USER'S GUIDE 

FOR GPS OBSERVATIONS 

AT TIDE AND WATER LEVEL STATION 

BENCH MARKS

 Updated November 2008 

Engineering Division 

Center for Operational Oceanographic Products and Services 

National Ocean Service 

National Oceanic and Atmospheric Administration
TABLE OF CONTENTS 

1.0 INTRODUCTION ........................................................................................................... 1

1.1 REQUIREMENT ............................................................................................................... 1

2.0. EQUIPMENT AND SETUP ........................................................................................... 2

2.1. DATA COLLECTION AND SETUP ........................................................................................ 2

3.0 GEODETIC AND GPS CONNECTIONS ........................................................................ 3

3.1. GPS BENCH MARK ........................................................................................................... 3

3.1.1. Criteria for Bench Mark Selection for GPS Observations ................................... 3

3.1.2. Planning for GPS Bench Mark Selection ............................................................... 5

3.1.3. Recording of Position Accuracies of the GPS Bench Mark .................................. 5

3.1.4. Photographs of the GPS Bench Mark ..................................................................... 5

3.2. GPS OBSERVATIONS ......................................................................................................... 8

3.2.1. References .................................................................................................................. 8

3.2.2. Static Surveys ............................................................................................................ 8

3.2.3. Connections to Ellipsoidal Datums – GPS Ties ...................................................... 8

3.2.4. North American Datum 1983 (NAD 83) GPS Tie .................................................. 9

3.2.5. GPS Data Processing Using OPUS .......................................................................... 9

3.2.6. NAVD 88 GPS Tie ................................................................................................... 21

4.0 GPS DELIVERABLES .................................................................................................... 22

4.1. POINTS OF CONTACT FOR GPS DELIVERABLES ............................................................ 22
User’s Guide for GPS Observations, Updated November 2008 Page 1 

USER’S GUIDE FOR GPS OBSERVATIONS 

AT TIDE AND WATER LEVEL STATION BENCH MARKS

1.0 Introduction 

This User’s Guide for Global Positioning System (GPS) Observations at tide and water level 

station bench marks is prepared to support the Center for Operational Oceanographic Products 

and Services (CO-OPS) GPS Implementation Plan. The field observation procedures are 

developed in collaboration with the National Ocean Service (NOS), National Geodetic Survey 

(NGS), to obtain relative accuracy in connecting water level stations to the International 

Terrestrial Reference Frame (ITRF) and the North American Datum of 1983 (NAD 83) 

coordinate systems. 

The GPS is a valuable tool for tidal surveyors. It provides an easy and accurate way to position 

marks, track their stability over time on a global reference frame, and increase access to tidal 

datums by integrating them with nationwide leveling and GPS survey networks for modern 

mapping and navigation uses. 

This guide describes just one GPS method, static GPS surveying, which is accurate, automated, 

and available at all our tide and water level station locations. The field requirements are simple 

and the data processing and publishing via NOAA's Online-Online Positioning User Service 

(OPUS) are quick and easy. 

It is assumed that the field personnel are familiar with the basic operating principles of the GPS 

equipment, the cable connections and the antenna/tripod setup procedures. A detailed discussion 

of GPS processing software and processing procedures is outside the scope of this Guide. GPS 

data collected by CO-OPS or CO-OPS’ contractors for the National Water Level Observation 

Network (NWLON), for hydrographic and photogrammetric surveys either by NOS Office of 

Coast Survey (OCS) and NGS field parties shall be submitted to NGS Online Positioning User 

Service (OPUS) Data Base. OPUS allows qualified users to submit results for publication in the 

NGS database and all results must be submitted to OPUS for publication. 

 

All GPS data must be collected as per NGS specifications and as described later in this 

document, and processed using OPUS (database publication). 

1.1 Requirement 

When required in project instructions, or as stated in the contract documents for each tide or 

water level station visited, carefully perform at least one static GPS observation of minimum 

fours hours on one tidal or water level bench mark and publish the data as OPUS datasheet. 

OPUS requires 7200 observations which translate to just under 4 hours of observations, so 

minimum 4 hours of GPS observations are required. If your observations happen to be in low 
User’s Guide for GPS Observations, Updated November 2008 Page 2 

lying areas such as valleys, then you may need more than 4 hours because the observations are 

based upon the number of satellites observed. Hence, as a general requirement, obtain minimum 

of 4 hours of GPS observations. 

2.0. Equipment and Setup 

High accuracy static differential GPS surveys require a geodetic quality, dual frequency, fullwavelength GPS receiver with a minimum of 10 channels for tracking GPS satellites. A choke 

ring antenna is preferred; however, any geodetic quality ground plane antenna may be used. 

