Year of Observation, 1998
Year of Computation, 1999

Chief of Party A. J. Lindsay
Observer Various
Computer Kathryn O Milbert

Spacial Reference System Division
Network Analysis Branch

***************************

Classification: A order, North American 1983 Datum.
Horizontal Datum: NAD 83 (1994)
Vertical Datum: NAVD 88
Epoch: 1997.0
Locality: Georgia, FBN Survey
Acc. No.: GPS 1273
Date of Field Work: 1998
Chief of Party: A. J. Lindsay

*******OFFICE COMPUTATION*******

Acc. No.: GPS 1273
Date of Computation: 1999
 

Number of Stations:
New: = 30	Main Scheme: = 94
Old: = 64	Supplemental: = 0
Fixed: = 14	Non-monumented: = 0
Readjusted: = 50	Temporary: = 0
Total = 94	Total = 94

Free adjustment variance of unit weight (s²_o): = 111.85
Constrained adjustment variance of unit weight (s²₁) = 226.05
Ratio: s²₁/s²_o = 2.021

This project is an A Order (1:10,000,000) GPS survey which covers the state of Georgia. The National Geodetic Survey (NGS), in accordance with the NGS strategic plan is engaging in a campaign of observing stations of the Federal Base Network (FBN) to complete the ellipsoidal and orthometric components of the FBN. This survey was performed to re-observe the 26 FBN stations in Georgia, to establish Primary Airport Control Stations (PACS) at airports in support of the FAA Area Navigation Approach (ANA) project, and to replace several destroyed or blocked Cooperative Base Network (CBN) stations. Project requirements for the FBN observations were to ensure 2-centimeter local accuracy in the horizontal component, as well as 2-centimeter local accuracy for the ellipsoid heights.
 
 

The programs CHKOBS and OBSCHK were run on the observation files to check the formats of the data files. No significant errors were found.
 
 

A three dimensional minimally constrained adjustment was run with the following fixed control:

Fixed Position: ATLANTA CORS ARP
Fixed Ellipsoid Height: ATLANTA CORS ARP 296.691 m.

The following vectors were rejected:
 

	Residual (Hor)	Residual (Up)
FAA BQK GDL ARP-OKE CP-2 (re-observed)	0.0803 m.	-0.3105 m.
FAA BQK GDL ARP-FAA TMA A (not re-observed)	0.0020 m.	-0.0538 m.
DNL B-ATLANTA CORS ARP (re-observed)	0.0056 m.	0.0493 m.
ATLANTA CORS ARP-CAPE CANAVERAL 1 CORS ARP (re-observed)	0.0326 m.	-0.0443 m.

A variance of 111.85 with 987 degrees of freedom resulted from the final free adjustment.

Scatter plots (see attachments 1a and 1b) were produced to display residuals in the horizontal and height component. The remaining outlier was the vector observation between DNL B and SBO A (hor=0.0541 m, up=0.0048 m). Due to a lack of redundancy (only 2 vector sessions included SBO A), this could not be rejected. SBO A will be downgraded to B Order. In order to resolve this problem, more observations should be taken at SBO A.
 
 

Most of the published NAD83 coordinates for the CORS stations were transformed from ITRF94 (epoch 1996.0). The only exception was Atlanta (ATL1) which was transformed from ITRF96 (epoch 1997.0). For consistency, using HTDP, Atlanta was transformed to the same epoch (1996.0) as the other CORS stations. All CORS vectors were reduced to the ARP in this project. A test adjustment was run, constraining the published coordinates for Asheville (ASHV), Cape Canaveral 1 (CCV1), Charleston 1 (CHA1), Millers Ferry 1 (MLF1) and the epoch 1996.0 transformed coordinates for Atlanta (ATL1). A variance of 150.03 with 999 degrees of freedom resulted from this adjustment.

Scatter plots (see attachments 2a and 2b) were produced to display residuals in the horizontal and height component. There was a wide scattering of residuals in the up component (4.9 cm to -5.1 cm).

In order to see if better results could be achieved, another test adjustment was run. This adjustment, used CORS coordinates that were transformed from ITRF96 (epoch 1997.0) to NAD83 (epoch 1997.0), using the program HTDP. See attachment 3 for a listing of these transformations. A variance of 121.68 with 999 degrees of freedom resulted from this adjustment.

