GPS DerivedHgts1

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Published on February 11, 2008

Author: Renato

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GPS-Derived Heights Part 1 Development and Description of NGS Guidelines:  GPS-Derived Heights Part 1 Development and Description of NGS Guidelines To understand how to achieve GPS-derived orthometric heights at centimeter-level accuracy, three questions must be answered: :  1) What types of heights are involved? • Orthometric heights • Ellipsoid heights • Geoid heights 2) How are these heights defined and related? 3) How accurately can these heights be determined? To understand how to achieve GPS-derived orthometric heights at centimeter-level accuracy, three questions must be answered: Slide3:  Leveled Height Differences A C B Topography Slide4:  Level Surfaces and Orthometric Heights Level Surfaces Plumb Line “Geoid” PO P Level Surface = Equipotential Surface (W) H (Orthometric Height) = Distance along plumb line (PO to P) Earth’s Surface Ocean Mean Sea Level Geopotential Number (CP) = WP -WO WO WP Heights Based on Geopotential Number (C):  Heights Based on Geopotential Number (C) Normal Height (NGVD 29) H* = C /   = Average normal gravity along plumb line Dynamic Height (IGLD 55, 85) Hdyn = C / 45 45 = Normal gravity at 45° latitude Orthometric Height H = C / g g = Average gravity along the plumb line Helmert Height (NAVD 88) H = C / (g + 0.0424 H0) g = Surface gravity measurement (mgals) Slide6:  Equipotential Surfaces HC HA Reference Surface (Geoid) HAC  hAB + hBC Observed difference in orthometric height, H, depends on the leveling route. A C B Topography  hAB  h = local leveled differences Leveled Height vs. Orthometric Height =  hBC H = relative orthometric heights Slide7:  27 Satellites 6 Planes, 55° Rotation 4/5 Satellites /Plane 20,183 km Orbit 1 Revolution /12 Hrs Global Positioning System Slide8:  Z Y X -Z -X -Y Zero Meridian Mean Equatorial Plane Slide9:  Earth-Centered-Earth-Fixed Coordinates Z Axis X Axis Y Axis (X,Y,Z) Earth’s Surface Zero Meridian Mean Equatorial Plane P Origin (0,0,0) Center of Mass X Y Z Conventional Terrestrial Pole The Ellipsoid:  The Ellipsoid N b a S f = a-b = Flattening a a = 6,378,137.000 meters (semi-major axis) 1/f = 298.25722210088 (flattening) Geodetic Reference System 1980 a = Semi major axis b = Semi minor axis b = 6,356,752.3141403 m (semi-minor axis) Slide11:  GPS - Derived Ellipsoid Heights   Z Axis X Axis Y Axis (X,Y,Z) = P (,,h) h Earth’s Surface Zero Meridian Mean Equatorial Plane Reference Ellipsoid P Slide12:  Ellipsoid, Geoid, and Orthometric Heights “Geoid” PO P H (Orthometric Height) = Distance along plumb line (PO to P) Earth’s Surface Ocean Mean Sea Level Ellipsoid “h = H + N” N h Q N (Geoid Height) = Distance along ellipsoid normal (Q to PO) h (Ellipsoid Height) = Distance along ellipsoid normal (Q to P) Plumb Line Ellipsoid Heights (NAD 83 vs. ITRF 97):  Ellipsoid Heights (NAD 83 vs. ITRF 97) NAD 83: Origin and ellipsoid (GRS-80) a = 6,378,137.000 meters (semi-major axis) 1/f = 298.25722210088 (flattening) ITRF 97: Origin (best estimate of earth’s C.O.M.) NAD 83 is non-geocentric relative to ITRF97 origin by 1 - 2 meters ITRF 97 ellipsoid heights: Use a NAD 83 shaped ellipsoid centered at the ITRF97 origin Ellipsoid height differences between NAD 83 and ITRF97 reflect the non-geocentricity of NAD 83 Slide14:  Simplified Concept of ITRF 97 vs. NAD 83 2.2 meters NAD 83 Origin ITRF 97 Origin Earth’s Surface h83 h97 Identically shaped ellipsoids (GRS-80) a = 6,378,137.000 meters (semi-major axis) 1/f = 