Measurement Types and Statistics

The MeasurementStatistics property comprises a list of measurement models with associated defining parameters supported by this object. Measurements of the types contained in this list can be generated during simulations and processed during estimation.

Measurement Types

Depending on the object in question, the following measurement types are available:

Measurement Types
Type Description
1W Bistatic Range Ranging using links to two separate facilities:
  1. Uplink - from Ground Station to Satellite (uses Relay transponder on satellite if the receive station is configured for Transponder tracking)
  2. Downlink to Bistatic (Receive) Ground Station

The statistics for this measurement should be added to the bistatic receiving ground station.

NOTE: If the receive ground station is configured for transponder tracking (using the Ranging/Method attribute) then a Relay transponder on the satellite is used, if it exists. Both the transponder delay and the locations of the associated antennas are used in the modeling of the measurement in this case.

2L CA Pseudo-range

Two legged coarse acquisition pseudo-range. For a ground based GPS receiver, the range from the ground based receiver to a SV through a transponder (relay type) on the user spacecraft is the modeled measurement. Otherwise, the range from a GPS SV through a transponder (relay type) on the user spacecraft to a ground based receiver is the modeled measurement.

Receiver clock phase error and clock frequency error (group receiver clock) along with the transponder delay at the user spacecraft are modeled and estimated. Tropospheric effects are modeled at the ground receiver location.

3L Doppler 3L Doppler is a measurement type used by the TDRS satellite system. It is also called "Return Link Doppler", and there are 3 legs to this measurement. One leg is a pilot tone, transmitted from the ground to the TDRS satellite and used by the TDRS satellite in handling the Doppler signal. The Doppler signal is generated by the user satellite (Hubble, TOPEX, etc), and transmitted through the TDRS satellite to the ground station. The measurement is in units of Hz, and is the frequency difference between the received signal and a reference generated on the ground.
4L Range TDRSS Range model: A four legged Range measurement measuring total time for signal to travel the following four links:
  1. Uplink - from Ground Station to a Relay Satellite
  2. Forward - from the Relay Satellite to a User Satellite
  3. Return - from the User Satellite back to the Relay Satellite
  4. Downlink - from the Relay Satellite back to the Ground Station
5L Doppler TDRSS Doppler model: a phase count measuring the Doppler shift caused by the relative motion of the Relay and User satellite to each other and to the ground station. This is a 5 legged model where 4 legs are as defined in the 4L Range model (above) and the fifth leg is an uplink pilot tone leg from the ground station to the Relay Satellite arriving at the Relay satellite at the downlink time.
Accel

Linear acceleration measurement reported by a single accelerometer sensor. The measurement is indicative of sensed acceleration in the direction specified by the referenced accelerometer sensor. Sensed accelerations include all non-conservative accelerations such as atmospheric drag, solar radiation pressure and thrusting. Additional accelerations (gravity gradient and centripetal) are sensed if the sensor is displaced relative to the center of mass of the satellite.

The statistics for this measurement should be added to the MeasurementStatistics set for the associated AccelerometerSensor object.

Azimuth
Elevation

A pair of ground station angle measurements which together can be used to determine a line of sight pointing vector from the ground station to the satellite. Azimuth is a horizontal angle measured in the local tangent plane clockwise (eastward) from the North. Elevation is a vertical angle measured from the local horizon, positive up to the satellite. Azimuth and Elevation can be modeled with or without light time delay. If light time delay is included then the modeling assumes one way measurements with the measurement time tag as the ground reception time.

Aberration corrections are applied based on the facility AberrationCorrection setting when LightTimeDelay setting is set to true.

BRTS Doppler Same as 5L Doppler (above) except that a ground (BRTS) transponder replaces the User satellite.
BRTS Range Same as 4L Range (above) except that a ground (BRTS) transponder replaces the User satellite.
CA DD Pseudo-range Course acquisition double difference pseudo-range: The modeled measurement is the difference of two distinct single differenced C/A code range measurements. These measurements are free from the effects of receiver and GPS satellite clock errors. However, ionosphere has not been eliminated. Unlike single differenced measurements, double differenced measurements must be constructed outside of ODTK.
CA Nav Sol Navigation solutions generated from coarse acquisition pseudo-range. X, Y and Z components share the same statistical parameters. Solution specific (X, Y, Z get the same or independent values) white noise sigmas may be specified via the navsol format and enabled by setting the scenario-level attribute, EmbeddedWNSigmas. Use, to true. Alternatively, the input white noise sigma can be automatically scaled based on Dilution Of Precision (DOP) if the associated GPS satellite ids are specified in the navsol formatted data. The use of DOP based deweighting is controlled by the WhiteNoiseDeweighting setting in the measurement statistics.

NOTE: If DOP based deweighting is used AND custom sigma values are read in from a navsol formatted data file, the custom sigma values will be scaled by the DOP.

CA Pseudo-range Coarse acquisition pseudo-range: CA L1 pseudo-range is the input measurement. The range between the GNSS space vehicle (SV) and the user's receiver is the modeled measurement.
CA SD Pseudo-range Coarse acquisition single difference pseudo-range: The modeled measurement is the difference of two distinct SV C/A code range measurements. Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. If CA SD measurements have been requested (by adding CA SD Pseudo-range to the GPS receiver MeasurementStatistics and to the MeasTypes on the satellite), then CA measurements are converted to CA SD measurements, and no pure CA measurements are processed.
ClockNoiseScaling Scale factor for deweighting of GNSS phase measurements to account for the unknown variation of GNSS satellite and GNSS receiver clocks over the count interval for the phase measurement. Set the value to 1.0 to deweight measurements based on the total process noise for all relevant clocks. Set the value to 0.0 to ignore variations in clock behavior over the count interval. This setting only has an effect when the GNSS receiver and/or the GNSS satellite clocks are being estimated and is usually only used for simulations where the distinction between clock behavior and white noise is known. For SD phase measurements, deweighting is only computed based on the GNSS satellite clocks since the effects of the GNSS receiver clocks are differenced out. No additional deweighting is performed for DD phase measurements.

