Changes are tracked in the file ChangeLog.md in the ldd-rings directory. The Body_Ident_Base class provides multiple attributes that can be used to identify a physical object (spacecraft, planet instrument, transmitter, system barycenter, etc.). At least one must be used. The Central_Body_Ident class uniquely identifies the body that is the central body associated with an observation (e.g., Saturn for Saturn system observations). This class provides the parameters used to generate a ring model which are specific to the central body. This class is meant to collect attributes that are intended for use as column headers within data products. These attributes have been defined in this dictionary in order to promote clarity and uniformity, and in turn this class is defined in order to give these attributes a logical home. Because it is not intended for this class to ever be used in a label, its maximum occurrences is set to zero. The Frame_Ident_Base class provides multiple attributes that can be used to identify a reference frame. At least one must be used. This class provides the general parameters used to generate a ring model. This class provides the normal mode parameters if one is present in the described ring. This class replaces the Radio_Occultation and Stellar_Occultation classes. It is used for all ring occultation profiles regardless of the occultation type. This class is required for all radio ring occultation calibration and geometry supplemental files. This class supports occultation data organized as a time series. The Reference_Frame_Ident class is a base class for identifying reference frames. These are frames in the NAIF sense, i.e., three orthogonal axes with a specified orientation, but without a fixed origin. This class provides the parameters describing reprojection geometry when the ring(s) is reprojected based on a fixed grid of coordinates (e.g., radius vs. longitude). This class contains reprojection grid resolution parameters This class identifies the specific ring to which the parameters given in the enclosing class apply. This class provides the parameters used to generate a ring model. This is an umbrella class for all of the classes and attributes in this dictionary. This class provides the orbital element values for a specific ring which were generated in a ring model. This class provides the parameters used to describe ring reprojection geometry. This class provides the parameters used to describe ring spectra or spectrograms. This class identifies the specific satellite to which the parameters given in the enclosing class apply. This class provides the parameters used to generate a ring model which are specific to a single satellite. The Uniformly_Sampled_Radius class provides attributes describing the spectral characteristics of an axis of an Array object or the rows of a Table object, in cases where the spectral sampling interval is regular and the sampling parameters are in wavelength units. The axis is identified either by using Local_Internal_Reference, or by using axis name. The latter may be simpler to use if this class applies to multiple Array objects. This class contains the three wavelength attributes This section contains the simpleTypes that provide more constraints than those at the base data type level. The simpleTypes defined here build on the base data types. This is another component of the common dictionary and therefore falls within the common namespace. along_track_timing_offset is a timing offset to the along track spacecraft position. It is the value that minimizes differences in radii of matching circular ring features observed on the ingress and egress sides of the occultation track. Optional in labels for radio occultation. average_unocculted_signal indicates the average of the signal in counts/second received from outside the rings or from nominally transparent regions of the rings after subtraction of background signal. Strongly recommended in labels of ring solar occultation observations if the value is constant. For solar occultations, if the value is not constant, strongly recommended to be used as a field in the data table. Not used for radio occultations. The axis_name attribute contains a string that matches the axis_name attribute in an axis_array class of an associated array object. background_signal indicates the anticipated signal (in counts, counts per second, or other specified units) received when no occulted source signal reaches the detector. This is the signal level that indicates an opaque ring. Strongly recommended in labels of ring occultation observations if the value is constant, or strongly recommended to be used as a field in the data table if the value is not constant. Normally not used for radio occultations. The corotating_flag is a yes-or-no flag that indicates whether or not a corotating frame is used. The ring longitude in the corotating frame. The zero longitude is defined as the prime meridian at the epoch specified by epoch_reprojection_basis_utc. Therefore, zero corotating longitude in the corotating frame at time t corresponds to an inertial longitude of (t-epoch)*corotation_rate. The corotation rate associated with the data. data_quality_index provides a more precise subjective assessment by the data provider of the quality of the observed/predicted ring occultation. data_quality_score indicates the overall quality of the data, based on a subjective evaluation by the data provider. Required in labels of ring occultation radial profiles. Normally not intended as a value for a table field. dsn_station_number identifies the receiving DSN station. Required in labels for radio occultations; not used for stellar occultations. Nillable in which case the nil_reason should be 'inapplicable'. earth_received_start_time_utc gives the UTC time corresponding to the earliest time for the data product at which telemetry or other photons were received on Earth. Optional for occultation data. earth_received_stop_time_utc gives the UTC time corresponding to the latest time for the data product at which telemetry or other photons were received on Earth. Optional for occultation data. earth_received_time provides the time at which telemetry or other photons were received on