An infrared imaging system for detecting hydrogen sulfide (H2S) gas, the imaging system comprising: an optical detector array (136, 236, 336, 456); and an optical filter that selectively transfers light within a band of IR wavelengths to the optical detector array (136, 236, 336, 456); characterized in that the imaging system comprises processing electronics configured to process image data received by the optical detector array (136, 236, 336, 456), the processing electronics configured to detect H2S gas based on the captured image data, wherein, within the band of IR wavelengths, a convolution of the optical filter with an absorption spectrum of H2S gas is greater than a convolution of the optical filter with an absorption spectrum of carbon dioxide, or methane, or sulfur dioxide, or water (H2O), wherein the optical detector array (136, 236, 336, 456) comprises an optical focal plane array unit and a plurality of spatially and spectrally different optical channels to transfer infrared radiation from a scene towards the optical FPA unit, each optical channel positioned to transfer a portion of the IR radiation incident on the imaging system from the scene towards the optical FPA unit, wherein a first channel of the plurality of optical channels comprises the optical filter and wherein a second channel of the plurality of optical channels comprises a second optical filter, the second optical filter configured to pass broadband background radiation within a second band of IR wavelengths, wherein the processing electronics are configured to identify hydrogen sulfide (H2S) gas in the scene based at least in part on a difference between a first signal transferred from the optical filter and a second signal transferred from the second optical filter, wherein a third channel of the plurality of optical channels selectively transfers a third signal to the optical detector array (136, 236, 336, 456) that is representative of carbon dioxide, methane, sulfur dioxide, or water (H2O), and wherein the processing electronics are configured to identify at least one of carbon dioxide, methane, sulfur dioxide, and water (H2O) based at least in part on a difference between the third signal and the second signal. an optical detector array (136, 236, 336, 456); and an optical filter that selectively transfers light within a band of IR wavelengths to the optical detector array (136, 236, 336, 456); characterized in that the imaging system comprises processing electronics configured to process image data received by the optical detector array (136, 236, 336, 456), the processing electronics configured to detect H2S gas based on the captured image data, wherein, within the band of IR wavelengths, a convolution of the optical filter with an absorption spectrum of H2S gas is greater than a convolution of the optical filter with an absorption spectrum of carbon dioxide, or methane, or sulfur dioxide, or water (H2O), wherein the optical detector array (136, 236, 336, 456) comprises an optical focal plane array unit and a plurality of spatially and spectrally different optical channels to transfer infrared radiation from a scene towards the optical FPA unit, each optical channel positioned to transfer a portion of the IR radiation incident on the imaging system from the scene towards the optical FPA unit, wherein a first channel of the plurality of optical channels comprises the optical filter and wherein a second channel of the plurality of optical channels comprises a second optical filter, the second optical filter configured to pass broadband background radiation within a second band of IR wavelengths, wherein the processing electronics are configured to identify hydrogen sulfide (H2S) gas in the scene based at least in part on a difference between a first signal transferred from the optical filter and a second signal transferred from the second optical filter, wherein a third channel of the plurality of optical channels selectively transfers a third signal to the optical detector array (136, 236, 336, 456) that is representative of carbon dioxide, methane, sulfur dioxide, or water (H2O), and wherein the processing electronics are configured to identify at least one of carbon dioxide, methane, sulfur dioxide, and water (H2O) based at least in part on a difference between the third signal and the second signal.