# Presentation: 670181

##           NGS Products for Accurate

-           NGS Products for Accurate
-                GPS Positioning
- Tomás Soler & CORS Team
- March 2001

- CORS Industry Forum

## 	 Coordinates and Velocities                                                                                 	 Transformation software

- 	 Coordinates and Velocities                                                                                 	 Transformation software
- 	 GPS Orbital Data
- 	 GPS Antenna Phase Pattern Models
- 	 Geoid99
- 	 Total Electron Content (TEC) Mapping

-           Primary GPS Related Products

##                ITRF Horizontal Velocities (mm/yr)

-                ITRF Horizontal Velocities (mm/yr)

##            ITRF97, epoch 1997.0 [soon: ITRF2000]

- 	 NGS provides accurate coordinates and 		    velocities for 216 CORS stations
-            ITRF97, epoch 1997.0 [soon: ITRF2000]
- 	       NAD 83 (CORS96), epoch 1997.0
- 	 These positions and velocity field form the 	    reference framework of the National Spatial 	    Reference System (NSRS) and are available 	    on-line from NGS Data Base

-        Coordinates and Velocities (03-26-01)

## 		       CORS Network

- 	 NGS computes and monitors the position of all 	    CORS stations on a daily basis
- 	 Coordinates and velocities are updated 		    whenever a new ITRF frame is released
-  	 NGS collaborates with the International Earth 	    Rotation Service (IERS) and provides CORS 	    positions and velocities that are integrated into 	    ITRF global solutions

- 		       CORS Network

## Position Time Series (last 60 days)

**http://www.ngs.noaa.gov/CORS/download2**

## Position Time Series (long-term)

##     	Transforms positions and velocities between spatial 	reference frames [ITRFxx, WGS84 (G873), NAD 83]

-     	Transforms positions and velocities between spatial 	reference frames [ITRFxx, WGS84 (G873), NAD 83]
-       	Updates positions and/or observations between dates 	(epochs)* **	*
-      	Predicts velocities due to crustal motion
-       	Predicts displacements between dates
-       	Transforms positions between the ITRF97 frame and 	the NAD 83 datum using 14 parameters

- Horizontal Time-Dependent Positioning Software (HTDP)
**http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.html**

## http://www.ngs.noaa.gov/CORS/metada1/ 

- 14 Parameter Transformation
**http://www.ngs.noaa.gov/CORS/metada1/**

## http://www.ngs.noaa.gov/GPS/GPS.html             

-            NGS is one of the seven International GPS Service 	      (IGS) Analysis Centers (AC) participating in the 	      production of accurate GPS orbits:
-                  Final Precise (~ 13 days latency) [<5 cm]
- 	         Clock estimates [0.1-0.2 nanoseconds]
-                  Rapid (14 hours latency) [<10 cm]
-                  Ultra-Rapid (supports real-time) [<25 cm]
-            Satellite positions in SP3 format are given (once 	      every 15 minutes) in current ITRFxx frame        *    *

- NGS Satellite Ephemerides
**http://www.ngs.noaa.gov/GPS/GPS.html**

##        GPS Antenna Phase Pattern Calibrations

- 	 Each antenna type has a unique phase pattern
- 	 Each antenna type has a unique set of constants
- 	 GPS antennas must be calibrated
-    	 Mixing uncorrected antenna types can produce errors 	    of up to 10 cm in the vertical component
- 	 NGS is at the forefront in relative field 		   	    calibration of GPS antennas
- 	 NGS maintains a calibration database with  	   	    parameters for 88 antenna types (03-26-01)* *

-        GPS Antenna Phase Pattern Calibrations
**        ****http://www.grdl.noaa.gov/GRD/GPS/Projects/ANTCAL**

## Antenna Calibration Facility in Corbin, Virginia 

- Antenna Calibration Facility in Corbin, Virginia

##              Height Systems and the Geoid

-        GPS determines *geodetic heights* (geometric): h
-        Leveling determines *orthometric heights*: H
-        The above heights are related through the *geoid **	**height**:* N    h = N + H  dH = dh - dN
-        Geoid: The equipotential surface of the Earth’s 	gravity field which best fits, in a least squares 	sense, global mean sea level
-        NGS produces GEOID99, a geoid consistent with 	NAD 83 and NAVD88

-              Height Systems and the Geoid
**                          ****http://www.grdl.noaa.gov/GEOID/**

## GEOID99 the Link Between GPS Heights and Leveling 

- GEOID99 the Link Between GPS Heights and Leveling

##        GPS Derived Total Electron Content (TEC)

- 	 Sun light forms free electrons and positively 		    charged ions. Maximum disturbances occur at about 	    300 km height (Ionosphere)
- 	 Free electrons alter the speed that electromagnetic 	   waves travel through the ionosphere. The effect is 	   frequency dependent and disrupt communications
- 	 The differential effect on the two GPS frequencies 	    may be applied to measure the distribution of free 	    electrons
- 	 TEC is highly correlated with the location of the sun

-        GPS Derived Total Electron Content (TEC)
**               ****http://www.grdl.noaa.gov/GRD/GPS/Projects/TEC**

##        GPS Derived TEC (units 1016 electrons/m2)

-        GPS Derived TEC (units 1016 electrons/m2)

##         GPS Derived TEC (units 1016 electrons/m2)

-         GPS Derived TEC (units 1016 electrons/m2)

##                          Conclusions

-       NGS has extensive experience on GPS data gathering, 	archiving, managing, and interpretation of final 		processed results.
-       NGS GPS products are monitored daily and updated
-       The information is free, available 24 hours a day, and 	reachable through a simple link to our Internet server
-       NGS is open to suggestions from interested GPS		users to make available and/or improve our current 	line of products

## Please join us now for the Q&A Session