Name: earth shape and gps height models
Uploaded: 2025-03-26T15:38:43.000Z
Duration: 1 min 28 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Earth and Space Science

Earth's Place in the Universe

9-12.ESS.1.2.e

Geoid and Ellipsoid

أفضل وصف للأرض هي شكل بيضاوي الشكل ، أو كروي مفلطح ، يتكون من تدوير القطع الناقص حول محوره الصغير. هذا الشكل مسطح قليلا عند القطبين، حيث يكون المحور القطبي أقصر بحوالي 21 كيلومترا من المحور الاستوائي.في المقابل، يمثل الجيود شكل الأرض بناء على قوى الجاذبية، ويتماشى بشكل وثيق مع متوسط مستوى سطح البحر أو MSL فوق المحيطات عند استبعاد التأثيرات الخارجية مثل المد والجزر. إنه سطح متساوي الجهد، مع جاذبية تعمل بشكل عمودي في جميع النقاط. على عكس الشكل الإهليلجي الأملس ، فإن الجيود غير منتظم بسبب اختلافات التوزيع الكتلي ، مما يتسبب في تموجات MSL العالمية التي تصل إلى 100 متر.تاريخيا، أشار المساحون إلى MSL أو الجيود باستخدام مستويات الروح، مع التركيز على القياسات المحلية. ومع ذلك، يوفر نظام تحديد المواقع العالمي (GPS) الحديث منظورا عالميا، يقيس الارتفاع بالنسبة إلى الشكل الإهليلجي. استنادا إلى النظام الجيوديسي العالمي لعام 1984 ، يجب تحويل هذه البيانات باستخدام نموذج جيود لتقريب MSL للاستخدام العملي.  تحسب ملاحظات GPS الإحداثيات الديكارتية في نظام متمحور حول الأرض وثابت الأرض ، والتي يتم تحويلها إلى إحداثيات جغرافية مثل خطوط العرض والعرض والارتفاع لرسم الخرائط والمسح الدقيق.

الجيود والإهليلجي

أفضل وصف لشكل الأرض هو شكل بيضاوي الشكل ، وهو كرة مسطحة قليلا تم إنشاؤها عن طريق تدوير القطع الناقص حول محورها الصغير. ينتج عن هذا التسطيح أن يكون المحور القطبي أقصر بحوالي 21 كيلومترا من المحور الاستوائي. في المقابل ، يمثل الجيود شكل جاذبية الأرض ويتماشى مع متوسط مستوى سطح البحر (MSL). الجيود هو سطح متساوي الجهد غير منتظم حيث تكون الجاذبية متعامدة في كل نقطة. تتسبب الاختلافات في توزيع كتلة الأرض في حدوث تموجات جيودية ، مما يؤدي إلى اختلافات MSL عالمية تصل إلى 100 متر. تقليديا ، تم قياس المسافات الرأسية باستخدام مستويات الروح ، في إشارة إلى MSL أو الجيود. كانت هذه الطريقة مناسبة للمسوحات الصغيرة ولكنها تجاهلت الشكل الإهليلجي للأرض والتأثيرات الجيوديسية العالمية. يستخدم المسح الحديث تقنية GPS ، التي تقيس الارتفاعات بالنسبة لنموذج بيضاوي الشكل ، مثل النظام الجيوديسي العالمي 1984 (WGS 84). WGS 84 ، المتوافق مع النظام المرجعي الجيوديسي 1980 (GRS 80) ، يشتمل على بيانات الأقمار الصناعية لتحسين قياسات حجم الأرض وشكلها وقوى الجاذبية ، مما يحسن الدقة بشكل كبير. يستخدم نظام الإحداثيات المتمحور حول الأرض والثابت على الأرض (ECEF) على نطاق واسع لوصف المواضع على الشكل الإهليلجي. يعود أصل هذا النظام الديكارتي إلى مركز كتلة الأرض ، حيث يمتد المحور x إلى خط الاستواء عند خط الزوال في غرينتش ، والمحور y عموديا على المحور x على المستوى الاستوائي ، والمحور z محاذاة مع المحور القطبي ، عموديا على المستوى xy. باستخدام نظام تحديد المواقع العالمي (GPS) ، يمكن حساب الإحداثيات الديكارتية وتحويلها إلى خطوط الطول والعرض والارتفاع الإهليلجي. يتم تحويل هذه الإحداثيات إلى أنظمة مثل إحداثيات مستوى الحالة ، للمهام العملية مثل المسح ورسم الخرائط. يضمن دمج البيانات الإهليلجية والجيويدية الدقة في القياسات الجغرافية المكانية وتطبيقات تحديد المواقع العالمية.

The Earth's shape is best described as an ellipsoid, a slightly flattened sphere created by rotating an ellipse around its minor axis. This flattening ...

