Observations and Measurements

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In FreeFlyer, an Observation represents a collection of Measurements taken at the same time. The observer and object being observed are the same for all the Measurements in a given Observation. Each Measurement contains its own statistics, such as pre- and post-update residuals. Currently, FreeFlyer supports several types of Observations, each with different available Measurements:

 

Observation Type

Measurement Types

File Type(s)

BRTS Observations

Two-way Doppler

Two-way Range

BRTS UTDF File

DSN Observations[1]

Range

Range Rate

Azimuth

Elevation

Right Ascension

Declination

DSN 60-Byte Observation File

TRK-2-34 File

Ground Station Observations[1]

Range

Range Rate

Azimuth

Elevation

Right Ascension

Declination

FF Ground Observation File

UTDF File

Point Solution Observations

X

Y

Z

Vx

Vy

Vz

BlackJack Point Solution File

GPS Pivot Point Solution File

Pseudorange Observations

C1

C2

P1

P2

Iono-Free

Rinex Observation File

 

Spacecraft Observations

Azimuth

Elevation

Range

Range Rate

Right Ascension

Declination

Spacecraft Observation File

 

TDRS Observations

One-way Doppler

Two-way Doppler

Two-way Range

TDRS UTDF File

 

[1] Note: Ground Station observations and DSN observations support both 2-way and 3-way Doppler measurements. See Simulating 3-way Observations for more information.

 

At the Observation level there are multiple "Use" flags corresponding to the available measurement types for that observation. When simulating an observation, these flags control whether or not the particular measurement is simulated. When processing an observation, these flags control whether or not the measurement is processed by the estimator. For example, if the UseRange property of the GroundStationObservation object is set to 1 (true), then the range measurement will be simulated when the Spacecraft.SimulateTrackingData() method is called and processed when the Observation object is processed using a KalmanFilterOD, SquareRootInformationFilterOD, UnscentedKalmanFilterOD, or BatchLeastSquaresOD object.

 

Each Measurement includes the following properties:

 

ComputedValue

ExpectedResidual

ObservedValue

PostUpdateResidual

PreUpdateResidual

ProcessingStatus

Validity

 

Each of these properties is read-only, with the exceptions of the Observed Value and the Validity flag. The read-only properties are automatically set when a Measurement is processed by a KalmanFilterOD, SquareRootInformationFilterOD, UnscentedKalmanFilterOD, or BatchLeastSquaresOD object.

 

These properties can be used to gain insight into the state estimation process. For example, in the following script a Measurement's pre- and post-update residuals are inspected:
 

// Report the pre- and post-update residuals for a position measurement

 

Report PointSolutionObs1.X.PreUpdateResidual, PointSolutionObs1.X.PostUpdateResidual;

 

 

See Also


Tracking Data File Formats

Simulating Tracking Data

Generating Tracking Data Files

Using the Tracking Data Editor