About Our GPS Base Station Site …

The geodetic component of the Survey Section makes extensive use of Global Positioning System technology to establish a highly accurate control network and supply geodetic coordinates for all projects undertaken by the Department.

We operate a full-time GPS base station for the benefit of mapping activities within the Department as well as for outside governmental and private sector mapping and surveying groups.

NHDOT GPS Site Details

CONCORD COOP CORS ARP (NHDT) PID = DE6240

Datum: NAD83 (2007)
Latitude: 43 12' 46.19677" N
Longitude: 71 31' 11.47465" W
Ellipsoid height: 89.394 m
Elevation Mask: 12
Logging Interval: 5 s
Rollover period: 1 hour
Antenna height: 0.000 m (ARP)

Data collected with Trimble 4000 SSE GPS receiver with a Trimble Compact L1/L2 antenna (TRM22020.00+GP) and URS software.

Site Coordinates | Station Log | Antenna Calibration Data Sheet

Our base station has suffered a major software/computer hardware malfunction that has shut it down for now and the foreseeable future. We have data up until noon on the 13th of July.

Downloading GPS Files Using Your Browser …

Each file is named using a TYMMDDHH.zip format. T is a character identifying the data type (D for dat and S for SSF), Y is the year, MM the month, DD the day of the month (local day) and HH is the start time of the data file in UTC Time (24-hour format). For example, an SSF file containing data for 2:00 pm to 3:00 pm on January 15, 2009 would be named S9011519.zip.

• SSF Files - Trimble Navigation Limited's proprietary data format for use with their Pathfinder Office Software.
• DAT Files- Universal Reference Station raw GPS data, including pseudoprange, carrier phase, and ephemeris information as well as differential corrections.

RINEX data files are now stored in a format which has made them compatible with the National CORS; YYMMDDHH.zip format. YY is the year, MM the month, DD the day of the month (local day) and HH is the start time of the data file in UTC Time (24-hour format).

• RINEX Files (Receiver Independent Exchange Format) - developed by the Astronomical Institute of the University of Berne for easy exchange of GPS data.

Data Files are normally available online for at least 30 days. Data is archived by the Geodetic Survey Section of the NHDOT prior to deletion and is available on request. Users are encouraged to download data as soon as practicable.

Setting Up A Pathfinder Connection …

Below are instructions in setting up a connection in Pathfinder Office 2.51 (and later versions) to download base files automatically.

1. Pull down the "Utilities" menu and select "Differential Correction."
2. In "Rover Files," select a file to correct.
3. In "Base Files," click "Internet Search" box and select "New."
4. In "New Provider," check "Enter the details yourself."
5. In "Provider Properties" many entries are optional, the required entries include:
   1. "General" tab: "Organization" type: "NHDOT"
   2. "Internet Server" tab: "Address Format" type:
      
      http://dot.nh.gov/gpsdata/ssf/s9%mmddhh%.zip and "Base Server Type" select: "Other, GPS Time (UTC)"
6. Select "OK" and complete the set up to return to the Differential Correction screen and proceed with the corrections as usual.

Note: The "Address Format" will need to be updated every year. The "9" in "s9" reflects the last digit of the current year, i.e. 2009. This will be s0 in 2010. Substituting rinex/09 or dat/d9 for ssf/s9 will link to the RINEX or DAT directories if desired.

For More Information …

National Geodetic Survey - National CORS
The National Geodetic Survey coordinates a network of continuously operating reference stations (CORS) that provide GPS measurements in support of 3-dimensional positioning activities throughout the United States and its territories

National Geodetic Survey - Cooperative CORS
The Cooperative CORS Web Page is a mechanism by which the public can have a centralized location with links to GPS continuously operating reference stations.

NHDOT Geodetic Control Online
Geodetic Control data is available online at New Hampshire's Statewide Geographic Information System (GIS) Clearinghouse, NH GRANIT. Complete coordinate data and location information can be accessed through the site’s GRANIT Data Mapper

We'd like to thank The New Hampshire Geographically Referenced Analysis and Information Transfer System (NH GRANIT) and the University of New Hampshire for their continued support and assistance.

Do you have a question or comment about this information? Contact:
Brian Easler
New Hampshire Department of Transportation
P.O. Box 483,
Concord, NH 03302.
Tel: (603) 271-1600 Fax: (603) 271-7025
E-mail Brian Easler