instrupy.radiometer_model — Radiometer Model

Description

This module provides the RadiometerModel class (and supporting classes) which can be used to represent microwave radiometers. The module consists of separate classes for handling each of the radiometric systems (listed in SystemType), all with identical interface functions. Similarly there are separate classes to handle different scan techniques (listed in ScanTech), all with identical interface functions. By having identical interface functions, the functions can be invoked without consideration of the underlying radiometric system class.

The RadiometerModel object can be obtained from json/ dict representations using the from_json or from_dict functions. Please refer to radiometer model for description of the instrument model and the expected key/value pairs.

Refer to the base module and OrbitPy coverage calculator module (orbitpy.coveragecalculator) to know how to use the RadiometerModel object for coverage calculations.

The calc_data_metrics function can be used to calculate the data-metrics given the spacecraft-state and observed-location (target). The expected key/value pairs for the spacecraft-state input argument (of type dict) are:

Column	Data type	Units	Description
time [JDUT1]	float	JDUT1	Time in Julian Day UT1. Corresponds to the time of observation.
x [km], y [km], z [km]	float	km	Cartesian coordinates of satellite in EARTH_CENTERED_INERTIAL frame at the time of observation.
vx [km/s], vy [km/s], vz [km/s]	float	km/s	Velocity of spacecraft in EARTH_CENTERED_INERTIAL frame at the time of observation.

The expected key/value pairs for the observed-location input argument (of type dict) are:

Column	Data type	Units	Description
lat [deg], lon [deg]	float	degrees	Ground-point accessed (geocentric latitude, geocentric longitude).

instru_look_angle_from_target_inc_angle flag

In addition to the above mentioned input-arguments to the calc_data_metrics function, there is an additional optional flag which can be specified to instruct how to obtain the instrument look-angle. If the instru_look_angle_from_target_inc_angle flag is set to False (also default value), the instrument look-angle is obtained from the instrument orientation specification. If the flag is set to True, the instrument look-angle is obtained from the target location incidence-angle.

Examples

1. Define a total-power radiometer (with component-level predetection-stage specifications) with FIXED scan configuration and calculate metrics. The instru_look_angle_from_target_inc_angle flag is set to False in this example and hence it implies that the instrument look-angle is derived from the instrument orientation. Beam-efficiency for circular aperture antennas is not currently supported and hence is output as nan.

   Note

   The swath-width is calculated more precisely as compared to the pixel-resolution calculations. This leads to a slight difference as can be seen in the below results. (For FIXED scan, the entire radiometric image corresponds to a single pixel and hence pixel size is equal to the swath-width.)

   from instrupy.radiometer_model import RadiometerModel
   
   # instrument specifications as a dict
   radio1_json = {"@type": "Radiometer", "name": "ray1", "mass": 50, "volume": 3, "power": 10,
                  "orientation": {"referenceFrame": "SC_BODY_FIXED", "convention": "REF_FRAME_ALIGNED"},
                  "bitsPerPixel": 16,
                  "operatingFrequency": 1.25e9,
                  "antenna": {"shape": "CIRCULAR", "diameter": 1, "apertureExcitationProfile": "UNIFORM",
                              "radiationEfficiency": 0.8, "phyTemp": 300},
                  "system": {"tlLoss": 0.5, "tlPhyTemp": 290,
                              "rfAmpGain": 30, "rfAmpInpNoiseTemp": 200,
                              "rfAmpGainVariation": 10, "mixerGain": 23, "mixerInpNoiseTemp": 1200,
                              "mixerGainVariation": 2, "ifAmpGain": 30, "ifAmpInputNoiseTemp": 100,
                              "ifAmpGainVariation": 10, "integratorVoltageGain": 1, "integrationTime": 100e-3,
                              "bandwidth": 10e6, "@type": "TOTAL_POWER"},
                  "scan": {"@type": "FIXED"},
                  "targetBrightnessTemp": 345
                  }
   
   # define the viewing-geometry (observer state and target location)
   epoch_JDUT1 =  2458543.06088 # 2019 Feb 28 13:27:40 is time at which the ECEF and ECI frames approximately align, hence ECEF to ECI rotation is identity. See <https://www.celnav.de/longterm.htm> online calculator of GMST.
   SpacecraftOrbitState = {'time [JDUT1]':epoch_JDUT1, 'x [km]': 6878.137, 'y [km]': 0, 'z [km]': 0, 'vx [km/s]': 0, 'vy [km/s]': 7.6126, 'vz [km/s]': 0} # altitude 500 km
   TargetCoords = {'lat [deg]': 0, 'lon [deg]': 0.5}
   
   radio1 = RadiometerModel.from_json(self.radio1_json)
   data_metrics = radio1.calc_data_metrics(sc_orbit_state=SpacecraftOrbitState, target_coords=TargetCoords, instru_look_angle_from_target_inc_angle=False)
   print(data_metrics)
   
   >> {'ground pixel along-track resolution [m]': 120708.29, 'ground pixel cross-track resolution [m]': 121567.92, 'swath-width [m]': 120565.56,
       'sensitivity [K]': 17.94, 'incidence angle [deg]': 6.82, 'beam efficiency': nan}
   

   In the below snippet, the instrument look angle is considered from the incidence angle at the target ground-point (6.82 deg). Note that the calculated swath-width is different compared to the former case.

   data_metrics = o.calc_data_metrics(sc_orbit_state=SpacecraftOrbitState, target_coords=TargetCoords, instru_look_angle_from_target_inc_angle=True)
   print(data_metrics)
   
   >> {'ground pixel along-track resolution [m]': 120708.29, 'ground pixel cross-track resolution [m]': 121567.92, 'swath-width [m]': 122255.0,
         'sensitivity [K]': 17.94, 'incidence angle [deg]': 6.82, 'beam efficiency': nan}
   

API

Classes

Functions