NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean Service National Geodetic Survey 1 GPS-Derived Heights, Focus on NGS 59 Guidelines NGS Webinar May 13, 2010 Silver Spring, Maryland David B. Zilkoski (704) 556-6793 [email protected]
GPS-Derived Heights, Focus on NGS 59 Guidelines. NGS Webinar May 13, 2010 Silver Spring, Maryland David B. Zilkoski (704) 556-6793 [email protected]. Borrowed slides from several presentations by the following NGS employees: Edward Carlson Curtis Smith Dan Roman. Acknowledgements. - PowerPoint PPT Presentation
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GPS-Derived Orthometric Heights*
NGS Webinar
*
Borrowed slides from several presentations by the following NGS
employees:
Edward Carlson
Curtis Smith
Dan Roman
GOAL: Ultimately obtaining GPS derived orthometric heights.
Need to understand the three different heights to fully understand
GPS derived orthometric heights.
Heights & Datums - traditionally orthometric heights meant
above sea level. Now we must be aware of factors affecting our
understanding and use of level interpretations.
You need to be aware of the pitfalls of each height system and
potential problems encountered which may not be fully understood
when using GPS to determine heights.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Review of types of heights and their accuracies
How NGS guidelines can help to reduce, detect, and/or eliminate
error sources
Summary of NGS 58-Guidelines for Establishing GPS-Derived Ellipsoid
Heights
A step-by-step description of NGS 59-Guidelines for Establishing
GPS-Derived Orthometric Heights
Brief discussion of the next National Vertical Datum in 2018
GOAL: Ultimately obtaining GPS derived orthometric heights.
Need to understand the three different heights to fully understand
GPS derived orthometric heights.
Heights & Datums - traditionally orthometric heights meant
above sea level. Now we must be aware of factors affecting our
understanding and use of level interpretations.
You need to be aware of the pitfalls of each height system and
potential problems encountered which may not be fully understood
when using GPS to determine heights.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
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
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Heights & Datums - traditionally orthometric heights meant
above sea level.
Need to understand the three different heights to fully understand
GPS derived orthometric heights.
Need to be aware of the limitations of each height system to
understand what you get when using GPS to determine heights.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
“Geoid”
PO
P
H (Orthometric Height) = Distance along plumb line (PO to P)
Earth’s
N (Geoid Height) = Distance along ellipsoid normal (Q to PO)
h (Ellipsoid Height) = Distance along ellipsoid normal (Q to
P)
Plumb Line
*
Geoid Heights (GEOID09)
Relative differences should typically be less a few mm in 10
km
Total misfit is 1.4 cm squared
Leveling-Derived Heights
Less than 1 cm in 10 km for third-order leveling
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
From: Geodesy, Geoids, and Vertical Datums:
A Perspective from the U.S. National Geodetic Survey
Daniel R. ROMAN, Yan Ming WANG, Jarir SALEH, and Xiaopeng LI
FIG Paper 3768
*
Definitions: GEOIDS versus GEOID HEIGHTS
“The equipotential surface of the Earth’s gravity field which best
fits, in the least squares sense, (global) mean sea level.”*
Can’t see the surface or measure it directly.
Can be modeled from gravity data as they are mathematically
related.
Note that the geoid is a vertical datum surface.
A geoid height is the ellipsoidal height from an ellipsoidal datum
to a geoid.
Hence, geoid height models are directly tied to the geoid and
ellipsoid that define them (i.e., geoid height models are not
interchangeable).
*Definition from the Geodetic Glossary, September 1986
*
-What does equipotential surface mean?
-If we could see or measure the geoid, this could be our vertical
datum.
-It may be in the future, and we must plan for a transition.
-For now, we are dependant on leveling observations on the surface
to create our datum.
-The leveling datum may or may not be a true equipotential surface
(i.e., NAVD 88 =/ true geoid).
-use the geoid height models to transform between the ellipsoidal
and vertical datums.
-the discussion of geoid height models will be reserved fr the
datum transfrormation section as that is there intended use.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
USGG2009 – TOITRF00 => USGG2009*
Use same math model to predict on even grid (15’)
Interpolate grid to 1’
GEOID09 = USGG2009 – Conversion Surface
*
Terrain: EGM08 implicit 5’
EGM08 was used to reject 450,000 points.
Subsequent work has determined a better means of filtering that
only rejects 1300 or so points by accounting for 3” to 5’ RTM
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
*
Space leveling
*
Space leveling
*
Earth Gravitational Model 2008 (EGM2008)
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
*
Shuttle Radar Topography Mission
*
*
Most of the rejected points were in the northern Rockies – hence,
the big shift there.
