Tag: tide gauge

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Linda Armwood, April 29, 2006

NOAA Teacher at Sea
Linda Armwood
Onboard NOAA Ship Fairweather
April 25 – May 5, 2006

Mission: Hydrographic Survey
Geographical Area: Aleutian Islands, Alaska
Date: April 29, 2006

Weather Data from Bridge 
Visibility: 10 nautical miles (nm)
Wind direction: 200 °
Wind speed:  15 kt
Sea wave height: 1 ft.
Swell wave dir: 280
Swell wave height: 2-3 ft.
Seawater temp: 7.2
Sea level pressure: 1016.6mb
Present weather: Overcast
Temperature:  °C~ 8.2dry/6.5wet

Science and Technology Log 

My assignment today was to work with the benchmark descriptions and level run team.  The responsibility of the team is to accurately and completely describe the benchmarks.  The description must include the following items:

  • directions for location
  • exact location relative to other structures including the tide gauge
  • sketch of location
  • latitude and longitude
  • above datum of tabulation in meters
  • date of establishment/recovery
  • photograph of benchmark
  • statement that benchmark disk is flush in raised concrete

The team is also responsible for completing the level run assignment.  The purpose of the level run is to level the primary benchmark to the staff stop.  This procedure provides the elevation of the staff stop. In helping with the level run, I assisted the Tides Director in the recording of rod readings. These measurements are read in three parts: top thread, middle thread and bottom thread.  Ideally, thread intervals should be equal.  However, if the thread intervals are not equal, they must be within 2 to be an acceptable reading.  Many of our readings were acceptable upon the first recording.  For the few readings that were not acceptable, the software in the I-Pod associated with the 3 stadia leveler would indicate as such.  Readings were redone accordingly.

In addition to providing assistance to the Tides Director as a recorder, I participated in holding the rod at benchmark locations for level readings.  The indication that the rod would be level is when the surveyor succeeds in moving the rod so that the bubble inside the gauge would sit on the center circle. The tide staff observation was my third assignment for the day.  The completion of these observations provides you with the elevation of your orifice to your staff stop. The tide gauge is located on the pier leg facing the benchmarks.  The boat was placed in a vantage spot that enabled a survey tech and I to monitor and record the tide height every 6 minutes for three hours.  This recorded data would later be compared to the data received by the tide gauge set-up on the pier.

Personal Log 

It was great to get out of the bitter, cold, sleeting weather conditions to the warmth of the ship. The food on the FAIRWEATHER is absolutely delectable!

Question of the Day 

Environmental Science and Geospatial Semester Students 

In which two months are the largest tidal ranges?

Mrs. Armwood

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Linda Armwood, April 28, 2006

NOAA Teacher at Sea
Linda Armwood
Onboard NOAA Ship Fairweather
April 25 – May 5, 2006

Mission: Hydrographic Survey
Geographical Area: Aleutian Islands, Alaska
Date: April 28, 2006

Weather Data from Bridge 
Visibility: 10 nautical miles (nm)
Wind direction: 190 °
Wind speed:  13 kt
Sea wave height: 1 ft.
Swell waves dir: 310
Swell waves height: 2 ft.
Seawater temp: 7.3
Sea level pressure: 1012.4mb
Present weather: Mostly cloudy
Temperature:  °C~ 6.5dry/5.0wet

NOAA divers preparing to install a tide gauge at Noyes Island, AK
NOAA divers preparing to install a tide gauge at Noyes Island, AK

Science and Technology Log 

The project’s first priority for the day was to get the tide gauge installed and to set tidal benchmarks.  The tides party consisted of three onshore crews: the reconnaissance and planning team; the benchmark recovery and installation team; and the dive and install team.  I was assigned to the dive and install team boat in order to observe the divers install the tide gauge. I did not observe the underwater installation below the pier; however, the secure installation of the above water equipment was a major undertaking!  The tide gauge installation involves the proper placement of the following items:

  • satellite antenna
  • gps antenna
  • hydro gauge
  • solar panel
  • 12-volt battery
  • nitrogen cylinder
  • nitrogen regulator

I assisted in drilling with the benchmark recovery and installation team.  The historic benchmark was located about 15 feet from the low water line and the next four benchmark locations were set at 200 feet apart from one another in somewhat of a straight line from the historic benchmark.  Benchmarks are important because they represent permanent marks of the land leveling system.  The tidal gauge will automatically read water pressure which it then converts to depth every six minutes over the next 30 days in order to determine the constituents of the tide-generating force. Determining these constituents allows the survey technicians to form possible hypotheses related to ranges, heights, rates and future directions of tides.

Ensign Matthew Glazewski drills to establish a benchmark on Noyes Island, AK.
Ensign Matthew Glazewski drills to establish a benchmark on Noyes Island, AK.

Personal Log 

At the time of this writing, the weather was as stated above; however, during the tides party the weather was miserable with intermittent showers of sleet followed by sunshine and overcast.  The kindness extended to the crew by the Noyes’ Island caretaker will be remembered.

Question of the Day 

Environmental Science and Geospatial Semester Students 

Give some possible non-human factors that may have an effect on the decision-making of tide gauge location.

