rss_ringoccs.diffrec.diffraction_correction module

Purpose:

Provide the DiffractionCorrection class for performing the necessary mathematics to correct for the diffraction effects that are obtained during occultation observations of planetary rings using radio waves.

Dependencies:

1. numpy
2. scipy
3. rss_ringoccs

class rss_ringoccs.diffrec.diffraction_correction.DiffractionCorrection(DLP, res, rng='all', wtype='kbmd20', fwd=False, norm=True, verbose=False, bfac=True, sigma=2e-13, psitype='fresnel4', write_file=False, res_factor=0.75, eccentricity=0.0, periapse=0.0)

Bases: object

Purpose:

Perform diffraction correction for a ring occultation on a data set that is a near radially symmetric function of the ring radius, or ring intercept point (RIP).

Arguments:

DLP (object):

The data set, usually an instance of the DiffractionLimitedProfile class from the rss_ringoccs Calibration subpackage. This instance MUST contain the following attributes and have the same names.

rho_km_vals: Ring Radius (km)

phi_rad_vals: Ring Azimuth Angle (Radians)

p_norm_vals: Normalized Power

phase_rad_vals: Phase (Radians)

B_rad_vals: Elevation Angle (Radians)

D_km_vals: RIP-Distance (km)

f_sky_hz_vals: Sky Frequency (Hertz)

rho_dot_kms_vals: RIP-velocity (km/s)

history: History dictionary

res (float or int):  

The requested resolution for processing (km). This must be a positive real number.

Keywords:

rng (list or str):  

The requested range for diffraction correction. Preferred input is rng = [a,b]. Arrays are allowed and the range will be set as:

rng = [MIN(array), MAX(array)]

Finally, certain strings containing a few of the regions of interests within the rings of Saturn are allowed. Permissable strings are:

‘all’ [1.0, 400000.0]

‘cringripples’ [77690.0, 77760.0]

‘encke’ [132900.0, 134200.0]

‘enckegap’ [132900.0, 134200.0]

‘janusepimetheus’ [96200.0, 96800.0]

‘maxwell’ [87410.0, 87610.0]

‘maxwellringlet’ [87410.0, 87610.0]

‘titan’ [77870.0, 77930.0]

‘titanringlet’ [77870.0, 77930.0]

‘huygens’ [117650.0, 117950.0]

‘huygensringlet’ [117650.0, 117950.0]

Strings are neither case nor space sensitive. For other planets use rng = [a,b]. Default value is set to ‘all’ which processes [1, 400000] Values MUST be set in kilometers.

wtype (*str):

The requested tapering function for diffraction correction. A string with several allowed inputs:

‘rect’ Rectangular Window.

‘coss’ Squared Cosine Window.

‘kb20’ Kaiser-Bessel 2.0 Window.

‘kb25’ Kaiser-Bessel 2.5 Window.

‘kb35’ Kaiser-Bessel 3.5 Window.

‘kbmd20’ Modified kb20 Window.

‘kbmd25’ Modified kb25 Window.

The variable is neither case nor space sensitive. Default window is set to ‘kb25’. See window_functions submodule for further documentation.

fwd (bool):

A Boolean for determining whether or not forward modelling will be computed. This is good starting point for deciding if the diffraction correction is physically significant or valid. If the reconstruction is good, the forward model should reproduce the p_norm_vals attribute from the input DLP instance. Default is set to False.

norm (bool):

A Boolean for determining whether or not the reconstructed complex transmittance is normalize by the window width. This normalization is the complex transmittance that is computed by using free space divided by the complex transmittance that is computed using free space weighted by the selected tapering function. Default is True.

bfac (bool):

A Boolean for determining whether or not the ‘b’ factor in the window width computation is used. This is equivalent to setting the Allen Deviation for the spacecraft to a positive value or to zero. If set to False, the Allen Deviation is assumed to be zero. If set to True the Allen Deviation is set to 2e-13, or whichever number you wish to specify in the sigma keyword (See below). Default is True.

sigma (float):

The Allen deviation for the spacecraft. If the bfac keyword (See above) is set to False, this is ignored. If bfac is set to True, and sigma is NOT specified, then sigma=2e-13 will be used, which is the Allen deviation for Cassini with 1 second integration time. For spacecraft other than Cassini, you should provide the Allen deviation yourself. Default is sigma=2e-13

psitype (str):

A string for determining what approximation to the geometrical ‘psi’ function is used. Several strings are allowed:

‘full’ No Approximation is applied.