298.25722210088 (flattening) Slide15:  NAD83(86) to ITRF97(97) Ellipsoid Heights (meters) High Resolution Geoid Models:  High Resolution Geoid Models G96SSS 1.8 million gravity measurements (marine, land, altimetry) 30 second DTED updated with Canadian Rockies data Earth Gravity Model of 1996 (EGM96) 2 min x 2 min spacing International Terrestrial Reference Frame ITRF94 (1996.0) GEOID96 Begin with G96SSS model 2951 GPS/Level Bench Marks (NAD83/NAVD88) Converts NAD83 (86) into NAVD 88 Relative to non-geocentric GRS-80 ellipsoid High Resolution Geoid Models G99SSS (Scientific Model):  High Resolution Geoid Models G99SSS (Scientific Model) 2.6 million terrestrial, ship, and altimetric gravity measurements 30 arc second Digital Elevation Data 3 arc second DEM for the Northwest USA Decimated from 1 arc second NGSDEM99 Earth Gravity Model of 1996 (EGM96) Computed on 1 x 1 arc minute grid spacing GRS-80 ellipsoid centered at ITRF97 origin Slide18:  NGSDEM99 is a 1 x 1 arc-second Digital Elevation Model (DEM) of the Northwest United States, covering the region 39 - 49N latitude, and 234 - 265E longitude. High Resolution Geoid Models GEOID99:  High Resolution Geoid Models GEOID99 Begin with G99SSS model 6169 NAD83 GPS heights on NAVD88 leveled benchmarks Determine national bias and trend relative to GPS/BMs Create grid to model local (state-wide) remaining differences ITRF97/NAD83 transformation Compute and remove conversion surface from G99SSS Relative to non-geocentric GRS-80 ellipsoid 4.6 cm RMS nationally when compared to BM data RMS 16% improvement over GEOID96 Slide21:  For the conterminous United States (CONUS), GEOID99 heights range from a low of -50.97 meters (magenta) in the Atlantic Ocean to a high of 3.23 meters (red) in the Labrador Strait. GEOID99 Tidal Datums:  Tidal Datums Heights Measured Above Local Mean Sea Level National Tidal Datum epoch; 19 year series Encompasses all significant tidal periods including 18.6 year period for regression of Moon’s nodes Averages out nearly all meteorological, hydrological, and oceanographic variability Leveling is used to determine relationship between bench marks and tidal gauges Slide24:  AL, AK, CA, CT, FL, GA, LA, MD, MS, NJ, NY, NC, OR, RI, SC, WA Privately Owned Uplands State Owned Tidelands Territorial Seas State Submerged Lands Contiguous Zone Exclusive Economic Zone Federal Submerged Lands High Seas Privately Owned State Owned TX 3 n. mi. 12 n. mi. 200 n. mi. Privately Owned State Owned DE, MA, ME, NH, PA, VA MHHW MHW MLLW Importance of Shoreline Chart Datum National Geodetic Vertical Datum 1929 (NGVD 29):  National Geodetic Vertical Datum 1929 (NGVD 29) Defined by heights of 26 tidal stations in U.S. and Canada Tide gages were connected to the network by leveling from tide gage staffs to bench marks Water-level transfers used to connect leveling across Great Lakes Normal Orthometric Heights: H* = C /  C = model (“normal”) geopotential number  = from normal gravity formula H* = 0 level is NOT a level surface Slide27:  First-Order Leveling Network NGVD 29 North American Vertical Datum 1988 (NAVD 88):  North American Vertical Datum 1988 (NAVD 88) Defined by one height (Father Point/Rimouski) Water-level transfers connect leveling across Great Lakes Adjustment performed in Geopotential Numbers Helmert Orthometric Heights: H = C / (g + 0.0424 H0) C = geopotential number g = surface gravity measurement (mgals) H0 = approximate orthometric height (km) H = 0 level is nearly a level surface H = 0 level is biased relative to global mean sea level Slide29:  Vertical Control Network NAVD 88 