Earth. Intended to be used as a table field which is optional for stellar occultations, and is not used for radio occultation data (one of either observed_event_time or observed_event_tdb is used instead). earth_received_time is given in numeric seconds as an offset from the specified UTC reference time. The reference time is preferably the start of a day, and is required to be given in the label using the attribute reference_time_utc. This is equivalent to OBSERVED_EVENT_TIME for radio occultations. It is an optional table field for stellar occultations and is not used for radio occultations. When earth_received_time is used, the attribute reference_time_utc is required in the label. The eccentricity of the orbit of the body or ring identified in the enclosing class. The uncertainty in the value for the eccentricity of the orbit of the body or ring identified in the enclosing class. The emission_angle element provides a measure of the relationship between the instrument viewing position and the surface normal vector at the intercept point. Specifically, it is the angle, measured at the intercept point, between the local surface normal vector and a vector in the direction of the outgoing photon to the observing instrument. In the context of planetary rings, the local surface normal vector is always on the side of the ring plane illuminated by the light source. Thus, the emission_angle varies from 0 degrees when the spacecraft is viewing the illuminated side of the rings face-on, to 90 degrees when viewing the rings edge-on (that is, the spacecraft is in the ring plane), to 180 degrees when the spacecraft is viewing the unlit side of the rings face-on. The basis epoch for the corotating frame. Format is YYYY-MM-DDTHH:MM:SS.SSSZ and may be truncated. The corotating frame is defined so that zero corotating longitude is equal to zero inertial longitude defined at the epoch specified by epoch_reprojection_basis_utc. Thus, zero corotating longitude in the corotating frame at time t corresponds to an inertial longitude of (t-epoch)*corotation_rate. The epoch for the ring orbital elements given in this product. Format is YYYY-MM-DDTHH:MM:SS.SSSZ and may be truncated. The first_ring_radius attribute provides the value of the first increment along the radius axis of an array given in units of length. The root mean square residuals for the semimajor axis of the body or ring identified in the enclosing class. fractional_error_star_counts indicates the fractional error (1-sigma) in star counts used for square-well model fit. The frequency_band attribute provides the one or two letter identifier for the frequency band associated with radio occultation data. Required in labels for radio occultations; not used for stellar occultations. fresnel_scale is sqrt(lambda * D/2), where lambda is the central wavelength of the observation and D is the average distance between the observer and the occulting ring. This is an average value for the entire occultation and is a measure of the limit on the radial resolution of ring structure due to diffraction. Note that the actual overall resolution is affected as well by the projected diameter of the occulted star and the instrumental time constant, if any. The product of the Gravitational constant and the mass of the identified body. The reference radius for the gravitational harmonic coefficients of the body identified in the enclosing class. highest_detectable_normal_optical_depth gives the theoretical highest possible normal optical depth that can be detected in the observation based on the background signal and unocculted signal measurements. Optical depth is equal to -ln(T), where the transparency T is the ratio between received signal and transmitted signal. Normal optical depth is defined as the observed_optical_depth times the sine of observed_ring_elevation. highest_detectable_opacity indicates the rough value for the largest normal ring opacity that can be detected in the data at the resolution provided, incorporating both statistical effects and calibration uncertainties. Opacity is equal to 1-T, where the transparency T is the ratio between received signal and transmitted signal. -1.0 indicates the signal was too poor to allow the calculation of the value. Strongly recommended in labels of ring occultation observations. Not intended as a value for a table field. The incidence_angle element provides a measure of the lighting condition at the intercept point. Specifically, it is the angle, measured at the intercept point, between a vector in the direction of an incoming photon from the illumination source and the local surface normal vector. In the context of planetary rings, the local surface normal vector is always on the side of the ring plane illuminated by the light source. Thus, the incidence_angle varies from 0 degrees if the light source illuminates the rings face-on, to 90 degrees if the light source illuminates the rings edge-on. The inclination of the orbit of the body or ring identified in the enclosing class. The uncertainty in the value for the inclination of the orbit of the body or ring identified in the enclosing class. inertial_ring_longitude specifies the inertial longitude of a ring feature relative to the prime meridian. In planetary ring systems, the prime meridian is the ascending node of the planet's invariable plane on the Earth's mean equator of J2000. Longitudes are measured in the direction of orbital motion along the planet's invariable plane to the ring's ascending node, and thence along the ring plane. Values range from 0 to 360 in units of degrees. Note: The invariable plane of a planet is equivalent to its equatorial plane for every ringed planet except Neptune. Required to be the second field in ring occultation profiles. In labels, the min and max attributes are required. The J2 gravitational harmonic coefficient of the body identified in the enclosing class. The J4 gravitational harmonic coefficient of the body identified in the enclosing class. The J6 gravitational harmonic coefficient of the body identified in the enclosing class. The J8 gravitational harmonic coefficient of the body identified in the enclosing class. The last_ring_radius attribute provides the value of the last