Monthly Archives: March 2017 - 2. page

Earth Orbit Edition

ISS Issue

From Sea to Space

November Alpha One Sierra Sierra, this is November Yankee Zero Victor, Maritime Mobile, copy?…”

“… November Alpha One Sierra Sierra heard you loud and clear.”

Station Commander Shane Kimbrough’s (Radio call sign NA1SS) voice was met with clapping and cheers When Tom Vinson (NY0V) made contact. The crew in the International Space Station is extremely busy and a few previous attempts to chat didn’t pan out. So the crowd gathered on the bridge of the Mermaid Vigilance knew this talk was special.

Sallie Smith jumped on the microphone first and asked if he had a message for the kids and educators following along on our expedition. He said he has a soft spot in his heart for educators and his message for the kids was, “You have to work hard. Things don’t come easy. Things like this require a lot of work, as well as anything that’s worthwhile in life. So study hard, work your tail off. Find something you are passionate about and then get after it and you will be amazed at what you can accomplish.” Cap’n Joe was next and he told Kimbrough it was an honor to be speaking with the commander. They chatted about how the ISS crew will be heading home in three weeks on April 10th to complete their six-month mission. Joe asked if they talk Earth politics with the cosmonauts. It turns out that part is similar to ship etiquette; the diverse group stays away from politics and just keeps things business and pleasure. Marika then asked about his favorite thing to do in the unique environment. Kimbrough said his favorite thing is to look out the window back at our beautiful planet.

Next Oleks said a quick few words to Russian Cosmonaut Sergey Ryzhikov wishing him a successful and safe stay and return from space. Then Sergiy got to speak with Sergey! Our ship’s ETO and the cosmonaut chatted in Russian about how little free time there is up there and the beauty of life out the window. I think our Sergiy wins the award for the biggest smile through the event. Tom explained what we are up to out here looking for the Electra and Kimbrough asked how the search was going. Tom said all was well and mentioned we were using a REMUS AUV from WHOI searching at 5,500 meters depth.

The very exciting exchange ended with an agreement to try to get astronaut Peggy Whitson on the line next time. “Chat again on Sunday. NA1SS, out”

— Marika Lorraine

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Central Pacific Edition

Spring on the Mermaid

Declination: Zero!

While much of the United States digs out from under a blanket of late winter snow, spring has sprung on the Mermaid. Under azure blue skies filled with puffy clouds and gentle east winds, we survey our way into the new season.

The vernal equinox (vernal meaning “spring” and equinox meaning “equal nights”) is when daytime is exactly as long as the night. There is another one in the fall. If we’re still out here at that time, I’ll be sure to write to you again. This is the one day of the year in which the sun makes a northerly crossing of the Equator. This means that for one instant, the sun will be directly overhead on the Equator at a predicted time and location. Its declination (angular distance from the celestial equator) will be zero degrees. Let’s look into that. The resource needed is a book cal led the Nautical Almanac. It’s a required publication carried on all commercial vessels. Published by a number of sources, it amounts to a directory of the stars, sun, moon and planets in our solar system and their location addresses at any point in time and for any location on earth during the year. Navigators use this information when they make celestial observations of these bodies. Certainly Fred Noonan used it when he and Amelia Earhart navigated their way around the world.

For the sun at equinox, we know that its location is on the Equator, but when and where on the Equator? We have to go to the Nautical Almanac.

Open the book to any page. On the right hand page is a column for the sun. The information is tabulated for each day and hour of the year. The equivalent of latitude for the sun is called declination. Declination changes with time due to the earth’s orbit around the sun and the spinning on its axis. Go to the pages for the early part of the year. The sun’s declination is South in January, February and March. But it is getting less south each day. So we look for the day of the crossing, and it occurs in March. Now observe that declination changes from south to north on March 20th. It occurs exactly between the hours of 10 and 11 Greenwich Mean Time. So we can see that at 1030 GMT on March 20 the equinox occurs. In local time on the Mermaid (-11), that’s March 19th at 2330, just before midnight tonight.

But wait there’s more. What about where it occurs? It is only on the Equator for an instant as it moves northward. Back to the Nautical Almanac, back to the page for March 20th, back to the column for the sun, back to the hours 10 and 11. There is an equivalent for the sun’s longitude call GHA, Greenwich Hour Angle. This is the angle starting at Greenwich that sweeps westward, counterclockwise looking down from the North Pole. GHA is tabulated for each hour. We can see at 10 GMT, GHA is 328 degrees 8.8 minutes, 328° 08.8’. At 11 GMT, GHA has increased to 343° 09.0’. By simple mathematical interpolation, the GHA for 1030 would be exactly in the middle, 335° 38.9’. A GHA angle of this amount is the same as measuring longitude east or west. In this case, we would measure it to the west of Greenwich 24° 21.1’W longitude. Where’s that?

