# GPS-Derived Orthometric Heights - PowerPoint by pengtt

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```									       GPS-Derived Heights
Part 1

Development and Description of NGS
Guidelines

NOAA, NOS, NGS
To understand how to achieve GPS-derived
orthometric heights at centimeter-level accuracy,

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?

NOAA, NOS, NGS
Leveled Height Differences

B                     Topography

A
C

NOAA, NOS, NGS
Level Surfaces and Orthometric Heights

WP
Level Surfaces                                  P

Plumb
Line

Mean
Sea                                                                   “Geoid”
Level                                                                   WO
PO

Ocean             Level Surface = Equipotential Surface (W)
Geopotential Number (CP) = WP -WO
H (Orthometric Height) = Distance along plumb line (PO to P)

NOAA, NOS, NGS
Heights Based on Geopotential Number (C)

• Normal Height (NGVD 29)                              H* = C / 
    = Average normal gravity along plumb line
dyn
• Dynamic Height (IGLD 55, 85) H                     = 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)

NOAA, NOS, NGS
Leveled Height vs. Orthometric Height
 h = local leveled differences
H = relative orthometric heights

B                                   Topography

 hAB =  hBC
A
C

HA                                HC
HAC  hAB + hBC

Observed difference in orthometric height,
H, depends on the leveling route.

NOAA, NOS, NGS
Global Positioning
System
27 Satellites
6 Planes, 55° Rotation
4/5 Satellites /Plane
20,183 km Orbit
1 Revolution /12 Hrs

NOAA, NOS, NGS
Z
Zero
Meridian
-X
-Y

Y
X

Mean
Equatorial Plane

-Z
NOAA, NOS, NGS
Earth-Centered-Earth-Fixed Coordinates
Conventional
Z Axis        Terrestrial
Pole
P   (X,Y,Z)

Earth’s
Surface

Zero
Meridian
Z

Origin
(0,0,0)                                            Y Axis
Center of Mass

X
Y

X Axis                                     Mean Equatorial Plane

NOAA, NOS, NGS
The Ellipsoid
a = Semi major axis
N
b = Semi minor axis
f = a-b = Flattening
b                           a

a

Geodetic Reference System 1980
S         a = 6,378,137.000 meters (semi-major axis)
b = 6,356,752.3141403 m (semi-minor axis)
1/f = 298.25722210088 (flattening)

NOAA, NOS, NGS
GPS - Derived Ellipsoid Heights
Z Axis
P    (X,Y,Z) = P (,,h)
h
Earth’s
Surface

Zero
Meridian

Reference Ellipsoid

Y Axis




X Axis                          Mean Equatorial Plane

NOAA, NOS, NGS
Ellipsoid, Geoid, and Orthometric Heights
“h = H + N”
P
Ellipsoid                                                         Plumb Line
h

Q

Mean                                                                 N
Sea                                                                         “Geoid”
Level
PO

Ocean            h (Ellipsoid Height) = Distance along ellipsoid normal (Q to P)
N (Geoid Height) = Distance along ellipsoid normal (Q to PO)
H (Orthometric Height) = Distance along plumb line (PO to P)

NOAA, NOS, NGS
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

NOAA, NOS, NGS
Simplified Concept of ITRF 97 vs. NAD 83

h83
h97         Earth’s
Surface

ITRF 97
Origin

NAD 83             Identically shaped ellipsoids (GRS-80)
Origin
a = 6,378,137.000 meters (semi-major axis)
1/f = 298.25722210088 (flattening)

NOAA, NOS, NGS
NAD83(86) to ITRF97(97) Ellipsoid Heights (meters)

NOAA, NOS, NGS
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

NOAA, NOS, NGS
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

NOAA, NOS, NGS
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.

NOAA, NOS, NGS
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
   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

NOAA, NOS, NGS
NOAA, NOS, NGS
GEOID99

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.

NOAA, NOS, NGS
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

NOAA, NOS, NGS
NOAA, NOS, NGS
Importance of Shoreline
AL, AK, CA, CT, FL, GA, LA, MD,
MS, NJ, NY, NC, OR, RI, SC, WA                Territorial Seas

Privately Owned       State Owned                      Contiguous Zone
Uplands             Tidelands

Exclusive Economic Zone
State Submerged Lands
Federal Submerged Lands
3 n. mi.                                High Seas
12 n. mi.
MHHW                                                    200 n. mi.
MHW

MLLW                       Chart Datum

Privately State
Owned Owned                  Privately State
Owned Owned
TX
DE, MA, ME, NH, PA, VA                 NOAA, NOS, NGS
NAVD 88 minus
LMSL (1960-1978)
(units = cm)

NOAA, NOS, NGS
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

NOAA, NOS, NGS
First-Order Leveling Network NGVD 29

NOAA, NOS, NGS
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

NOAA, NOS, NGS
Vertical Control Network NAVD 88

NOAA, NOS, NGS
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

NOAA, NOS, NGS
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

NOAA, NOS, NGS
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

Published Information:
• Orthometric Height Type        Normal             Helmert
• Orthometric Height Units       Meters             Meters
• Gravity Value                  Normal             “Actual”

NOAA, NOS, NGS
Height Differences Between NAVD 88 and NGVD 29

NOAA, NOS, NGS
NOAA, NOS, NGS
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

NOAA, NOS, NGS
GPS-Derived Ellipsoid Height
Guidelines

• GPS related error sources

• Pilot projects were used to develop guidelines

• NOAA Technical Memorandum NOS NGS-58

NOAA, NOS, NGS
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

NOAA, NOS, NGS
GPS Error Sources
• Precise or broadcast orbit error              • Multipath
   Satellite relationship center-of-mass         Antenna phase center variation
to L1 antenna phase center
   Circular polarization
• Satellite clock error (nominal)                     L1-L2 phase center offset
   SA dither (minimized)                         Receiver clock offset
   Satellite inter-channel bias                  Receiver inter-channel bias
   L1-L2 antenna phase center offset
   Transmission multipath                  • Height of phase center above mark
   Marker stability
• Ionospheric effects
   Earth tides - direct effect
   Wet troposphere delay                         Crustal motion

