Output datagrams
• The length field is only included when logging to tape and/or
disk, but not for datagrams logged to a remote location.
The length can then be derived from the network software.
Systems logging data remotely should add this length at the
start of each datagram. This length is required if the data are
to be used with Kongsberg Maritime post-processing systems.
• The time stamp resolution is 1 millisecond and includes
the century. The time stamp is binary. The date is given
as 10000*year(4 digits) + 100*month + day, for example
19950226 for February 26, 1995. All date fields in the
output datagrams use this format. A time is usually given (in
milliseconds) from midnight.
• The datagrams identify the multibeam echo sounder model
and its serial number. The system model number is 120 for
the EM 120, 300 for the EM 300, etc. For the EM 3000D (the
dual head system) the model number was originally given as
3002 and the serial number is that of Sonar Head number 1.
However in the depth datagram model numbers 3003-3008
are now used to also identify the actual transmit and sampling
frequencies of the two heads. If only one head is activate on
the EM 3000D, it is coded as a single head system. For EM
3002 the model number is 3020. The EM 3002 has separate
datagrams (depth, range, seabed image, water column) for the
two sonar heads.
• Due care has been taken to include all parameters needed in
postprocessing in the relevant datagrams, with a minimum of
data duplication. Where resolution of a data field is variable, a
resolution descriptor is included.
• Invalid data are always identified by the highest positive
number allowed in a field unless otherwise noted.
• A real-time parameter datagram has been added to enable
logging of parameters not used in postprocessing, but which
may be important in checking the quality of the logged data,
or to allow tracing of reasons for possible malfunctions.
• Attitude data as time continuous records and raw ranges
and beam pointing angles are logged to allow eventual
postprocessing corrections. The logged attitudes are valid
at the transmit transducer, and are corrected for any sensor
offsets.
• A new
Range and beam angle datagram
(type f), is included,
that contains more details. (From January 2004).
For the new models of multibeams, starting with the EM 710, i.e.
EM 122, EM 302, EM 710, EM2040 and ME 70, three datagram
formats have been changed and are given new type numbers
(November 2005):
• XYZ 88 (type X), replaces type D.
850-160692/M
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