This happens to be a point on the Equator located in the middle of the Atlantic Ocean. What is near it? It’s about equal distant from two prominent points of land: the eastern elbow of Brazil, close to Natal, and the western elbow of Africa, close to Dakar. Does that ring a bell? Those were the starting and ending points for Amelia Earhart’s crossing of the Atlantic on her Around the World Flight attempt. Small world, isn’t it?

— Spence King

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Central Pacific Edition

The World from Here

A Milestone from the Radio Guys

Last night [written March 15] I finally worked into Europe. [That means made contact with a fellow ham, in amateur radio lingo – ed.] This finishes up a “Worked all Continents” from the good ship Mermaid Vigilance. One would think that Antarctica might be the last one in the bag. Not this time. I had found RI1ANC at the Russian Antarctic station earlier in our expedition. Europe, however is a difficult one from here in the Central Pacific. The reason for this is that EU is due north on the great circle path. That of course takes your signal up and over the North Pole where there is a convergence of our earth’s magnetic fields. These, plus any Aurora Borealis will significantly disturb the electromagnetic waves of our radio signal. Signals will often be watery or hollow sounding when this occurs.

I finally bagged HA4FF in Hungary on our “greyline” or “terminator” path. Greyline is when the sun is either rising or setting, that is, the sky is not full daylight and not fully night. At these two times per day there are opportunities for having better signals along these paths. This phenomena is caused by the very rapid ionization or de-ionization of the ionosphere. When the greyline for two stations is in good alignment, there is an opportunity to have communications between the two stations which might not occur otherwise. On the lower frequency bands these openings may be only seconds to maybe 15 minutes long! Yes, talk fast!

Another milestone we reached with this station is 25 countries. In our amateur radio world some of these “countries” are entities that belong to other countries, but are separated by at least 250 km. There are other rules established for what determines an entity that I won’t bore you with here. So Hawaii and Alaska are counted as separate “countries.” Another example is the far reaches of the island nation of Kiribati. The country’s islands stretch over 2,000 miles. There are West, Central, and Eastern Kiribati entities that are surrounding us here near Howland Island. These were the former British Phoenix, Caroline, and Line island groups. Each group counts as a separate entity.

Some of the more exotic of the countries contacted are: Macao, Ghana, Namibia, Pitcairn Island (of Mutiny on the Bounty fame), Austral Islands, Tonga, Temotu province, San Andres Island, and Nepal. You may wish to google these locations. Radio is good for your geography! — Tom Vinson (NY0V)

Majuro

At the end of our expedition, we are planning to dock in Majuro, the capital and and largest city of the Republic of the Marshall Islands. Though it spans an area of 114 square miles, most of that is lagoon, and the land area of the 64 islands in the atoll amounts of a mere 3.7 square miles! The highest elevation on the island is a scant 10 feet above sea level. The Marshall group is comprised of some 34 coral islands or atolls lying north of Kiribati and Micronesia and extending to the west as far as the Marianas.

Most of the population of close to 30,000 live on the eastern end of the chain, where most of the land area lies. The airport is on a narrow strip to the south. The economy depends on the operation of the U.S. missile testing rang on Kwajalein and some tourism. Most of the outer island people live on subsistence farming and fishing, and the production of copra.

The island has seem human habitation for 2,000 years or more. In the modern era, the atoll along with the rest of the Marshall Islands was claimed by Germany, but was captured and occupied by the Japanese during Word War I. In January, 1944 American troops invaded the island, finding it undefended. It was used as a forward base of operations for the U.S. Navy during the rest of the war. The territory was retained by the United States until it was granted independence in 1986.

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Central Pacific Edition

Sound Advice

Is There an Echo in Here?

The amazing images we are seeing from the ocean floor are derived from echoes of sound bouncing off the undersea terrain and returning to our sonar. Making sense of this information depends critically on the speed of sound in the water. This varies quite a bit depending on conditions, so the REMUS is equipped with a CTD (Conductivity- Temperature-Depth) sensor that is used to calculate sound speed. Although we are only interested in the speed near the bottom, the sensor operates as soon as it hits the water and so will give us measurements all the way down. We took the opportunity to look at this “sound velocity profile” to see what it might tell us.

Under standard lab conditions, sound travels about 1,560 meters per second in seawater (much faster than the 340 meters per second in air). That’s just about a mile per second. But it varies quite a bit as the elasticity* of the water changes in response to changes in temperature, depth, and to a lesser extent, salinity. The biggest effect is temperature, which has a very complicated influence on elasticity due the the unique structure of the H2O molecule. With most fluids, sound speed decreases with temperature, but with water it actually increases by about 3 m/sec for every 1 °C increase. Sound speed also increases with depth (because the pressure increases and changes elasticity) by about 1.7 m/sec for every 100 m change in depth.

