Pyorbital

Pyorbital is a python package to compute orbital parameters for satellites from TLE files as well as astronomical parameters of interest for satellite remote sensing. Currently Pyorbital only supports low earth orbit satellites.

Installation

Pyorbital is available from the Python Package Index (PyPI) via pip or from the conda-forge conda channel. To install from PyPI in an existing environment:

pip install pyorbital

Or in an existing conda-based environment:

conda install -c conda-forge pyorbital

From Source

Pyorbital can also be installed from source. If you want to install pyorbital from the latest in-development version on GitHub you can run:

pip install git+https://github.com/pytroll/pyorbital.git

However, if you instead want to edit the source code and see the changes reflected when you run the code you can clone the git repository and install it in “editable” mode:

git clone git://github.com/pytroll/pyorbital.git
cd pyorbital
pip install -e .

Add platform missing information

Pyorbital comes with a file platforms.txt that maps a satellite name to the NORAD identifier.

This file already contain many low earth orbiting environmental or meteorological satellites and thus likely be sufficient for your purpose.

But should it not contain your satellites of interest make a copy of the platforms.txt file and add the missing satellites and their NORAD identifiers and place the file in the directory pointed to by PYORBITAL_CONFIG_PATH.

The NORAD identifier can be found as the first number of each line in the Two-Line Elements files (eg. from celestrak).

Pyorbital comes with a small script check_platform.py to check whether a satellite is already supported.

python -m pyorbital.check_platform -s NOAA-21

[INFO: 2023-01-22 21:20:25 : pyorbital.tlefile] Satellite NOAA-21 is supported. NORAD number: 54234
[INFO: 2023-01-22 21:20:25 : pyorbital.tlefile] Satellite names and NORAD numbers are defined in /path/to/pyorbital/etc/directory/platforms.txt

TLE files

Pyorbital has a module for parsing NORAD TLE-files

>>> from pyorbital import tlefile
>>> tle = tlefile.read('noaa 18', '/path/to/my/tle_file.txt')
>>> tle.inclination
99.043499999999995

If no path is provided pyorbital first tries to read any local TLE files defined by the environment variable TLES giving a glob pattern that can be used to retrieve all relevant files:

TLES=/path/to/tle_files/*/tle*txt

If this variable is not set Pyorbital will try get the earth observation TLE files over the internet from celestrak. Note this downloading only happens if no specific TLE file is provided or if the TLES environment variable is not set.

TLE download and database

The historical TLE files can be requested from celestrak’s request page.

There is also a script, fetch_tles.py, that can be used to collect TLE data from several locations. The currently supported locations are:

generic network locations without login
Space-Track (login credentials needed)
local files

The data are saved in a SQLite3 database, and can be written to a file after each run. To see configuration options, see the example configuration in examples/tle.yaml.

Computing satellite position

The orbital module enables computation of satellite position and velocity at a specific time:

>>> from pyorbital.orbital import Orbital
>>> from datetime import datetime
>>> # Use current TLEs from the internet:
>>> orb = Orbital("Suomi NPP")
>>> now = datetime.utcnow()
>>> # Get normalized position and velocity of the satellite:
>>> orb.get_position(now)
(array([-0.20015267,  0.09001458,  1.10686756]),
 array([ 0.06148495,  0.03234914,  0.00846805]))
>>> # Get longitude, latitude and altitude of the satellite:
>>> orb.get_lonlatalt(now)
(40.374855865574951, 78.849923885700363, 839.62504115338368)

Use actual TLEs to increase accuracy

>>> from pyorbital.orbital import Orbital
>>> from datetime import datetime
>>> orb = Orbital("Suomi NPP")
>>> dtobj = datetime(2015,2,7,3,0)
>>> orb.get_lonlatalt(dtobj)
(152.11564698762811, 20.475251739329622, 829.37355785502211)

