ICT 4 GEOMATICS GNSS Positioning PDF

ICT 4 GEOMATICS GNSS positioning: Principles and strategies Prof. MARCO PIRAS The principle of STAND ALONE positioning The concept of point positioning is a trilateration ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS The pr...

ICT 4 GEOMATICS GNSS positioning: Principles and strategies Prof. MARCO PIRAS The principle of STAND ALONE positioning The concept of point positioning is a trilateration ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS The principle of STAND ALONE positioning Is it totally true? ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  The principle of STAND ALONE positioning The concept of point positioning is a trilateration j on space with survey “range” of at least 4 satellites. ri j We can write a range equation for each satellite j: Z i rij (t ) = ( X j (t ) − X I )2 + (Y j (t ) − YI )2 + (Z j (t ) − ZI )2 Y (XYZ) j: satellite coordinates (known by ephemeris) X (XYZ) i: receiver coordinates (unknown) Two questions: 1) How is known the satellite’s position? (Ephemerids see later) 2) How is possible to measure the distance SAT-REC? ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  Point positioning with pseudorange (impulsive / code) tj=0 j(t) i(t) ti=0 Δt ta=0 ( Ri j (t ) = c t j − ti = ct ) but….considering clock offset: Rij = c [t +  j(t) - i(t)] = c [t + i j(t)] i (t) = offset receiver clock (~10-3 s *3*108 m/s= 300 km ) UNKNOWN! ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  Point positioning with pseudorange (impulsive / code) Pseudorange equation (rover-satellite) is: ( Ri j (t ) = r i j (t ) − c  j (t ) +  i (t ) ) ri = j (X j − X ) + (Y i 2 j − Y ) + (Z i 2 j −Z ) i 2 Considering t j as data streaming time from satellite to receiver, time needs to be corrected as : t = t −  (t ) j j j where  j (t ) = a0 + a1 (t − toc ) + a2 (t − toc )2 + tr − TGD t r TGD Relativistic delay and group delay Dividing unknown and known terms: Ri j (t ) + c j (t ) = r i j (t ) − c i (t ) We have to linearize this equation around an approx values : X i( 0 )Yi ( 0 ) Z i( 0 ) X i = X i( 0) + xi ; Yi = Yi ( 0) + yi ; Z i = Z i( 0) + zi ; xi , yi , zi = corrections (unknowns) ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  Point positioning with pseudorange (impulsive / code) ri = j (X j − Xi ) + (Y 2 j − Yi ) + (Z 2 j − Zi ) 2 We have to linearize this equation around an approx values : X i = X i( 0) + xi ; Yi = Yi ( 0) + yi ; Z i = Z i( 0) + zi ; X i( 0 )Yi ( 0 ) Z i( 0 ) = «a priori» values xi , yi , zi = corrections (unknowns) ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS Solution estimated using least squares 𝑌෠ = 𝐴 𝑥ො + 𝑏𝑜 v= 𝑌 − 𝑌෠ ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  Point positioning with pseudorange (impulsive / code) A Positioning is SAT 1 X i( 0 ) − X (1) Yi ( 0 ) − Y (1) Z i( 0 ) − Z (1)  − 1 realized epoch  r 1( 0 )  (0) i ( 2) r i1( 0) r i1( 0)  x Y res by epoch. SAT 2  X i − X Yi ( 0 ) − Y ( 2 ) Z i( 0 ) − Z ( 2 )  − 1 x  R (1) + c (1) − r 1( 0 )   v (1)   r 2 (0)  i   ( 2)   ( 2)  i i r i2 ( 0) r i2 ( 0)  ( 0 ) i ( 3)    Ri + c − r i   v  ( 2) 2(0) Considering 5 satellites SAT 3  X i − X Yi ( 0 ) − Y (3) Z i( 0 ) − Z (3)   yi   ( 3 ) − 1   − Ri + c (3) − r i3( 0 )  =  v (3)   r i3( 0 ) r i3( 0) r i3( 0)  zi     (apex), the  (0)    Ri + c − r i   v  ( 4 ) ( 4 ) 4 ( 0 ) ( 4 ) − Yi ( 0 ) − Y ( 4 ) Z i( 0 ) − Z ( 4 ) − 1 c i   R (5) + c (5) − r 5( 0 )   v (5)  ( 4) linearized X SAT 4  i X model is:  r i4 ( 0 ) r i4 ( 0) r i4 ( 0)   i i     X ( 0 ) − X (5) Yi ( 0 ) − Y (5) Z i( 0 ) − Z (5)  SAT 5  i 5 ( 0 ) − 1  r i r i5 ( 0) r i5 ( 0)  It is better to define the Receiver Clock Offset in meter (multiplied by speed light) to avoid the condition of ill-conditioned matrix. ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  Point positioning GNSS with pseudorange (impulsive / code) G=GPS, R=GLONASS, E=Galileo Three different time reference scale→ three different receiver offsets!!  X r − X 1 G   Yr − Y 1 G   Z r − Z 1G         r 1G     r 1G   −1 00  r 1G r  (0)  r  (0)  r  (0)   X − X 2 G   Yr − Y 2 G   Zr − Z 2 G    r 2 G      −1 0 0 GPS  rr   (0)  r 2G   r  (0)  r 2G   r  (0)     Rr1 G + c 1 G − r r1 G ( 0 )   X r − X   Yr − Y 3 G   Zr − Z 3 G  X r   2 G  3G     −1 0 0   r r3 G   (0)  r 3G    (0)  r 3G    (0)  Y   Rr + c 2 G − r r2 G ( 0 )    r   R 3G + c 3 G − r r3 G ( 0 )  r r  Xr − X  1R  Yr − Y 1 R   Zr − Z1 R    Z r   r   r 1 G     r 1G     r 1G   0 − 1 0  G  −  Rr1 R + c 1 R − r r1 R ( 0 )  = v  r  (0)  r  (0)  r  (0)  c r (t )   R 2 R + c 2 R − r r2 R ( 0 )   GLONASS  X r − X 2 R   Yr − Y 2 R   Zr − Z 2 R   c rR (t )   r1 E       r 2G     r 2G   0 − 1 0  E   Rr + c 1 E − r r1 E ( 0 )   rr  c r (t )   R 2 E  2G  (0)  r  (0)  r  (0) + c 2 E − r r2 E ( 0 )   X − X 1 E    r  Yr − Y  1E  Zr − Z 1E   r 1G      0 0 − 1   rr   r 1G   r 1G    (0)  r  (0)  r  (0) GALILEO    X r − X   Yr − Y   Zr − Z  2 E 2 E 2 E      0 0 − 1  r 1G   (0)  r 1G    (0)  r 1G    (0)   r r r  ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS Point positioning with carrier phase (sinusoidal) ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS Point positioning with carrier phase L1, L2 e L5 (  20 cm) Range =   (phase displacements) + n° cycles from t0 Phase ambiguity N j 1 Clock offsets i j(t)  i (t ) = j r ij (t ) + N i j + f j  i j (t ) t0  Z Nij N is a new unknown for Nij each satellite Y c(t) ij(t) ij(t0) ➔ N is constant, if i X continuous satellite c(t0)=0 tracking (no cycle slip) ’(t) ➔ Positioning only N estimation (Initialization). ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS Source J. DuttonICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  Point positioning with carrier phase (kinematic) Model is similar to code case, but phase ambiguities are included: SAT 1  X i( 0 ) − X (1) Yi ( 0 ) − Y (1) Z i( 0 ) − Z (1)  x  (i1) 0 0 0 0 − 1 i   (0) r 1( 0 ) i r i1( 0) r i1( 0)   yi   Xi − X Yi ( 0 ) − Y ( 2 ) Z i( 0 ) − Z ( 2 )   ( 2) SAT 2 0 (i 2) 0 0 0 − 1 zi   i + c − r i   v  (1) (1) 1( 0 ) (1)  r 2 (0) r i2 ( 0) r i2 ( 0)  ( 0 ) i ( 3)  N i   i + c − r i   v  (1) ( 2) ( 2) 2(0) ( 2) SAT 3  Xi − X Yi ( 0 ) − Y (3) Z i( 0 ) − Z (3) 0 0 (i 3) 0 0 − 1 N i( 2 )  −  i(3) + c (3) − r i3( 0 )  =  v (3)   r i3( 0 ) r i3( 0) r i3( 0)  ( 3)      (0)  N i   i + c − r i   v  ( 4) ( 4) 4(0) ( 4 ) − ( 4) Yi ( 0 ) − Y ( 4 ) Z i( 0 ) − Z ( 4 ) − 1 N ( 4 )    (5) + c (5) − r 5( 0 )   v (5)   X X SAT 4 i 0 0 0 (i 4) 0  r i4 ( 0 ) r i4 ( 0) r i4 ( 0)  i   i i     X ( 0 ) − X (5) Yi ( 0 ) − Y (5) Z i( 0 ) − Z (5)  N i(5)   i 5(0) 0 0 0 0 (i 5) − 1   c i  SAT 5  r i r i5 ( 0) r i5 ( 0) It is necessary to collect more epochs to estimate the ambiguities. When N are estimates, they are removed by unknowns. The procedure devoted to estimate N is called INITIALIZATION. ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  TIME REFERENCE SCALE The «Time» is one of the main observations in the GNSS positioning, and each system has a own time reference scale. The more importand stardard are: TAI (International Atomic Time) is a very accurate time scale defined by the radiation of the cesium atom and maintained by 200 atomic clocks located in more than 70 laboratories around the world. The instant zero is fixed at January 1st 1958, and in a day TAI there are exactly 86400 seconds GMT (Greenwich Mean Time Medium) is based on celestial observations related to the time of Earth's rotation. The changes in the rotational speed of the delay with respect to the GMT time of atomic clocks. UTC (Coordinated Universal Time), which was adopted for the definition of time zones. Derived from GMT but it is not based on the observation of celestial phenomena but is maintained by atomic clocks. The difference between the two time scales is maintained with a maximum deviation of 0.9 s, every 1.5 years by applying the correction of 1 or leap second, since 1972. ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  TIME REFERENCE SCALE The time scale TAI that originates in 1958, differs from UTC time, starting from 1972, additional leap seconds and the difference between the two scales, 2016, is 37 seconds. GPS time is maintained by the atomic clock of the Master Control Station, without any correction for the astronomical Earth's rotation. On 6/1/1980, was perfectly coincided with the UTC time. Due to the fixes it departs today from the UTC time of 18 leap seconds (+ 1s in DEC 2016). https://gssc.esa.int/navipedia/index.php/Time_References_in_GNSS#:~:text=GPS%20Time%20(GPST)%20is%20a,5th%20to%206th%201980%20(6. ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  TIME REFERENCE SCALE The GLONASS time (GLONASST) is kept by the clock of the Central Syncronizer Maser (CS) Time and is periodically corrected by an integer number of seconds (leap seconds) to align it with the UTC time. The time scale Soviet UTC (SU) = UTC + 3 hours (with a difference of 1 ms) Galileo Time: GST (Galileo System Time): starts at 00:00 on 22 August 1999. The navigation message contains the coefficients used to calculate the offset between the GST and scale the UTC and GPS for interoperability between constellations. time scale Beidou: BDT (Beidou navigation satellite system Time). The start time is 00:00:00 on January 1, 2006 UTC time. periodically checked to have an offset to UTC time less than 100 ns ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  REFERENCE SYSTEM Each constellation has a different referent system, therefore the coordinates are defined in different ways: GPS → WGS84 GLONASS → PZ90 GALILEO → GTRF BEIDOU → CTRF It is needed to transform the coordinates into a unique RS (WGS84) (see next section) ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  BIASES Sat. Clock error Pseudorange Ephemeris error IONO delay multipath Carrier Phase range TROPO delay phase center Rec. Clock error antenna variation ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  BIASES & Spatial Correlation Biases can have spatial or time correlation (spatial correlation is usually stronger), can be depending or not on signal frequency (different on L1 and L2) Nature of bias Bias Spatial correlation Not dispersive Ephemeris High on big distance (>100 km) (frequency independent) Troposphere Regional (about 10 km) Not dispersive Receiver clock Identical on the same station (but frequency dep.) Satellite clock Identical on the same satellite Dispersive Ionosphere Regional (about 10 km) (depending on f and they are Multipath No correlation. Site depending different on L1 o L2) center phase No correlation. Site depending antenna variation ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  BIASES & Spatial Correlation Biases can have spatial or time correlation (spatial correlation is usually stronger), can depend or not on signal frequency (different on L1 and L2) It is