**General Specifications for Aeronautical Surveys**

**Volume I.**

Establishment of Geodetic Control on Airports

### First Edition, June 2000

<http://www.ngs.noaa.gov/AERO/aero.html>

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TABLE OF CONTENTS

[SUBJECT PAGE]{.underline}

[1.0
INTRODUCTION](#INTRO)\...\...\...\...\...\...\...\...\...\...\...\...\.....
1

[2.0 RECONNAISSANCE REQUIREMENTS](#RECONNAISSANC)
\...\...\...\...\...\...\...\... 2

2.1 Station Descriptions in the NGS Data Base\...\.... 2

2.2 Contact with Airport Authorities\...\...\...\...\.... 2

2.3 Reconnaissance of Existing Marks\...\...\...\...\.... 3

2.4 PACS and SACS Selection Guidelines\...\...\...\..... 4

2.4.1 Use of Existing Marks For PACS and SACS.. 4

> 2.4.2 PACS and SACS Stability\...\...\...\...\...\... 5

2.4.3 Proximity to Airport Features\...\...\...\... 5

2.4.4 GPS Satellite Visibility\...\...\...\...\..... 6

2.4.5 Use of Marks Set by Other Agencies\...\.... 6

2.4.6 Marks on Private Property\...\...\...\...\.... 6

2.4.7 Damaged Survey Marks\...\...\...\...\...\...\... 6

2.4.8 Approval of Proposed Sites for New Marks. 7

2.5 National Spatial Reference System (NSRS) Ties\... 7

2.6 Photographs\...\...\...\...\...\...\...\...\...\...\...\.... 7

2.7 Station Location Sketch and Visibility Diagram.. 8

2.8 Station Descriptions\...\...\...\...\...\...\...\...\.... 9

2.9 Reconnaissance Report and GPS Observation Plan.. 9

[3.0 SETTING NEW
MONUMENTS](#SETTINGNEWMARKS)\...\...\...\...\...\...\...\...\...\.....11

3.1 Stamping\...\...\...\...\...\...\...\...\...\...\...\...\....11

3.2 Bronze Disks\...\...\...\...\...\...\...\...\...\...\...\...12

3.3 Stainless Steel Rod Marks\...\...\...\...\...\...\.....12

3.4 Concrete Marks\...\...\...\...\...\...\...\...\...\...\....13

3.5 Mark Setting Materials\...\...\...\...\...\...\...\.....13

3.6 Witness Posts\...\...\...\...\...\...\...\...\...\...\.....13

[4.0 GPS
OBSERVATIONS](#GPSPOSITIONING)\...\...\...\...\...\...\...\...\...\...\...\....14

4.1 CORS Selection\...\...\...\...\...\...\...\...\...\...\....14

4.2 CTCORS Selection \...\...\...\...\...\...\...\...\...\....14

4.3 GPS Observation Requirements\...\...\...\...\...\.....15

4.3.1 CTCORS\...\...\...\...\...\...\...\...\...\...\.....15

4.3.2 PACS and HARN Tie\...\...\...\...\...\...\...\...16

4.3.3 SACS\...\...\...\...\...\...\...\...\...\...\...\....17

4.3.4 Bench Mark Ties\...\...\...\...\...\...\...\.....17

4.4 GPS Occupation at all survey stations\...\...\.....19

4.4.1 Antenna Set-up\...\...\...\...\...\...\...\...\...19

4.4.2 Epoch Interval / Elevation Mask\...\...\....19

4.4.3 Station Rubbings\...\...\...\...\...\...\...\....19

4.4.4 Weather Data\...\...\...\...\...\...\...\...\.....19

4.4.5 Observation Logs\...\...\...\...\...\...\...\....20

4.5 Accuracy Standards\...\...\...\...\...\...\...\...\...\...20

4.6 Recommended Equipment\...\...\...\...\...\...\...\...\...20

[5.0 VECTOR
PROCESSING](#VECTOR)\...\...\...\...\...\...\...\...\...\...\...\...22

5.1 CORS to CORS Vectors\...\...\...\...\...\...\...\...\....23

5.2 CORS to CTCORS Vectors\...\...\...\...\...\...\...\.....24

5.3 PACS, SACS, and NSRS Tie Vectors\...\...\...\...\....24

[6.0 ADJUSTMENT
PROCESSING](#ADJUST)\...\...\...\...\...\...\...\...\...\.....27

[7.0 FINAL PROJECT REPORT AND DIGITAL DATA SUBMISSION](#FINAL)\.....31

[GLOSSARY](#GLOSSARY)
\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...34

**[ATTACHMENTS]{.underline}**

ATTACHMENT 1 -- "Know These Markers" Pamplhet

ATTACHMENT 2 - *FBN Station Selection Guidelines*

ATTACHMENT 3 -- Example Reconnaissance Photographs of Stations

ATTACHMENT 4 -- Station Location Sketch and Visibility Diagram

ATTACHMENT 5 -- Writing Station Descriptions with DDPROC

ATTACHMENT 6 -- Example Airport Reconnaissance Station Table

ATTACHMENT 7 - Setting a Concrete Monument

ATTACHMENT 8 - Setting a Disk in Rock Outcrop or Structure

ATTACHMENT 9 - Setting a NGS 3-D Monument*,* List of Mark Setting
Materials

ATTACHMENT 10 - Photographic Documentation of Setting a NGS 3-D Monument

ATTACHMENT 11 -- Simplified Diagrams of GPS Positioning Requirements

ATTACHMENT 12 -- Example GPS Observation Scheme

ATTACHMENT 13 -- GPS Observation Log, Pencil Rubbing Form

ATTACHMENT 14 - GPS Antenna Height Measuring Instructions

ATTACHMENT 15 -- Information, Data, and Software available on the World
Wide Web

ATTACHMENT 16 -- Outline for Processing Airport Geodetic Control Surveys
with PAGE-NT

ATTACHMENT 17 -- Outline for Adjusting GPS data for Airport Geodetic
Control Surveys

ATTACHMENT 18 -- Example Coordinate Comparison Spreadsheet

[]{#INTRO .anchor}**[1.0 INTRODUCTION]{.underline}**:

The National Geodetic Survey (NGS), in accordance with interagency
agreements with the Federal Aviation Administration (FAA), provides
geodetic control at airports selected throughout the United States for
GPS Area Navigation Approach (ANA) procedure development. This geodetic
control, which consists of a Primary Airport Control Station (PACS) and
two or more Secondary Airport Control Stations (SACS), is tied to the
National Spatial Reference System (NSRS) and will be used to support
high accuracy surveys of airport features and obstructions. These
General Specifications provide the requirements for performing the
geodetic control phase for these surveys.

FAA No. 405, Fourth Edition, September 1996, Appendices 3 and 5 provides
general guidance concerning PACS and SACS, including accuracy
requirements, with more detailed information in this document. Any
exception or deviation from these documents must be stated in writing in
the Reconnaissance Report and/or Final Report, depending on timing.
Recommendations to exceed or deviate will be considered if written
justification is provided.

Airport Geodetic Control Network

**[2.0]{.underline}** []{#RECONNAISSANC .anchor}**[RECONNAISSANCE
REQUIREMENTS]{.underline}**:

Reconnaissance activities for each survey will include the following:
Review of station descriptions in the NGS Data Base; interviews with
airport management; recovery of all survey monuments on the airport;
selection of PACS, SACS, and NSRS ties; preparation of required
descriptions, sketches, photographs, and other documentation; and
compilation of a reconnaissance report.

**[2.1]{.underline}** **[STATION DESCRIPTIONS IN THE NGS
DATABASE]{.underline}**:

The contractor is responsible for reviewing NGS data sheets for existing
control on and around the airport prior to performing the field
reconnaissance. The review will be used to form a list of control to be
recovered on the airport, and a priority list of High Accuracy Reference
Network (HARN) stations and Bench Marks to be recovered as NSRS ties.

USC&GS (U.S. Coast & Geodetic Survey) and NGS monument descriptions are
contained in the NGS data base, are published on CD-ROM, and are
available via the NGS web site ([http://www.ngs.noaa.gov]() ) by
selecting the red Data Sheets\" link. A database search of all marks
within a short distance of the airport location will reveal USC&GS and
NGS marks. This type of search can be performed via the Data Sheet web
page or by using an NGS Data Sheet CD-ROM. Note, the CD-ROMs for each
region are only updated once per year.

Some National Ocean Service (NOS) or Calibration Baseline (CBL)
descriptions for stations on airports are classified in the NGS database
as non-publishable until new positions are determined. When
non-publishable, the descriptions will not be available through the NGS
Home Page and will not be published on NGS CD-ROMs. NGS will supply
these descriptions on floppy disk for each project.

[**2.2 CONTACT WITH AIRPORT AUTHORITIES**:]{.underline}

Close communication with airport management is a critical element of the
reconnaissance. Appointments with airport management should be made well
in advance to ensure a qualified airport representative is available to
discuss the survey and the procedures for working on the airport. Proper
clearances to work in the aircraft operations areas must be obtained
before performing any work at an airport. A security and safety briefing
may be required before field crews are allowed to work on the airfield.
Follow standard safety procedures and equip all vehicles with flashing
yellow lights and aircraft radios. Contact with the airport traffic
control tower is mandatory during surveys at controlled airports unless
an escort is provided.