NGVD 29 Versus NAVD 88:  NGVD 29 Versus NAVD 88 Datum Considerations: NGVD 29 NAVD 88 Defining Height(s) 26 Local MSL 1 Local MSL Tidal Epoch Various 1960-78 (18.6 years) Treatment of Leveling Data: Gravity Correction Ortho Correction Geopotential Nos. (normal gravity) (observed gravity) Other Corrections Level, Rod, Temp. Level, Rod, Astro, Temp, Magnetic, and Refraction NGVD 29 Versus NAVD 88 (continued):  NGVD 29 Versus NAVD 88 (continued) Adjustments Considerations: NGVD 29 NAVD 88 Method Least-squares Least-squares Technique Condition Eq. Observation Eq. Units of Measure Meters Geopotential Units Observation Type Links Between Height Differences Junction Points Between Adjacent BMs NGVD 29 Versus NAVD 88 (continued):  NGVD 29 Versus NAVD 88 (continued) Adjustments Statistics : NGVD 29 NAVD 88 No. of Bench Marks 100,000 (est) 450,000 (US only) Km of Leveling Data 75,159 (US) 1,001,500 31,565 (Canada) Published Information: Orthometric Height Type Normal Helmert Orthometric Height Units Meters Meters Gravity Value Normal “Actual” Slide33:  Height Differences Between NAVD 88 and NGVD 29 Expected Accuracies:  Expected Accuracies GPS-Derived Ellipsoid Heights 2 centimeters Geoid Heights (GEOID99) 2.5 cm correlated error (randomizing at 40 km) Relative differences typically less than 1 cm in 10 km 4.6 cm RMS about the mean Leveling-Derived Heights Less than 1 cm in 10 km for third-order leveling GPS-Derived Ellipsoid Height Guidelines:  GPS-Derived Ellipsoid Height Guidelines GPS related error sources Pilot projects were used to develop guidelines NOAA Technical Memorandum NOS NGS-58 Execution of Surveys; Sources of Error:  Execution of Surveys; Sources of Error Errors may be characterized as random, systematic, or blunders Random error represents the effect of unpredictable variations in the instruments, the environment, and the observing procedures employed Systematic error represents the effect of consistent inaccuracies in the instruments or in the observing procedures Blunders or mistakes are typically caused by carelessness and are detected by systematic checking of all work through observational procedures and methodology designed to allow their detection and elimination GPS Error Sources:  GPS Error Sources Precise or broadcast orbit error Satellite relationship center-of-mass to L1 antenna phase center Satellite clock error (nominal) SA dither (minimized) Satellite inter-channel bias L1-L2 antenna phase center offset Transmission multipath Ionospheric effects Tropospheric effects Dry (hydrostatic) troposphere delay Wet troposphere delay Multipath Antenna phase center variation Circular polarization L1-L2 phase center offset Receiver clock offset Receiver inter-channel bias Height of phase center above mark Marker stability Earth tides - direct effect Ocean tide loading Atmospheric loading Crustal motion Slide40:  The images compare the accuracy of GPS with and without selective availability (SA). Each plot shows the positional scatter of 24 hours of data (0000 to 2359 UTC) taken at one of the Continuously Operating Reference Stations (CORS) operated by the NCAD Corp. at Erlanger, Kentucky. On May 2, 2000, SA was set to zero. The plots show that SA causes 95% of the points to fall within a radius of 45.0 meters. Without SA, 95% of the points fall within a radius of 6.3 meters. As illustration, consider a football stadium. With SA activated, you really only know if you are on the field or in the stands at that football stadium; with SA switched off, you know which yard marker you are standing on. Atmospheric Error Sources:  