Petrel User Manual 0.1
8
Underwater Mode
While in Underwater Mode, the Petrel will turn off all non-essential functionality and put itself
into a sleep state to minimize power consumption. At regular intervals (every 5 minutes by
default), the Petrel unit will perform a water sense check to determine if it is above water or
submerged. If the check indicates that the unit is above water, it will exit Underwater Mode and
return to GPS Search Mode.
Due to environmental concerns such as biofouling, it is possible for the water sense check to
result in false positives. To combat this problem, the Petrel has a backup counter that
automatically returns the unit to GPS Search Mode when it expires. In the event the unit surfaces,
but cannot sense the lack of water due to biofouling, the unit will still progress to GPS Search
Mode when the backup timer expires. The duration of this timer is user-adjustable by changing
the GPS Timeout setting.
If the backup counter expires while the unit is still underwater, it will transition to GPS Search
Mode while underwater. In this situation, the unit will not be able to receive messages from any
GPS satellites at sufficient signal integrity. It will therefore return to Underwater Mode in
approximately 5 minutes to avoid spending excessive power on GPS searches while underwater.