NOAA, NOS, NGS
NOAA, NOS, NGS
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
NOAA, NOS, NGS
stands at that football stadium; with SA switched off, you know which yard marker you are standing on.
NOAA, NOS, NGS
Atmospheric Error Sources

• Ionosphere                            • Hydrostatic (“Dry”)
   Greatest at 1400 (local time)      Troposphere
   Typical 5 to 15 m at zenith            90% of total effect
   Extreme 0.15 to 50 m at zenith         Model accuracy only 2 to 5%
   Higher frequencies have less           Need surface atmospheric pressure
effect                                  and temperatures
   Error correction by dual               Accurate pressure is critical
frequency                              About 2.2 m at zenith

• “Wet” Troposphere
   10% of total effect
   Model accuracy only 10 to 50%
   Need humidity along path
   About 20 cm at zenith

NOAA, NOS, NGS
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
NOAA, NOS, NGS
Multipath Delay :                    T = 2hSinø
(meters)                                    c

d(T )ƒ~ hCosø
Multipath Freq. :
dt     3
(Cycles/hr)

h                                            d ø ~ 2 rad.
dt 12 hr.
ø             ø

Figure 1
Multipath Description

August 1987 -Ionospheric refraction and Multipath Effects in GPS Carrier Phase Observations
IUGG XIX General Assembly Meeting, Vancouver, Canada
NOAA, NOS, NGS
Equipment Requirements
 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

NOAA, NOS, NGS
Different
Phase Patterns

Note that SV elevation and
varying phase patterns affect
signal interpretation differently
Antenna           Antenna
Type A            Type B

NOAA, NOS, NGS
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

NOAA, NOS, NGS
Northridge Earthquake Project

Pearblossom
Castaic
Santa Paula

Los Angles

Norwalk

Palos Verdes      Tidal B

NOAA, NOS, NGS
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

NOAA, NOS, NGS
Harris-Galveston Coastal Subsidence District
Riverside

P2
LAKE HOUSTON
CORS
P1

LaGrange                                                P   PAM
P3         NORTHEAST
GPS Site

P4

Edna

NOAA, NOS, NGS
Port-a-Measure PAM

NOAA, NOS, NGS
LAKE HOUSTON to NORTHEAST (23 km)
("Hands-Off" Automatic Processing)

3

2
Up Component (cm)

1
Std. Dev. (0.91 cm)

0
300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

327

328

329

330
-1

-2

-3

Day of Year ( 24 hour solutions using 15 degree elevation cut-off value)

NOAA, NOS, NGS
24 - Hour Solutions
LAKE HOUSTON to NORTHEAST- (23 km)                                                Day 300   -5.15
Day 301   -5.95
Days 300 - 304; 6 Hour Solutions - With Tropo Modeling                                  Day 302   -5.70
Day 303   -5.97
Day 304   -5.80
0
0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18
-1

-2
Mean = -3.1
Ellipsoid Height Correction (cm)

Day 302
 = 0.5
-3
Day 300

-4

-5

-6

-7
Mean = -7.5
 = 0.3                                              Day 304
-8
Day 301
Day 303
-9

-10

Time (0 = 0 to 6 hr, 1 = 1 to 7 hr,....., 18 = 18 to 24 hr)

NOAA, NOS, NGS
ADDICKS to PAM 3 (4.2 km)
Days 130 and 131 (3 hour solutions - w/o Sat 15)

3.5

Day 130
Mean (1.33 cm) / Std. Dev. (0.83 cm)
3.0

2.5
Up Component (cm)

Day 131
2.0                                          Mean (1.01 cm) / Std. Dev. (0.47 cm)

1.3
1.5

0.8                   0.9
1.0

0.5

0.6
0.0
3   4   5   6     7    8     9    10   11     12     13     14      15        16   17     18   19    20   21

Time (3 = 3 to 6 hr, 4 = 4 to 7 hr, ...., 21 = 21 to 24 hr)

NOAA, NOS, NGS
ADDICKS to PAM 3 (4.2 km)
Days 130 and 131 ( 2 hour solutions - w/o Sat 15)

4.5
Day 130
Mean (1.33 cm) / Std. Dev. (1.15 cm)
4.0

3.5

3.0
Day 131
Up Component (cm)

Mean (1.03 cm) / Std. Dev. (0.58 cm)
2.5

2.0
2.0
1.2
1.5

0.5                                     0.7
1.0

0.5

0.0
3   4   5   6    7    8     9    10    11     12      13     14    15         16   17     18    19   20   21   22

-0.5

Time (3 = 3 to 5 hr, 4 = 4 to 6 hr, ...., 22 = 22 to 24 hr)

NOAA, NOS, NGS
Day 130
Mean (1.02 cm) / Std. Dev. (1.54 cm)

Day 131
Mean (1.05 cm) / Std. Dev. (0.96 cm)

2.0
1.6

0.2

0.3

NOAA, NOS, NGS
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

NOAA, NOS, NGS
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

NOAA, NOS, NGS
FGCS 48 Hour Pseudo-Kinematic
Network        RAPID

STATIC

KINEMATIC
HOLDAHL

DICKERSON                                   SURVEY
(TCORS)

TS19977
WINGATE
STRANGE
NBS 5 (TCORS)
REMONDI                     NBS 102
LOVE
ANDERSON

NOAA, NOS, NGS
Distances to Stations from TCORS
RAPID
RAPID
26.1 km
25.0 km

STATIC
STATIC
19.9 km
21.5 km

KINEMATIC
KINEMATIC
15.0 km
17.8 km
HOLDAHL
HOLDAHL       SURVEY                                           8.3 km
SURVEY
16.1 km       10.1 km
DICKERSON                                                                                                   15.2 km
DICKERSON
(TCORS)
(TCORS)
TS19977
TS19977
5.1 km
15.9 km
WINGATE                                                               WINGATE
25.1 km                                                               9.3 km
STRANGE                                                            STRANGE                                    NBS 5 (TCORS)
NBS 5 (TCORS)
19.9 km                                                            6.9 km
REMONDI                                                           REMONDI
14.9 km   LOVE              NBS 102                               9.2 km   LOVE                 NBS 102
9.9 km ANDERSON   0.1 km                                         12.2 km              19.4 km
ANDERSON
4.5 km                                                              16.8 km

