A method comprising: emitting, from a light source , directional light through fuel contained in a fuel tank ; determining a refraction angle of the directional light after the directional light passes through an interface with the fuel, wherein determining the refraction angle of the directional light comprises: identifying, using a thermal imager , a location of an interior of the fuel tank intersected by the directional light after the directional light passes through the interface with the fuel; identifying, using the thermal imager , a location of the interior of the fuel tank intersected by the directional light after the directional light passes, non-refracted, through the fuel tank; determining a distance (D 1 ) between the location of the interior of the fuel tank intersected by the directional light after passing thought the interface with the fuel and the location of the interior of the fuel tank corresponding to non-refraction of the directional light; and determining the refraction angle of the directional light after the directional light passes through the interface with the fuel using the determined distance (D 1 ) and a known level of the interface with the fuel; determining, by a processing device, an index of refraction of the fuel based on the determined refraction angle; measuring, using the thermal imager , a temperature of the fuel; and determining, by the processing device, a density of the fuel based on the determined index of refraction of the fuel, wherein determining the density of the fuel based on the determined index of refraction of the fuel comprises determining the density of the fuel based on the determined index of refraction of the fuel and the measured temperature of the fuel. emitting, from a light source , directional light through fuel contained in a fuel tank ; determining a refraction angle of the directional light after the directional light passes through an interface with the fuel, wherein determining the refraction angle of the directional light comprises: identifying, using a thermal imager , a location of an interior of the fuel tank intersected by the directional light after the directional light passes through the interface with the fuel; identifying, using the thermal imager , a location of the interior of the fuel tank intersected by the directional light after the directional light passes, non-refracted, through the fuel tank; determining a distance (D 1 ) between the location of the interior of the fuel tank intersected by the directional light after passing thought the interface with the fuel and the location of the interior of the fuel tank corresponding to non-refraction of the directional light; and determining the refraction angle of the directional light after the directional light passes through the interface with the fuel using the determined distance (D 1 ) and a known level of the interface with the fuel; determining, by a processing device, an index of refraction of the fuel based on the determined refraction angle; measuring, using the thermal imager , a temperature of the fuel; and determining, by the processing device, a density of the fuel based on the determined index of refraction of the fuel, wherein determining the density of the fuel based on the determined index of refraction of the fuel comprises determining the density of the fuel based on the determined index of refraction of the fuel and the measured temperature of the fuel. <EOS>