Scatter plots (see attachments 4a and 4b) were produced to display residuals in the horizontal and height component. The scattering of residuals in the up component (3.7 cm to -3.7 cm) was significantly improved in this adjustment. Therefore, these CORS transformed coordinates will be used as control in this project.
 
 

To determine how the previously published HARN control was shifting in relation to the Continuously Operating Stations (CORS), the resulting coordinates from the test adjustment that constrained the transformed NAD83 coordinates from ITRF96 (epoch 1997.0) (see attachment 3 for fixed control) were compared to the published coordinates. A variance of 121.68 with 999 degrees of freedom resulted from this adjustment. Attachments 5a and 5b illustrate the horizontal positional differences. Attachment 6a lists the exact ellipsoidal height differences and attachment 6b illustrates these differences (approximate, at the 0.5 cm level) on a sketch.

Horizontally, there was a systematic directional shift between the CORS controlled adjusted coordinates and the published HARN coordinates. The only exception was L 293. The position for L 293 was originally determined by a single vector observation in GPS1273/7A (Georgia ANA-Cherokee AP PACS). It has two vector observations that are consistent with each other in this project. A problem with the original reductions is suspected. It's position will be re-determined, using the observations from this project. The magnitude of the shifts ranged from 1.1 cm to 9.7 cm horizontally and from -7.7 cm to 4.0 cm vertically.

Since the Georgia HARN (1994) was observed prior to the existence of the CORS network, discontinuity in both the ellipsoid heights and positions between the HARN and CORS was expected in this state. In fact, some of the A Order stations in this area have already been readjusted as a result of an analysis of the Eastern Strain Network Project (GPS1008, 1996). Appendix A contains a paper that documents this analysis.

It is NGS's policy to perform a readjustment analysis whenever shifts between the CORS and HARN exceed the 5 cm level horizontally or vertically. In Georgia, many of the coordinate comparisons exceeded this tolerance.

In order to achieve FBN/CBN coordinates that are the most consistent with the CORS, all previously published HARN coordinates should be readjusted based on CORS control. However, a partial readjustment of the A Order network based on the CORS has already been performed in Georgia. To maximize consistency across the region, it is desirable to constrain stations that participated in the Eastern Strain Network Analysis (GPS1008, 1996). In addition, the North Carolina/South Carolina HARN (GPS852, 1995) was also tied to the CORS, so it was desirable to constrain coordinates from that project as well.

A constrained adjustment was run, constraining the following coordinates:
 

STATION NAME	ELLIPSOID HEIGHT (m)	SOURCE
ASHEVILLE CORS ARP	660.497	CORS *
ATLANTA CORS ARP	296.691	CORS *
CAPE CANAVERAL 1 CORS ARP	-22.673	CORS *
CARROLLTON NCMN 2	300.942	GPS366
CHARLESTON 1 CORS ARP	-27.575	CORS *
CORNPORT	409.334	GPS852
ELBPORT	150.485	GPS852/B
FAA 4J6 B	-22.238	GPS721/D
FAA 53A B	76.522	GPS721/D
L 374	71.280	GPS852/B
MILLERS FERRY 1 CORS ARP	10.454	CORS *
MOODY	-30.216	GPS852/B
MULGEE	49.593	GPS852
STONE MOUNTAIN RESET	483.820	GPS721/D

* CORS transformed to the NAD83 (Epoch 1997.0) from ITRF96 (Epoch 1997.0)

A variance of 226.05 with 1026 degrees of freedom resulted from this adjustment.

In order to insure that this constrained adjustment produced results that were within the 5 cm tolerance, a comparison was made between the coordinates from the constrained adjustment and the adjustment that was solely controlled by the CORS. Attachments 7a and 7b illustrate the horizontal positional differences. Attachment 8a lists the exact ellipsoidal height differences and attachment 8b illustrates these differences (approximate, at the 0.5 cm level) on a sketch. All comparisons met the 5 cm tolerance. Therefore, it was decided to use this constrained adjustment as the final constrained adjustment for this project.

