multibeam sonar – Page 3 – NOAA Teacher at Sea Blog

July 26, 2018July 26, 2018

David Tourtellot: A Musical Perspective of Sonar, July 24, 2018

NOAA Teacher at Sea

David Tourtellot

Aboard NOAA Ship Thomas Jefferson

July 9-26, 2018

Mission: Hydrographic Survey – Approaches to Houston

Geographic Area of Cruise: Gulf of Mexico

Date: July 24^th, 2018

Weather Data from the Bridge

Latitude: 29°09.1270’N

Longitude: 093°46.5544’W

Visibility: 5 Nautical Miles

Sky Condition: 8/8

Wind: Direction: 70.1°, Speed: 13.3 knots

Temperature:

Seawater: 29.24°C

Air: Dry bulb:26.9°C Wet bulb: 24.7°C

Science and Technology Log

Coming to NOAA Ship Thomas Jefferson, I was eager to learn all I could about sonar. I am amazed that we have the ability to explore the ocean floor using sound.

An uncharted wreck discovered by NOAA Ship Thomas Jefferson

Over the course of my previous blog entries, I have described the tools and processes used to survey using sonar. This time, I am going to try to frame the sounds that the sonars are using in a musical context, in the hope that doing so will help students (and myself) better understand the underlying concepts.

Note – many aspects of music are not standardized. For the purpose of this blog post, all musical tuning will be in equal temperament, at A=440. When I reference the range of a piano, I will be referencing a standard 88-key instrument. Many of the sonar frequencies do not correspond exactly to an in-tune pitch, so they have been written to the nearest pitch, with a comment regarding if the true frequency is higher or lower than the one written.

In sonar and in music, when considering soundwaves it is important to know their frequency, a measure of how many waves occur over the course of a set period of time. Frequency is measured in a unit called Hertz (abbreviated as Hz), which measures how many soundwaves occur in one second. One Hertz is equal to one soundwave per second. For example, if you heard a sound with a frequency of 100Hz, your ears would be detecting 100 soundwaves every second. Musicians also are concerned with frequency, but will use another name for it: pitch. These words are synonymous – sounds that are higher in pitch are higher in frequency, and sounds that are lower in pitch are lower in frequency.

Below are the eight octaves of the note A that are found on a piano, each labeled with their frequency. The notes’ frequencies have an exponential relationship – as you move from low to high by octave, each note has a frequency that is double that of its predecessor.

Piano As with frequencies — The frequency of each A on a piano

The highest note on a piano, C, has a frequency of 4186.01Hz

Average, healthy young humans hear sounds ranging from 20Hz to 20,000Hz. All sounds outside of that range are inaudible to people, but otherwise no different from sounds that fall within the human range of hearing. The highest note we would be able to hear would be an E♭, at a frequency of 19,912.16Hz (a frequency of exactly 20,000Hz would fall in between E♭ and E♮, though would be closer to E♭). If put on a musical staff, it would look like this:

High Eb 19kHz — The frequency of the highest note in the human range of hearing

The hull of NOAA Ship Thomas Jefferson is equipped with several sonar transmitters and receivers, which can operate at a wide variety of frequencies.

TJ Sonar — The hull of NOAA Ship Thomas Jefferson, with several sonars. Note that the projectors that transmit lower frequencies are larger than the ones that transmit higher frequencies. This is similar to musical instruments – instruments that make lower sounds, like the tuba or the double bass, are larger than instruments that make higher sounds, like the trumpet or the violin

Higher frequencies provide higher resolution returns for the sonar, but they dissipate more quickly as they travel through water than lower frequencies do. Surveyors assess the depth of the water they are surveying, and choose the frequency that will give them the best return based on their conditions. Most of the sonar frequencies are too high for humans to hear. The ship’s multi-beam echo sounder has a variable frequency range of 200,000Hz-400,000Hz, though as I’ve been on board they’ve been scanning with it at 300,000Hz. Likewise, the multi-beam sonars on the launches have also been running at 300,000Hz. The ship has a sub-bottom profiler, which is a sonar used for surveying beneath the seafloor. It operates at a frequency of 12,000Hz, and has the distinction of being the only sonar on the ship that is audible to humans, however, we have not had a need to use it during my time aboard the Thomas Jefferson.

The ship’s side scan towfish (which I described in my previous blog entry) operates at 455,000Hz.