NOTE: When simulating L1 Phase, L2 Phase, and deviating clocks, then ClockNoiseScaling should be = 1.

Delta Declination A single differenced declination measurement. If Delta Declination measurements are requested, by adding Delta Declination to the Facility MeasurementStatistics, then observation sets containing more than one declination measurement will be converted into a new observation set containing one declination measurement from the original set with other declination measurements replaced by corresponding delta declination measurements which are referenced to the remaining original. ODTK cannot directly simulate Delta Declination measurements. This measurement type is useful in estimating the orbits of closely spaced objects.
Delta Right Ascension A single differenced right ascension measurement. If Delta Right Ascension measurements are requested, by adding Delta Right Ascension to the Facility MeasurementStatistics, then observation sets containing more than one right ascension measurement will be converted into a new observation set containing one right ascension measurement from the original set with other right ascension measurements replaced by corresponding delta right ascension measurements which are referenced to the remaining original. ODTK cannot directly simulate Delta Right Ascension measurements. This measurement type is useful in estimating the orbits of closely spaced objects.
Delta SB Dec A single differenced space based declination measurement. If Delta SB Dec measurements are requested, by adding Delta SB Dec to the Facility MeasurementStatistics, then observation sets containing more than one space based declination measurement will be converted into a new observation set containing one space based declination measurement from the original set with other space based declination measurements replaced by corresponding space based delta declination measurements which are referenced to the remaining original. ODTK cannot directly simulate Delta SB Dec measurements. This measurement type is useful in estimating the orbits of closely spaced objects.
Delta SB RA A single differenced space based right ascension measurement. If Delta SB RA measurements are requested, by adding Delta SB RA to the Facility MeasurementStatistics, then observation sets containing more than one space based right ascension measurement will be converted into a new observation set containing one space based right ascension measurement from the original set with other space based right ascension measurements replaced by corresponding delta right ascension measurements which are referenced to the remaining original. ODTK cannot directly simulate Delta SB RA measurements. This measurement type is useful in estimating the orbits of closely spaced objects.
Differenced One Way Doppler (DOWD) Constructed by differencing two simultaneous one way TDRS Doppler measurements (3L Doppler). Typically used in early orbit operations, prior to availability of the primary tracking system, for user satellites which do not have TDRS transponders or ultra-stable oscillators. The differencing operation removes the effects of the user satellite clock.
DirCos East and North

A pair of ground station direction cosine measurements. The East direction cosine is measured as the projection of the relative position unit vector onto the local antenna East direction. The North direction cosine is measured as the projection of the relative position unit vector onto the local antenna North direction. The local antenna reference frame directions differ from the standard topocentric East and North direction by a rotation about the zenith direction given by the DirectionCosineAzimuthOffset which specifies the azimuth of the antenna local North direction. The DirectionCosineAzimuthOffset may be specified when the AntennaMountType is set to DirCos_EW. Direction cosine measurements can be modeled with or without light time delay. If light time delay is included then the modeling assumes one way measurements with the measurement time tag as the ground reception time.

Aberration corrections are applied based on the facility AberrationCorrection setting when LightTimeDelay setting is set to true.

Direction cosine measurements may be read in directly from the tracking data or may be constructed from input azimuth and elevation measurements. The construction from azimuth and elevation will occur if: the direction cosine measurement types are included in the measurement statistics and direction cosine measurements are included in the MeasTypes list of the estimation process.

DF DD Phase Double-difference (dual-frequency) phase count: The modeled measurement is the difference of two single difference dual frequency phase-count measurements. These measurements are free from the effects of the ionosphere and receiver and GPS satellite clock errors. Unlike single differenced measurements, double differenced measurements must be constructed outside of ODTK.
DF DD Pseudo-range A double differenced dual frequency pseudo-range. The modeled measurement is the difference of two distinct single differenced DF code range measurements. These measurements are free from the effects of the ionosphere and receiver and GPS satellite clock errors. Unlike single differenced measurements, double differenced measurements must be constructed outside of ODTK.
DF Nav Sol Navigation solutions generated from dual frequency pseudo-range. X, Y and Z components share the same statistical parameters. Solution specific (X, Y, Z get the same or independent values) white noise sigmas may be specified via the navsol format and enabled by setting the scenario-level attribute, EmbeddedWNSigmas.Use, to true. Alternatively, the input white noise sigma can be automatically scaled based on Dilution Of Precision (DOP) if the associated GPS satellite ids are specified in the navsol formatted data. The use of DOP based deweighting is controlled by the WhiteNoiseDeweighting setting in the measurement statistics.

NOTE: If DOP based deweighting is used AND custom sigma values are read in from a navsol formatted data file, the custom sigma values will be scaled by the DOP.

