Earth Curvature and GPS Surveying - Essay Example

 Earth Curvature, and GPS Surveying Introduction GPS is a system capable of providing position information anywhere on earth, a constellation of orbiting satellites, various orbits around the earth, NAVSTAR GPS, and it is also a user receivers acquired signal and determines its position. GPS (Global Positioning System) is a triangulation-based technology which was developed by DOD that cost them $10 billion. The purpose of which is it can operate in any kind of weather, it has a non-stop operation which means it can operate 24 hours and is always available anywhere. It has also a very economical use, it increases productivity, customer service is improved and the accuracy (3-D data, Velocity timing) is not a question. GPS is used mostly on land, sea and airborne navigation, also in surveying, geophysical exploration, mapping and geodesy, vehicle location system, farming and transportation systems. Also for telecommunication infrastructure applications include network timing and enhanced 999 for mobile users. It is also important to global delivery of precise and common time to fixe and mobile users. How does the GPS work? Under the GPS System components are three segments, 1) the user segment, 2) the control segment and 3) the space segment. The GPS System Components In the user segment we find GPS user equipment that are portable and fixed and are used by military and civilian for navigation, surveying and GIS. In the control segment are also two uses. One is ground facilities which are responsible for: 1) satellite tracking, 2) telemetry, 3) orbit and ephemeris computations, 4) up-linking of the computed data, 5) supervising the daily management of the space segment, 6) five ground control stations (Monitor Stations), 7) one Master Control Station. The second use is the Master Control Station that: 1) receive tracking data from the monitor stations, 2) calculates satellites ephemeris, 3) adjust satellite clocks, 4) maneuvers satellites if needed, 4) encrypts signals and 5) maintain GPS reference system (WGS84). The space segment likewise has also different uses like 1) constellation of 24 satellites, 2) in six orbital planes around the equator (60 degrees apart), 3) four satellite per orbit and 4) orbital planes inclined 55 degrees from the equator. Characteristics of GPS Satellite: a) seven satellites are typically visible 10 degrees or more above the horizon, b) each satellite is about 2 to 3k lbs, c) satellites orbit the earth every 12 hours, d) time can be figured to within 100 nano secs. There are several basic concept of GPS Satellites: 1) satellites are reference points to locations on earth (their locations are known), 2) a location of a point on earth is identified by “triangulation”, 3) signals from the three satellites are used, 4) travel time of each signal is determined, 5) signals travel at the speed of light (distance = travel time x speed of light. The triangulation equation has 3 variables and one is, where exactly are the satellites? From orbital mechanics, the location of satellites are determined, an almanac of orbital information for all satellites are stored in each satellite and a ground control-stations continuously update location information of each satellite and transmit it to them (i.e. ephemeris). The second variable is: how long does it take for the radio signal to travel the distance. Under this equation are the functions of satellite like maintain an accurate time using on board atomic clocks, another is receive and store data transmitted by the control stations such as constellation almanac and individual ephimeris and still another is to transmit signal containing time and orbital information to the user receiver. The third variable is how far is the point from the satellite. Pointers for survey: Identify points to be surveyed, for example, stations. First group should contain a control station and each group should include at least one station from another group – pivoting station. All stations in a group should be observed during the same session and pivoting stations are observed twice. Collect GPS data at each station and process the data in the office using corrections at the control station. Results of the field data gathering at National Watersports Centre, Holme Pierrepont, Nottingham. Results of the field data gathering at the watersports centre. The following are the results of the data gathering done at the National Watersports Centre: The steps done were, first, station A was established in one of the corners of the lake. Then another station B was set on the other corner of the lake. The horizontal distance from point A to B was recorded together with the horizontal angles as well as the vertical angles. After taking the shots at point A, the instrument was transferred to point B. The instrument