Temperature compensated thermal radiation detectors

Thermal radiation detection apparatus comprising a first high impedance thermal radiation detector element shunted by a low leakage device, said detector element being disposed on a mount and placed to receive radiation from a scene and thereby change in temperature and produce an output signal between two terminals on the element, one terminal of the detector element being connected to a first impedance converter and thence to an output, and a reference low leakage device, one terminal of which is connected to a second impedance converter nominally identical to the first impedance converter and thence via a high gain negative feedback loop to the other terminal of the reference low leakage device and also to the other terminal of the detector element via a detector common line so that the output of the second impedance converter is at zero potential whereby any offset in the second impedance converter is compensated and hence any offset in the first impedance converter is substantially compensated, characterised in that the reference low leakage device is shunted by a reference radiation detector element nominally identical to the first radiation detector element and disposed on the mount adjacent the first radiation detector element, but shielded from scene radiation, whereby ambient temperature changes affect both the detector and reference elements equally and hence the detector element output caused by ambient temperature changes is substantially compensated by the reference element output caused by the ambient temperature changes.