# Presentation: 236758

## National Readjustment

**Dale Pursell**
**   ****Observation and Analysis Division**
**National Geodetic Survey**
**	**
**League of CA Surveyors Org.**
**December 7, 2006**

**Notes:**
My introduction
I Came to NGS in 1975 to automate abstracts of classical observations
I was heavily involved in all phases of the NAD83(86) adjustment
Since then, I continued to be involved in all types of adjustments
Spent 5 years as an orbiteer, adjusting orbits through PAGE (s)
Got involved in CSRC
Selected as Chief of the project analysis Branch
Became familiar with leveling observations and adjustments

## NATIONAL READJUSTMENT

**WHAT?**
**WHY**
**HOW**
**WHEN**
**POST**
**QUESTIONS**

**Notes:**
Briefly explain:
What is the NSRS (all things to all people)
Why do we need a national readjustment (The What will explain why we just can’t have CORS)
How the national readjustment will be accomplished  The steps involved
The all important (critical) timelines as to when it will start and finish
After completion, what to do?
Finally, questions?

## NATIONAL SPATIAL REFERENCE SYSTEM

**A component of the National Spatial Data Infrastructure (NSDI) -   ****http://www.fgdc.gov/nsdi/nsdi.html**
**Contains all geodetic control contained in the National Geodetic Survey (NGS) Integrated Data Base:****	**
**Horizontal and vertical control points**
**Geoid models such as GEOID 03**
**Gravity**
**Precise GPS orbits**
**Continuously Operating Reference Stations (CORS)**
**National Shoreline data as observed by NGS**
**Standards and Specifications for data submittal**

**Notes:**
Under the Federal Geographic Data Committee (FGDC)
NSDI enables a Consistent means to share geographic data among all users 

Includes all classical metadata used in the original NAD83(86)
Includes over 5000 GPS surveys added since 1986
Includes all other COOPCORS and CGPS Sites
Includes models describing dynamic geophysical processes affecting spatial measurements-e.g subsidence and tectonic movement.

## NATIONAL SPATIAL REFERENCE SYSTEM

**MULTIPURPOSE – Supports Geodesy, Geophysics, Land Surveying, Navigation, Mapping, Charting and GIS **
**ACTIVE – Accessible through Continuously Operating Reference Stations (CORS) and derived products**
**INTEGRATED – Related to International services and standards (e.g. International Earth Rotation Service, International GPS Service etc.)**
**DOCUMENTED – Complete metadata is provided for elements.**

**Notes:**
The NSRS was designed to be comprehensive-serve the positioning needs of as many people as possible.   PASSIVE STATIONS
The NSRS is Completely integrated with the IGS and the IERS through CORS. But also integrated because all data is accessible through one database-not several as in the past.

Metadata –we spend much time with definitions and explanations of what we publish and what it means.   (THE DREADED BLUEBOOK)

All data is contained in NGS’ integrated database (NGSIDB)

NGS is investigating the feasibility of creating a new geospatial database to either co exist or replace our current integrated database.

Since positioning has become so easy, a new demand as emerged to create a repository for less accurate geospatial data especially for GIS purposes.

OPUS DB is a new and exciting concept currently being developed to enable users the ability to add data into a database.  This will also be a good reason for a consistent database.

## NATIONAL GEODETIC SURVEY

**WEB SITE**
- http://www.ngs.noaa.gov

**Notes:**
Obtain Data 
Obtain Software 
Interactive (OPUS, Online adjustment utilities etc)
Information about NGS activities and programs
	Height Mod
	national readjustment
	Geoid development

## NATIONAL READJUSTMENT

**WHAT**
**WHY?**
**HOW**
**WHEN**
**POST**
**QUESTIONS**

**Notes:**
In order to answer why, briefly describe what has happened over the last 20 years and explain why we now have inconsistencies in our network.

## The NAD83(86) Adjustment Team

**Notes:**
Spanned over 12 years
Involved automation of abstracts, checking archived data
This slide of the adjustment team was taken around 1980.  Recognize anyone?
Ed McKay, Dave Doyle, Nancy Doyle,  Charlie Challstrom, Libby Wade, Dennis Milbert and Kathy, Maralyn, Myself.

**Notes:**
When it came time to determine a new datum, All available Extraterrestrial data were incorporated Through VLBI and  --- next slide  ----

Although before we leave this one-these sites were the beginnings of our modern CORS network-many of them converted to that very quickly upon completion of the NAD83

## NAD83(86) DOPPLER STATIONS

**Notes:**
Apologize that this slide does not have the Canadian Doppler-this (and all our slides) were created for US audiences
Doppler to tie the North and Central American countries, including Hawaii and the Carribean islands together.  

The TCT (explain) and many new Astro Azimuths were also incorporated to further determine Scale and orientation for the new datum.

Orientation of the ellipsoid was determined by the BIH Terrestrial System of 1984 (BTS(84).

