Task 2 Satellite Geodesy

Task 2 Satellite Geodesy 1. Geodetic Astronomy a. General Characteristics The Geodetic Astronomical System is the oldest satellite geodetic system (system which uses the help of celestial objects whose coordinates are known). For example, the geodetic astronomical system has been used since 1884 for determination latitude carefully at Potsdam and contributed since 1890 to the observations polar movement. Geodetic astronomy is based on observations Bintang, although limited to certain applications, is still used today. The basic principles of geodetic astronomy use the evolving nature of the earth towards the sun, rotates periodically, and the properties of other celestial objects. Astronomical observations aims to determine geographic latitude and longitude, as well as azimuth on land (terrestrial). In geodetic astronomy, based on the rules of spherical astronomy, the orientation of the local gravity vector, and the astronomical azimuth of the terrestrial landmark determined from observations of several stars. Several types of deep calculations geodetic astronomy, including: - Gravimetric calculations will produce the gravity force which is magnification of the acceleration vector of the gravity field. - Terrestrial geodetic calculations will produce horizontal angles, distances, and zenith angle. - Height difference calculation - Calculation of surface point locations. b. Known Parameters The known parameter in the geodetic astronomy system is the sun's declination and the latitude and longitude of the observer's location. c. Measured Quantity The quantities measured are the observation time, the angle between the sun and the target, sun height angle (zenith and tilt angle), air pressure, and temperature. d. How to get the position of a point from parameters and their magnitudes Determining position using the Geodesic Astronomy method can be done by two ways, namely: Sun height method - When observing, look for the sun's declination and sun height angle and correct them with wrong index. - Then calculate the value of intermediate refraction (rm), barometer correction factor (cp) and temperature correction (ct), refraction value (r), and parallax value. r = rm x Cp x Ct Calculate the vertical angle from the center of the earth to the sun if using the zenith angle z = zu – s.i + r – p If using an oblique angle, h = hu - s.i – r + p Calculate the azimuth value, cos A= sin  - (sin  sin z / (cos  cos z)) After getting the azimuth, find the coordinates of the specified point using coordinates of frame points as a reference. Time angle method - Look for the UT value - Convert degrees of longitude into units of time by dividing by 15o - Then find the value of t, t = UT + E +  -24 Search Amatahari, tan Amatahari = -sin t /  -t – If the target is to the right of the sun then, A= Amatahari +  If the target is to the left of the sun then, A= Amatahari-  Then, using azimuth, find the coordinates of the point with using the coordinates of the frame points as a reference. 2. SLR (Satellite Laser Ranging) a. General Characteristics Satellite Laser Ranging (SLR) is an absolute positioning system most thorough at the moment. SLR is based on measuring the distance with a laser to a satellite equipped with a laser retro reflector. The working principle of SLR is distance measurement measures the time interval required for the pulses emitted by the transmitter laser to the satellite and back to the transmitting location. b. Known Parameters The known parameters of the positioning system using the SLR method are laser wavelength (λ), latitude and altitude of the observing station (H), correction satellite eccentricity, eccentricity correction on the ground, refraction correction, and errors randomness and bias remain. c. Measured Quantity The quantity measured in the SLR method is the laser pulse travel time interval which is fired from the observation station towards the satellite and then reflected back to the observer station on earth (Δt), the laser frequency (f(λ)), then the distance between the satellite and the observing station (d). d. How to get the position of a point from parameters and their magnitudes - The distance between the satellite and the observing station can be formulated using the following equation: c. Δt 2 d = + Δdo + Δds + Δdb + Δdf + Δdr + η c = Speed of light Δt = Laser pulse travel time Δdo = Eccentricity correction in the ground Δds = Eccentricity correction at the satellite Δ db = Signal delay in the ground system Δ dr = Refractive correction η = Remaining random error and bias The laser frequency parameter (f(λ)) can be calculated using the equation: 𝑓(λ) = 0,9650 + 0,0164 λ 2 + 0,000228 λ 4 Where, λ = laser wavelength (m) - The local function of the laser station f (φ,H) is: 𝑓(ϕ, 𝐻) = 1 − 0.026 cos 2ϕ − 0.00031H Where, φ = Latitude of the observing station H = Height of the observation station (km) LLR (Lunar Laser Ranging) a. General Characteristics Lunar Laser Ranging (LLR) is a method of measuring distances between the surface of the Earth and Moon using a laser range. Distance can be calculated based on the time interval of light pulses reflected back to the earth by the surface the Moon or with one of the five retroreflectors installed on the Moon. LLR is one of the old systems but until now this system is still the same used and applied in the field of geodesy, including: - Careful determination of the absolute position of the point - Determination of earth orientation parameters - Determination of the gravitational constant of the earth and moon - Determination of the moon's orbit and variations in its rotation - Study of the lunar gravity field - Study of the dynamic interactions of the earth and moon as well - Determination of relativity parameters b. Known Parameters The parameters that need to be known in the LLR system are the inner telescope coordinates CTS system (rE), reflector coordinates on the moon in the barycentric system (mR), coordinates telescopes in the barycentric system (r0), lunar coefficients, and the speed of light. c. Measured Quantity The only quantity that needs to be measured in practice with the LLR system is the distance from Earth to Moon (ρ). However, there are several phenomena that influence the magnitude These are