Technical Information & Links

Silsoe Spray Drift Model (SiMoD):
SiMoD Drift Model

SiMoD (otherwise known as the Silsoe Spray Drift Model) has been under development since the 1980s.  This latest release is based on the Jan 2018 version, as yet unpublished.

The model of spray drift was developed from a particle tracking model (Miller and Hadfield, 1989), in turn derived from an earlier model (Thompson and Ley, 1983).  The extended and updated model, published in 2010 (Butler Ellis and Miller, 2010a), includes the effects of multiple nozzles on a boom and a forward speed so that it is better able to simulate application conditions appropriate to current field practice, particularly in the UK.

The model was specifically developed for improving estimates of bystander dermal and inhaled spray drift exposure.  It was validated against three experimental data sets of downwind airborne spry and ground deposit for FF110/1.2/3.0 conventional flat fan nozzles spraying over either short grass or 0.65 m tall wheat crop.

The model showed good agreement with measurements.  Further data comparisons were undertaken (Butler Ellis and Miller, 2010b) with the Spray Drift Task Force data, and showed good agreement. Developments since 2010 have recently been compared with other field data under the SETAC DRAW programme (

For the time being, we are not making the software generally available as a download, as we would prefer to work with those who have an interest in it, so that we can make sure it is used within its capabilities.  Please contact Clare if you would like to find out more.

Dr. Clare Butler Ellis

Silsoe Spray Applications Unit


Support for developments since 2012 has been provided by the following organisations:

Defra (via UK Chemicals Regulation Directorate) – project PS2030 (2011 – 2014)

European Crop Protection Association (via SETAC DRAW)

US Forest Service – Grant Number 16-IC-11420004-304