XY FILE FORMAT

CDIP's xy files contain the displacement time series for

directional buoys. These data are not corrected for magnetic declination.

The files include x (magnetic North-South, N positive),

y (West-East, W positive), and z (vertical) displacement values.

These files are formatted as follows:

Name: POINT LA JOLLA BUOY                           (start of header)

Station: 09501

Deployment latitude: 32 51.10' N

Deployment longitude: 117 21.00' W

Water depth(m):  179.83

Local magnetic variation(deg): 13 E

Data type: Datawell vectors

Gauge type: Datawell Mark 2 directional buoy

Sample rate(Hz): 1.280

Field software version: datawell_acq v2

Field station type: sun

Method of analysis: Datawell

GPS: yes

Start time: 20001224185950 UTC

End time:   20001224192949 UTC

Sample length(hh:mm:ss): 00:30:00

Total number of vectors:  2304

Error-free vectors: 100.0%

--------------------------------------------------  (end of header)

20001224185950      3     31     49                 (start of data)

20001224185951      6      2     55

20001224185952      9    -26     63

20001224185952     16    -39     44

20001224185953     17    -30     12

20001224185954     33     -8     13

20001224185955     52     -7     16

20001224185955     54    -25     20

20001224185956     51    -44      7

20001224185957     42    -49    -21

20001224185958     21    -31    -63

20001224185959    -13     13    -77

20001224185959    -27     45    -68

20001224190000    -29     46    -37

20001224190001    -16     33     -6

. . . .

The Header

The header of the xy file is copied directly from the corresponding

Datawell vector (df) file. It contains two sections. The first gives

basic information about the sensor: the position, the sample rate, the

buoy type, etc. The second section contains the start

time, end time, and sample length of the data. It also contains diagnostic

information that depends on the sensor type. For directional buoys, this is

the total number of vectors received and the percentage of these vectors

that are considered to be error-free. (Note that only the start time

is set in the field and returned with the data; all other entries in

this section are calculated and added by CDIP's processing programs.)

Comments may have been added at the bottom of the third section. A dashed

line (----------) separates the header from the data; all comments are

placed above this line.

It is possible that the start and end times in the header will not

correspond to the actual start and end times of the displacement data

in the file. This is because any displacement values which are not

clearly received at the shore station are omitted from the xy file.

Only vectors that are marked 'Error-free' by the Datawell receiver

(i.e. vectors with error codes of one or zero) are included in the xy file.

Thus whenever the header value 'Error-free vectors' is less than 100%,

there will be time gaps within the displacement data; when a gap falls at

the beginning or end of the data, the start or end time will not match its

header value. (For a more detailed discussion of the error codes and their

interpretation, see the Datawell vector description,

.docs/processing/directional_buoys/df_format.txt)

The Data

Each line of data in the xy file consists of four columns. The

first column gives the UTC time of the sample to the nearest second; the

format of this number is YYYYMMDDhhmmss. The second column is the x

(North-South, N positive) displacement in centimeters, the third column is

the y (West-East, W positive) displacement in cm, and the fourth and final

column is the z (vertical) displacement in cm.

Time:           X disp  Y disp  Z disp

YYYYMMDDhhmmss    (cm)   (cm)   (cm)

. . . .

20001224185953     17    -30     12

20001224185954     33     -8     13

20001224185955     52     -7     16

20001224185955     54    -25     20

20001224185956     51    -44      7

20001224185957     42    -49    -21

20001224185958     21    -31    -63

. . . .

Since the sample period is less than a second - 0.78125 secs - many of the

lines are marked with the same time, e.g. there are two at 20001224185955

in the example above. Of course these two samples were taken .78125 seconds

apart, not at the same time; to the nearest second, however, they are

both from 2000/12/24 18:59:55 UTC.

Where data is not clearly received and is marked with an error code greater

than 1 in the diskfarm file, there will be a gap in the displacements in the

xy file. For example, below there is a two-minute gap in the data (where the

time skips from 19:02:57 to 19:04:58):

. . . .

20001224190250     10     33    -39

20001224190251      0     56    -20

20001224190252    -13     61     29

20001224190253    -11     35     63

20001224190254      1     -4     65

20001224190254     11    -37     54

20001224190255     16    -57     29

20001224190256     13    -72     23

20001224190257      8    -82     18

20001224190458     -4    -21      0

20001224190459     -1    -22    -19

20001224190459      0    -12    -51

20001224190500    -17      9    -58

20001224190501    -31     34    -60

20001224190502    -42     63    -53

20001224190503    -48     97    -12

. . . .

To look at the error codes and the (likely erroneous) displacements from this

gap, refer to the corresponding diskfarm (df) file. Note that not all

problematic vectors are flagged bad by the receiver, and that spikes will

sometimes be present in the xy files' displacements. These spikes are

not edited out, but written to the xy files without modification. In general,

however, it can be assumed that these spikes are transmission related, and

are not present in the buoys' internal time series that are used for

spectral and parameter processing.