Here, we can see what those frequencies would look like if they were to be put on a musical staff.

Assorted Sonars and reference pitches — The frequencies of sonar, with reference pitches

Altering the frequency isn’t the only way to affect the quality of the reading which the sonar is getting. Surveyors can also change the pulse of the sonar. The pulse is the duration of the ping. To think about it in musical terms, changing the pulse would be akin to switching from playing quarter notes to playing half notes, while keeping the tempo and pitch the same. Different sonar pulses yield different readings. Shorter pulses provide higher resolution, but like higher frequency pings, dissipate faster in water, whereas longer pulses provide lower resolution, but can reach greater depths.

Personal Log

Mariners have a reputation for being a rather superstitious bunch, so I decided to ask around to see if that held true for the crew of the Thomas Jefferson. Overall, I found that most didn’t strictly adhere to any, but they were happy to share some of their favorites.

Everyone I spoke to told me that it is considered bad luck to leave port on a Friday, though the Commanding Officer, CDR Chris van Westendorp, assured me that you could counteract that bad luck by making three 360° turns to the left as soon as the ship is able. Many on the crew are also avid fishermen, and told me that bringing bananas aboard would lead to a bad catch, and one went so far as to be mistrustful of yellow lighters as well.

Certain tattoos are said to bring good luck – I was told that sailors often have a chicken and a pig tattooed on their feet. According to custom, those animals were often stored in wooden crates that would float if a ship went down, and having them tattooed onto you would afford you the same benefit. When asked if he was superstitious one of our helmsmen Jim proudly showed me a tattoo he has of a dolphin. He explained that having a sea creature tattooed on your body would prevent drowning. “It works!” he said with a grin, “I’ve never drowned!”

Several maritime superstitions deal with foul weather. Umbrellas are said to cause bad weather, as is split pea soup. Whistling while on the bridge is said to “whistle in the winds.” While not a superstition per se, many crew members told me variations of the same meteorological mantra: Red sky at night, sailor’s delight. Red sky in the morning, sailors take warning.

One of the NOAA Corps Officers aboard, ENS Garrison Grant, knew several old superstitions related to shipbuilding. When laying the keel (the first piece of the ship to be put into place), shipbuilders would scatter evergreen boughs and tie red ribbons around it to ward off witches. Historically, having women aboard was considered bad luck, though, conversely it was said that if they showed their bare breasts to a storm, it would subside. This is why several ancient ships had topless women carved into the masthead. Legend has it that in order to assure that a ship would float, when it was ready to be launched for the first time, virgins would be tied to the rails that guided the ship from the ship yard into the water. The weight of the ship would crush them, and their blood would act as a lubricant, allowing the ship to slide into the water for the first time. Yikes! Thankfully, as society became more civilized, this practice evolved into the custom of breaking a bottle of champagne against a ship’s bow!

Did you know? Musical instruments play an important role in ship safety! In accordance with maritime law, ships will use auditory cues to make other vessels aware of their presence in heavy fog. For large ships, this includes the ringing of a gong at regular intervals.

Latest Highlight: During this week’s fire drill, I got to try the fire hose. It was very powerful and a lot of fun!

July 18, 2018September 19, 2018

Meredith Salmon: Setting Sail! July 12, 2018

NOAA Teacher at Sea

Meredith Salmon

Aboard NOAA Ship Okeanos Explorer

July 12 – 31, 2018

Mission: Mapping Deep-Water Areas Southeast of Bermuda in Support of the Galway Statement on Atlantic Ocean Cooperation

Geographic Area: Atlantic Ocean, south of Bermuda

Date: July 12, 2018

Weather Data from the Okeanos Explorer Bridge – July 12, 2018

Latitude: 32.094°N

Longitude: 69.591°W

Air Temperature: 26.2°C

Wind Speed: 10.7 knots

Conditions: Sunny

Depth: 693 meters

Survey Area — Map showing the planned operations area for the expedition outlined in yellow. Image courtesy of the NOAA Office of Ocean Exploration and Research.

Science and Technology Log

According to the Oceanic Institute, the oceans cover 71% of the Earth’s surface. This is calculated to be 335,258,000 square kilometers! Recently, the Okeanos Explorer mapped over 1,000,000 square kilometers of the seafloor using high- resolution multibeam sonar. Although this may not seem like much, that region is larger than the areas of Arizona and Texas combined!