*
*
GPSBM2009 (GEOID09 Control Data)
20446 total less 1003 rejected leaves 18,867 (CONUS) plus 576
(Canada)
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
*
Hybrid Geoid biased to fit local benchmarks
e = h – H - N
h
h
h
h
h
H
H
H
H
H
N
N
N
N
N
to transform from the NGS gravimetric geoid to NAVD 88 is more
complicated
Gravimetric geoid is from derived from gravity measurements
NAVD 88 bench marks are adjusted using a sea level height at Point
au Pere
There is going to be a slight difference between the 2. If we want
to use geoid to compute NAVD 88 heights, it must be consistent with
the NAVD 88
Therefore we “bias” the geoid to be consistent with the NAVD 88
using high accuracy GPS on NAVD 88 bench marks.
Use Least Squares Collocation to determine the systematic
components while allowing for random GPS observation errors (2-5 cm
standard).
-Use the control points (GPSBM’s) to define a surface that can be
interpolated to make internally consistent predictions (precision
versus accuracy).
As you can easily see, the quality and distribution of the control,
data will directly impact the quality of the predictions.
also note that the error vector residual (e) is a function of all
the errors sources: from the GPS observations (usually random, but
each HARN could have systematic errors), the gravimetric geoid
height model (errors in gravity & terrain data as well as
theoretical/processing errors can contribute here) as well as any
errors in the NAVD 88 network.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
*
*
*
*
*
*
*
National Geodetic Survey, Retrieval Date = JANUARY 29, 2010 BL2014
***********************************************************************
BL2014 PACS - This is a Primary Airport Control Station.
BL2014 DESIGNATION - CONPORT
BL2014 PID - BL2014
BL2014 STATE/COUNTY- TX/MONTGOMERY
BL2014
BL2014* NAD 83(2007)- 30 21 11.32003(N) 095 25 02.13449(W)
ADJUSTED
BL2014* NAVD 88 - 71.493 (meters) 234.56 (feet) ADJUSTED
BL2014
___________________________________________________________________
BL2014 LAPLACE CORR- 0.08 (seconds) USDV2009
BL2014 ELLIP HEIGHT- 43.982 (meters) (02/10/07) ADJUSTED
BL2014 GEOID HEIGHT- -27.51 (meters) GEOID09
BL2014 DYNAMIC HT - 71.398 (meters) 234.24 (feet) COMP
BL2014
BL2014 Type PID Designation North East Ellip
BL2014
-------------------------------------------------------------------
BL2014
-------------------------------------------------------------------
BL2014
N
H
h
NAVD88 – Ellip Ht + Geoid Ht = …
71.493 – 43.982 – 28.549 = -1.038 USGG2009
71.493 – 43.982 – 27.514 = -0.003 GEOID09
71.493 – 43.982 – 27.538 = -0.027 GEOID03
-In a perfect world these heights would add up mathematically. But
every height is derived in a way that includes some measure of
error, whether it is from an observation and adjustment process or
simply because it is derived from a model. The purpose of creating
a version of the geoid model that is biased to fit the NAVD88 is to
provide a means to compute that NAVD88 height from GPS and the
model alone. You can see here how the change from the scientific
model to the hybrid model provides a better fit between the 3
heights. And as the geoid model improves, along with our ability to
measure and compute better ellipsoid heights, these differences
will get smaller and smaller.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Earth’s Surface
Hybrid Geoid Model warped to fit local bench marks
h
h
h
h
h
H
H
H
H
H
N
N
N
N
N
*
*
Future changes will likely not be as great
Similar to changes seen in ITRF series
Changes from GEOID03 to GEOID09 are significant
Largely driven by GPSBM changes
GEOID09 best matches heights in database now
GEOID03 does not
*
GEOID Team
*
Review of types of heights and their accuracies
How NGS guidelines can help to reduce, detect, and/or eliminate
error sources
Summary of NGS 58-Guidelines for Establishing GPS-Derived Ellipsoid
Heights
A step-by-step description of NGS 59-Guidelines for Establishing
GPS-Derived Orthometric Heights
Brief discussion of the next National Vertical Datum in 2018
GOAL: Ultimately obtaining GPS derived orthometric heights.
Need to understand the three different heights to fully understand
GPS derived orthometric heights.
Heights & Datums - traditionally orthometric heights meant
above sea level. Now we must be aware of factors affecting our
understanding and use of level interpretations.