Attachments 9a and 9b illustrate the horizontal differences between the final positions (some readjusted) and the published values. Attachment 10a lists the exact ellipsoidal height differences and attachment 10b illustrates these differences (approximate, at the 0.5 cm level) on a sketch. Readjusted coordinates will supersede the published values in the integrated database as a result of this adjustment.

The following positions were determined as no check in this adjustment:

C 79
D 234
G 186
N 67
W 64

Since several HARN coordinates were readjusted in this project, it is necessary to analyze the effects of these changes on the HARN network in this region. In order to maintain a consistent set of HARN coordinates, further readjustment of other A and B Order projects is sometimes necessary. Appendix B documents this analysis.
 
 

A minimally constrained adjustment was run, using the final blue book from the constrained adjustment as input, to compute accuracies over all observed lines (see attachment 11). A variance of 111.85 with 987 degrees of freedom resulted from this adjustment.

The following length relative accuracies did not meet the A Order standard of 1 part in 10,000,000:
 

STATION 1	STATION 2	ACCURACY	DIST (m)
DNL B	L 374	1:1347273	13598
MBDRYDEN	R 143	1:1454585	145
FAA 4J6 B	FAA BQK GDL ARP	1:1764826	56465
ATLANTA CORS ARP	CARROLLTON NCMN 2	1:2143307	67838
MOODY	FORT PULASKY	1:3142348	3930
ATLANTA CORS ARP	RYY C	1:3986042	11739
FAA 53A B	FAA ABY ARP 2	1:4203316	86855
FAA BQK GDL ARP	JEKPORT	1:4584171	21416
ATLANTA CORS ARP	STONE MOUNTAIN RESET	1:5308720	37499
MULGEE	FAA BQK GDL ARP	1:5537985	131382
GBATH	FAA BQK GDL ARP	1:5979621	30147
DNL B	MULGEE	1:7505820	185054
DNL B	ELBPORT	1:8815292	100512
SKING	FAA BQK GDL ARP	1:9224652	45168
ATLANTA CORS ARP	E 57	1:9583563	32876

The reason that these accuracies do not meet A Order standards is rooted in the basic inconsistency between the CORS positions and the previously determined HARN positions that were held in the constrained adjustment. Although the differences are small (under 5 cm), the length relative accuracy is computed by dividing the distance between points by the freely adjusted shift in position. Thus, even small discontinuities can cause poor length relative accuracies. No further readjustment of positions was performed as a result of these accuracies.

The program ELLACC was run to determine ellipsoid height accuracies (see attachment 12).
 
 

The program GEOID96 was run to update the geoid heights in the blue book, using the GEOID96 FFT model.

A minimally constrained adjustment was run, fixing the position for ATLANTA CORS ARP and the NAVD 88 orthometric height for D 234 (86.933 m., L17225). A variance of 111.85 with 987 degrees of freedom resulted from this adjustment.

An elevation comparison was made between the adjusted elevations from the minimally constrained adjustment and the published values. These differences were plotted on a project sketch and analyzed in relation to the geoid model. No anomalies were found and it was possible to constrain all bench mark control in this project.

In addition, an analysis of the GPS derived elevations was performed. NAVD 88 GPS derived elevations that were consistent with these data at the 5 cm level were also constrained.

A final vertically constrained adjustment was run. The following NAVD 88 elevations were held in this adjustment:
 

