E-THEMIS Thermal Anomaly Simulation Observations

This dataset contains 100,000 simulated observations of Europa with the E-THEMIS instrument. Each observation was generated by randomly selecting (1) one of 46 planned Europa flybys by the Europa Clipper from the 17F12_V2 trajectory and (2) the distance of the spacecraft to Europa (±50,000 km from closest approach). We used the KRC thermal model to simulate the Europa surface temperature as a function of latitude, longitude, and local solar time (Sun position). We simulated the appearance of Europa within the E-THEMIS field of view given the Europa radius of 1591 km. We used ray tracing to determine, given the surface temperature model and the relative positions of Europa and the spacecraft, the amount of thermal radiation from Europa that a given pixel would collect. We used Monte Carlo integration over 100 uniformly random sub-pixel locations within each pixel.

We injected artificial thermal anomalies into the simulated Europa observations by selecting a random radius between 1 m and 25 km and random temperature between 75 K and 275 K, then modifying the modeled surface temperature. We used an instrument model that converts temperature to digital numbers to generate the final E-THEMIS data product.

The ethemis_dn_to_temp.npz file contains the mapping from digital number to temperature in each of the three E-THEMIS bands. Each observation is also a NPY-formatted file containing the following entries:

• event_time: the simulated time at which the observation was acquired
• trial: the trial identifier (should match the file name)
• samples: the number of samples used in the Monte Carlo integration
• anomaly_radius_m: the (circular) anomaly radius in meters
• temperature: the temperature of the anomaly
• band1_dn: the digital number for each pixel in the observation (similar entries exist for the other bands)
• band1_mask: a mask specifying the fraction of each pixel containing an anomaly (similar entries exist for the other bands)

The extracted dataset is roughly 18 Gb in size.