UCL Department of Space and Climate Physics


Remote Sensing Detectors Modelling

An important activity for instrument performance is software modelling, which allows us to understand the complex interplay of factors that affect performance

  1. Prediction of performance of an instrument. This can indicate whether the instrument will achieve its requirements/goals, and which parameters need to be optimised
  2. Comparison of a software model with actual behaviour. This can help identify problems in an instrument or areas where further improvements can be made, or it can confirm that the instrument is behaving as well as it was designed to.

We use various modelling tools for different instruments and detectors:

  • Optical ray-tracing: We use packages (usually Zemax) to calculate the performance of photon illumination systems.
  • Radiation/absorption modelling: Packages such as GEANT4 and the MULASSIS (MUlti-LAyered Shielding SImulation Software) front-end allow simulation of the absorption of radiation particles either desirably in detectors, or undesirably as sources of damage for electronic components.
  • Bespoke software: In many cases, there is no convenient off-the-shelf package to do exactly what we want. In this case, we write our own code to simulate instument performance, e.g. sensitivity as a function of wavelength, effects of noise on performance. The code can be implemented as spreadsheets, in graphical tools such as LabVIEW, or using more conventional programming languages.

Optical Ray Tracing

Optical Ray Tracing is used at MSSL in the design of the highly complex optical systems (telescopes and calibration standards), often in partnership with other institutes or consultants.

It can also be used for mechanical and thermal tolerancing studies, stray light studies,  full opto-mechanical system simulations, optical system assembly, alignment, final system performance verification and integration.

Here are some existing designs which were used at various stages, from the initial proposal to the final missions, in flight. 


An important aspect of any space instrument is calibration. This means knowing and understanding the performance of the instrument in terms of sensitivity, resolution, noise factors. Even when these aspects are known, the work continues, as various parameters change with time, temperature and radiation dose in space. So calibration is a combination of testing the instrument before launch against known standards, and monitoring performance in orbit (e.g. regular specific observations of standard astronomical objects). At MSSL we have calibration experts whose role is to monitor and maintain the performance of instruments using a combination of pre-launch and in-flight testing and monitoring.