GNSS reflectometry
GNSS reflectometry 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 centre[1] and is also known as GPS reflectometry.
Deliberately bouncing signals off something to learn about it (e.g. radar, echolocation) is active sensing; sensing what is already available in the surrounding environment without changing the environment to do so (e.g. eyesight, hearing) is passive sensing. 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). As a result, the Delay Doppler Map as basic data product is obtained on which further analyses rely.
The receiver can be of different kind: Stationary stations, ship measurements, air planes or satellites, like the UK-DMC satellite, part of the Disaster Monitoring Constellation built by Surrey Satellite Technology Ltd. It carries 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.[2][3]
GPS signal reflections have also been used to measure soil moisture and snow depth[4] as well as other variables in the cryosphere like sea ice presence[1], thickness and age.
References
- ^ a b Komjathy, A.; Maslanik, J.; Zavorotny, V.U.; Axelrad, P.; Katzberg, S.J. (2000). "Sea ice remote sensing using surface reflected GPS signals". IGARSS 2000. IEEE 2000 International Geoscience and Remote Sensing Symposium. Taking the Pulse of the Planet: The Role of Remote Sensing in Managing the Environment. Proceedings (Cat. No.00CH37120). 7. Honolulu, HI, USA: IEEE: 2855–2857. doi:10.1109/IGARSS.2000.860270. ISBN 978-0-7803-6359-5.
- ^ Gleason, 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. doi:10.1109/TGRS.2005.845643.
- ^ 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.
- ^ GPS: Got plenty of snow?, Phil Berardelli, ScienceNOW Daily News, 29 September 2009.
Further reading
- Zavorotny, Valery U.; Gleason, Scott; Cardellach, Estel; Camps, Adriano (2014). "Tutorial on Remote Sensing Using GNSS Bistatic Radar of Opportunity". IEEE Geoscience and Remote Sensing Magazine. Vol. 2, no. 4. pp. 8–45. doi:10.1109/MGRS.2014.2374220. ISSN 2168-6831.
- Larson, Kristine M.; Small, Eric E.; Braun, John; Zavorotny, Valery (2014). "Environmental Sensing: A Revolution in GNSS Applications". InsideGNSS. Vol. 9, no. 4. pp. 36–46. ISSN 1559-503X.
- Cardellach, Estel (2015): E-GEM – GNSS-R Earth Monitoring; State of the Art Description Document.
External links
- Reflecting on the future, The Engineer Online, 28 November 2006.
- GNSS Applications and Methods, Artech House, September 2009.