Showing posts sorted by relevance for query Fathom. Sort by date Show all posts
Showing posts sorted by relevance for query Fathom. Sort by date Show all posts

Tuesday, May 16, 2023

Fathom

Fathom (probounced fath-uhm)

(1) A unit of length equal to six feet (1.8288 m): used chiefly in nautical measurements and Admiralty papers.

(2) To measure the depth of by means of a sounding line; sound.

(3) In mining, a unit of volume usually equal to six cubic feet, used in measuring ore bodies (largely obsolete).

(4) In forestry, a unit of volume equal to six cubic feet, used for measuring timber (largely obsolete).

(5) To penetrate to the truth of; comprehend; understand.

Pre 900: From the Old English fæðm (length of the outstretched arm (a measure of about six feet), and figuratively, "power") from the Proto-Germanic fathmaz (embrace), related to the Old Norse faðmr (embrace) and the Old Saxon fathmos (the outstretched arms) and the Dutch vadem (a measure of six feet (1.8 m)).  The Middle English was fathme, cognate with the German Faden (a six-foot measure) and related to the Old English fæðmian (to embrace, surround, envelop), most forms at least influenced by the primitive Indo-European pot(ə)-mo-, a suffixed form of the root pete- (to spread).  Probable cognates included the Old Frisian fethem and the German faden (thread), the connection said to be the sense of "spreading out."  As a unit of measure, in an early gloss it appears for the Latin passus, which was about 5 feet (1.5 m).  The meaning "take soundings" is from circa 1600; its figurative sense of "get to the bottom of, understand" came some twenty years later.  The verb fathom was from the Old English fæðmian (to embrace, surround, envelop), from a Proto-Germanic verb derived from the source of the noun fathom, the cognates including the Old High German fademon and the Old Norse faþma.  The admiralty term fathomless (an adjective meaning literally "bottomless") is from the 1640s, later extended to figurative use (not to be comprehended).  Fathom is a noun and verb, fathomer & fathometer are nouns and fathomable, fathomless & (the predictably common) unfathomable are adjectives; the noun plural is fathoms.

The One-Hundred Fathom Line

UK Admiralty chart of the hundred fathom line, circa 1911.

The one-hundred fathom line is an Admiralty term for marking sea charts to delineate where the seabed lies at depths less or greater than 100 fathoms; it can thus be thought a particular expression of the continental shelf (though defined for military rather than geographical purposes).  Thus the distance from the coastlines of each land mass varies and it's related not at all to other boundaries established by the United Nation's (UN) Law of the Sea or other conventions such as territorial waters (historically 3 miles (5 km) and now 12 (20) or a state's Exclusive Economic Zone (EEZ) (200 (320)).  The hundred fathom line is now of little military significance (although it remains of interest to submariners) but it was cited as recently as 1952 in negotiations between the post-war Churchill (1951-1955) and Truman administrations (1945-1953) in defining the areas of preponderant operations for the Royal Navy and US Navy.

Lindsay Lohan GIF from A Beautiful Life (music video).  Although often photographed in the water, there's no evidence to suggest Ms Lohan has ever descended deeper than a a couple of fathoms.

Wednesday, June 8, 2022

Bathymetry

Bathymetry (pronounced buh-thim-i-tree)

(1) The science and practice of the measurement of the depths of oceans, seas, rivers or other large bodies of water.

(2) The data derived from such measurement, especially as compiled in a data set or topographic map.

1860–1865: The construct was bathy- + -metry.  The prefix bathy- (the alternative form in oceanography and related fields is batho-) was from the Ancient Greek βαθύς (bathús) (deep), zero-grade of the root of βένθος (bénthos), possibly from the primitive Indo-European gehd- (to sink, submerge) or perhaps cognate with the Sanskrit गाढ (gāha) (profound, intense, deep, dense, thick, fast, deep (of a color)).  Despite the appearance, it’s unrelated wither to βυσσός (bussós) or βυθός (buthós).  The construct of the suffix –metry (used to form nouns relating to measures and measurement) was -meter + -y.  Metre was from the Ancient Greek μέτρον (métron) (measure), from the primitive Indo-European meh- (to measure) + -τρον (-tron) (a suffix denoting an instrument, as in ancient Greek ροτρον (plow) and familiar in English for the used in electronics and physics such as cyclotron.  The –y suffix is from the Middle English –y & -i, from the Old English - (-y, -ic), from the Proto-Germanic -īgaz (-y, -ic), from the primitive Indo-European -kos, -ikos, & -ios (-y, -ic).  It was cognate with the Scots -ie (-y), the West Frisian -ich (-y), the Dutch -ig (-y), the Low German -ig (-y), the German -ig (-y), the Swedish -ig (-y), the Latin -icus (-y, -ic), the Sanskrit -इक (-ika) and the Ancient Greek -ικός (-ikós); a doublet of -ic.  The –y suffix was added to (1) nouns and adjectives to form adjectives meaning “having the quality of” and (2) verbs to form adjectives meaning "inclined to".

