N O A A T e c h n ic a l M e m o r a n d u m N O S N G S - 5 8

G U ID E L IN E S F O R E S T A B L IS H IN G G P S - D E R IV E D E L L IP S O ID H E IG H T S( S T A N D A R D S : 2 C M A N D 5 C M )V E R S IO N 4 .3

D a v id B . Z i lk o s k iJ o s e p h D . D 'O n o f r ioS t e p h e n J . F r a k e s

S i lv e r S p r in g , M D

N o v e m b e r 1 9 9 7

U . S . D E P A R T M E N T O F N a t i o n a l O c e a n i c a n d N a t i o n a l O c e a n N a t i o n a l G e o d e t i cC O M M E R C E A t m o s p h e r i c A d m i n i s t r a t i o n S e r v ic e S u r v e y

LINK TO SLIDES:

ftp://ftp.ngs.noaa.gov/dist/whenning/FWS2011/

PROJECT POSITIONING CHOICESEQUIPMENT PRECISION (95% CONFIDENCE) ADVANTAGES DISADVANTAGES

TOTAL STATION 3 MM h, 3 MM v VERY PRECISE COSTLY, STEEP LEARNING CURVE, HEAVY, LINE OF SIGHT ONLY, NEEDS AT LEAST TWO PEOPLE

ROBOTIC TOTAL STATION 3 MM h, 3 MM v VERY PRECISE, ONE PERSON CAN OPERATE COSTLY, STEEP LEARNING CURVE, HEAVY, LINE OF SIGHT ONLY

DIGITAL GEODETIC LEVELING 1 MM v (ONLY) MOST PRECISE VERTICAL POSSIBLE LABOR AND TIME INTENSIVE, STEEP LEARNING CURVE FOR PROCESSING,

REQUIRES USING STANDARDS & SPECIFICATIONS, RECOVERY OF PASSIVE MARKS,

USUALLY TAKES THREE PROPLE, NO HORIZONTAL RESULTS

OPUS 2 CM h, 5 CM v EASY RESULTS, DIRECT TIE TO DATUMSPOINT POSITION ONLY, MAY NOT AGREE WITH PASSIVE CONTROL, ORTHOS FROM GEOID MODEL

STATIC GNSS 5 MM h, 1.5 CM v MOST PRECISE GNSS, NETWORK ADJUSTMENT, POST PROCESSING CAPABILITY REQUIRED, LONG SESSIONS, PLANNING REQUIRED

OPUS CAPABLE, ENABLES DATA EVALUATION

SINGLE BASE RTK 7 MM h, 1.5 CM vFAST DATA CAPTURE, COORDINATES IN THE FIELD,

MARK RECOVERY, LACK OF METADATA, TWO GNSS UNITS REQUIRED, RADIOS (UHF FCC LICENSURE)

ONE PERSON CAN OPERATE OR DATA MODEMS (CELL PROVIDER) REQUIRED UNLESS LINE OF SIGHT, BASE BABYSITTER

RTN 1 CM h, 5 CM v1/2 THE EQUIPMENT OR DOUBLE THE PRODUCTION FEE BASED SERVICE, LEAST ACCURATE OF THE LISTED METHODS

OF SINGLE BASE RTK, NO PPM ERROR, NO MARK

RECOVERY

HeightModernization

-faster-cheaper

-Nearly as good

differential leveling

GNSS

HEIGHT MODERNIZATION-BACKGROUND

CHA – CHING $$$$$$$ ♪♪♪

ELLIPSOID, GEOID & ORTHO HEIGHTS

H88 = h83 – N03

NAD 83 (HARN) USE GEOID O3NAD 83 (CORS 96) USE GEOID 09

ITRF USE SCIENTIFIC GEOID (USGG)

TOTAL STATION ∆ HEIGHTS

• INTERNET DATA VIA CELL TECHNOLOGY

• SOFTWARE/FIRMWARE ALGORITHMS

• GNSS HARDWARE

• SATELLITE CONSTELLATIONS

• SATELLITE CODES/FREQUENCIES

THE USE OF RTK- A CONFLUENCE OF TECHNOLOGY

GLONASS- FULL OPERATIONAL CAPABILITY 2010 EUROPEAN UNION - GALILEO CHINA – COMPASS/BEIDOU JAPAN- QZSS FIRST LAUNCH 2010

CHANGES IN GNSS

GPS:• L2C• L5 CARRIER• New Code on L5• L1C

1-3 m

BETTER RESISTANCE TO INTERFERENCEFASTER AMBIGUITY RESOLUTIONAUGMENTED CODE APPLICATIONS

10-15 cm???

= 115 SATELLITES?

DUAL CONSTELLATION RT POSSIBILITIES:GPS ≥ 5, GLN = 0 GPS = 4, GLN = 2 GPS = 3, GLN = 3 GPS = 2, GLN = 4 (Can't initialize with only GLN Sats.)

GPS AND GLN

BEST SCENARIO = 7 OR MORE GPSGLN “K” SATS WILL HAVE A CDMA (L3) FORMAT SIGNAL

SO – WHAT CAN I EXPECT FROM A RTN?

MOST RTN PRODUCE “GOOD” HORIZONTAL VALUES. OUR HORIZONTAL SYSTEM IS BASED ON ACTIVE REFERENCE STATIONS (NGS CORS), AS ARE THE RTN STATIONS.

BECAUSE ORTHOMETRIC HEIGHTS (‘ELEVATIONS’) ARE BASED ON PASSIVE MONUMENTS, THE RTN USER SHOULD, FOR THE MOST PART, CONSTRAIN THE PASSIVE MARK VALUES IN A LOCALIZATION.