Education

JoVE Core

Civil Engineering

الهندسة المدنية

Unit 1

الوحدة الأولى

Global Positioning System (GPS)

نظام تحديد المواقع العالمي (GPS)

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الرئيسية

earth shape and gps height models

Earth shape and GPS height models are explained using the ellipsoid, the geoid, and modern coordinate systems. The Earth is best described as an ellipsoid, which is a slightly flattened sphere formed by rotating an ellipse around its minor axis. This flattening makes the polar axis about 21 kilometers shorter than the equatorial axis.

The geoid shows a different side of Earth’s shape. It is the Earth’s gravitational shape and matches mean sea level, or MSL. The geoid is an irregular equipotential surface, which means gravity is perpendicular to it at every point. Because Earth’s mass is not evenly distributed, the geoid has undulations. These changes can make global MSL differ by as much as 100 meters.

Surveying once relied on spirit levels to measure vertical distance from MSL or the geoid. That method worked well for small surveys, but it did not account for the Earth’s ellipsoidal shape or larger geodesic effects. Modern surveying uses GPS technology instead. GPS measures heights relative to an ellipsoidal model such as the World Geodetic System 1984, or WGS 84.

WGS 84 is aligned with the Geodetic Reference System 1980, or GRS 80. It uses satellite data to improve measurements of Earth’s size, shape, and gravitational forces. The Earth-Centered, Earth-Fixed, or ECEF, coordinate system is also used to describe positions on the ellipsoid. In this Cartesian system, the origin is at Earth’s center of mass. The x-axis reaches the equator at the Greenwich meridian, the y-axis lies on the equatorial plane and is perpendicular to the x-axis, and the z-axis follows the polar axis and is perpendicular to the xy-plane.

GPS can be used to calculate Cartesian coordinates and then convert them into latitude, longitude, and ellipsoidal height. These coordinates can also be transformed into systems such as state plane coordinates for surveying and mapping. Using both ellipsoidal and geoidal data improves precision in geospatial measurements and global positioning applications.

Earth Shape and GPS Height Models

introduction to global positioning system

introduction-to-global-positioning-system

How GPS Satellites Find Your Location

The Global Positioning System, or GPS, finds a location on Earth by using satellites and radio signal timing. It changed how people navigate and how many industries work. GPS was developed in 1978 by the U.S. Department of Defense for military use. It became available for civilian use in 1983. GPS satellites orbit in medium Earth orbit about 20,200 kilometers above Earth. Each satellite takes about 11 hours and 58 minutes to complete one orbit. A full GPS constellation has 24 satellites, which...

errors in global positioning system

GPS Error Sources and Accuracy Limits

GPS accuracy can change because of signal delays, reflections, and device problems. These errors come from the atmosphere, nearby surfaces, satellites, and the receiver itself. To get reliable positioning, GPS systems must reduce these effects as much as possible. As GPS signals pass through the ionosphere and troposphere, they slow down. The ionosphere contains charged particles and is strongly affected by solar activity. The troposphere contains water vapor, which also changes how the signal...

geoid and ellipsoid

Earth shape and GPS height models are explained using the ellipsoid, the geoid, and modern coordinate systems. The Earth is best described as an ellipsoid, which is a slightly flattened sphere formed by rotating an ellipse around its minor axis. This flattening makes the polar axis about 21 kilometers shorter than the equatorial axis. The geoid shows a different side of Earth’s shape. It is the Earth’s gravitational shape and matches mean sea level, or MSL. The geoid is an irregular...

field application of global positioning system

field-application-of-global-positioning-system

GPS Field Mapping for Surveying Sites

Global Positioning System (GPS) helps map field locations for surveying, navigation, and infrastructure work. Satellite signals let a GPS receiver find an object’s position very quickly, often in less than a second. This speed makes GPS a practical tool for fieldwork. Modern GPS receivers are small, light, and energy efficient. They are built for portable use in real field conditions. GPS signals use the microwave spectrum, so they can work in rain and fog. Even so, ionospheric disturbances...

types of global positioning system surveys

types-of-global-positioning-system-surveys

GPS Surveying for Accuracy and Speed

GPS surveying uses different methods to balance accuracy, speed, and field conditions. The main approaches are static GPS, kinematic GPS, and real-time kinematic (RTK) surveying. Each one collects position data in a different way, so each fits a different kind of surveying and mapping job. Static GPS uses two receivers. One stays at a known reference point, and the other is placed at the target point. It measures several satellite ranges over a long time, which can give centimeter-level...

design example: identifying the locations of monuments in the field using global positioning system device

design-example-identifying-locations-monuments-field-using-global

GPS Surveying for Park Monument Coordinates

Global Positioning System (GPS) surveying can be used to find the coordinates and elevations of park monuments. Surveyors use this method to measure precise points on Earth. In this survey, GPS receivers were used to locate two monument markers and record their height above the ground model. The work began with mission planning. Surveyors checked satellite visibility and tried to reduce Position Dilution of Precision, or PDOP, which is a measure of how satellite geometry can affect accuracy. A...

key terms and concepts

Learn how the ellipsoid, geoid, WGS 84, and ECEF coordinates work together in GPS surveying, mapping, and Earth height measurements.

Earth Shape and GPS Height Models | JoVE K12

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Earth Shape and GPS Height Models

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