DF Phase Computed by mathematically combining the L1 and L2 Phase measurements to produce a measurement that is independent of the first order effects of the ionosphere. If the user selects DF Phase measurements, L1 and L2 Phase measurements are converted to DF Phase measurements, and no L1 or L2 Phase measurements are processed.
DF Phase Range Dual frequency phase measurements modeled as range measurements with unknown initial bias. Processing of this type of measurements requires the addition of states for each receiver/GPS satellite combination. These measurements are free from the effects of the ionosphere.
DF Pseudo-range Computed by mathematically combining the P1 and P2 measurements to produce a measurement that is independent of the first order effects of the ionosphere. If the user selects DF measurements, P1 and P2 measurements are converted to DF measurements, and no P1 or P2 measurements are processed.
DF SD Phase A singly differenced dual frequency phase-count. This means that the DF Phase is computed for two satellites that are being simultaneously tracked and that these two DF measurements are then differenced. These types of measurements are free from the effects of the ionosphere and the receiver clock bias.
DF SD Pseudo-range A singly differenced dual frequency pseudo-range. This means that the DF pseudo-range is computed for two satellites that are being simultaneously tracked and that these two DF measurements are then differenced. These types of measurements are free from the effects of the ionosphere and the receiver clock bias.
Doppler A phase count measuring the change in frequency of a signal (Doppler shift) caused by the relative motion of the ground station and the satellite. An option is available to allow this measurement to be modeled as instantaneous range-rate.
DSN Seq Rng Deep Space Network Sequential Range. The sequential range measurement is an ambiguous two way range measurement where the length of the ranging code is provided with the observation. DSN Sequential Range measurements are always modeled in the solar system barycentric reference frame.
DSN PN Rng Deep Space Network Pseudo Noise Range. The pseudo noise (PN) measurement is an ambiguous two way range measurement where the length of the ranging code is provided with the observation.
DSN Doppler Deep Space Network Doppler. The DSN Doppler measurement is a coherent two way measurement of the number of carrier cycles received at the DSN downlink station over a count interval specified with the observation. The transmitted frequency from the uplink station can either be constant or ramped. The frequency (ramp) schedule for transmitting ground stations is provided in the tracking data file. The time tag of this measurement is in the center of the count interval. The uplink and downlink stations are the same.
DSN 3W Doppler Deep Space Network Three Way Doppler. Similar to the DSN Doppler measurement except that the uplink and downlink stations are different.
DSN TCP Deep Space Network Total Count Phase. The DSN Total Count Phase measurement is a coherent two way measurement of the number of carrier cycles received at the DSN downlink station since an epoch specified with the observation. The transmitted frequency from the uplink station can either be constant or ramped. The frequency (ramp) schedule for transmitting ground stations is provided in the tracking data file. The time tag of this measurement is at the end of the count interval. The uplink and downlink stations are the same.
DSN 3W TCP Deep Space Network Three Way Total Count Phase. Similar to the DSN Total Count Phase measurement except that the uplink and downlink stations are different.
Eph Pos

Used to process ephemeris position components as measurements.

The statistics for this measurement should be added to the associated satellite object. Position X, Y, Z share the same statistical parameters. In addition this measurement must be included as a choice in the measurement type list in the associated satellite object if it is to be processed.

Eph Vel

Used to process ephemeris velocity components as measurements.

The statistics for this measurement should be added to the associated satellite object. Velocity X, Y, Z share the same statistical parameters. In addition this measurement must be included as a choice in the measurement type list in the associated satellite object if it is to be processed. Processing "Eph Vel" measurements may used together with or separately form processing "Eph Pos" measurements.

Face Horizontal And Face Vertical

A pair of angle measurements pertaining to Phased Array radars. The Face Vertical angle measures the angle down from the radar "face" normal. The Face Horizontal angle is measured in the local radar "face" plane clockwise from the local x-axis. The local frame has the z-axis aligned with face normal. The orientation of the local frame is derived from the two Facility input properties "BoresightAzimuth" and "BoresightElevation". The orientation is consistent with the STK Azimuth-Elevation Orientation Method, About Boresight Rotate option. Refer to the {BoresightAzimuth, BoresightElevation} properties for a further description of the local frame orientation.

Face angle measurements can be modeled with or without light time delay. If light time delay is included then the modeling assumes one way measurements with the measurement time tag as the ground reception time.

Aberration corrections are applied based on the facility AberrationCorrection setting when LightTimeDelay setting is set to true.

Face angle measurements may be read in directly from the tracking data or may be constructed from input azimuth and elevation measurements. The construction from azimuth and elevation will occur if the face angle measurement types are included in the measurement statistics and face angle measurements are included in the MeasTypes list of the estimation process.