increment along the radius axis of an array given in units of length. light_source_incidence_angle is an angle measured from the local surface normal vector to the direction of a photon arriving from the light source. For rings, the normal vector is that on the same side of the rings as the light source, so values always range between 0 and 90 in units of degrees. For ring occultations, this value is always equal to 90 - | observed_ring_elevation | This will enable users to perform database searches based on the effective ring opening angle when they are not concerned about the distinction between northside and southside viewpoints. We have included the 'light source' prefix to the term so that this quantity is not confused with 'incidence angle', a term that is generally associated with sunlight rather than stars or radio transmitters. Required in the label if the value is constant for the observation. If the angle varies for the observation, the min and max attributes are required in the label. Optional as a field in the data table. longitudinal_resolution indicates the nominal longitudinal size of a single pixel. Note: this value may be either smaller or larger than that of radial_sampling_interval because a derived product can be over-sampled or under-sampled. Required in labels if the value is fixed. If the value varies, the corresponding mean and minimum and maximum attributes must be used in labels and longitudinal_resolution should be a table field. lowest_detectable_normal_optical_depth gives the theoretical lowest possible normal optical depth that can be detected in the observation based on the background signal and unocculted signal measurements. Optical depth is equal to -ln(T), where the transparency T is the ratio between received signal and transmitted signal. Normal optical depth is defined as the observed_optical_depth times the sine of observed_ring_elevation. lowest_detectable_opacity indicates the rough value for the smallest normal ring opacity that can be detected in the data at the resolution provided, incorporating both statistical effects and calibration uncertainties. Opacity is equal to 1-T, where the transparency T is the ratio between received signal and transmitted signal. -1.0 indicates the signal was too poor to allow the calculation of the value. Strongly recommended in labels of ring occultation observations. Not intended as a value for a table field. The maximum value in this product for ring longitude in the corotating frame. The zero longitude is defined as the prime meridian at the epoch specified by epoch_reprojection_basis_utc. Therefore, zero corotating longitude in the corotating frame at time t corresponds to an inertial longitude of (t-epoch)*corotation_rate. The maximum_emission_angle element provides the largest value during the observation for the emission angle at the target. The maximum_incidence_angle element provides the largest value during the observation for the incidence angle at the target. maximum_inertial_ring_longitude specifies one boundary for the ring longitude range in the data; normally the largest value. However, for ranges that cross the prime meridian, the maximum ring longitude will have a value less than the minimum ring longitude. Values range from 0 to 360 in units of degrees. Required in label files for ring occultation data. maximum_light_source_incidence_angle specifies the largest value for light_source_incidence_angle in the observation. Only used if the value is not constant over the observation. Values range from 0 to +90 in units of degrees. Not intended for use in the data file. maximum_longitudinal_resolution indicates the largest longitudinal size of a single pixel. Note: this value may be either smaller or larger than that of radial_sampling_interval because a derived product can be over-sampled or under-sampled. Required in labels if the value of longitudinal_resolution varies. Not intended to be used as a table field. maximum_observed_event_time gives the largest value for observed_event_time in the associated data file. It is given in numeric seconds as an offset from the specified UTC reference time. maximum_observed_event_time is optional in labels since the data file time interval end point values are given by the required start_date_time_utc and stop_date_time_utc attributes in the Time_Coordinates class. maximum_observed_ring_azimuth specifies the largest value for observed_ring_azimuth in the data file. Values range from 0 to 360 in units of degrees. Required in label files for ring occultation data. maximum_observed_ring_elevation specifies the largest value for observed_ring_elevation in the data file. Only used if the value is not constant over the observation. Values range from -90 to +90 in units of degrees. Not intended for use in the data file. The maximum_phase_angle element provides the largest value during the observation for the phase angle at the target. maximum_projected_sun_diameter provides the largest value of projected_sun_diameter in the observation. maximum_radial_resolution indicates the largest radial size of a single pixel. Note: this value may be either smaller or larger than that of radial_sampling_interval because a derived product can be over-sampled or under-sampled. Required in labels if the value of radial_resolution varies. Not intended to be used as a table field. maximum_radial_sampling_interval indicates the largest radial spacing between consecutive points in a ring profile. In practice, this may be somewhat smaller than the radial_resolution because a profile may be over-sampled. If the value of radial_sampling_interval varies, the minimum and maximum attributes are required in labels. Not intended to be used as a table field. maximum_reflectivity indicates the largest value of I/F within the data object. maximum_ring_intercept_resolution indicates the largest value for ring_intercept_resolution in the data product. maximum_ring_longitude_observed_minus_sub-solar specifies largest separation in ring longitude between the observation and the subsolar point. maximum_ring_radius indicates the largest ring radius value in the data table. Values are always positive. Required in label files for ring occultation