The plot on this page shows how the measured temperature and calculated sound velocity changed as the REMUS descended to the depths on one of its missions. This is a classic profile. The temperature at the surface was a balmy 27.5°C (82°F), but dropped sharply to about 5°C just 1,000 m down. By the time REMUS reached 5,500 m it was a bone chilling 1.3°C, just above freezing. Influenced by the temperature, the sound velocity dropped sharply down to the first 1,000 m. At that point, the relentless increase in pressure with depth took over as the temperature stabilized, and the sound velocity rose back to and above its surface value. (Salinity effects were also calculated but were small.) The sound speed changed by more than 4% over this range.

Besides its effect on the sidescan sonar, changes in sound velocity cause the paths sounds travel to vary, much like a lens alters the path of light. As a wave of sound passes through the water, some parts of the wavefront move faster than others causing the sound to bend away from areas of higher velocity. A particular consequence of this can be seen if we look at the shallower (first 200 m depth) of this plot. Mixing of surface water warmed during the day to deeper regions, and subsequent cooling at night, will typically cause an “isothermal” (constant temperature) layer near the surface, or even a temperature “inversion,” where it gets warmer as one goes deeper, to a point. This can occur in tropical waters thanks to intense solar heating and strong wave action. Below that layer, the temperature will drop as described earlier. This thermal layer can cause large variations in sound wave propagation. Submariners take advantage of this as a submarine lurking just below the layer can be “hidden” from sonars listening at the surface, since its sounds will bend to greater depths. On the other hand, a ship on the surface may escape the attention of the submarine below the layer since its sounds may remain confined to shallower regions. In some cases, the sound can be trapped in a “surface duct” and propagate for many miles horizontally, while making not a whisper below the layer.

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Central Pacific Edition

In the Zone

Elgen Tells More Than You Wanted to Know About Time

There is a direct but unconnected relationship between the measurement of time and the world in which we live. Daily time is tied to the movement of the sun, but time standards are a human construct. Believe it or not, the United States did not have official universally accepted time zones until Congress passed The Standard Time Act of March 19, 1918, and that was just 9 years before I was born. Yikes! I’m nearly as old as our times zones in the United States!

In the centuries when the world was believed to be flat, and it was thought that there was nothing but water to the west between Europe and China there was little transportation or commerce between the few people then on earth, and little need or desire to keep track of time. The sun came up, and the sun went down, and for those living so went the days of their lives.

Marco Polo, Christopher Columbus, Magellan, and several other adventurers discovered there was a very large world out there that could supply things that would add wealth to their countries’ coffers. This immediately stimulated transportation to acquire the wealth overseas that could be had for the taking, and ships in the oceans needed a standard means of telling time to be able to navigate precisely across those oceans to access that wealth.

Greenwich Mean Time (GMT) was established when the London Royal Observatory was built in 1675. I t provided a standard time connected to the stars that ships needed so they could navigate across the oceans to provide the means of commerce. That spawned the need for clocks that were able to keep accurate time aboard ships in order to calculate longitude. The first useful marine chronometer was invented by John Harrison in 1761. His story is told the the book Longitude by Dava Sobel, a classic tale of the founding of an accurate chronometer for ships. Another excellent (and more technically accurate) source i s Plotting the Globe by Avraham Ariel.

Except for ships at sea, there was little need for a standard time zone as most people in the United States and around the world were happier to have their time controlled locally. Communities of any size had the their own observatories that would measure exactly when the sun was highest and everyone would then set their clocks to 12 o’clock noon. Locally it worked great and everybody was quite content with it.

Even at seaports around the world the local observatory’s time worked very well for the ships in the harbor. Before ships carried radios, most major ports in the world had a ball like the one in Times Square (used on New Years Eve) that could be seen from almost anywhere in the harbor. At noon every day the harbor city’s local observatory would countdown to the handler of the ball so that it would reach the bottom at exactly 12 o’clock noon. If a ship’s navigator knew when the local time was exactly high-noon he would know what his longitude was, and vice-versa.

Decades before the U.S. Congress ever assigned the official time zones for our country the railroads had already found out that each city having its own special time was unworkable. So in the latter part of the 19th century the railroads divided the country into railroad time zones with most of the borders passing through the railway stations of major cities.

In 1883 on November 18 each railroad station clock was reset as standard time noon was reached in each time zone. This became known as “the day of two noons.” Detroit was the last major city to leave its local time zone. On the boundary between zones, the city adopted Central Time in 1900 and finally settled on Eastern Time with the rest of the state in 1916, two years before the congressional act that ended the confusion for good.

During the early part of the 20th century various countries accepted the GMT system with (usually) regional even-hour offsets, though there are some exceptions that use a half-hour offset and even a few locales with quarter-hour offsets. Nepal was the country last to join in 1986 with an offset of 5 hours and 45 minutes.

I have not mentioned the use of UTC (Coordinated Universal Time) which is “Z” or Zulu time, and will save that topic for the next time we meet.

— Elgen Long

REMUS Image of the Day

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