An approach to noninvasively and remotely detect the presence, location, and/or quantity of a target substance in a scene via a spectral imaging system comprising a spectral filter array and image capture array. For a chosen target substance, a spectral filter array is provided that is sensitive to selected wavelengths characterizing the electromagnetic spectrum of the target substance. Elements of the image capture array are optically aligned with elements of the spectral filter array to simultaneously capture spectrally filtered images. These filtered images identify the spectrum of the target substance. Program instructions analyze the acquired images to compute information about the target substance throughout the scene. A color-coded output image may be displayed on a smartphone or computing device to indicate spatial and quantitative information about the detected target substance. The system desirably includes a library of interchangeable spectral filter arrays, each sensitive to one or more target substances.