Mrs. Armwood

The Tidal Party recovered this historic benchmark recovered from Noyes Island, AK
The Tidal Party recovered this historic benchmark recovered from Noyes Island, AK
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James Miller, August 22, 2005

NOAA Teacher at Sea
James Miller
Onboard NOAA Ship Rainier
August 13 – 27, 2005

Mission: Hydrographic Survey
Geographical Area: North Pacific, Alaska
Date: August 22, 2005

Location: Anchored in Fish Range Bay; north of Mitrofinia Island
Weather: Sunny, low 70’s
Wind: variable
Seas: 1-2 foot swell
Itinerary:  Working in Fish Range Bay area for couple of days

Science and Technology Log 

Due to the deteriorating weather forecast for the entire area around Mitrofania Island we are packing up and moving out.  There were two things that needed to be done today. First, a tide gauge that the crew installed on Mitrofania earlier in the season had to be removed.  The gauge sent tide information via satellite to a facility on the mainland.  Second, the differential global positioning system (DGPS) that was also installed on the Island earlier in the season had to be removed.  The DGPS was installed to enhance GPS signals when launches are surveying in the area.

I was assigned to help break down the DGPS with two officers and a survey technician. We headed out early in one of the skiffs for the island.  The DGPS consists of a tall antenna mounted on aluminum framing which is supported by lines tied off to stakes in the ground. It also has a watertight box that acts as the main processor for transmitting and receiving.  The processor is powered by six 12v car batteries, which get charged by a series of solar panels. Soon after being dropped off we realized we all forgot to bring bug dope, and soon after that the bugs were swarming.  It’s amazing the motivational power of flying, pestering insects.  We had the station apart and lugged down to the beach in under an hour.  Unfortunately the amount of gear and people exceed the capacity of the skiff, so it required more than one trip.  I drew the short straw along with one of the officers to wait on the island for the skiff to return.  It took about an hour so we did a little treasure hunting along the beach at the high tide line.  Earlier in the season, some of the crew found antique fishing trap floats made of blown glass.  I’m unsure of how old they are, but let’s just say very.  We didn’t find anything as interesting.

Personal Log 

I’m sorry to be leaving Mitrofania Island, partly because it is so beautiful, and also because it marks the end of the work for this leg of the trip.  We got underway for Chiginigak Bay around 4:00pm to basically run from the oncoming storm.  The travel time was about 8 hours.  The seas had already started to build when we left. For the first half of the trip we were traveling with the seas, which made for a smoother ride, however, we had to turn broadside (parallel) to the seas for the second half. When running broadside to the sea the ship pitches from side to side at pretty steep angles. I was typing up some logs in the computer room when all the books and games on the shelf came tumbling down, what a mess.  Anyway, it certainly wasn’t as bad as we anticipated and we arrived in the bay some time around midnight.

Before bed I went up to the bridge to see how the ship was handling in the seas.  One of the newer officers to the ship gave me some more navigation lessons, which was cool.

Sleeping hasn’t been a problem, even with the constant noise of the engines and rolling of the ship. In fact, I sleep deeply and have to drag myself out of bed in the morning. My cabin doesn’t have a porthole so NO light gets in.  It could be the middle of the day and I wouldn’t know it.

Despite all the fun I’m having, I have to say I really miss my home and family.  I give the crew a lot of credit for doing this all year long.  One of the crewmembers said that longing for home is a great feeling, it keeps you going, and that’s why you can’t make the ship your home.  Seems like good advice for newcomers on the ship.

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JoAnne Kronberg, July 19, 2005

NOAA Teacher at Sea
JoAnne Kronberg
Onboard NOAA Ship Rainier
July 12 – 22, 2005

Mission: Hydrographic Survey
Geographical Area: North Pacific
Date: July 19, 2005

Weather Data
Waves: 8ft during the day diminishing to 6 ft in the evening
Winds:  NW 25-39 knots

Science and Technology Log

We arrived at Mitrofania Island at about 5:00 am and anchored in Cushing Bay.  Our mission today was to do a Tide Station Installment.  The National Water Level Observation Network operates 175 continuous observatory stations in the U.S. coastal zone and the Great Lakes. All are equipped with satellite radios.  Of course, a Tide Station would only be placed in the coastal areas that are affected by tides.  Water Level Stations operate in the Great Lakes.

We had to replace the Tide Station in Cushing Bay.  The sensor that is installed is called a Bubbler Orifice. It is anchoring to the bottom of the bay and is powered by a long tube that is filled with Nitrogen gas.  Two divers went down to anchor the Bubbler and attach the tube. Meanwhile, other people in another launch were setting up a Tide Staff.  A Tide Staff is just a long stick that is marked with levels like a yardstick.  The Tide Staff has to be set up to correspond with the Bench Marks that have been already determined.  The Bench Marks may be located at different sea levels.  Both the Bubbler Orifice and the Tide Staff have to be at the same sea level to be accurate.

After the Bubbler Orifice is established and the Tide Staff is set up, we started taking the readings from these two sources. Readings were taken every 6 minutes for a period of one hour. If the readings after an hour are not the same, then the Bubbler Orifice has to be adjusted.

