Product specifications

13
shorter period of time. COAST technology provides more consistent positioning
during periods when signal loss occurs, thus bridging the gap to when the signal is
reacquired. This means that the Crescent module is more tolerant than competing
products to loss of SBAS or externally input RTCM SC-104 corrections.
L OCAL D IFFERENTIAL O PTION
Local differential is a specialized message type that can only be sent between two
Crescent-based receivers. One receiver is used as the base station and must remain
stationary. It is extremely useful to know the coordinates of the base station
position, but averaging the position over several days will also suffice. The second
receiver is used as a rover and the messages may be sent either through a cable or
over a radio link.
S TART - UP
When you turn the Crescent on with the Local Differential application running,
it will require several commands to initialize the proprietary messages that
are sent over the air. These commands are outlined in Chapter 6.
L OCAL D IFFERENTIAL P ERFORMANCE
The positioning performance of the Crescent unit in Local Dif mode is
dependant upon the environment of the base and rover receivers, the
distance between them and the accuracy of the entered coordinates of the
base station.
We suggest that you perform your own testing at your location to determine
the level of performance that you would expect to see on average. When
testing this feature, it’s a good idea to look at a lengthy test of 12-24 hours,
different environments and monitor performance against a known coordinate.
This should be done over a number of days with different states of the
ionosphere. You can monitor the energy level of the ionosphere based upon
the amount of solar flare activity at the following Web sites:
o iono.jpl.nasa.gov//latest.html
o iono.jpl.nasa.gov//gim_dailymovie.html
o www.spaceweather.com
P OST P ROCESSING
The Crescent module is able to output raw measurement data for post processing
applications. The raw measurement and ephemeris data are contained in the Bin 95
and 96 messages documented in this manual. Both messages must be logged in a
binary file.
Depending on your application, you can include site data within the binary file and
perform the translation to RINEX yourself.