I am reading text on physical geodesy. It says, we can not compute the gravity potential directly because we don't have sufficient information of density structure of the Earth. Why is so?
Despite significant advancements in geophysical techniques and technologies, we still do not have sufficient knowledge about the density structure of the entire Earth for several reasons:
The Earth's interior is inaccessible: The deepest hole ever drilled on Earth, the Kola Superdeep Borehole, is only 12 kilometers deep, which is only a tiny fraction of the Earth's radius of 6,371 kilometers. This means that most of the Earth's interior is beyond our reach, making it challenging to study the density structure of the Earth's core and lower mantle.
Variations in density: The Earth's density is not uniform, and it varies with depth, temperature, and pressure. Therefore, studying the density structure of the Earth requires detailed measurements at different depths and locations, which can be challenging.
Limited geophysical data: While several geophysical techniques, such as seismic tomography, have been developed to study the Earth's interior, they provide only indirect information about the Earth's density structure. Moreover, these techniques have limited spatial resolution and coverage, making it challenging to study the density structure of the entire Earth.
Complexity of the Earth's interior: The Earth's interior is a complex system, and its density structure is influenced by several factors, including the distribution of elements and minerals, phase changes, and the presence of partial melting zones. Understanding the density structure of the Earth requires a comprehensive understanding of these complex processes.
Overall, while significant progress has been made in studying the density structure of the Earth, we still have a long way to go before we can fully understand the composition and structure of our planet's interior. We must use new techniques.
The gravity potential is a measure of the strength and direction of gravity at different points on the Earth's surface. It depends on the distribution of mass within the Earth, which in turn is related to the density structure of the Earth.
However, we do not have direct measurements of the density structure of the Earth. We can only infer it from indirect measurements such as seismic waves, gravitational anomalies, and magnetic anomalies. These methods provide information about the Earth's interior but are limited in their resolution and accuracy.
Furthermore, the Earth's density structure is not uniform and varies with depth. This means that even if we have accurate measurements at one depth, we cannot directly extrapolate them to other depths without making assumptions about the Earth's composition and structure.
As a result, it is not possible to compute the gravity potential directly from the density structure of the Earth. Instead, we use mathematical models and techniques such as spherical harmonics and the finite element method to approximate the gravity potential based on available data and assumptions about the Earth's density structure.