Note:  GPS was not yet developed to be a significant part-   ONLY 5 observations

At this point in time NAD83 and The original WGS84 were equivalent.

When it came time to decide on a datum, we  had the foresight to make it earth centered

Unfortunately, we now know we were about 2 meters off ( 1 meter horizontal and 1 meter vertical). (my opinion about why-weaknesses in Doppler as control and lack of further iterations) 

## COMPARISON OF DATUM ELEMENTS

**                         **_**NAD 27**_**                         **_**NAD 83**_
**ELLIPSOID          CLARKE 1866                        GRS80**
**                            ****a=6,378,206.4 m                  a=6,378,137 m**
**                            ****1/f = 294.9786982               1/f = 298.257222101**
**DATUM POINT     Triangulation Station            NONE**
**                            ****Meades Ranch, Kansas          Earth Mass Center**
**ADJUSTMENT       25k Stations                          250k Stations**
**                             ****few hundred Base lines        30k EDMI base lines**
**	****	****	****         ****few hundred Astro Az           5k Astro Azimuths**
**	****	****	****	****	****	****                ****Doppler and VLBI**

**Notes:**
This slide gives you an idea of how many stations went into each adjustment and the characteristics of the datum.  

The size and shape of the ellipsoid was recommended by the IAG (International Association of Geodesy).

The new adjustment will be defined Exactly the same-ie earth centered and with the GRS80 ellipsoid.
We will continue to use NAD83 as the datum because of legal issues in the US.
To jump ahead slightly, we will also publish ITRF coordinates as part of the transition for the future

## NAD 27 and NAD 83

**Notes:**
The magnitude of the shifts across the US from nearly zero to 100 meters on the west coast. And this doesn’t even show Alaska and Hawaii-several hundred meters.

Because of the magnitude, USGS maps had to be modified as well as many other programs (ie. State Plane Coordinate programs).

Despite our many efforts to inform and prepare everyone for this change, many people were still caught off guard and SURPRISED. Fewer venues for publicizing the adjustment. ACSM and major professional journals were our primary focus.   

We are making every effort to inform the public and this time it is enhanced by the electronic age. I can email an article to the local newsletters of every state with the push of a button, e.g.

Anticipated shifts for the new adjustment will be no where near this magnitude.  Dale will talk more on this later. 

## Results of NAD83(86)

**Network Accuracy  -  1 Meter**
**Local Accuracy – First-Order **
**	****	****	****          ****(1 part in 100,000)**

**Notes:**
Through the effort of many people, We achieved a Very consistent and accurate network based on classical (ie terrestrial) observations-and putting it into today’s terms-
After 12 years of hard labor, we were done. 
We celebrated, I took a month long vacation and lounged in our success. I was going to have it easy for the next 20 years!
But No sooner had I returned than projects with these strange new 3 dimensional observations began to arrive and the phone started to ring-why weren’t this surveys checking the control-both were first order!...

## NAD 83(86) NETWORK PROBLEMS

**Not “GPSABLE”**
**POOR STATION ACCESSIBILITY**
**IRREGULARLY SPACED**
**POSITIONAL ACCURACY**

**Notes:**
COMPLAINTS from this new technology called ‘GPS’ were pointing out problems in our brand new datum already.
Existing marks were hard to reach, especially with a few hundred pound GPS receiver.
Questionable satellite visibility at existing stations.
GPS was already pointing out inadequacies in the network. Not just logistical but technical also-why were there decimeter differences in the coordinates using GPS and what was published as first order?
We had always prided ourselves that our network was a degree of accuracy better than the technology that surveyors were using so that it would serve as control. And it was for those that were using ‘old’ technology. But not for a very vocal group who were investing in the ‘new’ technology and for those in the research end of preparing us for the new generation of technology.

## HIGH PRECISION GPS NETWORKS

**“****GPSABLE”**
**Clear Horizons for Satellite Signal Acquisition**
**EASY ACCESSIBILITY**
**Few Special Vehicle or Property Entrance Requirements**
**REGULARLY SPACED**
**Always within 20-100 Km**
**HIGH HORIZONTAL ACCURACY**
**A-Order (5 mm + 1:10,000,000)**
**B-Order (8mm + 1:1,000,000)**

**Notes:**
Dale tells the story of a meeting with Tenn. Delegates who developed a new network in their state.
I had received their GPS data, observed by a Macrometer and reduced through our new program,OMNI, producing 4 minute epochs.   POOR NETWORK DESIGN ALSO
You could almost lose a whole satellite between 4 minute epochs.  
He, not wanting to upset our brand new network, did manage to crowbar in their new vectors into our existing network with just a small, little distortion of the vectors while producing close to a 1:1,000,000 accuracy.  
Unfortunately for him and NGS, fortunately for the future and NGS, Tenn. Refused to allow him to distort their brand new vectors.  Thus a new network was born.  The HARN.
And Tenn was not unique, Florida and Wisconsin were struggling with the same issues as they observed new statewide surveys (I might mention quickly and easily) with even better equipment. I remember meetings about how in the world were we going to handle the Wisconsin data with the marked differences to the established network and our desire not to upset all these obviously wonderful NAD83 coordinates that we had worked so hard to produce but being faced with differences that simply could not be ignored or, as Dale says, crowbared in?
And so NGS took on the job of providing a high accuracy GPS network in each state to which all other stations coordinates in the state would be adjusted. It would still be NAD83 but an updated version. 

