8. MediaCorrections

class MediaCorrections(name: str, instrument: Instrument)

Bases: Measurement

Calculates media correction delays for ionosophere and troposphere that is applied to real models. Performs a summation of coefficients that are added together and used to return a delay uncertainty in the RTLT.

Parameters:

• name (str) – The name of the measurement model

• instrument (Body) – The observation ground station.

See also

scarabaeus.Units

Utilizes Dimensions in its construction.

scarabaeus.ArrayWUnits

Dependent on Units and Dimensions.

References

[1]

https://descanso.jpl.nasa.gov/monograph/series2/Descanso2_all.pdf

[2]

https://ntrs.nasa.gov/api/citations/19950013586/downloads/19950013586.pdf

Examples

MediaCorrection objects can be constructed with strings:

# initial setup
import scarabaeus as scb
import numpy as np

# create a MediCorrection object using a string
media_correction = MediaCorrection(
    name="GS1 Doppler Media Corrections",
    instrument=scb.GroundStation("DSS-24"),
)

Attributes

instrument	The instrument.
name	The name of the model.

Methods

compute_coefficient_sum(media_data, ...)	Generates the sum of media correction coefficients related to ionosphere, troposphere, or seasonal model.
compute_partials(target, epoch_array[, frame])	Stacks together measurement partials for an epoch array at different epochs.
computed_rtlt_delays(media_file_path, ...[, ...])	Computes the media correction delay between target and instrument (2-way).
generate_measurement_dataset(dataset_name, ...)	Generates a MeasurementDataSet object that can be used by filters downstream.
observed_measurements(file_name[, ...])	Reads measurements from a .json file.
residuals(observed_meas, computed_meas)	Generates the measurement model's residuals given observed and computed ArrayWFrames.
write_observed_measurements(target[, ...])	Generates synthetic measurements and write them as a .json file.

compute_coefficient_sum(media_data, epoch_time, media_type, epoch_index) → float

Generates the sum of media correction coefficients related to ionosphere, troposphere, or seasonal model.

Parameters:

• media_data (pandas dataframe) – Coefficients and relevant information for media corrections

• epoch_time (scb.Epoch) – Time tag epochs in ET as scb Epoch object

• media_type (str) – Name of the media correction model ‘tropo’, ‘iono’, or ‘seasonal’

• epoch_index (int) – Row index for data with matching epoch time range

Return type:

Float

Notes

All inputs are automatically determined through the computed_rtlt_delays method

compute_partials(target: ~scarabaeus.spacecraft.Spacecraft.Spacecraft, epoch_array: ~scarabaeus.timeAndFrame.EpochArray.EpochArray, frame: ~scarabaeus.timeAndFrame.Frame.Frame = J2000 (0 - SOLAR SYSTEM BARYCENTER)) → list

Stacks together measurement partials for an epoch array at different epochs.

Parameters:

• target (Spacecraft) – The target spacecraft.

• epoch_array (EpochArray) – The epochs.

• frame (Frame, optional) – The reference frame. Defaults to a J2000 Frame object.

Returns:

partials – A list with all the partials evaluated at different epochs in the epoch_array.

Return type:

list

computed_rtlt_delays(media_file_path: str, target, frequency_array, frame: ~scarabaeus.timeAndFrame.Frame.Frame = J2000 (0 - SOLAR SYSTEM BARYCENTER), epoch_array: ~scarabaeus.timeAndFrame.EpochArray.EpochArray = None) → ArrayWFrame

Computes the media correction delay between target and instrument (2-way).

Parameters:

• media_file_path (str) – String name of .json file path containing the media coefficient measurement information

• target (Body | Spacecraft) – Target spacecraft as Spacecraft or Body object

• frequency_array (list | numpy.ndarray) – Array with frequencies for specific leg of light path, used to compute the ionosphere rtlt delay

• frame (str | Frame) – Frame to be used to write the output AWF. Defaults to J2000 Frame object.

• epoch_array (list | numpy.ndarray) – Array with recieve or transmit time tags (ET) as scb Epoch array object

Returns:

• Array with troposphere corrections

• Array with ionosphere corrections

Notes

Needs to be run for both t3 and t1 epochs, then outputs are summed into a total delta epoch_array and frequency_array should be the same size array

Examples

media_correction.computed_rtlt_delays(
    media_file_path = 'Users/data/Media_corrections_2021_121_2021_152.json',
    target = "-64",
    frequency_array = [124092, 1249049, 1249345],
    frame = 'ITRF93',
    epoch_array = [128401294, 182492924, 189481294],
)

generate_measurement_dataset(dataset_name: str, measurement_type: str, target: ~scarabaeus.body.Body.Body, observed_meas: ~scarabaeus.timeAndFrame.ArrayWFrame.ArrayWFrame = None, frame: ~scarabaeus.timeAndFrame.Frame.Frame = J2000 (0 - SOLAR SYSTEM BARYCENTER), noisy: bool = False, prior_range_bias=None) → list[MeasurementDataSet]

Generates a MeasurementDataSet object that can be used by filters downstream.