Antenna type must have been calibrated by NGS so that data can be accepted in the OPUS. 

A fixed height precise GPS antenna tripod is required for this type of a survey. This is a fixed 

height, 2 meter pole with three adjustable legs, a bulls-eye bubble to plumb the antenna, and a 

magnetic compass to align the antenna to North. These fixed height tripods reduce the chance of 

introducing a Height of Instrument (HI) “blunder” during the post-processing of the data. There 

are situations where it may be necessary to use the adjustable precise GPS antenna tripod, such 

as when a bench mark is elevated above ground level or when using air transportation. The 

center pole is adjustable on this tripod; therefore, if not fully extended to the 2 meter position, 

the antenna height is measured with a steel tape (several times) and entered into the receiver and 

onto the GPS Observation Log Sheet. In fact, even in the 2 meter position, it is recommended 

that the adjustable tripod be measured to verify the length. There is a screw-on point at the 

bottom of the center pole of both - the fixed and adjustable tripods - that must be inspected each 

time the tripod is setup to ensure that the point is tight and not bent. The tripod must be stable 

during observations; therefore, the tripod legs must be secured, preferably with sand bags. 

Antenna set-up is critical to the success of the project. Plumbing bubbles on the antenna pole of 

the fixed-height tripod must be shaded when plumbness is determined. Plumbing bubbles must 

be shaded for at least 3 minutes before checking and/or re-plumbing. 

2.1. Data Collection and setup 

 

Set the epoch update or recording interval (REC INT) for 15-seconds, which should agree with 

the recording interval of the reference stations (CORS) used to post-process the data. The 

elevation mask (ELEV MASK) is typically set for 10 degrees for static surveys; low angle 

satellites can degrade the final solution. Set the minimum number of satellites to zero. 

It is suggested that as much data as possible GPS data should be collected if time and schedule 

permit, so that blunders or invalid data, if any, can be removed during processing still leaving the 

required minimum number of hours of valid data for one GPS session. At least four hours of 

GPS data shall be collected on a water level (tidal or geodetic) bench mark for one GPS session; 

this is a minimum requirement. 
User’s Guide for GPS Observations, Updated November 2008 Page 3 

3.0 Geodetic and GPS Connections 

Water level datums at different locations are local vertical datums which may vary considerably 

within a geographical area. A geodetic datum is a reference surface relative to which heights are 

determined. The North American Vertical Datum of 1988 (NAVD 88) is the accepted geodetic 

vertical datum of the National Spatial Reference System (NSRS) for the conterminous United 

States and Alaska and is officially supported by NGS. The relationships of tidal datums to 

geodetic datums such as NAVD 88 and to ellipsoid heights (above GRS 80 ellipsoid) support 

many hydrographic, coastal mapping, and engineering applications including monitoring of sea 

level changes, the deployment of GPS Electronic Chart Display and Information Systems 

(ECDIS), and NOS Vertical Datum (VDatum) transformation tool, etc. 

Existing Geodetic Bench Marks (GBM) in the vicinity (up to 1.6 km (1 mile) leveling distance) 

of a water level station (primary and subordinate) shall be searched for and recovered. If a mark 

is either not recovered or not used in the survey/project, a separate non-recovery note (report) 

shall be made using the NGS on-line Mark Recovery Entry Form at 

http://www.ngs.noaa.gov/ngs-cgi-bin/recvy_entry_www.prl 

An orthometric level connection and ellipsoidal GPS tie is required at each water level station 

(primary and subordinate) which has at least one GBM located nearby (within 1.6 km (1 mi) 

leveling distance of a water level station). The required “NAVD 88 Level Tie” is described in 

the Standing Project Instructions which are available on CO-OPS’ web page at 

http://tidesandcurrents.noaa.gov/pub. The required GPS tie is described under the section “NAD 

83 GPS Tie” in this document. 

3.1. GPS Bench Mark 

3.1.1. Criteria for Bench Mark Selection for GPS Observations 

The GPS Water Level Station Bench Mark (GPSBM) shall be selected based on the following 

criteria: (a) Permanence and Stability; (b) Historic GPS use; (c) Satellite Visibility; and (d) 

Safety and Convenience. 

(a) Permanence and Stability of Bench Marks 

NGS has defined the following monumentation quality codes, also called the stability codes, for 

various bench mark settings. 

Stability code A – monuments of the most reliable nature which may be expected to hold their 

elevations very well; e.g. Class A rod marks, or marks installed on large boulders/rock outcrop. 

