We all studied geography at school and are familiar with the term "height above sea level" firsthand. This definition can be found in popular science television programs, on the pages of magazines, newspapers and other media. Let's look at modern ways of defining it.
Sea level, relative to which the distance to an object is measured, is the water surface at rest, which is perpendicular to the resultant forces applied to the body of water. The water level changes very often and this is due to the phases of the moon, the strength of the sun and wind, and evaporation. Therefore, to calculate the average value, it is necessary to conduct the necessary calculations for years.
Height above sea level is a point (coordinate) in a three-dimensional area that indicates at what height a certain object is in relation to sea level, taken as zero. Also, it can be roughly defined as the vertical from the object to the mean height above sea level, without taking into account the tides. The height of a point located above the level is considered positive, below - negative. The other two coordinates of the geographic location of the object are longitude and latitude.
If we take Russia as an example, then its highest point is Elbrus - 5642 meters, and the lowest is the Caspian Sea, the highest point of which is approximately 28 meters.
How to find the altitude above sea level
In the old-fashioned way, the height above sea level can be viewed in special topographic maps, which display all heights. But there are more modern methods.
- You can find out what height above sea level using a satellite navigator running on a specific program, for example, Google or Google Earth (Google Earth). First you need to download one of the applications on your smartphone or computer and use the prompts to determine the distance from sea level to the object you need. Working with the programs is very simple: point the cursor at the right place on the map, and the information is displayed automatically.
- Measurement of the level of a specific area is available on GPS devices. Instruments determine heights based on information received from satellites. GPS-receivers with a built-in barometer-altimeter have the highest accuracy of indicators.
- In the search bar of the Yandex browser, drive in “height above sea level” and the city, country, mountain, etc. you need. This information will be especially useful for travelers who are going to conquer mountain peaks. So you can know in advance what heights you will have to overcome and prepare for the ascent.
- How to determine the height knows an application called Altitude, installed on smartphones. It determines the point above sea level in real time, as well as the speed of movement and other data. The results may not be entirely accurate with a discrepancy of one and a half to two divisions.
Also, measurements of the height of the terrain above sea level can be carried out using an altimeter - an instrument that is used to measure the height of a rise or a point above sea level. Using the altimeter is very simple:
- start the device and determine the value of blood pressure corresponding to the current weather conditions;
- calibrate the device and hold the "Set" button. After that, the device will automatically switch to the desired mode and indicate the altitude pressure in the current time;
- reduce the readings to normal using the "Set" button. After saving the obtained parameters in the main menu, the screen will display the height above sea level of the desired object.
Altimeter - a device for measuring altitude above sea level How to find out the height above sea level using one method or another is a purely individual matter, but the altimeter will give more accurate readings compared to mobile applications and GPS.
Highest and lowest piece of land above sea level
If we talk about the highest and lowest points on a global scale, then Mount Everest, the real name of Chomolungma, belongs to the first. It is located in the Himalayan mountain system at an altitude of 8848 m above sea level. The second peak of the mountain rises at an altitude of 8760 meters.
Everest is a clear winner among all the mountains of the planet in terms of elevation. Back in the 19th century, a geodetic service worker Radhanat Sikdar from India measured its height. But since then, the data has changed, and the mountain turned out to be even higher than originally stated.
The lowest point above sea level is considered not one, but two at once. The first is on land. This is the coast of the Dead Sea on the border of Israel and Jordan. The point is located at around 417 meters below sea level, but as experts say, every year this figure increases by 1 meter.
The second point is called the Mariana Trench and is located deep under the waters of the Pacific Ocean. This is a bottomless crater, which at its lowest point has a depth of more than 11 thousand meters below sea level.
Dependence of pressure on height above sea level
At different altitudes, the atmospheric pressure will also be different. Many people regularly face the problem of the close relationship between poor health and atmospheric fluctuations. For this reason, it is impossible to hike in the mountains and fly on airplanes, especially over long distances.
According to the researchers, the dependence of pressure on height above sea level is determined by such indicators: an increase of 10 meters causes a decrease in pressure by one mark, i.e. for every 100 m, there is an average decrease of 7.5 mm. rt. Art. Until the height reaches 500 meters, no changes are felt, but if you climb 5 kilometers, the values \u200b\u200bare half the optimal, which will affect your well-being. This happens due to liquefied air and a decrease in the amount of oxygen necessary for living organisms.
Map Description:
Here is a world map from Google, opened in Novosibirsk. The map can be overlaid with a color coloring of heights above sea level, a grid in Latitude/Longitude or QTH-locator format, shading indicating day/night. The search bar allows you to find the place you are interested in by QTH locator, address, or geographic coordinates.
The first click on the map sets the first (“ H” – initial) point. The second click on the map sets the second (“ TO” – end) point. After setting both points on the map, a red line of the radio wave propagation path will be drawn, below the map a graph of the height profile between the specified points will be displayed. Left - start point, right - end point, vertical height above sea level.
