Earth Observations: Optical Transient Detector (OTD)

The Optical Transient Detector (OTD), a space-based lightning imager on the Orbview-1 satellite, operated during April 1995 to March 2000 as a  Lightning Imaging Sensor (LIS) prototype.  OTD detected total lightning (cloud-to-cloud, cloud-to-ground, and intracloud flashes) between +/- 75 degrees latitude, but could not distinguish between lightning types.

The OTD was essentially a wide field-of-view telescope that captured 500 Earth surface snapshots per second.  The supporting electronics monitored these videos for the rapid pulses of light produced by lightning. The pulses were used to detect lightning at any time of day and determine the optical properties such as lightning location, radiant energy, and number of illuminated pixels. 

Detection efficiency varied between 0.37 (noon) and 0.52 (~6pm), changing with sensor threshold settings, time, location, and storm structure.  Detection efficiency was much less in the South Atlantic Anomaly where high radiation levels interfered with instrument measurement.  If a storm had optically thick clouds, reflection off middle cloud layers, or low flash altitudes, the lightning signal was difficult to detect.

Data obtained include amount, rate, and radiant energy of total lightning during both day and night, lightning distribution, and variability of total lightning.