U.S. Department of the InteriorU.S. Geological Survey

ESTABLISHMENT OF THE USGS GPS COMMITTEE, CHARGE AND CURRENT PROGRESS

NAVD 88 DATUM CONVERSION UPDATE

Paul H. Rydlund Jr. PLSU.S. Geological Survey Missouri Water Science Center

Current Guidance – Vertical DatumTechniques of Water-Resources Investigations

of the United States Geological Survey

Chapter A19

LEVELS AT STREAMFLOW GAGING STATIONS

Suggested criteria for tying to NGVD 29 control.

Suggested distance under 8 miles, greater than 8 miles should wait or defer to other agencies to establish benchmarks.

“Ordinary Levels” – describes Third Order levels run with ordinary equipment and procedures (as opposed to special equipment and meticulous procedures designed to minimize systematic errors). Fourth order levels are run for the purpose of referencing gaging-station datums to NGVD 29. First order (ft)

Second order Class I & II (ft)

Third order (ft) M0.050

M0.035

M0.017

Current Guidance – Vertical Datum

Techniques of Water-Resources Investigationsof the United States Geological Survey

Chapter A19

LEVELS AT STREAMFLOW GAGING STATIONS

Suggested criteria for tying to NGVD 29 control.

• Double run lines • Sight lengths limited to 300 feet• Rods read to 0.01 ft• Closure errors kept under Third Order, exceptions due to rough or hilly terrain.

Third order (ft)

Rough/Hilly exception (ft) M0.10

M0.050

Establishment of the USGS GPS Committee, charge and current progress

GPS

Why????

Stuff Stuff

OSW sponsored, Liaison Robert R. Holmes, Jr.,PhD,PE

Committee Members

Paul H. Rydlund Jr., PLS, Chair (MOWSC)Brian Fiehler (MCGSC)Doug Nagle (SCWSC)Chad Ostheimer, PE (OHWSC)Kenneth Skinner (IDWSC)Brenda Woodward (NEWSC)

Establishment of the USGS GPS Committee, charge and current progress

ChargeAction Plan: Addressing needs of technically strongGPS activities in the USGS and a set of actions thatwill address such needs and set a firm foundation for sound and robust use of GPS to achieve accurate and defensible survey data

Completion of 2 or 3 highest priority actions from the Action Plan

Accomplishment of the remainder of priority action items

USGS GPS Survey Web Portal

Introduction• Mission & Members• USGS State Contacts• National Equipment Inventory• Training And Workshops• On-line References• Status Of GNSS

Coastal Storm Surge Sensors• Coastal State Control Evaluation• GPS Campaign Guidence

• Pre-deployment preparedness• Methods• Data dissemination• USGS publications

Real-Time Networks• State Network Overview & Contacts• Method

USGS GPS Survey Web Portal - Linked Pages

USGS Projects Involving GPS• Well Field Surveys• Flood Studies• Land Science Aerial and Ground-based LiDAR Verification• Hydrographic Surveys

USGS GPS Survey Web Portal - Linked Pages

Techniques and Methods Anticipated Publication Methodology in establishing datum by GPS methods

Variable methods of practice and guidelines in ensuring minimum solution standards

Survey grade RTK• Single base• Network RTN

Survey grade Post Processed• Static• Kinematic• Fast Static

Data Dissemination

CAS

E ST

UD

IES

CAS

E ST

UD

IES

Techniques and Methods Anticipated Publication Guidelines and Procedures for Different Real-Time

Accuracy Classes

CLASS RT1

CLASS RT2

CLASS RT3

12 miles

13 miles

4 miles

5 miles

3rd Order

2nd Order

2nd Order

2nd Order

• Occupy approximate midpoint 5 mile baseline • Redundant rover observations (180 epochs each) tied to bridge• Occupy approximate midpoint 4 mile baseline• Redundant rover observations 180 epochs tied to bridge and 3rd Order check• Occupy different base location near midpoint 5 mile baseline (best 2nd Order control source)• Redundant rover observations (180 epochs) tied to bridge

Derivation of Class RT1 or Class RT2 Procedures,

Bridge & Gage

Autonomous field base at midpoint

Autonomous field base at midpoint

2nd Order Bridge Difference 3rd Order Bridge Difference

Given 751.75 ? 763.25 ?

1st Autonomous

152.36 123.45 -28.91 143.88 103.48 -40.40

2nd Autonomous

161.54 132.71 -28.83 138.52 98.25 -40.27

Elevation 722.88 -28.87avg 722.91 -40.34avg

Techniques and Methods Anticipated Publication“RTK as a level”

• Consider beginning with outer network first.• Consider minimally and fully constraining inner network.

Datum brought in using Static

Benchmark

Autonomous

Autonomous

Benchmark

Techniques and Methods Anticipated Publication“GPS over large areas”

NGS-NWS-USGS Streamgage Datum Conversion Committee

NGS: Renee Shields, Christine GallagherNWS: Victor Hom, Laurie Hogan (NY), John Sikora (WV), Jonathon Brazzell (LA)USGS: Jim Kolva, Paul Rydlund (MO), Brenda Woodward (NE)NCGS: Gary Thompson, Scott Lokken

Objective: To develop a coordinated effort toconvert existing NVGD 1929 datum to NAVD 1988 while ensuring a datum quality sufficient for public and cooperative interest

NGS-NWS-USGS Streamgage Datum Conversion Committee

VERTCON

2 cm at 1 sigma 68% confidence4 cm at 2 sigma 95% confidence

Cooperative GPS Campaigns

Methods sufficient to meet accuracy needs

• USGS database updated to include NWS location IDs

• NCGS setting control to aid USGS gaging stations

• Additional parameter dissemination from USGS database to local partners

• Missouri conducting local pilot studyLocal spreadsheet (database) nearly complete (needed to scope)3-4 cm accuracies at NWS forecast sites (other criteria?)Anticipated cooperation with NGS state advisor, NWS, and USACE

NGS-NWS-USGS Streamgage Datum Conversion Committee