Inquire about planned construction or changes in the airport layout.
Briefly summarize any future construction plans in the reconnaissance
report. Present the Aeronautical Survey Program Brochure and/or Letter
to the Airport Manager, explain the survey work that will be performed,
and describe the purpose of the PACS and SACS. Discuss optimal locations
for the practical use and survivability of the monuments and finalize
the PACS and SACS monument selections with airport management. Inquire
about underground utilities and other hazards to setting monuments.
Emphasize the importance of keeping the area surrounding the monuments,
especially the PACS, clear of any future equipment installations or
construction that may block intervisibility between the monuments,
visibility to GPS satellites, or become a source of multipath
interference.

[**2.3 RECONNAISSANCE OF EXISTING MARKS**:]{.underline}

All USC&GS (U.S. Coast & Geodetic Survey), NGS (National Geodetic
Survey), and NOS (National Ocean Survey or National Ocean Service)
monuments at the airport shall be recovered, including writing or
updating descriptions as required. See ATTACHMENT 1, for diagrams of
these survey disks. All required High Accuracy Reference Network (HARN)
stations and Bench Marks (BM) will also be recovered.

Full, three paragraph, NGS-format station descriptions must be written
or revised for stations recovered that are determined to be ANA
suitable. ANA suitable stations are defined as a survey disk, rod, or
similar type monument, meeting at least a stability code of "C",
considered suitable for GPS observations, and recovered in good
condition. Photographs and station location sketches as described in
this document are required for all ANA suitable stations recovered. Plot
all ANA suitable stations on the airport layout diagram.

Stations recovered that are determined NOT to be ANA suitable will be
noted as such in the digital recovery note for that station. A full,
three paragraph description is NOT required for these stations. A
recovery note which states the reason why the station is NOT ANA
suitable, the condition of the mark, and providing any updates to the
"to reach" description IS required. Photographs and station location
sketches are NOT required for these stations.

See section 2.8 and ATTACHMENT 5 for detailed information on writing
digital station descriptions and recovery notes. A complete, correctly
formatted, digital D-FILE from NGS DDPROC software shall be submitted
with the final report. This D-FILE shall include updated descriptions or
recovery notes for all stations recovered during the project, and shall
correlate with the adjustment B-FILE and G-FILE. The contractor shall
provide draft station descriptions as requested by NGS for quality
control purposes.

4.  **[PACS and SACS SELECTION GUIDELINES]{.underline}**:

Proper monument site selection for PACS and SACS is a primary goal for
these surveys and must be carefully considered. FAA No. 405, Appendix 3,
provides control station siting guidelines. NGS shall review all
contractor recommended PACS, SACS, and NSRS tie station selections for
approval.

Factors to consider are monument stability, intervisibility
requirements, visibility from the monuments to airport features such as
runways, navigation aids, and airport obstructions off the end of
runways, any previous high accuracy connection to the National Spatial
Reference System (NSRS), accessibility, and survivability of the
monuments. The monuments must be accessible to survey crews, and allow
for unattended, secure setup of GPS equipment for long periods without
hindering airport operations. PACS and SACS must allow for setup of both
conventional (optical) and satellite surveying equipment. If possible,
SACS should be sited on high ground near the approach end of the primary
runways so they can be better utilized for obstruction surveys.
Monuments must be established in areas clear of future construction, and
should be slightly recessed to protect them from snow removal and mowing
equipment.

**Minimum requirements, as listed in FAA No. 405, Fourth Edition, must
be met.** Also, see ATTACHMENT 2, *Federal Base Network Station
Selection Guidelines* for additional guidelines.

**[2.4.1 Use of Existing Marks for PACS and SACS]{.underline}**:

An extensive effort should be made to recover existing survey marks.
Existing marks should be used if they meet the PACS and SACS
requirements. Use of existing marks reduces the proliferation of marks
on airports, reduces mark setting costs, and makes it easier to maintain
an accurate, up-to-date survey data base. For a discussion of \"Existing
Monumentation in the Vertical Network\" see page 43-44, *Geodetic Bench
Marks*, NGS, 1978.

Before an existing mark is used, its description must be thoroughly
checked to confirm the station\'s identity, stability, and location, and
to provide input for an updated description. Stamping will not be done
on existing disks or logo caps.

A or B-order marks have been set at many airports by NGS. These marks
should be used if they meet PACS requirements.

If there is an existing \"A\" or \"B\" order station just off an
airport, and it has visibility onto the airport, an exception to the
rule that a PACS must be on the airport may be granted. Make a
recommendation, with justification, in the Reconnaissance Report.

If there is an existing \"A\" or \"B\" order station just off an
airport, and it does not see onto the airport, an exception to the rule
may also be granted if an intermediate station (a third SACS) can be set
providing visibility from the \"A\" or \"B\" order station through the
third SACS to the other two SACS on the airport. The third SACS may be
off the airport. Again, make a recommendation, with justification, in
the Reconnaissance Report.

**[2.4.2 PACS and SACS Stability]{.underline}**:

**PACS** - An existing mark may be used as a PACS if the mark meets the
stability quality codes of A or B in that order of preference, as
defined in ATTACHMENT 2, *Federal Base Network Station Selection
Guidelines*.

In addition, an existing concrete mark with stability code C (and 4+
feet deep, belled bottom) may be used for a PACS if the disk is a
pre-stamped USC&GS or NGS mark and it meets all siting, construction,
and intervisibility requirements.

Note, an existing HARN station (\"A\" or \"B\" order station) does not
necessarily qualify to be a PACS, it must still meet PACS stability and
siting requirements.

**SACS** - Other USC&GS, NGS, or NOS marks should be used as SACS if
they meet all siting, construction, and intervisibility requirements.

**Concrete Monuments**- The DDPROC (description software) default code
for a concrete monument set in an irregular mass of concrete is the
stability code \"D.\" If a monument, such as a NGS calibration base line
(CBL) monument (normally \"C\" stability), is classified as a code \"D\"
and appears to be better than a \"D,\" contact NGS with a
recommendation. Note, a \"tile probe\" (long steel rod) may be used to
help determine the underground extent of a concrete monument. CBL
locations and data are available on the NGS WWW Home Page, under
\"PRODUCTS & SERVICES\". Note, most CBL descriptions are not in the NGS
database, but can be provided by NGS.

**[2.4.3 PACS and SACS Proximity to Airport Features]{.underline}**:

PACS and SACS siting requirements are listed in FAA No. 405, Appendix 3.
PACS and SACS should be established in a secure area on airport
property. If establishing the PACS and SACS requires new monumentation,
the new monuments should be set no closer than 60 meters from a runway
edge, or 60 meters from the imaginary runway extension. If an existing
control station is used, the station should be at least 15 meters from a
runway edge. PACS and/or SACS should be at least 400 meters apart, and
in locations that will not interfere with airport operations, including
propeller and jet blast. The monuments must not be within 305 meters
(1000 ft) of the critical side of an:

Instrument Landing System (ILS) Glideslope Antenna,

Instrument Landing System (ILS) Localizer,

> Microwave Landing System Elevation Station,

Microwave Landing System Azimuth Station.

**[2.4.4 GPS Satellite Visibility]{.underline}**:

The GPS satellite visibility should be minimally restricted from 20
degrees above the horizon to the zenith, in all directions. Minor
obstructions are acceptable, but must be depicted on the Visibility
Obstruction Diagram. Select a site relatively free of present and future
anticipated obstructions. Utility poles in the GPS field of view are
tolerable, and they provide security and a reference to help locate the
mark, but set a mark at least 2 meters from the pole, to the south if
possible. Likewise, marks within 2 meters of a pole should not be used.
Marks should not be set or used if within 5 meters of a chain link
fence.

**[2.4.5 Use of Marks Set by Other Agencies]{.underline}**:

An existing mark of another organization may be used as a **PACS** if it
meets all siting, construction, and intervisibility requirements.
Normally this would be limited to a disk set in a drill hole in bedrock,
or a stainless steel rod if there is an indication that the rod was
driven to NGS driving requirements.

Marks previously established by other organizations may be used for a
**SACS** if they meet all siting, construction, and intervisibility
requirements, and are stability A, B, or C.

**[2.4.6 Marks on Private Property]{.underline}**:

Before using a mark on private property, owners must be contacted to
request permission. Take care to return landscape to the original
condition. Do NOT include the name and phone number of the property
owner in the station description unless the land is owned by a business,
or the owner agrees to have the information included in the description.

**[2.4.7 Damaged Survey Marks]{.underline}**:

Metal disks which have been moved or defaced so that they can no longer
serve as survey marks are to be removed, have updated descriptions
written describing the mark as destroyed, and the disk sent to NGS. A
mark will not be described as destroyed unless the disk is found and
returned to NGS. State the number of person-hours spent searching for a
mark that is reported as \"not found.\"

Any existing disk which is selected to be used as a PACS or a SACS
should be repaired if found loose or with edges exposed. Any work done
to repair a disk should be described completely in the updated recovery
description. Care must be taken not to alter the existing horizontal or
vertical position of the disk. Disk longevity can be increased
substantially by simply adding highway epoxy or equivalent when the
edges of a disk are exposed, thus preventing a vandal from prying the
disk from its location.