## HARN/HPGN ADJUSTMENT

**A-Order Adjusted to VLBI-Existing FBN-CORS**
**B-Order Adjusted to A-Order**
**Existing Horizontal (Conventional & GPS) Readjusted to A/B-Order**
**New Adjustment Date Tag e.g. NAD83(1991.35)**

**Notes:**
CA HPGN 1991 only held ONE CORS (MOJAVE) along with existing VLBI 
This slide basically shows the adjustment process.
The A-Order was determined by very long GPS vectors to ‘CORS’ in Florida, Mass., and California. 
 The original eastern strain network-  also was used to define the A-order.  Unfortunately, the original eastern stain network turned out to have many problems. It was simply done too early and not enough was known (and not enough satellites were available) to produce high quality results.
LAYERED APPROACH, ending in a complete readjustment of ALL data within each state. Including classical
DATE TAG was born.  Each state with a different tag for the year it was observed.  And while we were struggling to maintain consistency, even when we did it didn’t look like we had it because adjacent stations across borders appeared to be different.
FEATHERED SHIFTS- To further complicate the issue, because not all states were done at the same time or even sequentially with their neighbors, we feathered the residual shifts into the neighboring states creating further inconsistencies in the network (although we were trying to maintain consistency without a general readjustment).

INCONSISTENCY BETWEEN STATES BEGAN!!!

## HIGH ACCURACY REFERENCE NETWORK

**Notes:**
This slide shows the “HARN” network in each state-generally the more points, the more involved the state itself was in the reobservations.

## HPGN/HARN & STATEWIDE 

**GPS & CLASSICAL ADJUSTMENTS COMPLETED**

**GPS ADJUSTMENT COMPLETED**

**1990**

**-GPS170**

**1990**

**-GPS120**

**1991**

**GPS222**

**1992**

**GPS366**

**1997**

**GPS1179**

**1992**

**    ****GPS412**

**1992**

**    ****GPS383**

**1992**

**GPS450**

**1992**

**GPS419**

**1992**

**GPS394**

**1992**

**GPS341**

**1993**

**  **

**  ****1993**

** **

**GPS585**

**1993**

**          ****GPS667**

**1992**

**GPS376**

**1995**

**GPS887**

**1997**

**.**

** **

**GPS577**

**1991**

**GPS197**

**GPS260**

**1991**

**  **

** ****1995**

**GPS908**

**GPS610**

**1993**

**  **

**  ****GPS725**

**HPGN/HARN & STATEWIDE**** **

**NETWORK STATUS**

**1993**

**1994**

**GPS404**

**GPS611**

**1994**

**GPS633**

**1991**

**   ****GP S291**

**       **

**reobs 9/97**

**1994**

**  ****GPS721**

**reos 7/96 **

**GPS1047**

**reos 1/96 GPS936**

**1997**

**GPS1133**

**reos-6/95-GPS904**

**1995**

**GPS852**

**1995**

**GPS882**

**1993**

**GPS606**

**1996**

**GPS1048**

**1996**

**GPS805**

**1996**

**GPS941**

**1994**

**GPS730**

**1996**

**GPS1121**

** ****1997**

**GPS1178**

**1997**

**   ****GPS**

**   ****1200**

**1997**

**GPS1150**

**reos-1996**

**Notes:**
This slide shows the date for each HARN  network in that state.-you can see the plethora of dates and since readjustments followed the HARN, how difficult it was to deal with cross-boundary issues for early and later HARN projects.
Alaska’s classical network was not and will not be readjusted.

RELAXATION TIME AGAIN!!, we again looked forward to relaxation until retirement.

## FEDERAL BASE NETWORK

**NGS FUNDED**
**NGS MARK MAINTENANCE**
**MINIMUM 100 KM STATION SPACING**
**A and B-ORDER HORIZONTAL ACCURACY**
**FIRST-ORDER CLASS II ORTHOMETRIC HEIGHTS **
**or**
**SECOND-ORDER CLASS I ORTHOMETRIC HEIGHTS**
**SECOND-ORDER CLASS I ELLIPSOIDAL HEIGHTS**
**REVISIT EVERY 3 TO 5 YEARS**

**Notes:**
The existing HARN networks weren’t fitting with the CORS.  The phone again began to ring off the hook. Here we go again.
					EMBARKED ON A NEW CAMPAIGN with
BETTER TECHNOLOGY, BETTER MODELS, MORE EXPERIENCE, MORE ACCURATE ELLIPSOID HEIGHTS through BETTER OBSERVING SCHEMES and MORE SATELITES
REOBSERVE ENTIRE COUNTRY THROUGH FBN’S
5 CM TOLERANCE- SOME STATES DID SOME DID NOT!
more inconsistencies! !

