NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean Service National Geodetic Survey 1...

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
*
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
*
Heights & Datums - traditionally orthometric heights meant above sea level.
Need to be aware of the limitations of each height system to understand what you get when using GPS to determine heights.
*
“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
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.
*
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
*
*
Space leveling
*
Space leveling
*
Earth Gravitational Model 2008 (EGM2008)
*
*
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)
*
*
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 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.
*
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
*
*
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
*
Special Projects Are Performed to Develop Guidelines
Guidelines Are Modified as Procedures, Equipment, and Models Improve
*
= 4.4
Chart1
0
0
0
0
0
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
4
4
4
4
4
5
5
5
5
5
6
6
6
6
6
7
7
7
7
7
8
8
8
8
8
9
9
9
9
9
10
10
10
10
10
11
11
11
11
11
12
12
12
12
12
13
13
13
13
13
14
14
14
14
14
15
15
15
15
15
16
16
16
16
16
17
17
17
17
17
18
18
18
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
3
4
4
5
5
6
6
7
7
8
8
9
9
10
10
11
11
12
12
13
13
14
14
15
15
16
16
17
17
18
18
19
19
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
4
4
5
5
6
6
7
7
8
8
9
9
10
10
11
11
12
12
13
13
14
14
15
15
16
16
17
17
18
18
19
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
4
5
5
6
6
7
7
8
8
9
9
10
10
11
11
12
12
13
13
14
14
15
15
16
16
17
17
18
18
19
19
20
20
21
21
22
22
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
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
10
11
11
12
12
13
13
14
14
15
15
16
16
17
17
18
18
19
19
20
20
21
21
22
22
23
23
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
*
*
(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.
*
*
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
*
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
*
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
*
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
*
*
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
*
*
*
*
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.
*
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.
*
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.
*
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.
*
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.
*
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.
*
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.
*
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.
*
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.
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.
*
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.
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.
*
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.
*
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
*
*
$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.
*
*
Mission, Vision and Strategy
Modernized agency
Vetted through NSPS/AAGS
Cm-accuracy access to all coordinates
Customer-focused agency
*
*
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
*
*
*
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
*
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
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
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
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
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
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

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean Service National Geodetic Survey 1...

Documents

Transcript of NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION National Ocean Service National Geodetic Survey 1...