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.