Welcome to the SLRfield package

This package is an archive of scientific routines for data processing related to SLR(Satellite Laser Ranging). Currently, operations on SLR data include:

1. Download CPF(Consolidated Prediction Format) ephemeris files automatically from CDDIS(Crustal Dynamics Data Information System) or EDC(EUROLAS Data Center);
2. Parse the CPF ephemeris files;
3. Predict the positions of targets in topocentric reference frame, and compute the time of flight for laser pulse;
4. Calculate the position of targets in GCRF;

How to Install

On Linux, macOS and Windows architectures, the binary wheels can be installed using pip by executing one of the following commands:

pip install slrfield
pip install slrfield --upgrade # to upgrade a pre-existing installation

How to use

Download the latest CPF ephemeris files at the current moment

If the ephemeris release center is not provided, the CPF ephemeris files are downloaded from CDDIS by default.

Download all currently available targets

>>> from slrfield import cpf_download
>>> cpf_dir_cddis,cpf_files_cddis = cpf_download() # From CDDIS by default;
>>> print(cpf_dir,cpf_files)

A directory where CPF files are stored, such as CPF/CDDIS/2020-10-02/, will be automatically created.

Download a set of targets which are specified by user

>>> sat_lists = ['ajisai','lageos1','etalon2','jason3']
>>> cpf_dir_edc,cpf_files_edc = cpf_download(sat_lists,source = 'EDC',keep=False) # From EDC

Note: by setting keep = False, the cpf files storage directory will be automatically emptied beforehand.

Download the latest CPF ephemeris files before a specific date and time

>>> sat_lists = ['starlette','lageos1']
>>> date = '2017-01-01 11:30:00'
>>> cpf_dir_cddis,cpf_files_cddis = cpf_download(sat_lists,date)

Parse the CPF ephemeris files and read the data

Information from the parsed CPF ephemeris files includes the following contents:

• Format
• Format Version
• Ephemeris Source
• Date and time of ephemeris production
• Ephemeris Sequence number
• Target name
• COSPAR ID
• SIC
• NORAD ID
• Starting date and time of ephemeris
• Ending date and time of ephemeris
• Time between table entries (UTC seconds)
• Target type
• Reference frame
• Rotational angle type
• Center of mass correction
• Direction type
• Modified Julian Date
• Second of Day
• Leap Second
• Time moment in UTC
• Target positions in meters

Parse CPF ephemeris files

>>> from slrfield import CPF
>>> cpf_data_cddis = CPF.from_files(cpf_dir_cddis)
>>> print(cpf_data_cddis.info)

Make predictions w.r.t. a site

The azimuth, altitude, distance of a target w.r.t. a given site, and the time of flight for laser pulse etc. can be easily predicted by calling a method pred_azalt. The output prediction files named with target names are generated by default.

• There are two modes for the prediction. If the mode is set to geometric, then the transmitting direction of the laser will coincide with the receiving direction at a certain moment. In this case, the output prediction file will not contain the difference between the receiving direction and the transmitting direction. If the mode is set to apparent, then the transmitting direction of the laser is inconsistent with the receiving direction at a certain moment. In this case, the output prediction file will contain the difference between the receiving direction and the transmitting direction. The default mode is set to apparent.
• The 10-point(degree 9) Lagrange polynomial interpolation method is used to interpolate the CPF ephemeris.
• Effects of leap second have been considered in the prediction generation.

Coordinates of station can either be geocentric(x, y, z) in meters or geodetic(lon, lat, height) in degrees and meters. The default coordinates type is set to geodetic.

For geodetic(lon, lat, height) site coordinates

t_start = '2017-01-02 17:06:40'
t_end = '2017-01-03 09:06:40'
t_increment = 0.5 # second

station = [46.877230,7.465222,951.33] # geodetic(lon, lat, height) coordinates in degrees and meters by default
cpf_data_cddis.pred_azalt(station,t_start,t_end,t_increment)

For geocentric(x, y, z) site coordinates

t_start = '2017-01-02 17:06:40'
t_end = '2017-01-03 09:06:40'
t_increment = 2 # second

station = [4331283.557, 567549.902,4633140.353] # geocentric(x, y, z) coordinates in meters
cpf_data_cddis.pred_azalt(station,t_start,t_end,t_increment,coord_type = 'geocentric',mode='geometric')

Make predictions in GCRF

The cartesian coordinates of targets in GCRF(Geocentric Celestial Reference Frame) can be easily predicted by calling a method pred_xyz.

t_start = '2017-01-02 17:06:40'
t_end = '2017-01-03 09:06:40'
t_increment = 5 # second

cpf_data_cddis.pred_xyz(t_start,t_end,t_increment)

Change log

• 0.2.1 — jul 16, 2023

  • Added time system for loading/updating the EOP file and Leap Second file from IERS

• 0.2.0 — Feb 24, 2022

  • Added support for calculating the cartesian coordinates of targets in GCRF

  • Added support for quickly computing the passing-site prediction

  • Removed the module related to TLE data

  • Removed the module related to satellite catalog querying

• 0.1.17 — Nov 04, 2021

  • Fixed the problem of response failure caused by accessing a large amount of data from discos remote server using API
  • Fixed the problem that requested URL's length exceeds the capacity limit of the space-track server.
  • Change the process printing style of query from static to dynamic with color
  • Added support for orbital eccentricity in celestrak_query and target_query, including options of filtering and sorting
  • Added support for output of standard(intrinsic) magnitudes of targets in target_query

• 0.1.14 — Jun 18, 2021

  Fixed the problem that EOP could not be downloaded normally from IERS.

• 0.1.13 — Jun 05, 2021

  Now you may inject the NORAD IDs of a large number of targets by an input file such as noradids.txt to target_query.

• 0.1.11 — Oct 03, 2020

  The CDDIS will discontinue anonymous ftp access to its archive in October 2020, therefore, this package implements the transition from ftp to EARTHDATA for downloading CPF files.

• 0.1.9 — Jul 26, 2020

  Added progress bar for downloading data

• 0.1.5 — Jun 9, 2020

  Expanded the following functions：

  • Automatically download TLE/3LE data from SPACETRACK
  • Pick out space targets that meets specific demands from DISCOS(Database and Information System Characterising Objects in Space) and CELESTRAK database by setting a series of parameters, such as mass, shape, RCS(Radar Cross Section), and orbit altitude etc.
  • Calculate one-day prediction and multiple-day visible passes for space targets based on TLE/3LE data

• 0.0.2 — Apr 21, 2020

  • The slrfield package was released.

Next release

• Add functions to download and parse the CRD(Consolidated Laser Ranging Data Format) observations

Reference

• Python package for satellite laser ranging file formats
• Consolidated Laser Ranging Prediction Format Version 1.01
• sample code on ILRS