So why is it so important for the Okeanos Explorer to map the seafloor? The ocean’s terrain plays a very important role in ecosystems since underwater valleys determine currents and weather patterns, sea topography influences fishery management, and seamounts serve as protection against unpredictable storms. Therefore, high-resolution maps allow scientists to categorize marine habitats, provide information vital to protecting and tracking marine life, and enable us to make smart decisions for solid, sustainable conservation measures.

In order to successfully map the ocean floor, multibeam sonar is used. The Okeanos Explorer uses an EM 302 multibeam system that is designed to map a large portion of the ocean floor with exceptional resolution and accuracy. The EM 302 transducers point at different angles on both sides of the ship to create a swath of signals. Transducers are underwater speakers that are responsible for sending an acoustic pulse (known as a ping) into the water. If the seafloor or object is in the path of the ping, then sound bounces off the object and returns an echo to the transducer. The EM 302 has the ability to produce up to 864 depth soundings in a single ping. The time interval between the actual signal transmission and arrival of the return echo (two way travel time) are combined with a sound velocity profile to estimate depth over the area of the swath. In addition, the intensity of the return echo can be used to infer bottom characteristics that can be utilized for habitat mapping. Since the EM 302 creates high density, high-resolution data as well as water column features, this sonar system is ideal for exploring the seabed for geographic features.

The image below shows data being collected by the multibeam sonar on the Okeanos Explorer. The colors are used to indicate swath depth (warm colors indicate shallow waters while cool colors indicate deeper waters).

Multibeam sonar data including backscatter (lower left), depth (upper center) and water column data (lower center) from 7/12/2018 the Okeanos Explorer

As this data is being collected, it must be “cleaned” to eliminate any erroneous points. Data is collected and cleaned in both the Dry Lab and Mission Control Room.

Mission Control Room aboard the Okeanos Explorer

Since we have not reached the survey area yet, we have been monitoring the depth of our path thus far. We are collecting transit data which is considered to still be valuable data for unmapped seafloor area, but it may not be as high quality as focused mapping data. We will continue to collect transit data until we reach the survey area near Bermuda.

Personal Log

Life onboard the Okeanos Explorer has been a very interesting and fun learning experience! The ship runs on a 24/7 operation schedule and people are working diligently at all hours of the day. Everyone on the ship has been really welcoming and willing to share their stories and insights about their careers at sea. I am really looking forward to speaking with more people to learn about their experiences!

We set sail out of Norfolk today and began our 3.5 day/4 day transit to the survey area near Bermuda. This morning, we found out that we will need to schedule an emergency dry dock towards the end of our mission to solve an issue with a stern thruster necessary for ROV cruises. As a result, we will not be ending up in port in St. George, but we will still be able to map the area 200 nautical miles off the coast of Bermuda, so that is great!

norfolk out to sea! — NOAAS Okeanos Explorer (port quarter aspect) navigating the Elizabeth River outbound for sea from the NOAA pier in Norfolk, VA on July 12, 2018. [Photo by Commander Briana Hillstrom, NOAA

Did You Know?

Sonar is short for Sound Navigation and Ranging.

Check out this video for a visual representation of the process sonar uses to generate data! https://oceanservice.noaa.gov/caribbean-mapping/mapping-video.html

Resources:

https://www.oceanicinstitute.org/aboutoceans/aquafacts.html

https://oceanexplorer.noaa.gov/okeanos/one-million/welcome.html

July 2, 2018July 3, 2018

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.

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.

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.

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.

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/

May 13, 2018December 14, 2018

Cindy Byers: Mapping in the ice! May 11, 2018

NOAA Teacher at Sea
Cindy Byers
Aboard NOAA Ship Fairweather
April 29 – May 13

Mission: Southeast Alaska Hydrographic Survey

Geographic Area of Cruise: Southeast Alaska

Date: May 11, 2018

Weather from the Bridge:

Latitude:57°43.3 N
Longitude:133°35.5 W
Sea Wave Height: 0
Wind Speed: 5 knots
Wind Direction: variable
Visibility:3 nautical miles
Air Temperature: 11.5°C
Sky:100% cloud coverage

Cindy on Flydeck — Me ready to get on a launch with a float coat and hard hat

Science and Technology Log

The area that NOAA Ship Fairweather is surveying is Tracy Arm and Endicott Arm. These are fjords, which are glacial valleys carved by a receding (melting) glacier. Before the surveying could begin the launches(small boats) were sent up the fjords, in pairs for safety, to see how far up the fjord they could safely travel. There were reports of ice closer to the glacier. Because the glacier is receding, some of the area has never been mapped. This is an area important for tourism, as it is used by cruise ships. I was assigned to go up Endicott Arm towards Dawes Glacier.