At this time, because of the cross state problems, we realized that a general readjustment was inevitable and began to prepare for that once the new network high accuracy observations  were completed.   A 5 cm tolerance was established by NGS management for any readjustments of position or ellipsoidal height to minimize changes that were going to take place between the beginning of the reobservations and the general readjustment.  And in fact , the vast majority of horizontal coordinates met this criteria and did not need readjustment. Ellipsoid heights were different-most did need readjustment especially the oldest ones and so began another round of readjustments (this time GPS stations only) with the goal of making all ellipsoid heights in a state consistent. And a few states opted to request readjustment of both the horizontal pos and the ellipsoid heights regardless of the shift. 

## FBN/CBN SURVEYS

**FBN GPS ADJUSTMENT COMPLETED**

**FBN/CBN SURVEYS**

**GPS READJUSTMENT COMPLETED**

**1999**

**GPS1347**

**1998**

**GPS1273**

**    ****1997**

**GPS1250**

**1998**

**GPS1267**

**1998**

**GPS1264**

**   ****1998**

**GPS1258**

**1999**

**GPS1394**

**1999**

**GPS1397**

**  **

**1997**

**GPS1207**

**1999**

**GPS1378**

**1999**

**GPS1370**

**1999**

**GPS1356**

**1998**

**GPS1288**

**1998**

**GPS1333**

**1998**

**GPS1340**

**1999**

**GPS1377**

**1999**

**GPS1381**

**1999**

**GPS1399**

** **

**2000**

**GPS1411**

**     **

**2001**

**  ****GPS1629**

**     ****2000**

**  ****GPS1463**

**     **

**  ****2000**

**  ****GPS1462**

**     ****2000**

**  ****GPS1481**

**   ****2000  **

** ****GPS1492**

** **

**     ****2000  **

** ****GPS1506**

**     ****2000  **

** ****GPS1514           **

**     ****2000  **

** ****GPS1519**

**     ****2000  **

** ****GPS1530**

**     **

**2000**

**  ****GPS1188**

**     **

**2001**

**  ****GPS1712**

**     **

**2001**

**GPS1554**

**     **

**2001**

**GPS1641**

**     **

**2001**

**  ****GPS1596**

**     **

**2002**

**  ****GPS1686**

**    **

**     **

**2002**

**  ****GPS1687**

**     **

**2002**

**    ****GPS1731**

**  **

**     **

**2003**

**  ****GPS1752**

**     **

**    **

**2003**

** ****GPS1825**

**     **

**2003**

**     ****GPS1851**

**2003**** ****GPS1753**

**   **

**2003**

**   ****GPS**

**   ****1850**

** ****MEANS**

**     **

**2003**

**  ****GPS1682**

**WILLIAMS**

**     **

**2003**

**  ****GPS1726**

**2002**

**  ****GPS-1547**

**Notes:**
This slide shows a graphical display of the new project ids for each state and the years at which they were observed.
As discussed, GPS data within each state was readjusted through a layered approach to redetermine and to make the positions and/or ellipsoid heights consistent.
Discuss special analysis for California-which directly relates to planning for the general readjustment as it is testing models, procedures and in addition will preclude another major analysis during the general readjustment since this has been extensive and lengthy.   CA also includes Hector Mine project (GPS1460) and North Region Ht Mod Survey (GPS1988)
Modeled velocities on Non CORS sites.
All observations brought up to a common epoch (2004.0)
Re-scaling of weights based on age and length of vectors
Rejections of earlier observations when determined by more recent observations
Rigid Constraints of over 180 CORS sites  

It should be noted that all this is being done with 3 personnel!

Alaska did not have an FBN observed.

## http://www.ngs.noaa.gov/PROJECTS/FBN/

**Notes:**
This is a snapshot from our webpage showing our interactive map.  

Go to our webpage and click on Products and Services link; then click on FBN Surveys link

By clicking on a state, you are brought into that state showing --- the next slide  ---

## http://www.ngs.noaa.gov/PROJECTS/FBN/

**http://www.ngs.noaa.gov/PROJECTS/FBN/**

**Notes:**
This snapshot is also an interactive map.  By clicking on any symbol, you immediately bring in the datasheet for that site.
Or you can see a complete list of the stations which went into the FBN adjustment by clicking on the Station List Map on the left.

