# Satellite triangulation

Satellite triangulation emerged quite recently - in 1963. But this "child" of astronautics shows great promise. It is not only a matter of specifying the shape of the Earth, in drawing up more and more accurate maps, which, of course, is very important for the practical, industrial activity of man. With the help of satellites, you can find out how our planet changes in time, how the continents move, how slowly the masses are redistributed in the solid body of the Earth - in a word, how our planet "breathes" and "lives". And some of these tasks are being successfully solved today.

Artificial satellites of the Earth play a huge role in elucidating the shape of its physical surface. Let's find out what the so-called satellite triangulation is - a method that allows us to talk about space geodesy as one of the "space" disciplines.

Imagine three ground stations - A, B and C (Fig. 1). Satellite S1 is observed (visually or photographically) from all three stations, satellite S2 - from stations A and B, satellite S3 - from stations B and C. By the way, the method is also applicable when S1, S2 and S3 are not three different satellites, but three positions of the same satellite at different points in time.

Observations of satellite S1 from stations A and B determine the direction of straight lines AS1 and BS1 relative to the stars and thereby fix the position of the plane ABS1. Similarly, according to the observations of the satellite S2, the position of the plane ABS2 in space is found. Obviously, these planes intersect along the straight line AB. The BC position is determined from the intersection of the BCS1 and BCS3 planes. Straight lines AB and BC fix the plane of triangle ABC, and their intersection with ACS1 defines the segment AC. Therefore, according to the satellite data, it is possible to find the sides and angles of the ABC triangle, i.e., to solve the first main triangle in the triangulation network. If in this triangle the positions of points A and B (and therefore the basis AB) are known, then the position of the third peak, C, is found from the satellites. It is noteworthy that it is necessary to know not the exact position of the satellites in space, but the direction to them from ground stations. To make observations from different stations synchronous, special flash lamps are installed on the "geodetic" satellites, which give very bright flashes. These flashes are recorded by cameras of all satellite triangulation stations.

In ground triangulation, the sides of the triangles, as a rule, are equal to 20-30 km. In the "cosmic" triangulation network, triangles are tens and hundreds of times larger, which sharply reduces the intermediate stages of measurements. The old method was only good for sushi. For satellite triangulation, even the oceans are not an insurmountable obstacle - the satellite can be simultaneously observed from different continents, for example, from Europe and from America.