High Precision GNSS for Mapping & GIS Professionals

Transcription

1 High Precision GNSS for Mapping & GIS Professionals

2 Agenda Address your needs for GNSS knowledge. GNSS Basics Satellite Ranging Fundamentals (Code $ Carrier) Differential Corrections (Post Processed $ Real Time) Real Time Corrections (Radio & Cellular) GNSS System Components Geodesy 101 Are you practicing Land Surveying? The Gray Area.

3 Your Needs for GNSS Knowledge Who s using it? (You/Coworkers) What kind of unit/precision? (10m or 10cm) Where are you using it? (Locally/Remotely) When are you using it? (Daily Use/Project Specific) Why are you using it? (Requirement/Value Added) How are you using it? (Business Line/Application)

4 GNSS: Global Navigation Satellite System

5 GNSS: Global Navigation Satellite System NAVSTAR GLONASS

6 The Constellations NAVSTAR aka GPS (United States DoD) 31/36 (Block III) GLONASS (Russian Federation) 24/27 Galileo (European Union) /30 BeiDou aka Compass (People s Republic of China) 21/35 QZSS (Japan Regional) We might be able to use this. IRNSS (Indian Regional Navigation Satellite System)

7 So that s cool, but how do we get PRECISION??? We must know where the satellite is, and we must determine the distance to it. We refer to this as satellite RANGING.

8 Four Satellite Minimum (X, Y, Z, Time)

9 Code Ranging From Satellite Measurement of time difference between the same part of code. To Receiver Distance = Speed Of Light x Time Difference

10 Carrier Ranging = First Partial Wavelength N = Integer Ambiguity Solving for the integer ambiguity yields centimeter precision.

11 So that s cool, but how do we get PRECISION??? We must have a second receiver on a known point. From this receiver second, we can generate a DIFFERENTIAL correction.

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13 CORS Our gateway to accessing the National Spatial Reference System AGC Geodetic Control

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16 Real Time Correction Comparison RADIO Limited Range Relies on a Battery Requires a FCC License Limited by baseline length More Equipment / Investment CELLULAR DATA Limited to Cell Availability Requires a cellular data plan May require subscription. Allows for Multi Station Solution (Better) Less Equipment / Typically 60% Investment vs Radio.

17 Rover Receiver Rover Radio Antenna Rover Pole Data Collector Bipod

18 xxxxx Radio Antenna Base Receiver Radio Data Cable Antenna Cable Tribrach Base Receiver Battery Base Receiver Tripod Data Collector Base Radio Base Radio Tripod Base Radio Battery

19 So that s cool, but how do we get ACCURACY??? 1. Use a High Precision GNSS Receiver 2. Use Proper Field Procedures 3. Apply sound Geodetic Principles

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21 Anchorage Ellipsoid (e.g., GRS 80, WGS 84) Earth Centered Earth Fixed (ECEF) +Z axis (parallel to axis of rotation) +Y axis (90 E) Coordinates: ( X 1, Y 1, +Z 1 ) (φ 1, λ 1, h 1 ) h 1 +Z 1 X axis (180 W) X 1 φ 1 Earth mass center +X axis (Prime meridian) Equatorial plane Y 1 λ 1 Y axis (90 W) Z axis Geoid ( mean sea level ) p4

22 PUBLIC SERVICE ANNOUNCEMENTS: WGS84 IS NOT THE SAME AS NAD83 PUBLISHED LATITUDES & LONGITUDES ON PUBLIC DATA SOURCES SHOULD REFERENCE NAD83 BE WEARY. ALASKA: US SURVEY FEET

23 Relationship between the MANY flavors of nad83 and GNSSderived NAVD88 HEIGHTS NAD83 (2011) NAD83 (1986) NAD83 (1997) NAD83 (2011) All hybrid geoid models from NGS are intended for use with NAD83, but for the most consistent results, ensure that the geoid model used matches the correct flavor of NAD83 Alaska: For NAD83(1986) use Geoid06 For NAD83(2007), NAD83(CORS96) use Geoid09 For NAD83(2011) use Geoid 12A/B NAD83 (2007) Adjustments to the National Spatial Reference System (NSRS) Birth: NAD83(1986) Differential leveling only 1 st adjustment NAD83(1997) GNSS/HARN and more leveling also: NAD83(HARN) NAD83(CORS96) GNSS/CORS ( epoch in AK) 2 nd adjustment NAD83(2007) GNSS/CORS 3 rd adjustment NAD83(2011) CORS Note: for Alaska these are the only three hybrid geoid models that exist

24 THE GEOID FOR ALASKA: GEOIDxx

25 SPCS vs. UTM SPCS: 1 in 10,000 UTM: 1 in 2500

26 AS (13) "practice of land surveying" means the teaching of land surveying courses at an institution of higher learning, or any service or work the adequate performance of which involves the application of special knowledge of the principles of mathematics, the related physical and applied sciences, and the relevant requirements of law for adequate evidence of the act of measuring and locating land, geodetic and cadastral surveys for the location and monumentation of property boundaries, for the platting and planning of land and subdivisions of land, including the topography, alignment, and grades for streets, and for the preparation and perpetuation of maps, record plats, field note records, and property descriptions that represent these surveys;

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