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

Table of contents

Advantages
Drawbacks
Description
Message format
Examples
a) Basic (e.g. SVPB, FGGE)
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:

Manages Argos 28-bit ID numbers.

Format is independent of the strategy used to collect the data: Users can transmit all the memorised data or only the most recent data if they wish. For memorized data, period between two observations is flexible.

It is easy to add extra sensors: just add them at the end of the Argos message.

Argos messages are short => low power consumption => increased life-time

All blocks have the same format, hence simplifying decoding software.

Observation time computed upon reception is the exact time of observation even in case the buoy onboard clock drifts with time.

Drawbacks:

There is a risk of not receiving the most recent observation during a satellite pass, if too many blocks are transmitted in a cycle. Therefore, for operational purposes, a certain amount of caution is advised. One solution consists in alternating the most recent observation with a stored observation, different each time. Another solution consists in optimising the number of blocks in a cycle.

Less bits are being used for "rank", "submergence", "battery voltage", and "wind direction" when compared with DBCP-M1 format. Hence resolution is a bit lower for these variables but this is still considered as acceptable.

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.

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

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