Bathymetry bathymetrist & bathymeter are nouns, bathymetric & bathymetrical are adjectives and bathymetrically is an adverb; the noun plural is bathymetries.  The derived noun paleobathymetry describes the bathymetry of prehistoric seas.  Paleo was from the Ancient Greek παλαιός (palaiós) (old), from πάλαι (pálai) (long ago).  Most etymologists suggest it was probably cognate with the Mycenaean Greek parajo, which is generally held to mean “old”.  If true, this connection hints at a link with the Proto-Hellenic palai(y)ós and casts doubt on the once often proposed etymology from the primitive Indo-European kwel.

In the UK, the Royal Navy's early use of bathymetric data was to add indications of depth to the Admiralty's charts, the most famous of which was the one which drew the "hundred fathom line" around the British Isles.

When coined in the mid-nineteenth century, bathymetry referred to the ocean's depth relative to sea level, reflecting the information available, given the technology of the time. In the twentieth century, it came to mean “sub-marine topography”, the rendering in images of the depths and shapes of underwater terrain.  In this it’s analogous with topographic maps of land masses which represent the three-dimensional features (or relief) of overland terrain.  Bathymetric maps typically represent variations in sea-floor relief by depicting the changes with color and contour lines called depth contours or isobaths.  Bathymetry provides the baseline data which made possible the modern discipline of hydrography which measures the physical features of a water body.  Hydrography compliments bathymetric data with measurements of the shape and features of shorelines, the characteristics of tides, currents and waves as well as the physical and chemical properties of the water itself.

Bathymetry is thus the study and mapping of the sea floor. It involves obtaining measurements of the depth of the ocean and is the equivalent to mapping the height of features on land.  Bathymetric data is used for a range of purposes including charting and ship navigation, fisheries management, establishing baseline data to support environmental monitoring, the determination of maritime boundaries, alternative energy assessments (most obviously regarding offshore wind and wave & tidal energy), research into coastal processes and ocean currents (the best known aspect of which is tsunami modelling, assessment of the environmental impact on marine geology of resource extraction proposals and the identification of geohazards, such as underwater landslides

Bathymetry map of East Flower Garden Banks National Marine Sanctuary (FGBNMS), a United States National Marine Sanctuary 100 nautical miles (190 km) off Galveston, Texas, in the northwestern Gulf of Mexico.

However, despite the progress of over a century, relatively little is known about the sea floor compared with the surface of the Earth, the Moon and indeed many of the solar system’s other planets and moons.  By area, most map of the sea floor are derived from satellites an low resolution, provide only a vague indication of water depth although whatever the limitations, the technology is clever, the satellite altimetry measuring the height of the ocean surface.  If hills or maintains exist on the seabed at the point of the image, the gravitational pull around that area will be greater and hence the sea surface will bulge and from this measurement maps can be generated showing general features over a large area at low resolution.  More precise maps can be built using single beam echosounders which produce a single line of depth points directly under the equipment.  Taken usually from a moving vessel, they’re typically used to identify general sea floor patterns or schools of fish.  More accurate, high definition maps can be generated by using devices called multibeam echosounders (or swath echosounders) and airborne laser measurements (LADS) which capture swathes of data by acquiring multiple depth points in each area, these data grabbers are accurate to within 1 metre (39 inches).  It was a bathymetric survey which revealed the world’s tallest mountain is not Mount Everest but the Mauna Kea volcano on Hawaii.  Much of its base is on the ocean floor, some 6,000 m (19,685 feet) below the sea-surface and its peak is the highest point in the state of Hawaii, giving an overall height of 10,000 m (32,808 feet).  Mauna Kea is thus a significantly higher feature than Mount Everest which rises 8,800 m (28,870 feet) odd.

Modern electronics represent quite an advance over the nineteenth century techniques of bathymetric measurement which began with a heavy rope being thrown over the side of a ship, the only data gained being recording the length of rope it took to reach the seafloor.  These measurements were however incomplete, and prone to inaccuracy, the rope often shifted by sub-surface currents before reaching the seabed.  At best the data was indicative because the rope could measure depth only one point at a time and there was no way to tell if the point of impact was flat or sloping.  Depending on the area of interest, scientists would have needed dozens, hundreds or even thousands of measurements, something obviously rarely possible.  Accordingly, until the modern age, scientists and navigators estimated the topography of the seafloor and for experienced sailors, the hills and valleys were sometimes easy to predict but the sea can be deceptive and ocean trenches and sandbars often surprised navigators.  Many ships and cargos were lost to ships running aground.