data. maximum_sub_stellar_clock_angle specifies the largest value for sub_stellar_clock_angle in the data file. Values range from 0 to 360 in units of degrees. Optional label attribute for Cassini VIMS occultation data; not used for other occultation data. maximum_sub_stellar_ring_azimuth specifies the largest value for sub_stellar_ring_azimuth in the data file. Values range from 0 to 360 in units of degrees. Optional label attribute for Cassini UVIS occultation data; not used for other occultation data. maximum_wavelength is the largest wavelength used in the observation. Optional in labels. Used with minimum_wavelength when the observation is over a wavelength range. The mean_emission_angle element provides the mean value during the observation for the emission angle at the target. The mean_incidence_angle element provides the mean value during the observation for the incidence angle at the target. mean_longitudinal_resolution indicates the mean longitudinal size of a single pixel. Note: this value may be either smaller or larger than that of radial_sampling_interval because a derived product can be over-sampled or under-sampled. Required in labels if the value of longitudinal_resolution varies. Not intended to be used as a table field. mean_observed_ring_elevation specifies the mean value for observed_ring_elevation in the data file. The mean_phase_angle element provides the mean value during the observation for the phase angle at the target. mean_radial_resolution indicates the mean radial size of a single pixel. Note: this value may be either smaller or larger than that of radial_sampling_interval because a derived product can be over-sampled or under-sampled. Required in labels if the value of radial_resolution varies. Not intended to be used as a table field. The minimum value in this product for ring longitude in the corotating frame. The zero longitude is defined as the prime meridian at the epoch specified by epoch_reprojection_basis_utc. Therefore, zero corotating longitude in the corotating frame at time t corresponds to an inertial longitude of (t-epoch)*corotation_rate. The minimum_emission_angle attribute provides the smallest value during the observation for the emission angle at the target. The minimum_incidence_angle attribute provides the smallest value during the observation for the incidence angle at the target. minimum_inertial_ring_longitude specifies one boundary for the ring longitude range in the data; normally the smallest value. However, for ranges that cross the prime meridian, the minimum ring longitude will have a value greater than the maximum ring longitude. Values range from 0 to 360 in units of degrees. Required in label files for ring occultation data. minimum_light_source_incidence_angle specifies the smallest value for light_source_incidence_angle in the observation. Only used if the value is not constant over the observation. Values range from 0 to +90 in units of degrees. Not intended for use in the data file. minimum_longitudinal_resolution indicates the smallest longitudinal size of a single pixel. Note: this value may be either smaller or larger than that of radial_sampling_interval because a derived product can be over-sampled or under-sampled. Required in labels if the value of longitudinal_resolution varies. Not intended to be used as a table field. minimum_observed_event_time gives the smallest value for observed_event_time in the associated data file. It is given in numeric seconds as an offset from the specified UTC reference time. minimum_observed_event_time is optional in labels since the data file time interval end point values are given by the required start_date_time_utc and stop_date_time_utc attributes in the Time_Coordinates class. minimum_observed_ring_azimuth specifies the smallest value for observed_ring_azimuth in the data file. Values range from 0 to 360 in units of degrees. Required in label files for ring occultation data. minimum_observed_ring_elevation specifies the smallest value for observed_ring_elevation in the data file. Only used if the value is not constant over the observation. Values range from -90 to +90 in units of degrees. Not intended for use in the data file. The minimum_phase_angle attribute provides the smallest value during the observation for the phase angle at the target. minimum_projected_sun_diameter provides the smallest value of projected_sun_diameter in the observation. minimum_radial_resolution indicates the smallest radial size of a single pixel. Note: this value may be either smaller or larger than that of radial_sampling_interva because a derived product can be over-sampled or under-sampled. Required in labels if the value of radial_resolution varies. Not intended to be used as a table field. minimum_radial_sampling_interval indicates the smallest radial spacing between consecutive points in a ring profile. In practice, this may be somewhat smaller than the radial_resolution because a profile may be over-sampled. If the value of radial_sampling_interval varies, the minimum and maximum attributes are required in labels. Not intended to be used as a table field. minimum_reflectivity indicates the smallest value of I/F within the data object. minimum_ring_intercept_resolution indicates the smallest value for ring_intercept_resolution in the data product. minimum_ring_longitude_observed_minus_subsolar specifies smallest separation in ring longitude between the observation and the sub-solar point. minimum_ring_radius indicates the smallest ring radius value in the data table. Values are always positive. Required in label files for ring occultation data. minimum_sub_stellar_clock_angle specifies the smallest value for sub_stellar_clock_angle in the data file. Values range from 0 to 360 in units of degrees. Optional label attribute for Cassini VIMS occultation data; not used for other occultation data. minimum_sub_stellar_ring_azimuth specifies the smallest value for sub_stellar_ring_azimuth in the data file. Values range from 0 to 360 in units of degrees. Optional label attribute for Cassini UVIS occultation data; not used for other occultation data. minimum_wavelength is the smallest wavelength used in the observation. Optional in labels. Used with maximum_wavelength when