For all marks used in this survey, perform mark maintenance as required,
including replacing logo cap lids if missing. Contact NGS for
recommendations in unusual cases. Notify NGS of any other marks that
need mark maintenance. Examples of mark maintenance problems include:
loose disk, exposed edge of disk, missing logo cap, missing log cap lid,
and exposed edge of concrete monument.

**[2.4.8 Approval of Proposed Sites for New Marks]{.underline}:**

Proposed sites for new PACS and SACS must be approved by NGS prior to
setting the marks. NGS may approve station selections based on
preliminary reconnaissance reports to facilitate efficient field
operations. New PACS and SACS should only be set if no existing mark can
meet the requirements. See section 3.0, Setting New Marks, for mark
setting guidelines.

**[2.5 NATIONAL SPATIAL REFERENCE SYSTEM (NSRS) TIES:]{.underline}**

Each PACS must be tied to at least one "A" or "B" order High Accuracy
Reference Network (HARN) station and two First or Second order North
American Vertical Datum (NAVD) bench mark stations. The stations
selected for these ties must be recovered during the field
reconnaissance. Details for selecting and positioning the PACS (and
CTCORS) ties are listed in section 4.3 "GPS OBSERVATION REQUIREMENTS."
All reconnaissance deliverables required for "ANA Suitable" stations are
also required for the NSRS ties.

**[2.6 PHOTOGRAPHS:]{.underline}**

**Existing Monuments**- Two photographs shall be taken of all ANA
suitable monuments recovered during the survey. To show the condition of
the monument, clear the brush, grass, and dirt from the concrete or rock
surface area of the monument and clean the disk or logo cap with a whisk
broom or wire brush before taking the photographs.

The first photograph will show the monument from directly above and
cover an area about 1 meter in diameter. If it is a rod mark, the logo
cap should be open. Include a small sign in this photograph with the
station designation written so it is clearly visible in the photograph.

The second photograph will show the mark in the foreground, and its
identifying surroundings and any unusual obstructions in the background.
Place a sign in each photograph with the name (or identifier) of the
airport, the station designation and PID, compass orientation, station
type (i.e. PACS, SACS, etc.), and date. See ATTACHMENT 3 for examples of
the required photographs.

Submit both a color paper copy and digital copy of each photograph to
NGS. The project instructions will specify the format and file naming
convention to be used for the digital photographs. The photographs shall
be included in the Reconnaissance Report and may be published on the NGS
web site as a link for each station's data sheet.

**New Monuments**- Submit the second photograph as described above for
proposed monument locations. Mark the monument location with a tool or
lath if possible and include the sign as described above. When the
monument is being set, take an additional photograph of the empty hole
before pouring the concrete. Place a rod staff or other rigid measuring
device in the hole to indicate the depth of the hole. Take the picture
from near directly above the hole to show as much of the shape of the
hole and the soil structure that will be surrounding the monument as
possible. Label each photograph with the station name and submit in
digital form (no paper copy required). When the monument is complete,
take and submit a overhead view photograph as described for Existing
Monuments above.

**[2.7 STATION LOCATION SKETCH AND VISIBILITY DIAGRAM]{.underline}:**

Submit a station location sketch and visibility diagram for all ANA
suitable stations recovered during the survey, and for all new monuments
that will be set (See ATTACHMENT 4). The location sketch should show the
monument in relation to nearby features such as runway ends, taxiways,
airport lights, fence lines, buildings, etc. Label prominent features
and draw dashed lines along the reference measurements to indicate the
reference objects that are listed in the D-FILE description for the
station. Complete the visibility diagram and sketch the inscription and
stamping detail of the disk in the space provided.

The form must be neatly and accurately completed. Submit both the paper
copy and a scanned digital copy to NGS. The project instructions will
specify the format and file naming convention to be used for the digital
graphic files. Graphic files must be reduced to a size that will print
clearly and completely on one page when viewed and printed from a
standard web browser. The digital graphic of the completed form will be
published in the NGS data base as a data sheet link for each station.

**[2.8 STATION DESCRIPTIONS:]{.underline}**

NGS-style station descriptions or recovery notes shall be written for
all marks set, searched for, recovered, or occupied during the survey.
The descriptions and recovery notes will be submitted in digital
(D-file) format in accordance with chapter 3, vol. I, of Input Formats
and Specifications for the NGS Data Base (Blue book). (The Blue Book is
available on the NGS web site <http://www.ngs.noaa.gov/FGCS/BlueBook/>)
Hard Copy of the Blue Book can be obtained from NGS Information Services
Branch (301) 713-3242. The latest version of NGS DDPROC software should
be used to write the descriptions in the proper D-file format. Standard
NGS format will be used for all descriptions. See ATTACHMENT 5 for
detailed information on writing station descriptions and examples of
descriptions in D-file format.

**[2.9 RECONNAISSANCE REPORT and GPS OBSERVATION PLAN]{.underline}**:

A reconnaissance report and GPS observation plan shall be submitted to
NGS for review prior to field observations. This report(s) may be
submitted at intervals during the reconnaissance. NGS will respond with
an approval or comment letter as soon as possible, normally within 5
working days. GPS observation requirements are detailed in Section 4.

**The station designation (name) and PID (Permanent Identifier), exactly
as listed in the NGS data base, must be used in all survey records**.

The reconnaissance report will include the following information:

-   [Airport Summary Report]{.underline} - A separate paragraph for each
    airport to include: Airport contact and access information; whether
    airport is controlled; whether escort is required; airport radio
    frequencies; intervisibility conditions between the PACS and SACS;
    comments on any future construction, unusual circumstances, use of
    witness posts, and any other miscellaneous information. Include any
    comments on deviations from these General Specifications. The
    Airport Summary Report can be combined with the Station Table
    described below.

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-   [Station Table]{.underline} - For each airport submit a table which
    lists Station Name, PID Number, Establishing Agency, Order,
    Stability, Condition at Recovery, and Comments for each station.
    List proposed name and monument type of any new stations to be set.
    Identify the PACS, SACS, and all NSRS ties for the airport. Give
    status of marks not used and the reason. See ATTACHMENT 6 for an
    example.

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-   [Airport Control Plot]{.underline} - Plot all "ANA suitable" control
    that is on or near each airport on an airport map. Label each
    station with it's designation and indicate if it is a PACS, SACS,
    Bench Mark, HARN Tie, or subsidiary control. Hand plotting on 8.5 x
    11 paper is acceptable. See ATTACHMENT 6 for an example.

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-   [Photographs]{.underline} -- Submit photographs in accordance with
    section 2.6 for all ANA suitable stations recovered during the
    survey, and for all new monuments that will be set.

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-   [Station Location Sketch and Visibility Diagrams]{.underline} -
    Submit for all ANA suitable stations recovered during the survey,
    and for all new monuments that will be set (See section 2.7).

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-   [Station Descriptions]{.underline} - Submit Recovery Notes or
    Descriptions for existing marks. Encode the descriptions using
    DDPROC software. Note, these descriptions should be reviewed and
    corrected by GPS observers when they travel to marks. See section
    2.8 and ATTACHMENT 5 for details on writing station descriptions.

-   [GPS observing scheme]{.underline} - Group airports together that
    will be observed/processed simultaneously. Include length of
    sessions and number of occupations. List CORS, HARN, Bench Mark, and
    any A-order ties for each airport. See ATTACHMENT 12 for an example.

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-   [Project Vector Diagram]{.underline} - Depict entire project area
    (state) with all occupied stations, except SACS (because of scale).
    Symbolically distinguish whether each station is a CORS, PACS, HARN
    Tie, Bench Mark or combination. Include 300km (or appropriate scale)
    dashed circles around CORS and CTCORS, and 50 km circles around
    PACS. Show the GPS vectors that will be processed. Recommend one
    sheet of large size and additional smaller sheets depicting
    individual airports or airports grouped together for GPS
    observations. Provide a scale or note distances from the PACS to the
    CORS, HARN, and Bench Mark Ties.

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-   [Proposed instrumentation list]{.underline} -- Tabulate the brand
    and model numbers of GPS equipment.

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-   [Data Processing Software]{.underline} -- Specify software name and
    version for the software used. Ensure that the current version of
    all software is used.

[]{#SETTINGNEWMARKS .anchor}**[3.0 SETTING NEW MONUMENTS]{.underline}**:

The importance of setting quality monuments cannot be over emphasized.
Monuments that are properly located and set can provide decades of
valuable use for surveying operations. Proper attention and workmanship
must be given to all the steps in the process including the basic tasks
of hole digging, rod driving, concrete mixing and pouring, and finishing
the monument. The only physical evidence remaining after a survey has
been completed are the monuments; therefore, permanency and neatness of
the monument and the surrounding area are of utmost importance.

Where new marks are required, PACS and SACS will be monumented in
accordance with the following criteria: in paragraphs below, in
attachments to this document, and in FAA No. 405, Fourth Edition,
Appendix 3. Additional requirements are found in: *Federal Base Network
Station Selection Guidelines;* and *NOAA Manual NOS NGS1, Geodetic Bench
Marks*, Floyd, 1978.