NOAA, NOS, NGS
NGS 48 Hour Test of GPS Vertical Guidelines (June 13 thru 15, 1995)

Differences of session ellipsoid Heights from mean value; Units = cm
Northern Line from NBS 5                                                               Western Line from NBS 5

NBS 5        NBS 102    TS19977      SURVEY KINEMATIC        STATIC      RAPID       WINGATE      STRANGE      REMONDI     LOVE       ANDERSON HOLDAHL
Base        (0.1 km)   (5.1 km)     (10.1 km)   (15.0 km)   (19.9 km)   (25.0 km)    (25.1 km)    (19.9 km)   (14.9 km)   (9.9 km)    (4.9 km)   (16.1 km)
Session 1        0.2         3.8          1.2        2.9          2.8         4.0         -3.0         -1.9        4.2         0.8        -2.8
Session 2        -0.7        3.0          0.9        0.3          2.3         1.6         -0.2          0.3        -1.4       -0.7        -0.3
Session 3        -0.8       -1.2         -0.6        0.2         -1.3        -2.5         17.1 F        5.0 *      1.6         0.5        -1.5
Session 4        -0.4        2.2         -0.3        -1.0        -0.1         0.0         3.6          -0.2        1.9         0.8         4.0         0.0
Session 5        -0.2       -1.7         -1.4        0.6          1.8        -1.0         4.1           1.8        2.0         2.6         0.2        -0.3
Session 6        0.1        -2.4          0.4        1.2         -1.2        -1.2         0.7          10.4 F      -1.0        0.2         0.8
Session 7        0.5         6.6 * H      0.4        -1.4        -2.9        -0.4        -36.6 F       -3.2        -3.8       -0.6         0.0
Session 8        0.1        -2.7         -0.4        -0.7        -0.9         0.1         -5.1 *       -3.1        -1.9        0.0        -1.7
Session 9        0.8        -0.7         -0.2        -0.8        -1.9        -1.1         0.2           0.9        -1.9       -1.3        -1.4        -1.0
Session 10       0.0        -7.3 * H      0.2        -1.1         1.3         0.8         57.0 F        0.2        0.3        -1.8         3.0         1.3

Average         0.0        0.0          0.0         0.0         0.0         0.0          0.0          0.0         0.0         0.1         0.0        0.0
Std. Dev.       0.5        3.8          0.7         1.3         1.8         1.7          3.1          2.4         2.3         1.2         2.0        0.8

F - Could not fix integers - (FLOAT solution) - Not included in statistics
H - RMS value greater than 1.5                                 Summary:
* - Difference greater than 5 cm                                 FLOAT Solutions - Large Residuals
High RMS Values - Large Residuals

NOAA, NOS, NGS
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

NOAA, NOS, NGS
FGCS 24 Hour Pseudo-Kinematic
Network         RAPID

STATIC

KINEMATIC

DICKERSON
(TCORS)                           SURVEY

TS19977

WINGATE
NBS 5 (TCORS)
STRANGE
NBS 102
REMONDI
LOVE              KIN C
ANDERSON

NOAA, NOS, NGS
NGS 24 Hour Test of GPS Vertical Guidelines (November 28 thru 29, 1995)

Differences of session ellipsoid Heights from mean value; Units = cm

Northern Line from NBS 5                                                                Western Line from NBS 5

NBS 5        KIN C      TS19977     SURVEY      KINEMATIC     STATIC      RAPID       WINGATE      STRANGE      REMONDI      LOVE           ANDERSON     NBS 102
Base       (0.1 km)   (5.1 km)    (10.1 km)    (15.0 km)    (19.9 km)   (25.0 km)    (25.1 km)    (19.9 km)   (14.9 km)    (9.9 km)        (4.9 km)    (0.1 km)
Session 1      1.9         1.0   H     -0.2         2.0           1.5         3.0         -3.3         -0.7        -0.1         2.1   H        1.3          -1.4 H
Session 2      0.6         4.0   H     13.1 H       -1.3   H     -0.2        23.4 F       -0.1 H                   -2.9   H    -1.1   H        -2.3   H
Session 3      -0.8       -4.7   H     -3.1 H       3.5    H     -2.1        -4.1          1.5         0.1 H        5.4   H    -0.7   H        1.9    H
Session 4      0.5        -5.8   H     -7.0         -4.9   H      2.5 H      -5.0 F                                -1.2        -2.2            -2.0   H
Session 5      3.1 H      -2.4         2.0          1.0           2.1         0.8         -1.6         -2.7         0.3        -1.8            1.5    H     1.4
Session 6      -1.5        8.3   H     1.1 H        -0.3          1.6                                  -0.3 H      -1.4         3.2            -0.5   H
Session 7      -3.5       -0.5   H     1.4 H        -1.4         -5.9 H      0.3           6.9         3.8 H       -4.2   F    -1.4      H     0.4
Session 8      -0.6       33.3   H     -7.0 H       1.4    H      0.7 H                   -3.6 H                   29.7   F     2.0      H     -0.6   H

Average         0.0        0.0         0.0          0.0          0.0         0.0          0.0          0.0         0.0          0.0             0.0         0.0
Std. Dev.       1.9        4.6         6.0          2.4          2.6         2.6          3.6          2.1         2.6          1.9             1.5         1.4

48 Hour
3.8         0.7          1.3          1.8         1.7          3.1          2.4         2.3          1.2             2.0         0.5
Results
Difference
0.8         5.3          1.1          0.8         0.9          0.5          -0.3        0.3          0.7            -0.5         0.9
24 - 48 Hour

