Filename Conventions

ILRS

The International Laser Ranging Service (ILRS) is responsible for the organisation of Satellite and lunar ranging campaigns resulting in data that is used in support of satellite orbit determination, geodesy, lunar science and fundamental physics (monitoring and determination of the fundamental constants).

The ILRS data available from the GSSC is provided in two formats:

CRD

This file format is an evolution from older formats taking into account the adoption of new technologies. The technology drivers are the increased adoption of kHz firing-rate laser and anticipated transponder missions. The former made the use of the older format with full rate data a bit cumbersome and the later had some problems with fields (some had to be created), and some were too small to accommodate then new data.

Instead of patching the old format to accommodate for the three types of data provided, the ILRS decided to go for a a completely new format to accommodate the three data types: full rate, sampled engineering and normal points.

The file contains three sections including the header with information on the station in use, target and session, information on configuration including detector configuration and clocks and, at last, the data itself.

The GSSC supports two resource types for CRD data: ‘SLR full rate data’ and ‘SLR Normal point data’.

The latest version of the Standard can be found here. This version (v2.01) superseded v1.01 in the 1st of August 2022.

Example Code to read/write and manipulate CRD files can be found here.

CPF

Again, for the same reasons mentioned above for then renewal of the predictions files, the ILRS realised the older format could no longer efficiently support then prediction data. Here another factor had to be taken into account: with the increase number of satellites in GNSS constellation the ILRS had to optimise orbit predictions so that a schedule that could accommodate the larger number satellites in need of observations could be easily accommodated. The result was the CPF files: the data contained in these files is the data used by the ILRS stations to schedule observations.

The file contains several headers with general information about the station, the clocks used, the lasers and of course also the predictions for satellite visibility for the relevant stations.

An old version (v1.0) for the CPF files format can be found here and the new version (v2.0) here. V2.0 supersedes V1.0 since the 1st of October 2021. Example code for file creation and edition is available here. File examples can also be found here

The GSSC uses resource type ‘Predicted Orbits’ to handle CPF files.

International Earth Rotation and Reference Systems Service (IERS) files

The IERS is responsible for providing accurate data on the earth rotation and also accurate definition of several Reference Frames essential for accurate positioning on the surface of the Earth. Because of its close interplay with GNSS data, it is perfectly natural to also include those in the GSSC.

Earth Orientation Parameters files

The Earth Orientation Parameters are the rotation part in the coordinate transformation from the International Terrestrial Reference Frame to the International Celestial Reference Frame. The orientation parameters provided are computed from a combination of data obtained though DORIS, VLBI, SLR and GNSS (available from the IGS produced Earth Rotation Parameter files as discussed above (Sec. 1.3)). It should be obvious for every reader who got this far in the GSSC that without a precise determination of the Earth Orientation Parameters, precision PNT is not possible.

Earth Orientation files contain displacements of the pole in arcsec, associated errors and nutation and precession of the pole and associated errors as well as UT fluctuations.

Different types of data can be provided quick look analysis results, the final daily values and predictions. Also, comparison is performed with different IAU1980 and IAU2000 models.

Details, formats and plots of the current time series can be found here. The explanatory supplement for the Earth Orientation parameters is available here. This document contain more technical details on the preparation of the Earth Orientation Parameters Files. 

NORAD Two Line Elements Sets (TLE) files

TLE files describe in an extremely compact way (only two lines) the approximated trajectories of any objects orbiting the Earth. They are designed to provide input to NORAD’s SGP, SGP4SDP4, SGP8 and SDP8 simplified perturbations orbital models. Using the correct projection formula the orbital data provided in the files can provide the state (position and velocity) of the relevant object in the past or the future. 

Interestingly enough the format was designed to be input to a computing apparatus as a series of three punch cards.

The Two line element contains in fact three lines:

  • Line 1: Name of object (max 24 characters)
  • Line 2: Miscellaneous information on ephemeris and drag coefficients. The last field is a check sum
  • Line 3: Orbital elements. The last field is a check sum  

These models are widely used in not only in the prediction of orbital tracks as well as in the the prediction of future tracks of orbital debris and provide great help in characterising risks and plan collision avoidance manoeuvres.

Networked Transport of RTCM via Internet Protocol (NTRIP)

NTRIP is a protocol used by Real-Time Kinematic (RTK) positioning, a method used by an RTK-enabled GPS receiver to obtain extremely precise positions by using data from an RTK base station (a second GPS receiver) that is transmitted over the internet.

RTK uses a fixed base station broadcasting regularly on the internet accurate corrections to its position to any rover (e.g. a user’s mobile phone) listening in order to allow the rover to get its position to 1 cm accuracy. On the hardware side we have a GNSS system working in a normal GNSS configuration, a user’s device (for the purpose of NTRIP called the rover) and a fixed baseline station. On the software side we have a NTRIP server associated with the base station running the NTRIP caster broadcasting information from the base station and on the client side, associated with the rover we have the NTRIP client listening to the information broadcast by the server.

Here any content can be included

e.g. tables:

testheadertest header2
lowerother
caption of table