KASCADE is a series of programs which provides a complete 3D simulation of cosmic ray and gamma ray induced air showers.
Through the use of the imaging atmospheric Cherenkov technique (IACT), ground based gamma ray telescopes probe the universe in the energy range ~50 GeV to ~50 TeV. Unlike conventional telescopes in other wave bands, gamma ray telescopes do not concentrate and focus the incident astronomical gamma ray. Instead they detect the incident gamma ray by indirect means. The incident gamma ray undergoes an electromagnetic interaction with an atom in the Earth’s upper atmosphere, initiating an electromagnetic cascade of electrons, positrons, and high energy photons known as an air shower. These electrons and positrons travel faster than the local speed of light, and thus emit Cherenkov radiation. Ground based IACT telescopes can detect this flash of Cherenkov light which ultimately provides information about the nature of the incident particle. The atmospheric cascade itself is a fairly complicated process, and the details of the detection characteristics of the telescope is also complicated. Simulation studies (often referred to as Monte Carlo studies in reference to the random nature of many of the physical processes involved) are used to understand and predict the characteristics of the air shower cascades and of the telescope response to the air shower.
KASCADE is a series of programs which provides a complete 3D simulation of cosmic ray and gamma ray induced air showers. Programs in KASCADE generate air showers, generate the associated Cherenkov photons, and test for telescope triggers. KASCADE also contains routines for determining rate curves, energy threshold, and collection areas from the simulated telescope trigger. KASCADE was intentionally designed as a modular system to increase its use and flexibility. For example, the characteristics of the air shower and the Cherenkov light are determined by physics, not by telescope design, so these parts of the program are useful to anyone. The telescope detection characteristics obviously depend on the telescope, and models must be coded individually for different systems. The telescope model currently used for the VERITAS telescopes has grown in complexity to the point where it has essentially a one to one match with individual components of the telescope electronics.
A paper detailing the KASCADE system can be found here: https://www.sciencedirect.com/science/article/abs/pii/016890029490247X