Atmospheric Error Sources Ionosphere Greatest at 1400 (local time) Typical 5 to 15 m at zenith Extreme 0.15 to 50 m at zenith Higher frequencies have less effect Error correction by dual frequency “Wet” Troposphere 10% of total effect Model accuracy only 10 to 50% Need humidity along path About 20 cm at zenith Hydrostatic (“Dry”) Troposphere 90% of total effect Model accuracy only 2 to 5% Need surface atmospheric pressure and temperatures Accurate pressure is critical About 2.2 m at zenith Signal Multipath:  Signal Multipath Satellite signal arriving at receiver via multiple paths due to reflection (Leick 1995) Quasi-periodic signal; 5 to 50 minutes Maximum multipath is a fraction of wavelength (L1 = 19 cm; L2 = 24 cm) typically 2 cm to 5 cm Geometric relationship between satellite, antenna, and surroundings Same pattern in same satellite geometry on consecutive days produces similar results; similar effects Slide44:  August 1987 -Ionospheric refraction and Multipath Effects in GPS Carrier Phase Observations Yola Georgiadou and Alfred Kleusberg IUGG XIX General Assembly Meeting, Vancouver, Canada ø ø Figure 1 Multipath Description h Equipment Requirements:  Equipment Requirements Dual-frequency, full-wavelength GPS receivers Required for all observations greater than 10 km Preferred type for ALL observations regardless of length Geodetic quality antennas with ground planes Choke ring antennas; highly recommended Successfully modeled L1/L2 offsets and phase patterns Use identical antenna types if possible Corrections must be utilized by processing software when mixing antenna types Slide46:  SV 14 SV 14 SV 20 SV 20 Antenna Type A Antenna Type B Different Phase Patterns Note that SV elevation and varying phase patterns affect signal interpretation differently Analyses of Data from Pilot Projects:  Analyses of Data from Pilot Projects Northridge Earthquake Project 1994 GPS on leveling-derived bench marks Two 3-hour sessions On different days Different times of day Provided 2 cm results for short lines, i.e. 5 to 10 km Northridge Earthquake Project:  Northridge Earthquake Project Analyses of Data from Pilot Projects:  Analyses of Data from Pilot Projects Harris-Galveston Coastal Subsidence District’s CORS and PAMs 7 stations in a 25 km radius collecting data 24 hours a day for 2+ years Various length baselines 24, 6, 3, 2 and 1 hour solutions 20 minute to epoch-by-epoch solutions Real-life influences due to multipath, atmosphere, and satellite geometry Harris-Galveston Coastal Subsidence District:  Harris-Galveston Coastal Subsidence District Port-a-Measure PAM:  Port-a-Measure PAM Slide52:  Std. Dev. (0.91 cm) Slide53:  24 - Hour Solutions Day 300 -5.15 Day 301 -5.95 Day 302 -5.70 Day 303 -5.97 Day 304 -5.80 Day 303 Day 301 Day 300 Day 302 Day 304 Mean = -7.5  = 0.3 Mean = -3.1  = 0.5 Slide54:  Day 130 Mean (1.33 cm) / Std. Dev. (0.83 cm) Day 131 Mean (1.01 cm) / Std. Dev. (0.47 cm) 0.9 0.8 0.6 1.3 Slide55:  Day 130 Mean (1.33 cm) / Std. Dev. (1.15 cm) Day 131 Mean (1.03 cm) / Std. Dev. (0.58 cm) 1.2 0.7 0.5 2.0 Slide56:  Day 130 Mean (1.02 cm) / Std. Dev. (1.54 cm) Day 131 Mean (1.05 cm) / Std. Dev. (0.96 cm) 1.6 0.2 0.3 2.0 Results from Pilot Project:  Results from Pilot Project 24 hour solutions of data taken during “bad” atmospheric conditions may not always provide 2 cm results 1, 2, 3, and 6 hour solutions will repeat very well from day to day when observations are collected at about the same time on different days, but may produce significantly different results using data collected during different times of the days, i.e. having