Proposed sites for new marks should be discussed with airport management
after existing marks have been recovered. Inquire about underground
utilities and future construction that might affect mark longevity.
\"MISS UTILITY\" type services should be contacted before driving rod or
digging, and may be required by state or local regulation.

**PACS** - New PACS must meet stability code A or B requirements as
defined in ATTACHMENT 2, *FBN Station Selection Guidelines*. New rod
marks must meet the \"Quality Code B\" requirements found in ATTACHMENT
9 and *Geodetic Bench Marks.*

**SACS** - New SACS must meet stability code A, B, or C requirements as
defined in ATTACHMENT 2, *FBN Station Selection Guidelines*. Bronze
disks set in rock outcrops, massive structures, or as concrete monuments
will be used for new SACS.

Submit updated photographs, descriptions, and sketches of the new
stations to update the Reconnaissance Report.

1.  **[STAMPING:]{.underline}**

New PACS and SACS will have a unique stamping. Marks set at a site with
an official FAA location identifier shall be stamped with that
identifier, followed by a sequential letter, followed by the year the
mark was set; see requirements in FAA No. 405, Fourth Edition, Appendix
3. Disks and \"logo caps\" should be stamped before they are set in
place.

2.  **[BRONZE DISKS:]{.underline}**

Standard NGS bronze, horizontal disks will be used for rock outcrop,
massive structure, and concrete marks. A rock outcrop in which a disk is
set must be hard and a part of the main ledge and NOT a detached
fragment. A disk set in a drill hole must be well counter-sunk and
adequately fixed in place using highway epoxy or equivalent. The disks
must be fastened so that they will effectively resist: extraction,
change of elevation, or rotation. Disks must be well countersunk,
especially in areas where snow plowing is possible. If the top of the
disk is not below the level of the surrounding material, a snow plow can
scrap off the brass from the top of the disk, or worse, break the disk
off the stem. Traditionally, NGS has set disks so that the lettering can
be read normally (correct side up) when the observer is south of the
disk and facing north across the disk. NGS will supply the standard (3.6
inch diameter) bronze disks with pre-stamped NGS logo. For detailed
instructions on setting bronze disks, see Section 3.4, ATTACHMENT 7 and
ATTACHMENT 8.

3.  **[STAINLESS STEEL ROD MARKS:]{.underline}**

A NGS 3-D rod mark meeting quality code \"B\" for stability, may be set
for PACS. A 1 meter long, grease filled, finned sleeve will be used with
this mark. Instructions are in ATTACHMENT 9, SETTING A NGS 3-D
MONUMENT. See also, ATTACHMENT 10, \"PHOTOGRAPHIC DOCUMENTATION OF
SETTING A NGS 3-D GEODETIC CONTROL MONUMENT.\" Standard NGS aluminum
protective covers (\"logo caps\") will be used over rod marks. NGS will
supply stainless steel rod sections, including studs and driving points.
Pre-manufactured datum points will not be used. Survey disks will not be
affixed to stainless steel rods.

Note, either a 5 inch or a 6 inch diameter PVC pipe may be used as long
as the logo cap fits correctly. One manufacturer\'s version of the logo
cap will fit inside one diameter and outside the other diameter.

Record the length of rod driven for entry into the station description.
Note, the minimum acceptable length of rod is 4 meters (see Table 3,
page 27, *Geodetic Bench Marks* Manual) unless the rod becomes embedded
in rock and cannot be extracted. New rod marks should be allowed to
settle for at least 1 day before observations.

If bedrock is found only a few feet beneath the surface, a concrete mark
may be set instead of a rod mark if the concrete will rest directly on
the bedrock. Drill several holes in the bedrock so that the concrete
monument will be affixed to the bedrock. Utilize rebar to anchor the
monument if feasible. The area of the bedrock where the concrete will be
placed must be brushed or washed off thoroughly. Install a standard
concrete monument with brass disk. See ATTACHMENT 7.

4.  **[CONCRETE MARKS:]{.underline}**

New concrete marks, with standard NGS bronze disks, may be used for SACS
only. Construction requirements are in ATTACHMENT 7, SETTING A CONCRETE
MONUMENT. New concrete marks should be set slightly recessed with the
ground and should be allowed to settle for at least 1 day before
observations. Disks set in concrete will be centered in the top of the
concrete surface, will be flush or slightly recessed with the surface of
the concrete, and the top of the disk will be free of concrete. A round
form will be used for the top of all concrete marks and protective
collars. This will help ensure a neat finish and help protect against
\"mushrooming\" which could result in frost heave. Black tar paper (felt
paper) can be used to easily construct a form. All loose concrete and
other debris around the construction site must be removed and the site
left in excellent condition.

**[3.5 MARK SETTING MATERIALS:]{.underline}**

A listing of mark setting materials can be found in ATTACHMENT 9. All
NGS supplied materials will be specified in the project instructions.
NGS will generally provide the stainless steel rod, threaded studs, logo
caps, brass disks, and witness posts. NGS inscribed materials,
including: disks, protective covers (logo caps), and witness posts, etc.
shall not be used outside the scope of this project.

6.  **[WITNESS POSTS:]{.underline}**

Placement of witness posts on airport property must be pre-approved by
the airport manager. Witness posts should be used on an airport only
when they can be placed in a non-obtrusive area such as a fence line or
no-mow/snowplow area, and should be driven as deep as practical so they
do not obstruct any restricted safety areas. Witness posts should not be
used when the property owner objects, when the post cannot be driven, or
when the mark should not be made easily visible because of a high risk
of vandalism. All witness posts set must contain the standard NGS
witness post logo.

[]{#GPSPOSITIONING .anchor}**[4.0 GPS OBSERVATIONS]{.underline}**:

GPS observation requirements are summarized in ATTACHMENT 11 and
detailed in the paragraphs below. A GPS equipment list and GPS
observation scheme must be approved by NGS prior to commencing the field
observations. Observing windows shall be selected, and modified as
necessary, to maximize satellite visibility and minimize Positional
Dilution of Precision (PDOP) for each session. Incorporate any
information from Notice Advisory to NAVSTAR Users (NANU) messages,
available from the USCG Navigation Center web page, when scheduling GPS
observations to ensure optimal survey conditions.

**[4.1 CORS SELECTION]{.underline}**:

The CORS sites selected must be included in the NGS National CORS
system. Use as many National CORS sites in the project area as feasible.
Position each PACS directly to the nearest National CORS station. If a
PACS is not within 300km of a CORS, a CTCORS must be established.

CORS maps, data, and information are available on the NGS National CORS
web site (See ATTACHMENT 15 for access). Each CORS is designated by a
three or four letter name, followed by the antenna number. The correct
antenna name must be used when downloading data and the antenna\'s
coordinate information. Each CORS site usually has two or more antennas.
Check the "data availability" feature on the NGS CORS web site to
determine which CORS antenna was in use during observations, and to see
if there are any gaps in the data. The CORS station coordinate file
contains several positions based on different Antenna Reference Points
(ARP), and either the ITRF or NAD 83 reference system. Ensure the proper
coordinates are used when processing the data.

The survey disks (usually two) at each CORS site may have names similar
to the antenna names. The disk names and positions must not be confused
with the antenna names and positions.

The weekly \"CORS NEWSLETTER\" is available through the NGS CORS Data
web page described above. The Newsletter provides information on the
status of the CORS system. Users may subscribe to the newsletter at this
site.

**[4.2 CTCORS SELECTION]{.underline}**:

A Central Temporary Continuously Operating Reference Station (CTCORS)
must be used if the nearest CORS is more than 300 km from the PACS. The
CTCORS will be established by setting up a GPS receiver on a suitable
existing horizontal NSRS station, and will provide the CORS function in
the positioning of the PACS. The position of the CTCORS will be verified
by using the GPS observation requirements in section 4.3.1. Because of
the long distances involved and the additional stations which will be
positioned from the CTCORS, extreme care should be taken during the
observation and processing of this data. Separate tripod set-ups are
required at both the CTCORS and the PACS for each session. During all
CTCORS operations, ensure that the CTCORS antenna remains fixed.
Sandbags are recommended to stabilize the tripod and frequent checks
should be made of the antenna\'s centering and height.

CTCORS Station Selection Criteria are listed below. The CTCORS station
selection must be approved by NGS prior to commencing field
observations.

[STATION IS]{.underline} [STATION IS]{.underline}

[PRIORITY]{.underline} [TYPE OF STATION]{.underline} [BENCH
MARK]{.underline} [AT AIRPORT]{.underline}

1\. WAAS, USCG, or USACE CORS mark YES YES

2\. \" YES NO

3\. \" NO YES

4\. \" NO NO

5\. A-ORDER HARN STATION YES YES

6\. \" YES NO

7 \" NO YES

8\. \" NO NO

9\. B-ORDER HARN STATION YES YES

10\. \" YES NO

11\. \" NO YES

12\. \" NO NO

Acronyms:

Wide Area Augmentation System (WAAS); FAA

U. S. Coast Guard (USCG)

U.S. Army Corps of Engineers (USACE)

High Accuracy Reference Network (HARN)

**[4.3 GPS OBSERVATION REQUIREMENTS:]{.underline}**

GPS observation requirements are described in the sections below for
each type of mark. Note that when 4 hour sessions are specified, at
least 4 hours of data are required in the final computer reductions.
Therefore, observation of sessions longer than 4 hours is highly
recommended. Likewise for 1.5 hour sessions. Separate tripod set-ups are
required for each session.