But since we are interested in knowing the position of the Suomi-NPP more than two and half years from now (September 26, 2017) we can not rely on the current TLEs, but rather need a TLE closer to the time of interest:

>>> snpp = Orbital('Suomi NPP', tle_file='/path/to/tle/files/tle-20150207.txt')
>>> snpp.get_lonlatalt(dtobj)
(105.37373804512762, 79.160752404540133, 838.94605490133154)

If we take a TLE from one week earlier we get a slightly different result:

>>> snpp = Orbital('Suomi NPP', tle_file='/path/to/tle/files/tle-20150131.txt')
>>> snpp.get_lonlatalt(dtobj)
(104.1539184988462, 79.328272480878141, 838.81555967963391)

Computing astronomical parameters

The astronomy module enables computation of certain parameters of interest for satellite remote sensing for instance the Sun-zenith angle:

>>> from pyorbital import astronomy
>>> from datetime import datetime
>>> utc_time = datetime(2012, 5, 15, 15, 45)
>>> lon, lat = 12, 56
>>> astronomy.sun_zenith_angle(utc_time, lon, lat)
62.685986438071602

PYORBITAL_CONFIG_PATH

It is possible (but not mandatory) to define this environment variable to have full control of certain static data used by Pyorbital:

Pyorbital comes with a file platforms.txt that maps a satellite name to the NORAD identifier. This internal file is accessed by Pyorbital without the user having to do anything. But if you need to change or update this file you can make your own copy and place in the directory pointed to by this environment variable.

TLES

Two Line Element (TLE) files are accessed automatically over the internet without the user having to do anything. When doing that Pyorbital will fetch the most recent TLE data which may not be the most optimal for historic data for instance. Also, it may not be sustainable in a production environment.

However, it is possible to let Pyorbital look for the necessary and more optimal TLE data locally, by specifying locations where such local TLE files are located. If the TLES environment variable is set to a glob pattern to local locations, Pyorbital will first search for the needed TLEs there. This can both be useful in an operational setup where access to the internet is restricted, and when processing old/historic satellite data.

It is possible (but not mandatory) to define this environment variable.

API

Orbital computations

Module for computing the orbital parameters of satellites.

class pyorbital.orbital.OrbitElements(tle): Class holding the orbital elements.

class pyorbital.orbital.Orbital(satellite, tle_file=None, line1=None, line2=None)

Class for orbital computations.

The satellite parameter is the name of the satellite to work on and is used to retrieve the right TLE data for internet or from tle_file in case it is provided.

find_aol(utc_time, lon, lat): Find AOL.

find_aos(utc_time, lon, lat): Find AOS.

get_equatorial_crossing_time(tstart, tend, node='ascending', local_time=False, rtol=1e-09)

Estimate the equatorial crossing time of an orbit.

The crossing time is determined via the orbit number, which increases by one if the spacecraft passes the ascending node at the equator. A bisection algorithm is used to find the time of that passage.

Parameters:

tstart – Start time of the orbit
tend – End time of the orbit. Orbit number at the end must be at least one greater than at the start. If there are multiple revolutions in the given time interval, the crossing time of the last revolution in that interval will be computed.
node – Specifies whether to compute the crossing time at the ascending or descending node. Choices: (‘ascending’, ‘descending’).
local_time – By default the UTC crossing time is returned. Use this flag to convert UTC to local time.
rtol – Tolerance of the bisection algorithm. The smaller the tolerance, the more accurate the result.

get_last_an_time(utc_time): Calculate time of last ascending node relative to the specified time.

get_lonlatalt(utc_time)

Calculate sublon, sublat and altitude of satellite.

http://celestrak.com/columns/v02n03/

get_next_passes(utc_time, length, lon, lat, alt, tol=0.001, horizon=0)

Calculate passes for the next hours for a given start time and a given observer.

Original by Martin.

