DBCP-M1 Recommended format

DBCP-M1 Recommended format

(Meteo)

Attention: This format is now obsolete. Please use DBCP-M2 as far as practicable instead

(see also complete list of DBCP recommended formats)

This Argos message format was recommended by M�t�o France

(Please contact pierre.blouch@meteo.fr for details)

Table of contents

Advantages
Drawbacks
Description
Message format
Examples

Basic (e.g. SVPB,FGGE)
Wind (e.g. SVPBW,wind FGGE)

Advantages of this format are:
- 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.

Description

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

	Item	Bits	Min	Max	Formula / Comments (n = word value)
CHK	Checksum	8	0	255	Checksum = Lower 8 bits of the sum of other bytes
Rank	Rank of observation	6	0	63	Rank = n (see � 3)
AGEB	Age of observation at the time of next block update	6	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).
BP	Barometric Pressure	11	850.0	1054.7	Press(hPa) = 0.1 n + 850
SST	Sea Surface Temp.	9	-5.0	35.88	SST(�C) = 0.08 n - 5
APT	Air Pressure tendency	9	-25.5	25.6	APT(hPa) = 0.1 n - 25.5
SubM	Submergence Count	7	0	100	Percent of time submerged = 100 n / 127
VBat	Battery Voltage	7	5.0	17.7	Vbat(V) = 0.1 n + 5
WD	Wind Direction	8	0.0	360.06	WD(deg) = 1.412 n n=255 indicates no Wind Direction sensor present
WS	Wind Speed	6	0.0	63	WS(m/s) = n
AT	Air Temperature	8	-20.0	43.75	AT(�C) = 0.25 N - 20
Cond	Conductivity	11	25.0	55.705	Cond(mmho/cm) = 0.015 n + 25
Tz	Subsurface Temp.	10	-5	35.92	Tz(�C) = 0.04 n - 5
Depth	Depth (pressure)	8	0	255	Depth(m) = N
Extra	Extra sensor #1	?	?	?	?
…	…	…	…	…	…

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.

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:

Basic format (e.g. SVPB, FGGE)

0								8						14						20											31
Checksum								Rank						AgeB						Barometric Pressure											(o)

								40									49							56							63
Sea Surface Temperature								Barometric Tendency									Submergence count							Battery Voltage							(x)

(o) First bit of Sea Surface Temperature

(x) Not used

The message length is 64 bits.

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 96 bits. The parameters are :

0								8						14						20											31
Checksum								Rank						AgeB						Barometric Pressure											(o)

								40									49							56							63
Sea Surface Temperature								Barometric Tendency									Submergence count							Battery Voltage							(x)

							71						77								85
Wind Direction							Wind Speed						Air Temperature								Conductivity

(o) First bit of Sea Surface Temperature

(x) First bit of Wind Direction

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.