STATION NAME	CODE	ELEVATION (m)	SOURCE
12 C 2 GAGS	B	314.091	L24726
B 188	B	40.385	L25356/40
BV 061 204	G	459.13	GPS721/B
C 186	B	197.550	L16764
C 79	B	97.012	L4456
CARROLLTON NCMN 2	G	329.98	GPS721
CORNPORT	G	439.12	GPS852/F
CULLODEN	G	228.58	GPS721/B
D 234	B	86.933	L17225
DARROW RESET	B	59.776	L25314/1
E 301	B	89.237	L18633
E 57	B	264.567	L4310
ELBPORT	G	179.75	GPS852/F
FAA 4J6 B	G	6.28	GPS721
FAA 53A B	G	102.98	GPS721
FAA ABY ARP 2	G	58.09	GPS721/B
FAA BQK GDL ARP	G	7.16	GPS721/B
FAA MGR ARP	B	86.926	L17781
FAA TMA A	G	106.75	GPS721/B
FORT PULASKI	B	9.069	L25273
G 186	B	115.571	L17215
GLYNN CBL 1410	B	4.724	L25272
HOMEPORT	G	55.70	GPS721/B
HUGHES PLACE	G	147.44	GPS721/B
K 175	B	112.597	L23246
L 293	B	194.042	L21429
L 374	B	100.919	L24575
LINDA AZ MK	G	25.99	GPS721/B
MERLE	G	84.17	GPS721/B
MOODY	B	1.188	L25273
MUDGE=A 47	B	64.240	L24442/2
MULGEE	G	77.61	GPS721
N 67	B	361.435	L1133
PINEPORT	G	272.40	GPS721/B
R 143	B	35.381	L16186
S 185	B	388.830	L17743
STONE MOUNTAIN RESET	G	513.29	GPS721/B
T 74	B	90.481	L1284
W 63	B	188.174	L1127
W 64	B	278.012	L1127
WESTON RESET	G	170.76	GPS390
Z 128	B	218.609	L3877
ZTL A	B	272.587	L25558

A variance of 139.67 with 1029 degrees of freedom resulted from this adjustment.

The following currently published NAVD 88 orthometric elevations were readjusted in this project:
 

STATION NAME	IDB ELEV (m)	CODE/SOURCE	READJUSTED ELEV (m)
BV 146 209	277.34	G/GPS721/B	277.42
FAA 3J7 A	205.85	G/GPS721/B	205.75

No elevations were determined as no check in this adjustment.
 
 

The program ELEVUP was run to merge the elevations from the vertical adjustment with the positions and ellipsoid heights from the constrained adjustment.
 
 

The programs OLDU2NEW, SDISCREP, SNEIGHBOR were run on the description files to check for format errors and inconsistencies with the integrated data base. No significant errors were found. The description for GLYNN CBL 1410 (PID=BR1752) was removed from the description file since it was duplicated in the integrated database.
 

INTRODUCTION:

*Note: The A Order Portion of the Georgia HARN was previously analyzed relative to the CORS as a part of the Eastern Strain Network Project (1996) and was not included in this analysis.

Based on analysis performed during the adjustment of the FBN/CBN (GPS1273), the single vector observation between ATLANTA CORS L1 PHASE CENTER and L 293 was rejected and the coordinates for L 293 were constrained in all adjustments.

In order to verify internal consistency of these data, a free adjustment was run. A variance of 59.64 with 471 degrees of freedom resulted from this adjustment. Scatter plots (see attachments 1a and 1b) were produced to display residuals in the horizontal and height component. No large outliers were found.
 

COORDINATE COMPARISONS:

A variance of 142.77 with 564 degrees of freedom resulted from this adjustment.

Attachments 2a and 2b illustrate the horizontal positional differences between this test constrained adjustment and the currently published positions. Attachment 3a lists the exact ellipsoidal height differences and attachment 3b illustrates these differences (approximate, at the 0.5 cm level) on a sketch.

In all cases large (greater than 5 cm) horizontal shifts are either at stations that were already readjusted in the Georgia FBN/CBN (GPS1273), at stations located in Florida, or at stations directly connected to control in Florida. The following stations had horizontal shifts greater than 5 cm.
 

STATION NAME	HORIZONTAL SHIFT (m) (Constrained versus Published)
B 188	0.057	*
DARROW RESET	0.056	*
FAA ABY ARP 2	0.054	*
FAA BQK GDL ARP	0.060	*
FAA MGR ARP	0.059	*
FAA TMA A	0.052	*
FAA VLD ARP	0.065	**
FLGPS 71	0.057	***
HOMEPORT	0.070	*
L 293	0.103	*
LANE RESET	0.062	**
MERLE	0.055	*
R 143	0.071	*
S 183	0.054	**

*	This station's horizontal position has been readjusted in the GeorgiaFBN/CBN (GPS1273). It's position was constrained in this adjustment. It'scurrently published position will be superseded in the integrated database by the readjusted value.
**	This station was directly connected to a station in Florida.
***	This station was located in Florida.