significantly different satellite geometry Increasing the elevation cut-off angle will decrease the effects due to multipath, but it will also decrease the number of available satellites which may significantly decrease accuracy of short observing sessions Analyses of Data from Pilot Projects:  Analyses of Data from Pilot Projects FGCS 48 Hour Pseudo-Kinematic Network, Gaithersburg, MD (June 13 - 15, 1995) 12 stations occupied in network Two TCORS and one rover 10 minute observing sessions at each site continuously over 48 hour time span 10 different occupations at each site Baselines ranged from 100 meters to 26.1 km FGCS 48 Hour Pseudo-Kinematic Network:  FGCS 48 Hour Pseudo-Kinematic Network Distances to Stations from TCORS:  Distances to Stations from TCORS Slide61:  F - Could not fix integers - (FLOAT solution) - Not included in statistics H - RMS value greater than 1.5 * - Difference greater than 5 cm Summary: FLOAT Solutions - Large Residuals High RMS Values - Large Residuals * * F F F F * * H H Analyses of Data from Pilot Projects:  Analyses of Data from Pilot Projects FGCS 24 Hour Pseudo-Kinematic Network, Gaithersburg, MD (November 28 - 29, 1995) 12 stations occupied in network Two TCORS and two rovers Simultaneous 10 minute observing sessions between rovers continuously over 24 hour time span 8 different occupations each site Baselines ranged from 100 meters to 26.1 km FGCS 24 Hour Pseudo-Kinematic Network:  FGCS 24 Hour Pseudo-Kinematic Network Slide64:  F - Could not fix integers - (FLOAT solution) - Not included in statistics H - RMS value greater than 1.5 F F H H H H H H H H H H H H H H H H H H H H H H H H H H H F F H H H H H H H H H H H H “Bad” Weather High RMS Values Results from Pilot Project:  Results from Pilot Project Base lines with high RMS produced outliers Base lines where integers could not be fixed produced outliers Standard deviation of a single 10 minute occupation during “good” atmospheric conditions was 2.1 cm Standard deviation of the mean of two 10 minute occupations during “good” atmospheric conditions was 1.4 cm Standard deviation of a single 10 minute occupation during “bad” atmospheric conditions was larger than a single 10 minute occupation obtained during “good” atmospheric conditions, i.e. 3.0 cm versus 2.1 cm Analyses of Data from Pilot Projects:  Analyses of Data from Pilot Projects San Francisco Bay Demonstration Project Test of guidelines and modifications based on results Phase I: Static survey test for 2 cm accuracy Mixture of base line lengths; 2 to 50 km Long observing sessions; minimum of 3 hours Phase II: Kinematic survey test for 5 cm accuracy Short base line lengths; less than 5 km Short observing sessions; 15 minutes “Real-world” conditions, i.e., traffic, trees, buildings San Francisco Bay Demonstration Project:  San Francisco Bay Demonstration Project CORS GPS Site BRIONE CHABOT WINTON MOLATE PT. BLUNT L 1241 U 1320 S 1320 941 4290 N 941 4819 TIDAL 32 RV 223 941 4873 TIDAL 17 941 4863 TIDAL 5 R 1393 YACHT N 1197 M 148 M 554 941 4750 TIDAL 7 PORT 1 941 4779 ASFB 0 5 10 KM Slide70:  Two Days/Same Time -10.254 -10.251 > -10.253 Difference = 0.3 cm “Truth” = -10.276 Difference = 2.3 cm Two Days/Different Times -10.254 -10.295 > -10.275 Difference = 4.1 cm “Truth” = -10.276 Difference = 0.1 cm Slide71:  Two Days/Same Time 20.660 20.662 > 20.661 Difference = -0.2 cm “Truth” = 20.615 Difference = 4.6 cm Two Days/Different Times 20.660 20.614 > 20.637 Difference = 4.6 cm “Truth” = 20.615 Difference = 2.3 cm Slide72:  Two Days/Different Times -9.184 -9.185 > -9.185 Difference = 0.1 cm “Truth” = -9.218 Difference = 3.3 cm Need a Network! Line is greater than 10 km Results from Pilot Project:  Results from Pilot Project Base lines with high RMS produced outliers Base lines where integers could not be fixed produced outliers Standard deviation of a 30 minute session for short lines, i.e. less than 10 km, was 1.2 cm Standard deviation of the mean of two 30 minute occupations on two different days and different times of day was 0.8 cm Standard deviation of a 10 minute session for short lines, i.e. less than 10 km, was 1.7 cm Standard deviation of the mean of two 10 minute occupations on two different days and different times of day was 1.1 cm Slide74:  CORS Establish / Monitor Project Control Precision With CORS:  Precision With CORS How GPS positioning is affected by baseline length Minimum occupation time required to meet established specifications Twice the rms @ ±2 cm for horizontal components Twice the rms @ ±4 cm for vertical components Twice the rms being approximately equal to a 95% confidence region Varying length baselines formed from 19 CORS 10 days data from each site; various session lengths Design of Research:  Design of Research 6 - 4 hour sessions  10 days  12 baselines = 720 4 - 6 “ “ “ “ = 480 3 - 8 “ “ “ “ = 360 2 - 12 “ “ “ “ = 240 1 -24 “ “ “ “ = 120 (Total # of Sessions) 1920 Sessions Processed Processing:  Processing One station constrained Second station computed ITRF97 (X, Y, and Z) @ epoch January 1, 1999 X, Y, and Z position of second station is source of results Automatic integer fixing (on) Tropospheric model (on) Antenna phase patterns (ant_info.001) Precise ephemerides (NGS ephemeredes) Slide82:  Time Scatter Plots (Horizontal) Slide85:  Multiple Occupation Estimates Comments About Results With CORS Data:  Comments About Results With CORS Data Majority of time you are less than 300 km from CORS (continental U.S.) Baseline length has little effect on positional accuracy No setup error or antenna measurement blunders < 300 kilometers Using NGS’ PAGES software Precise ephemeris, Tropo models, and antenna patterns Horizontal and vertical specifications can be met in one 4-hour session Recommendations to Guidelines Based on These Tests:  Recommendations to Guidelines Based on These Tests Must repeat base lines Different days Different times of day Detect, remove, reduce effects due to multipath and having almost the same satellite geometry Must FIX integers Base lines must have low RMS values, i.e., < 1.5 cm Slide89:  Available On-Line at the NGS Web Site: www.ngs.noaa.gov Station Selection and Reconnaissance:  Station Selection and Reconnaissance Assure accurate connections to control stations NGS approved CORS TCORS (temporary or project CORS) HPGN / HARN Federal Base Network (FBN) Cooperative Base Network (CBN) User Densified Network (UDN) NAVD 88 Bench Marks NGS Database and data sheets Identify GPS-usable stations Slide91:  NGS Internet Page www.ngs.noaa.gov Primary or Secondary Station Selection Criteria:  Primary or Secondary Station Selection Criteria 1. HPGN / HARN either FBN or CBN Level ties to A or B stability bench marks during this project 2. Bench marks of A or B stability quality Or HPGN / HARN previously tied to A or B stability BMs 3. UDN stations Level ties to A or B stability bench marks during this project 4. Bench marks of C stability quality Special guidelines for areas of subsidence or uplift Four Basic Control Requirements:  Four Basic Control Requirements BCR-1: Occupy stations with known NAVD 88 orthometric heights Stations should be evenly distributed throughout project