The World Meteorological Organisation (WMO) Observing Systems Capability Analysis and Review (OSCAR) Tool describes the High-Resolution Imager (HRI) (which flies on Pléades-1A and -1B, among other satellites) fire fractional cover capability as limited to "daylight only". The same for Landsats Operational Land Imager (OLI). But fires should be visible at night, why would the fire fractional cover capability be limited to daylight observations? Do they switch off the sensor to limit energy/bandwidth/storage or is there a more technical reason?