**Notes:**
Sample datasheet produced from interactive map.

Note: 

The epoch date of the position.
ITRF positions available
Superseded values for 1986 and 1991.35
Descriptions

## IMPROVING POSITIONAL ACCURACY

**	****	****	****TIME****	****	****NETWORK****	****	****LOCAL**
_**NETWORK**__**	**__**SPAN**__**	**__**	**__**ACCURACY**__**	**__**	**__**ACCURACY**_
**NAD 27****	****	****1927-1986****	****10 METERS****	****	****(1 part in 100,000)**
**NAD83(86)****	****1986-1990****	****1 METER****	****	****(1 part in 100,000)**
**HARN****	****	****1990-1997****	****0.1 METER           B-order  (1 part in 1 million)**
**	****	****	****	****	****                            ****A-order (1 part in 10 million)**
**CORS****	****	****1996 -****	****	****0.01 meter****	****	****0.01 meter**

**Notes:**
ACURRACY BUT NOT CONSISTENCY!!

To summarize:  This slide shows how far we’ve come since 1986, really since 1927.
Unfortunately, ---  Next slide  ----

## Reasons for Readjustment

**Multiple epoch dates**
**Inconsistencies between states**
**Need to be Consistent with CORS**
**Compute Network and Local accuracies**
**September 24, 2003 NGS Executive Steering Committee approved a plan for the readjustment of the horizontal positions and ellipsoid heights for GPS stations in the contiguous United States.**
**Orthometric Height adjustment will not be attempted**

**Notes:**
Our multiple adjustments over time have produced Inconsistencies between the states
Mass confusion with multiple epoch dates,
Consistency with the CORS, very important when we begin to utilize OPUS solutions and as people generally begin to use CORS more in their lower order surveys.
But most of all, we will now be able to remove the Order/class codes which were somewhat misleading or in error with a new way of representing the accuracy of the coordinates.
We Will readjust ALL horizontal positions and ellipsoid heights for only GPS stations.

## What about Orthometric Heights?

**Decision was made not to perform a National Readjustment of orthometric heights at this time**
**Control = NAVD 88 not the CORS**
**Since no change in control most orthometric elevations would not change significantly**
**Network & Local Accuracy numbers for the orthometric heights would be the primary reason for readjustment**
**Would require relevant network accuracies for the NAVD 88 network-This would require a complete analysis of the NAVD 88 network**

**Notes:**
Very few CORS have NAVD88 heights.
We will not attempt to do a GPS derived orthometric height adjustment at this time.
Bottom line, we would need to know the network accuracies of the NAVD88 marks in existence.  
Have you ever tried to do an orthometric height adjustment on just a small project or county?  You would then see the incredible and probably impossible task that would be involved.  
HEIGHT MOD will be the answer.

## NATIONAL READJUSTMENT

- WHAT
- WHY
- HOW?
- WHEN
- POST
- QUESTIONS

## NGS Adjustment Team (1986)

**Notes:**
Compare first adjustment team to now!   	
        We were all young!!  Government cuts, retirements
Of course there are many people behind the scenes:  Systems, Lab, database
Between us three, we’ve accumulated over 60 years of adjustment experience.
Maralyn-  Nothing gets in the database without going through her!
        Major player during the last readjustment.
        Project Manager for the new readjustment.
Gloria- Has performed most of the FBN and state readjustments over the last 10 years.  
Myself- Began the first HARN’s and state readjustments,               
       Moved into ORBIT determinations for 5 years
       Became involved in the establishment and coordination of the CSRC
       Recently took on the monstrous task of analyzing and adjusting CA.

## NAD 83 READJUSTMENT

**ONLY GPS DATA WILL BE USED**
**CONTINUOUSLY OPERATING REFERENCE STATIONS**
**FEDERAL BASE NETWORK**
**COOPERATIVE BASE NETWORK**
**USER DENSIFICATION NETWORK**
**AIRPORT SURVEYS**

**Notes:**
Basically ALL GPS data loaded through the following networks and projects
I’ve already mentioned the FBN.  Critical network tying system to CORS
– next slide --

## COOPERATIVE BASE NETWORK

**STATE/LOCAL FUNDED**
**STATE/LOCAL MARK MAINTENANCE**
**25 TO 30 KM STATION SPACING**
**B-ORDER HORIZONTAL ACCURACY**
**THIRD-ORDER CLASS I ORTHOMETRIC HEIGHT**
**THIRD-ORDER CLASS I ELLIPSOIDAL HEIGHT**
**REVISIT AS NEEDED**

**Notes:**
The CBN’s were created to further densify the state through state/local funding.
NGS Responsibility is to assist and advise cooperating agencies.
Responsibility also placed on state/local organizations for maintenance.

