, we spent the day running the sonar up and down and up and down the areas that needed to be surveyed. Again, this is a little like mowing the lawn. At one point, I was on bow watch. On bow watch, you sit at the front of the boat and look out for hazards. Since this area hasn’t been surveyed since before 1939, it is possible that there could be hazards that are not charted. Also, I worked down in the cabin of the boat with the data acquisition/sonar tuning. Some important things to do below deck including communicating the plan of attack with the coxswain (boat driver), activating the sonar, and adjusting the sonar for the correct depth. I helped adjust the range of the sonar which basically tells the sonar how long to listen. If you are in deeper water, you want the sonar to listen longer, because it takes more time for the ping to come back. I also adjusted the power which controls how loud the sound ping is. Again, if you are surveying a deeper area, you might want your ping to be a little louder.
Tuesday, I helped Survey Tech Christie Rieser and Physical Scientist Fernando Ortiz with night processing. When the launches come back after acquiring sonar data, someone has to make all that data make sense and apply it to the charts, so we can determine what needs to be completed the following day. Making sense of the data is what night processing is all about. First, we converted the raw data into a form that the program for charting (CARIS) can understand. The computer does the converting, but we have to tell it to do so. Then, we apply all of the correctors that I spoke about in a previous blog in the following order: POS/MV (Position and Orientation Systems for Marine Vessels) corrector, Tides corrector, and CTD (Conductivity, Temperature, and Depth) corrector. POS/MV corrects for the rocking of the boat. For the tides corrector, we use predicted tides for now, and once all the data is collected from our tidal stations, we will add that in as well. Finally, the CTD corrects for the change in sound velocity due to differences in the water as I discussed above.
After applying all of the correctors, we have the computer use an algorithm (basically a complicated formula) to determine, based on the data, where the sea floor is. Basically, when you are collecting sonar data there is always going to be some noise (random data that is meaningless) due to reflection, refraction, kelp, fish, and even the sound from the boat. The algorithm is usually able to recognize this noise and doesn’t include it when calculating the location of the seafloor. The last step is manually cleaning the data. This is where you hide the noise, so you can get a better view of the ocean floor. Also, when you are cleaning, you are double checking the algorithm in a way, because some things that are easy for a human to distinguish as noise may have thrown off the algorithm a bit, so you can manually correct for that. Cleaning the data took the longest amount of time. It took a couple of hours. While processing the data, we did notice a possible ship wreck, but the data we have isn’t detailed enough to say whether it’s a shipwreck or a rock. Senior Tech Jackson noted in the acquisition log that it was “A wreckish looking rock or a rockish looking wreck.” We are going to have the launches go over that area several more times today to get a more clear picture of is going on at that spot.
Monday was the most spectacular day for wildlife viewing! First, I saw a bald eagle. Then, I saw more sea otters. The most amazing experience of my trip so far happened next. Orcas were swimming all around us. They breached (came up for air) less than 6 feet from the boat. They were so beautiful! I got some good pictures, too! As if that wasn’t good enough, we also saw another type of whale from far away. I could see the blow (spray) from the whale and a dorsal fin, but I am not sure if it is was a Humpback Whale or a Fin Whale. Too cool!
Did You Know?
Killer whales are technically dolphins, because they are more closely related to other dolphins than they are to whales.