GEOMETRI ELLIPSOID DAN ELLIPSOIDA REFERENSI BUMI SERTA KOORDINAT PADA ELLIPSOIDA (BUMI) Bagian 1

Summary

This video explains the geometric concepts of ellipsoids and Earth's reference ellipsoid. It covers the mathematical definition of an ellipsoid, its different forms, including the oblate biaxial ellipsoid, which represents Earth’s shape due to rotational forces. The video also explores the key parameters used to define Earth's reference ellipsoid, including its equatorial and polar radii. The reference ellipsoid is essential for geodesy and positioning systems, providing a model for global coordinates. Future videos will delve into coordinate systems on the ellipsoid, specifically focusing on Earth’s positioning and mapping.

Takeaways

• 😀 The Earth is often modeled as an ellipsoid in geodesy, which is a 3D version of an ellipse where the sum of distances to two foci is constant.
• 😀 There are different types of ellipsoids, such as triaxial and biaxial ellipsoids, with the oblate ellipsoid being the most relevant for Earth.
• 😀 The Earth’s reference ellipsoid is an oblate ellipsoid, meaning it is slightly flattened at the poles and bulging at the equator due to Earth's rotation.
• 😀 The centrifugal force from Earth’s rotation causes it to spread out along the equator, making the equatorial radius larger than the polar radius.
• 😀 The Earth’s reference ellipsoid is widely used in geodesy, GPS, and satellite-based positioning systems like WGS 84.
• 😀 The equatorial and polar radii of the Earth’s reference ellipsoid are approximately 6378 km and 6356 km, respectively.
• 😀 The intersection of the prime meridian and the equator defines the origin for geographic coordinates (0° latitude and 0° longitude), located in the Gulf of Guinea, West Africa.
• 😀 Various ellipsoid models have been proposed, but the WGS 84 ellipsoid is currently the most accurate and widely used model for Earth.
• 😀 Geodesy relies on understanding the Earth’s ellipsoid to accurately measure distances, locations, and satellite data.
• 😀 The use of an ellipsoid model provides a consistent framework for geodetic measurements and mapping at a global scale.

Q & A

What is an ellipsoid in the context of geodesy?

In geodesy, an ellipsoid is a mathematically defined surface that approximates the shape of the Earth, modeled as a three-dimensional shape based on the two-dimensional ellipse. It is used for geodetic and geophysical calculations.

What is the significance of the 'reference ellipsoid' in relation to the Earth?

The reference ellipsoid is a mathematical model used to approximate the Earth's shape. It is specifically tailored to represent the Earth's surface in geodesic calculations and satellite positioning systems. The reference ellipsoid helps standardize measurements and is commonly used in GPS and other geospatial systems.

How does the Earth's rotation affect its shape?

The Earth's rotation causes a centrifugal force that causes the planet to expand at the equator and flatten at the poles, resulting in an oblate spheroid shape. This is why the reference ellipsoid used in geodesy is defined as an oblate rotational biaxial ellipsoid, with the equatorial radius being larger than the polar radius.

What are the key parameters of an ellipsoid?

Key parameters of an ellipsoid include the semi-major axis (a), semi-minor axis (b), and the flattening (f), which is the difference between the major and minor axes divided by the semi-major axis. The eccentricity (e) is another important parameter that indicates the 'elongation' of the ellipsoid.

What is the difference between a biaxial and triaxial ellipsoid?

A biaxial ellipsoid has two equal axes, while a triaxial ellipsoid has three distinct axes of different lengths. The Earth’s ellipsoid is typically modeled as a biaxial ellipsoid, where the equatorial radius (a) is larger than the polar radius (b), but a triaxial ellipsoid may be used for more detailed models of other celestial bodies.

What role does the WGS84 reference ellipsoid play in modern geodesy?

The WGS84 (World Geodetic System 1984) reference ellipsoid is the current standard for positioning and navigation systems, including GPS. It is widely used due to its high accuracy in modeling the Earth's shape and its compatibility with modern satellite systems.

How do scientists use the concept of the ellipsoid to map the Earth?

Scientists use the ellipsoid as a reference surface in geodesic calculations to define coordinates, measure distances, and analyze geographic features. This model simplifies the Earth’s complex shape and allows for accurate representation and measurement of geographic locations.

Why is the Earth’s equatorial radius larger than its polar radius?

The Earth's equatorial radius is larger than its polar radius due to the centrifugal force generated by Earth's rotation. This force causes the Earth to bulge outward at the equator and flatten at the poles, making the equatorial diameter greater than the polar diameter.

What is the role of the Prime Meridian and Equator in defining geographic coordinates?

The Prime Meridian (located at 0° longitude) and the Equator (located at 0° latitude) serve as the reference points for geographic coordinates. They are used to define latitude and longitude on the Earth, with the intersection of the two forming the origin point for global coordinate systems.

How do satellite measurements contribute to understanding the Earth's shape?

Satellite measurements, such as those taken by the Grace mission, help refine our understanding of the Earth's shape by detecting gravitational anomalies and providing precise data on the Earth's ellipsoid model. These measurements verify that the Earth approximates a rotational biaxial ellipsoid, with slight variations due to the planet’s dynamic nature.