F - Could not fix integers - (FLOAT solution) - Not included in statistics
H - RMS value greater than 1.5
High RMS Values

NOAA, NOS, NGS
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

NOAA, NOS, NGS
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

NOAA, NOS, NGS
San Francisco Bay Demonstration Project
R 1393

941 4873 TIDAL 17         MOLATE

941 4863 TIDAL 5      BRIONE
RV 223
CORS
PT. BLUNT
941 4819 TIDAL 32                      YACHT                             GPS Site

941 4290 N             941 4779 ASFB                    0    5     10
PORT 1
S 1320                                            KM
941 4750 TIDAL 7

M 554           CHABOT
U 1320
M 148
L 1241                                 N 1197

WINTON

NOAA, NOS, NGS
NOAA, NOS, NGS
NOAA, NOS, NGS
Comparison of 30 Minute Solutions - Precise Orbit; Hopfield (0); IONOFREE
(30 Minute solutions computed on the hour and the half hour)                                      Two Days/Same Time
-10.254 > -10.253
MOLA to RV22 10.8 Km
-10.251
Day 264 *               Mean dh *        Difference = 0.3 cm
dh      Hours                    dh       minus diff   Mean dh    minus diff
Day 264                          Day 265
(m)       Diff.                  (m)      Day 265 >2      (m)      "Truth" >2      “Truth” = -10.276
(cm)   cm                (cm)   cm
Difference = 2.3 cm
14:00-14:30   -10.281   27hrs    17:00-17:30   -10.279    -0.2         -10.280     -0.5
14:30-15:00   -10.278   27hrs    17:30-18:00   -10.270    -0.8         -10.274      0.2
15:00-15:30   -10.281   27hrs    18:00-18:30   -10.278    -0.3         -10.280     -0.4
15:30-16:00   -10.291   27hrs    18:30-19:00   -10.274    -1.7         -10.283     -0.7        Two Days/Different Times
16:00-16:30   -10.274   27hrs    19:00-19:30   -10.274     0.0         -10.274      0.2
16:30-17:00   -10.287   27hrs    19:30-20:00   -10.276    -1.1         -10.282     -0.6            -10.254 > -10.275
17:00-17:30   -10.279   27hrs    20:00-20:30   -10.261    -1.8         -10.270      0.6             -10.295
17:30-18:00   -10.270   27hrs    20:30-21:00   -10.251    -1.9         -10.261      1.5
18:00-18:30   -10.277   21hrs    15:00-15:30   -10.270    -0.7         -10.274      0.2            Difference = 4.1 cm
18:30-19:00   -10.271   21hrs    15:30-16:00   -10.276     0.5         -10.274      0.2
19:00-19:30   -10.277   21hrs    16:00-16:30   -10.278     0.1         -10.278     -0.2            “Truth” = -10.276
19:30-20:00   -10.271   21hrs    16:30-17:00   -10.286     1.5         -10.279     -0.3
20:00-20:30   -10.259   18hrs    14:00-14:30   -10.278     1.9         -10.269      0.7            Difference = 0.1 cm
20:30-21:00   -10.254   18hrs    14:30-15:00   -10.295     4.1    *    -10.275      0.1
"Truth"
14:00-21:00   -10.275            14:00-21:00   -10.276     0.1         -10.276

NOAA, NOS, NGS
Comparison of 30 Minute Solutions - Precise Orbit; Hopfield (0); IONOFREE
(30 Minute solutions computed on the hour and the half hour)                                    Two Days/Same Time
20.660 > 20.661
S132 to L132 7.9 Km                                                                              20.662
Day 264 *               Mean dh *        Difference = -0.2 cm
dh     Hours                    dh      minus diff   Mean dh    minus diff
Day 264
(m)      Diff.
Day 265
(m)     Day 265 >2      (m)      "Truth" >2      “Truth” = 20.615
(cm)   cm                (cm)   cm
Difference = 4.6 cm
14:00-14:30   20.599   27hrs    17:00-17:30   20.624    -2.5    *    20.612      -0.3
14:30-15:00   20.610   27hrs    17:30-18:00   20.613    -0.3         20.612      -0.3
15:00-15:30   20.613   27hrs    18:00-18:30   20.620    -0.7         20.617       0.2
15:30-16:00   20.607   27hrs    18:30-19:00   20.611    -0.4         20.609      -0.5
Two Days/Different Times
16:00-16:30   20.594   27hrs    19:00-19:30   20.615    -2.1    *    20.605      -1.0
16:30-17:00   20.612   27hrs    19:30-20:00   20.619    -0.7         20.616       0.1
20.660 > 20.637
17:00-17:30   20.610   27hrs    20:00-20:30   20.662    -5.2    *    20.636       2.1   *         20.614
17:30-18:00   20.615   27hrs    20:30-21:00   20.621    -0.6         20.618       0.3
18:00-18:30   20.614   21hrs    15:00-15:30
Difference = 4.6 cm
18:30-19:00   20.608   21hrs    15:30-16:00   20.625    -1.7         20.617       0.2
19:00-19:30   20.609   21hrs    16:00-16:30   20.601     0.8         20.605      -0.9            “Truth” = 20.615
19:30-20:00   20.620   21hrs    16:30-17:00   20.628    -0.8         20.624       1.0            Difference = 2.3 cm
20:00-20:30   20.660   18hrs    14:00-14:30   20.614     4.6    *    20.637       2.3   *
20:30-21:00   20.618   18hrs    14:30-15:00   20.630    -1.2         20.624       0.9
"Truth"
14:00-21:00   20.609            14:00-21:00   20.620    -1.1         20.615

NOAA, NOS, NGS
Two Days/Different Times
Comparison of 30 Minute Solutions - Precise Orbit; Hopfield (0); IONOFREE                        -9.184 > -9.185
(30 Minute solutions computed on the hour and the half hour)                                      -9.185
MOLA to YACH 12.9 Km                                                                             Difference = 0.1 cm

