# Presentation: 089036

## CORS GuidelinesGiovanni SellaSpatial Reference DivisionNational Geodetic SurveyNational Oceanic and Atmospheric Administration

## Goal

- Upgrade the quality of CORS data and accuracy of associated meta data
**Why Now? **
-  The network is mature more than 1 site every 150km
-  Quality versus quantity. Users want improved accuracy
-  L2C is here, Galileo on its way and L5 is coming

## CONUS National CORS Coverage April 2006

## How

- CORS network is 98% volunteer i.e. non-NGS
- - Changes must be consistent with the needs of both NGS and the site operators
- - Guidelines must accommodate a diverse group of site operators and data users
**CORS Networks** - **Same standards**
**National** - less dense, position checked daily, NGS distributes and permanently archives data
**Cooperative** - high density, position checked daily, site operator distributes and archives data for at least 30 days

## Choose site location carefully 

**Monument ****(structure that attaches the antenna to the ground)**
-  	Must maintain a constant 3-D position NOT affected by short term surface motion/monument motion (well coupled with the earth)
**Environment**
- 	The space around the antenna should not change for the lifetime of the site (minimum 15 years). No vegetation growth, additional structures, etc.
**Choose site location carefully**

## Guidelines - Equipment

**Antennas**
- - L1 and  L2
- - Radomes NOT recommended
- 	WHY: distort signal and not required in design of antenna
- - Oriented to true North
- 	WHY: apply antenna phase center values correctly
- - Reference mark to antenna reference point (ARP) constant
- 	WHY: change antenna same coordinate
**Receivers**
- - Cutoff angle 5o required, 0o preferred
- 	WHY: important for vertical positioning
- - Collect hourly files, not daily

## Problem tribrach “feet” cannot be locked height can be changed

- Problem lightning rod obstructs satellites

- Antennas on towers with guy wires poor stability

- Problem wooden support
- U-bolts height can change

## Good top surface of pillar narrower than antenna 

- Good top surface of pillar narrower than antenna
- problem no orienting  & leveling device

- Good rooftop
- with orienting & leveling device

- Good orienting & leveling devices

## Guidelines - Meta-data

**Site Log** - Written record of all equipment ever used and contact info for a site
-  Must be machine readable (ASCII/text file)
-  NGS will soon (< 1 month) have a web based log file creator
**Photographs**** **- Visual record of equipment and monument
- 	We require 10-12 pictures

## Implementation

**Site Selection Team** - Assess all new CORS based on current guidelines and requests changes if needed
- 	3-4 people meet every 2 weeks
- 	submit sites to ngs.proposed.cors@noaa.gov
**Guidelines available at**
- www.ngs.noaa.gov/CORS/Establish_Operate_CORS.html
**Meta-data** - Revamping all meta-data via NGS Integrated Database

## CORS Quality Check

- Individual site quality assessment is based on a comparison to the network as a whole, not an arbitrary standard
- The worst performing sites will be encouraged to upgrade and may be dropped from the CORS network if a better site is available

**Guidelines available at**
- www.ngs.noaa.gov/CORS/Establish_Operate_CORS.html