Accelerometer Sensor

In ODTK an Accelerometer Sensor is a sensor that measures linear acceleration along a single direction. This direction is fixed in the body frame of the host object (in ODTK, a satellite). Typically, multiple accelerometer sensors are grouped together under a single Accelerometer object and are oriented in orthogonal directions and used collectively to produce the 3D estimate of acceleration.

An Accelerometer Sensor is represented in the Browser and in the ODTK toolbar by the (Accelerometer Sensor Icon) icon. For each Accelerometer Sensor under the Accelerometer object, the following properties can be accessed and, if desired, changed using the Object Properties window:

Accelerometer Sensor Properties
Property Description
MeasurementProcessing
  • Enabled - set to true if acceleration measurements associated with this sensor are to be processed or simulated.
  • TrackingID associated with AccelerometerSensor. This positive integer id is unique for all AccelerometerSensors associated with a given Satellite (i.e. sensors contained within different Accelerometers associated with the same satellite must have unique ids). For accelerometer measurements this id must be the first tracking ID in the CAgODGenericObs TrackerIDs list and the satellite tracking id must be the second id in the list for the measurement to be processed.
BodyPosition X, Y, Z vector defining the position, in body frame coordinates, of the accelerometer relative to the satellite center of mass. If the sensor is located away from the center of mass, sensed accelerations will include gravity gradient and centripetal effects.
BodyAlignUnitVec X, Y, Z unit vector defining the (fixed) direction of the sensor in the body frame of the (host) satellite object. Sensed accelerations are reported as positive in the same direction as the body alignment vector.
MeasurementStatistics Accelerometer measurement modeling properties. See Measurement Types and Statistics. Note that the there are two properties that are unique to this measurement. The first is a "ScaleFactor", and the second is a two parameter Bias model (Bias and Drift). The reported acceleration is equal to the actual acceleration multiplied by the scale factor plus the bias. Reference the ODTK math spec for more details.

Measurement Statistics

For the accelerometer sensor scale factor and bias, one or more of the following measurement statistics can be set:

Measurement Statistics
Property Description
ScaleFactorModel
BiasModel
BiasDriftModel		 Identifies the Stochastic Model to be used to model the accelerometer sensor scale factor, bias or bias drift.
  • 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.
WhiteNoiseSigma Square root of the variance representing the random uncertainty in the measurements.
EstimateScaleFactor Set to true if a measurement scale factor is to be estimated for this accelerometer sensor.
EstimateBias Set to true if a measurement bias is to be estimated for this accelerometer sensor.
EstimateBiasDrift Set to true if a measurement bias drift is to be estimated for this accelerometer sensor.