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 idea of using reflected GNSS signal for earth observation became more and more popular in the mid-1990s at
NASA Langley Research Center[1] and is also known as GPS reflectometry. Research applications of GNSS-R are found in
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 (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 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.[4][7]
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abGleason, S.; Hodgart, S.; Yiping Sun; Gommenginger, C.; MacKin, S.; Adjrad, M.; Unwin, M. (2005). "Detection and Processing of bistatically reflected GPS signals from low Earth orbit for the purpose of ocean remote sensing". IEEE Transactions on Geoscience and Remote Sensing. 43 (6): 1229–1241.
Bibcode:
2005ITGRS..43.1229G.
doi:
10.1109/TGRS.2005.845643.
S2CID6851145.
Emery, William and Camps, Adriano (2017): Introduction to Satellite Remote Sensing 1st Edition Atmosphere, Ocean, Land and Cryosphere Applications, Chapter 6: Remote Sensing Using Global Navigation Satellite System Signals of Opportunity, Elsevier, 20th September 2017, Paperback
ISBN9780128092545, eBook
ISBN9780128092590