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Why was Lageos placed in a high orbit above Earth?

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Diagram showing the deflection of the vertical from the geoid to the ellipsoid or spheroid, with labeled lines for geoid, spheroid, rock surface, ocean, and geoid height in a geology context. — geoid Deflection of the vertical from the geoid to the spheroid.

Lageos (Laser Geodynamic Satellite) was placed in a high, nearly circular orbit at an altitude of approximately 6,000 kilometers to minimize the influence of two specific factors that could interfere with precise geodetic measurements: atmospheric drag and local gravity anomalies.1

By positioning the satellite at this significant elevation, scientists were able to reduce the disruptive effects of the atmosphere and localized gravitational variations, allowing for more accurate tracking of the satellite's orbit. However, this high altitude also results in the attenuation of the gravitational effects being studied, as these signals decrease with distance from the Earth. Consequently, while Lageos is highly effective for determining certain long-wavelength features of the Earth's gravity field, measurements of surface gravity are still required to capture smaller-scale, local effects.1