You need to be aware of the pitfalls of each height system and
potential problems encountered which may not be fully understood
when using GPS to determine heights.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
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
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Special Projects Are Performed to Develop Guidelines
Guidelines Are Modified as Procedures, Equipment, and Models
Improve
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
= 4.4
Chart1
0
0
0
0
0
1
1
1
1
1
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18
18
Time (0 = 0 to 6 hr, 1 = 1 to 7 hr,....., 18 = 18 to 24 hr)
Ellipsoid Height Correction (cm)
LAKE HOUSTON to NORTHEAST- (23 km) Days 300 - 304; 6 Hour Solutions
- With Tropo Modeling
-5.1
-5.5
-6
-8.3
-8.7
-5.25
-5.8
-6.1
-7.8
-8.05
-5.3
-5
-5
-7
-7
-7
-5.5
-5.8
-7.8
-6.2
-7
-5.4
-5
-6.4
-5.1
-6.8
-5.6
-4.6
-6.8
-5.9
-7.7
-5.9
-4.1
-7.4
-5.3
-5.7
-5
-3.3
-6.2
-5.1
-5.1
-5.8
-4.2
-6.05
-5.15
-5.9
-5.4
-5.7
-6.1
-5.2
-4.6
-3.8
-5.95
-5.3
-4.9
-4.9
-4.2
-5.9
-4.9
-5.7
-2.8
-4.3
-5
-3.3
-4.3
-4.1
-5.9
-6.5
-5
-5.8
-5.9
-6.2
-6.8
-5.3
-6.7
-3.1
-5.1
-4.9
-4.1
-4.95
-2.85
-7
-4.7
-3.3
-4.05
-3
-7
-5.8
-4.3
-4.25
-5.95
-6.8
-5.9
-5.35
-5.3
Sheet1
0
-5.1
-5.5
-6
-8.3
-8.7
1
-5.25
-5.8
-6.1
-7.8
-8.05
2
-5.3
-5
-5
-7
-7
3
-7
-5.5
-5.8
-7.8
-6.2
4
-7
-5.4
-5
-6.4
-5.1
5
-6.8
-5.6
-4.6
-6.8
-5.9
6
-7.7
-5.9
-4.1
-7.4
-5.3
7
-5.7
-5
-3.3
-6.2
-5.1
8
-5.1
-5.8
-4.2
-6.05
-5.15
9
-5.9
-5.4
-5.7
-6.1
-5.2
10
-4.6
-3.8
-5.95
-5.3
-4.9
11
-4.9
-4.2
-5.9
-4.9
-5.7
12
-2.8
-4.3
-5
-3.3
-4.3
13
-4.1
-5.9
-6.5
-5
-5.8
14
-5.9
-6.2
-6.8
-5.3
-6.7
15
-3.1
-5.1
-4.9
-4.1
-4.95
16
-2.85
-7
-4.7
-3.3
-4.05
17
-3
-7
-5.8
-4.3
-4.25
18
-5.95
-6.8
-5.9
-5.35
-5.3
Sheet2
Sheet3
*
Day 131
0.6
1.3
= 1.3
Chart1
3
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20
20
21
21
Time (3 = 3 to 6 hr, 4 = 4 to 7 hr, ...., 21 = 21 to 24 hr)
Up Component (cm)
ADDICKS to PAM 3 (4.2 km) Days 130 and 131 (3 hour solutions - w/o
Sat 15)
1.4
1.2
1.2
1.3
1.4
1.7
1.6
1.95
1
1.6
0.6
1.1
0.4
0.8
0.9
0.7
0.8
0.5
1.2
0.4
1.2
0.55
1.1
0.5
0.65
1.1
0.7
0.9
0.8
1.6
1.2
0.7
2.8
0.6
3.4
0.9
3
1.4
Sheet1
3
1.4
1.2
4
1.2
1.3
5
1.4
1.7
6
1.6
1.95
7
1
1.6
8
0.6
1.1
9
0.4
0.8
10
0.9
0.7
11
0.8
0.5
12
1.2
0.4
13
1.2
0.55
14
1.1
0.5
15
0.65
1.1
16
0.7
0.9
17
0.8
1.6
18
1.2
0.7
19
2.8
0.6
20
3.4
0.9
21
3
1.4
Sheet2
Sheet3
*
Day 131
0.5
2.0
= 2.1
Chart1
3
3
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17
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18
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19
20
20
21
21
Time (3 = 3 to 6 hrs, 4 = 4 to 7 hrs,...., 21 = 21 to 24 hrs)
Up Component (cm)
ADDICK to PAM 3 Days 130 and 131 (3 hour solutions - w/o Sat
15)
1.4
1.2
1.2
1.3
1.4
1.7
1.6
1.95
1
1.6
0.6
1.1
0.4
0.8
0.9
0.7
0.8
0.5
1.2
0.4
1.2
0.55
1.1
0.5
0.65
1.1
0.7
0.9
0.8
1.6
1.2
0.7
2.8
0.6
3.4
0.9
3
1.4
Chart2
3
3
4
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20
21
21
22
22
Time (3 = 3 to 5 hr, 4 = 4 to 6 hr, ...., 22 = 22 to 24 hr)
Up Component (cm)
ADDICKS to PAM 3 (4.2 km) Days 130 and 131 ( 2 hour solutions - w/o
Sat 15)
1.75
1.3
1
1.2
1.2
1.3
1.6
1.9
1.8