the observation is over a wavelength range. The regression rate of the node of the orbit of the body or ring identified in the enclosing class. A flag indicating the constraints used to determine the node regression rate of the orbit of the body or ring identified in the enclosing class. The uncertainty in the value for the periapse precession rate of the orbit of the body or ring identified in the enclosing class. The longitude of the ascending node of the orbit of the body or ring identified in the enclosing class. The uncertainty in the value for the longitude of the ascending node of the orbit of the body or ring identified in the enclosing class. The amplitude of the normal mode for the ring identified in the enclosing class. A value of -9.99X10^99 indicates there is no normal mode for the ring. The uncertainty in the value for the normal mode of the ring identified in the enclosing class. A value of -9.99X10^99 indicates there is no normal mode for the ring. The pattern speed of the normal mode in the ring identified in the enclosing class. A value of -9.99X10^99 indicates there is no normal mode for the ring. The uncertainty in the pattern speed of the normal mode in the ring identified in the enclosing class. A value of -9.99X10^99 indicates there is no normal mode for the ring. The phase of the normal mode at epoch specified by epoch_ring_fit_utc for the ring identified in the enclosing class. A value of -9.99X10^99 indicates there is no normal mode for the ring. The uncertainty in the value for the normal_mode_phase of the ring identified in the enclosing class. A value of -9.99X10^99 indicates there is no normal mode for the ring. The wave number of the normal mode in the ring identified in the enclosing class. A value of -999 indicates there is no normal mode for the ring. Normal optical depth is defined as the observed_optical_depth times the sine of observed_ring_elevation. Optical depth is equal to -ln(T), where the transparency T is the ratio of incident to transmitted radiant power, corrected for background_signal. Typically negative values are used to indicate the signal was too poor to allow the calculation of the value. Number of fitted data points for the orbit of the body or ring identified in the enclosing class. observed_event_start_tdb indicates the value for earliest time in the described data, and is given in elapsed seconds since the J2000 epoch. Optional in labels; not intended for use as a table field. observed_event_start_time_utc indicates the UTC value for earliest time in the described data. It is part of a start/stop pair. If one of observed_event_start_time_utc and observed_event_stop_time_utc is used, both must be used. observed_event_stop_tdb indicates the value for latest time in the described data, and is given in elapsed seconds since the J2000 epoch. Optional in labels; not intended for use as a table field. observed_event_stop_time_utc indicates the UTC value for latest time in the described data. It is part of a start/stop pair. If one of observed_event_start_time_utc and observed_event_stop_time_utc is used, both must be used. observed_event_tdb indicates the instant at which photons were received at the instrument. It is represented in the 'Barycentric Dynamical Time' system, as a number of elapsed seconds since the J2000 epoch. This is consistent with the definition of 'ephemeris time' as used in the SPICE toolkit. In a label the corresponding values are given by the optional start_observed_event_tdb and stop_observed_event_tdb attributes. At least one of either observed_event_time or observed_event_tdb, must be a table field for occultation data. Both may be used. observed_event_time is equivalent to spacecraft_event_time for spacecraft data and to earth_received_time for Earth-based data. It is always the photon arrival time, so in this regard we treat typical spacecraft radio occultation data as Earth-based, referring to the time at the DSN receiving station. For an uplink radio occultation, this is the spacecraft event time. observed_event_time indicates the instant at which photons were received at the instrument. As a field in an occultation profile table, it is given in numeric seconds as an offset from the specified UTC reference time. The reference time is preferably the start of a day. In a label the corresponding time interval end point values are given by the required start_date_time_utc and stop_date_time_utc attributes in the Time_Coordinates class. At least one of either observed_event_time or observed_event_tdb, must be a table field for occultation data. Both may be used. observed_event_time is equivalent to spacecraft_event_time for spacecraft data and to earth_received_time for Earth-based data. It is always the photon arrival time, so in this regard we treat typical spacecraft radio occultation data as Earth-based, referring to the time at the DSN receiving station. For an uplink radio occultation, this is the spacecraft event time. Note: For occultation data, PDS prefers year-month-day format for dates rather than year plus day-of-year format. However, either format is permitted. This attribute is intended to be used as a column in a table. observed_event_time_utc indicates the UTC time corresponding to the instant at which photons were received at the instrument. In a label the corresponding values may be given by the optional start_observed_event_utc and stop_observed_event_utc attributes (or the corresponding values using Barycentric Dynamical Time, _tdb). At least one of either observed_event_time_utc or observed_event_tdb, must be a table field for occultation data. Both may be used. observed_event_time is equivalent to spacecraft_event_time for spacecraft data and to earth_received_time for Earth-based data. It is always the photon arrival time, so in this regard we treat typical spacecraft radio occultation data as Earth-based, referring to the time at the DSN receiving station. For an uplink radio occultation, this is the spacecraft event time. Optical depth is equal to -ln(T), where the transparency T is the ratio of incident to transmitted radiant power, corrected for background_signal. Typically negative values are used to indicate the signal was too poor to allow the