Utc_time:: Observation time (datetime object)
Length:: Number of hours to find passes (int)
Lon:: Longitude of observer position on ground (float)
Lat:: Latitude of observer position on ground (float)
Alt:: Altitude above sea-level (geoid) in km of observer position on ground (float)
Tol:: precision of the result in seconds
Horizon:: the elevation of horizon to compute risetime and falltime.
Returns:: [(rise-time, fall-time, max-elevation-time), …]

get_observer_look(utc_time, lon, lat, alt)

Calculate observers look angle to a satellite.

See http://celestrak.com/columns/v02n02/

utc_time: Observation time (datetime object) lon: Longitude of observer position on ground in degrees east lat: Latitude of observer position on ground in degrees north alt: Altitude above sea-level (geoid) of observer position on ground in km

Return: (Azimuth, Elevation)

get_orbit_number(utc_time, tbus_style=False, as_float=False)

Calculate orbit number at specified time.

Parameters:

utc_time – UTC time as a datetime.datetime object.
tbus_style – If True, use TBUS-style orbit numbering (TLE orbit number + 1)
as_float – Return a continuous orbit number as float.

get_position(utc_time, normalize=True): Get the cartesian position and velocity from the satellite.

utc2local(utc_time): Convert UTC to local time.

exception pyorbital.orbital.OrbitalError: Custom exception for the Orbital class.

pyorbital.orbital.get_observer_look(sat_lon, sat_lat, sat_alt, utc_time, lon, lat, alt)

Calculate observers look angle to a satellite.

http://celestrak.com/columns/v02n02/

Utc_time:: Observation time (datetime object)
Lon:: Longitude of observer position on ground in degrees east
Lat:: Latitude of observer position on ground in degrees north
Alt:: Altitude above sea-level (geoid) of observer position on ground in km
Returns:: (Azimuth, Elevation)

pyorbital.orbital.kep2xyz(kep)

Keppler to cartesian coordinates conversion.

(Not sure what ‘kep’ actually refers to, just guessing! FIXME!)

TLE handling

Classes and functions for handling TLE files.

exception pyorbital.tlefile.ChecksumError: ChecksumError.

class pyorbital.tlefile.Downloader(config)

Class for downloading TLE data.

fetch_plain_tle(): Fetch plain text-formated TLE data.

fetch_spacetrack(): Fetch TLE data from Space-Track.

read_tle_files(): Read TLE data from files.

read_xml_admin_messages(): Read Eumetsat admin messages in XML format.

pyorbital.tlefile.SATELLITES = {'ALOS-2': '39766', 'CALIPSO': '29108', 'CLOUDSAT': '29107', 'CRYOSAT-2': '36508', 'CSK-1': '31598', 'CSK-2': '32376', 'CSK-3': '33412', 'CSK-4': '37216', 'DMSP-F15': '25991', 'DMSP-F16': '28054', 'DMSP-F17': '29522', 'DMSP-F18': '35951', 'DMSP-F19': '39630', 'EOS-AQUA': '27424', 'EOS-AURA': '28376', 'EOS-TERRA': '25994', 'FY-2D': '29640', 'FY-2E': '33463', 'FY-2F': '38049', 'FY-2G': '40367', 'FY-3A': '32958', 'FY-3B': '37214', 'FY-3C': '39260', 'FY-3D': '43010', 'FY-3E': '49008', 'FY-3F': '57490', 'FY-3G': '56232', 'GOES-13': '29155', 'GOES-14': '35491', 'GOES-15': '36411', 'GOES-16': '41866', 'GOES-17': '43226', 'GOES-18': '51850', 'GOES-19': '60133', 'HIMAWARI-6': '28622', 'HIMAWARI-7': '28937', 'HIMAWARI-8': '40267', 'HIMAWARI-9': '41836', 'INSAT-3A': '27714', 'INSAT-3C': '27298', 'INSAT-3D': '39216', 'JASON-2': '33105', 'KALPANA-1': '27525', 'LANDSAT-7': '25682', 'LANDSAT-8': '39084', 'METEOSAT-10': '38552', 'METEOSAT-11': '40732', 'METEOSAT-12': '54743', 'METEOSAT-7': '24932', 'METEOSAT-8': '27509', 'METEOSAT-9': '28912', 'METOP-A': '29499', 'METOP-B': '38771', 'METOP-C': '43689', 'NOAA-10': '16969', 'NOAA-11': '19531', 'NOAA-12': '21263', 'NOAA-14': '23455', 'NOAA-15': '25338', 'NOAA-16': '26536', 'NOAA-17': '27453', 'NOAA-18': '28654', 'NOAA-19': '33591', 'NOAA-20': '43013', 'NOAA-21': '54234', 'NOAA-6': '11416', 'NOAA-7': '12553', 'NOAA-8': '13923', 'NOAA-9': '15427', 'RADARSAT-2': '32382', 'SENTINEL-1A': '39634', 'SENTINEL-1B': '41456', 'SENTINEL-2A': '40697', 'SENTINEL-2B': '42063', 'SENTINEL-3A': '41335', 'SENTINEL-3B': '43437', 'SENTINEL-5P': '42969', 'SMOS': '36036', 'SPOT-5': '27421', 'SPOT-6': '38755', 'SPOT-7': '40053', 'SUOMI-NPP': '37849', 'TANDEM-X': '36605', 'TERRASAR-X': '31698', 'TIROS-N': '11060'}