FDOA Frequency Difference of Arrival measurement. A signal travels from an emitter through relay transponders on two satellites (path 1 and path 2) to a common receive station. The measurement is time tagged at the time of receipt on path 1 and is computed as (received frequency on path 2 minus received frequency on path 1).
FDOA 2 Receivers Frequency Difference of Arrival measurement. A signal travels from a ground based emitter through relay transponders on two satellites (path 1 and path 2) to two receive stations. Signal path 1 is emitter-satellite 1-station 1. Signal path 2 is emitter-satellite 2-station 2. The measurement is time tagged at the time of receipt at station 2 and is computed as (received frequency on path 2 minus received frequency on path 1).
Ground FDOA Frequency Difference of Arrival measurement. A signal travels from a satellite based emitter to two receiver stations. The measurement is time tagged at the time of receipt at station 2 and is computed as (received frequency at station 2 minus received frequency at station 1).
Ground FDOADot Frequency Difference of Arrival Dot measurement. A signal travels from a satellite based emitter to two receiver stations. The measurement is time tagged at the time of receipt at station 2 and is computed as (received frequency rate at station 2 minus received frequency rate at station 1).
GroundTDOA Time Difference of Arrival measurement. A signal travels from a satellite based emitter to two receiver stations. The measurement is time tagged at the time of receipt at station 2 and is computed as (time of receipt at station 2 minus time of receipt at station 1).
L1 Phase
L2 Phase
Carrier phase-count measurements computed on the basis of the P code on the L1 (P1) and L2 (P2) frequencies. It is these two phase-counts that are combined to generate the DF phase-count (see below). A GPS receiver directly measures P1 and P2 carrier phase-counts. P1 and P2, however, are available only to military receivers and a new class of receivers that use patented algorithms to measure P1 and P2 without directly locking onto the P code.
L1 DD Phase
L2 DD Phase
LA DD Phase
Double-difference (single-frequency) phase count: The modeled measurement is the difference of two single difference phase-count measurements (two L1 SD Phase, two L2 SD Phase or two LA SD Phase measurements). These measurements are free from the effects of receiver and GPS satellite clock errors. However, ionosphere has not been eliminated. Unlike single differenced measurements, double differenced measurements must be constructed outside of ODTK.
L1 SD Phase
L2 SD Phase
LA SD Phase
Single-difference (single-frequency) phase count: The modeled measurement is the difference of two SV phase-count measurements (two L1, or two L2, or two LA measurements). Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. However, ionosphere has not been eliminated. If SD Phase measurements have been requested, then the "raw" phase-count measurements are converted to SD Phase measurements, and no "raw" phase-count measurements are processed.
LA Phase Carrier phase-count measurements computed on the basis of the C/A code on the L1 frequency.
L1C Phase GPS civilian carrier phase broadcast on the L1 frequency. This measurement is available with the first Block III launch.
L1C SD Phase L1C Single-difference (single-frequency) phase count: The modeled measurement is the difference of two SV phase-count measurements (two L1C measurements). Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. However, ionosphere has not been eliminated. If SD Phase measurements have been requested, then the "raw" phase-count measurements are converted to SD Phase measurements, and no "raw" phase-count measurements are processed.
L1C Pseudo-range GPS L1 civilian pseudo-range. This measurement is available with the first Block III launch. The range between the GNSS space vehicle (SV) and the user's receiver is the modeled measurement.
L1C SD Pseudo-range L1C single difference pseudo-range: The modeled measurement is the difference of two distinct SV L1 C code range measurements. Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. If L1C SD measurements have been requested (by adding L1 SD Pseudo-range to the GPS receiver MeasurementStatistics and to the MeasTypes on the satellite), then L1C measurements are converted to L1C SD measurements, and no pure L1C measurements are processed.
L2C Phase GPS civilian carrier phase broadcast on the L2 frequency. This measurement is available with Block IIR-M and later.
L2C SD Phase L2C Single-difference (single-frequency) phase count: The modeled measurement is the difference of two SV phase-count measurements (two L2C measurements). Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. However, ionosphere has not been eliminated. If SD Phase measurements have been requested, then the "raw" phase-count measurements are converted to SD Phase measurements, and no "raw" phase-count measurements are processed.
L2C Pseudo-range GPS L2 civilian pseudo-range. This measurement is available with the first Block IIR-M and later. The range between the GNSS space vehicle (SV) and the user's receiver is the modeled measurement.
L2C SD Pseudo-range L2C single difference pseudo-range: The modeled measurement is the difference of two distinct SV L2 C code range measurements. Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. If L2C SD measurements have been requested (by adding L2 SD Pseudo-range to the GPS receiver MeasurementStatistics and to the MeasTypes on the satellite), then L2C measurements are converted to L2C SD measurements, and no pure L2C measurements are processed.
L5 Phase GPS civilian carrier phase broadcast on the L5 frequency. This measurement is available with Block IIF and later.
L5 SD Phase L5C Single-difference (single-frequency) phase count: The modeled measurement is the difference of two SV phase-count measurements (two L5 measurements). Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. However, ionosphere has not been eliminated. If SD Phase measurements have been requested, then the "raw" phase-count measurements are converted to SD Phase measurements, and no "raw" phase-count measurements are processed.
L5 Pseudo-range GPS L5 civilian pseudo-range. This measurement is available with the first Block IIF and later. The range between the GNSS space vehicle (SV) and the user's receiver is the modeled measurement.
L5 SD Pseudo-range L5 single difference pseudo-range: The modeled measurement is the difference of two distinct SV L5 C code range measurements. Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. If L5C SD measurements have been requested (by adding L5 SD Pseudo-range to the GPS receiver MeasurementStatistics and to the MeasTypes on the satellite), then L5C measurements are converted to L5 SD measurements, and no pure L5 measurements are processed.

L2C_L1C DF Phase

L2C_L1CA DF Phase

L5_L1CA DF Phase

L5_L2C DF Phase

L5_L1C DF SD Phase

GPS dual frequency (DF) phase measurements (using the modernization signals) computed by mathematically by combining the two single-frequency “raw” carrier phase measurements to produce a measurement that is independent of the first order effects of the ionosphere. If the user selects DF measurements, then the corresponding “raw” single-frequency measurements are converted to DF measurements, and no single-frequency measurements are processed.
L2C_L1C DF SD Phase

L2C_L1CA DF SD Phase

L5_L1CA DF SD Phase

L5_L1C DF SD Phase

L5_L2C DF SD Phase

A singly differenced dual frequency measurement using GPS modernization signals’ DF phase. This means that the DF Phase is computed for two satellites that are being simultaneously tracked and that these two DF measurements are then differenced. These types of measurements are free from the effects of the ionosphere and the receiver clock bias.

L2C_L1C DF Pseudo-range

L2C_L1CA DF Pseudo-range

L5_L1CA DF Pseudo-range

L5_L2C DF Pseudo-range

L5_L1C DF SD Pseudo-range

GPS dual frequency (DF) range measurements (using the modernization signals) computed by mathematically by combining the two single-frequency “raw” pseudo-range measurements to produce a measurement that is independent of the first order effects of the ionosphere. If the user selects DF measurements, then the corresponding “raw” single-frequency measurements are converted to DF measurements, and no single-frequency measurements are processed.

