The in-plane Mueller matrix bidirectional reflectance distribution function (MMBRDF) is measured for a Spectralon calibration target with a reflectance of 99%. Measurements are acquired using a Mueller matrix active imaging, goniometric polarimeter operated in the near infrared at 1550nm. The Spectralon is measured for both incident and scattering angles from -80 degrees to 80 degrees to within 20 degrees of retro-reflection. A range of polarization states is generated and scattered polarization states are analyzed by means of a dual rotating retarder Mueller matrix polarimeter. Complete Mueller matrix data is measured with a high-resolution camera in image form. Polarization scatter data is presented in Mueller matrix angular arrays. As expected the Spectralon is a strong depolarizer and weak s-plane oriented diattenuator. It was also a weak retarder. Diattenuation and retardance are strongest at horizontal and vertical polarizations, and weakest for circular polarization states.