**[4.3.1 CTCORS Sites]{.underline}**:

-   The position of the CTCORS shall be checked by observing three or
    more independent, continuous, simultaneous observation sessions of
    at least 4 hours with a CORS station. These three sessions should be
    the first sessions observed while positioning various PACS. In
    addition, one 4 hour session will be used as a check at the end of
    the project. If the distance between the CORS and CTCORS is greater
    than 300 km, contact NGS for guidance on increasing the length of
    observation sessions. All CTCORS will be tied by GPS surveys to
    nearby, GPS-suitable, North American Vertical Datum of 1988
    (NAVD 88) bench mark(s). See specific requirements in the Bench Mark
    Ties section below.

**[4.3.2 PACS and HARN Tie]{.underline}**:

If a CTCORS is required for connections, substitute CTCORS for CORS in
the following paragraphs.

-   Each PACS shall be positioned from the CORS in two or more
    independent, continuous, observation sessions of at least 4 hours in
    length. The observations to position the PACS must be performed
    simultaneously with the CORS observations. The start time of one
    PACS observing session should be at least 2.5 hours different than
    the second PACS session to incorporate different satellite geometry.

-   All PACS must have a separate positional check by simultaneously
    observing at least one session of 4 hours or more in length with a
    \"A\" or \"B\" order HARN station. The HARN station should be within
    100 km of the PACS and should be at least 50 km from the CORS. Tie
    to as many \"A\" order stations as possible during the project.
    []{.mark}

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-   A single HARN station can satisfy the tie requirements for more than
    one PACS if it meets the distance requirements for each PACS.
    Generally, no more than two PACS should be tied to a single HARN
    station in one session. Use additional observation sessions on the
    same HARN, or occupy an additional HARN station to satisfy the HARN
    tie to other PACS in the same area.

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-   An existing \"A\" or \"B\" order HARN station on an airport should
    be used as a PACS if it meets the siting, construction, and
    intervisibility requirements. The station must be checked with at
    least one 4 hour session to a CORS. A tie to an additional HARN
    station is not required.

-   The vector processing results of the two PACS sessions must check
    within 3cm. The final adjusted positions of the HARN ties should
    check within 5 cm horizontal and 10 cm ellipsoidal height with their
    published positions.

**[4.3.3 SACS]{.underline}**:

Each SACS shall be observed in two or more independent, continuous
sessions of at least 1.5 hours. The session start times must be
separated by at least 2.5 hours to ensure a significant change in
satellite geometry.

-   These observations will be simultaneous with PACS observations for
    that airport.

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-   If a SACS is also one of the bench marks or a HARN tie, the two or
    more 1.5 hour sessions are adequate for the tie, rather than the
    normal 4 hour requirement. This is due to the short distance from
    the PACS to the SACS.

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-   The vector processing results for the two SACS sessions must check
    within 3cm.

**[4.3.4 Bench Mark Ties]{.underline}**:

-   Ties to two separate NSRS NAVD 88 bench marks are required for each
    PACS and CTCORS station. The ties will be performed by observing
    each bench mark for at least one session of 4 hours or more in
    length simultaneously with the PACS or CTCORS. The two bench marks
    do not need to be observed during the same session.

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-   Bench mark ties will be selected in accordance with the Bench Mark
    Priority Table on the following page. Use of first order bench marks
    is highly desirable. The two bench marks should be as close as
    possible to, and no further than 50km from, the PACS or CTCORS.
    Bench marks should be at least 1 km apart, to help ensure that they
    are not both affected by the same upheaval or subsidence effect. If
    the PACS or CTCORS has a published bench mark elevation, that
    elevation satisfies one of the bench mark tie requirements.

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-   A single bench mark may satisfy one of the tie requirements for more
    than one PACS if it meets the distance requirements for each PACS.
    Generally, no more than two PACS should be tied to a single bench
    mark station in one session. Occupy additional bench marks, or use
    additional observation sessions on the same bench mark to satisfy
    the bench mark ties for other PACS in the same area.

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-   Bench mark ellipsoidal heights should agree within 10 cm and bench
    mark orthometric heights within 15 cm of published elevations.

-   All bench mark elevations used in this survey must be published NSRS
    NAVD 88 bench mark elevations, in meters.

**BM PRIORITY TABLE**:

+---------+----------------------+------------------------------------+
| P       | DISTANCE TO CLOSEST  | SELECTION CRITERIA                 |
| RIORITY |                      |                                    |
|         | FIRST-ORDER BM       |                                    |
+---------+----------------------+------------------------------------+
| 1       | \< 25 KM             | Use first-order BM.                |
+---------+----------------------+------------------------------------+
| 2       | 25 -- 50 KM          | Use first-order BM if closest;     |
|         |                      |                                    |
|         |                      | Second-order BM may be used if it  |
|         |                      | is less than ½ the distance to the |
|         |                      | first-order BM.                    |
+---------+----------------------+------------------------------------+
| 3       | \> 50 KM             | Use a second-order BM if it is     |
|         |                      | less than 25 KM away; Otherwise    |
|         |                      | contact NGS.                       |
+---------+----------------------+------------------------------------+

-   Differential geodetic (spirit) leveling (run in both directions) may
    be performed to satisfy the bench mark ties. These level ties must
    be less than 3 km. Two bench marks are required for the beginning of
    a line of differential (spirit) leveling. Identify these two bench
    marks in the reconnaissance report. If the PACS is tied to two bench
    marks by spirit leveling (within acceptable tolerances), then the
    two bench mark requirement has been met. Leveling must meet
    third-order (or better) requirements listed in: *Interim FGCS
    Specifications and Procedures to Incorporate Electronic
    Digital/Bar-Code Leveling Systems*, version 4.0, 15 JUL 94;
    *Standards and Specifications for Geodetic Control Networks*, FGCC,
    1984; and NOAA Manual NOS NGS 3, *Geodetic Leveling*, 1981. Leveling
    data will be submitted in \"Blue Book\" format on floppy disks
    containing the final version of the following files: HGF, HGZ, and
    HA in direct access format and RPT and ABS in sequential format.
    Note, this case (third-order) is an exception to the NGS policy that
    second-order, class II is the lowest order leveling that will be
    accepted by NGS.

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-   Third-order elevations determined by spirit leveling (run from
    various agencies\' bench marks) already exist at airports that are
    in the Airport Obstruction Chart (AOC) Program. These elevations
    (National Geodetic Vertical Datum of 1929 (NGVD 29)) are listed on
    the NOS paper description form as a Mean Sea Level (MSL) elevation,
    in feet. For the AOC airports that have been entered into the NGS
    database by headquarters, the NGVD 29 elevations have been
    automatically converted to NAVD 88 elevations using program VERTCON
    and will be printed on the standard station data sheets, in meters,
    with a reference to VERTCON. Check these AOC third-order elevations
    against elevations determined in this survey and tabulate the
    result.

**[4.4 GPS OCCUPATION AT ALL SURVEY STATIONS]{.underline}**:

GPS observations will be performed using FGCS approved dual frequency
GPS receivers. Fixed height tripods will be used whenever practical.
Separate tripod set ups are required for each occupation of a station.
General information on GPS equipment requirements and surveying can be
found in the NGS GPS SURVEY MANUAL, available on line at
(<http://www.ngs.noaa.gov/ADVISORS/FBN/GPSmanual/>).

Follow the additional guidance below:

**[4.4.1 Antenna Set-up]{.underline}**:

GPS antenna setups must be done independently for each session. The word
\"independent\" means separate tripod setups, separate height
determinations, and separate solutions. The HI must be measured in both
meters and feet, unless a fixed-height tripod is used. See ATTACHMENT
14, "GPS Antenna Height Measuring Instructions." Minimize the mixing of
GPS receiver and antenna types used for observations. Record the
manufacturer, model name, and part number of the antenna on the field
log.

**[4.4.2 Epoch Interval / Elevation Mask]{.underline}**:

GPS data will be collected at 15 or 30-second epochs; and a 15 degree
elevation mask. Data may be processed at a 15 second or 30 second
interval. A NGS CORS station which collects at a 30 second interval may
be used.

3.  **[Station Rubbings]{.underline}**:

A rubbing of the occupied mark shall be made at [each]{.underline}
occupation of a station. When not feasible to make the required rubbing,
a plan sketch of the mark or a photograph must be substituted,
accurately and legibly recording all markings. This photograph, if used,
is in addition to the photographs required in the Reconnaissance Report,
and the stamping must be readable in this photograph.

**[4.4.4 Weather Data]{.underline}**:

Before taking weather observations, the meteorological instruments
should be allowed ample time (approximately 10 minutes) to stabilize to
ambient conditions. Observations of wet-bulb and dry-bulb temperatures
must be observed and recorded to the nearest 1 degree Celsius.
Barometric readings must be observed and recorded to the nearest
millibar (or English equivalent). Meteorological data should be
collected at each station at the beginning, middle, and end of each
session. Meteorological data should also be collected to delineate
unusual weather events, such as sudden changes in temperature or
pressure, and immediately after an obvious weather front passes during a
session and immediately before it passes, if possible. Perform
temperature, relative humidity, and pressure measurements near and about
the same height as the antenna phase center. All antenna height and
weather measurements are to be recorded in raw form, and all field
calculations should be independently checked. Unusual weather
conditions, such as passing fronts and storms, are to be noted on the
observation log. Meteorological instruments must be compared against a
known standard before and after each project. Note, severe weather may
degrade GPS data.