Parameters:

• dataset_name (str) – The name of the MeasurementDataSet.

• target (Spacecraft) – The target spacecraft.

• epoch_list (EpochArray, optional) – The epochs. Defaults to None.

• epoch_start (EpochArray, optional) – The starting epoch. Defaults to None.

• epoch_end (EpochArray, optional) – The end epoch. Defaults to None.

• tstep (int, optional) – The integration timestep. Defaults to 1.

• observed_measurements (list, optional) – The observed measurements. Defaults to None.

• frame (Frame, optional) – The reference frame. Defaults to a J2000 Frame object.

• noisy (bool, optional) – Indicates if noise is added to the measurements or not. Defaults to False.

Returns:

mds_list – A list of MeasurementDataSet objects representing the measurements with their key properties to be used by a filter.

Return type:

list[MeasurementDataSet]

Notes

The MeasurementDataSet output is generated in 6 steps:

1. Computed measurements

2. Partials

3. Residuals

4. Sigmas

5. Pack everything in a list

6. Pack the list in a MeasurementDataSet object

observed_measurements(file_name, meas_name: str = 'meas_ideal', units: ~scarabaeus.units.Units.Units = unitless, frame: ~scarabaeus.timeAndFrame.Frame.Frame = J2000 (0 - SOLAR SYSTEM BARYCENTER)) → Tuple[EpochArray, ndarray, ArrayWFrame]

Reads measurements from a .json file.

Parameters:

• file_name (str) – The filename of the .json file containig the measurement information.

• meas_name (str, optional) – The name of the measurement data to access from the dictionary. Defaults to 'meas_ideal'.

• units (Units, optional) – Units to be used to write the output AWU. Defaults to unitless.

• frame (Frame, optional) – Frame to be used to write the output AWF. Defaults to a J2000 Frame object.

Returns:

meas_time_et, meas_sec, meas_obs – A tuple with the following values corresponding to their respective indices:

• [0] = meas_time_etEpochArray

  The time in ephemeris time.

• [1] = meas_Secnumpy.ndarray

  The times in seconds.

• [2] = meas_obsArrayWFrame

  An AWF with the quantities in AWU.

Return type:

Tuple[EpochArray, numpy.ndarray, ArrayWFrame]

Notes

The writing of the json assumes or requires units and frames.

residuals(observed_meas: ArrayWFrame, computed_meas: ArrayWFrame) → ArrayWFrame

Generates the measurement model’s residuals given observed and computed ArrayWFrames.

Parameters:

• observed_meas (ArrayWFrame) – The observed measurements values (O).

• computed_meas (ArrayWFrame) – The computed measurements values (C).

Returns:

residuals – AWF with the residual O-C.

Return type:

ArrayWFrame

write_observed_measurements(target: Spacecraft, epoch_array: EpochArray = None, epoch_start: EpochArray = None, epoch_end: EpochArray = None, tstep: float = 1, frame: Frame = None, noisy: bool = False, prior_range_bias: float = None, file_name: str = 'ideal_measurement') → None

Generates synthetic measurements and write them as a .json file. The input of this method encapsulate the ones needed for the “computed_meas” method in each measurement model class.

Parameters:

• target (Spacecraft) – The target spacecraft for which the range measurement is to be computed.

• epoch_array (EpochArray, optional) – An array of epochs (times) at which the range measurements should be computed. If provided, overrides epoch_start, epoch_end, and tstep.

• epoch_start (EpochArray, optional) – The starting epoch for the range measurement computations. Required if epoch_array is not provided.

• epoch_end (EpochArray, optional) – The ending epoch for the range measurement computations. Required if epoch_array is not provided.

• tstep (float, optional) – The time step, in seconds, between consecutive range measurements. If epoch_array is not provided. Defaults to 1 second.

• frame (Frame , optional) – The reference frame in which the range computation is performed. Defaults to None.

• noisy (bool , optional) – Whether to add noise to the computed range measurement. Defaults to False.

• prior_range_bias (float, optional) – A prior bias value to add to the computed range measurements. Defaults to None.

• file_name (str, optional) – The filename of the JSON in which the measurement is saved, Defaults to 'ideal_measurement'.

Return type:

None

property instrument: Instrument

The instrument.

property name: str

The name of the model.