## USER DENSIFICATION NETWORK

**STATE/LOCAL FUNDED**
**STATION SPACING AS REQUIRED**
**GPS OBSERVATIONS ONLY (HORIZONTAL)**
**FIRST-ORDER HORIZONTAL ACCURACY**
**REVISIT AS NEEDED**

**Notes:**
UDN’s supplied even greater densification at a lower accuracy level.
UDN’s will be included if tied directly or indirectly to HARN’s 
And finally – next slide --

## AIRPORT SURVEYS

**AIRPORT SURVEYS**

**Notes:**
Area Navigation Approach (ANA) airport surveys 
PACS (primary Airport Control) A/B order
SACS (Secondary Airport Control) A/B/1st 
Used to survey in runways and obstructions to flight paths and tied to NSRS.

## Project Adjustment Analysis

**3375 Projects complete**
**Free Adjustment**
**Residual Plot **
**Outliers Rejected**
**Connectivity to A/B Order Network Verified**
**Summary sheet with Project Information Created**
**69117 stations**

**Notes:**
For Years leading up to the start of the readjustment we analyzed individual projects

Residual plots generated for both the horizontal and up components
On occasion, further outliers were rejected.
We’ve actually found projects that were not tied to the NSRS
This process will greatly aid us during the analysis of the NSRS 

## TRASH

**Projects Not Recommended for Inclusion**
**Currently 149 Projects with 9903 stations**
**Many Third Order FAA Projects from 1980’s**
**Some Projects that have no ties to the Network**
**Original TN HARN (Macrometer Data)**
**Original Eastern Strain Network Project**

**Notes:**
Through our initial analysis of all existing projects we’ve determined:

Ah, the ADAM program, those first attempts to put surveyed positions on nearly all the minor airport runway ends!

Projects with NO TIES to network

The original East Coast Strain Network, funded by the Department of Energy, was fraught with suspicious reductions, which particularly were later seen in comparisons of ellipsoidal heights.  A lot of things such as how long one needs to stay on station, were objectively studied after this survey was thoroughly analyzed.

TENNESSEE HARN  (bad OBSERVING SCHEME)

 A list of these projects will be on our soon to be web site dedicated solely to the national readjustment.

## The National Readjustment General Comments

**The CORS/CGPS sites will provide the control**
**Only GPS projects will participate**
**The FBN/CBN Surveys are a key element since these are high accuracy (2 cm) surveys that tie the HARN to the CORS throughout the contiguous United States and provide more accurate values for the ellipsoid heights of most HPGN stations.**
**The required free adjustment analysis of each GPS project that contributes to the National Spatial Reference System is complete. **

**Notes:**
We will make every effort to RIGIDLY constrain the CORS coordinates which are based on a MULTIYEAR solution.

MULTIYEAR SOLUTION  This will be done in the ITRF reference frame and transformed into NAD83 (NSRS).  More on that later.  The multiyear solution is comprised of “rotating” 3-day (72hour) data sets reduced with the PAGES processing software on a computer running under the UNIX operating system, using the Precise Ephemeris over a period Of at least 2 1⁄2 years.  From analysis of these sequential data sets not only does NGS derive a very good set of coordinates, but also change over time.  You might consider this a 4-dimensional adjustment.

Stress the fact -  only GPS projects will be included!

A retrieval of every project from NGSIDB has been completed  -- next slide ---

## The National Readjustment More Comments

**Computation and database loading of scale factors for each project is complete.**
**Statewide GPS Readjustments are providing extra information about the network on a state by state basis.**

**Notes:**
Scale factors-basically rescale the uncertainties associated with the horizontal and vertical components of the GPS vectors.

Important step if we are to obtain realistic accuracies on both the horizontal and ellipsoidal components.

The process of determining relative weights by assigning appropriate apriori standard errors to vector components is underway right now.  It is a process of pulling individual projects out of the data base, running a free adjustment and then scaling by some form of the “variance of unit weight” rotated into local horizontal and vertical components – remember, vectors are stored in a cartesian system with the Z component parallel to a virtual N-S polar axis, and X and Y aren’t State Plane X and Y, but rather oriented towards or 90 degrees from the greenwich meridian.

Statewide readjustments are giving us an indication of what to expect when all states are combined.

## Concept of Operation

**Helmert Blocking strategy will be used.**
**NETSTAT- New Helmert Blocking software developed for the entire adjustment process incorporating more quality control and significant time saving features.**
**Coordinates Produced and Published for both NAD83 (NSRS) and ITRF **
**Adjustment in NAD83-Transformed to ITRF**
**Network and Local Accuracies Produced**

**Notes:**
We’ll finally get those formal statistics so we can compute or use local and network accuracies in our own adjustments or put them on coordinates.

## Helmert Blocks

**CORS/CGPS provides control at top block**
**	****    ****CGPS coordinates were determined by Sector projected **
**        ****to the 2007.0 epoch.**
**Each state will comprise a separate block of data**
**California broken into two blocks (North and South)**

**Notes:**
Statistics from Helmert blocking will be the exact same as if we were able to adjust all data simultaneously.

A method of network adjustment in which the network is broken up into a hierarchy of smaller networks. Adjustment is carried out first in the smallest members of the hierarchy, which are then combined by means of common points into next-larger members which also are adjusted. The process continues until the entire network has been adjusted. The final result is the same as that of a simultaneous least squares adjustment of the entire network. Helmert blocking is a special form of solving by partitioning of the normal matrix, where the observations and unknowns are partitioned geographically. The method is especially applicable to the large, sparse systems of equations typical of large geodetic networks. 