‘MTR2’ Second Order Series from MTR86.

‘MTR3’ Third Order Series from MTR86.

‘MTR4’ Fourth Order Series from MTR86.

‘Fresnel’ Standard Fresnel approximation.

The variable is neither case nor space sensitive. Default is set to ‘full’.

verbose (bool):

A Boolean for determining if various pieces of information are printed to the screen or not. Default is False.

Attributes:

bfac (bool):Boolean for bfac (See keywords). dathist (dict):History from DLP instance. dx_km (float):Radial spacing for the data points (km). f_sky_hz_vals (np.ndarray):  Recieved frequency from the spacecraft (Hz). finish (int):Final point that was reconstructed. fwd (bool):Boolean for fwd (See keywords). history (dict):History for the DiffractionCorrection class. This contains system info and user info, including what operating system was used, username, hostname, computer name, and the inputs provided. lambda_sky_km_vals (np.ndarray):  Wavelength of recieved signal from spacecraft (km). mu_vals (np.ndarray):  The sine of the ring opening angle (Unitless). n_used (int):Number of points that were reconstructed. norm (bool):Boolean for norm (See keywords). norm_eq (float):  Normalized equivalent width computed from window that was used during reconstruction. See the window_functions submodule for more information. p_norm_fwd_vals (np.ndarray):  Normalized power computer from the forward modelling of the reconstructed data. This will be a None type variable unless fwd=True is set. If the reconstruction went well, this should mimic the raw data, p_norm_vals. p_norm_vals (np.ndarray):  Normalized power from the diffracted signal. This is the square of the absolute value of the recieved complex transmittance. phase_fwd_vals (np.ndarray):  Phase computed from the forward model of the reconstructed data. This will be a None type variable unless fwd=True is set. If the reconstruction went well, this should mimic phase_rad_vals. This variable is in radians. phase_rad_vals (np.ndarray):  Phase from the diffracted signal (Radians). phase_vals (np.ndarray):  Reconstructed phase (Radians). phi_rad_vals (np.ndarray):  Ring azimuth angle of the ring intercept (Radians). phi_rl_rad_vals (np.ndarray):  Ring longitude angle. This will be a None type unless it was provided in the DLP class. Otherwise, this variable is in radians. power_vals (np.ndarray):  Normalized reconstructed power. psitype (str):String for psitype (See keywords). raw_tau_threshold_vals (np.ndarray):  Threshold optical depth for the diffracted data. This will be a None type unless provided for in the DLP class. res (float):Requested resolution (See arguments). In kilometers. rho_corr_pole_km_vals (np.ndarray):  Radial corrections from the Planet’s pole. This will be a None type variable unless provided in the DLP class. Otherwise, this is in kilometers. rho_corr_timing_km_vals (np.ndarray):  Radial corrections from timing offsets. This will be a None type variable unless provided in the DLP class. Otherwise, this is in kilometers. rho_dot_kms_vals (np.ndarray):  Time derivative of the ring intercept point (km/s). rho_km_vals (np.ndarray):  Ring-intercept-point (RIP) in kilometers. rng (list):Range that was used for reconstruction, taking into the range that was requested by the user. The actual range takes into account limits in the available data and limits in the required window sizes. rngreq (str or list):  Requested range (See keywords). sigma (float):Requested Allen deviation (See keywords). start (int):First point that was reconstructed. t_oet_spm_vals (np.ndarray):  Time the signal is measured on Earth. This is a None type unless provided for in the DLP class. t_ret_spm_vals (np.ndarray):  Time the signal passes through the diffracting medium. This is a None type unless provided for in the DLP class. t_set_spm_vals (np.ndarray):  Time the signal is emitted from the spacecraft. This is a None type unless provided in the DLP class. tau_threshold_vals (np.ndarray):  Threshold optical depth of the reconstructed data. tau_vals (np.ndarray):  Optical depth of the reconstructed data. verbose (bool):Boolean for Verbose (See keywords). w_km_vals (np.ndarray):  Window width as a function of radius (km). wtype (str):String for wtype (See keywords).