The Mixing Zephyr Pages

Mixing Zephyr Program
ALVIN Data Files

The raw data from ALVIN can be found in ../data/rawdat. Files with the extensions 1. .dat, 2. .meso and .meso.txt, and 3. .svp are recorded.

.dat Files

The data logging system in ALVIN records a variety of data from instruments installed on the submersible. These are recorded in a file named <dive number>.dat. The data files produced are self-documenting, i.e., there is a header on each file documenting the nature of data that it contains. At the beginning of the dive series, the system is configured as desired by the scientific party. The configuration defines packets of data, grouped by the recording period, in the order in which they appear in that record. The packets used were twos (2 second period), tens (10 second period), twom (2 minute period), and nav (period set by the navigation controller, usually 15 seconds, and consisting of NAV0 records with the ship ping transmitted on the minute and recorded at :15 seconds after the minute, and NAV1 records with the sub pings transmitted at :15, :30 and :45 seconds after the minutes and recorded at :30, :45, and on the next minute, respectively. The packet configuration for the Mixing Zephyr Program was (note change of configuration in twos packet beginning Dive 2932):
#name		packet	mode	digits	prec	comments

D_TIME		twos	cur	8	2
ALTITUDE	twos	cur	4	1	#Benthos instrument in tail
DSALT_RANGE	twos	cur	7	1	#Datasonics instrument skids
DEPTH_3		twos	cur	6	1	#Paroscientific
TEMP_LOW	twos	cur	3	1
TEMP_HIGH	twos	cur	4	1
HEADING		twos	cur	4	1	#gyro
DEPTH_1		twos	cur	6	0
PITCH           twos    cur     7       3       # + = bow up  *2932- only
ROLL            twos    cur     7       3       # + = starboard  *2932- only

D_TIME		tens	cur	8	2	# computed time
DATE		tens	cur	6	0
DIVE		tens	cur	4	0
ALTITUDE	tens	cur	4	1
DSALT_RANGE	tens	cur	7	1
DEPTH_3		tens	cur	6	1
HEADING		tens	cur	4	1
TEMP_WINDOW	tens	cur	3	1
DSALT_TEMP	tens	cur	7	1
TEMP_LOW	tens	cur	3	1
TEMP_HIGH	tens	cur	4	1
DEPTH_1		tens	cur	6	0

D_TIME		twom	cur	8	2	# computed time
DIVE		twom	cur	4	0
VB_PRES		twom	cur	5	1
VB_TEMP		twom	cur	3	1
HP_AIR_PRES	twom	cur	5	1
CAM_1_CNT	twom	cur	3	0
CAM_2_CNT	twom	cur	3 	0	
INTERR_FREQ	twom	cur	3	1
TRACK_FREQ	twom	cur	3	1
DEPTH_1		twom	cur	6	0

SHIP_SUB	nav	cur	1	0
D_TIME		nav	cur	8	2	# computed time
ALTITUDE	nav	cur	4	1
DSALT_RANGE	nav	cur	7	1
DEPTH_3		nav	cur	5	1
HEADING	 	nav	cur	4	1	
TEMP_WINDOW	nav	cur 	3	1
INTERR_FREQ	nav	cur	3	1
TRACK_FREQ	nav	cur	3	1
LBL_0_FREQ	nav	cur	3	1
LBL_0_TIME	nav	cur	6	4
LBL_1_FREQ	nav	cur	3	1
LBL_1_TIME	nav	cur	6	4
LBL_2_FREQ	nav	cur	3	1
LBL_2_TIME	nav	cur	6	4
LBL_3_FREQ	nav	cur	3	1
LBL_3_TIME	nav	cur	6	4
X_POS		nav	cur	7	2	#computed from LBL0/LBL1
Y_POS		nav	cur	7	2
LAT_D		nav	cur	2	0
LAT_M		nav	cur	5	3
LON_D		nav	cur	3	0
LON_M		nav	cur	5	3
DEPTH_1		nav	cur	6	0

.meso and .meso.txt Files

Data from the Mesotech sonar imaging system is recorded in a separate file, named <dive number>.meso. These data are in a binary format and a second ascii-encoded file is produced by the program mesoread at the time when the data are transferred from the sub to the shipboard data system with the filename <dive number>.meso.txt. These records consist of a brief header with information on the origin of the file, followed by a series of blocks of data delimited by two header lines. After the two header lines in each block (which are self-documenting), there are a series of two-way travel times. A number of programs, developed by Dan Scheirer (, are available to work with data in this form. These can be found in $ZEPHYR/mesoproc/.

During our program we recognized that the number of travel times recorded did not seem consistent with the information in the header. After e-mail discussion with Bill Chadwick ( and Dan Scheirer, we set up to acquire raw data from the instrument with the following results. Scheirer made the observation that the problem may be in the assumption that the angle of the final ping of one sweep equals the starting angle of the next sweep. While the Mesotech manual was ambiguous on this point, we did find that the raw data coming on the serial line from the Mesotech to the data logger would have the answer, so Ken Feldman (, the WHOI SSSG technician on board, set up to record that data directly. The records output, for a nominal 30 degree scan, were

L 0740 0
L 0736 0
R 0740 0
R 0744 0
28 records deleted
R 0860 0
R 0864 0
L 0860 0
The direction reported is the direction prior to the ping, the 4 digit number is the angle in units of .225 degree and 0 was the range (deck test). Thus the extreme left position was 165.6 degrees and the extreme right position was 194.4 degrees, a scan of 28.8 degrees which seems to be what Mesotech considers a nominal 30 degrees.

The ####.meso.txt records produced with mesoread for these same data contain the header when the transition occurs from L to R and report that angle as the start angle. Thus for these scans the start angles in the header were 166.5 and 193.5. The geometric pattern of the beams is thus:

Scheirer is working on modifications to his code (e-mail dated 6/8/95) to correct these problems.

.svp Files

Finally, a small file containing sound velocity as computed from temperature is recorded, having the file name <dive number>.svp. These containing three fields per record, the depth in meters, the sound velocity in meters per sec and the temperature in degrees Celsius. The last record has two fields with values of -1.

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Content Last Modified 7/10/95
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