L2C_L1C DF SD Pseudo-range

L2C_L1CA DF

SD Pseudo-range

L5_L1CA DF SD Pseudo-range

L5_L2C DF SD Pseudo-range

L5_L1C DF SD Pseudo-range

A singly differenced dual frequency measurement using the GPS modernization signals’ DF pseudo-range. This means that the DF Pseudo-range is computed for two satellites that are being simultaneously tracked and that these two DF measurements are then differenced. These types of measurements are free from the effects of the ionosphere and the receiver clock bias.
LEX Phase QZSS experimental measurement. Carrier phase measurement broadcast on the LEX frequency (same as Galileo E6 frequency). Not currently supported (TBS).
LEX SD Phase LEX Single-difference (single-frequency) phase count. Not currently supported (TBS).

LEX Pseudo-range

QZSS experimental measurement. Range measurement using LEX frequency (same as Galileo E6 frequency). Not currently supported (TBS).
LEX SD Pseudo-range LEX single difference pseudo-range: Not currently supported (TBS).

E1 Phase

E5a Phase

E5b Phase

E6 Phase

E5ab Phase

E2 Phase

Galileo Carrier Phase Measurements broadcast on the E1, E5a, E5b, and E6 frequencies respectively.

E1 SD Phase

E5a SD Phase

E5b SD Phase

E6 SD Phase

E5ab SD Phase

E2 SD Phase

Galileo single-difference (single-frequency) phase count: The modeled measurement is the difference of two SV phase-count measurements (two E1, or two E5a, or two E5b, or two E6 measurements). Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. However, ionosphere has not been eliminated. If SD Phase measurements have been requested, then the "raw" phase-count measurements are converted to SD Phase measurements, and no "raw" phase-count measurements are processed.

E1_E5a DF Phase

E1_E5b DF Phase

Galileo dual frequency (DF) phase measurements computed by mathematically by combining the two single-frequency “raw” phase measurements to produce a measurement that is independent of the first order effects of the ionosphere. If the user selects DF measurements, then the corresponding “raw” single-frequency measurements are converted to DF measurements, and no single-frequency measurements are processed.

E1_E5a DF SD Phase

E1_E5b SD DF Phase

A singly differenced dual frequency measurement using Galileo signals’ DF phase. This means that the DF phase is computed for two satellites that are being simultaneously tracked and that these two DF measurements are then differenced. These types of measurements are free from the effects of the ionosphere and the receiver clock bias.

E1 Pseudo-range

E5a Pseudo-range

E5b Pseudo-range

E6 Pseudo-range

E5ab Pseudo-range

E2 Pseudo-range

Galileo pseudo-range measurements using the E1, E5a, E5b, and E6 frequency bands.

E1 SD Pseudo-range

E5a SD Pseudo-range

E5b SD Pseudo-range

E6 SD Pseudo-range

E5ab SD Pseudo-range

E2 SD Pseudo-range

Galileo single-difference (single-frequency) pseudo-range: The modeled measurement is the difference of two SV pseudo-range measurements (two E1, or two E5a, or two E5b, or two E6 measurements). Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. However, ionosphere has not been eliminated. If SD pseudo-range measurements have been requested, then the "raw" pseudo-range measurements are converted to SD pseudo-range measurements, and no "raw" pseudo-range measurements are processed.

E1_E5a DF Pseudo-range

E1_E5b DF Pseudo-range

Galileo dual frequency (DF) range measurements) computed by mathematically by combining the two single-frequency “raw” pseudo-range measurements to produce a measurement that is independent of the first order effects of the ionosphere. If the user selects DF measurements, then the corresponding “raw” single-frequency measurements are converted to DF measurements, and no single-frequency measurements are processed.

E1_E5a DF SD Pseudo-range

E1_E5b SD DF Pseudo-range

A singly differenced dual frequency measurement using Galileo signals’ DF pseudo-range. This means that the DF Pseudo-range is computed for two satellites that are being simultaneously tracked and that these two DF measurements are then differenced. These types of measurements are free from the effects of the ionosphere and the receiver clock bias.

RCA Pseudo-range

RCB Pseudo-range

GLONASS SA pseudo-ranges. RCA is associated with the G1 frequency; RCB is associated with the G2 frequency. The range between the GNSS space vehicle (SV) and the user's receiver is the modeled measurement.

RCA SD Pseudo-range

RCB SD Pseudo-range

GLONASS SA single difference pseudo-range: The modeled measurement is the difference of two distinct SV SA pseudo- range measurements. Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. If RCA/RCB measurements have been requested (by adding RCA SD Pseudo-range or RCB SD Pseudo-range to the receiver MeasurementStatistics and to the MeasTypes on the satellite), then “raw” measurements are converted to SD measurements, and no pure “raw” measurements are processed.
RDF

Pseudo-range

 

GLONASS dual frequency (DF) range measurements) computed by mathematically by combining the two HA single-frequency RP1 and RP2 pseudo-range measurements to produce a measurement that is independent of the first order effects of the ionosphere. If the user selects DF measurements, then the corresponding “raw” single-frequency measurements are converted to DF measurements, and no single-frequency measurements are processed.

 

RDF SD Pseudo-range

A singly differenced dual frequency measurement using GLONASS DF pseudo-range. This means that the DF Pseudo-range is computed for two satellites that are being simultaneously tracked and that these two DF measurements are then differenced. These types of measurements are free from the effects of the ionosphere and the receiver clock bias.

RP1 Pseudo-range

RP2 Pseudo-range

GLONASS HA pseudo-ranges. RP1 is associated with the G1 frequency; RP2 is associated with the G2 frequency. The range between the GNSS space vehicle (SV) and the user's receiver is the modeled measurement.