Day 264 *               Mean dh *
“Truth” = -9.218
Day 264
dh     Hours
Day 265
dh      minus diff   Mean dh    minus diff      Difference = 3.3 cm
(m)      Diff.                  (m)     Day 265 >2      (m)      "Truth" >2
(cm)   cm                (cm)   cm

14:00-14:30
14:30-15:00
15:00-15:30
Need a Network!
15:30-16:00
16:00-16:30                                                                                  Line is greater than 10 km
16:30-17:00
17:00-17:30
17:30-18:00
18:00-18:30   -9.216   20hrs    14:00-14:30   -9.205
18:30-19:00   -9.228   20hrs    14:30-15:00   -9.220    -0.8          -9.224     -0.6
19:00-19:30   -9.219   20hrs    15:00-15:30   -9.193    -2.6          -9.206      1.2
19:30-20:00   -9.203   20hrs    15:30-16:00   -9.208     0.5          -9.206      1.2
20:00-20:30   -9.184   20hrs    16:00-16:30   -9.185     0.1          -9.185      3.3   *
20:30-21:00   -9.210   20hrs    16:30-17:00   -9.186    -2.4    *     -9.198      2.0
"Truth"
18:00-21:00   -9.217            14:00-17:00   -9.218     0.1          -9.218

NOAA, NOS, NGS
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

NOAA, NOS, NGS
Establish / Monitor
Project Control

CORS
NOAA, NOS, NGS
NOAA, NOS, NGS
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

NOAA, NOS, NGS
Design of Research

Sessions Processed

•   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

NOAA, NOS, NGS
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)

NOAA, NOS, NGS
North rms Relative to Distance
Mean rms - 10 Days of Observation
0.010
r m s N o r th

0.005

0.000
25    50    75    100 125 150 175 200 225 250 275 300
Baseline Length (kilometers)

4 Hrs.        6 Hrs.       NOAA, 12 Hrs.NGS 24 Hrs
8 Hrs.   NOS,
East rms Relative to Distance
Mean rms - 10 Days of Observation

0.010
rm s E a st

0.005

0.000
25   50   75   100 125 150 175 200 225 250 275 3
Baseline Length (kilometers)

4 Hrs.      6 Hrs.   NOAA, NOS,Hrs.
8 Hrs. 12 NGS      24 Hrs
Up rms Relative to Distance
Mean rms - 10 Days of Observation
0.030
rm s U p

0.020

0.010

0.000
25    50    75 100 125 150 175 200 225 250 275 300
Baseline Length (kilometers)

4 Hrs.     6 Hrs.       NOAA, 12 Hrs.NGS 24 Hrs
8 Hrs.   NOS,
4 Hr/160 K                                                                                                                                    6 Hr/160 K

North Offset from 24 hr. Mean (m)
North Offset from 24 hr. Mean (m)
0.05                                                                                                                                          0.05

0.04                                                                                                                                          0.04

0.03                                                                                                                                          0.03

0.02                                                                                                                                          0.02

0.01                                                                                                                                          0.01

0.00                                                                                                                                          0.00

-0.01                                                                                                                                         -0.01

-0.02                                                                                                                                         -0.02

-0.03                                                                                                                                         -0.03

-0.04                                                                                                                                         -0.04

-0.05                                                                                                                                         -0.05
-0.05 -0.04 -0.03 -0.02 -0.01 0.00 0.01 0.02 0.03 0.04 0.05                                                                                   -0.05 -0.04 -0.03 -0.02 -0.01 0.00 0.01 0.02 0.03 0.04 0.05

24 Hrs/160 K
8 Hr/160 K 24 hr. Mean (m) 12 Hr/160East Offset from 24 hr. Mean (m)
East Offset from                  K

North Offset from 24 hr. Mean (m)
North Offset from 24 hr. Mean (m)

0.05                                                                                       North Offset from 24 hr. Mean (m)   0.05                                                                                                                         0.05

0.04                                                                                                                           0.04                                                                                                                         0.04

0.03                                                                                                                           0.03                                                                                                                         0.03

0.02                                                                                                                           0.02                                                                                                                         0.02

0.01                                                                                                                           0.01                                                                                                                         0.01

0.00                                                                                                                           0.00                                                                                                                         0.00

-0.01                                                                                                                          -0.01                                                                                                                        -0.01

-0.02                                                                                                                          -0.02                                                                                                                        -0.02

-0.03                                                                                                                          -0.03                                                                                                                        -0.03

-0.04                                                                                                                          -0.04                                                                                                                        -0.04

-0.05                                                                                                                          -0.05                                                           -0.05
-0.05 -0.04 -0.03 -0.02 -0.01 0.00 0.01 0.02 0.03 0.04 0.05                                                                    -0.05 -0.04 -0.03 -0.02 -0.01 0.00 0.01 0.02 0.03 0.04 0.05     -0.05 -0.04 -0.03 -0.02 -0.01 0.00 0.01 0.02 0.03 0.04 0

East Offset from 24 hr. Mean (m)                                           East Offset from (Horizontal) East Offset from 24 hr. Mean (m)
Time Scatter Plots 24 hr. Mean (m)

NOAA, NOS, NGS
Up Scatter @ 160 Kilometers

0.060
Up Offset from 24 hr. Mean (m)

0.040

0.020

0.000

-0.020

-0.040

-0.060
0   4    8       12     16      20       24
Observation Time in Hours

NOAA, NOS, NGS
Up rms Relative to Time
Mean rms - 10 Days of Observation
rm s U p   0.03

