Trimble Outdoors JUNO ST handheld - Manual (Page 50)

5 Using GPS
48 Juno ST Handheld User Guide
Factors that affect accuracy
The Juno ST handheld has an integrated GPS receiver that provides accurate
positioning with real-time or postprocessed differential correction of between two and
five meters.
The accuracy that you obtain from your Juno ST handheld handheld is affected by a
number of factors, including whether the data is differentially corrected in real-time or
after data collection, and the availability of GPS satellites in the sky when you collect
the data.
Differential GPS
Use differential GPS to correct errors in your collected data. Differential GPS (DGPS)
requires two or more receivers. One receiver, called the reference station, is located at
a known point to determine the GPS measurement errors and compute corrections to
these errors. An unlimited number of mobile GPS receivers, called rovers, collect GPS
data at unknown locations within the vicinity of the reference station. Errors common
at both the reference and rover receivers are corrected with DGPS either in real time or
during postprocessing.
Real-time DGPS
Use a real-time differential GPS (DGPS) source to receive differential corrections in
real-time and give you better accuracy as you collect data. In real-time DGPS, the
reference station calculates and broadcasts the error for each satellite as each
measurement is received, enabling you to apply corrections while in the field and
collect accurate GPS data.
Real-time DGPS sources include Satellite Based Augmentation Systems (SBAS). An
SBAS system uses multiple reference stations in a network to calculate the DGPS
corrections, which are then delivered to the user from a Geostationary satellite (SBAS).
The Juno ST handheld supports the WAAS SBAS system, which provides real-time
DGPS coverage for the United States of America.
Factors that affect real-time DGPS accuracy include how often the corrections are
updated, how far you are from the reference station, and whether the coordinate
system used by the correction source matches the coordinate system used by the GPS
receiver.
Postprocessed DGPS
In postprocessed DGPS, the collected GPS data is transferred to an office computer,
and measurements from the reference station are downloaded. Postprocessing
software such as the GPS Pathfinder Office software or the Trimble GPS Analyst
extension for ESRI ArcGIS software is used to differentially correct the collected data.