Historical LAGEOS Data 1976 to 1993:
GSFC-formed Normal
Points from Full-Rate Data
This is a second release of the data set previously released on January
31, 2007, removing the data from March 1, 1990 up to the end of the file
from the original release. The data over that period exist as official ILRS
NPs in the appropriate locations, and additionally, it seems that this portion
of the "transformed" NPs are corrected TWICE for the LAGEOS CoM
offset, making it difficult to work with. Those who prefer to work with
the original data set, they should take into account this overcorrection
and account for it, otherwise, their orbital fits will be unreasonably high.
The LAGEOS data that are contained in the CDDIS file:
https://cddis.nasa.gov/archive/slr/data/fr/lageos1/npt/lageos1_GSFC_npt.1976_1990.Z
are Normal Points formed according to the official ILRS rules, using the
NASA Goddard GEODYN s/w package. They are provided in the so-called MERIT
II format, the current official ILRS Full Rate format, because of the way
they were recovered. The NP data formed by GEODYN are delivered in an internal
binary format specific to GEODYN. In order to make the data set available
to a community wider than just the GEODYN users, we developed s/w that read
the binary file and generated the FR-format file. The binary file is missing
a lot of (useful) information nominally available in the standard FR as
well as Quick Look NP formats, so converting to any other format would be
an unnecessary complication. The one-way LAGEOS center of mass offset that
was adopted at the time, 240 mm, has been applied, and it is thus up to
the users to either apply an additional correction (e.g. 11 mm) to bring
this in line with the currently accepted value of 251 mm for most sites
(i.e. in case of Herstmonceux add only 5 mm to apply the 245 mm offset),
or apply corrections appropriate for the individual stations if these are
available.
Along with this file, users will find two additional files, one that contains a list of data periods when the data for certain
sites should be edited (DELETE file) and one file (MBIAS) that
contains (primarily) engineering-determined biases at a few key-sites (Haleakala,
Arequipa, Orroral) that should be applied for highest possible
accuracy in the data utilization. These files were developed locally and
it is up to the user to use “as
is” or to further scrutinize them or even replace them with their
own equivalents.
