This paper describes two aspects of work carried out at British Aerospace on a family of suspended resistor infrared scene generators intended as sources for exercising infrared seeker systems in simulation environments. In the first aspect, a 256 X 256 system has matured and entered service with hardware-in-the-loop (HWIL) simulation facilities. This system, designated TPS4 (for thermal picture synthesizer) has performance suitable for air target tracking studies, and certain aspects of its characteristics in use are described. In the second aspect, research work has been carried out on the extension of the system performance to enable the representation of higher temperature targets, such as are required for countermeasures work. These improved devices are designated TPS5, and aspects of their rationale, design, and evaluation are described. Prototype arrays suitable for eventual systems of complexity 512 X 512 and beyond have been tested.