2.2
0.5
1.1
0.3
0.7
0.65
0.75
1
0.6
0.7
0.3
1.4
0.3
1.5
0.6
0.65
0.7
0.6
0.8
1.3
1.5
0.8
1.6
-0.4
0.4
4.5
0.4
3.6
1.6
2.6
1.65
Sheet1
3
1.75
1.3
4
1
1.2
5
1.2
1.3
6
1.6
1.9
7
1.8
2.2
8
0.5
1.1
9
0.3
0.7
10
0.65
0.75
11
1
0.6
12
0.7
0.3
13
1.4
0.3
14
1.5
0.6
15
0.65
0.7
16
0.6
0.8
17
1.3
1.5
18
0.8
1.6
19
-0.4
0.4
20
4.5
0.4
21
3.6
1.6
22
2.6
1.65
Sheet2
Sheet3
*
Day 131
0.3
2.0
= 2.4
Chart1
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20
20
21
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22
22
23
23
Time (3 = 3 to 4 hr, 4 = 4 to 5 hr, ...., 23 = 23 to 24 hr)
Up Component (cm)
ADDICKS to PAM 3 (4.2 km) Days 130 and 131 (1 hour solutions - w/o
Sat 15)
1.8
1.5
0.8
0.7
1.2
1.2
1.1
1.3
1.8
2.2
0.6
1.9
-0.3
0.5
0.7
0.9
0.9
0.6
-0.2
1.5
0.3
0.1
1.9
0.3
0.8
1.7
0.3
0
1
1.4
1.7
1.5
-2
1.6
-1.6
-2
5.2
2
3.2
1.9
2.5
1.4
Sheet1
3
1.8
1.5
4
0.8
0.7
5
1.2
1.2
6
1.1
1.3
7
1.8
2.2
8
0.6
1.9
9
-0.3
0.5
10
0.7
0.9
11
0.9
0.6
12
-0.2
1.5
13
0.3
0.1
14
1.9
0.3
15
0.8
1.7
16
0.3
0
17
1
1.4
18
1.7
1.5
19
-2
1.6
20
-1.6
-2
21
5.2
2
22
3.2
1.9
23
2.5
1.4
Sheet2
Sheet3
*
Sheet1
Comparison of 30 Minute Solutions - Precise Orbit; Hopfield (0);
IONOFREE
(30 Minute solutions computed on the hour and the half hour)
MOLA to YACH 12.9 Km
Day 264
dh (m)
Hours Diff.
Day 265
dh (m)
* diff >2 cm
Mean dh (m)
* diff >2 cm
*
Based on Special Studies
Must repeat base lines on different days and at different times of
the day
Must reobserve repeat base lines that disagree by more than 2
cm
Must FIX integers
Stations Must Be Connected to at Least its Two Nearest
Neighbors
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Review of types of heights and their accuracies
How NGS guidelines can help to reduce, detect, and/or eliminate
error sources
Summary of NGS 58-Guidelines for Establishing GPS-Derived Ellipsoid
Heights
A step-by-step description of NGS 59-Guidelines for Establishing
GPS-Derived Orthometric Heights
Brief discussion of the next National Vertical Datum in 2018
GOAL: Ultimately obtaining GPS derived orthometric heights.
Need to understand the three different heights to fully understand
GPS derived orthometric heights.
Heights & Datums - traditionally orthometric heights meant
above sea level. Now we must be aware of factors affecting our
understanding and use of level interpretations.
You need to be aware of the pitfalls of each height system and
potential problems encountered which may not be fully understood
when using GPS to determine heights.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
(Standards: 2 cm and 5 cm)
Guidelines - will eventually become routine; not so much
explanation of why its done but provides background information.
Repeat baselines, station spacing, fixed height antenna setups,
identify and control all error sources, tie local networks
together, etc..
NOS NGS-58 GPS-Derived Ellipsoid Heights Guidelines will lay the
foundation for GPS-Derived Orthometric Heights Guidelines. Produce
2 cm ellipsoid heights to be able to obtain 2 cm orthometric
heights.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
*
Basic Requirements:
5 Hour Sessions / 3 Days (ARE 5 HOURS SESSIONS STILL
NECESSARY?)