Stability code B – monuments which probably hold their elevations well; e.g. Class B rod marks, 

or marks installed on large concrete footings/foundations. 
User’s Guide for GPS Observations, Updated November 2008 Page 4 

Stability code C – monuments which may hold their elevations but which are commonly subject 

to surface ground movements; e.g. pavement or concrete monuments. 

Stability code D – movements of questionable or unknown reliability. 

The station bench mark selected for GPS observations shall be of stability code A or B and in 

rare case of stability C only when NGS has previously made GPS observations on that mark. 

GPS observations on the PBM are preferred (if the PBM has either stability code A or B) and if 

it is suitable for satellite observations. Leveling history, if available, can also show if a mark is 

stable or not. 

(b) Historic GPS Use 

In many states, CO-OPS has provided NGS with lists of selected marks suitable for GPS 

observations at water level stations, and NGS has completed observations on these marks. Some 

tidal marks designated as Federal Base Network (FBN) or Cooperative Base Network (CBN) 

marks may be of stability code C. Generally once a mark is selected for GPS observations, 

future GPS observations shall be done on the same mark. If leveling reveals instability of the 

mark over time, select another mark. 

Priority shall be given to a GBM for GPS observations because the GBM already has a NAVD 

88 height. The GBM considered here is one of the 10 tidal or water level bench marks at a 

NWLON water level station, or one of the 5 bench marks for subordinate station for survey or 

special projects. 

(c) Satellite Visibility 

The most desirable GPSBM should have 360 degrees clearance around the mark at 10 degrees 

and greater above the horizon. Newly established marks shall be set in locations that have these 

clearances, if at all possible. If a station does not have any marks suitable for GPS observations, 

and it has been selected as needing GPS observations, a new stable mark shall be established. 

This new mark shall be connected to the station bench mark network through conventional 

geodetic leveling, and GPS observations shall be made. 

All existing station bench marks at operating stations shall be assessed for feasibility of GPS 

observations, as time and resources permit. A note shall be made, either in the APP field of the 

electronic leveling HA file, or on a copy of the published bench mark sheet, stating the 

suitability of GPS observations for each mark. 

(d) Safety and Convenience 

The location of the GPSBM should be safe, secure, and convenient. Bench mark locations 

which allow unattended GPS data collection are desirable as the field crew can multi-task at the 

same time while collecting the GPS data. The safety of the GPS equipment (from vandalism or 
User’s Guide for GPS Observations, Updated November 2008 Page 5 

theft) should be considered in the bench mark selection process. 

The GPSBM should be located on public property rather than on private property, as permissions 

from private owners may be required in the future to access the bench mark and for collecting 

the GPS data. The distance to the GPS mark from the station Data Collection Platform (DCP) 

should also be convenient (within 1 mile). 

Consider adding a new tidal bench mark when practical, in cases where no existing marks meet 

the above requirements and the new mark would provide a substantial improvement. Information 

about mark descriptors, images, recovery, reset, etc., are available at 

http://www.ngs.noaa.gov/marks/

3.1.2. Planning for GPS Bench Mark Selection 

To determine the suitability of a mark for GPS observations, a review should be made first of the 

historical bench mark information in the station files and level records, if access to that 

information via database is available, or if the information is available. Stable marks from the 

level records are identified and copies of the descriptions and sketches are made. Descriptions 

and sketches are examined and marks are eliminated that have obvious obstructions, such as 

vertical marks, marks set several meters from medium to large structures, etc. Do not eliminate 

marks that are near poles, fences or about 20 meters from small structures at this time during the 

preliminary planning. If no other mark is available or found suitable, and time does not permit 

the installation of a new GPSBM, it may be necessary to use one of these marks. In selecting a 

GPSBM, priority should be given to the NWLON PBM or an NGS, NSRS, mark with a First or 

Second-Order NAVD 88 height on a NGS datasheet. 

3.1.3. Recording of Position Accuracies of the GPS Bench Mark 

GPS (horizontal) positions (latitude and longitude) of each bench mark installed or recovered 

shall be listed on the HA files for laser levels, if used, or on the bench mark descriptions sheet 

for optical leveling, as applicable, at each water level station occupied for all projects. The 

position of each bench mark recovered using a hand held GPS receiver shall be listed in the 

following format: degrees, minutes, seconds and tenth of a second (e.g. 45 degrees 34’ 45.6”). 

The position of the bench mark as obtained from OPUS shall be recorded on the site report or ESite report (where applicable) as degrees, minutes, seconds and one hundred thousands of a 

second (e.g. 55 degrees, 42’ 25.78912”), and the elevation above the ellipsoid shall be listed as 

+/- XX.XXX m (e.g. -22.907 m). 