0.02

0.01

0.00
4 Hrs.          6 Hrs.           8 Hrs.       12 Hrs.     24 Hrs.
Observation Time
26 k        57 k            101 k        127 k       153 k      160 k
201 k       252 k                   299 NOS, 300 k
253 k NOAA,k     NGS
TABLE 2 - Multiple Session rms (21, 2
)
Number of Sessions (n)
North (n)
1           2           3             4         5           6
4 hour           0.010       0.007       0.006         0.005     0.004       0.004
6 hour           0.008       0.006       0.005         0.004
8 hour           0.006       0.004       0.004                                   Multiple Occupation
12 hour          0.005       0.004
24 hour          0.003                                                                Estimates
East (e)
4 hour           0.010       0.007        0.006       0.005      0.005       0.004
6 hour           0.007       0.005        0.004       0.004
8 hour           0.006       0.004        0.004
12 hour          0.006       0.004
24 hour          0.004
Up (u)
4 hour           0.036       0.026        0.021     0.018        0.016       0.015
6 hour           0.029       0.020        0.017     0.014
8 hour           0.027       0.019        0.015
12 hour          0.021       0.015
24 hour          0.016
2
1
Table values are computed using the formula         where is the rms and n is the
n
number of sessions.
2
All baseline distances are included in the computations of the rms of each session
lengths

NOAA, NOS, NGS
NOAA, NOS, NGS
• 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

NOAA, NOS, NGS
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

NOAA, NOS, NGS
NOAA Technical Memorandum NOS NGS-58                                                     Available On-Line at
GUIDELINES FOR ESTABLISHING GPS-DERIVED ELLIPSOID HEIGHTS
(STANDARDS: 2 CM AND 5 CM)
the NGS Web Site:
VERSION 4.3

www.ngs.noaa.gov
David B. Zilkoski
Joseph D. D'Onofrio
Stephen J. Frakes

Silver Spring, MD

November 1997

U.S. DEPARTMENT OF   National Oceanic and         National Ocean   National Geodetic

NOAA, NOS, NGS
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

NOAA, NOS, NGS
NGS Internet Page
www.ngs.noaa.gov

NOAA, NOS, NGS
NOAA, NOS, NGS
NOAA, NOS, NGS
NOAA, NOS, NGS
NOAA, NOS, NGS
NOAA, NOS, NGS
NOAA, NOS, NGS
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

NOAA, NOS, NGS
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

NOAA, NOS, NGS
Obstruction Visibility
Diagram

NOAA, NOS, NGS
Equipment Requirements
 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

NOAA, NOS, NGS
http://www.grdl/GRD/GPS/Projects/ANTCAL/index.shtml

NOAA, NOS, NGS
Trimble Geodetic L1/L2 Antenna
(TRM 22020.00)

Ashtech Geodetic III Antenna
U.S.C.G. V Antenna (ASH 700829.A1)

NOAA, NOS, NGS
NOAA, NOS, NGS
NOAA, NOS, NGS
NOAA, NOS, NGS
NOAA, NOS, NGS
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

NOAA, NOS, NGS
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

NOAA, NOS, NGS
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

NOAA, NOS, NGS
“Fixed” Height
Tripod

NOAA, NOS, NGS
“Slip-leg” Tripod

and

Slant Height
Measurement

NOAA, NOS, NGS
Table 1. -- Summary of Guidelines
Table 1. -- Summary of Guidelines.

Control              Primary Base           Primary Base          Secondary Base         Secondary Base          Local Network           Local Network
2 and 5 cm                2 cm                   5 cm                   2 cm                   5 cm                    2 cm                   5 cm

Dual Frequency             Yes, if base line is   Yes, if base line is   Yes, if base line is   Yes, if base line is   Yes, if base line is    Yes, if base line is    Yes, if base line is
Required                greater than 10 km     greater than 10 km     greater than 10 km     greater than 10 km     greater than 10 km      greater than 10 km      greater than 10 km
Geodetic Quality
Antenna with Ground                 Yes                   Yes                    Yes                    Yes                    Yes                     Yes                     Yes
Plane
Min. Number of                                                                                       No                     No                      No                      No
3                      3                     3
Stations                                                                                       Minimum                Minimum                 Minimum                 Minimum

1                          1                       1                      1
Occupation Time                5 Hours                5 Hours               5 Hours               30 Minutes             30 Minutes              30 Minutes             No Minimum

Number of Days Station                                                                                       2                      2                       2                      2
3                      3                     3                      2                      2                       2                      2
Is Occupied
Max. Distance Between
Same or Higher-Order              75 km                 40 km                  50 km                   15 km                 20 km                   10 km                   20 km
Stations
Average Distance
No Maximum            No Maximum             No Maximum             No Maximum             No Maximum                   7 km                   10 km
Between Stations

Repeat                             3                     3                      3                     3                          3                       3                      3
YES                   YES                    YES                   YES                     YES                     YES                     YES
"Base Line"

Collect Met Data                   Yes                   Yes                    Yes                   Yes                     Yes                      No                      No

Fixed Height Pole                  Yes                   Yes                     No                   Yes                      No                     Yes                      No

Rubbing of Mark                    Yes                   Yes                    Yes                   Yes                     Yes                     Yes                     Yes

Precise Ephemerides                 Yes                   Yes                    Yes                   Yes                     Yes                     Yes                     Yes

4                     5                      5
Fix Integers                     Yes                   Yes                    Yes                   Yes                     Yes                     Yes                     Yes

Notes for Table of Summary of Guidelines:
1
Analyses have indicated that when following all guidelines in this document, 30 minutes of observations over base lines that are typically less than 10 kilometers will meet the standards.
For base lines greater than 10 km, but less than 15 km, 1 hour sessions should meet the standards. For observing sessions greater than 30 minutes, collect data at 15-second epoch interval.
For sessions less than 30 minutes, collect data at 5-second epoch interval. Track satellites down to at least 10-degree elevation cut-off.
2
Base lines must be reobserved on different days with significantly different satellite geometry.
3
The observing scheme requires that all adjacent stations have base lines observed at least twice on two different days with significantly different geometry.
4
If base line is greater than 40 kilometers, a partially fixed or float solution is permitted.
5
For all station pairs except those involved with control stations (see note 4
NOAA, NOS, NGS
Appendix B. - - GPS Ellipsoid Height Hierarchy

HARN/Control Stations
(75 km)

Primary Base
(40 km)

Secondary Base
(15 km)

Local Network Stations
(7 to 10 km)