Spacing between PBS cannot exceed 40 km
Each PBS must be connected to at least its nearest PBS neighbor and
nearest control station
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Used to Bridge Gap Between Primary and Local Control Stations
Spacing between SBS cannot exceed 15 km (may need to be reobserved
more often due to length)
All base stations (primary and secondary) must be connected to at
least its 2 nearest primary or secondary base station
neighbors
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
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
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Local Network Stations
Basic Requirement 30 Minute Sessions / 2 Days / Different times of
the day
NOTE: In order to obtain 30 minutes of good, valid data, the user
should occupy the station for at least 45 minutes
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
*
Table 1. -- Summary of Guidelines
Summary of the guidelines broken down into columns indicating 2 cm
or 5 cm standards with the rows identifying key elements discussed
in the NOS NGS-58 GPS-Derived Ellipsoid Heights Guidelines.
Guidelines - will eventually become routine; not so much why they
work but will provide background information. Repeat baselines,
station spacing, fixed height antenna setups, etc. Control all
error sources, tie local networks together.
Table 1. -- Summary of Guidelines.
Control
Geodetic Quality Antenna with Ground
Plane
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
Guidelines - version 4.3 (November 1997) 1
_977042228.unknown
*
Basic Concept of Guidelines
Stations in one local 3-dimensional network connected to another
local network to better than 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
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
*
Review of types of heights and their accuracies
How NGS guidelines can help to reduce, detect, and/or eliminate
error sources
Summary of NGS 58-Guidelines for Establishing GPS-Derived Ellipsoid
Heights
A step-by-step description of NGS 59-Guidelines for Establishing
GPS-Derived Orthometric Heights
Brief discussion of the next National Vertical Datum in 2018
GOAL: Ultimately obtaining GPS derived orthometric heights.
Need to understand the three different heights to fully understand
GPS derived orthometric heights.
Heights & Datums - traditionally orthometric heights meant
above sea level. Now we must be aware of factors affecting our
understanding and use of level interpretations.
You need to be aware of the pitfalls of each height system and
potential problems encountered which may not be fully understood
when using GPS to determine heights.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
*
Guidelines - will eventually become routine; not so much
explanation of why its done but provides background information.
Repeat baselines, station spacing, fixed height antenna setups,
identify and control all error sources, tie local networks
together, etc..
NOS NGS-58 GPS-Derived Ellipsoid Heights Guidelines will lay the
foundation for GPS-Derived Orthometric Heights Guidelines. Produce
2 cm ellipsoid heights to be able to obtain 2 cm orthometric
heights.
NOAA Technical Memorandum NOS NGS-59
GUIDELINES FOR ESTABLISHING GPS-DERIVED ORTHOMETRIC HEIGHTS
VERSION 1.5
U.S. DEPARTMENT OF National Oceanic and National Ocean National
Geodetic
COMMERCE Atmospheric Administration Service Survey
EMBED WPDraw30.Drawing
*
The 3-4-5 System
*
Rule 2:
Rule 3:
Pretty straight forward.
*
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
This same information is required by the GPS-derived Orthometric
heights guidelines. Producing ellipsoid heights at the 2 cm level
of accuracy is essential to producing accurate GPS-derived
orthometric heights.
Surrounding project areas will be difficult in many instances with
existing NAVD88 bench marks. Level ties may be necessary to provide
this requirement.
Extra bench marks allow independent analysis through the adjustment
process and may help identify potential bench marks with
questionable stability or poor published elevations.
Bench marks at base and top of mountains may help identify/rectify
issues that are not otherwise apparent in the geoid model.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
the 20 km rule was met.
BCR2: This requirement is not applicable because the project is
greater than 20 km on a side.
BCR4: This requirement is not applicable because project is not in
a mountainous region.
BCR Example
BCR3: Circled bench marks are mandatory. Analysis must indicate
bench marks have valid
NAVD 88 heights. Other BMs can be substituted but user must adhere
to 20 km requirement.
Sample GPS-derived orthometric height project illustrating
conditions of basic control requirements.
NAVD88 bench marks shown as yellow boxes. Project area is larger
than 20 km so minimum 20 km spacing between bench marks is
required. Bench marks are scattered throughout and surround project
area.
Circled bench marks are required to satisfy guidelines. Additional
bench marks provide redundancy, allow checks on adjusted
elevations, and could be alternate marks if one or more of the
circled mark’s published elevations don’t fit the survey.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
BAP-1: Perform 3-D minimum-constraint least squares adjustment of
GPS survey project
Constrain 1 latitude, 1 longitude, 1 orthometric height
BAP-2: Analyze adjustment results from BP-1
Detect and remove all data outliers
The basic procedures describe the network adjustment and analysis
routine. You are starting with good GPS-derived ellipsoid heights.
If you don’t achieve 2 cm ellipsoid heights you can’t expect 2 cm
orthometric heights.
Constraining one orthometric height shifts the adjusted elevations
from ellipsoid height plus geoid height to the orthometric “plane.”
