Next: 1.4 Applications of Satellite Up: I. Introduction to Space Previous: 1.2 Basic concepts of
Next: 1.4 Applications
of Satellite Up: I. Introduction
to Space Previous: 1.2 Basic
concepts of
Some of the first significant events:
1957: Launch of SPUTNIK-1: the Doppler shift signal can be used to get precise position anywhere (exact time of closest approach + ephemerides -John Hopkins Appl. Physics Lab.-)
1958: Earth flatenning from satellite
data (
)
1958: Launch of EXPLORER-1
1959:
Third zonal harmonic (pear shape of the earth)
1960: Launch of
TRANSIT-1B
...
1962: Geodetic connection between France and
Algeria
...
1964: Connection between diferent datums (
m).
There are 3 phases:
1) 1958-1970: development of basic methods for the satellite computation and observation.
2) 1970-1980: Scientific projects and new observation techniques: SLR, TRANSIT and satellite altimetry.
3) 1980-1993: Operational use of satellite techniques in geodesy, geodynamics and surveying (first results with GPS, reemplacement of astrometric methods)
4) 1993-now: Exhaustive use of GPS; altimeters, Synthetic Aperture Radar (SAR) -TOPEX, ERS-I, ERS-II, ENVISAT,...-.
Presently (February 2009) GPS, especially, and also GLONASS satellite-based navegation systems are working nowadays.
New Global Navigation Satellite Systems (GNSS) are planned to provide service soon: the European project Galileo (since 2013?) and the Chinese system Compass (since 2011?)
Moreover, motivated in improving service for civil aviation (in particular for integrity) new Augmentation systems of GPS have been developed in the last years: Satellite Based Augmentation systems (SBAS, such as WAAS, EGNOS, MSAS in USA, Europe and Japan respectively) and Ground Based Augmentation Systems (GBAS), still under development, specific for landing in airports..
GNSS functioning are based on three segments:
SPACE SEGMENT: formed by the constellation of satellites transmitting the ranging signals.
CONTROL SEGMENT, responsible for steering the whole system, typically a master station coordinating all activities, monitor stations forming the tracking network and ground antenntas as upward/downward communication link to the satellites.
USER SEGMENT, which comprises the GNSS receivers and which can be considered from different aspects: user categories (civil/militar), receiver types (single/multifrequency, single/multiconstellation, type of observables...) and “information services” (International GNSS Service...).