NOAA, NOS, NGS
HARN/Control Stations

CS1

CS2            75 km            CS3

NOAA, NOS, NGS
Primary Base Stations
CS1
PB1

PB2             40 km            PB3

CS2                                            CS3

NOAA, NOS, NGS
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

NOAA, NOS, NGS
Secondary Base Stations
CS1
PB1
SB1                   SB2

SB3       15 km       SB4

PB2                               PB3

CS2                                             CS3

NOAA, NOS, NGS
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

NOAA, NOS, NGS
Local Network Stations
CS1
PB1
LN1
SB1                            SB2
LN2            LN3

LN4                           LN5

LN6    7 km    LN7

SB3                            SB4
PB2                                        PB3

CS2                                               CS3

NOAA, NOS, NGS
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

NOAA, NOS, NGS
Sample Project Showing Connections
CS2
CS1
LN4
LN1                     LN3
LN2                           PB2
PB1

SB1               LN5         SB2

SB3

SB5
SB4
PB3                                             PB4

CS3                                                           CS4

NOAA, NOS, NGS
Sample Project

NOAA, NOS, NGS
Project Information

• Area: East San Francisco Bay Project
 Latitude   37° 50” N to 38° 10” N
 Longitude 121° 45” W to 122° 25” W

• Standards: 2 cm GPS-Derived Heights

NOAA, NOS, NGS
GPS-Usable Stations
38°20’N
CORS
HARN
NAVD’88 BM
New Station
Spacing Station
Primary Base Station

122°35’W                          LONGITUDE                    121°40’W

NOAA, NOS, NGS
Primary Base Stations
38°20’N
CORS
HARN
NAVD’88 BM                                  D191
New Station               10CC

Primary Base Station

LAKE
MART
MOLA

122°35’W                           LONGITUDE                         121°40’W

NOAA, NOS, NGS
East Bay Project Points
38°16’N
CORS
HARN                                    TIDD             D191
NAVD’88 BM
New Station             10LC
Spacing Station
Primary Base Station
MONT            X469        Z190
DROU
BM20
Q555

04KU
CATT             TOLA
TIDE          5144

ZINC
PT14                                          R100
P371
04HK

MART                                          LAKE

122°20’W                                        LONGITUDE                                     121°40’W

NOAA, NOS, NGS
Observation Sessions
38°16’N
CORS          Session F
Session E
HARN
NAVD’88 BM                                                     Session D
New Station
Spacing Station
Primary Base Station

Session G

Session A
Session C
Session B
122°20’W                               LONGITUDE                          121°40’W

NOAA, NOS, NGS
Independent Base Lines
38°16’N
CORS
HARN
NAVD’88 BM
New Station
Spacing Station
Primary Base Station

122°20’W                              LONGITUDE                    121°40’W

NOAA, NOS, NGS
Observation Schedule
Day   Session          Start Time   Stop Time
1       A               8:00 AM     8:45 AM
1       B               9:15 AM    10:00 AM
1       C              10:30 AM    11:15 AM
1       D              11:45 AM    12:30 PM
1       E               1:00 PM     1:45 PM
1       F               2:15 PM     3:00 PM
1       G               3:30 PM     4:15 PM
2       D               8:00 AM     8:45 AM
2       E               9:15 AM    10:00 AM
2       F              10:30 AM    11:15 AM
2       G              11:45 AM    12:30 PM
2       A               1:00 PM     1:45 PM
2       B               2:15 PM     3:00 PM
2       C               3:30 PM     4:15 PM

NOAA, NOS, NGS
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

NOAA, NOS, NGS
4-Char ID:           Station Name:                                                                                   Day of Year:              Date (UTC):
GPS Station               BEAV                      BEAVER MARSH                                                                                 230                      08/18/98
Observation
Log              Location:                                                                                                            Observing Agency Full Name:
(04-06-99)                       In Beaver Marsh, OR                                                                                     Nat ional Geodet ic Survey

Station PID:            Project Name:                                                                                                        Project Number:           Station SSN:
PB0632                                Oregon FBN, 1998                                                                                    GPS- 1333                       0026

Station                       Latitude                                       Longitude                                Elevation (h) Information         Datum-Ellipsoid:        Session Obs.
Coords.                                                                                                                                                                            230 A
4308' 00.33708"                    N                  1 48' 1 91
21     7.21 5"                   W      Ellipsoidal _1392.66 _ meters              NAD-83

Observing Period:
Scheduled Start (UTC) __1500 ___         Actual Start (UTC) ___1447____
Epoch Interval
15 Second ___ X__
Geoid (96) ___-21 _ _meters
.41

41 58
Orthometric _1 4.1 _meters
Operator Name:
Curt L. Smit h
Phone Number:
Sample Observation Log
Scheduled Start (UTC)   __2030 ___       Actual Stop (UTC)   ___2030 ____              30 Second _______                                                         503-986-3543

TRACKING EQUIPMENT
Trimble 4000SSE
ANTENNA HEIGHT COMPUTATIONS
(Front Side)
Receiver MFR & Model:                                                                      Slant/Vertical Height Measurements
351 0453                                        Measurements Taken                                  Before                                          After
From/To Or Notch #                     (M)                       (FT)                    (M)                     (FT)
Reciver P/N:     18292-20

Antenna Manufacturer:    Trimble
Top of Mark t o #4                       1.286                     4.22                   1.286
Antenna Model:                   /L2
Compact L1 w/GP
Bottom of Ground Plane

Antenna S/N:             0220003686
#8                           1.285                   1.286                   1.285
Antenna Part Number:     22020-00
Antenna Mounting Method: Fixed Height Pole (FHP)___
Fixed Mount: ____    Slip Leg Tripod: __ X _
_                              #12                           1.285                                            1.285

Tripod/FHP Manufacturer: _Wild_____ S/N: _A_____              Mean Slant Height                       1.2853                                            1.2853
_
Tribrach: Wild GDF 22: _X Topcon: ____ None: ___
Trivet: ____ Other: ____ Calibration Date:08/08/98
Vertical Height to ARP                 1.2084                                             1.2084

