Optical transient detector
From Glossary of Meteorology
Optical Transient Detector
(Abbreviated OTD.) An instrument, designed to detect lightning from space, that was launched on 3 April 1995 aboard the MicroLab-1 satellite into a near polar orbit at an inclination of 70°.
The OTD was an engineering prototype of the Lightning Imaging Sensor that was subsequently launched on the TRMM satellite.