Remember once the GPS data is submitted to OPUS, and the data is accepted then position is 

determined by OPUS. If the bench mark has a Permanent Identification (PID) number assigned 

by NGS, you may be able to retrieve the position from the NGS web. 

3.1.4. Photographs of the GPS Bench Mark 
User’s Guide for GPS Observations, Updated November 2008 Page 6 

NGS requires a minimum of two photos of the GPS bench mark taken as follows: (1) close-up of 

the disk face (see Figure 1 A); (2) horizontal view of the location of the bench mark and 

direction of view (see Figure 1 C). 

CO-OPS requires two additional photos as follows: (3) chest level or eye level view of disk and 

setting (see Figure 1 B); and (4) a horizontal view of bench mark and direction at perpendicular 

to the direction of the photo taken in (2) above (see Figure 1 D). Thus two photos in the vertical 

direction (Figures 1A and 1B) and two photos in the horizontal direction (Figures 1 C and 1D) as 

described above are required. If these four photos have been taken previously and are available 

to be included in the documentation, another set of photos is not necessary. 

There are no file naming rules for OPUS but there are some suggestions for naming of the files 

as follows, compatible with the file naming for tidal/water level marks. 

All digital station bench mark photo files should be named such that the name of the file will 

indicate the station number, dash, PID number (if available), dash, stamping or designation, 

dash, photo type, dash, date, dot.jpg. For new mark, the PID is not applicable as it is 

unavailable. Close-up photo vertically taken of the bench mark is photo type 1, eye level photo 

vertically taken of the bench mark is photo type 2, and the horizontal view taken of the bench 

mark is photo type 3. For photo type 3 include the cardinal direction (N, NE, S, SE, etc) that the 

camera is pointing. If there are more than one type of photo taken then re-name them as 1A, 1B, 

2A, 2B, 3A, 3B, etc. If a PID is available, then use designation instead of stamping for the 

naming of the file. Use a maximum of 30 alpha numeric characters to the left of the dot. So if 

you are exceeding 30 alpha numeric characters in the name, then truncate the stamping or 

designation so that maximum characters in the name are 30. For example, the bench mark E 

close-up photo for Seattle water level station should be named as 9447130-7130 E 1990-1-

20090101.jpg. 

Sample file names for photo files 

New bench mark without a PID and disk face 

photo 

9414290-4290A2008-1-20090101.jpg 

Existing bench mark with a PID and eye level 

view photo 

9410660-DY2512-BM N-2-20090101.jpg 

Existing bench mark without a PID and north 

direction photo 

9447130-7130E1990-3N-20090101.jpg 

In addition, put a caption for each photograph, as shown in Figures 11- 13, indicating the 

stamping or designation of the mark, PID, photo type with cardinal direction, and the date of 

photograph taken. Additional information about caption is available at the following resource: 
User’s Guide for GPS Observations, Updated November 2008 Page 7 

http://tidesandcurrents.noaa.gov/publications/AttachmentR_Requirements_for_Digital_Photogra

phs_of_Survey_Control_Std_V13C_updated_January_2008.pdf 

NGS Coastal Mapping Surveys require a slightly different file naming convention as described 

in Attachment R of the NGS Specs which is located at 

http://www.ngs.noaa.gov/ContractingOpportunities/SOW_Main_Text_V13B_new.pdf . All 

photos collected for NGS Coastal Mapping Surveys for both contract and in-house projects shall 

be named according to NGS convention. 

Figure 1 A: Close Up View of Face of Mark Figure 1 B: Eye Level Settings View of Mark 

Figure 1 C: Horizontal View 1 of Mark Figure 1 D: Horizontal view 2 of Mark
User’s Guide for GPS Observations, Updated November 2008 Page 8 

3.2. GPS Observations 

3.2.1. References 

These guidelines are written for establishing GPS derived ellipsoid height accuracy standards of 

2 cm for all NWLON, PORTS®, hydrographic/Photogrammetry survey projects, COASTAL 

projects, and special project applications. 

3.2.2. Static Surveys 

Static GPS surveys shall be conducted on a minimum of one tidal bench mark at each water level 

station, according to the priority levels below. Generally, one bench mark at each station is 

designated as the GPSBM and observations shall be made to that mark (as per the required GPS 

observation frequency) unless otherwise specified in the Station Specific Requirements, Project 

Instructions, or contract documents. 

1. National Water Level Observation Network (NWLON), PORTS®, and tsunami stations. 

2. Long term operating secondary water level stations. 

3. New and historic tertiary stations supporting hydrographic and photogrammetric surveys, 

COASTAL stations, and special project stations. 