BCR-2: Project areas less than 20 km on a side, surround project with NAVD 88 bench marks i.e., minimum number of stations is four; one in each corner of project BCR-3: Project areas greater than 20 km on a side, keep distances between GPS-occupied NAVD 88 bench marks to less than 20 km BCR-4: Projects located in mountainous regions, occupy bench marks at base and summit of mountains, even if distance is less than 20 km Slide100:  Obstruction Visibility Diagram Equipment Requirements:  Equipment Requirements Dual-frequency, full-wavelength GPS receivers Required for all observations greater than 10 km Preferred type for ALL observations regardless of length Geodetic quality antennas with ground planes Choke ring antennas; highly recommended Successfully modeled L1/L2 offsets and phase patterns Use identical antenna types if possible Corrections must be utilized by processing software when mixing antenna types Slide102:  http://www.grdl/GRD/GPS/Projects/ANTCAL/index.shtml Slide103:  Ashtech Geodetic III Antenna U.S.C.G. V Antenna (ASH 700829.A1) Trimble Geodetic L1/L2 Antenna (TRM 22020.00) Data Collection Parameters:  Data Collection Parameters VDOP < 6 for 90% or longer of 30 minute session Shorter session lengths stay < 6 always Schedule travel during periods of higher VDOP Session lengths > 30 minutes collect 15 second data Session lengths < 30 minutes collect 5 second data Track satellites down to 10° elevation angle Meteorological Data:  Meteorological Data Weather data must be collected at control, primary, and secondary base stations at height of antenna PC Wet and dry temperatures, atmospheric pressure Sessions > 2 hrs; record beginning, midpoint, ending Sessions < 2 hrs > 30 min; record beginning and ending Sessions < 30 min; record at midpoint Note on obs log where recorded and unusual conditions Stabilize equipment to ambient conditions Check equipment prior to observations Antenna Setup:  Antenna Setup Fixed-height tripods required for 2 cm standard Shade plumbing bubbles at least 3 min prior to plumbing Check perpendicularity of poles at beginning of project Fixed-height poles preferred for 5 cm standard Alternate tripod setups; antenna heights MUST be measured carefully and accurately Check measuring system before project Check and adjust tribrachs at beginning of project Perform totally independent meter and feet measurements Have measurement computations checked by someone else Slide111:  “Fixed” Height Tripod Slide112:  “Slip-leg” Tripod and Slant Height Measurement Slide113:  Table 1. -- Summary of Guidelines Slide114:  HARN/Control Stations (75 km) Primary Base (40 km) Secondary Base (15 km) Local Network Stations (7 to 10 km) Appendix B. - - GPS Ellipsoid Height Hierarchy Slide115:  HARN/Control Stations CS1 CS2 CS3 75 km Slide116:  Primary Base Stations CS1 CS2 CS3 40 km PB2 PB3 PB1 Primary Base Stations:  Primary Base Stations Basic Requirements: 5 Hour Sessions / 3 Days Spacing between PBS cannot exceed 40 km Each PBS must be connected to at least its nearest PBS neighbor and nearest control station PBS must be traceable back to 2 control stations along independent paths; i.e., base lines PB1 - CS1 and PB1 - PB2 plus PB2 - CS2, or PB1 - CS1 and PB1 - PB3 plus PB3 - CS3 Slide118:  Secondary Base Stations CS1 CS2 CS3 15 km PB2 PB3 PB1 SB1 SB3 SB2 SB4 Secondary Base Stations:  Secondary Base Stations Basic Requirements: 30 Minute Sessions / 2 Days /Different times of day Spacing between SBS (or between primary and SBS) cannot exceed 15 km All base stations (primary and secondary) must be connected to at least