Starting to see ice — Starting to See Ice in Endicott Arm

launch at Dawes Glacier — A Launch at Dawes Glacier

Almost as soon as we turned into the arm, we saw that there was ice. As we continued farther, the ice pieces got more numerous. We were being very careful not to hit ice or get the launch into a dangerous place. The launch is very sturdy, but the equipment used to map the ocean floor is on the hull of the boat and needs to be protected. We were able to get to within about 8 kilometers of the glacier, which was very exciting.

The launches have been going out every day this week to map areas in Tracy Arm. I have been out two of the days doing surveying and bottom sampling. During this time I have really enjoyed looking at the glacial ice. It looks different from ice that you might find in a glass of soda. Glacial ice is actually different. It is called firn. What happens is that snow falls and is compacted by the snow that falls on top of it. This squeezes the air out of of the snow and it becomes more compact. In addition, there is some thawing and refreezing that goes on over many seasons. This causes the ice crystals to grow. The firn ends up to be a very dense ice.

ice on Endicott Arm — Ice in Endicott Arm

Glaciers are like slow moving rivers. Like a river, they move down a slope and carve out the land underneath them. Glaciers move by interior deformation, which means the ice crystals actually change shape and cause the ice to move forward, and by basal sliding, which means the ice is sliding on a layer of water.

The front of a glacier will calve or break off. The big pieces of ice that we saw in the water was caused by calving of the glacier. What is also very interesting about this ice is that it looks blue. White light, of course, has different wavelengths. The red wavelengths are longer and are absorbed by the ice. The blue waves are shorter and are scattered. This light does not get far into the ice and is scattered back to your eyes. This is why it looks blue.

Meltwater is also a beautiful blue-green color. This is also caused by the way that light scatters off the sediment that melts out of the glacial ice. This sediment, which got ground up in the glacier is called rock flour.

green blue water Endicott — This is the green-blue water from glacial melt water

waterfall in Endicott Arm — Waterfall in Endicott Arm

Mapping and bottom sampling in the ice

NOAA Ship Fairweather has spent the last four days mapping the area of Tracy Arm that is accessible to the launches. This means each boat going back and forth in assigned areas with the multibeam sonar running. The launches also stop and take CTD (Conductivity, Temperature and Depth) casts. These are taken to increase the accuracy of the sound speed data.

Rock Sample — Rocks and a sediment chart from a bottom sample

Today I went out on a launch to take bottom samples. This information is important to have for boats that are wanting to anchor in the area. Most of the bottom samples we found were a fine sand. Some had silt and clay in them also. All three of these sediment types are the products of the rocks that have been ground up by ice and water. The color ranged from gray-green to tan. The sediment size was small, except in one area that did not have sand, but instead had small rocks.

The instrument used to grab the bottom sediment had a camera attached and so videos

were taken of each of the 8 bottom grabs. It was exciting to see the bottom, including some sea life such as sea stars, sea pens and we even picked up a small sea urchin. My students will remember seeing a bottom sample of Lake Huron this year. The video today looked much the same.

Personal Log

I have seen three bears since we arrived in Holkham Bay where the ship is anchored. Two of them have been black. Today’s bear was brown. It was very fun to watch from our safe distance in the launch.

I have really enjoyed watching the birds too. There are many waterfowl that I do not know. My students would certainly recognize the northern loons that we have seen quite often.

I have not really talked about the three amazing meals we get each day. In the morning we are treated to fresh fruit, hot and cold cereal, yogurt, made to order eggs, potatoes, and pancakes or waffles. Last night it was prime rib and shrimp. There is always fresh vegetables for salad and a cooked vegetable too. Carrie is famous for her desserts, which are out for lunch and dinner. Lunches have homemade cookies and dinners have their own new cake type. If we are out on a launch there is a cooler filled with sandwich fixings, chips, cookies, fruit snacks, trail mix, hummus and vegetables.

The cereal and milk is always available for snacks, along with fresh fruit, ice cream, peanut butter, jelly and different breads. Often there are granola bars and chips. It would be hard to ever be hungry!