CHOOSE THE RTN WITH A BUSINESS MODEL THAT BEST FITS YOUR NEEDS.

THE TECHNOLOGY SWEET SPOT• SBAS: 2 M H, 6 M V, 0.3 M SMOOTHED H, CHEAP• COMMERCIAL DGPS: FEW DM, $$• USCG BEACON: METER+, CHEAP• DIFFERENTIAL LEVELING: 1-3 CM, LABOR/TIME INTENSIVE, $$$• GEODETIC LEVELING: mm, LABOR/TIME INTENSIVE, $$$$$• USER BASE RTK: 1-3 CM H, 2-4 CM V, REQUIRES INITIAL INVESTMENT• RTN: 3-4 CM H, 5-7 CM V, REQUIRES INITIAL INVESTMENT(BUT ½ OF

RTK)• AERIAL MAPPING: .10 M H, .20 M V, $$$• LIDAR: 0.10 – 0.3 M V• SATELLITE IMAGERY: 0.5 METER H RESOLUTION, 3 M LOCATION, $$$• LOW ALTITUDE AERIAL IMAGERY: 2-4 CM H, 3-5 CM V, $$$• TERRESTRIAL LASER SCANNING/MMS: PROJECT SITES ONLY, 0.015 M

H, 0.02 M V, REQUIRES INITIAL INVESTMENT

PRECISION VS. ACCURACY

• “PRECISION” IS A COMPUTED STATISTICAL QUANTITY TO THE SOURCE OF THE MEASUREMENT - ALIGNMENT TO THE RTN OR PASSIVE MARK SHOWS PRECISION OF THE OBSERVATION (PER THE DATA COLLECTOR).

• “ACCURACY” IS A COMPUTED STATISTICAL QUANTITY TO THE REALIZATION OF THE DATUM - ALIGNMENT OF THE RTN OR PASSIVE MARK TO THE NSRS SHOWS ACCURACY (PER ESTABLISHED METHODOLGY)

•

Typical RTN precisions at the 95% confidence level are: horizontal 2-3 cm , vertical (ellipsoid) 3-5 cm, orthometric heights 5-7 cm (typical-using the NGS hybrid geoid model). Exceptional RTN derived precisions are at the current limit of the RT technology: horizontal : ≤ 1 cm, vertical (ellipsoid) ≤ 1 cm, possible orthometric height ≤ 2 cm.

Accuracy is a measure of how the positions are aligned to “truth”. NGS wishes to encourage all RTN to provide users with alignment to the NSRS as the representation of truth.

Since RTN positioning is a differential solution from a base station to a point of interest, the results are displayed in the data collector as measures of the precision, or repeatability, of the solution. On the other hand, the alignment of the base station to the user-selected datum (as part of the NSRS or otherwise) can be considered the level of accuracy.

PRECISION/ACCURACY

PASSIVE/ACTIVE• NAD 83 REALIZED THROUGH NATIONAL CORS

• NAVD 88 REALIZED FROM PASSIVE MARKS

• NGSIDB HAS 1,000,000 PASSIVE MARKS

• PASSIVE MARKS IN STATES HAVE MANY CAMPAIGNS OVER MANY YEARS WITH MANY ACCURACIES IN MANY SEPARATE ADJUSTMENTS. RTN MAY NOT AGREE WITH THESE REQUIRING CONSTRAINTS TO THE MONUMENTS FOR PROJECT WORK.

• PASSIVE MARKS COORDINATES ARE A SNAPSHOT IN TIME AND CAN BE RELIED ON TO BE ACCURATE ONLY AT THE RECORDED OBSERVATION TIME.

• 2020+ = NEW GEOMETRIC DATUM / 1 CM GRAVIMETRIC GEOID, VELOCITIES ON A GEOCENTRIC DATUM

• THE METHOD OF CHOICE TO ACCESS THE NSRS IS ACTIVE MONUMENTATION (CORS, OPUS, RTN)

THE PROBLEM WITH PASSIVE MARKS….

Normal to ellipsoid

THREE SURFACES

NEW NATIONAL VERTICAL DATUM

• A PURELY GRAVIMETRIC SURFACE• BASED ON A HIGH RESOLUTION, 1 CM GEOID FROM

GRAV-D PROGRAM

• ACCURATE TO 2 CM (ALLOWING FOR GNSS ERROR)

• ACCESSABILITY: BROUGHT TO A PROJECT SITE VIA ACTIVE REFERENCE STATIONS (NATIONAL CORS), DENSIFIED TO PROJECT ACCURACY NEEDS. (ALTERNATIVE: USE BMs PREVIOUSLY TIED TO THE DATUM-CAVEAT EMPTOR)

• ETD: 2022?

RTN GUIDELINES FOR GNSS POSITIONING–WILL NOT SPECIFY OR

DEFINE A STANDARD, BUT WILL HELP

ADMINISTRATORS AND USERS TO BE AWARE OF

ALL THE ISSUES INVOLVED WITH THIS NEW TECHNOLOGY

60+ CONTRIBUTORS:

• NGS ADVISORS• DOT

• STATE GEODETIC SURVEYS• GNSS

MANUFACTURERS• SRCs

• BLM, NPS

http://www.ngs.noaa.gov/PUBS_LIB/NGS.RTN.Public.v1.6.pdf

NGS SINGLE BASE GUIDELINES

WHY SINGLE-BASE?- ACCOMMODATE LEGACY

USERS

- CLOSEST BASE NETWORKS

- AREAS WITH NO CELL COVERAGE

- PROJECT SITE APPLICATIONS, SUCH AS MACHINE CONTROL

http://www.ngs.noaa.gov/PUBS_LIB/pub_GPS.shtml

DRAFT GUIDELINES- 95% CONFIDENCE