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USER MANUAL / MANUEL UTILISATEUR
6. IRIDIUM DATA PACKETS FORMATS
6.1. Overview
The data transmission process begins as soon as an ascent profile is completed. It starts with reduction of
the data. PROVBIO-B then formats and transmits the message.
The reduction of data processing consists in storing the significant points of the CTD triplets and optical
measurements arithmetic mean with the layer format.
For a given descent-drift-ascent-transmit cycle, the transmission of all of the data will usually require several
messages of the same type.
CTD and optical data packets all include recorded physical measurements.
The technical packet includes data corresponding to the float configuration and operation as well as the
buoyancy control mechanism.
Each data packet is composed of 140 bytes. Each packet is added up until a 1960 bytes message size be
reached, the message is then transmitted. If the transmission fails after the first try, the same message can
be sent up to 10 times. If after 10 tries the transmission fails again, the size of the message is reduced. The
following sizes are managed: 1960, 980, 420 and 140 bytes.
6.2. CTD data packets
6.2.1. Format
The average data sorted by type (descent, drift, ascent) are transmitted on the basis of 2 octets by
measurement.
Each packet is composed as follows:
•
Type 1: Descent, 2: Drift, 3: Ascent
•
Date and time of 1
st
•
1
sample C, T, D + standard deviation C,T
nd
•
2
sample C, T, D
•
th
•
N
triplet
6.2.2. Data coding
•
Only the first sample is dated.
•
The pressure is coded into 16 bits two's complement with a resolution of 1 cBar.
•
The temperature is coded into 16 bits two's complement with a resolution of 1/1000°C.
•
The salinity is coded into 16 bits from 0 to 65535 PSU with a resolution of 1/1000 PSU.
•
The standard deviations are coded with a resolution of 1/1000.
PROVBIO-B
DATA
st
CTD sample
PAGE : 20 / 72
DATE : 26/03/2008
INDEX : A
REF. : DOC08018
FORMAT (Bytes)
1
4
6 + 2 bytes
8
8
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