**[4.4.5 Observation Logs]{.underline}**:

-   An observation log must be filled out for each occupation of a
    station. See ATTACHMENT 13 for a sample GPS Station Observation Log.
    Data recorded on the observation log must include the following
    equipment information:

\(1\) receiver manufacturer,

\(2\) antenna manufacturer,

\(3\) receiver model number (part number)

\(4\) antenna model number (part number),

\(5\) the complete serial number of the receiver,

\(6\) the complete serial number of the antenna,

\(7\) tripod model and serial number, and

\(8\) tribrach model and serial number;

-   Carefully monitor the receiver operation and antenna setup during
    each observing session. Note any unusual circumstances regarding
    satellite visibility, receiver operation, equipment malfunction, DOD
    adjustment of the satellite orbit, obstructions, weather events,
    tripod stability, etc., on the observation log.

**[4.5 ACCURACY STANDARDS]{.underline}**:

See FAA No. 405, Fourth Edition, Appendix 5.

**[4.6 RECOMMENDED EQUIPMENT]{.underline}**:

Dual-frequency GPS receivers that meet the following requirements:

-   The receiver model has been evaluated against the Federal Geodetic
    Control Subcommittee (FGCS) test network.

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-   State-of-the-art dual frequency with high quality C/A code or P code
    pseudo-ranges.

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-   Capable of measuring full wavelength L2 carrier phase.

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-   Must function acceptably in an Anti-Spoofing environment.

Any dual frequency receiver that is L2-squared capable may be used for
SACS observations.

Use GPS antenna models that have been calibrated by NGS (See the NGS
Antenna Calibration web page at
<http://www.grdl.noaa.gov/GRD/GPS/Projects/ANTCAL/> )

Antennas equipped with a ground plane or choke ring are preferred for
observations on the PACS and NSRS ties.

[]{#VECTOR .anchor}**[5.0 VECTOR PROCESSING]{.underline}**:

Vector processing will be performed using the latest version of the NGS
software package PAGE-NT or equivalent. The \'equivalent\' of PAGE-NT is
subjective, based on the software\'s ability to correct for the same
systematic errors that PAGE-NT corrects, apply the NGS required antenna
offsets, and its ability to reproduce the same results as PAGE-NT. This
determination will be made by NGS.

The NGS PAGE-NT software package and User's Manual are available via
anonymous FTP from NGS (see ATTACHMENT 15). Follow the vector processing
guidance below, The PAGE-NT User's Manual, and the Vector Processing
Outline in ATTACHMENT 16.

-   The grouping of vectors into processing sessions for each day of
    observations are determined by two factors: 1) The required
    reference station, and 2) The distance of each solve station from
    the reference station. This vector distance determines the final
    solution type to be run in PAGE-NT. Reference station requirements
    are detailed in the sections below. Use the following table for
    grouping vectors together into sessions according to vector length:

**PAGE-NT Final Solution Type Determination**

  ------------------------- ---------------------------------------------
  Vector Distance for       Final Solution Type
  Processing Session        

  under 5km                 L1 Fixed

  5-15km                    Better of L1 Fixed and Ion-Free Fixed

  15-100km                  Ion-Free Fixed

  100+km                    Ion-Free Fixed or Partially Fixed
  ------------------------- ---------------------------------------------

-   IGS precise orbit data and NGS National CORS data must be used in
    data processing. For information on down loading CORS data and
    ephemeris data from NGS via the Internet see ATTACHMENT 15.

-   **International Terrestrial Reference Frame (ITRF) station
    coordinates will be used for all vector reductions.** Information
    about ITRF is available on the NGS WWW Home Page, under \"PRODUCTS
    SERVICES\". The current ITRF epoch must be used in computations.

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-   The Antenna Height value entered into the PAGE-NT "Station
    Information" Menu, "Up" field, is the monument to the Antenna
    Reference Point (ARP). For example, 2.000 for a fixed height tripod.
    The monument for a CORS is generally coincident with the ARP,
    therefore, 0.000 is entered for a CORS station unless an offset is
    listed on the CORS coordinate sheet. PAGE-NT will automatically add
    a constant factor for the ARP to L1 phase center distance when it
    merges the data.

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-   Set the Tropospheric scale height in accordance with the following
    table:

**Tropospheric Unknown Settings for PAGE-NT Sessions**

+-----------------------+-----------------------+-----------------------+
| Vector Length         | Reference Station     | Solve Station Setting |
|                       | Setting               |                       |
+-----------------------+-----------------------+-----------------------+
| Under 3km\*           | OFF/FIXED             | OFF/FIXED             |
|                       |                       |                       |
|                       | (Not Highlighted)     | (Not Highlighted)     |
+-----------------------+-----------------------+-----------------------+
| 3-100km               | OFF/FIXED             | ON/SOLVE              |
|                       |                       |                       |
|                       | (Not Highlighted)     | (Highlighted)         |
+-----------------------+-----------------------+-----------------------+
| 100+km                | ON/SOLVE              | ON/SOLVE              |
|                       |                       |                       |
|                       | (Highlighted)         | (Highlighted)         |
+-----------------------+-----------------------+-----------------------+

\*If a station is within 3km of the reference station AND differs in
height with the reference station by 5 meters or more, set the
tropospheric scale height setting to SLV for that station.

-   Review the PAGE-NT generated plots and text outputs to analyze each
    processing session. PAGE-NT's overall RMS-of-fit of the post-fit
    double-difference residuals should not exceed 2.0 cm. Investigate
    individual satellites with a relatively high RMS or where integers
    could not be fixed. Also review the files for input errors such as
    improper reference station coordinates, antennae height errors, or
    improper station names.

-   Compare the ITRF coordinates of all repeat baselines and for NSRS
    ties that were occupied more than once. Investigate any station
    coordinate comparisons that do not agree within 3cm.

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-   Submit all files and printouts as required in ATTACHMENT 16.

**[5.1 CORS to CORS VECTORS]{.underline}:**

Utilize data from as many National CORS in the project area as feasible.
CORS to CORS vectors strengthen the GPS network and allow for easier
error detection. Discuss with NGS the CORS to CORS vectors to be
processed. Generally, two 24 hour vectors will be processed between the
CORS stations to form an interconnecting network. See section 4.1 for
more information on CORS data.

**[5.2 CORS to CTCORS VECTORS]{.underline}:**

Three independent sessions between the CORS and CTCORS are required at
the beginning of the project and one session, as a check, at the very
end of the project. Process these three sessions using the most recent
ITRF coordinates published by NGS for the CORS. If the new computed ITRF
coordinates of the CTCORS differ from the NGS ITRF coordinates by more
than 3 cm in horizontal or 10 cm in vertical (ellipsoidal or
orthometric), call NGS immediately for further instructions. These
instructions may include processing additional CORS to CTCORS sessions.
Any discrepancy, even if resolved, must be described in the project
report. Note, the PACS accuracy requirement is relative to a CORS, not a
CTCORS, so any discrepancy in the CTCORS position will need to be
included in the error budget for the PACS. The last session at the
CTCORS will be used to again check the position of the CTCORS relative
to the CORS.

**[5.3 PACS, SACS, and NSRS TIE VECTORS]{.underline}**:

The sequential order of vector processing is listed below. The selection
of either L1 or Ion-Free for the final solution type is based on vector
lengths. See the Solution Type Determination Table (Section 5.0) for
guidance when grouping vectors together for a processing session.

Discuss the plan for processing any "shared" HARN and bench mark ties
with NGS. Generally, each HARN or BM observation should be included in
only one processing session. Use the following guidance for preparing
the processing plan:

-   If a HARN station tie is NOT also a PACS, SACS, or BM tie for an
    airport, and it is greater than 50km from a PACS, it may be
    processed in the CORS to PACS session. The PACS observed
    simultaneously with the HARN to "share" the tie will be tied to it
    indirectly in the group adjustment. Separate processing sessions
    from the PACS to the HARN are not required.

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-   If a HARN station tie is NOT also a PACS, SACS, or BM tie for an
    airport, and it is within 50km of a PACS, it should be processed
    directly from the closest PACS. A second nearby PACS that was
    observed simultaneously to "share" the HARN tie will be tied to it
    indirectly in the group adjustment. A separate processing session
    from the second PACS to the HARN is not required.

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-   Shared bench mark ties should be processed to their closest PACS.
    The second, simultaneously observed, PACS will be tied to the bench
    mark indirectly in the adjustment. Again, a processing session from
    the second PACS to the BM is not required.

Substitute CTCORS for CORS in the steps below if applicable:. The
sequential order of vector processing is:

Step 1 ‑ Process first CORS-to-PACS vector, with CORS as reference,
using the latest ITRF coordinates. Note, if more than one PACS was
observed simultaneously, include these PACS in the session if they
conform to the vector distance limitations for the session (See Solution
Type Determination table above). Also include any appropriate HARN
stations in the session.

