Protocols

GPS Protocol for the LTER Laboratory

Retired

In use from 2008-07-15 to 2012-03-30

Abstract

The LTER GPS units are used for recording the locations of microplots, experiments, instrumentation, plot corners, sampling sites, events and many other LTER features. They are also used to navigate back to these locations and to navigate to new locations whose coordinates have been uploaded to the GPS.

When using the Trimble XRS Pro GPS with the Omnistar real-time correction service or the internal Coast Guard beacon we can expect submeter accuracy (approximately + 20 to +70). We keep the Omnistar real-time correction service on the GPS I data logger and the Coast Guard beacon on GPS II. We can always start the Omnistar service on GPS II if needed for $400/year.

We switched to the Coast Guard beacon from 25 June 2008- 3 August 2009 but we went back to the Omnistar service because the connection to the Coast Guard beacon wasn’t dependable . We are in a weak spot for the beacon and also in high humidity conditions it is more difficult to receive the signal. When we were able to get the connection the resolution was similar (5 cm – 30cm less accurate than Omnistar during the testing periods).

Protocol

Hardware

The KBS LTER has two identical Trimble GPS units. “GPS I” is to be used exclusively by the KBS LTER staff. “GPS II” can be loaned to others with permission by the LTER Project Manager.

Two components make up each GPS unit: the Trimble TSCe Data Logger with touch screen, and the Trimble Receiver Type Pro XRS model 33302-51.

Software

  1. Windows CE.net- Operating system on the TSCe Data Logger.
  2. TerraSync – Used for collecting and updating GPS data on the Trimble Data Logger.
  3. Trimble GPS Pathfinder Office (Version 4.1)- Used to import, export, and post-process the GPS data on the PC.
  4. Microsoft Active Sync 4.5 – Used to connect your PC to the Trimble Data Logger in order to transfer data.

Accuracy

When using the Trimble XRS Pro GPS with the Omnistar real-time correction service or the internal Coast Guard beacon we can expect submeter accuracy (approximately + 20 to +70). Previously we used the Omnistar real-time correction service but now we will be using the internal Coast Guard beacon; the Coast Guard beacon has similar accuracy at no cost.

Data Collection

Prior to collecting data, the Trimble Planning software is used to determine occasional times throughout the day when the satellites alignment is suboptimal. This allows us avoid data collection at these times.

Thirty positions are collected at 1 second intervals for each feature and are averaged.

The GPS is set to only allow collection of data when the PDOP (position- dilution of precision) does not exceed 4. This can be relaxed when collecting data in forested sites if needed.

Post-processing of data is carried out using the Trimble GPS Pathfinder Office software and a nearby CORS (Continuously Operating Reference Stations) station.

The Trimble GPS files are sent to the LTER database manager for long-term storage on the LTER website.

Detailed instructions for using the KBS LTER GPS can also be found on the internal LTER website under instructions.

Author:

Datatables