I have received a number of questions, and seen a number of posts, regarding the Locus kinematic alarm. I thought it would be beneficial to post a description of exactly how the alarm works.

To maintain initialization of a kinematic survey, the Locus receiver must maintain continuous lock on at least 5 satellites throughout the data collection period. During kinematic data collection, the Locus receiver continually monitors the status of satellite lock for each satellite being observed. If, at any given moment, the Locus receiver detects that it has not maintained lock on at least 5 satellites, the receiver activates the kinematic alarm. This is a warning to the user that initialization may have been lost. The user should initialize again before continuing with data collection.

I said above that the kinematic alarm indicates to the user that initialization MAY have been lost. I say MAY for the following reasons:

- Technically, only 4 satellites are required to maintain kinematic initialization. The kinematic alarm is activated if lock is not maintained on at least 5. We took this conservative approach to ensure success when data is processed. Maintaining kinematic initialization when observing only 4 satellites is very tenuous. There is no redundancy whatsoever in the solution. It is not possible, with only 4 satellites, to detect a bad solution due to a problematic satellite.

- Determining whether continuous satellite lock has been maintained is not an exact science. To be truthful, it is not possible for the Locus receiver to absolutely determine if continuous satellite lock has been maintained. There is some interpretation involved. To determine if continuous lock on a satellite is maintained, the Locus receiver monitors the noise in the satellite signal. If the noise reaches a set threshold value, Locus assumes that lock has been lost on this satellite. Again, we were conservative at setting the noise threshold for loss-of-lock indication to ensure that we do not miss a loss-of-lock. Missing a loss-of-lock could result in an un-detected loss of initialization. So, due to the conservative approach, it is possible that Locus will determine lock on a satellite has been lost even when it has not.

Due to the reasons listed above, it is possible that the kinematic alarm will be activated even if initialization has not been lost. This inconvenience is required to ensure that the opposite does not occur, i.e. initialization is lost yet the alarm is not activated.

Below are more important details about the functionality of the kinematic alarm:

- The kinematic alarm will be activated if the Locus receiver detects that continuous lock has not been maintained on at least 5 satellites whose elevation is above 15 degrees. The Locus receiver will track and log data on satellites down to 10 degrees. Any satellites that are between 10 and 15 degrees are not considered by the kinematic alarm. This is important for the following reason. The Satellite LED on the Locus receiver indicates satellites tracked above 10 degrees. A green LED flash indicates a healthy satellite, above 10 degrees, being logged to memory. A natural tendency is to look at the Satellite LED when the kinematic alarm is activated. A user could question why the kinematic alarm has been activated when 6 green flashes are seen on the Satellite LED. It is possible that some of these satellites indicated on the Satellite LED are between 10 and 15 degrees elevation.

- Once activated, the kinematic alarm will continue to sound for a set period of time. I cannot remember exactly how long, something like 30 - 45 seconds. The alarm will not stop sounding any sooner, even if the receiver detects that satellites have been re-acquired. It will sound for the set period of time regardless. When the 30-45 seconds have passed, the alarm will stop. It will be activated again if fewer than 5 satelli

Excellent and very informative post, Bill!

I really appreciate you taking the time to explain some of the why's & wherefor's of the operation of the hardware and software. I get real nervous when I have to "just trust the machine" w/o knowing what's going on.

If you ever run fro president of Ashtech, you'll get my vote.

(And I promise it won't be a "dimpled chad"! ;^(

Thanks Bill.... very timely and imformative

I have found that the kinematic alarm is a pretty good indicator that satellite lock has been lost.

When I process a topo, I notice that often the shot just prior to, or just after a kinematic alarm, usually near a large tree, is a failed shot.

This time of year, when the leaves are off the trees, I can get better static results, however kinematic is particular, it needs 7 or 8 sats and fairly clear sky.