In the place you are interested in on the height map, you can click, this will lead to the installation of a special marker (“ ! “) in the corresponding place of the main map. By moving the mouse to the area of the main map, you can explore in detail the surroundings around the set marker. By moving the mouse over the elevation profile map, you see the parameters of the current point, and a marker is displayed on the main map in the corresponding geographical location (“ X“). You can change the scale of the map for better detail of objects, the map will be automatically positioned so that the marker is displayed in the center of the screen.
In addition to the height profile, a straight radio beam line is drawn on the map connecting the antenna suspension points, an ellipse of the first Fresnel zone, and the received signal power is calculated along the entire path.
The calculated power values are conventionally indicated by the colors of the earth's surface:
- Red- 7-9 or more points on the S-meter scale;
- Orange- 4-6 points;
- yellow- 1-3 points;
- green- less than 1 point;
- the black- no signal.
On the height profile graph, you can select and enlarge any area of interest to you - to do this, click the left mouse button, drag the rectangle that appears to the desired map fragment, then release the mouse button. To restore the original scale of the map, right-click on the map.
At any time, by clicking on the main map, you will set a new end point, the height map will be rebuilt to display the profile to the newly selected point.
This service also allows you to build the COVERAGE AREA of the radio signal emitted from point 1 (“ H“). After setting the starting point and setting the initial data, click the "Calculate" button - you will see the coverage area drawn in real time. The Stop / Hide-Show button allows you to stop the ongoing calculation of the coverage area or “Hide-Show” the coverage area. The larger the selected number of readings, the higher the accuracy of calculating the coverage area, but the longer it will take to carry it out. (Moreover, the calculation time to a greater extent depends not on the power of your computer, but on the speed of issuing topographic information by Google servers.)
You can change the automatically selected width of the lines indicating the signal level by color using the buttons “ + " And " – “, and then fix them permanently by ticking the FIX field.
Button on the main map “ Clear markers” deletes all set markers and calculation results of the Coverage Zone, it is advisable to use it if you want to set a new starting point and perform a new calculation cycle. Button " full screen” switches the map display to full-screen mode, pressing again returns the standard windowed mode.
For ease of use, the current coordinates of the cursor are constantly displayed on the map: latitude (Lat), longitude (Lng), QTH-locator, height (Eval).
Altitude above sea level ... This term, perhaps, is known to every schoolchild. We often meet him in newspapers, on websites, in popular science magazines, as well as when watching documentaries.
Now let's try to give it a more precise definition.
Section 1. Altitude above sea level. general information
This term should be understood as the absolute height or absolute mark, i.e. such a coordinate in which shows at what height in relation to sea level this or that object is located.
Two other indications of the geographical location of an object are longitude and latitude.
Here, for example, Moscow. The height above sea level of this city is very different: the maximum is 255 m (not far from the metro station "Teply Stan"), and the minimum - 114.2 m - is located near the Besedinsky bridges, exactly where the Moscow River leaves the city.
In general, if we operate with purely physical measurements, then the height above sea level is nothing more than the vertical distance from, in fact, the single object itself to the average level of the sea surface, which should not be disturbed by either tides or waves.
This value can be both positive and negative. Well, everything is relatively simple here: what is above the sea acquires a plus sign, and below, respectively, a minus sign.
By the way, it is impossible not to note the fact that with an increase in its value, a decrease in atmospheric pressure is observed.
If we talk about our country, then the 5642-meter Elbrus is rightfully considered the highest land point in the Russian Federation, but the lowest can be called with an absolute height of about 28 m.
Section 2. Altitude above sea level. The highest place on the planet
Well, of course, this is Everest - a well-known mountain located in the central part of the Himalayas, just on the border of two South Asian states, Nepal and Tibet.
Today its height is 8848 meters. The words "today" are not accidental. According to scientists, the earth's surface is still continuing to form, so this peak, although imperceptibly, is growing every year.
If you delve into history, then almost immediately you can find information that the first brave conquerors of Chomolungma were (New Zealand) and Tenzing Norgay (Nepal). They made their truly heroic ascent on May 28, 1953. Since then, Everest has become a kind of Mecca for hundreds and thousands of rock climbers, climbers and other daring adventurers.
Section 3. Altitude above sea level. The lowest place on the planet
In this case, things are a little more complicated. The fact is that there are two such points on Earth at once: one of them - the coast of the Dead Sea - is located on land, and the second bears the name and is located deep under the water column of the Pacific Ocean.
Let's dwell on each of them in more detail.
So, the Dead Sea, as you know, can be found on the border of three countries: Israel, Palestine and Jordan. It is not only the most salty body of water on the planet, but the lowest piece of land.