Step 2 ‑ Process the second CORS-to-PACS vector, with CORS as reference,
as above. Again, include appropriate PACS or HARN stations that were
observed simultaneously into this session.

Step 3 -- Compare the resulting ITRF coordinates of the PACS sessions.
Use a spreadsheet to show the differences between the sessions and the
calculation of the mean (See ATTACHMENT 18 for an example). The two PACS
coordinates should compare within 3 cm. If they do, mean the positions
and go on to Step 4. If not, contact NGS. The PACS may need to be
reprocessed or reobserved.

Note, Steps 4-7 must be completed individually for each airport (Each
PACS must be the reference station for its respective SACS, etc.).

Step 4 ‑ Process the first PACS to (HARN and/or BM) session using the
PACS as the reference station and using the mean ITRF position
calculated in step 3. Include stations for this airport that are over
about 5km from the PACS. BM or HARN stations that are less than 5km from
the PACS will be processed in a separate L1 session. The frequency of
the final solutions is based on the length of the vectors. Use the Final
Solution Type Determination Table for guidance on grouping vectors
together for processing.

Step 5 - Process the second PACS session, as above.

Step 6 - Process the first PACS to SACS session using the PACS as the
reference station and using the mean ITRF position calculated in step 3.
BMs and HARN stations that are within 5km of the PACS may be included
in these sessions. Process these short lines using the L1 frequency
only.

Step 7 - Process the second session SACS data as above.

Step 8 -- Compare the ITRF coordinates of all repeat baselines and NSRS
ties that were occupied more than once. Include this comparison on the
same spreadsheet used for the PACS comparison. Investigate any station
coordinate comparisons that do not agree within 3cm (if vectors are from
the same reference station) or 5cm (if vectors are from different
reference stations).

[]{#ADJUST .anchor}**[6.0 ADJUSTMENT PROCESSING]{.underline}**:

All airports in a project area should be adjusted together, or the area
can be subdivided into groups of airports which are located close
together and share tie stations (CORS, BM, HARN). Airports can be
adjusted individually only if approved by NGS. Discuss an adjustment
plan with NGS prior to running the adjustment.

The adjust software package can be downloaded from the NGS home page
([http://www.ngs.noaa.gov](http://www.ngs.noaa.gov/)) by accessing the
"PC Programs" link. ATTACHMENT 17 contains a detailed outline of the
adjustment process for airport geodetic control projects. Follow the
attached outline, the guidelines found below, and the written Adjust
documentation when performing the adjustment.

Six adjustments are required: (1) free, (2) constrained with only CORS
or CTCORS held, (3) constrained with CORS or CTCORS and HARN stations
held, (4) a final free with accuracies, (5) a free vertical holding one
bench mark in the center of the project, and (6) a fully constrained
vertical (with all approved bench marks held).

-   ADJUST\'s \'Mean Absolute Residual\' statistics (from Adjustment #1)
    must not exceed 2.0 cm in NORTH or in EAST, and must not exceed 5.0
    cm in UP.

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-   ADJUST\'s maximum residual (from Adjustment #1) should not exceed
    3.0 cm and must not exceed 5.0 cm on the horizontal components. The
    estimates could be twice as large for the vertical component.

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-   Vectors may be rejected if the residual exceeds 4.0 cm in any
    horizontal component, but may not be rejected if it supplies the
    only redundancy for a station. A written justification for rejecting
    the vector should be included in the Final Report.

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-   HARN ties to \"A\" or \"B\" order stations should check within 5 cm
    horizontal and 10 cm ellipsoidal height compared to their published
    positions. Notify NGS immediately if checks exceed these tolerances.
    Show the coordinate comparisons on a spreadsheet (See ATTACHMENT
    18).

-   Bench mark ellipsoidal heights should agree within 10 cm and bench
    mark orthometric heights within 15 cm of published elevations.
    Notify NGS immediately if checks exceed these tolerances. Show the
    height comparisons on a spreadsheet (See ATTACHMENT 18).

Section 7 of the Bluebook, Annex L, are superseded by the following
guidelines for adjustment processing and submittal. Use these guidelines
along with the step by step Outline of the Adjust Procedure in
ATTACHMENT 17.

All adjustments will be run in three dimensions. Do NOT scale the gfile
for ANA geodetic control projects. Ensure all input files are complete
and free of format errors by utilizing the checking programs. \*86\*
records should be in the bfile before beginning the adjustment. Do not
insert GEOID heights until the horizontal adjustments are complete.

Ensure the proper code was inserted into the solution coordinate system
code (cc 52-53) of the G-file created by PAGE-NT. Adjust will use this
code to internally transform the ITRF vector components to the NAD 83
reference system.

**ADJUSTMENT ONE-** A free adjustment to determine the strength of the
GPS network. Hold the NAD 83 position and ellipsoid height of one CORS
station fixed. Constrain the CORS that was used for the majority of the
vector reductions or that is located near the center of the project
area.

Residuals on any vector component should not exceed 3cm and must not
exceed 5 cm. Outliers remaining after a review of the vector reductions
may be rejected if sufficient redundancy exists or upon approval from
NGS headquarters.

**ADJUSTMENT TWO-** A fully constrained horizontal adjustment to
determine new NAD 83 coordinates. Constrain the NAD 83 coordinates
(latitude, longitude, ellipsoid height) of all CORS or CTCORS stations
used in processing. This adjustment would be run in a similar fashion to
the free, except for holding any additional CORS or CTCORS stations
fixed which might have been used in the project.

NGS will determine if all the PACS are to be positioned relative to the
published or newly computed coordinates of the CTCORS, on a
project-by-project basis.

A comparison shall be made between the coordinates determined in this
adjustment and those currently published by NGS. Use a spreadsheet to
calculate the differences in the X, Y, and Z components (See example in
ATTACHMENT 18). Program INVERSE3D should be used to determine the exact
Delta Height and Ellipsoidal Distance for comparisons that do not fall
well within tolerance. As noted previously, differences of 5 cm
horizontally and/or 10 cm in ellipsoidal height with published positions
should be immediately brought to the attention of NGS for investigation.
Submit all comparisons with the final report.

**ADJUSTMENT THREE-** A supplemental, horizontally constrained
adjustment holding all CORS and HARN stations fixed for NGS use in
deciding on the final constraints. Submit the results of this
adjustment, but use the results of the previous adjustment (holding all
CORS stations only) for the final files and for computing accuracies.

**ADJUSTMENT FOUR-** A minimally constrained free adjustment to
determine the length relative accuracies of the adjustment. Run program
QQRECORD to add QQ records to the afile. Hold the NAD 83 position and
ellipsoid height of one CORS station fixed. Use the output bfile from
adjustment 2 as the input bluebook.

Use program BBACCUR to derive a listing of the accuracies. Examine the
accuracies to determine that all lines meet the requirements for the
order the stations will be published, e.g., CTCORS to PACS should be
1:1,000,000; PACS to SACS should be l:100,000. PACS will be published as
B-order; SACS and bench marks as first-order. Discuss any problems with
NGS and detail them in the report. NOTE: The final PACS and SACS
coordinates must meet FAA document No 405, Fourth Edition, accuracy
requirements. The computed accuracies will help in the analysis of
meeting those requirements.

Use program ELLAC to derive the order/type of the ellipsoid heights.
This value must be edited into the \*86\* records of the final B-file.
The value chosen should be that of the majority of the lines and will be
used for all stations.

**ADJUSTMENT FIVE-** A free vertical adjustment to determine the
strength of the vertical network. Insert geoid heights into the output
bfile from adjustment 2 and use it as the input bfile. Use the latest
version of NGS geoid software to derive the geoid heights. Hold the NAD
83 latitude and longitude of one CORS station and the NAVD 88
orthometric height of one bench mark (center of project area) fixed.
Compare the published bench mark elevations with those obtained in this
adjustment and notify NGS of any exceeding 15 cm.

**ADJUSTMENT SIX-** A constrained vertical adjustment to determine the
new GPS derived elevations for the project. This adjustment may need to
be run several times to determine the optimal selection of bench marks
to use as vertical constraints. Constrain the NAVD 88 elevations of
bench marks that checked the best with their published positions based
on the free vertical adjustment. Run the adjustment and review the
results. Continue to add constraints until any "poor fitting" bench
marks are determined. Allow poor fitting bench marks to float in the
final vertical adjustment. Use the orthometric heights from this
adjustment for the final B-file.

Submit a spreadsheet which shows the height difference between the
published NAD 83 bench marks and their final adjusted elevations.
Discuss any outliers in the project report. Also document any actions
taken as the result of poor bench mark checks.

The **final B-file** submitted must contain the positions and
ellipsoidal heights derived from the final constrained adjustment
(ADJUSTMENT TWO) and the orthometric elevations from the final vertical
adjustment (ADJUSTMENT SIX). Program ELEVUP can be used to easily
combine the files. The B-file must satisfactorily run through the
required checking programs.