calculation of the value. observed_ring_azimuth is an angle measured at a point in the ring plane, starting from the direction of a photon heading to the observer, and ending at the direction of a local radial vector. This angle is projected into the ring plane and measured in the prograde direction. Note that, as seen from the observer, it equals 90 degrees along the right ansa and 270 degrees along the left ansa. Values range from 0 to 360 in units of degrees. Required to be the third field in ring occultation profiles. In labels, the min and max attributes are required. observed_ring_elevation is an angle measured at a point in the ring plane, starting from the ring plane to the direction of a photon heading to the observer. This angle is positive on the side of the ring plane defined by positive angular momentum, and negative on the opposite side. Values range from -90 to +90 in units of degrees. This angle is constant for stellar occultations, but may vary significantly during radio occultations. Note: The direction of positive angular momentum points toward the IAU-defined north side of the ring plane for Jupiter, Saturn and Neptune, but IAU-defined south side of the ring plane for Uranus. Required in the label if the value is constant for the observation. If the angle varies for the observation, the min and max attributes are required in the label, and observed_ring_elevation is strongly recommended as a field in the data table. The above definition of observed_ring_elevation is equivalent to the most common usage of the term 'ring open angle', B. occultation_direction indicates the direction of an occultation track as observed. Permitted values are 'ingress', 'egress', 'both', and 'multiple'. This attribute refers to the observed occultation track overall, not to the subset that might appear in a product such as a derived ring profile. For example, if an observed occultation includes both ingress and egress portions, each of those two portions will usually be represented by its own derived ring profile which will have occultation_direction set to Both and ring_profile_direction set to Ingress or Egress as the case may be. Required in labels of ring occultation observations. Not intended as a value for a table field. occultation_type distinguishes between three types of occultation experiments: Stellar, Solar, or Radio. Stellar occultations involve observing a star as a targeted ring or body passes in front, as seen from either a spacecraft or Earth-based observatory. Solar occultations are similar to stellar occultations except that the Sun is used in place of a star. Radio occultations typically involve observing the continuous-wave radio transmissions from a spacecraft as it passes behind the target as seen from a radio telescope on Earth or another spacecraft. Required in labels of occultation observations. Normally not intended as a value for a table field. orbit_number if present is the value assigned by the mission for the orbit number associated with the observation. Optional in labels of occultation observations and may be used multiple times. The longitude of periapse for the orbit of the body or ring identified in the enclosing class. The uncertainty in the value for the longitude of periapse for the orbit of the body or ring identified in the enclosing class. The precession rate of the periapse of the orbit of the body or ring identified in the enclosing class. A flag indicating the constraints used to determine the periapse precession rate of the orbit of the body or ring identified in the enclosing class. The uncertainty in the value for the periapse precession rate of the orbit of the body or ring identified in the enclosing class. The phase_angle element provides a measure of the relationship between the instrument viewing position and incident illumination (such as solar light). Specifically, it is the angle, measured at the intercept point, between a vector in the direction of an incoming photon from the illumination source and a vector in the direction of an outgoing photon to the observing instrument. If illumination is from behind the instrument, phase_angle will be small. The planetary_occultation_flag is a yes-or-no flag that indicates whether a occultation track also intersects the planet. Required in labels of ring occultation observations. Normally not intended as a value for a table field. The declination (Dec) of the pole of the body identified in the enclosing class, given in angular measurements. The uncertainty of the declination (Dec) of the pole of the body identified in the enclosing class, given in angular measurements. The right ascension (RA) of the pole of the body identified in the enclosing class, given in angular measurements. The uncertainty of the right ascension (RA) of the pole of the body identified in the enclosing class, given in angular measurements. projected_star_diameter provides the projected angular diameter of the occulted star, from observer to occulting object. projected_sun_diameter provides the diameter of the sun projected onto the ring plane radius based on the line of sight from the observer to the ring plane at the start of the integration assuming the sun subtends a circular disk with an angular size based on the distance of the central body from the sun. radial_resolution indicates the nominal radial size of a single pixel. Note: this value may be either smaller or larger than that of radial_sampling_interval because a derived product can be over-sampled or under-sampled. Required in labels if the value is fixed. If the value varies, the corresponding mean and minimum and maximum attributes must be used in labels and radial_resolution should be a table field. radial_sampling_interval indicates the radial spacing between consecutive points in a ring profile. In practice, this may be somewhat smaller than the radial_resolution because a profile may be over-sampled. Required in labels if the value is fixed. If the value varies, the corresponding minimum and and maximum attributes must be used instead. Not intended to be used as a table field. reference_time_utc provides a date and time in UTC format. Given in a label when time values in a table are given as elapsed seconds offset