## HELMERT BLOCKING STRATEGY

**HELMERT BLOCKING STRATEGY**

**This is how each state fits into the National Readjustment**

## Network Accuracy

**Network accuracy of a control point**
**A value that represents the uncertainty of its coordinates with respect to the geodetic datum at the 95-percent confidence level**
**Datum is considered to be best expressed by the Continuous Operating Reference Stations (CORS)**
**Local and Network accuracy values at CORS sites are considered to be infinitesimal (approach zero)**
**These accuracies will be implemented with the National Readjustment**

**Notes:**
Network – how well the absolute coordinates are known

A deciding factor for approving a new national readjustment is because of new accuracy standards. 

Neither of these accuracy values can be calculated without the covariance matrix for the observations and this matrix can only be calculated from a simultaneous adjustment of all the observational data.

## Local Accuracy

**Local Accuracy of a control point:**
**A value that represents the uncertainty of its coordinates relative to other directly connected, adjacent control points at the 95-percent confidence level**
**An approximate average of the individual local accuracy values between this control point and other observed control points used to establish its coordinates**

**Notes:**
Local Accuracies– show how well the coordinates are defined relative to other points in the network

 NGS will no longer indicate Order/Class on datasheets.

## NEW STANDARDS FOR GEODETIC CONTROL

-                          **    ****(http://fgdc.er.usgs.gov/standards/status/swgstat.html)**
-    **local accuracy  --------------   adjacent points**
**   ****network accuracy ----------   relative to CORS**
**Numeric quantities, units in cm (or mm)**
**Both are relative accuracy measures**
**Will not use distance dependent expression**
**Order/Class codes will no longer be used**

**Notes:**
The new standards can be found in the following web site.

ERROR ELLIPSES

## ANTICIPATED SHIFTS

**Based on a preliminary adjustment of all FBN’s to the published values.**
**  ****< 5 cm. in the horizontal component with an**
**       ****average shift of 2.2 cm.**
**       ****< 10 cm. in the vertical component with **
**        ****an average shift of 4.6 cm.**

**Notes:**
I was hoping to have a plot in time for ACSM.  Unfortunately, I didn’t have time to create it.  

I can tell you, we did do a preliminary adjustment of just the FBN.

Results were less than 5 cm. in horizontal with an average of 2 cm.
         less than 10 cm. in the up component with an average shift of 4.6 cm.

## 			ISSUES

**New realization of the CORS coordinates will not be available-we are recommending the use of 2002 coordinates as published. The new Policy statement is posted on the NSRS Readjustment webpage..**
**To be decided-will another adjustment be run after the next CORS realization (2005) is released and new CORS coordinates published. **

**Notes:**
Question-  With Absolute antenna calibrations now implemented with ITRF05, what effect will this have on previously reduced vectors which used relative antenna calibrations when combined with new reductions?

## CURRENT STATUS

**Four free iterations completed with decreasing  numbers of residuals over 5 cm and with decreasing variances in each block and overall.   Analysis of each block continues.**
**	****No. of Observations = 842,976**
**	****No. of constrained parameters = 2043**
**	****No. of unknown parameters = 203,088**
**	****Degrees 0f Freedom = 641,928**
**Constrained adjustment analysis has begun.**
**	****	****486 National CORS and 195 CGPS sites**

## California STATISTICS

- Total # of Stations:                   3533
- Total # of Constraints:                195
- Total # of Adjusted Stations:     3338
- ISSUES:
- HTDP update (San Simeon and Parkfield Eq)
- Vertical velocity model non-existent

## CGPS CONSTRAINED SITE LOCATIONS

**Notes:**
Shows all CGPS site locations used as constraints for the national readjustment

## www.ngs.noaa.gov/NationalReadjustment

**Notes:**
Lists all vectors included in this lowest level block.  
Lists the horizontal residual (D RES), height residual (H RES)
Lists From and To station name, pids, ssns

This file can be downloaded and sorted anyway you like to look at any particular station or where the highest residuals occurred.

**Notes:**
Graphical display of the horizontal residual size and length for each vector.

**Notes:**
Lists the source and residual magnitude of every rejected vector.

**Notes:**
Lists the number of times a station is used either as a from or to station.
Generally, if a station is only used once or twice, it’s considered poorly determined.

It’s possible a station might have vectors coming in from neighboring blocks which would not show up in this station summary.

**Notes:**
Lists the preliminary position shifts from the epoch date currently in our database to the adjusted 2007.0 epoch.