reading was again recorder for taking the shot back at point A. The same procedure was done in taking the shots back at A and recording the horizontal distance, horizontal angles and the vertical angles. This time point C was established at still another corner of the lake and shots were taken from point B to point C, recording the same data done in point A. The instrument was again transferred to point C. Shots were taken for points A and B, and establishing point D, recording the same information needed. The last step was transferring the instrument at point D and taking shots at point A,B C. The recorded field notes are then taken to the field office for checking and editing for production for a topographic drawing. Field notes taken At point A At point B At point C At point D A – B B – A C – A D – A HD- 54.008 HD – 54.039 HD – 2224.212 HD – 46.796 HL – 152 22 00 HL – 100 17 45 HD - 197 52 50 HL – 102 47 40 HR – 332 22 11 HR - 280 17 40 HR - 17 52 35 HR – 282 47 35 VL - 90 01 57 VL – 89 59 40 VL – 90 00 15 HL – 90 02 50 VR – 270 00 50 VR – 270 00 50 VR – 270 00 50 VR – 269 57 20 B – C C – B D – A HD – 2224.701 HD – 2224.760 HD – 2226.066 HL - 66 12 25 HL - 196 29 10 HL - 15 40 05 HR - 266 12 35 HR - 16 29 00 HR - 15 40 05 VL - 90 01 07 VL - 90 00 10 VL - 90 00 10 VR - 269 59 31 VR - 269 59 20 VR - 269 59 55 C – D D - B HD - 46.797 HD - 2225.438 HL - 106 00 20 HL - 14 16 25 HR - 285 59 20 HR - 144 16 25 VL - 89 56 20 VL - 90 00 05 CR - 270 04 00 VR - 269 59 25 From the field data gathered the coordinates are computed and written in tabulated form The northings of point b is an erroneous result Computations: From the field data, we will check by computation the length of A-B Line A-B Easting Northing 462574.184 340049.414 462610.589 340009.591 36.405 39.823 Line A-B =  where a = difference of eastings of A and B =  b = difference of northings of A and B =  Line A-B = 53.956 For Line BC Eastings Northings 462610.589 340009.591 460965.890 338513.505 1644.70 1496.09 Line B-C =  Line B-C = 2223.158 For Line C-D Eastings Northings 460965.890 338513.505 460934.110 338484.048 31.780 The northings of line CD is not correct. The computations for the correct northings must be done. We will have to get the length of line C-D from the field data recorded. Line CD = 46.797 (Line CD)2 = a2 + b2  = 2 + b2 b2 = (46.797)2 - (31.780)2 b =  b = 34.35, compute for the value of the northings of point D 338513.505 + 34.350 338547.855 For Line DA Eastings northings 462574.184 340049.414 460934.110 338547.855 1640.074 1501.559 Line DA =  =  Line DA = 2223.628 The tabulations below is the corrected coordinates of point D From the table of the coordinates, we will be able to compute for the bearing, azimuth departure and the latitude. By using a programmable calculator that is especially used in the computations of surveys, I achieved the following results, Bearing Distance Azimuth Latitude Departure A-B S 42°23’ E 54.009 317°37’ -39.894 +36.407 B-C S 46°19’W 2223.876 46°19’ -1535.969 -1608.236 C-D N 42°46’W 46.796 137°24’ +34.354 -31.775 D-A N 46°19’E 2223.628 226°19’ 1535.969 1608.236 After we have computed for the bearing, we can now compute for the distance between the stations. We can also solve for the azimuth. The departure and latitude can also be computed. In the early days of surveying, all computations are done manually. Calculations done manually are more prone to mistakes. The surveying instruments used are even suggestive of errors. These days, surveying instruments results are more precise and accurate. There are scientific calculators which can be programmed to perform the computations of survey results. In the data gathering that was done, the survey results that are presented are edited and then produced as professional topographic drawing. A sketch of the rowing lake was plotted using the coordinates of the survey results. At Point A Bearing = S 42° 23’ E Distance = 54.00 Azimuth = 317°.37’ Int. Angle = 88°42’ At Point B Bearing = S 46°19’ W Distance = 2223.158 Azimuth = 46° 19’ Int. Angle = 91° 18’ At Point C Bearing = N 42°46’ W Distance = 2223.876 Azimuth = 137° 24’ Int. Angle = 89° 05’ At Point D Bearing = N 46°19’ E Distance = 46.796 Azimuth = 226° 19’ Int. Angle = 90° 55’ Sketch of the Rowing Lake Plotted by Coordinate System References Johnston, H., Redd, T., Tabrizi, A. GPS in Land Surveying. 2008. Edited by D. Spalton for the University of Derby. Gillesania, Dit. Civil Engineering Formulas Series. www.gertcrev.com. 2006. Diego Inocencio Tapang Gillesania Davis, Raymond E., Foote, Francis S., Kelly, Joe W., Surveying, Theory and Practice. 1980. McGraw Hill Book Company. Brinker, Russell C., Minnick, Roy, Modern Geodetic Engineering Handbook. 1987. Van Nostrand Reinhold Company Czerniak, Robert J., Reilly, James P., National Transportation. 1998. Booksgoogle.com/books?isbn=0309061164 Read More