from a reference time. Unless there are compelling reasons to do otherwise, reference_time_utc should correspond to the start of a day. Required anytime a table field is given relative to a specific date and time other than when Barycentric Dynamical Time is used (e.g., observed_event_tdb). reflectivity indicates I/F, a dimensionless standardized measure of reflectivity that is unity for a Lambertian surface viewed at normal incidence. reprojection_grid_longitudinal_sampling_interval indicates the longitudinal size of a single pixel in a reprojected image (a derived product). In practice, this may be either larger or smaller than the longitudinal_resolution because a profile or reprojection may be over-sampled or under-sampled. Required in labels for reprojected images, which are expected to have a fixed grid and thus a constant value for this attribute. reprojection_grid_radial_sampling_interval indicates the radial size of a single pixel in a reprojected image (a derived product). In practice, this may be either larger or smaller than the radial_resolution because a profile or reprojection may be over-sampled or under-sampled. Required in labels for reprojected images, which are expected to have a fixed grid and thus a constant value for this attribute. reprojection_plane identifies the plane onto which the reprojection is based. Possible values for the Saturn ring system are 'Equator', 'Laplace', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'Phoebe'. For the Uranus ring system values are 'Equator', 'Laplace', 'Six', 'Five', 'Four', 'Alpha', 'Beta', 'Eta', 'Gamma', 'Delta', 'Lambda','Epsilon',Nu, Mu. Required in labels of ring reprojection products. The ring_detected attribute is a yes-or-no flag that indicates whether a specific ring has been detected. Typically used in radial profiles of a single ring. ring_event_start_tdb indicates the value for earliest time in the described data, and is given in ring_event_tdb format. Optional in labels; not intended for use as a table field. ring_event_start_time_utc gives the UTC time corresponding to the earliest time given by ring_event_time or ring_event_tdb in the data table. ring_event_start_time_utc is required for all ring occultation data. ring_event_stop_tdb indicates the value for latest time in the described data, and is given in ring_event_tdb format. Optional in labels; not intended for use as a table field. ring_event_stop_time_utc gives the UTC time corresponding to the latest time given by ring_event_time or ring_event_tdb in the data table. ring_event_stop_time_utc is required for all ring occultation data. ring_event_tdb indicates the instant at which photons associated with a particular ring observation left the ring plane. This time is earlier than the associated observed_event_tbd by an amount equal to the light travel time. ring_event_tdb is represented in the 'Barycentric Dynamical Time' system, as a number of elapsed seconds since the J2000 epoch. This is consistent with the definition of 'ephemeris time' as used in the SPICE toolkit. One of ring_event_time or ring_event_tdb is a required table field for all ring occultations. Both may be used. ring_event_time indicates the instant at which photons associated with a particular ring observation intercepted the ring plane. This time is earlier than the associated observed_event_time by an amount equal to the light travel time. ring_event_time is a required table field for ring occultation data. The time is given in numeric seconds as an offset from the specified UTC reference time. The reference time is preferably the start of a day, and is required to be given in the label using the attribute reference_time_utc. One of ring_event_time or ring_event_tdb is a required table field for all ring occultations. One of ring_event_time or ring_event_tdb is a required table field for all ring occultations. Both may be used. If ring_event_time is used, the attribute reference_time_utc is required in the label. ring_intercept_resolution is the size of edge of a pixel at the distance of the ring intercept point. If the pixel shape is not square, it is defined by the smaller of the two edges. Unlike the quantity ‘radial resolution’, these values are not projected into the ring plane. ring_longitude_observed_minus_subsolar provides the difference between the inertial ring longitude of the observation and inertial ring longitude of the sub-solar point. ring_plane indicates the plane upon which parameters such as ring_radius are based. Possible values for the Saturn ring system are 'Equator', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'Phoebe'. For the Uranus ring system values are 'Equator', 'six', 'five', 'four', 'alpha', 'beta', 'eta', 'gamma', 'delta', 'lambda','epsilon',nu, mu. An additional value, 'individual' is also defined. Note that the named rings of Saturn are in title case while those of Uranus are lower case, consistent with normal usage by the community. Required in labels of ring occultation observations. ring_profile_direction indicates the radial direction of a ring occultation within a particular data product. Possible values are 'Ingress', 'Egress', or 'Multiple'. This attribute refers to the subset of an occultation that might appear in a product such as a derived ring profile, not to the observed occultation track overall. For example, if an observed occultation includes both ingress and egress portions, each of those two portions will usually be represented by its own derived ring profile which will have occultation_direction set to Both and ring_profile_direction set to Ingress or Egress as the case may be. Required in labels of ring occultation observations. Not intended as a value for a table field. ring_radius indicates a radial location within a planetary ring system. Radii are measured from the center of mass of the planet along the nominal ring plane. Values are always positive. Required to be the first field in ring occultation profiles. Data are always organized with ring radius increasing. In labels, the min and max attributes are required. The sampling_base attribute indicates the numeric base of the associated logarithmic or exponential sampling interval. The sampling_interval_length attribute