This invention consists of sensors and algorithms to image, detect, and quantify the presence of hydrocarbon gas (for example from leaks) using a short-wave infrared radiation detector array with multiple spectral filters under natural sunlight or artificial illumination, in combination with the hydrodynamics of turbulent gas jets and buoyant plumes. Multiple embodiments are recited and address detection and quantification of methane gas leaks. Quantification includes gas column densities, gas concentration estimates, total mass, hole size estimates, and estimated emission flux (leak rate) of gas from holes and cracks in pressurized vessels, pipes, components, and general gas infrastructure, and from surface patches (for example due to gas leaks in underground pipes) under the action of buoyancy and wind. These and similar embodiments are applicable more generally to natural gas and other hydrocarbon gases, liquids, emulsions, solids, and particulates, and to emissions monitoring of greenhouse gases methane and carbon dioxide.