NOAA Teacher at Sea
Lauren Wilmoth
Aboard NOAA Ship Rainier
October 4 – 17, 2014
Mission: Hydrographic Survey
Geographical area of cruise: Kodiak Island, Alaska
Date: Sunday, October 12, 2014
Weather Data from the Bridge
Air Temperature: 1.92 °C
Wind Speed: 13 knots
Latitude: 58°00.411′ N
Longitude: 153°10.035′ W
Science and Technology Log
In a previous post, I discussed how the multibeam sonar data has to be corrected for tides, but where does the tide data come from? Yesterday, I learned first hand where this data comes from. Rainier‘s crew sets up temporary tidal stations that monitor the tides continuously for at least 30 days. If we were working somewhere where there were permanent tidal station, we could just use the data from the permanent stations. For example, the Atlantic coast has many more permanent tidal stations than the places in Alaska where Rainier works. Since we are in a more remote area, these gauges must be installed before sonar data is collected in an area.
We are returning to an area where the majority of the hydrographic data was collected several weeks ago, so I didn’t get to see a full tidal station install, but I did go with the shore party to determine whether or not the tidal station was still in working condition.
A tidal station consists of several parts: 1) an underwater orifice 2) tube running nitrogen gas to the orifice 3) a nitrogen tank 4) a tidal gauge (pressure sensor and computer to record data) 5) solar panel 6) a satellite antennae.
Let me explain how these things work. Nitrogen is bubbled into the orifice through the tubing. The pressure gauge that is located on land in a weatherproof box with a laptop computer is recording how much pressure is required to push those bubbles out of the orifice. Basically, if the water is deep (high tide) there will be greater water pressure, so it will require more pressure to push bubbles out of the orifice. Using this pressure measurement, we can determine the level of the tide. Additionally, the solar panel powers the whole setup, and the satellite antennae transmits the data to the ship. For more information on the particulars of tidal stations click here
The tidal station in Terror Bay did need some repairs. The orifice was still in place which is very good news, because reinstalling the orifice would have required divers. However, the tidal gauge needed to be replaced. Some of the equipment was submerged at one point and a bear pooped on the solar panel. No joke!
After the tidal gauge was installed, we had to confirm that the orifice hadn’t shifted. To do this, we take manual readings of the tide using a staff that the crew set-up during installation of the tidal station. To take manual (staff) observations, you just measure and record the water level every 6 minutes. If the manual (staff) observations match the readings we are getting from the tidal gauge, then the orifice is likely in the correct spot.
Just to be sure that the staff didn’t shift, we also use a level to compare the location of the staff to the location of 5 known tidal benchmarks that were set when the station was being set up as well. As you can see, accounting for the tides is a complex process with multiple checks and double checks in place. These checks may seem a bit much, but a lot of shifting and movement can occur in these areas. Plus, these checks are the best way to ensure our data is accurate.
Today, I went to shore again to a different area called Driver Bay. This time we were taking down the equipment from a tidal gauge, because Rainier is quickly approaching the end of her 2014 season. Driver Bay is a beautiful location, but the weather wasn’t quite as pretty as the location. It snowed on our way in! Junior Officer Micki Ream who has been doing this for a few years said this was the first time she’d experienced snow while going on a tidal launch. Because of the wave action, this is a very dynamic area which means it changes a lot.
In fact, the staff that had been originally used to manually measure tides was completely gone, so we just needed to take down the tidal gauges, satellite antenna, solar panels, and orifice tubing. The orifice itself was to be removed later by a dive team, because it is under water. After completing the tidal gauge breakdown, we hopped back on the boat for a very bumpy ride back to Rainier. I got a little water in my boots when I was hopping back aboard the smaller boat, but it wasn’t as cold as I had expected. Fortunately, the boat has washers and driers. It looks like tonight will be laundry night.