possible to distinguish between “DISPERSIVE” or “NOT DISPERSIVE” biases, considering if the effect generates a spreading out or dispersion of the signals. Bias Source Dispersive Spatial correlation Frequency dependency Ephemerids NO High but with long distance NO (>100 km) Satellite clock offset NO Identical in the same satellite YES Receiver clock offset NO Identical in the same station YES Ionospheric delay YES Regional (about 10 km) YES Tropospheric delay YES Regional (about 10 km) NO Multipath NO NO YES Phase center Variation NO NO YES ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS Atmospheric delays ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS IONOSPHERIC DELAY ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  IONOSPHERIC DELAY Source :ASI Matera TEC means Total Electron Content, and it is a measure of the total number of free electrons in a column of the Earth's ionosphere along the line of sight between satellite and receiver. TEC is typically expressed in TEC units (TECU), with 1 TECU equal to 10^16 electrons per square meter. ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  IONOSPHERIC DELAY Ionospheric delay changes with position, time and sun activities; it is correlable with lenght of baseline (spatial correlation) Effect changes from few mm/s to 2 cm/s. → Update correction: every 10s Ionospheric delay could be estimated with a model, for example, Klobuchar: Only 50% of delay is removed!! It is based on 8 parameters: 4 ION_ALPHA and 4 ION_BETA They define the coefficients of a polynomial function (3° degree), which allows to estimate the zenith delay and model period ION_ALPHA and ION_BETA usually are in the header of the navigation file (see later) ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  IONOSPHERIC DELAY 0:00-2:45 2:45-5:30 5:30-8:15 8:15-11:00 11:00-13:45 13:45-16:30 16:30-19:15 19:15-22:00 22:00-24:00 ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS IONOSPHERIC DELAY ION (ver) a elev ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  IONOFREE COMBINATION (L3) Ionospheric delay could be modelled with: B1 B2 B1 B2 R1 = − 2 − 4... R2 = − 2 − 4... B depends on the electronic density (TEC) f1 f1 f2 f2 Bi = Ai  N i (h)ds N= electronic density and depend on height h, r0 A = constant to be estimated, s= path B1 Working with high frequencies, 2° terms is negligible: R = − f2 It is possible to remove the ionospheric delay, making a combination so called IONOFREE with L1 and L2 (defined in m) : f12 f 22 LIONO − FREE = 2 L1 − 2 L2 = f1 − f 22 f1 − f 22  2.54 L1 − 1.54 L2 But increasing the noise, that is bigger than single L1 or L2 ( 3 times)  IONO − FREE = 2.552 + 1.552  L  3 L ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  Ionospheric Scintillation (or fluctuation) Ionospheric scintillation is a rapid fluctuation in the amplitude and phase of radio signals from GNSS satellites when it pass in the IONOSPHERE. These fluctuations are caused by small- scale irregularities in the ionosphere, which can occur in regions of high electron density, such as the equatorial and polar regions. GNSS scintillation can lead to errors in the calculated position and timing information provided by GNSS receivers, especially in regions where the ionosphere is highly variable. ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  TROPOSPHERE & EPHEMERIS Troposphere - Wet and Dry component Zenith value: 2-3 m. It changes with a “mapping function” described by 1/cos z; It changes slower than ionospheric delay ➔ update correction: every 10-30 seconds; it is very difficult to separate ephemeris error from tropospheric delay. They are often considered together as geometrical biases. Ephemeris It changes slowly (quickly if the constellation changes (IODE)) ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  TROPOSPHERE & EPHEMERIS ZTD (zenith total delay) ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  TROPOSPHERIC DELAY It is possible to estimate a model (e.g.Hopfield, Saastamoinen …) ZTD (zenith total delay) K L Rtrop = + cos( z 2 + 6,25) cos( z 2 + 2,25) P Dry component: K = 155.28 * 10 −7 ( 40136 + 148.72TK ) TK z eP Wet component L = ( −0.028512TK + 817.96) TK2 Rtrop = (R0 – R) tropospheric error Mapping function: R = geometrical range 1/cos (z) R0 = range measured P = pressure [millibar]; TK = temperature [K] eP = partial vapour pression ICT for geomatics: [millibar] navigation and maps - 01QWUBH Prof. PIRAS TROPOSPHERIC DELAY Elevation mask or cut off angle ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  Water contents and precipitations GPS PWV measurements were used both operationally to track a North American Monsoon event and forecast flash flooding. Circles represent PW (cm) for radiosondes at San Diego, California (blue), and Yuma, Arizona (black). Solid traces show GPS PW measurements at San Diego, California (blue), Durmid, California (red), Glamis, California (black), and Yuma, Arizona (dotted black). Arrows indicate the times of passage of an upper low at the identified GPS-Met sites. https://doi.org/10.1029/2018GL081318 ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  EPHEMERIDES ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  EPHEMERIDES Orbita / Accuracy latency rate Clock Broadcast Orbit  100 cm Real time daily Clock sat. RMS  5 ns   2.5 ns Ultrarapid Orbit  5 cm Real time 15 minutes (predicted) Clock sat. RMS  35 ns   1.5 ns Ultrarapid Orbit  3 cm 3–9 15 minutes (observed) Clock sat. RMS  150 ps   50 ps hours Rapid Orbit  2.5 cm 17 – 41 15 minutes Clock sat. RMS  75 ps   25 ps hours 5 minutes Final Orbit  2.5 cm 12 – 18 15 minutes Clock sat. RMS  75 ps   20 ps days 30 seconds ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS PHASE CENTER VARIATION (PCV) ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  PHASE CENTER VARIATION (PCV) Phase center variation depends on satellite elevation. It is usually considered with cylindrical symmetry. CHOKE RING - L1.0 1.4 2.4 3.2 3.8 4.2 4.4 4.6 4.7 4.8 4.7 4.5 4.2 3.7 3.0 2.0.7.0.0 Geodetic Antenna - L1.0 4.6 8.9 12.6 15.8 18.3 20.0 20.9 21.1 20.6 19.5 18.1 16.3 14.5 13.0 12.0 11.8.0.0 Calibration: it is made by producer or NGS (www.ngs.noaa.com) in comparison to a reference antenna. Sometimes it can be different, in particular if satellite has low elevation. Source: NGS ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  PHASE CENTER VARIATION (PCV) Wubbena et al, (2000) have proposed a calibration using an antenna movement, considering azimuth and elevation TYPE= LEIAT503 NO OF FREQUENCIES=2 OFFSETS L1=-0.00055 0.00046 0.06083 OFFSETS L2=-0.00012 0.00019 0.08499 ELEVATION INCREMENT=5 AZIMUTH INCREMENT=5 VARIATIONS L1= -0.00799 -0.00513 -0.00260 -0.00026 0.00189 0.00374 0.00511 0.00588.... -0.00790 -0.00502 -0.00247 -0.00012 0.00204 0.00388 0.00524 0.00598.... -0.00782 -0.00492 -0.00236 0.00001 0.00217 0.00402 0.00536 0.00608.... -0.00777 -0.00484 -0.00226 0.00011 0.00229 0.00413 0.00545 0.00615.... -0.00774 -0.00477 -0.00218 0.00020 0.00238 0.00421 0.00553 0.00621.... -0.00772 -0.00472 -0.00211 0.00027 0.00244 0.00427 0.00557 0.00624.... -0.00772 -0.00467 -0.00206 0.00031 0.00247 0.00429 0.00558 0.00625.... -0.00772 -0.00463 -0.00203 0.00033 0.00247 0.00427 0.00556 0.00623.... -0.00774 -0.00461 -0.00202 0.00031 0.00243 0.00422 0.00552 0.00619.... -0.00775 -0.00461 -0.00203 0.00027 0.00236 0.00415 0.00544 0.00613.... -0.00777 -0.00463 -0.00208 0.00019 0.00227 0.00405 0.00535 0.00605........................... ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  MULTIPATH ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS PHASE CENTER VARIATION (PCV) ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  INTER-CHANNEL BIAS (ICB) The signal makes the following paths: Satellite-antenna (it is unique for all satellites) From antenna to electronic receiver components ➔ several biases Lki ,GLO for each satellite K It could be devided in: Constant part Li,GLO Inter-channel biases  Lki ,GLO = Li ,GLO +  ik,IC to calibrate or estimate GLONASS equation: Rik,GLO (t ) + c ik,GLO (t ) = r ik,GLO (t ) − c i ,GLO (t ) + cLki ,GLO = ( ) = r ik,GLO (t ) − c  i ,GLO (t ) − Li ,GLO + c  ik, IC ICB estimation is MANDATORY with carrier phase positioning (high precision) ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  ERRORS (total budget) VALUE* = VALUE + BIASES + AE + GE where VALUE = real values (range) VALUE* = pseudorange or carrier phase obs. BIASES = systematic errors AE = accidental errors → measurements noise → 1%  GE = gross error (outlier) → error due to human factor ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  POSITIONING Not modelled error clock (receiver and satellite) ephemeris bias ionospheric delay tropospheric delay others (multipath, phase center antenna variation, receiver noise …) ➔ The presence of bias decreases position accuracy. For high positioning accuracy we can follow two ways: 1) Relative positioning The aim is to reduce common bias by differencing the position of two receivers. Differential positioning: The aim is to reduce common bias by differencing position of two receivers. 2) Precise Point Positioning (PPP): The aim is to model bias in a combined phase and code observations in a single receiver. ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  JAMMING Jamming is the presence of a competing signal that prevents the GNSS receiver from decoding the real satellite signal. Jamming from other sources of radio transmission can be intentional (malicious) or unintentional. Unintentional jamming: Radar or communication transmitters, although operating in a different frequency band, may interfere with GNSS reception due to their scattering power. Intentional jamming: GNSS jammers, although illegal in most countries, are readily available on the Internet. Announced as privacy jammers, they can disable GNSS reception over several kilometres. ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  Some critical aspects Russia’s Jamming Force Could Isolate Ukrainian Troops—So Artillery Can Destroy Them https://https://www.forbes.com/ ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  Some critical aspects Russia expected to ditch GLONASS for Loran in Ukraine invasion https://www.gpsworld.com/russia-expected-to-ditch-glonass-for-loran-in-ukraine-invasion/ ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  SPOOFING Spoofing is the intentional transmission of fake GNSS signals to divert users from their real position. Spoofing requires sophisticated equipment to recreate satellite signals. Spoofing is more difficult to detect than jamming. ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS  SPOOFING ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS WHAT ARE THE POSSIBLE RISKS? ICT for geomatics: navigation and maps - 01QWUBH Prof. PIRAS