Heather O’Connell: Surveying Tracy Arm, June 20, 2018


NOAA Teacher at Sea

Heather O’Connell

NOAA Ship Rainier

June 7 – 22, 2018

Mission: Hydrographic Survey

Geographic Area of Cruise: Seattle, Washington to Sitka, Alaska

Date: 6/20/18

Weather Data from the Bridge

Latitude and Longitude: 57°52.9’ N, 133 °38.7’ W, Sky Condition: Broken, Visibility: 10+ nautical miles, Wind Speed: Light Variable, Sea Level Pressure: 1013.5 millibars, Sea Water Temperature: 3.9°C, Air Temperature: Dry bulb: 17.8°C, Wet bulb: 14°C

Science and Technology Log

After the morning meeting of hearing everyone’s risk assessment before getting on the launches, I was part of the four person crew on launch RA-6. Our task for the day was to clean up the data, or collect data in places within the Tracy Arm polygon that weren’t already surveyed. We had to fill in the gaps in L and M polygons on the East point. The entire area of Tracy Arm needed to be surveyed because there are several cruise ships that are coming into this area now that Sawyer Glacier is receding and the area has not been surveyed since the late nineties. Navigation charts must be updated to ensure that the safety of the people that are visiting the area.

Launch going out to survey

Launch going out to survey

Once on the launch, the bright orange POS MV, or Positioning Orientation System Marine Vessel, must be powered to start the survey process. The new acquisition log was created as an excel spreadsheet to record the different casts along with the latitude and longitude, the maximum depth and the sound speed of the water at about approximately one meter. With all of the valuable data recorded, it is important to have a consistent system for managing all of the data so that it can be accessed and managed efficiently.

The EM-2040 Konsberg Sonar S.I.S., Seafloor Information System, program was powered on next. The EM processing unit, which is connected to the multi-beam sonar, has three lines of information when properly communicating with sonar. The right hand monitor in the launch displays the information from the sonar. Creating the file name is another crucial way of ensuring that the data can be managed properly. It is from this computer that you can manually adjust the angle of the beam swath with the sound pings.

Sonar Computer Systems

Sonar Computer Systems

Once the computers were started and communicating with each other, we completed a C.T.D. cast to obtain the sound speed profile of the water. There is also a device that measures this right on the multibeam sonar, but it is important that two devices have a similar sound speed profile to ensure data accuracy. If there is a large discrepancy between the two values, then another cast must be taken. Initially, the measuring sound speed profile at the interface was 1437.2 and the C.T.D. sound speed was 1437.8. The final algorithm that determines the depth of the water will take this information into account. Since we were somewhat close to a waterfall, the fresh water input most likely affected the sound profile of the water.

Preparing the CTD

Preparing the CTD

After viewing the data acquired in the sheet, or the assigned area of Tracy Arm to survey, Greg found areas where there were holes. He put a target on the map on the monitor on the left hand side computer. This HYSWEEP interface for multibeam and side scan sonar (which is a subset of HYPAC which is the multibeam software) screen shows a chart of the area with depths in fathoms and any rocks or shoals that would impede driving ability along with a red boat image of the vessel. This display is what the coxswain driving above also sees so that he or she is aware of what direction to travel. Once logging data, this screen also displays the beam so that you can ensure that all necessary data is being acquired. Previous surveys are depicted in a more subdued color so that you can see that the missing data is being collected. From the monitor, the survey technician must control the view of the map to be sure that it includes the targeted area, along with the path of the boat so that future obstructions can be avoided.

Multi-beam Sonar Work Station

Multi-beam Sonar Work Station

Since we were avoiding icebergs in the initial part of the clean up, we were going at about two knots. This slow pace allows for an increase in returns, nodes and soundings that increase the data density. Shallow waters take much longer to survey due to the smaller swath width. It is important to have accurate, high resolution data for shorelines since this is the area where many vessels will be traveling.  When a sonar pings, every swath, or fan-shaped area of soundings, returns five hundred soundings. Five hundred soundings times a rate of seven pings per second means there are thirty five hundred soundings per second total. This data density enhances the resolution of the maps that will be generated once the data has been processed.

Since there are sometimes safety hazards when surveying there are several different approaches that can be used to ensure the entire area is surveyed in a safe manner. Half stepping included going back over previous coverage far enough away from the hazard. Scalloping is another method which involves turning right before the rock or obstruction. This sends the beam swath near the rock without putting the vessel in danger. Some areas that were too close to icebergs could not be surveyed since it was not safe. But, this hydrographic survey was able to acquire data closer to the Sawyer Glacier than ever before. Being a part of this data collection was gratifying on many levels!

Personal Log

Seeing a white mountain goat amongst some of the most beautiful geological features that I have ever laid eyes on was another benefit of being out on the launch for the day. When a grizzly bear cub ran by a waterfall I continued to appreciate a day on the launch. Seals perched on icebergs were always a fun sight to see. And, the endless pieces of ice drifting by in the sea during our surveying never ceased to amaze me. 

Seals on an Ice Berg

Seals on an Iceberg

After a day of surveying, kayaking to a waterfall in William’s Cove and exploring proved to be another fun adventure.

OLYMPUS DIGITAL CAMERA

Waterfall in William’s Cove

Growing Muscle like Growing Character

The other day as I ran on the treadmill, I had a realization. While looking at the lifting weights, I realized that in order to build muscle, one must tear old muscles and rebuild new strands of protein. When these new fibers build on top of each other, muscles grow. I realized that new officers go through a similar process of developing skills and character. Junior officers come in with a two year responsibility where they learn an incredible amount. They are constantly put into new and challenging learning experiences where they tear their muscles. As they acclimate to these experiences, they build character, or muscle. The cycle repeats with subsequent occurrences.

Junior Officer ENS Airlie Pickett has a small triangle tattooed on her inner left bicep. When I asked her the significance of it, she said that the only way that you can truly understand something is to observe how it changes. In math, integrals and derivatives explain this change.

As I appreciated her tattoo, I considered that she must learn quite a lot about herself as a junior officer constantly learning new things. I’ve appreciated the opportunity to experience and observe myself in an unfamiliar surrounding on Rainier. It’s humbling to not understand the nautical terms, endless acronyms of surveying and NOAA Corps structure of life. I appreciated that all hands on Rainier made me feel welcomed, and were patient with explaining new concepts to me. I am grateful for the opportunity to experience the Inside Passage while learning about hydrographic surveying. Living on a ship, learning about navigation and meeting all of the hard working people on Rainier has been an unique experience. Overall, this has been an incredible opportunity. Mahalo nui loa! (Thank you very much). A hui hou Rainier! (Until we meet again)!

Did You Know?

Barometers measure atmospheric pressure in millimeters of mercury or atmospheres. An atmosphere is the amount of air wrapped around the Earth and one atmosphere, atm, is the amount of pressure at sea level at fifteen degrees Celsius. As altitude increases, the amount of pressure decreases since the density of the air decreases and less pressure is exerted. A decrease in altitude increases the amount of pressure exerted and the density of the air increases.

Changes in pressure can signify weather patterns. A drop in barometric pressure means a low pressure system is coming in and  there is not enough force to blow away the weather. Weather indicative of this includes windy, cloudy and/or rainy weather. An increase in barometric pressure means a high pressure system is coming in and  cool, dry air pushes out the weather resulting in clear skies.

https://www.nationalgeographic.org/encyclopedia/barometer/

 

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