The MOPITT Airborne Test Radiometer (MATR) is a gas correlation filter radiometer that was developed to support and validate the MOPITT satellite program. It is a scaled-down version of the MOPITT instrument that comprises two thermal channels near 4.6 µm for measuring CO and one solar channel near 2.33 µm (or 2.27 µm) for measuring CO (or CH4). Inasmuch as its spatial resolution (1.2 km x 1.2 km) is much higher than that of the MOPITT radiometer (22 km x 22 km), MATR measurements provide an opportunity to look at the horizontal distribution of CO in more detail, which is especially useful for investigating localized pollution sources.