Static GPS surveys shall be conducted at water level stations periodically over time to establish a 

history of relationship between the tidal or water level datums, and the ellipsoid. 

As of October 2008, 20 NWLON stations have been identified where annual GPS observations 

are required because of the sea level rise in those areas. These 20 NWLON stations – 8 in 

Alaska and 12 in the Gulf of Mexico – will be identified in the annual Project Instructions. The 

rest of the NWLON stations require GPS observations every five years. These guidelines will be 

updated as GPS technology improves and the policy or regulations change in the future. 

As specified in the Annual Project Instructions, Annual Station Specific Requirements, or in the 

contract documents, installer shall be required to perform GPS observations at each water level 

station at specified intervals over time, depending on the rate of sea level rise in that water area 

of the coast. 

3.2.3. Connections to Ellipsoidal Datums – GPS Ties 

The connections to ellipsoidal datums involve the following two ties: 

(1) NAD 83 GPS Tie 

(2) NAVD88 GPS Tie 
User’s Guide for GPS Observations, Updated November 2008 Page 9 

3.2.4. North American Datum 1983 (NAD 83) GPS Tie 

At each water level station, GPS observations shall be performed as listed in the Annual Project 

Instructions, Annual Station Specific Requirements, and contract documents. 

The NGS OPUS with publication option is now used for processing and storing of the GPS data 

for a variety of applications. 

The expected ellipsoid height accuracy for a single four-hour OPUS solution is 1.8 cm, (at the 

67% confidence level), and that is desirable, practical, and achievable. Confidence increases 

with repeated observations. 

For all water level stations, collect a minimum of 4 hours of GPS data on the GPSBM. Extra 

care shall be taken to ensure that the antenna height is precisely recorded, and that the antenna 

setup is stable. A continuous session of at least 4 hours is required. 

3.2.5. GPS Data Processing Using OPUS 

After GPS data is collected, the collector shall submit the GPS data to NGS OPUS for processing 

the GPS observations and determining the position of the GPSBM. OPUS provides an easily 

accessible, rapid method for submitting GPS data and receiving an almost instantaneous solution 

response from NGS via email. 

OPUS allows users to submit their GPS data files to NGS, where the data will be processed to 

determine a NAD-83 position using NGS computers and software. Each data file that is 

submitted will be processed with respect to three CORS sites. The CORS sites selected may not 

be the nearest to the observed site, but CORS sites are selected automatically based upon 

distance to the observed site, number of observations, site stability, etc. The position for the 

observed data will be reported back to you via email in both - ITRF and NAD 83 coordinates as 

well as Universal Transverse Mercator (UTM), U. S. National Grid (USNG) and State Plane 

Coordinates (SPC) northing and easting. 

To publish OPUS datasheets, you must meet the minimal field and data requirements for OPUS 

publishing. These evolving requirements are described at 

http://www.ngs.noaa.gov/OPUS/view.jsp and are hereby superseded where any requirement 

below exceeds that of OPUS. 

 Always use a calibrated 2-meter fixed-height tripod, unless prevented by logistics 

circumstances (e.g., air cargo limits, unusual setup). 

 Alternate tripod or antenna mount must allow precise antenna positioning and height 

measurement. 

 Verify tripod stability and antenna height at the beginning and end of every session. 

Tripod leveling bubbles should be shaded when not in use. 
User’s Guide for GPS Observations, Updated November 2008 Page 10 

 A digital camera is required to capture mark close-up and horizon photos. 

 In addition to the 2 photos required by OPUS, provide for CO-OPS two additional photos 

as described in Section 3.1.4 Photographs of the GPS Bench Mark. 

 Submit to OPUS all mark information listed as both required and optional on OPUS 

forms. See figures 7 & 8 below for current form elements. 
User’s Guide for GPS Observations, Updated November 2008 Page 11 

Step 1 of 4: 

(A) OPUS requires only a minimal amount of information from the user. The NGS OPUS web 

page can be obtained at http://www.ngs.noaa.gov/OPUS/. Then enter the following information: 

(1) The email address where you want the results sent 

(2) The GPS data file that you want to process (which you may select using the browse 

feature; raw or RINEX accepted) 

(3) The antenna type used to collect this data file (selected from a list of calibrated GPS 

antennas) 

(4) The height of the Antenna Reference Point (ARP) above the monument or mark that 

you are positioning. 

(5a) Customize your solution, report, and publishing options. Click on the Option button. 