## NATIONAL READJUSTMENT

**WHAT**
**WHY**
**HOW**
**WHEN?**
**POST**
**QUESTIONS**

## Time-line for National Readjustment Positions and Ellipsoid Heights

**All projects loaded in the NGS database prior to November 15, 2005 were included in the National Readjustment**
**Projects submitted after 11/15/2005 will be accepted and loaded into the database but will not be included in the readjustment**
**Anticipated completion by February 10, 2007**
**Project Report**
**6 months-February, 2007 through July, 2007**

**Notes:**
February 10, 2007 will be the 200th anniversary of the Coast and Geodetic Survey established by Thomas Jefferson.

## We will be celebrating our 200th anniversary on February 10, 2007

***We will be celebrating our 200******th****** anniversary on February 10, 2007***

**Notes:**
No one knew more about the geography of North America in his own day than Thomas Jefferson. A skilled surveyor and cartographer, he was engaged in a lifelong search for geographic knowledge. Jefferson studied the history of geography from the emerging worldviews of the ancients to the latest exploratory charts and maps of the American West. He amassed a remarkably thorough and varied collection of explorers’ accounts, geographic works, and maps for his personal library. Moreover, although Jefferson himself never traveled west of Warm Springs, Virginia, he was America’s first great Westerner

Recognizing the America’s dependency on overseas trade to grow its economy, on February 10, 1807, Thomas Jefferson signed Congressional legislation establishing the Survey of the Coast.  

Jefferson, in a message to Congress had recommended its establishment.  The intent was to determine the geographical position of certain prominent points along the coast by astronomical and trigonometric methods, and to connect these points with lines so as to form a basis upon which the nautical survey of the channels, shoals, and shore approaches could be made.

## Slide 60

**Notes:**
Promoter of four attempts to reach the Pacific,Jefferson personally planned the successful expedition led by Meriwether Lewis and William Clark from 1804 to 1806. 

NGS is presently establishing commemorative monuments with precise positioning along the route.
This slide can be found on our webpage which also contains more information and scheduling.
The next big event will be in Great Falls, Montana in June.

## NATIONAL READJUSTMENT

**WHAT**
**WHY**
**HOW**
**WHEN**
**POST?**
**QUESTIONS**

## For Stations not Included

**NGS recommends that NAD 83 data that is **_**NOT**_** part of the NSRS readjustment be readjusted by contractor/user with the original observations.**
**A set of national transformation parameters for “classical” non-GPS stations and GPS stations that were excluded from the National Readjustment will be developed by NGS.**
**Because of the relatively small shifts anticipated, a model such as NADCON will not be developed between previously determined GPS coordinates.**

**Notes:**
Projects submitted during the next two years will be accepted and constrained to existing network.  Readjusted after the national readjustment is complete.

Best alternative

Transforming old triangulation and traverse stations into the NAD83 (NSRS) with some sort of “national” set of seven parameters will be studied.  A lot will depend on whether or not random tests can determine valid transformation parameters

## Post National Readjustment

**New adjustment procedures will be developed that incorporate local and network accuracies.  **
**    ****New ADJUST workshop planned for ACSM 2007.**
**Design and Publish new data sheets.**
**A reference frame maintenance strategy (NAD83, ITRF, either or both) will be developed.**

**Notes:**
Weighted constraints based on local and network accuracies will be implemented in future adjustments 

we’ll be having lots of meetings to discuss the content of new data sheets.  It’s a great time to write in and tell NGS what they don’t all ready give you that you’d like to see.

## Important Facts

**COMPLETION DATE – February 10, 2007**
**NEW DATUM TAG -  NAD83(NSRS2007)**
**    ****For the latest information- visit the national readjustment webpage at:**
**         ****(http://www.ngs.noaa.gov/NationalReadjustment**

**Notes:**
We realize that in movement areas an epoch date will have to be included with subsequent adjustments.

California districts require epoch dates.

*** Hopefully, we’ll have a working prototype of a national readjustment website containing more detailed information such as trash projects, project details, up to date progress maps, FAQ’s etc.

## OTHER ISSUES	

**We will streamline the process of project acceptance and database loading**
**OPUS DB**
**Require that all projects (submitted after the November 15, 2005 deadline) be tied to CORS**
**Accept/require more data in digital format-e.g.. reports, logs...**
**Photographs**

**Notes:**
Simplified BLUEBOOK

In order to compute the best network accuracy, all future projects will be required to be tied to CORS. (i.e.  All future projects should incorporate CORS data into their reduction phase)

DATALOGGERS

## Slide 66

**Notes:**
Within the next two weeks NGS and CSRC will decide on 40 to 50 initial sites.

## NATIONAL READJUSTMENT

**WHAT**
**WHY**
**HOW**
**WHEN**
**POST**
**QUESTIONS?**

## Slide 68

## Slide 69

## Slide 70

- Any body of copy on the slide will go in here.
- Either bulleted
- Or not bulleted