We report on progress made in developing a polarimetric and multispectral imaging (MSI) camera that uses a coded filter mask to record spectral data on either a single frame or only a few frames depending on the design of the mask and the application. The design uses commercially available variable filters and beamsplitters to record spectral data simultaneously on a focal plane array, thus negating the need for scanning mechanisms or dispersive optical elements. The data rate depends on the design of the filter mask, pixel resolution, relative motion between target and camera, and the frame rate. The polarimetric data is recorded on a single frame thus eliminating latency. Multispectral data may be recorded on a few frames or a single frame, thus reducing the need for many multi-frame acquisitions. An optimum mask design matched to the imaging lens and focal plane array resolution, allows an object to be detected against spectral clutter or background on a single pixel. Thus a spatially resolved image is not required, alleviating the need for high magnification which would be a practical limitation where compact optical systems are required. The proof-of-principle is reported that uses a 1D variable filter mask to provide spectra of resolved target images in the near field for the visible spectrum. Test data are presented that show the potential for the concept and how it is readily extended to use a 2D mask in a modified design.

Polarimetric imaging (PI) is of increasing importance in determining additional scene information beyond that of conventional images. For very long-range surveillance, image quality is degraded due to turbulence. Furthermore, the high magnification required to create images with sufficient spatial resolution suitable for object recognition and identification require long focal length optical systems. These are incompatible with the size and weight restrictions for aircraft. Techniques which allow detection and recognition of an object at the single pixel level are therefore likely to provide advance warning of approaching threats or long-range object cueing.PI is a technique that has the potential to detect object signatures at the pixel level. Early attempts to develop PI used rotating polarisers (and spectral filters) which recorded sequential polarized images from which the complete Stokes matrix could be derived. This approach has built-in latency between frames and requires accurate registration of consecutive frames to analyze real-time video of moving objects. Alternatively, multiple optical systems and cameras have been demonstrated to remove latency, but this approach increases cost and bulk of the imaging system.In our investigation we present a simplified imaging system that divides an image into two orthogonal polarimetric components which are then simultaneously projected onto a single detector array. Thus polarimetric data is recorded without latency on a single snapshot. We further show that, for pixel-level objects, the data derived from only two orthogonal states (H and V) is sufficient to increase the probability of detection whilst reducing false alarms compared to conventional unpolarised imaging.