its 2 nearest primary or secondary base station neighbors SBS must be traceable back to 2 PBS along independent paths; i.e., base lines SB1 - PB1 and SB1 - SB3 plus SB3 - PB2, or SB1 - PB1 and SB1 - SB4 plus SB4 - PB3 SBS need not be established in surveys of small area extent Slide120:  Local Network Stations CS1 CS2 CS3 7 km PB2 PB3 PB1 SB1 SB3 SB2 SB4 LN1 LN2 LN3 LN4 LN5 LN6 LN7 Local Network Stations:  Local Network Stations Basic Requirements: 30 Minute Sessions / 2 Days / Different times of the day Spacing between LNS (or between base stations and local network stations) cannot exceed 10 km All LNS must be connected to at least its two nearest neighbors LNS must be traceable back to 2 primary base stations along independent paths; i.e., base lines LN1 - PB1 and LN1 - LN2 plus LN2 - SB1 plus SB1 - SB3 plus SB3 - PB2, or LN1 - PB1 and LN1 - LN3 plus LN3 - SB2 plus SB2 - SB4 plus SB4 - PB3 Slide122:  Sample Project Showing Connections CS1 PB2 SB2 LN4 LN3 LN2 LN5 LN1 SB1 SB3 SB5 SB4 PB4 PB1 PB3 CS2 CS4 CS3 Slide123:  Sample Project Project Information:  Project Information Area: East San Francisco Bay Project Latitude 37° 50” N to 38° 10” N Longitude 121° 45” W to 122° 25” W Receivers Available: 5 Standards: 2 cm GPS-Derived Heights Slide125:  GPS-Usable Stations CORS HARN NAVD’88 BM New Station 121°40’W 122°35’W 37°50’N 38°20’N LATITUDE LONGITUDE Spacing Station Primary Base Station 8.2km Slide126:  Primary Base Stations CORS HARN NAVD’88 BM New Station 121°40’W 122°35’W 37°50’N 38°20’N LATITUDE LONGITUDE Primary Base Station MOLA MART LAKE 10CC D191 29.6km 25.8km 38.7km 19.0km 28.7km 25.7km 38.3km 31.6km Slide127:  38°16’N CORS HARN NAVD’88 BM New Station Spacing Station 121°40’W 122°20’W 37°55’N LATITUDE LONGITUDE Primary Base Station 8.2km 10LC TIDD D191 MONT X469 Z190 DROU BM20 04KU TIDE ZINC PT14 MART 5144 P371 R100 LAKE 04HK CATT Q555 TOLA East Bay Project Points Slide128:  CORS HARN NAVD’88 BM New Station Spacing Station 121°40’W 122°20’W 37°55’N 38°16’N LATITUDE LONGITUDE Primary Base Station Session A Session B Session C Session D Session E Session F Session G Observation Sessions Slide129:  CORS HARN NAVD’88 BM New Station Spacing Station 121°40’W 122°20’W 37°55’N 38°16’N LATITUDE LONGITUDE Primary Base Station 8.2km Independent Base Lines Slide130:  Observation Schedule Field Observations:  Field Observations Observation logs Record complete receiver/antenna manufacturer, model part number, and serial numbers Record meteorological data and unusual conditions Record station and observer information Record height of antenna and measurement computations Obtain a clear station rubbing Rubbing for each occupation of station Make complete plan sketch of mark when rubbing not feasible Slide132:  Sample Observation Log (Front Side) Slide133:  Sample Observation Log (Back Side) Slide134:  Sample Station Rubbing Basic Concept of Guidelines:  Basic Concept of Guidelines Stations in local 3-dimensional network connected to NSRS to at least 5 cm uncertainty Stations within a local 3-dimensional network connected to each other to at least 2 cm uncertainty Stations established following guidelines are published to centimeters by NGS Slide136:  Network / Local Accuracy Points of Contact:  Points of Contact National Geodetic Survey NOAA, N/NGS12 Geodetic Services Division Bldg. SSMC3, Station 9202 1315 East-West Highway Silver Spring, MD 20910-3282 Phone: 301-713-3242 Fax: 301-713-4171 Internet Web Site: www.ngs.noaa.gov Curtis L. Smith Phone: 208-332-7197 E-mail: Curt.Smith@noaa.gov

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