Now the water level in it is 427 meters, but this is not the limit, because annually, according to experts, it falls by an average of 1 meter.
Altitude above sea level… Moscow, as mentioned above, is located in the range from 114 to 255 m. For us, this is, in principle, the norm. Considering that the capital of the Russian Federation can hardly be called very hilly, it is almost impossible to feel this difference.
And now let's pick up a globe or a physical map of the earth's surface: somewhere deep, deep in the Pacific Ocean, not far away, you can see a mark with the inscription So, it goes under water to a depth of a little more than 11 km.
How are heights measured?
This question is followed by related ones. What is absolute and relative height? Why are there triangulation marks on the tops? When was the height first determined? What does "above sea level" mean? Does this level fluctuate? How is altitude measured from aircraft? What are command points?
Displaying the area in a reduced form on diagrams and maps, people have always paid attention to the mountains. They were conspicuous and necessary reference points. The geographical map did not appear immediately: it went through its development from clay, parchment, birch bark samples to perfect cartographic models. At first, much depended on the draftsman, his sense of space, his ability to mentally survey the Earth from a height. The mathematical reliability of the relief, of course, was absent.
Over time, the profession of renter appeared. A measuring cord, a measuring wheel, a compass went into action. In the 16th century, prototypes of measuring geodetic instruments were invented - a measuring scale, a theodolite, then - rangefinders, levels. To measure the height of the mountain, or, as topographers say, "to take vertical marks", physicists helped.
Blaise Pascal asked his acquaintances in Clermont to climb Mount Puy-de-Dome with a mercury pipe. The scientist's assumption was confirmed at a height: the mercury column dropped. Since then, it has become customary to measure the height of the area using a mercury barometer. Appeared devices for determining the height of the temperature of the vapor of boiling water: hypsometer, thermobarometer, hypsothermometer. The principle of operation is as follows: as you rise, the air pressure decreases. At the same time, the boiling point of water also decreases - about 0.27 mm of mercury column. According to the tables, atmospheric pressure is noted accordingly, and the height of the terrain is determined from it.
This is, one might say, a "field" method. But not every peak is so easy to climb for measurement. And in the 17th century, the Dutch astronomer Snellius proposed a triangulation method, when heights are determined “from the side”, using reference points. This method is also used for topographic surveys from aircraft and artificial satellites.
Altitude marks of peaks began to be distinguished: absolute - from sea level and relative - from the foot of the mountain, from the underlying plain. It is clear that the absolute heights of mountains are always greater than the relative ones. For the unity of the measurement system in geographical science, it is customary to count these measurements from the level of the World Ocean. So, after indicating the height, a conspicuous prefix “above sea level” appeared, or if it is not there, then it is simply implied. But we know the ebb and flow. The levels of the seas are unstable: they began to be distinguished: instantaneous, tidal, average daily, average annual, average long-term. This latter, according to the developed international agreements, has become the most stable in order to "tie" the height of the mountains to it.
It is clear that many peaks and ridges in the oceans that do not come to the surface are measured differently. The highest marine seamount ever discovered was in 1953 near the Tonga Trench off New Zealand. It rises from the bottom of the sea to 8690 m, and its peak is 365 m below the surface of the water. And if we do not proceed from sea level, but measure the height from the underwater base, then the highest mountain in the world is Mauna Kea (“White Mountain”) in the Hawaiian Islands. Its total height is 10,203 m, of which only 4,205 m are above sea level.
When I studied at the institute as a meteorologist, we often carried out topographic surveys of the area and learned how to correctly measure the height above sea level. This knowledge has come in handy for me over and over again.
Why determine the height above sea level
Height above sea level is a rather broad and complex concept, which includes a lot of special terms that are understood only by people of special professions (for example, hydrologists). But I will try to explain to you what it is, in simple words.
Sea level is the water surface in a calm state, which has a perpendicular position to the resultant forces applied to the body of water.
The water level can change quite often. Therefore, measurements are carried out for years and even centuries in order to calculate the average value.
Many natural factors influence sea level fluctuations. For example:
- phase of the moon;
- wind power;
- evaporation;
- the forces of the sun.
There is also such a thing as three-dimensional space, which means a three-dimensional model of the whole world and the environment. So, the height above sea level is a value that shows how far an object is located relative to zero sea level in our three-dimensional space.
How to determine the height above sea level
For complete reliability, the height above sea level is measured only in a calm state of water, when there is no storm and wind.
There are several ways to do this:
- using an altimeter;
- by geodetic leveling;
- using mobile applications or special programs, such as Google Earth.
I would like to tell you how to measure the height above the sea using an altimeter.
To begin, turn on the device and set the atmospheric pressure value corresponding to the weather conditions.
Reduce them to normal, again using the "Set" button. After saving the received data in the main menu, you will see the altitude above sea level on the display.
