[IGSMAIL-5796]: Message for igsmail

[Wiley, Barbara]

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IGS Electronic Mail      22 Jul 13:11:44 PDT 2008      Message Number 5796
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Author: Leonard Weingarth, NGA

In close cooperation with CDDIS and the IGS Central Bureau, the National
Geospatial-Intelligence Agency (NGA) is now supplying tracking data from
11 stations of its global network.  The same stations are a major
component of the operational GPS tracking network, which will allow a
closer alignment of the WGS 84 and ITRF frames.

At each of NGA's monitor stations, two collocated receivers run from a
common antenna (an Ashtech Dorne-Margolin chokering) identified with a
single DOMES number.  The receivers in all cases are modified Ashtech
Z-12 models.  All NGA stations are equipped with
environmentally controlled Agilent 5071A cesium clocks except for the
station located at USNO, which references the USNO Master Clock
Ensemble.  Each receiver at each NGA site is connected to a separate
cesium clock, except at USNO.

NGA has supplied historic RINEX data to the IGS.  However, NGA internal
RINEX filenames do not map to a single, unique receiver as required by
the IGS.  In conjunction with this, it has been necessary to change site
names to conform to IGS and RINEX standards.  The details follow.

1. NGA internal site names and file formats

NGA uses an internal data filenaming and format scheme that differs from
the IGS standard.  The internal RINEX observation and navigation
filenames have the form:

[r]xx[#]ddda.yyo & [r]xx[#]ddda.yyn

where

[r] has a value of s or u and refers to whether the file was collected
by the [s]elected or [u]nselected receiver.  NGA designates an active,
or selected GPS receiver, and an unselected
receiver.  Either receiver/cesium 1 or receiver/cesium 2 can be the
selected receiver/clock. NGA does not change receiver/cesium pairing
except in the event of equipment failure.

xx is the NGA internal station number, from 01 to 14

[#] is the receiver/cesium pair, either 1 or 2

ddd is the day-of-year, from 001 to 366

a is the session designator.  For multiple sessions this value is
incremented

yy is the 2 digit year

o or n refers to observation or navigation file, respectively.
Meteorological data files are also collected at each site.

2.  New IGS site names to be used

To conform with IGS standards, NGA will modify its RINEX naming scheme
in the following way to map the internal filenames to these new names:

[r]021, [r]022	ade1, ade2		Adelaide, Australia
[r]031, [r]032	bue1, bue2  		Buenos Aires, Argentina
[r]041, [r]042	hrm1, hrm2    		Hermitage, UK
[r]051, [r]052	bhr1, bhr2  *   		Bahrain (See Item 3.)
[r]061, [r]062	qui1, qui2    		Quito, Ecuador
[r]071, [r]072	wdc1, wdc2 / wdc3, wdc4 *    USNO, Washington, DC (See
Item 4.)
[r]101, [r]102	eil1, eil2    		Eielson, Alaska, USA
[r]111, [r]112	wel1, wel2    		Wellington, New Zealand
[r]121, [r]132	pre1, pre2    		Pretoria, South Africa
[r]131, [r]132	osn1, osn2    		Osan, Korea
[r]141, [r]142	tah1, tah2    		Tahiti, Polynesia

[s]/[u]-type filenames have been available at CDDIS for some time and
some analysis groups have used those files.  Please be aware that the
old files will be replaced with the new names on 21 July 2008.  After
this date, all new data files from NGA will use the following names  and
conform to the RINEX 2.10 standards.  Users of the old files should
please discontinue that practice immediately.  NGA will submit updated
historic data in the near future.  An announcement will be sent when
that is accomplished.

Note that all of the new NGA stations have S-type DOMES numbers, so
the reference points are associated with the individual antennas and
the eccentricities are zero.  Only the previous IGS site bahr and its
new name bhr1/bhr2 has a marker DOMES number and a non-zero
eccentricity.

3. Station bahr to be replaced by bhr1

FOR July 21, 2008, NGA WILL STOP BAHR DATA SUPPLY and data file naming
will change.  In the past, the data supplied for bahr was the selected
receiver. This resulted in a mixture of data from the different
receivers.  While the data primarily corresponded to receiver 1,
whenever receiver 1 failed at Bahrain, receiver 2 data was supplied to
CDDIS as bahr data.  Using separate names (bhr1 and bhr2) for the
receiver/cesium pairs at Bahrain should eliminate possible confusion in
the future.

4. USNO antenna move:

The NGA receiver antenna at USNO was moved on 2006-07-17.   All data
prior to this date will use the site names wcd1 and wdc2, depending on
the receiver supplying the data.  Data newer than 2006-07-17 will use
the site names wdc3 or wdc4, respectively. The two locations for the
antenna correspond to distinct DOMES numbers at USNO as indicated in the
site logs.  Note that these stations are not the same as the existing
IGS stations, usno, usn1 (discontinued), or usn3.

5. Site logs

New site logs have been prepared using the new site names given above
and these will be deposited at the IGS Central Bureau.