GNSS and Remote Sensing for Agriculture PDF

Module M.SIA.I14M GIS and Remote Sensing for Agriculture L3: GNSS and its application Dr Jayan Wijesingha [email protected] +49 561 804-1245 GNSS GNSS stands for Global Navigation Satellite System GPS is the most popular GNS...

Module M.SIA.I14M GIS and Remote Sensing for Agriculture L3: GNSS and its application Dr Jayan Wijesingha [email protected] +49 561 804-1245 GNSS GNSS stands for Global Navigation Satellite System GPS is the most popular GNSS, which become a system for everyday life GPS – Global Positioning System https://www.lifewire.com/smartphone-or-car-gps-1683388 2 https://gssc.esa.int/navipedia/index.php/Handheld_Outdoor_Receivers  In old days before GNSS https://classic-sailing.com/article/the-many-uses-of-the-marine-sextant/ Celestial bodies based navigation Sextants Navigational charts/maps Radar/Sonar navigation Innovative navigation system Iter-Avto https://en.wikipedia.org/wiki/Nautical_chart 3 https://www.dailymail.co.uk/news/article-2147617/Iter-Avto-The-antique-route-The-sat-nav-1930-used-map-scroll.html Principle of Radionavigation Trilateration Time of arrival (tk) measurements 𝑟𝑟𝑘𝑘 = 𝑐𝑐. 𝑡𝑡𝑘𝑘 Distance (rk) to position (x, y) 𝑟𝑟𝑘𝑘 = 𝑥𝑥𝑘𝑘 − 𝑥𝑥 2 − 𝑦𝑦𝑘𝑘 − 𝑦𝑦 2 (Misra and Enge 2006) For 2D position, minimum three distance measurements must be known 4 Principle of GNSS (Misra and Enge 2006) 5 GNSS by names - I NAVSTAR GPS GLONASS Navigation System Globalnaya with Timing and Navigazionnaya Ranging Global Sputnikovaya Sistema Positioning System Since 2012 Since 1995 Russian MoD US MoD 24 satellites in 31 satellites in operation operation By https://www.glonass-iac.ru/guide/gnss/, Public Domain, By https://www.glonass-iac.ru/guide/gnss/, Fair use, https://commons.wikimedia.org/w/index.php?curid=56886687 https://en.wikipedia.org/w/index.php?curid=53414087 6 GNSS by names - II GALILEO BDS European Global BeiDou Navigation Navigation Satellite Satellite System System Chinese system Since 2016 Since 2000 ESA and 9 non-EU 35 satellites in countries operation 22 satellites in operation By Unknown author - http://www.esa.int/, Public Domain, By https://www.glonass-iac.ru/guide/gnss/, Fair use, https://commons.wikimedia.org/w/index.php?curid=42733223 https://en.wikipedia.org/w/index.php?curid=53414150 7 GNSS by names - III IRNSS QZSS Indian Regional Quasi-Zenith Satellite Navigation Satellite System System Japanese system Since 2013 Since 2010 7 satellites in 5 satellites in operation operation By https://www.glonass-iac.ru/guide/gnss/, Fair use, https://en.wikipedia.org/w/index.php?curid=53414113 8 GNSS - Components - Determined ephemerides Space Segment - Calculated Almanacs L1-carrier - Status of satellites - Time impulse - Time corrections - Ephemerides From ground to - Almanac control stations - Status - Date, time User Segment Control Segment (Zogg 2011) 9 Space segment – Satellite system Consist GNSS satellites constellation Each satellite contains up to 4 atomic clocks Each satellite transmits its precise position and time as a radio wave (wikipedia.com) Signal needs ca. 67.3 ms to the measurement point on earth at nadir gssc.esa.int/navipedia Space segment – Signal transmission Satellite time, synchronisation signal, ephemerides, time correction procedure, almanac, correction signal for calculation of run time, data on Ionosphere, technical status of satellite  duration 12.5 min Signal is transmitted with C/A-Code (Coarse/Acquisition-Code) on frequency of 1,023MHz (L1-channel) Each satellite has unique code of 1023 numbers (binary code) pattern has a length of 1 ms and is used for identification and measurement of run time 11 Control segment – Ground stations Master stations e.g., GPS has 2 master stations Adjust satellite orbit parameters and high precision clock Data uploading stations Monitoring station e.g. GPS has 16 monitoring stations (NovAtel 2015) Installed over broad geographic area Monitor satellite’s signals and status 12 User segment Consist of equipment that processes the received signal from the GNSS satellite Antenna Receiver Processing units (NovAtel 2015) 13 Selective availability (SA) Until May 2000 precision of GPS signal was artificially decreased Latest generation of satellites not supposed to have this possibility anymore (Zogg 2011) 14 Dilution of precision (DoP) Dilution of precision (DOP) is a measure of satellite geometry and indicates the quality of the GPS measurement (NovAtel 2015) 15 GNSS error sources Contributing source Error range Satellite clocks ± 2.0 m Orbit errors ± 2.5 m Ionospheric delays ± 5.0 m Tropospheric delays ± 0.5 m Receiver noise ± 0.3 m Multipath ± 1.0 m 16 Effect of atmosphere Atmosphere causes delays of satellite signal 4 to 5 m difference due to atmospheric disturbances Measured distance to satellite Ionosphere Troposphere Actual distance to satellite 17 Multipath Smooth surfaces (e.g., water) or high objects (e.g., buildings) can reflects the GNSS signal Leads to higher inaccuracy 18 Other errors Satellite clock and orbit error Continuously controlled and corrected Faulty antenna and or receiving devices Measurement noise 19 How to increase position accuracy Two-frequency measurement (L1/L2): Phase shift between different frequency bands (L1 und L2) used Geophysical correction models: only useful for confined areas Differential-GPS (DGPS) Post processing Real time 20 DGPS Rover Simultaneous reception of the same Base satellites Differential correction can be done real-time (RTC) or afterwards (post processed) 21