A method of detecting at least one chemical species comprising: obtaining at least a first image (610, 801) from a first electromagnetic radiation detector configured to detect the chemical species, the first image including a first plurality of pixels, each pixel having an associated intensity value; obtaining at least a second image (620, 802) from a second electromagnetic radiation detector configured to provide a reference background, the second image including a second plurality of pixels, each pixel having an associated intensity value; generating at least a first resultant image (605, 803) by determining the difference in intensity values between each of the first plurality of pixels of the first image and the corresponding pixels of the second plurality of pixels of the second image, using the difference in intensity as the intensity value for the corresponding plurality of resultant pixels of the first resultant image; characterized by further comprising determining one or more regions of interest based, at least in part, on the first resultant image by applying a resultant threshold criteria to the intensity values of the plurality of resultant pixels and grouping at least a portion of the plurality of resultant pixels satisfying the resultant threshold criteria into the one or more regions of interest; determining correlation between the first image, the second image, and the first resultant image for at least one of the one or more regions of interest using a correlation coefficient algorithm to: calculate a first correlation coefficient using the intensity values of a first subset of pixels from the first plurality of pixels and a corresponding subset of resultant pixels from the plurality of resultant pixels within at least one of the one or more regions of interest, and calculate a second correlation coefficient using the intensity values of a first subset of pixels from the second plurality of pixels and a corresponding subset of resultant pixels from the plurality of resultant pixels within the corresponding region of interest; and determining the presence of at least one chemical species based, at least in part, on the first correlation coefficient and the second correlation coefficient. obtaining at least a first image (610, 801) from a first electromagnetic radiation detector configured to detect the chemical species, the first image including a first plurality of pixels, each pixel having an associated intensity value; obtaining at least a second image (620, 802) from a second electromagnetic radiation detector configured to provide a reference background, the second image including a second plurality of pixels, each pixel having an associated intensity value; generating at least a first resultant image (605, 803) by determining the difference in intensity values between each of the first plurality of pixels of the first image and the corresponding pixels of the second plurality of pixels of the second image, using the difference in intensity as the intensity value for the corresponding plurality of resultant pixels of the first resultant image; characterized by further comprising determining one or more regions of interest based, at least in part, on the first resultant image by applying a resultant threshold criteria to the intensity values of the plurality of resultant pixels and grouping at least a portion of the plurality of resultant pixels satisfying the resultant threshold criteria into the one or more regions of interest; determining correlation between the first image, the second image, and the first resultant image for at least one of the one or more regions of interest using a correlation coefficient algorithm to: calculate a first correlation coefficient using the intensity values of a first subset of pixels from the first plurality of pixels and a corresponding subset of resultant pixels from the plurality of resultant pixels within at least one of the one or more regions of interest, and calculate a second correlation coefficient using the intensity values of a first subset of pixels from the second plurality of pixels and a corresponding subset of resultant pixels from the plurality of resultant pixels within the corresponding region of interest; and calculate a first correlation coefficient using the intensity values of a first subset of pixels from the first plurality of pixels and a corresponding subset of resultant pixels from the plurality of resultant pixels within at least one of the one or more regions of interest, and calculate a second correlation coefficient using the intensity values of a first subset of pixels from the second plurality of pixels and a corresponding subset of resultant pixels from the plurality of resultant pixels within the corresponding region of interest; and determining the presence of at least one chemical species based, at least in part, on the first correlation coefficient and the second correlation coefficient.