Lecture 1: Overview of Satellite Geodesy

Geodesy

  • The discipline that deals with the measurement and representation (geometry, physics, and temporal variations) of the Earth and other celestial bodies (International Association of Geodesy)

Satellite

  • A celestial body orbiting the Earth or another planet

Artificial Satellite

  • An artificial body placed in orbit round the Earth or another planet in order to collect information or for communication

Satellite Geodesy

  • Science of measuring Earth’s geometric shape, orientation in space, and gravitational field using artificial satellites.

Applications of Satellite Geodesy

  • Global Geodesy

    • General shape of the Earth’s figure and gravity field

    • Dimensions of a mean earth ellipsoid

    • Establishment of a global terrestrial reference frame

    • Detailed geoid as a reference surface on land and at sea

    • Connection between different geodetic datums

    • Connection of national datums with a global datum

  • Geodetic Control

    • Establishment of geodetic control for national networks

    • Installation of 3D homogenous networks

    • Analysis and improvements of existing terrestrial networks

    • Establishment of geodetic connections between islands or with the mainland

    • Densification of existing networks up to short interstation distances

  • Geodynamics

    • Control points for crustal motion

    • Polar motion, earth rotation

    • Solid earth tides

  • Applied and Plane Geodesy

    • Detailed plane surveying (cadastral, engineering, GIS, mapping, etc.)

    • Installation of special networks and control for engineering tasks

    • Terrestrial control points in Photogrammetric cameras

    • Control points for Cartography during expedition

  • Navigation and Marine Geodesy

    • Precise navigation of land, sea, and air vehicles

    • Precise positioning for marine mapping exploration, hydrography, oceanography, marine geology, and geophysics

    • Connections of tide gauges (unification of height systems)

  • Related Fields

    • Position and velocity determination of geophysical observations (gravimetric, magnetic, seismic survey) also at sea and in the air

    • Determination of ice motion in glaciology

Global

GPS — USA

  • Official name of GPS is Navigational Satellite Timing and Ranging Global Positioning System (NAVSTAR GPS)

  • The Global Positioning System (GPS) was designed for military applications

  • Its primary purpose was to allow soldiers to keep track of their position and to assist in guiding weapons to their targets

  • The satellites were built by Rockwell International and were launched by the US Air Force

  • The entire system is funded by the US government and controlled by the US Department of Defense

  • The total cost for implementing the system was over $12 billion

  • It costs about $750 million to manage and maintain the system per year

GLONASS: The “other” GPS — Russia

  • Global Navigation Satellite System

  • Two modes:

    • Standard Precision (SP)

    • High Precision (HP)

  • By April 2002, only 8 in operation

  • 3 more launched in 2006, 18 more by 2007-end

  • Aim: to make GLONASS performance comparable by 2010 with GPS and Galileo

  • Fully restored: 2011, 24 satellites

  • Strong at high altitudes

Galileo GPS (ESA) — EU

  • Constellation of 30 satellites in 3 orbital planes inclined at 54° and at an altitude of around 23,000 km

  • Full civilian control, high accuracy

  • Private-public partnerships (PPP)

  • 28 satellites

  • Excellent signal design for geodesy

BeiDou — China

  • 35 satellites

  • Strong Asia-Pacific geometry

  • Now fully interoperable with GPS/Galileo

Regional NSSs

  • Quasi-Zenith Satellite System — Japan

    • Regional focus: Japan / East Asia

    • 4-7 satellites (highly inclined orbits)

    • Always near zenith over Japan

    • Improves urban canyon and mountainous performance

    • Fully interoperable with GPS

  • NavIC (IRNSS) — India

    • Regional focus: India + ~1500 km

    • 7 satellites (GEO + IGSO)

    • Dual-frequency modernization underway

    • Strategic independence for India

Applications of GNSS

  • PNT - Position, Navigation, Timing

  • GNSS surveying

    • International Terrestrial Reference Frame (ITRF) Realization

    • Geodetic Network Establishment

  • Atmospheric studies

    • Tropospheric and ionospheric applications

  • Sea level and Ocean

    • Sea Surface Height

    • Co-location studies

Non-GNSS Satellites used for Geodesy

  • Satellite Radar Altimetry

    • Send radar or laser pulses straight down

    • They provide:

      • Global mean sea level rise

      • Marine geoid validation

      • Ice sheet elevation change

      • Vertical datum realization

      • Coastal sea-level monitoring

    • Altimetry + gravimetry = modern height systems

  • Satellite Gravity Missions

    • Detect tiny changes in gravity, which correspond to mass movement

  • Satellite Laser Ranging (SLR)

    • Used for defining the geocenter (Earth’s center of mass)

    • Absolute scale of the terrestrial reference frame

    • Earth rotation parameters (ERP)

    • Low-degree geavity field

    • Tests of general relativity

  • Synthetic Aperture Radar (SAR)

    • Earthquake deformation

    • Volcanic inflation / deflation

    • Land subsidence (groundwater extraction)

    • Landslides

    • InSAR gives dense spatial coverage where GNSS is sparse

  • Doppler and Radio Tracking Missions

    • Precise orbit determination

    • Plate motion studies

    • Earth rotation

    • Gravity field support

    • Still part of the International Earth Rotation and Reference Systems Service (IERS) geodetic observing system

  • Very Long Baseline Satellites (Indirect, but critical)

    • Earth rotation and reference frames

    • No dedicated satellites — but quasars act as fixed reference points

    • VLBI + SLR + GNSS = global reference frame backbone