After eliminating the large horizontal shifts of the constrained positions (from Georgia FBN/CBN), the only remaining large shifts are at stations either located in Florida or directly tied to stations located in Florida. These should be analyzed in conjunction with the Florida FBN/CBN project. Data from the Florida FBN/CBN project is not yet available.

In most cases large (greater than 5 cm) ellipsoidal height shifts are either at stations that were already readjusted in the Georgia FBN/CBN (GPS1273) or at stations located in adjacent states. The following stations had vertical shifts greater than 5 cm.
 

STATION NAME	VERTICAL SHIFT (m) (Constrained versus Published)
41 6	-0.071	**
A 223	-0.075	***
B 340	-0.075	***
FLNRC 1	-0.064	**
GPS 37	-0.068	**
HILLPORT	-0.084	**
HUGHES PLACE	0.068	*
LB BN BW	-0.079	****
MARIPORT	-0.147	**
ZTL A	-0.075	*
ZTL B	-0.075	***

*	This station's ellipsoid height has been readjusted in the GeorgiaFBN/CBN (GPS1273). It's ellipsoid height was constrained in this adjustment.It's currently published ellipsoid height will be superseded in the integrateddata base by the readjusted value.
**	This station is located in an adjacent state to Georgia.
***	This station is from GPS842.
****	This station's ellipsoid height has already been readjusted tothe CORS in the Atlanta Leica CORS Site Survey (GPS1286, 1998).

After eliminating ellipsoid heights that have already been readjusted to the CORS (GPS1273 or GPS1286), the only remaining large shifts are either from stations located in adjacent states or from GPS842 (Atlanta WAAS Site Survey, 1995). Ellipsoid heights from GPS842 should be readjusted in order to maintain consistency with the FBN/CBN.
 

ADDITIONAL READJUSTMENTS /GEORGIA:

INTRODUCTION:

The following projects located in Georgia were combined for readjustment of the horizontal positions and ellipsoid heights:
 

GPS842	Atlanta WAAS Site Survey (A Order, 1995)
GPS1273/3	Georgia ANA-Phase 2 Glynco Jetport (3rd Order, 1998)
GPS1273/7A	Georgia ANA-Cherokee AP PACS (B Order, 1999)
GPS1273/7B	Georgia ANA-Cherokee SACS (1st Order, 1999)
GPS1273/9	Georgia ANA-Moultrie Muni (3rd Order, 1999)

Based on analysis performed during the adjustment of the FBN/CBN (GPS1273), the single vector observation between ATLANTA CORS L1 PHASE CENTER and L 293 was rejected and coordinates for L 293 were constrained in all adjustments.

In order to verify internal consistency of these data, a free adjustment was run, using the following fixed control:
 

STATION NAME	ELLIPSOID HEIGHT (m)	SOURCE
ATLANTA CORS L1 PHASE CENTER	296.823	CORS0156
FAA BQK GDL ARP	-22.327	GPS1273
FAA MGR ARP	59.555	GPS1273
GAITHERSBURG CORS L1 PHASE CEN	109.047	CORS0095
L 293	164.680	GPS1273

A variance of 128.54 with 72 degrees of freedom resulted from this adjustment. Scatter plots (see attachments 4a and 4b) were produced to display residuals in the horizontal and height component. No large outliers were found.
 

CONSTRAINED ADJUSTMENT:

A variance of 121.61 with 87 degrees of freedom resulted from this adjustment.

The following positions were determined as no check in this adjustment:

A 223
B 340

COORDINATE COMPARISONS:

ACCURACIES:

This was a mixed order readjustment. All accuracies met the B Order standard of 1:1,000,000. The following length relative accuracy from the A Order Project (GPS842) did not meet the A Order standard of 1:10,000,000.
 

STATION 1	STATION 2	ACCURACY	DIST (m)
ZTL A	ZTL B	1:1863895	1239

This accuracy did not meet the A Order standard because of the short distance involved.
 

FINAL RESULTS/IDBLOAD NOTES:

The observation between ATLANTA CORS L1 PHASE CENTER and L 293 from GPS1273/7A should be rejected in the integrated database.