WFC3 grism image simulation

The following link to aXeSIMweb allows you to simulate WFC3 slitless images via a web application:

Disclaimer

The WFC3 slitless image simulator was developed independently of the STScI Exposure Time Calculator (ETC). While every effort has been made to ensure that the simulator provides similar estimates of detected counts to the ETC, differences are bound to result. The STScI ETC is to be taken as the official tool and should be used to determine exposure times for the purposes of critical time justification in Phase I and II HST proposals. The WFC3 ETC can be found here.