Basic Sensor Model

The basic sensor model can be used to represent basic properties of an instrument: the field-of-view (FOV)/ scene-field-of-view (sceneFOV)/ field-of-regard (FOR) and the orientation. Coverage (i.e. finding the locations which can be seen by the sensor) can be evaluated and viewing geometry parameters can calculated.

The model also allows to configure a detector array geometry on a Focal Plane Array (FPA) which can be used to to simulate imagery by interpolating geo-physical data onto projected (ground) pixel positions.

Note that the coverage calculation and pixel-projection operations are available in the OrbitPy package.

Todo

Explain the synthetic data feature.

Model parameters

A BasicSensorModel object can be obtained from a json/ dict by using the from_json(.) or from_dict(.) functions. The expected key/value pairs are described below:

Input parameter description

Parameter	Data type	Units	Description
@type	string		Must be Basic Sensor
@id	string		Unique identifier for the instrument. If None a random string is assigned.
name	string		Full name of the instrument
mass	float	kilograms	Total mass of this entity.
volume	float	\(m^3\)	Total volume of this entity.
power	float	Watts	Nominal operating power.
orientation	orientation json object		Orientation of the instrument. Default is alignment to the SC_BODY_FIXED frame.
fieldOfViewGeometry	fieldOfViewGeometry (Spherical-Geometry) json object		Field of view spherical geometry specification of the instrument.
sceneFieldOfViewGeometry	sceneFieldOfViewGeometry json object		The SceneFOV spherical geometry specification of the instrument. Default is the field-of-view spherical geometry.
maneuver	maneuver json object		Maneuver specifications (see Maneuverability and Field Of Regard (FOR) calculations).
pointingOption	pointingOption JSON object		List of orientations to which the instrument axis can be maneuvered.
syntheticDataConfig	syntheticDataConfig JSON object		Synthetic data configuration.
dataRate	float	Mega-bits-per-s	Rate of data recorded during nominal operations.
bitsPerPixel	integer		Bits encoded per pixel of image.
numberDetectorRows	integer		Number of detector rows (along the Y-axis of the SENOR_BODY_FIXED frame). If the SENSOR_BODY_FIXED frame is aligned to the NADIR_POINTING frame; this direction corresponds to the along-track direction.
numberDetectorCols	integer		Number of detector columns (along the X-axis of the SENOR_BODY_FIXED frame). If the SENSOR_BODY_FIXED frame is aligned to the NADIR_POINTING frame; this direction corresponds to the cross-track direction.

Model results

Using the basic-sensor model, coverage calculations (using the OrbitPy package) can be carried out over a region of interest. Coverage calculations which involve a grid (list of grid-points)) evaluate to see if the grid-points fall within the instrument sceneFOV (sceneFOV = FOV in most cases) or the FOR. The pointing-options feature further allows to automate coverage calculations for numerous instrument orientations.

Once the coverage has been evaluated, the observable locations and the observer (satellite) locations is known. The following data metrics at the observable location on the surface of Earth can be calculated:

Observation data metrics table

Metric	Data Type	Units	Description
incidence angle [deg]	float	degrees	Incidence-angle at the target point calculated assuming spherical Earth.
look angle [deg]	float	degrees	Look-angle to the target point calculated assuming spherical Earth. Positive sign => look is in positive half-space made by the orbit-plane (i.e. orbit plane normal vector) and vice-versa.
observation range [km]	float	kilometers	Distance from satellite to ground-point during the observation.
solar zenith [deg]	float	degrees	Solar-zenith-angle during observation.

Todo

Include AT, CT footprint size calculations.

Model description

• \(\mathbf{R = T - S}\)

• \(\gamma = \cos^{-1}(\mathbf{\dfrac{R}{|R|}} \cdot \mathbf{\dfrac{-S}{|S|}})\)

• \(\theta_i = \sin^{-1}(\sin\gamma \hspace{1mm} \dfrac{R_E + h}{R_E})\)

Assuming spherical Earth of radius \(R_E\)

where,

• \(\mathbf{S}\): Position-vector of the satellite in the EARTH_CENTERED_INERTIAL frame.

• \(\mathbf{T}\): Position-vector of the target ground-point in the EARTH_CENTERED_INERTIAL frame.

• \(\mathbf{R}\): Range vector from satellite to target ground point.

• \(\gamma\): Look-angle to target ground point from satellite.

• \(\theta_i\): Incidence-angle at the target ground point.

• \(R_E\): Nominal equatorial radius of Earth.

• \(h\): Altitude of satellite.

Please refer to the instrupy.util.GeoUtilityFunctions.compute_sun_zenith function for description of the calculation of the Sun-zenith angle.

Examples

Please see the examples folder.