 

Figure 2: OPUS Step 1 of 4 – OPUS Upload Screen 
User’s Guide for GPS Observations, Updated November 2008 Page 12 

(B) Once this information is complete, you then click the 5a Options button to customize the 

solution, report, and publishing options. Then you will see a screen like this. 

Figure 3: OPUS Step1 of 4 – OPUS Options Screen Shot 1 

The Options page asks you seven questions as described below: 

Leave options 1 through 6 as defaults and only select option 7 “Submit to Database” for the 

first try. 

(1) Select State Plane Coordinate zone: The default is 0 Auto, leave that as default and do not 

change this option. 

(2) Select CORS To Use – Or Not Use – As Base Stations: 

On the left side of the above screen, select the state your GPS bench mark is located and hit the 

“Set” button to limit the CORS choices. Please note the two boxes on the right side in the above 

figure – “CORS to include in this solution” and “CORS to exclude in this solution”. For the 

“CORS to include in this solution” box has a default of “Let OPUS Choose”. For the 1st

iteration let the OPUS choose the three closest CORS stations so leave the default option as it is. 
User’s Guide for GPS Observations, Updated November 2008 Page 13 

The 2nd box shows “CORS to Exclude from the solution shows” default option of “NONE”. For 

the 1st iteration, leave this option. For the 2nd iteration, if the OPUS solution fails to meet the 

minimum criteria as defined below, then one or more of the CORS stations can be excluded in 

this step. 

Figure 4: OPUS Step 1 of 4 - Options Screen Shot 2 

 

(3) Extended Output: The default is standard output, leave that as default. 

(4) Draft XML output: The default is “No, Thank You”. Select the default choice. 

(5) Submit to Project: This option is not applicable to CO-OPS’ water level work. So skip this 

option. 

(6) Set user Profile: Since CO-OPS water level stations are located in various different 

locations, skip this option. 

(7) Submit to Database: Make sure you select the option “Yes, Publish”. Then select the 

Static button only. Once you hit the Static Button that will bring the Step 2 of 4 “Identify Your 

Mark” screen as shown below. 
User’s Guide for GPS Observations, Updated November 2008 Page 14 

Step 2 of 4: 

Figure 5: OPUS Step 2 of 4 – Identify Your Mark 

You have two choices here – either “Describe New mark” or “Describe Recovered Mark”, as 

shown above. If the mark has a PID assigned by NGS, then only you can select the “Describe 

Recovered Mark” otherwise you must select “Describe New Mark”. 

Appropriate context sensitive help is also available here – if you hit “confused? New and 

recovered marks are described here” link, it will bring a help file (see the next screen) for mark 

description and recovery forms. 
User’s Guide for GPS Observations, Updated November 2008 Page 15 

 

Figure 6: OPUS Help File 

Use your web browser’s back button to go back from the help file. 

Step 3 of 4: 

If the GPSBM was a recovered mark, the next screen shows you “Step 3 of 4: Describe 

Recovered Mark”. Here (a) you must fill in the PID number (since it was a recovered mark), 

(b) attach two photos of the GPSBM– one for close up photo of disk face and second for horizon 

photo, 

(c) indicate the condition of the mark by selecting the appropriate radio button – good or poor, 

(d) provide description of the mark in CO-OPS format as per “User’s Guide for Writing Bench 

Mark Descriptions” which is available at CO-OPS web page at 

http://tidesandcurrents.noaa.gov/publications/bmguide5.pdf , 

(e) Then hit the “continue” button. 

Remember, the PID number and the two photos as listed above in (a) and (b) respectively are 

required; and the mark condition and the mark description as listed in (c) and (d) are optional for 

an existing mark, but you are encouraged to submit both optional items. If there are any changes 
User’s Guide for GPS Observations, Updated November 2008 Page 16 

needed to the stored description, then please submit the revised description. After completion of 

the information for this screen, hit the “Continue” button. 

Figure 7: OPUS Step 3 of 4 – Describe Recovered Mark 

If the mark was a new bench mark and you selected “Describe New Mark” in OPUS Step 2 of 4, 

then you will see the following screen.
User’s Guide for GPS Observations, Updated November 2008 Page 17 

Figure 8: OPUS Step 3 of 4 – Describe New Mark 
User’s Guide for GPS Observations, Updated November 2008 Page 18 

The “Describe New Mark” part as shown above has 7 required elements and 5 optional elements. 

The 7 required elements are as follows: designation, stamping, type, setting, descriptions, closeup digital photo, and horizon digital photo. Designation and stamping should be entered as per 

NOS convention. The selection for type and setting can be done through the choices listed in the 

drop down boxes as shown. Attach close-up and horizon digital photos of the new mark by 

indicating the location of the photos on your PC or server, as appropriate. 