[]{#FINAL .anchor}**[7.0 FINAL PROJECT REPORT and DIGITAL DATA
SUBMISSION]{.underline}**:

A final project report detailing the GPS observations, vector
processing, and adjustment shall be submitted to NGS. This report is in
addition to the Reconnaissance Report that is described in Section 2.9.
Photographs, updated sketches, descriptions, and other information
concerning mark setting performed for the project must be submitted
separately as a supplement to the Reconnaissance Report.

General guidance for project reports and data submitted to NGS can be
found in Annex L of the NGS Bluebook, and in *Policy of the National
Ocean Service Regarding the Incorporation of Geodetic Data of Other
Organizations into the National Geodetic Survey Data Base,* dated
September 1994 (available on line at
<http://www.ngs.noaa.gov/INFO/incorp_data.html>).

The **Project Report** shall contain at least the following:

-   An overview discussion of the field work, data processing, and
    adjustment performed. This discussion should include a summary of
    the results, problems encountered, and any unusual circumstances or
    deviations from the requirements in the Project Instructions or
    these General Specifications. Include comments on any deviations
    from the Reconnaissance Report.

-   A listing of personnel who worked in the field or were involved with
    the data processing for this project.

-   A listing of the brand, model number, and serial number for all the
    GPS receivers and antennas used in the project. List the quantity,
    brand, and type of tripods used. Include any instrumentation used
    for differential leveling.

-   A listing of all software, including version, used during the
    project for RINEX conversion, vector processing, adjustment, and
    verification (all checking programs).

-   A final station list. Use a table format to list each station, the
    station type (PACS, SACS, etc.), and each observation session for
    the station.

-   A final Project Vector Diagram. Update the vector diagram submitted
    with the Reconnaissance Report (see Section 2.9). Submit only the
    large size plot. Discuss the final layout with NGS. Include
    processing session designations on the vectors if feasible. Show
    indirect ties to "shared" HARN stations and bench marks.

-   Submit the original copy of all field logs (Observation logs, Pencil
    Rubbing forms, updated Station Location Sketch and Visibility
    Diagrams).

-   A vector processing scheme tabulated by airport and session which
    lists: reference station and solve stations with their station type;
    observation time for the vector, solution type (L3 fixed, etc.), and
    final RMS for the session. Note the tropospheric unknown settings
    for each session. Provide any comments on problems encountered or
    anomalies with the processing session. This table can be
    incorporated into the spreadsheet described below.

-   A spreadsheet showing the comparison of the ITRF coordinates (X ,Y,
    and Z) of all repeat baselines and for NSRS ties that were occupied
    more than once. Show the solution type, final RMS, and distance for
    each vector. Show the calculation of the mean PACS coordinate. See
    ATTACHMENT 18 for an example spreadsheet.

-   Submit paper copies of the COMBINED.SUM files for any processing
    sessions that were difficult to process or produced questionable
    results. Submit paper copies of any other files requested by NGS for
    quality control.

-   Submit paper copies of the coordinate sheet for all CORS and CTCORS
    stations used during vector processing.

-   Submit a detailed description of the project adjustment. Discuss
    each of the adjustments separately, including points held and the
    source of the position or elevation used. Explain unresolved error
    messages from the checking programs. Discuss the analysis performed
    and the results of the adjustments. Submit the spreadsheets or
    tables used to compare the adjusted coordinates with their published
    coordinates (see Section 6).

-   Submit a paper copy of the output for programs COMPGB, NEWCHKOB,
    OBSCHK, OBSDES, CHKDESC, BBACCUR and ELLACC. Submit any other paper
    copies of adjust files requested by NGS for quality control.

-   Submit a detailed directory tree listing, on paper, to be used as an
    index for locating all processing, adjustment, and supporting files
    that are submitted in digital format. Do not list the individual
    files within the PAGE-NT vector processing directory for each
    session or the files in the RAW and RINEX data directories; Just
    provide a summary explanation of the files to be found in these type
    directories.

-   If the RAW and RINEX data files are not named by their occupied
    station 4 character ID, submit an index of station name to RAW and
    RINEX file name.

-   Submit a transmittal letter listing all items submitted to NGS with
    the project report.

**Digital data** should be submitted on CD-ROM or IOMEGA ZIP disks. The
following digital files shall be submitted:

[PAGE-NT files]{.underline}-

-   Submit all the raw data, RINEX data, precise ephemeris, and PAGE-NT
    files in accordance with ATTACHMENT 16. Include the CORS RINEX data
    files used for processing.

-   Submit the spreadsheets used for comparing the vector processing
    results (see Section 5).

> [ADJUST files]{.underline}-

-   Submit all ADJUST and checking programs input and output files in
    accordance with ATTACHMENT 17.

-   Submit the spreadsheets used and/or INVERSE3D program output files
    used for comparing published coordinates with their adjusted
    coordinates.

-   Submit the digital data sheet or coordinate file for stations used
    for fixed control during the adjustment (CORS log/coordinate sheets,
    NGS data sheet for HARN and bench mark coordinates, etc.).

[Other Digital Files]{.underline}-

-   Submit the finalized description file (D-file and .ha format) from
    the NGS DDPROC software.

-   Submit any other digital files required by the Project Instructions,
    these General Specifications, or requested by NGS that were not
    submitted previous to this report.

[]{#GLOSSARY .anchor}[GLOSSARY]{.underline}

(For an additional glossary of terms, see FAA No. 405, Fourth Edition.)

ANA - Area Navigation Approach

ASAP - As Soon As Possible

AZ MK - Azimuth Mark: A marked point established in connection with a
triangulation (or traverse) station to provide a starting azimuth for
dependent surveys. Note, some azimuth marks also were positioned and
some have an underground disk. The azimuth mark is usually a pre-stamped
survey disk, generally 1/4 to 2 miles from the horizontal station. The
next consecutive azimuth mark number was used if an earlier number was
destroyed. See ATTACHMENT 1.

BM - Bench Mark

CD-ROM - Compact Disc - Read Only Memory

CBN - Cooperative Base Network (NGS)

CTCORS - Central Temporary Continuously Operating Reference Station. A
permanently monumented control station established near the center of a
300 km (radius) survey area (as defined elsewhere in this document) and
which functions as a temporary Continuously Operating Reference Station
(CORS).

CORS - Continuously Operating Reference Station, See FAA No. 405, Fourth
Edition, Glossary.

DISK - A thin metal plate about 9 cm in diameter, with a stem attached
to the center of the bottom. The plate is slightly convex (in vertical),
usually round (in horizontal) and contains the mark for which survey
information is known, or to be determined. The plate usually also
contains a designation, year, and the name of the agency setting the
plate. It is usually made of bronze, brass, or aluminum and may be set
in a drill hole or embedded in concrete.

DOD - Department of Defense

FAA - Federal Aviation Administration

FBN - Federal Base Network (NGS)

FGCC - Federal Geodetic Control Committee (Changed to FGCS in

October 1990)

FGCS - Federal Geodetic Control Subcommittee

GPS - Global Positioning System

HARN - High Accuracy Reference Network

ITRF - International Terrestrial Reference Frame

MARK - (1) A dot, the intersection of a pair of crossed lines, or any
other physical point corresponding to a point in a survey; (2) The
object, such as a disk, on which the mark (1) is placed; (3) The entire
monument, consisting of the mark (1), the object on which it occurs (2)
and the structure to which the object is fastened.

MONUMENT - A structure that marks the location of a point determined by
surveying. In the case of a disk in concrete, the monument would be the
entire structure. Mark, monument, and station can mean the same thing.

NAD 27 - North American Datum of 1927

NAD 83 - North American Datum of 1983

NAVD 88 - North American Vertical Datum of 1988

NGS - National Geodetic Survey, NOAA. Disks inscribed with this name
have been set from 1970 to the present.

NGVD 29 - National Geodetic Vertical Datum of 1929

NOAA - National Oceanic and Atmospheric Administration. No survey disks
have been set with this name.

NOS - National Ocean Survey, NOAA. Disks inscribed with this NOS name
were set from about 1970 to December, 1982.

NOS - National Ocean Service. Disks inscribed with this NOS name were
set from about 1983 to the present.

NSRS - National Spatial Reference System

PACS - Primary Airport Control Station

RM - Reference Mark: A survey mark of permanent character close to a
survey station, to which it is related by an accurately measured
distance and azimuth. For a triangulation station, reference marks are
pre-stamped survey disks, usually within 30 meters (one tape length) of
the triangulation station. Standard procedure was to set two reference
marks, numbered clockwise from north, with the next consecutive
reference number used if an earlier number was destroyed. See ATTACHMENT
1.

SACS - Secondary Airport Control Station

STATION - A physical location or site at which, from which, or to which
survey observations have been made. See also mark and monument.

USACE - U.S. Army Corps of Engineers (Blue Book abbreviation is USE)

USCG - U.S. Coast Guard

USC&GS - U.S. Coast and Geodetic Survey. Disks inscribed with USC&GS
were set from about 1900 to 1970. Over 10 different pre-stampings were
used. (Bluebook abbreviation is CGS)

USE - U.S. Army Corps of Engineers or U.S. Engineers Department (old
acronym; present Blue Book abbreviation)

WAAS - Wide Area Augmentation System (FAA)

WGS 84 - World Geodetic System 1984

National Agency abbreviations are listed in Bluebook, Appendix C.