RLA Phase

RLB Phase

GLONASS SA carrier phase measurements. RLA is associated with the G1 frequency; RLB is associated with the G2 frequency.

RLA SD Phase

RLB SD Phase

GLONASS SA single difference phase: The modeled measurement is the difference of two distinct SV SA phase measurements. Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. If RLA/RLB measurements have been requested (by adding RLA SD Pseudo-range or RLB SD Pseudo-range to the receiver MeasurementStatistics and to the MeasTypes on the satellite), then “raw” measurements are converted to SD measurements, and no pure “raw” measurements are processed.

RL1 Phase

RL2 Phase

GLONASS HA carrier phase measurements. RL1 is associated with the G1 frequency; RL2 is associated with the G2 frequency.

RL1 SD Phase

RL2 SD Phase

GLONASS HA single difference phase: The modeled measurement is the difference of two distinct SV SA phase measurements. Note that in this case, the receiver clock errors are eliminated from the measurement model, obviating the need to estimate receiver clock phase and frequency. If RL1/RL2 measurements have been requested (by adding RL1 SD Pseudo-range or RL2 SD Pseudo-range to the receiver MeasurementStatistics and to the MeasTypes on the satellite), then “raw” measurements are converted to SD measurements, and no pure “raw” measurements are processed.

RDF Phase

GLONASS dual frequency (DF) phase measurement computed by mathematically by combining the two HA single-frequency RL1 and RL2 phase measurements to produce a measurement that is independent of the first order effects of the ionosphere. If the user selects DF measurements, then the corresponding “raw” single-frequency measurements are converted to DF measurements, and no single-frequency measurements are processed.

RDF SD Phase

A singly differenced dual frequency measurement using GLONASS DF phase. This means that the DF Phase is computed for two satellites that are being simultaneously tracked and that these two DF measurements are then differenced. These types of measurements are free from the effects of the ionosphere and the receiver clock bias.
NPRange The model of range as a "Normal Point", as described by International Laser ranging Service. Normal Point Range has become the ILRS standard for reporting Satellite Laser Range data. Details of the formation of Normal Point data can be found on the ILRS web site http://ilrs.gsfc.nasa.gov/.
P1 Pseudo-range
P2 Pseudo-range
Pseudo ranges computed on the basis of the P code on the L1 (P1) and L2 (P2) frequencies. It is these two pseudo-ranges that are combined to generate the DF pseudo-range (see below). A GPS receiver directly measures CA, P1 and P2 pseudo-ranges. P1 and P2, however, are available only to military receivers and a new class of receivers that use patented algorithms to measure P1 and P2 without directly locking onto the P code.
Range Distance from the ground station to the satellite. More formally it is the time delay of a radio signal from transmitter to receiver. Internally, ODTK models the two-way range, i.e. the round trip light time delay from the ground station transmitter through the satellite transponder back to the ground station receiver, but can represent range related inputs and outputs as either one-way or two-way depending on the setting for the Scenario.RoundTripRepresentation attribute.
Right Ascension
Declination
A pair of ground station angle measurements which together can be used to determine a line of sight point vector from the ground station to the satellite. Given the definition of a reference frame with an "equator" and "north pole", Right Ascension is analogous to longitude and Declination is analogous to latitude. The reference frame may be MEME J2000, MEME of Date, TEME of Date or TETE of Date.
SB FDOA Frequency Difference of Arrival measurement. A signal travels from a ground based emitter to two satellites (path 1 and path 2). The path 1 satellite must have a TrackingInstrument sub-object defined. The measurement is time tagged at the time of receipt on path 1 and is computed as (received frequency on path 2 minus received frequency on path 1).
SB FDOA SBE Frequency Difference of Arrival measurement. A signal travels from a space based emitter to two satellites (path 1 and path 2). The path 1 satellite must have a TrackingInstrument sub-object defined. The measurement is time tagged at the time of receipt on path 1 and is computed as (received frequency on path 2 minus received frequency on path 1).

SB Range
SB Doppler
SB Azimuth
SB Elevation

Space-based Range is similar to Range except that the the observer is a satellite based TrackingInstrument instead of a ground station.

Space-based Doppler is similar to Doppler except that the the observer is a satellite based TrackingInstrument instead of a ground station.

Space-based Azimuth and Elevation are similar to Azimuth and Elevation except that the observer is a satellite based TrackingInstrument instead of a ground station and the azimuth plane is tangent to a sphere instead of the earth ellipsoid (as defined below). I.e., these are space-based angular measures from a tracking platform to a target. SBElevation is the angle made with the local horizontal plane, which is normal to the satellite position vector. SB elevation is positive above the local horizontal and negative below. SBAzimuth is measured in the local horizontal plane, from the instantaneous ECEF north, positive to the east. This measurement includes the light-time delay from the target to the tracker, and assumes the time tag is at receive time at the tracker.

The space-based azimuth and elevation coordinate system is a True Equator, True Equinox, Earth Centered, and Earth Fixed system. The azimuth plane is perpendicular to the radius vector from the Earth's center to the sensor. Azimuth is a horizontal angle measured in the azimuth plane clockwise (eastward) from the North. Elevation is a vertical angle measured from the azimuth plane, positive up to the satellite.

