NRCS Global Positioning Systems (GPS) NRCS Global Positioning Systems (GPS) &&

Geographic Information Systems (GIS)Geographic Information Systems (GIS)

RESOURCE INVENTORYSoil SurveyNational Resources Inventory (NRI)Wetlands InventorySnow SurveyOthersEasements

REMOTE SENSINGAerial PhotographyAerial Digital ImagerySatellite ImageryAirborne Video

CUSTOMER SERVICE TOOLKITConservation PlanningResource AssessmentInterpreted Soils Information

GLOBAL POSITIONING SYSTEM (GPS)

Where on Earth?!!?

MAPPINGDIGITIZING

ANALYSIS

MAP PREPARATION

COMPUTER ASSISTED DESIGN

MODELING•AGNPS•AnnAGNPS•Others

GPS is a data collection tool for GIS

Accuracy - Accuracy - Sources of GPS ErrorSources of GPS Error

Standard Positioning Service (SPS )• Selective Availability: 0 to 100 meters• Ionosphere: 5.0 to 7.0 meters• Troposphere: 0.5 to 0.7 meters• Satellite clocks: < 1 to 3.6 meters• Orbital errors: < 1 meter• Receiver noise: 0.3 to 1.5 meters• Multipath: undetermined• User error: Up to a kilometer or more

Errors are cumulative!

Accuracy Accuracy –– SPSSPS PerformancePerformance

Required GPS SPS Accuracy• Horizontal: 13 meters 95%• Vertical: 16 meters 95%

Observed GPS SPS Accuracy

• Horizontal: 6 metersGPS data averaged over 24 hour periods for 244 days

Must meet FGDC Geospatial data requirement: 10 meters @ 1:24,000 scale

Must meet NRCS Navigation and positioning requirements for NRCS programs and activities:

•National Resource Inventory: 5 -10 meters•Resource Planning: 5 - 10 meters•Soil Mapping: General 5 - 10 •Soil Mapping: Detailed 1 - 2 meters•Conservation Application: 1 - 2 meters•Conservation Certification: 1 - 2 meters•Survey & Engineering: Sub-meter

Accuracy - NRCS Requirements

Draft

Expected Accuracy varies by type of GPS unit

• Standard GPS - 15 m horizontal, 35m vertical

• NDGPS - 5 m horizontal

• WAAS - 7m total error, 3 m horizontal in tests

• Carrier Phase GPS - 10cm to 1meter

• Survey Grade - sub-centimeter

DGPSDGPS

Unit 1 – Overview of GPS, DGPS, Equipment & Applications

DGPS – Differential GPS The ability to use differential corrections to

improve GPS accuracy.

The use of differential corrections can be done in real time or “after the fact” or later time.

DGPS – DGPS – Correcting Errors & Correcting Errors & Improving AccuracyImproving Accuracy

Differential corrections attempt to eliminate or minimize the Ionospheric and Tropospheric errors that effect GPS accuracy.

Differential corrections can be provided by:

• GPS Reference Stations

• GPS Augmentations

DGPS – DGPS – Sources of Differential CorrectionsSources of Differential Corrections

GPS Reference Stations

• Local Area Reference Stations

• CORS – Continually Operating Reference Stations

GPS Augmentations

• FAA Augmentations

• Maritime & NDGPS

• High Accuracy NDGPS

DGPS SiteGPSReceiver

DGPS –DGPS – Post-processed Differential

NDGPS Site

NDGPS Receiver

GPSReceiver

DGPS –DGPS – Real Time Differential

DGPS AugmentationsDGPS Augmentations

Space Based Augmentations• FAA Wide Area Augmentation Service (WAAS)• Commercial L Band Services

Ground Based Augmentations• FAA Local Area Augmentation Service (LAAS)• CORS - Continuous Operating Reference Stations• Maritime Navigation System & NDGPS• High Accuracy NDGPS

Ground Based

Satellite Based

DGPS –DGPS – FAA Augmentations

Maritime & NDGPSMaritime & NDGPSNationwide Differential Global Positioning SystemNationwide Differential Global Positioning System

GPS Augmentation system• For Surface Transportation• that improves the accuracy and integrity of GPS for

safety-of-life applications

Expanding Maritime DGPS Network • Establishing Additional Radiobeacon Sites • Standard interoperable nationwide service• Transportation users include railroads, highways,

public transportation, and waterways

NDGPSNDGPSNational Differential Global Positioning SystemNational Differential Global Positioning System

September 200284 Active Sites

GPS Applications - Mobile MappingDual GPS / NDGPS External Antenna

Notebook PCRunning

ArcView / ArcPad

Mobile Communications

GPS Map 76

The USDA “Tool Box” Has An Assortment of Tools.

GPS ToolsConfiguration 1 & 2

Data Collection ToolsDigital Camera / Mobile Devices

Communication ToolsInternet / Mobile phones

Information ToolsDesktop Computing / Servers