NOAA Teacher at Sea
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.
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.
There are sea otters everywhere!