MR-i is an imaging Fourier-Transform spectro-radiometer. This field instrument generates spectral datacubes in the MWIR and LWIR. It is designed to acquire the spectral signatures of rapidly evolving events. The spectroradiometer is modular. The two output ports of the instrument can be populated with different combinations of detectors (imaging or not). For instance, to measure over a broad spectral range one output port can be equipped with a LWIR camera while the other port is equipped with a MWIR camera. No dichroic filters are used to split the bands, hence enhancing the sensitivity. Both ports can be equipped with cameras imaging the same spectral range but set at different sensitivity levels in order to increase the measurement dynamic range and avoid saturation of bright parts of the scene while simultaneously obtaining good measurements of the faintest parts of the scene. Various telescope options can be used for the input port.