The 5 optional elements are as follows: stability, magnetic, application, antenna serial number, 

and receiver serial number, model and firmware. The selection for stability, magnetic, and 

application can be done through the choices listed in the drop down boxes as shown. 

Everyone is strongly encouraged to provide the information about the optional elements also. 

After completion of the information for this screen, hit the “Continue” button. Then you will get 

the following message. 

Figure 9: OPUS Step 3 of 4 – Almost Done 
User’s Guide for GPS Observations, Updated November 2008 Page 19 

You will receive three e-mails, one of the e-mails will provide you the summary and that will 

look like the following window: 

Step 4 of 4: 

Figure 10: OPUS Step 4 of 4 – E-Mail Message and Statistics 

This e-mail provides you information about whether your submission passed or failed various 

checks as follows: 

(a) Ephemeris: The satellite configuration when the data was collected, whether OK or not. 

(b) % of Observations used for processing the data: 

(c) Observations: Number of GPS observations (data points) used 

(d) Fixed ambiguities: % of ambiguities fixed 

(e) Antenna type used: lists the antenna type that you provided as a input in Step 1 

(f) ARP height: lists the Antenna height that you provided as input in Step 1 

(g) RMS: provides you root mean square of the solution 

5001 

 5001 OPUS Quality Control Report 

 5001 

 5001 The RINEX dataset and supporting files submitted to OPUS 

failed to 

 5001 pass an initial set of quality control tests. 

 5001 

 5001 Please re-submit the data if you can correct the errors 

listed in the 

 5001 output from the verification process. 

 5001 

 5001 See hints at http://www.ngs.noaa.gov/OPUS/about.html#FAQ

 5001 

 

RINEX FILE: san1097o.06o.gz 

EPHEMERIS: OK. 

OBS USED: OK 73.64 %. 

OBSERVATIONS: OK 13212. 

FIXED AMB: OK 78.15 %. 

ANTENNA: THA800961+REC NONE. 

ARP HGT: OK 1.5 (m). 

RMS: OK 0.026 (m). 

LAT RANGE: FAILED --> LAT. peak to peak 0.088 (m) too high. A 

value less that or equal to 0.04 (m) is needed. 

LON RANGE: FAILED --> LON. peak to peak 0.055 (m) too high. A 

value less that or equal to 0.04 (m) is needed. 

HGT RANGE: FAILED --> HGT. peak to peak 0.153 (m) too high. A 

value less that or equal to 0.08 (m) is needed. 
User’s Guide for GPS Observations, Updated November 2008 Page 20 

(h) Lat Range: provides you information about the peak to peak errors for the latitude derived, 

the peak to peak errors for the latitude should be less than 0.04 m (4 cm) 

(i) Long Range: provides you information about the peak to peak errors for the longitude 

derived, the peak to peak errors for the longitude should be less than 0.04 m (4 cm) 

(j) HGT range: provides you information about the peak to peak errors for the height derived, 

the peak to peak errors for the height should be less than 0.08 m (8 cm) 

The following are some simple guidelines for analyzing the OPUS solutions. 

(a) Make sure the antenna type and the ARP height are correct. 

(b) Review the solution statistics: 

(I) A good quality OPUS run should typically use 70% or more of your observations. 

(II) OPUS should have fixed at least 70% of the ambiguities 

(III) The overall RMS should seldom exceed 3 cm. 

(IV) The maximum peak to peak errors should be less than 4 cm for horizontal (for both 

latitude and longitude) and 8 cm for vertical. 

If the OPUS solution e-mailed to you exceeds the allowable tolerances as specified in guidelines 

(b) above, then you must resubmit data but select an option for dropping one or more of the three 

CORS stations selected automatically by the NGS OPUS software and resubmit the data. To do 

so, check the OPUS solution e-mailed to you and select one of the CORS stations which shows 

the maximum errors that exceed the tolerances and then select the options button in Step 1 of 4, 

(B) (2) as shown above, and exclude that CORS station name and resubmit the GPS data by 

clicking the Upload to Static button. If the 2nd solution provided by the OPUS software does not 

meet the allowable tolerances as listed in (b), then submit the data to NGS for further evaluation. 

If your data does not meet OPUS guidelines after 2nd OPUS processing attempt and if you are 

still at the water level station site, then another option is to collect four hours of GPS data and 

resubmit it for processing. 

