The Airborne Multi-angle Spectro Polarimetric Imager (AirMSPI) was an airborne prototype instrument for obtaining multi-angle polarization imagery. AirMSPI flew on the NASA ER-2 aircraft. The instrument — which is similar to that of a future MSPI satellite instrument — was built by NASA's Jet Propulsion Laboratory.

AirMSPI was an 8-band (355, 380, 445, 470, 555, 660, 865, 935 nm) pushbroom camera, measuring polarization in the 470, 660, and 865 nm bands and mounted on a gimbal to acquire multi-angular observations over a ±67° along-track range. Two principal observing modes were employed: step-and-stare, in which 11 km x 11 km targets are observed at a discrete set of view angles with a spatial resolution of about 10 meters; and continuous sweep, in which the camera slews back and forth along the flight track between ±67° to acquire wide area coverage (11 km swath at nadir, target length 108 km) with about 25 m spatial resolution. Step-and-stare provided more angles, but continuous sweep gave greater coverage. 

Multiple observing modes could be programmed into the instrument and activated under cockpit control. Multi-angle radiance and polarization imagery from AirMSPI can:

• Provide three-dimensional scene context where clouds and aerosol plumes are present, plus constraints on radiometric closure, particularly over heterogeneous scenes where 3-D radiative transfer may dominate 
• Enable retrieval of aerosol and cloud macrophysical properties (distribution, height), microphysical properties (size distribution, single scattering albedo, shape), and optical depth. 

AirMSPI has been retired and replaced by AirMSPI-2.

GroundMSPI is portable ground-based instrument with an 8-band spectropolarimetric camera mounted on a rotating gimbal to acquire pushbroom imagery of outdoor landscapes. The camera uses a photoelastic-modulator-based polarimetric imaging technique to acquire Stokes vector measurements in three of the instrument's bands (470, 660, and 865 nm). Data collected via GroundMSPI are featured in the GroundMSPI_ACEPOL_Radiance_Data_9 data product.