Total Antenna Cable Length:                     0
_ 1 _ (M)                                                                                            ***See Back of Form****

Antenna Plumb Check: Before? __Y__ After? __Y__               Height Entered Into Receiver: _____1.2084_____ (M)                  Be Very Explicit as to Where and How Measured

Eccentric Occupation? Y _____, N __X (if Y, see back)
_                         Antenna Oriented True North? Yes _X No ____ if No, Explain
_

POWER SOURCE
Camcorder Batteries:     ________                                                                             WEATHER DATA
External 12 Volt:             ____ X____                                      Time            Temperature Dry           Temperature Wet            Reletive                  Pressure
Commercial AC 110 Volt:       ________                                       (UTC)             (F)       (C)             (F)        (C)           Humidity%        (in Hg)              (Mb)
Barometer MFR/Model: __W  allace-Tiernan___
Serial Number: __WP-551 _ Units Read: __Ft ___
79                                     Before           1457           58.0            14.4      56.0         13.3           90.0           29.98           1 5.3
01

Obstructions>10 degrees above horizon? __Y__ (Y or N)         Middle           1745           78.0            25.6      68.0        20.0            58.0           30.00            01
1 6.0
Obstruction Survey Performed?
Yes: ____     No: ____     Performed Previously: _ _X_         After         2031             82.0            27.8      64.0         17.8           36.0           30.01           1 6.3
01
Other (explain):
Mean of Readings                               22.6                                   61.3                           01
1 5.9

Data File Name (Format: aaaaddds.nnn)                                                              5-Digit Weather Code (see reverse for codes)
BEAV230A.DAT
Before:     02020                           Middle:          01
01 1                           After:     00102
aaaa=4-Char ID, ddd=julian day, s=session,
nnn=MFR or software dependent extension                       Weather Taken At Antenna Height? Yes: _ X No: ____ If Not Explain:
_

*Not e* Dimple on disk is about 3 mm deep
3
SV 1 list ed as unhealt hy
SV 24 Off/on due t o probable obst ruct ions
Note: Entries are Required in All Unshaded Areas.                       Vehicle is parked    10    meters      NE     (direction) from antenna.          Log Checked By:          JDD

NOAA, NOS, NGS
GPS           OBSERVATION                      LOG
RADIO FREQUENCY INTERFERENCE: (Report any problems that may be caused by RFI. Give source and location if known.)

/4
Microwave ant enna about 1 mile east of st at ion. No apparent int erference not iced during session.

Station Rubbing or Photograph on Separate Sheet / Unusual Antenna Setups Illustrated on Separate Sheets if Necessary.

Views of Antenna Setup and All Measurements (include known specific antenna constants, radius, and phase center measurements):

Sample Observation Log
(Back Side)

Indicate the distances of the plumb point relative to the station    Slant height measurements are read from the station mark to the
mark= reference point if the horizontal eccentricity for the
s                                                              following identifiable antenna feature, explain:
plumb point is greater than 0.5 mm.                                    Inside not ch, bot t om of ground plane.
TN     VERTICAL antenna height computations from the slant height


measurements (GP=ground plane; ARP=antenna reference point):

Identify ARP =       Bot t om of ant enna pre-amp

None Not ed                                             E (measured slant height) =        1.2853
R (ground plane radius)         = 0.2334
+                                        C (constant; GP to ARP)         = -0.0556
_________

VERTICAL H.I. to ARP = ( E 5 - R 5 ) + C

H.I. Computations to ARP                Feet/Meter Check
4.22              (M)
.26
1 396 + (-0.0556 )                                  
 0.3048
1.20836                (M)                1.286 3          (FT)
CODE         PROBLEM            VISIBILITY        TEMPERATURE            CLOUD COVER               WIND            CONDITION = ENTRY

NORMAL                                                        N,G,W,CL,C    =   00000
GOOD              (0 C TO 27C)            CLEAR                  CLAM             N,F,W,CL,C    =   01000
0         NO PROBLEMS        (OVER 15 MILES)       (32F TO 80F)         (BELOW 20 %)          (UNDER 5 MPH)         Pr,P,W,C,M   =   12001
N,G,W,F,M    =   00200
HOT
PROBLEM               FAIR             (OVER 27C)          PARTLY CLOUDY            MODERATE           N = NONE, P = POOR
1         ENCOUNTERED         (7 MI - 15 MI)       (OVER 80F)            (20 % - 70 %)       (5 MPH - 15 MPH)      W = WARM, F = FAIR
G = GOOD, C = CALM
COLD                                                         M = MODERATE
POOR               (BELOW 0 C)            OVERCAST               STRONG            Pr = PROBLEM
2           NOT USED        (UNDER 7 MILES)       (BELOW 32 F)           (OVER 70 %)          (OVER 15 MPH)         CL = CLEAR
NOAA, NOS, NGS
Rubbing of Survey Disk or Logo Cap

FBN/CBN Observations
Station Name:       OGILVIE                PID:        QC1049
Sample Station Rubbing
Location:       At John Day Airport , OR   County:     Grant

Observer:       Curt is L. Smit h          Date:       8/26/98

Agency/Company:          NGS               Phone:    (503) 986-3543

Stamping:           OGILVIE 1989

Monument by Agency:      ORDT / NGS

Remarks: Oregon Primary GPS St at ion Disk in t op 35 cm round
concret e monument recessed 1cm
NOAA, NOS, NGS
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

NOAA, NOS, NGS
Network / Local Accuracy

NOAA, NOS, NGS
Points of Contact

• National Geodetic Survey
NOAA, N/NGS12
Geodetic Services Division
Bldg. SSMC3, Station 9202      • Curtis L. Smith
1315 East-West Highway           Phone: 208-332-7197
Silver Spring, MD 20910-3282     E-mail: Curt.Smith@noaa.gov
Phone: 301-713-3242
Fax: 301-713-4171

• Internet Web Site:
 www.ngs.noaa.gov

NOAA, NOS, NGS

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