GNSS reflectometry (or GNSS-R) involves making measurements from the reflections from the Earth of navigation signals from Global Navigation Satellite Systems such as

GPS The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...

. The idea of using reflected GNSS signal for earth observation became more and more popular in the mid-1990s at NASA Langley Research Center and is also known as ''GPS reflectometry''. Research applications of GNSS-R are found in * Altimetry * Oceanography (Wave Height and Wind Speed) * Cryosphere monitoring * Soil moisture monitoring GNSS reflectometry is passive sensing that takes advantage of and relies on separate active sources - the satellites generating the navigation signals. For this, the GNSS receiver measures the signal delay from the satellite (the pseudorange measurement) and the rate of change of the range between satellite and observer (the Doppler measurement). The surface area of the reflected GNSS signal also provides the two parameters time delay and frequency change. As a result, the

Delay Doppler Map Delay (from Latin: dilatio) may refer to: Arts, entertainment, and media * ''Delay 1968'', a 1981 album by German experimental rock band Can * ''The Delay'', a 2012 Uruguayan film People * B. H. DeLay (1891–1923), American aviator and acto ...

(DDM) can be obtained as GNSS-R observable. The shape and power distribution of the signal within the DDM is dictated by two reflecting surface conditions: its

dielectric properties In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...

and its roughness state. Further derivation of geophysical information rely on these measurements. GNSS reflectometry works as a bi-static radar, where transmitter and receiver are separated by a significant distance. Since in GNSS reflectometry one receiver simultaneously can track multiple transmitters (i.e. GNSS satellites), the system also has the nature of multi-static radar. The receiver of the reflected GNSS signal can be of different kinds: Ground stations, ship measurements, airplanes or satellites, like the UK-DMC satellite, part of the Disaster Monitoring Constellation built by Surrey Satellite Technology Ltd. It carried a secondary reflectometry payload that has demonstrated the feasibility of receiving and measuring GPS signals reflected from the surface of the Earth's oceans from its track in low Earth orbit to determine wave motion and windspeed.M. P. Clarizia ''et al.''
Analysis of GNSS-R delay-Doppler maps from the UK-DMC satellite over the ocean
Geophysical Research Letters, 29 January 2009.

References

External links

The Engineer Online, 28 November 2006.

Artech House, September 2009. Satellite navigation Remote sensing

See also

References

Further reading

External links