Kayaking, see the ship in the background?

May 10, 2017May 10, 2017

Kimberly Scantlebury: The Night Shift, May 10, 2017

NOAA Teacher at Sea

Kimberly Scantlebury

Aboard NOAA Ship Pisces

May 1-May 12, 2017

Mission: SEAMAP Reef Fish Survey

Geographic Area of Cruise: Gulf of Mexico

Date: May 10, 2017

Weather Data from the Bridge

Time: 15:36

Latitude: 2804.2177 N, Longitude: 9042.0070 W

Wind Speed: 10.2 knots, Barometric Pressure: 1016.8 hPa

Air Temperature: 26.1 C, Water Temperature: 24.89 C

Salinity: 36.49 PSU, Conditions: Some cloud, light wind, 2-4 foot waves

Science and Technology Log

Research vessels do not just work during the day. It is a 24/7 operation. Tonight I checked in with the night shift to learn more about the sonar mapping that has been done in the dark ever since I boarded NOAA Ship Pisces.

The first thing I noticed entering the dry lab was a pad of paper with math all over it. Todd, the survey technician I interviewed earlier, had noticed the the picture the ship’s sonar was producing had a curved mustache-like error in the image. Details like temperature need to be taken into account because water has different properties in different conditions that affect how sound waves and light waves move through it. He used the SOH-CAH-TOA law to find the speed of sound where the face of the transducer head was orientated. He found a six meter difference between the laser angle and what the computer was calculating. Simple trigonometry on a pad of paper was able to check what an advanced computer system was not.

NOAA Ship Pisces is also equipped with an advanced multibeam sonar. (Sonar stands for SOund NAvigation and Ranging.) In fact, there are only eight like it in the world. One of Todd’s goals before he retires from NOAA is to tweak it and write about it so other people know more about operating it. Since they are so few and you need to go to them, there are fewer publications about it.

Another mapping device is the side scan sonar. It is towed behind the vessel and creates a 300 meter picture with a 50 meter blind spot in the center, which is what is underneath the device. Hydrographic vessels have more sonars to compensate for this blind spot. The purpose of the mapping is to identify new habitat areas, therefore expanding the sampling universe of the SEAMAP Reef Fish Surveys.

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Up on the bridge looks much different. The lights are off and monitors are covered with red film to not ruin the crew’s night vision. Everything is black or red, with a little green coming from the radar displays. This is to see boats trying to cross too close in front of NOAA Ship Pisces or boats with their lights off. Lieutenant Noblitt and Ensign Brendel are manning the ship.

Ensign Brendel noted to me that, “We have all of this fancy equipment, but the most important equipment are these here binoculars.” They are always keeping a lookout. The technology on board is built for redundancy. There are two of most everything and the ship’s location is also marked on paper charts in case the modern equipment has problems.

There are international rules on the water, just like the rules of the road. The difference is there are no signs out here and it is even less likely you know who is following them. Each boat or ship has a series of lights that color codes who they are or what they are doing. Since NOAA Ship Pisces is restricted in maneuverability at night due to mapping, they have the right of way in most cases. It is also true that it takes longer for larger vessels to get out of the way of a smaller vessel, especially in those instances that the smaller one tries to pass a little too close. This did happen the night before. It reminds me of lifeguarding. It is mostly watching, punctuated with moments of serious activity where training on how to remain calm, collected, and smart is key.

Personal Log

It has been a privilege seeing and touching many species I have not witnessed before. Adding to the list of caught species is bonito (Sarda sarda) and red porgy (Pagrus pagrus). I always think it is funny when the genus and species is the same name. We have also seen Atlantic spotted dolphins (Stenella frontalis) jumping around. There are 21 species of marine mammals indigenous to the Gulf of Mexico, most in deep water off of the continental shelf. I also learned that there are no seals down here.

One of the neatest experiences this trip was interacting with a sharksucker (Echeneis naucrates). It has a pad that looks like a shoe’s sole that grips to create a suction that sticks them to their species of choice. The one we caught prefers hosts like sharks, turtles…and sometimes science teachers.

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Did You Know?

Fishing boats use colored lights to indicate what kind of fishing they are doing, as the old proverb goes red over white fishing at night, green over white trawling tonight. Vessels also use international maritime signal flags for communication during the day.