Personal Log
The food here is great! Last night we had spaghetti and meatballs, and they were phenomenal. Every morning I get eggs cooked to order. On top of that, there is dessert for every lunch and dinner! Don’t judge me if I come back 10 lbs. heavier. Another cool perk is that we get to see movies that are still in the theaters! They order two movies a night that we can choose from. Lastly, I haven’t gotten seasick. Our transit from Seward to Kodiak was wavy, but I don’t think it was as bad as we were expecting. The motion sickness medicines did the trick, because I didn’t feel sick at all.
Did You Know?
NOAA (National Oceanic and Atmospheric Administration) contains several different branches including the National Weather Service which is responsible for forecasting weather and issuing weather alerts.
Animal Spotting
There are sea otters everywhere!
How long is the staff that is used to manually measure tides?
In a certain area, are the tide measurements consistent every time?
Have you gotten to touch any sea otters?
You must have a really good camera because your pictures are great!
Sincerely,
1st Period
We manually measure tides for 3 hours. That is what I am doing today, actually. I will sit on a boat and record the water depth EVERY 6 minutes for 3 hours.
It would probably be a really bad idea to touch a sea otter, so no, I haven’t. I think it would bite my hand off.
Thanks for the complements on my photos.
Since you get to watch movies while you’re on the ship, have you seen The Judge yet?
Why do they use Nitrogen gas for the tidal measurements? Why not another gas?
Did you clean the solar panel that was pooped on? #AlaskaProbs Or did you replace it? How high, exactly, are the solar panels? We’re imagining really big bears. In the picture, the panel looks awkwardly placed on a rock… so that’s a talented bear.
Love,
Your Favorite Class
I have not seen the Judge. It turns out they don’t use nitrogen anymore. I was misinformed. They used to use nitrogen, because it is a fairly inert gas and relatively inexpensive to get in a pressurized container. Plus, 78% of the air is nitrogen. Now, they have a system that just takes in regular air from the surroundings and pumps it through. I didn’t clean the solar panel, but someone else did. They replaced it temporarily, because it has been out in the elements, but they will check it back on the ship. If it still works, they will continue to use it. The bear, or something, first knocked down the solar panel and then pooped on it.
What is an orfice?
Miss you see you soon.
sincerely,
sc
An orifice is basically just a tube with a hole it where air can bubble out.
If the tide changes, how does that affect the tidal benchmarks? Where do you mark a tidal benchmark so that it doesn’t change?
Why do you use nitrogen?
What new movie did you see?
Love,
4th Period
The goal is for the tide or anything else for that matter to effect the tidal benchmark. The purpose of the tidal benchmark is to make sure the staff hasn’t moved, and the purpose of the staff is to make sure the gauge is measuring the tides correctly. You put tidal benchmarks on very large boulders or rocks in a cliff that aren’t likely go move. You have five, so you can check their position relative to one another and make sure they haven’t moved. That is what leveling is all about.
For the nitrogen question, see the response to 3rd periods comment.
I saw Captain America!
I am very sorry for not commenting earlier. I am wondering if you have helped the crew with anything that they haven’t known. I also want to know what the most interesting thing you think you have learned so far.
Each of the crew members have different specialties, so one member may know a lot about one topic, but another will be an expert in another topic. When it comes the the ship and questions about why we do what we do or how we do it, I can always find someone that knows the answer. Your second question is tough. I have learned so many great things. I think the most interesting thing I have learned is the very broad idea of how they update nautical charts, because that encompasses most of what I have learned. It is a much more complex process than I would have guessed. I also really enjoyed my conversation with the FOO Adam when he taught me how sonar data has the potential to be applied to fisheries.
Does the ship rock very often from the the tides moving the ship and make it hard to sleep?
A few nights it has rocked while we were sleeping, and I woke up a few times because of it. Usually it doesn’t rock too much. The times when it was rocking a lot was when we were moving across and large area of water, instead of tucked in a a cove away from big waves and one night we had a pretty nasty storm and the ship rocked a lot then, too.