REFERENCE MANUAL - FTP Directory Listing - Trimble

A
TRIMBLE STANDARD INTERFACE PROTOCOL (TSIP)
Elevation Mask
This is the minimum elevation angle for satellites to be used in a solution output by
the receiver. Satellites which are near the horizon are typically more difficult to track
due to signal attenuation, and are also generally less accurate due to higher variability
in the ionospheric and tropospheric corruption of the signal. When there are no
obstructions, the receiver can generally track a satellite down to near the horizon.
The benefit of a low elevation mask is that more satellites are available for use in a
solution resulting in a better PDOP. The current mask is set to five degrees and
provides a reasonable trade-off of the benefits and drawbacks. High accuracy users
may prefer a mask angle around ten degrees, where the ionosphere and troposphere
begin to be more predictable
130 Copernicus GPS Receiver