NGS needs to receive orbit data from International GPS Service (IGS) (soon to be renamed as 

International Global Navigation Satellite System) in order to obtain a solution. If the data is 

submitted too quickly (before NGS gets the orbit data from IGS), the submitter may need to resubmit the data at a later time. For best results, submit the GPS data to OPUS at least 17 hours 

after the first midnight (in Greenwich Mean Time) following the time when the observations 

were recorded. Compare the resultant solution to the last previous solution made at the station, if 

available, to ensure that you do not have a blunder in the antenna setup. This will be revealed by 

a noticeable discrepancy in the ellipsoid height. Include a copy of the OPUS solution as shown 

for samples in Figure 11, 12, 13 in the GPS Deliverables. 
User’s Guide for GPS Observations, Updated November 2008 Page 21 

WHAT TO DO IF OPUS FAILS? 

 Data submission to OPUS should be performed by the GPS observer as soon as is 

practical, while on-site, details are fresh in memory, and opportunity exists for additional 

observations. 

 Consider repeating the OPUS submission using the OPUS option #2, "CORS to 

Exclude", to remove a transient base station. 

 Consider repeating the OPUS submission on the afternoon following the observation day, 

after the GPS orbit models are updated. 

 Consider repeating your GPS observation at a different time of day (night observations 

may improve results at lower latitudes.) 

 Consult with the OPUS help desk on other suggestions to improve the data. 

ADDITIONAL SUGGESTIONS: 

 More GPS data is better than less. The minimum GPS observation duration requirement, 

currently 4 hours, should be extended whenever practicable, e.g., overnight in secure 

areas. 

 Horizon photos should be taken during the GPS observation, thereby documenting the 

GPS equipment in use and highlighting the mark location. 

 Additional photos are helpful alternatives to paper field logs (e.g., to document 

equipment serial #s, antenna height, observer and mark IDs, observation times, weather 

conditions, etc.) 

 Before your field campaign begins, test your GPS equipment by submitting to OPUS a 

sample dataset to confirm that your data format and GPS antenna type are OPUScapable. 

 Additional suggestions are available at 

http://www.ngs.noaa.gov/PROJECTS/INSTRUCTIONS/GPSmanual/

3.2.6. NAVD 88 GPS Tie 

The NAVD 88 GPS Tie involves simultaneous GPS observations at the GPSBM and one or 

more GBMs located up to 10 KM (6.26 mi) from the GPSBM. This tie is deferred until such 

time as NGS enables user-friendly blue-booking of campaign data (OPUS projects). 
User’s Guide for GPS Observations, Updated November 2008 Page 22 

4.0 GPS Deliverables 

Submit the OPUS results (sample datasheet as shown in Figures 11 or 12 or 13) and 4 photos of 

the GPSBM in electronic format for each observation for each water level station. For example, 

GPS submission for San Francisco tide station shall be provided in a folder as follows: 

9414290 San Francisco FY 09 Annual Inspection 

/GPS OPUS Results 

/Photos of GPSBM 

4.1. Points of Contact for GPS Deliverables 

All required GPS OPUS deliverables as listed in Section 4.0 above shall be submitted to proper 

point of contact as listed in the project instructions, contract documents, if applicable; or to NGS 

or CO-OPS within 15 business days of the GPS observations, the removal of the water level 

gauge, or as specified in the Statement of Work or contract, whichever is earlier. All GPS data 

and documentation shall be submitted to NGS OPUS. 

For all CO-OPS in-house work, and OCS contract hydrographic surveys, submit GPS 

Deliverables to: 

Chief, Engineering Division 

CO-OPS, N/OPS1, SSMC 4 

1305 East-West Highway, Station 6531 

Silver Spring, MD 20910-3233 

Tel: 301-713-2897 x 145 

For all CO-OPS contracts, submit GPS Deliverables to: 

Marty Welch, 

Contracting Officers Representative 

CO-OPS, SSMC 4 

1305 East-West Highway, Station 6544 

Silver Spring, MD 20910-3233 

Tel: 301-713-2981 x 129 

For NGS contract shoreline mapping surveys, submit GPS Deliverables to: 

Mr. George Leigh 

Contracting Officers Representative 

NOAA/NOS/National Geodetic Survey 

SSMC 3, Station # 8609 

1315 East-West Highway 

Silver Spring, MD 20910-3281 

Tel # 301-713- 3167 
User’s Guide for GPS Observations, Updated November 2008 Page 23 

Figure 11: Sample # 1 of OPUS Results 
User’s Guide for GPS Observations, Updated November 2008 Page 24 

Figure 12: Sample # 2 of OPUS Results
User’s Guide for GPS Observations, Updated November 2008 Page 25 

Figure # 13: Sample # 3 of OPUS Results