The platform numbers are given in a file $PYORBITAL_CONFIG_PATH/platforms.txt in the following format:

# Mappings between satellite catalogue numbers and corresponding
# platform names from OSCAR.
ALOS-2 39766
CloudSat 29107
CALIPSO 29108
CryoSat-2 36508
CSK-1 31598
CSK-2 32376
CSK-3 33412
CSK-4 37216
DMSP-F15 25991
DMSP-F16 28054
DMSP-F17 29522
DMSP-F18 35951
DMSP-F19 39630
EOS-Aqua 27424
EOS-Aura 28376
EOS-Terra 25994
FY-2D 29640
FY-2E 33463
FY-2F 38049
FY-2G 40367
FY-3A 32958
FY-3B 37214
FY-3C 39260
FY-3D 43010
FY-3E 49008
FY-3F 57490
FY-3G 56232
GOES-13 29155
GOES-14 35491
GOES-15 36411
GOES-16 41866
GOES-17 43226
GOES-18 51850
GOES-19 60133
Himawari-6 28622
Himawari-7 28937
Himawari-8 40267
Himawari-9 41836
INSAT-3A 27714
INSAT-3C 27298
INSAT-3D 39216
JASON-2 33105
Kalpana-1 27525
Landsat-7 25682
Landsat-8 39084
Meteosat-7 24932
Meteosat-8 27509
Meteosat-9 28912
Meteosat-10 38552
Meteosat-11 40732
Meteosat-12 54743
Metop-A 29499
Metop-B 38771
Metop-C 43689
TIROS-N 11060
NOAA-6 11416
NOAA-7 12553
NOAA-8 13923
NOAA-9 15427
NOAA-10 16969
NOAA-11 19531
NOAA-12 21263
NOAA-14 23455
NOAA-15 25338
NOAA-16 26536
NOAA-17 27453
NOAA-18 28654
NOAA-19 33591
NOAA-20 43013
NOAA-21 54234
RadarSat-2 32382
Sentinel-1A 39634
Sentinel-1B 41456
Sentinel-2A 40697
Sentinel-2B 42063
Sentinel-3A 41335
Sentinel-3B 43437
Sentinel-5P 42969
SMOS 36036
SPOT-5 27421
SPOT-6 38755
SPOT-7 40053
Suomi-NPP 37849
TanDEM-X 36605
TerraSAR-X 31698

class pyorbital.tlefile.SQLiteTLE(db_location, platforms, writer_config)

Store TLE data in a sqlite3 database.

close(): Close the database.

update_db(tle, source)

Update the collected data.

