# Optical transient detection
*sensing . methodologies*

High-frame-rate optical sensing that detects transient luminous events such as lightning flashes by their temporal signature rather than by spatial imaging.

## Specifications
- **family**: Optical event detection
- **requirements envelope**: {"kind":"spectral","spectral_range_nm":{"min":776.4,"max":778.4},"bands_min":1,"cloud_tolerant":true,"daylight_required":false}
- **entity type**: methodology
- **last verified date**: 2026-09-29
- **verified by**: agency-doc
- **claim status**: unclaimed
- **technology**: optical-spectral-sensing

## Editorial
Optical transient detection identifies transient luminous events, such as lightning flashes, by their temporal signature rather than by spatial imaging. Rather than resolving a scene structurally, the method looks for rapid photon-count pulses at a specific wavelength associated with the event of interest.

Implementations built for lightning detection center on the 777.4 nanometer neutral-atomic-oxygen emission line produced by lightning discharges. The Geostationary Lightning Mapper (GLM) [^noaa-goesr-glm] is a single-channel near-infrared detector with a bandpass of about 1 nanometer around this line, operating at a 2 millisecond frame rate with a nadir footprint of about 8 kilometers (widening to about 14 kilometers at the edge of its field of view). It detects total lightning, including in-cloud, cloud-to-cloud, and cloud-to-ground discharges, day and night, at a flash detection efficiency of 70 to 90 percent. GLM flies on GOES-16, GOES-17, GOES-18, and GOES-19.

The MTG Lightning Imager (LI) [^eumetsat-mtg-li] detects optical pulses in a wider band of about 1.9 nanometers centered on the same 777.4 nanometer oxygen line, using four cameras, each operating at 1 kilohertz, to cover four quadrants of the observed disc. It provides a sub-satellite spatial resolution of about 4.5 kilometers and continuous day and night detection of intra-cloud, cloud-to-cloud, and cloud-to-ground lightning. LI flies on MTG-I (Meteosat-12).

Because the method detects a temporal pulse rather than forming a conventional image, it requires only a single spectral band and does not depend on daylight, remaining tolerant of cloud cover for lightning-discharge detection.

## Sources
- [noaa-goesr-glm] | Instruments: Geostationary Lightning Mapper (GLM) | https://www.goes-r.gov/spacesegment/glm.html | tier=agency-doc | accessed=2026-09-29 | author=NOAA/NASA GOES-R Program
  GLM is a single-channel near-infrared optical transient detector centered on the 777.4 nm neutral-atomic-oxygen emission line (~1 nm bandpass), 2 ms frame rate, ~8 km nadir footprint (14 km at FOV edge), detects total lightning (in-cloud, cloud-to-cloud, cloud-to-ground) day and night at 70-90% flash detection efficiency; flown on GOES-16/17/18/19.
- [eumetsat-mtg-li] | MTG Lightning Imager | https://www.eumetsat.int/mtg-lightning-imager | tier=agency-doc | accessed=2026-09-29 | author=EUMETSAT
  MTG Lightning Imager detects optical pulses in a ~1.9 nm band centered at the same 777.4 nm oxygen line, using four 1 kHz cameras covering four disc quadrants, 4.5 km sub-satellite spatial resolution, continuous day/night detection of intra-cloud, cloud-to-cloud and cloud-to-ground lightning; flown on MTG-I (Meteosat-12).

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Source: https://eo-atlas.org/methodologies/optical-transient-detection
Maintainer: SpectraWorks B.V. (CC-BY 4.0)