DBCP-M2 Recommended format
(Meteo - 28 bit Argos ID)


This Argos message format is based upon DBCP-M1 format which was modified to take 28-bit Argos message IDs into account. See also complete list of DBCP recommended formats

  1. Advantages
  2. Drawbacks
  3. Description
  4. Message format
  5. Examples
  6. a) Basic (e.g. SVPB, FGGE)
  7. b) Wind (e.g. SVPBW, wind FGGE)

ATTENTION: This format is used only for Argos messages transmitted using 28-bit Argos IDs.

Advantages of this format are:

Drawbacks:

Description

With 28 bit Argos IDs, first block of data is comprised of 24 bits; following blocks of data have 32 bits. DBCP-M2 contains a minimum of two blocks, i.e. 24+32 bits = 56 bits.

Data are stored in the buoy memory in blocks of observations. Each block contains one single observation. Blocks are Block_Period minutes apart (e.g. every 30 minutes, every hour)). Normally, buoys are turned on at a round hour (e.g. 03h00) so that observations are made exactly at a round hour. However, this may not be the case and the on-board clock may drift in time. Transmitting the age of the observation at the time the message is transmitted to the satellite permits to recover the exact time of observation even in case the buoy real time clock has drifted.

One block (one observation) is transmitted in one Argos message. One Argos message contains only one block.

Hence, consecutive blocks can be transmitted using consecutive Argos messages using a transmission cycle. For example, if we pick a block_period of one hour, we could transmit the observations in a cycle of 3 Argos messages like this:

Block Rank
 
Block H 0
Block H-1 1
Block H-2 2
Block H 0
Block H-1 1
Block H-2 2
 

Rank is encoded in the Argos message. Rank of the most recent observation transmitted is 0. The rank of a given observation is incremented each time a new observation is carried out.

Age of the observation at the time of the next block update (AGEB) in the buoy memory is encoded in the Argos message. Age of the observation at the time of the Argos message transmission is therefore:

  • Age = Rank x Block_Period + AGEB
  • And observation time can therefore be computed as following:

  • Observation time = Acquisition time by the satellite - Age
  • If hourly observations are needed (Block_Period=60), the buoy must be activated so that a new observation is available on the hour. If synoptic observations are requested (Block_Period=180), the buoy must be activated accordingly.

     

    Message format

    In white are the first mandatory two blocks of data, i.e. 56 bits (24+32).
    In yellow is the following optional block of data, i.e. 32 bits
    In green are the following optional blocks of data, i.e. 32 bits or more.
    Total message length cannot exceed 248 bits.

     

     

    Item

    Bits

    Pos

    Min

    Max

    Formula / Comments (n = word value)

    Fixed bits in block (o)
    CHK Checksum

    8

    0

    0

    255

    Checksum = Lower 8 bits of the sum of other bytes Y
    Rank Rank of observation

    4

    8

    0

    15

    Rank = n (see 3) Y
    AGEB Age of observation at the time of next block update

    6

    12

    0

    63

    Age (minutes). This timer starts at 0 when the sensor data is updated in the transmission and in incremented in minutes until the next data update (block). Y
    BP Barometric Pressure

    11

    18

    850.0

    1054.7

    Press(hPa) = 0.1 n + 850 Y
    SST Sea Surface Temp.

    9

    29

    -5.0

    35.88

    SST(C) = 0.08 n - 5 Y
    APT Air Pressure tendency

    9

    38

    -25.5

    25.6

    APT(hPa) = 0.1 n - 25.5 Y
    SubM Submergence Count

    6

    47

    0

    100

    Percent of time submerged = 100 n / 63 Y
    VBat Battery Voltage

    3

    53

    free

    free

    free (e.g. voltage, % of charge, or table) Y
    WD Wind Direction

    7

    56

    0.0

    360.0

    WD(deg) = 3 n
    n=127 indicates no Wind Direction sensor present
    Y
    WS Wind Speed

    6

    63

    0.0

    63

    WS(m/s) = n Y
    AT Air Temperature

    8

    69

    -20.0

    43.75

    AT(C) = 0.25 N - 20 N
    Sal/Cond Conductivity or Salinity

    11

    77

    25.0

    55.705

    Cond(mmho/cm) = 0.015 n + 25
    Salinity (psu)=0.015 n + 25
    N
    Tz Subsurface Temp.

    10

    88

    -5

    35.92

    Tz(C) = 0.04 n - 5 N
    Depth Depth (pressure)

    8

    98

    0

    255

    Depth(m) = N N
    Extra Extra sensor #1

    ?

    106

    ?

    ?

    ? N

    ...

    N

    (o) Where "Fixed bits in blocks" is marked as "Y", it means that when a block is actually coded, the exact number of bits are reserved for the considered sensor or information if available. If there is no such sensor in the buoy, then those bits shall be considered as free and can be used for one or more other variables provided that this does not affect the bits used by the surrounding sensors. These bits can also be coded with all bits set to 1 in case they are completely useless. This permits some flexibility in the format.

    Offsets and resolutions are given here as examples and can be modified. The number of bits for each sensor must be changed only if it is not possible to do otherwise (see remark under (o) above).

    We chose to report the barometric tendency in one single word instead of two (one for the absolute value of pressure tendency, the other for the characteristic). Automatic stations are permitted to do so. On the GTS, the characteristic is coded as 2, 4 or 7, according to the sign of the tendency (positive, zero or negative, respectively). This solution is debatable.

    Examples:

    a) Basic format (e.g. SVPB, FGGE)

    0

                 

    8

          12           18          

    Checksum
    8 bits

    Rank
    4 bits

    AgeB
    6 bits

    Barometric Pressure
    11 bits

     
    24         29                 38                 47          

    53

       

    Barometric pressure (cont.)

    Sea Surface Temperature
    9 bits

    Barometric Tendency
    9 bits

    Submergence count
    6 bits

    Battery Voltage
    3 bits

    The message length is 56 bits.

    b) Wind and/or salinity buoys (e.g. SVPBW, Wind FGGE)

    This format concerns SVP-BW drifters and Wind FGGE buoys, possibly equipped for Air Temperature and/or Sea Surface Salinity measurements. The message length is 88 bits. The parameters are :

    0

                 

    8

          12           18          

    Checksum
    8 bits

    Rank
    4 bits

    AgeB
    6 bits

    Barometric Pressure
    11 bits

     
    24         29                 38                 47          

    53

       

    Barometric pressure (cont.)

    Sea Surface Temperature
    9 bits

    Barometric Tendency
    9 bits

    Submergence count
    6 bits

    Battery Voltage
    3 bits

    56             63           69               77                    

    Wind Direction
    7 bits

    Wind Speed
    6 bits

    Air Temperature
    8 bits

    Conductivity
    11 bits

    Air temperature and Conductivity rooms can be used by technological data such as Weather Classification and/or Wind speed from specific frequency bands in the case of SVP-BW drifters.