rapidCAST User’s Guide
March 2018
EAR-Controlled Technology Subject to Restrictions Contained on the Cover Page.
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49
Auto-Depth Customizable Parameters
Limit nominal target depth to [X] meter(s) maximum - The user can specify the maximum target
depth that Auto-Depth is allowed to set. If you are operating in deep waters and only want to profile the
upper 100 meters, for example, you can set this parameter so that any depth readings that are deeper are
capped to this value.
Timeout if no new readings received after [X] second(s) - Auto-Depth and Auto-Repeat will be
disabled if the NMEA stream has stopped and no valid readings are received within a user-selectable expi-
ration time. If this happens in the middle of a deployment, the current deployment will be allowed to com-
plete, but with Auto-Repeat disabled, additional casts will not be performed without operator authoriza-
tion. This feature ensures that if contact with the depth sounder is lost, rapidCAST Interface will not be
using old/outdated depth data. For operational safety, if depth readings resume, the user must manually
re-enable Auto-Depth and/or Auto-Repeat, as desired.
Use shallowest value from the last [X] depth reading(s) - This feature reduces the probability of
the probe hitting the seafloor if surveying in a complex environment with rapidly changing depths, or if
depth sounder readings are fluctuating/noisy. From a candidate pool of the most recent depth readings,
the shallowest of these readings is chosen as the target. The user can customize the size of the candidate
pool. If the user does not wish to select shallower alternatives, this value can be set to 1, causing the candi-
date pool to consist of only one reading, which defaults to the newest depth.
Transducer offset from waterline: [X] meters - Nominal Target Depth is specified as the desired
probe depth measured from the surface. Because the depth sounder may be mounted on different parts of
the vessel (along the keel versus off to the side, for example), the depth reported by the transducer may be
offset from the waterline. If a transducer is mounted 1.3 meters below the waterline, and it reports a DBT
value of 15 meters, the actual depth from the surface is 15 + 1.3 = 16.3 meters. The value of [X] in this ex-
ample should therefore be set to 1.3. This value will be added to each depth reading, correcting each one
to be relative to the surface. This offset may also be negative, if the user wants to subtract a fixed value
from each reported depth.
Reject sentences with bad NMEA checksums - The NMEA 0183 Standard specifies a checksum
value to be appended to the end of every sentence in order to guard against possible message corruption.
The sender of the message calculates a checksum based on the contents of the sentence that it is about to
send, and embeds that value at the end of the sentence. The receiver of the message should also calculate a
checksum based on the contents of the sentence that it has received. The sender’s checksum and the re-
ceiver’s checksum should match. If they do not, this indicates that the contents of the sentence have been
altered by noise or communication errors.
