Simultaneous Observations of Artificial Earth Satellites

observations of artificial earth satellites that are performed from two or more points on the earth’s surface at the same time. The methods used may permit the determination of the direction to the satellite (position observations), the distance to the satellite (range observations), or both the range and the distance. The results of such observations are used in solving astronomical, geophysical, and, especially, geodetic problems.

When a simultaneous determination is made of the directions to a satellite from two observation stations whose coordinates are known in some system of coordinates, the directions can be used to compute the coordinates of the satellite in the same system. In addition, the position of the plane passing through the two stations and the satellite can be computed. If the coordinates are known for just one station, such observations permit the position of this plane to be found. When two such planes are computed from the results of two observations of the same satellite or of different satellites, the intersection of the planes determines the direction of the chord of the earth that connects the two stations.

If range observations are made at the same time as position observations from at least one station, the elements of the triangle with vertices at the two observation stations and the satellite can be computed. The distance between the stations is one of the quantities that can be computed here. Through observations of this type, the known coordinates of a reference station can be used to determine the coordinates of a second station that is 1,000 km from the reference station. This technique of satellite geodesy is known as the geodetic vector step method.

Because it is extremely difficult to make observations at exactly the same time at stations that are remote from one another, observations are carried out in the same time interval (with an accuracy of tenths or hundredths of a second), and the results are then converted to the same moment in time by mathematical means.