Contents
GGP has now completed its first
year of operation. At this time SG groups should be
working hard to get the data ready for sending to the GGP
data Bank at ICET, and in doing other tasks as outlined
below.
The goal is to produce a continuous
high quality data set of 6 years in length from at least
15 participating stations. From past experience, an SG
group that fails to keep up with the data submission will
soon find it more difficult to process a lot of data at
once. The work that has been done in setting up GGP now
depends critically on the cooperation of the SG groups.
Moreover your GGP colleagues are also anxious to obtain
your data and to see your participation. Finally, the
scientific community at large (including some people on
this mailing list) will be looking closely to see how
well the GGP is being collected.
By the end of July, 1998 the
first month of data (July 1997) must be sent to ICET
in the form of gravity and pressure files, and files for
the logs and auxiliary data. Individual groups have had
this data for one year and now it is time to put it into
the GGP Data Bank for use by any of the GGP members.
Thereafter, at the end of each month of data should be
sent for the preceding year on a continuing basis for the
next 6 years.
It is important to emphasize
that delays in submitting the data should not occur save
for exceptional circumstances. If GGP is to work as
planned, it must be by the submission of the data in time
by all groups on a monthly basis.
Though all of the information has
appeared in previous Newsletters, the following is a
reminder of what to do.
- Note that each of the
following GGP files must include a header
which gives basic facts about the station,
instrument and format. Please note carefully
(from Newsletter #5) what the header should
contain and be sure to provide all the
information.
- The gravity and pressure
data have to be decimated, without any treatment
whatsoever, from their raw sampled values (at 1s,
2s, 10s ...) to samples at 1 minute, in volts.
The 1 minute data should be written to a single
file in GGP format. Details of the GGP format for
1 minute files can be found in GGP Newsletter #5
(p. 15 and 16). Note that some changes were made
to the original proposal (Newsletter #2, modified
in Newsletter # 3), so do not use the earlier
formats.
- The auxiliary data, rainfall
and/or groundwater if they exist, must also
be assembled in a file using GGP format. The
sampling interval for these variables is to be
either:
(a) by
decimation to 1 minute (if the sampling is more
frequent than 1 minute), or
(b) at 1 min or a longer
sampling interval corresponding to the data
acquisition rate for these data.
There is to be no data
treatment for these variables. The file structure
for the auxiliary data follows that for the
gravity/pressure data.
- The station log file is
to be supplied for the station for the month,
noting all the events which might cause a problem
in the data such as a helium refill, power loss,
calibration experiment, computer malfunction,
instrument failure, data loss, or cultural
disturbance. The date of the event and a brief
description should be supplied. The structure of
these files should be with the same header as
before, and with the appropriate date and time
stamp, but with the gravity and pressure values
replaced by a comment on the event in question.
- SG groups should sent their
decimation filter (from the high rate sampling to
1 min) to Olivier Francis at ICET. He will
evaluate the filters and notify the groups if
there any questions. If there are different
filters for the gravity and pressure, these
should both be sent.
In addition to the basic GGP data
described by the files above, GGP groups are strongly
encouraged to send cleaned (or fixed) data to ICET,
particularly for the gravity and pressure files. This
cleaned data is of two forms:
(a) Data recorded at a high
sampling rate with disturbances removed prior to
decimation to 1 min. This obviously is the highest
quality of data that can be produced and the type that
should be used for the most sensitive non-tidal analysis,
or
(b) The same 1 minute data as sent
to ICET, but with disturbances removed from the 1 minute
samples. This is easier to do than (a) because of the
smaller file sizes, but there is more data loss due to
the effect of the filters. Also disturbances in the 1 min
data are frequently more difficult to detect than in the
high rate data.
To date few SG groups have made the
effort to send earthquake data to ICET. In order to
reduce the work this requires, we have decided to request
at this time data for only one earthquake, as an
experiment. The earthquake, which is the largest in terms
of seismic moment since the start of GGP, is the
following one in the Balleny Islands Region:
| Year |
Month |
Day |
Orig Time |
Lat |
Long |
Depth (km) |
Mag (HRV) |
DC Moment |
| 1998 |
03 |
25 |
031225.07 |
-62.88 |
149.53 |
29 |
8.1 |
1.7 x
1021 N m |
The format for sending this data is
given in Newsletter #5. You should send 10 days of data
beginning with the day that includes the origin time and
the data should be the raw data (1s, 2s, ...).
Both GGP data and earthquake data
should be sent to ICET by ftp in the following way:
| GGP Data |
Earthquake
Data |
| address |
ftpserver.oma.be |
address |
ftpserver.oma.be |
| login: |
your
ICET username |
login: |
anonymous
|
| password:
|
your
ICET password |
password:
|
your
email address |
| directory |
directory
will be assigned |
directory: |
/pub/astro/ggp/bigquakes |
If you need to get
your ICET user name and password, please contact Olivier
Francis (francis@oma.be)
|
.
|
zip
|
compressed
version of all files |