SB Right Ascension
SB Declination
Space-based Right Ascension and Declination. Similar to Right Ascension and Declination except that the observer is a satellite based TrackingInstrument instead of a ground station.
SB TDOA Time Difference of Arrival measurement. A signal travels from a ground based emitter to two satellites (path 1 and path 2). The path 1 satellite must have a TrackingInstrument sub-object defined. The measurement is time tagged at the time of receipt on path 1 and is computed as (time of receipt on path 2 minus time of receipt on path 1).
SB TDOA SBE Time Difference of Arrival measurement. A signal travels from a space based emitter to two satellites (path 1 and path 2). The path 1 satellite must have a TrackingInstrument sub-object defined. The measurement is time tagged at the time of receipt on path 1 and is computed as (time of receipt on path 2 minus time of receipt on path 1).
SB TDOA Dot Rate of change of SB TDOA. Computed as an instantaneous derivative with respect to time.
SD DF Phase Range Single Differenced dual frequency phase range. The modeled measurement is the difference of two dual frequency phase range measurements. These measurements are free from the effects of the ionosphere and receiver clock errors.
SD FDOA Single Differenced Frequency Difference of Arrival measurement. The difference between two FDOA measurements at the same time with common relay satellites and a common receive station. Only the emitter is different. The measurement is computed as (FDOA 2 – FDOA 1). This type of measurement differences out errors in the downlink to the receive station, but also weakens the geometrical information.
SD TDOA Single Differenced Time Difference of Arrival measurement. The difference between two TDOA measurements at the same time with common relay satellites and a common receive station. Only the emitter is different. The measurement is computed as (TDOA 2 – TDOA 1). This type of measurement differences out errors in the downlink to the receive station, but also weakens the geometrical information.
TDOA Time Difference of Arrival measurement. A signal travels from an emitter through relay transponders on two satellites (path 1 and path 2) to a common receive station. The measurement is time tagged at the time of receipt on path 1 and is computed as (time of receipt on path 2 minus time of receipt on path 1).
TDOA 2 Emitters Time Difference of Arrival measurement. Signals travel from two emitters through a relay transponder on a satellite (path 1 and path 2) to a common receive station. The measurement is time tagged at the time of receipt on path 1 and is computed as (time of receipt on path 2 minus time of receipt on path 1).
TDOA 2 Receivers Time Difference of Arrival measurement. A signal travels from a ground based emitter through relay transponders on two satellites (path 1 and path 2) to two receive stations. Signal path 1 is emitter-satellite 1-station 1. Signal path 2 is emitter-satellite 2-station 2. The measurement is time tagged at the time of receipt at station 2 and is computed as (time of receipt on path 2 minus time of receipt on path 1).
TDOA Dot Rate of change of TDOA. Computed as an instantaneous derivative with respect to time.
TDOA Dot 2 Emitters Rate of change of TDOA 2 Emitters. Computed as the change in TDOA over the supplied count interval.
X Y Angles

A pair of ground station angle measurements. The X angle is measured as the angle between the zenith direction and the projection of the relative position vector into a reference plane. The Y angle is measured as the angle between the relative position vector and the reference plane. The orientation of the reference plane depends on the AntennaMountType. X and Y angles can be modeled with or without light time delay. If light time delay is included then the modeling assumes one way measurements with the measurement time tag as the ground reception time.

Aberration corrections are applied based on the facility AberrationCorrection setting when LightTimeDelay setting is set to true.

DSN Delta DOR DSN Delta Differential One Way Range. This measurement requires that a single quasar and spacecraft be tracked essentially simultaneously. Reference the description of the DSN DOR and DSN QDOR measurements. A Delta DOR measurement is formed by combining and processing three measurements: {QDOR at time t1, DOR at time t2, QDOR at time t3}. The QODR measurements are used to estimate a QDOR measurement at time t2; then the Delta DOR measurement at time t2 is formed by differencing DOR (t2) - QDODR(t2).
DSN DOR DSN (Spacecraft) Differential One Way Range. This is a range difference measurement requiring two DSN ground antennas and only using downlink from the spacecraft. The two antennas are located in DSN complexes on separate sides of the Earth. The imaginary line connecting the two antennas can be considered an interferometer where radio waves from the target spacecraft arrive at the interferometer in approximately parallel rays. The differential one way range measurement is then the path length difference of the signal arriving to each of the antennas.
DSN QDOR DSN (Quasar) Differential One Way Range. Similar to DSN DOR except that the measurement refers to light emitted from a quasar instead of a signal from a spacecraft.

For more complete descriptions of these measurement types, see ODTK Orbit Determination: Theorems & Equations. For a walkthrough of ODTK's TDRSS range and Doppler models, see Processing TDRSS Data with ODTK. For a walkthrough of ODTK's TDOA and FDOA models, see Processing TDOA and FDOA Data with ODTK.

Measurement Statistics

Depending on the measurement type, one or more of the following measurement statistics can be set:

Measurement Statistics
Property Description
BiasDriftModel

Identifies the Stochastic Model to be used to model the Bias Drift parameter. Currently this parameter only pertains to the accelerometer measurement.

  • GaussMarkov = Bias will be modeled as a scalar exponential Gauss Markov sequence
  • RandomWalk = Bias will be modeled using a Wiener (Brownian motion) sequence
  • Vasicek = Bias will be modeled using a Vasicek stochastic sequence. This is a two-parameter model that solves for both a short-term and long-term bias.

Reference the Stochastic Model section for the description and inputs associated with each model.

BiasModel

Identifies the Stochastic Model to be used to model the measurement bias.

  • GaussMarkov = Bias will be modeled as a scalar exponential Gauss Markov sequence
  • RandomWalk = Bias will be modeled using a Wiener (Brownian motion) sequence
  • Vasicek = Bias will be modeled using a Vasicek stochastic sequence. This is a two-parameter model that solves for both a short-term and long-term bias.

Reference the Stochastic Model section for the description and inputs associated with each model.

BoresightBiasModel

Relevant for Phased Array range and face angle measurements.