tides, abrasion, plate movement and relativity effects d. How to get the position of a point from parameters and their magnitudes The working principle of the LLR system is to fire a laser beam from the station at Earth on the reflector located on the Moon, then the rays will be reflected returned to Earth to determine the distance from Earth to the Moon. The CST system has a different system from the barycentric system because the influence of the earth's rotation, polar movement, precession and nutation. As is phenomena that influence the size of distance, in determining distance must also be corrections were made to the calculations. By analyzing data the size from the Earth to the Moon can be known rotation parameters of the Earth to the Moon, dynamics of the Earth-Moon system, as well as parameters relativity, can be determined observer station coordinates, reflector coordinates, position month and many other things related to position. VLBI (Very Long Baseline Interferometry) a. General Characteristics VLBI (Very Long Baseline Interferometry) is a method used to determine very precise distances using radio telescopes to studying the earth, the universe and monitoring its changes. In geodesy satellites, the VLBI method is seen as a relative positioning technique with using phase data from radio waves emitted by quasars, i.e celestial bodies that emit natural radio waves. Every VLBI station generally equipped with a receiver, atomic clock (oscillator), and data recorder (recorder). VLBI systems generally operate on 2 frequency bands, namely the X-band The wavelength is around 4 cm with a frequency of around 8 GHz and S-band. The wavelength is around 15 cm with a frequency of around 2 GHz. Weakness VLBI requires a large and expensive observation station. VLBI system used for geodetic applications, such as: - Realization of coordinate reference frames - Determination of earth orientation parameters - Geodynamic studies b. Known Parameters In a VLBI system, the parameters that must be known are the speed of light, quasar coordinate vector, and relative position between the two observing stations. c. Measured Quantity The quantity measured in the VLBI system is the difference in signal travel time from the quasar to the two station system, the phase difference of the two signals, and the speed of the both delays. d. How to get the position of a point from parameters and their magnitudes The VLBI working system is to observe the delay from the time difference journey. tobs known as signal “delay” is the difference in travel time between 2 VLBI antennas located above the earth's surface. tobs in the form of signal "noise", microwaves emitted by quasars/other cosmological radio sources. Tobs can be calculated with the following equation: Δtobs= Δtg +Δ tclock +Δ tinst +Δ ttrop+ Δ tionos +Δ t rel + … Where, Δtclock = Delay bias due to clock unsynchronization Δtinst = Delay bias in cables/other instruments Δ ttrop = Bias delay effect of toposphere refraction Δ tionos = Bias delay due to ionospheric refraction Δ t rel = Relativity effect delay bias. Δtg = Data geometric delay GPS (Global Positioning System) a. General Characteristics GPS (Global Positioning System) is a system for determining position and global navigation using satellites. GPS or NAVSTAR system GPS (Navigation Satellite Timing and Ranging Global Positioning System), has three segments, namely: • Satellites, tasked with receiving and storing transmitted data by controlling stations, storing and maintaining time information high precision (determined by atomic clocks on satellites), and transmit signals and information continuously to the receiving aircraft (receiver) from the user. • Controller, functions to control and control the satellite from the earth (checking satellite health, determining and predicting orbit and time, time synchronization between satellites, and sending data to the satellites). • Receiver, tasked with receiving data from satellites and processing it for determine the position (three-dimensional position, namely coordinates on the earth and altitude), direction, distance, and time required by the user. There are two The types of recipients are: - Navigation type (Trimble Ensign, Trimble Pathfinder, Garmin, Sony, etc etc). - Geodetic type (Topcon, Leica, Astech, Trimble 4000 series, etc.). GPS satellites that orbit the earth, with a fixed orbit and position (the exact coordinates) totaling 24 with 21 in active condition works and the remaining 3 pieces are spare. Basically GPS signals can be divided into 3 components, namely distance information (code) in the form of P code and C/A code, information satellite position (navigation message), and carrier wave (carrier beat phase). There are 3 types of GPS devices, each of which provides a level different degrees of accuracy, namely: - Navigation Type (Handheld, Handy GPS), the position accuracy provided by this type can only reach 3 to 6 meters. - Single frequency geodetic type (mapping type), used in surveys and mapping that requires positional accuracy of around centimeters to several decimeters. - Dual Frequency Geodetic Type, provides position accuracy up to millimeter. b. Known Parameters The parameters that must be known when determining position with GPS are coordinates of 3 or 4 satellites and the datum used. c. Measured Quantity The quantity measured in the GPS system is the distance between the satellite and the point of interest determined position on the Earth's surface. d. How to get the position of a point from parameters and their magnitudes Determining position with GPS is divided into two methods, namely: • Absolute / point positioning method. This method determines position based on 1 receiver (receiver) just. Position accuracy within a few meters (not high accuracy) and usually only intended for navigation purposes. • Relative / differential positioning method This method determines position using more than one receiver. One GPS is installed at a certain location on the earth and continuously will receive a signal from the satellite within a certain period of time and will serve as a reference for others. This method produces positions high precision (generally less than 1 meter) and is applied for geodetic survey or mapping needs that require high accuracy.