This provides a chance to compare the adjusted GPS-derived
orthometric heights with their published orthometric
elevations.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Plot of free adjustment ellipsoid height residuals by baseline
length.
Identify and investigate residuals greater than 2 cm. Reprocess if
possible, re-observe if necessary.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Station pairs with large residuals, i.e., greater than 2.5 cm, also
have large repeat base line differences. NGS guidelines for
estimating GPS-derived ellipsoid heights require user to re-observe
these base lines. Following NGS guidelines provides enough
redundancy for adjustment process to detect outliers and apply
residual on appropriate observation, i.e., the bad vector.
Repeat baseline comparisons also indicate which baselines will show
large residuals.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Five Basic Procedures
Compare free adjusted NAVD88 elevations against published
elevations. Determine trends from differences, such as slope, and
which bench marks don’t fit.
Check monument type and setting information, reported station
condition, and history data (i.e., mark set and leveled in 1950) to
see if there is a reason for station elevation to not fit with the
adjustment.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
GPS-Derived Orthometric Heights Minus NAVD88 Heights
All height differences are under 5 cm and most are less than 2 cm.
Almost all relative height differences between adjacent station
pairs are less than 2 cm. However, most of the height differences
appear to be positive relative to the southwest corner of the
project.
Geoid99
Units = Centimeters
Plot height differences on map to show trends, such as slope, and
note relationship of adjacent stations. A slope or tilt across the
project area is expected but large jumps between adjacent stations
should not happen.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
BAP-4: Determine which BMs have valid NAVD88 height values from
results from BP-3
Differences need to agree 2 cm for 2 cm survey
Differences need to agree 5 cm for 5 cm survey
May detect systematic tilt over large areas
Solve for geoidal slope and scale
BAP-5: Perform constrained adjustment with results from BP-4
Constrain 1 latitude, 1 longitude, all valid orthometric height
values
Ensure final heights not distorted in adjustment
Five Basic Procedures
(continued)
Constraining the selected bench marks at the 20 km spacing and
comparing how the NAVD88 orthometric heights fit at the rest of the
bench marks provides an excellent check on the validity of the
adjusted network.
The final constrained vertical adjustment includes all orthometric
heights at bench marks determined to be consistent with the rest of
the network. After final constrained adjustment has been performed
make sure that the constraints didn’t distort the rest of the
adjustment.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
To detect and remove any systematic trend, a tilted plane is best
fit to the height differences (Vincenty 1987, Zilkoski and Hothem
1989). After a trend has been removed, all the differences are less
than +/- 2 cm except for one and almost all relative differences
between adjacent stations are less than 2 cm.
GPS-Derived Orthometric Heights Minus NAVD88 Heights
Geoid99
Units = Centimeters
Plot height differences on map after tilted plane has been removed
and note relationships especially between of adjacent
stations.
The station in the far northwest corner of the project seems to be
the only one that falls outside of 2 cm. This was one of the
originally chosen 20 km stations. The “extra” stations allows this
one to be removed as a constraint yet provide NAVD88 bench marks at
the 20 km spacing.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
After rejecting the largest height difference (-2.4 cm), of all the
closely spaced station pairs only 3 are greater than 2 cm, 1 is
greater than 2.5 cm and none are greater than 3 cm.
GPS-Derived Orthometric Heights Minus NAVD88 Heights
Geoid99
Units = Centimeters
Plot height differences on map after tilted plane and the one
rejected NAVD88 constraint station has been removed. All remaining
constrained stations show that this project is within the 2 cm
standard.
The NAVD88 orthometric heights determined for the remaining
stations included in this network should reflect the same
differences as the constrained stations surrounding them.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
The NGS Data SheetSee file dsdata.txt for more information about
the datasheet.DATABASE = ,PROGRAM = datasheet, VERSION = 7.85
1 National Geodetic Survey, Retrieval Date = MAY 5, 2010
DF8611
***********************************************************************
DF8611 DESIGNATION - KEYS
DF8611 PID - DF8611
DF8611 STATE/COUNTY- CA/TUOLUMNE
DF8611
DF8611* NAD 83(2007)- 37 50 41.57945(N) 120 30 24.15335(W)
ADJUSTED
DF8611* NAVD 88 - 336.56 (meters) 1104.2 (feet) GPS OBS
DF8611
___________________________________________________________________
DF8611 LAPLACE CORR- 8.69 (seconds) DEFLEC09
DF8611 ELLIP HEIGHT- 306.911 (meters) (02/10/07) ADJUSTED
DF8611 GEOID HEIGHT- -29.65 (meters) GEOID09
DF8611
DF8611 Type PID Designation North East Ellip
DF8611
-------------------------------------------------------------------
DF8611
-------------------------------------------------------------------
DF8611
DF8611.and adjusted by the National Geodetic Survey in February
2007.