When set to true the applied bias and white noise will vary as function of the angle between the tracking direction and the face normal direction. Bias and noise change will increase as this angle increases by 1/cos(angle).

InstantaneousModel Applicable to Doppler only. Specifies that the Doppler measurement is to be modeled as “Instantaneous Range-rate”. This model optionally includes troposphere, ionosphere, measurement bias, and time bias corrections. Light time delay and phase center corrections are excluded.
CountInterval Applicable to Doppler only. Specifies the length of the interval over which the Doppler count is generated.
EditOnDoppler Applicable to 4L Range and BRTS Range only (for the TDRSS system). Range measurements will be rejected if a valid doppler measurement is not available at the same time. This flag should be set to false when processing simulated data in the generic observation format, since knowledge of simultaneous measurements is not available.
EstimateBias Set to true if the Filter is to estimate a measurement bias component for this particular measurement type. If estimated, then the bias will be modeled as a Gauss-Markov parameter using the given Gauss-Markov parameters. The estimate flag must also be set to true if this parameter is to be used as a Least Squares Consider State. When used as a consider state it is modeled as a constant.
LightTimeDelay Applicable to Range, Doppler, Azimuth, Elevation, Right Ascension, Declination, Delta Dec, SB Right Ascension, Delta SB RA, and Delta SB Dec. Select true to compute the light time delay correction during measurement modeling. If the reason for turning off light time delay effects is to model the measurement using only geometry, then to be consistent with that goal, aberration effects should be set to None in the Optical Properties of the tracker to prevent any aberration corrections from being applied.
ModelInSolarSystemBarycentricFrame Applicable to the Range model only. If true, the light time delay solution for the two-way range measurement is computed in the solar system barycentric frame. This option should be enabled when processing range measurements to deep space objects. Enabling this option is appropriate for the modeling of range measurements at any distance, but is more computationally intensive than the Geocentric model, which is used when the option is not enabled.
Randomize Applicable to singly differenced pseudo-range measurements only. Changes the order in which pseudo-ranges are combined for differencing from one observation time to the next.
RejectFirstNMeas Applicable to 4L Range and BRTS Range only (for the TDRSS system). If set to a number greater than 0, that many observations will be rejected at the beginning of each pass, in addition to the measurements edited out by the EditOnDoppler flag, if any.
Representation Applicable to Range and Doppler. This read-only value reflects the setting for the scenario-level attribute, RoundTripRepresentation.
ScaleFactor

Identifies the Stochastic Model to be used to model an Accelerometer Scale Factor.

  • GaussMarkov = Bias will be modeled as a scalar exponential Gauss Markov sequence
  • RandomWalk = Bias will be modeled using a Wiener (Brownian motion) sequence
  • Vasicek = Bias will be modeled using a Vasicek stochastic sequence. This is a two-parameter model that solves for both a short-term and long-term bias.

Reference the Stochastic Model section for the description and inputs associated with each model.

TropoNoiseScaling

Scale factor for deweighting of phase measurements to account for the unknown variation of the zenith tropospheric delay estimate over the count interval for the phase measurement. Set the value to 1.0 to deweight measurements based on the total process noise added to the tropospheric delay estimate mapped to the current elevation angle. Set the value to 0.0 to ignore variations in the troposphere over the count interval. This setting only has an effect when a troposphere correction is being estimated for the facility hosting the GPS receiver and is usually only used for simulations where the distinction between tropospheric behavior and white noise is known.

NOTE: When simulating L1 Phase, L2 Phase and deviating tropospheric refraction, then TropoNoiseScaling should be = 1

TropoSigma Not available on all measurement types. Specify the expected uncertainty in the tropospheric correction to the measurement as a fraction of the tropospheric correction (for example, a value of 0.05 therefore corresponds to a 5% uncertainty in the tropospheric correction). All available troposphere models provide range corrections. Only the SCF model currently computes a correction to the elevation angle. The computed tropospheric uncertainty is included as part (added in an RSS sense) of the measurement noise contribution to the measurement error variance during the filter measurement update when a zenith tropospheric correction is not being estimated.
WhiteNoiseDeweighting

Applicable to CA Nav Sol and DF Nav Sol only. This setting affects the processing of Nav Sol measurements during estimation. The effective use of this setting (if Constant is not selected) requires that a GPS constellation object be present and properly defined over the estimation time period and that the GPS satellites used in the generation of the navigation solution are identified in the tracking data. The GPS constellation is required to support the computation of the Dilution of Precision (DOP) associated with the navigation solution. Select between:

  • Constant - The input value of WhiteNoise is used without any additional scaling.
  • Scale by Component DOP - The white noise for each component of the navigation solution will be computed as the input value of WhiteNoise multiplied by the DOP in the direction of that component. The scenario-level attribute, EmbeddedWNSigmas.Use, must be set to true for this option to function properly.
  • Scale by PDOP - The white noise for all components of the navigation solution will be computed as the input value of WhiteNoise multiplied by the Position Dilution Of Precision (PDOP) where PDOP is determined as the square root of the sum of squares of the component DOPs. The scenario-level attribute, EmbeddedWNSigmas.Use, must be set to true for this option to function properly.

NOTE: A larger white noise value will be required during estimation if the Constant option is selected since it must cover all geometries. Also, the scaling by DOP has a greater impact on the estimation process when the receiver is tracking a smaller number of satellites.

NOTE: The input value of WhiteNoise comes from the tracking data provider if a white noise value is specified in the tracking data, otherwise it comes from the measurement statistics of the GPS receiver.

WhiteNoiseSigma Square root of the variance representing the random uncertainty in the measurements.

ODTK 6.5