provides the spacing of points, in units of length, at which data are sampled and at which a value for an instrument or data parameter is available. This sampling interval can be either the original (raw) sampling or the result of some resampling process. The sampling_scale attribute indicates the type of scale that applies to the sample interval increments. It must have a value of either Linear, Logarithmic or Exponential. sclk_start_time is the value of the spacecraft clock corresponding to the start_date_time given in the label. sclk_stop_time is the value of the spacecraft clock corresponding to the stop_date_time given in the label. The semimajor axis of the orbit of the body or ring identified in the enclosing class. The uncertainty in the value for the semimajor axis of the orbit of the body or ring identified in the enclosing class. sigma_projected_star_diameter indicates the uncertainty (1-sigma) in the projected_star_diameter. sigma_projected_sun_diameter indicates the Standard deviation (1-sigma) of projected_sun_diameter in the observation. sigma_time_constant indicates the uncertainty in the time_constant. See Eq. 9 Elliot et al. (1984) Astron. J. 1587-1603. If this attribute is used then the attribute time_constant also must be present. spacecraft_event_start_time_utc gives the UTC time corresponding to the earliest time given by spacecraft_event_time in the data table. However, while spacecraft_event_time is given as seconds offset from a reference time, spacecraft_event_start_time_utc is given as a UTC date time. Required in the label for radio occultation data. Not used for stellar occultations. spacecraft_event_stop_time_utc gives the UTC time corresponding to the latest time given by spacecraft_event_time in the data table. However, while spacecraft_event_time is given as seconds offset from a reference time, spacecraft_event_stop_time_utc is given as a UTC date time. Required in the label for radio occultation data. Not used for stellar occultations. spacecraft_event_time indicates the instant at which an event occurred at the spacecraft, e.g., the arrival or departure of a photon. Required table field for radio occultation data, but not used in stellar occultation data. The time is given in numeric seconds as an offset from the specified UTC reference time. The reference time is preferably the start of a day, and is required to be given in the label using the attribute reference_time_utc. Additionally, in radio occultation labels the corresponding time interval end point values are given by the required start_spacecraft_event_time_utc and stop_spacecraft_event_time_utc attributes. star_name provides the identifying name of star, including the catalog name if necessary. Examples include 'sigma Sgr' and 'SAO 123456' (for star number 123456 in the Smithsonian Astrophysical Observatory catalog). Use 'Sun' for solar occultations. Required in labels for stellar and solar occultations. Not used for radio occultations. stellar_signal_level indicates the anticipated signal from an un-occulted star, in the absence of any background signal. This is the signal level that defines the difference between a transparent ring and an opaque ring. Strongly recommended in labels of ring stellar occultation observations if the value is constant. For stellar occultations, if the value is not constant, strongly recommended to be used as a field in the data table. Not used for radio occultations. sub_stellar_clock_angle is an angle measured at a point in the ring plane, from the direction toward a star to the local radial direction. This angle is projected into the ring plane and measured in the clockwise (retrograde) direction. Equivalently, this is the prograde angle from the local radial direction to the direction toward the star. For stellar occultation data, this angle is equal to (180 - OBSERVED_RING_AZIMUTH) mod 360. It is available only for backward compatibility with previously published Cassini VIMS occultation data analysis; observed_ring_azimuth is the preferred quantity for archiving. sub_stellar_clock_angle is an optional data table field for Cassini VIMS occultation data; not recommended for other occultation data. In a label, the min and max variation attributes are optional for Cassini VIMS occultation data; not recommended for other occultation data. sub_stellar_ring_azimuth is an angle measured at a point in the ring plane, starting from the direction of a photon arriving from a star, and ending at the direction of a local radial vector. This angle is projected into the ring plane and measured in the prograde direction. Values range from 0 to 360 in units of degrees. For stellar occultation data, this angle is equal to (observed_ring_azimuth + 180) mod 360. It is available only for backward compatibility with previously published Cassini UVIS occultation data analysis; observed_ring_azimuth is the preferred quantity for archiving. sub_stellar_ring_azimuth is an optional data table field for Cassini UVIS occultation data; not recommended for other occultation data. In a label, the min and max variation attributes are optional for Cassini UVIS occultation data; not recommended for other occultation data. time_constant indicates the instrumental time constant of the detector. See Eq. 9 Elliot et al. (1984) Astron. J. 1587-1603. If this attribute is used then the attribute time_constant_type also must be present. time_constant_type distinguishes between three types of instrumental time constant assumed in a square-well model. This attribute is required if the time_constant attribute is present. time_series_direction indicates the direction the occultation proceeds through the target within a particular data product. Possible values are 'Ingress', 'Egress', 'Both' or 'Multiple'. The value 'Multiple' is used where the occultation track is not monotonic over relatively short time scales. Generally only used for some Hubble-based occultations. May be appropriate for extremely long duration occultations of a high proper motion star (e.g., u36). Not intended as a value for a table field. wavelength of the observation. Optional in labels. If the observation is over a wavelength range, use the corresponding minimum and maximum attributes instead.