DF8611
DF8611.The datum tag of NAD 83(2007) is equivalent to NAD
83(NSRS2007).
DF8611.See National Readjustment for more information.
DF8611.The horizontal coordinates are valid at the epoch date
displayed above.
DF8611.The epoch date for horizontal control is a decimal
equivalence
DF8611.of Year/Month/Day.
DF8611.The orthometric height was determined by GPS observations
and a
DF8611.high-resolution geoid model using precise GPS observation
and
DF8611.processing techniques.
DF8611
DF8611.The X, Y, and Z were computed from the position and the
ellipsoidal ht.
DF8611
DF8611
DF8611.and is referenced to NAD 83.
DF8611
Elevation published
to centimeters
Orthometric height
*
GEOID03 = 0.02 m
GEOID09 = 0.00 m
Following NGS guidelines, achieving 2 cm or 5 cm accuracy, and
submitting the project to NGS will get NAVD88 orthometric
elevations published to centimeters.
Metadata will define the method of determination as that done by
GPS observations using a high resolution geoid model using precise
GPS observations and processing techniques.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Topography
A
B
C
D
E
F
*
GPS-Derived Orthometric Heights
GEOID09
Ellipsoid
h
h
h
h
h
h
HGPS
HGPS
N
N
N
N
N
N
GEOID09
*
Published NAVD88 to GPS Derived
H =
102.431 =
GEOID96 = 0.17 m
GEOID99 = 0.11 m
GEOID03 = 0.05 m
GEOID09 = 0.02 m
Typical published NGS data sheet with current coordinate and height
information. This is one of the bench marks observed with GPS in
the San Francisco Bay Demonstration Project. GPS 2 cm heights
determined on a NAVD88 bench mark.
The published NAVD88 orthometric height does not equal the
published ellipsoid height minus the geoid height as indicated by
the equation H=h-N.
These heights were determined by two entirely different methods,
GPS-derived orthometric heights (ellipsoid heights minus geoid
heights) and leveling-derived orthometric heights (optical leveling
plus orthometric corrections), not to mention bench mark stability,
and reflects our uncertainty of each. As our understanding and
models improve this disparity should become smaller, as indicated
between the various geoid models, but will never really
equal.
HT2268 DESIGNATION - S 1320
HT2268
HT2268* NAD 83(1992)- 37 45 25.30727(N) 122 28 36.34687(W)
ADJUSTED
HT2268* NAVD 88 - 102.431 (meters) 336.06 (feet) ADJUSTED
HT2268
___________________________________________________________________
HT2268 LAPLACE CORR- 5.53 (seconds) DEFLEC03
HT2268 ELLIP HEIGHT- 69.78 (meters) GPS OBS
HT2268 GEOID HEIGHT- -32.60 (meters) GEOID03
HT2268 DYNAMIC HT - 102.363 (meters) 335.84 (feet) COMP
HT2268 MODELED GRAV- 979,964.0 (mgal) NAVD 88
HT2268
HT2268
*
Review of types of heights and their accuracies
How NGS guidelines can help to reduce, detect, and/or eliminate
error sources
Summary of NGS 58-Guidelines for Establishing GPS-Derived Ellipsoid
Heights
A step-by-step description of NGS 59-Guidelines for Establishing
GPS-Derived Orthometric Heights
Brief discussion of the next National Vertical Datum in 2018
GOAL: Ultimately obtaining GPS derived orthometric heights.
Need to understand the three different heights to fully understand
GPS derived orthometric heights.
Heights & Datums - traditionally orthometric heights meant
above sea level. Now we must be aware of factors affecting our
understanding and use of level interpretations.
You need to be aware of the pitfalls of each height system and
potential problems encountered which may not be fully understood
when using GPS to determine heights.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
$38.5M over 10 years
Airborne Gravity Snapshot
Absolute Gravity Tracking
Re-define the Vertical Datum of the USA by 2018 (if fully funded
beginning in 2009)
Part of the NGS 10 year plan (2008-2018)
Target: 2 cm accuracy orthometric heights from GNSS and a geoid
model
What is GRAV-D?
*
*
*
Note that in this picture the geoid is shown above the ellipsoid.
