A gas detector for revealing a target gas includes an image capturing unit with multiple optical channels, an image processing unit and a calculation unit. The image processing unit is adapted for deducing a value of a radiation transmission coefficient which relates to an analysis spectral band, and which is attributable to a quantity of the target gas present in a part of the field-of-view. Preferably multiple analysis bands are used in parallel. The calculation unit is adapted for deducing an evaluation of the quantity of the target gas based on the value of the radiation transmission coefficient which relates to each analysis band. Such a gas detector may have small dimensions, be easily transportable, including on board a drone, and can provide evaluation results for the quantity of the target gas in real-time or nearly real-time.