The data collected by the Bubbler Orifice is transmitted to the Data Collection Platform.  In turn, this information is transmitted to no less than four satellites and to the National Geodetic Survey.

The work today has taken most of the day.  We will stay anchored in Cushing Bay tonight. Early tomorrow morning, Wednesday, we will start cruising toward Chiniak Bay.

It was a very educational day and the weather was fantastic.  Thank you for this opportunity.

JoAnne Kronberg Teacher-at-Sea

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Leyf Peirce, July 7, 2004

NOAA Teacher at Sea
Leyf Peirce
Onboard NOAA Ship Rainier
July 6 – 15, 2004

Mission: Hydrographic Survey
Geographical Area: Eastern Aleutian Islands, Alaska
Date: July 7, 2004

Time: 10:15
Latitude: N 57°31.730
Longitude: W 154°58.325
Visibility: 10 + m
Wind direction: 250
Wind speed: 18 knots
Sea wave height: 2 – 3 feet
Swell wave height: 2 – 4 feet
Sea water temperature: 10.6 °C
Sea level pressure: 1020.1 mb
Air temperature: 12.2 °C
Cloud cover: 2/8

Science and Technology Log

I talked more with P.S. Shyla Allen about how the multibeam echo sounders work on the ship to gather data about the depths of the ocean. Both the RAINIER and the launch ships use the following method to gather data. All of these vessels use echo sounders with anywhere from 120 to 240 beams that scan the ocean floor. The following diagram illustrates how this is done:

Peirce 7-7-04 Fig1
Figure 1: Multibeam Echo Sounding

Here, “z” is an echo sounding two-way travel time beam, and the multibeams are spread over the footprint distance of “f”. The size of the sound footprint, “f”, depends on the depth at which the measurement is taken, “z”. The greater the depth is, the greater the footprint is. However, the greater the footprint is also means less accuracy on the outer edges of the footprint. Therefore, the ship will run a “mowing the lawn” pattern across the given section to get desired overlapping of data:

Peirce 7-7-04 Fig2
Figure 2: Mowing the Lawn pattern

The width of these lines is determined by: width of x = 3 * z. By using this rough equation, the ship will be able to overlap the areas of least accuracy, i.e. the areas on the outer range of the footprint:

Figure 3: Ship running mowing the lawn pattern so the footprints overlap.

From this data, the depth and contours of the ocean floor can be determined. I also asked P.S. Shyla Allen about the problems and sources of error associated with this data collection. She responded by detailing three main issues that must be corrected when cleaning the data, i.e. the data must undergo three main correction factors before accurate readings can be analyzed. These three factors include: a) tide changes, b) sound velocity, c) the motion of the ship and GPS positioning. To correct for tide changes, the researchers must have accurate readings of the tides. Tide gauges are installed along the coastline at various points, and all readings are reduced to Mean Lower Low Water (MLLW). This basically gives the average of the lowest possible depth at a given location. To correct for sound velocity changes, which is the most important correction factor dealt with, researchers take measurements of water temperature and salinity level at the given depth reading. For every change of 1 ppm in salinity, there is a change of 3 m/s in sound velocity. Therefore, salinity is perhaps one of the most important factors. Finally, the motion of the ship and GPS position need to be corrected for. This includes correcting for the pitch, roll, and gyration of the ship as well as error in the GPS system. Because the ship uses Differential GPS (DGPS), this error is already accounted for. However, for the pitch, roll, and gyration of the ship, two antennas are used to on the port and starboard sides. These antennas, often referred to as Motion Reference Units (MRU), are very stable feed into the same computers that process the data. Therefore, the computer takes into account the readings from these antennas and combines this information with the corrections made for the tidal changes, sound velocity factors, and positioning of the ship. After cleaning the static from the data, a nautical chart can be produced. This method of charting the ocean floor is definitely more efficient than when researchers used lead lines—long ropes with lead that would be dropped down and then measured to determine the depth!

Personal Log

I woke up this morning after sleeping for about 12 hours—I think the seasickness medicine I took last night made me very sleepy. Luckily, however, all traces of seasickness are gone; I can even sit here at the computer and type without noticing the pitching of the ship very much at all. I think all of my muscles must be getting stronger as a result of reacting to the changing ground and all of the stairs I go up and down every day. I spent some time on the bridge this morning mostly asking questions about the tools used there and what various measurements mean. I find it very interesting that simply reading tiny numbers and using small switches and knobs will run this 231 foot ship. However, my experience aboard ships tells me that it is not even close to impossible. I know that even the slightest adjustment at the helm on a sailboat can change the course of the boat. I am reminded of sailing in the British Virgin Islands and the dispute over if it was more important to maintain the way point or try to make the boat go very fast. However, that is not an issue on this boat. We are supposed to reach the Shumagin Islands tonight, and tomorrow we will start the launches—I can’t wait!

Question for the Day

How many sets of data points must be filtered out before the data is considered clean? On what does this number depend? How does one determine if a data point is an outlier or and actual reading?