In the continental United States, the geoid is actually below the
ellipsoid, so the value of the geoid height is negative.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
*
Mission, Vision and Strategy
Modernized agency
Vetted through NSPS/AAGS
Cm-accuracy access to all coordinates
Customer-focused agency
*
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
Ten-Year Milestones (2018)
1) NGS will compute a pole-to-equator, Alaska-to-Newfoundland geoid
model, preferably in conjunction with Mexico and Canada as well as
other interested governments, with an accuracy of 1 cm in as many
locations as possible
2) NGS redefines the vertical datum based on GNSS and a gravimetric
geoid
*
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
User registration - ID & password, Validation process,
OPUS solutions can be integrated into the NGS database
Data elements from OPUS , Additional metadata
Submission review by user and NGS
OPUS Projects
Managers can define a project
Process any number of stations under a project, Project can span
several days to weeks, Contract work
Project processing
Each dataset sent to OPUS but identified with a project, Results
returned to submitter a few minutes later, Manager can monitor
processing and submission
Final adjustment
Entire project adjusted as one campaign, Review & submission to
NGS
OPUS Rapid Static
User requests, Single frequency capability, Rapid static solutions
(10 – 15 minutes of data), Will be processed with carrier
phases
Accurate to several centimeters, Need more accurate ionospheric and
tropospheric modeling In development at OSU and NGS
OPUS GIS
Compute a differential pseudorange solution for less expensive GPS
receivers
Aimed at the GIS community who do not require cm level
accuracies
Allows processing in a consistent approach and “certify” their
locations in the NSRS
Generate rapid static solution from seconds or minutes of
data
Accuracies: A few decimeters to a meter horizontally
Pilot project underway in Phoenix, Arizona
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean
Service National Geodetic Survey
*
CORS 1
CORS 2
CORS 3
*
*
*
*
*
*
*
*
*
*
*
How Long is Long Enough?
Always Repeat Observations on a Different Day at a Different Time
of Day
Did You Detect, Reduce, and/or Eliminate Error Sources?
Always Follow Prescribed Guidelines
*
GUIDELINES FOR ESTABLISHING GPS -DERIVED ELLIPSOID HEIGHTS
(STANDARDS: 2 CM AN D 5 CM)
VERSION 4.3
U.S. DEPARTMENT OF National Oceanic and National Ocean National
Geodetic
COMMERCE Atmospheric Administration Service Survey
LAKE HOUSTON to NORTHEAST- (23 km)
Days 300 - 304; 6 Hour Solutions - With Tropo Modeling
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
0123456789
101112131415161718
Time (0 = 0 to 6 hr, 1 = 1 to 7 hr,....., 18 = 18 to 24 hr)
Ellipsoid Height Correction (cm)
Days 130 and 131 (3 hour solutions - w/o Sat 15)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
3456789101112131415161718192021
Time (3 = 3 to 6 hr, 4 = 4 to 7 hr, ...., 21 = 21 to 24 hr)
Up Component (cm)
Days 130 and 131 ( 2 hour solutions - w/o Sat 15)
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
345678910111213141516171819202122
Time (3 = 3 to 5 hr, 4 = 4 to 6 hr, ...., 22 = 22 to 24 hr)
Up Component (cm)
Days 130 and 131 (1 hour solutions - w/o Sat 15)
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
34567891011121314151617181920212223
Time (3 = 3 to 4 hr, 4 = 4 to 5 hr, ...., 23 = 23 to 24 hr)
Comparison of 30 Minute Solutions - Precise Orbit; Hopfield (0);
IONOFREE
(30 Minute solutions computed on the hour and the half hour)
MOLA to YACH 12.9 Km
Day 264
GUIDELINES FOR ESTABLISHING GPS-DERIVED ELLIPSOID HEIGHTS
(STANDARDS: 2 CM AND 5 CM)
VERSION 4.3
greater than 10 km
greater than 10 km
greate
greater than 10 km
greater than 10 km
greater than 10 km
greater than 10 km
1
An
alyses 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
session
-
-
-
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 geome
try.
4
If base line is greater than 40 kilometers, a partially fixed or
float solution is permitted.
5
h control stations (see note 4
NOAA Technical Memorandum NOS NGS -59
GUIDELINES FOR ESTABLISHING GPS -DERIVED ORTHOMETRIC HEIGHTS
VERSION 1.5
U.S. DEPARTMENT OF National Oceanic and National Ocean National
Geodetic
COMMERCE Atmospheric Administration Service Survey
HT2268 DESIGNATION - S 1320
HT2268
HT2268* NAD 83(1992)- 37 45 25.30727(N) 122 28 36.34687(W)
ADJUSTED
HT2268* NAVD 88 - 102.431 (meters) 336.06 (feet) ADJUSTED
HT2268 __________________________________________________
_________________
HT2268 LAPLACE CORR- 5.53 (seconds) DEFLEC03
HT2268 ELLIP HEIGHT- 69.78 (meters) GPS OBS
HT2268 GEOID HEIGHT- -32.60 (meters) GEOID03
HT2268 DYNAMIC HT - 102.363 (meters) 335.84 (feet) COMP
HT2268 MODELED GRAV- 979,964.0 (mgal) NAVD 88
HT2268
HT2268