Only data with newer epoch than the existing one is used.

write_tle_txt(): Write TLE data to a text file.

class pyorbital.tlefile.Tle(platform, tle_file=None, line1=None, line2=None)

Class holding TLE objects.

property line1: Return first TLE line.

property line2: Return second TLE line.

property platform: Return satellite platform name.

exception pyorbital.tlefile.TleDownloadTimeoutError: TLE download timeout exception.

pyorbital.tlefile.check_is_platform_supported(satname): Check if satellite is supported and print info.

pyorbital.tlefile.collect_filenames(paths): Collect all filenames from paths.

pyorbital.tlefile.fetch(destination): Fetch TLE from internet and save it to destination.

pyorbital.tlefile.get_platforms_filepath()

Get the platforms.txt file path.

Check that the file exists or raise an error.

pyorbital.tlefile.main(): Run a test TLE reading.

pyorbital.tlefile.read(platform, tle_file=None, line1=None, line2=None)

Read TLE for platform.

The data are read from tle_file, from line1 and line2, from the newest file provided in the TLES pattern, or from internet if none is provided.

pyorbital.tlefile.read_platform_numbers(filename, in_upper=False, num_as_int=False): Read platform numbers from $PYORBITAL_CONFIG_PATH/platforms.txt.

pyorbital.tlefile.read_tle_from_mmam_xml_file(fname): Read TLE data from MMAM XMl file (EUMETSAT).

pyorbital.tlefile.read_tles_from_mmam_xml_files(paths)

Read TLE data from a list of MMAM XMl file (EUMETSAT).

MMAM = Multi-Mission Administration Message

pyorbital.tlefile.table_exists(db, name): Check if the table ‘name’ exists in the database.

Astronomical computations

Angle and time-based astronomy functions.

Parts taken from http://www.geoastro.de/elevaz/basics/index.htm

Note on argument types

Many of these functions accept Python datetime objects, numpy datetime64 objects, or anything that can be turned into a numpy array of datetime64 objects. These objects are inherently 64-bit so if other arguments (ex. longitude and latitude arrays) are 32-bit floats internal operations will be automatically promoted to 64-bit floating point numbers. Where possible these are then converted back to 32-bit before being returned. In general scalar inputs will also produce scalar outputs.

pyorbital.astronomy.cos_zen(utc_time, lon, lat)

Derive the cosine of the sun-zenith angle for lon, lat at utc_time.

utc_time: datetime.datetime instance of the UTC time lon: Longitude in degrees lat: Latitude in degrees. Returns: Cosine of the sun zenith angle.

pyorbital.astronomy.get_alt_az(utc_time, lon, lat)

Return sun altitude and azimuth from utc_time, lon, and lat.

lon,lat in degrees The returned angles are given in radians.

pyorbital.astronomy.gmst(utc_time)

Greenwich mean sidereal utc_time, in radians.

As defined in the AIAA 2006 implementation: http://www.celestrak.com/publications/AIAA/2006-6753/

pyorbital.astronomy.jdays(utc_time): Get the julian day of utc_time.

pyorbital.astronomy.jdays2000(utc_time): Get the days since year 2000.

pyorbital.astronomy.observer_position(utc_time, lon, lat, alt)

Calculate observer ECI position.

http://celestrak.com/columns/v02n03/

pyorbital.astronomy.sun_earth_distance_correction(utc_time): Calculate the sun earth distance correction, relative to 1 AU.

pyorbital.astronomy.sun_ecliptic_longitude(utc_time): Ecliptic longitude of the sun at utc_time.

pyorbital.astronomy.sun_ra_dec(utc_time): Right ascension and declination of the sun at utc_time.

pyorbital.astronomy.sun_zenith_angle(utc_time, lon, lat)

Sun-zenith angle for lon, lat at utc_time.

lon,lat in degrees. The sun zenith angle returned is in degrees.