Microwave Photonic Imaging Radiometer

Abstract

Nano-satellites are gaining in popularity due to their low cost and ease of deployment. Reaching orbit as secondary payload to larger spacecraft enables science grade missions at disruptively low cost. Such miniaturized platforms impose severe constraints on the size, weight, and power (SWaP) of the payload, however, making large antenna apertures difficult to realize. Meanwhile, relatively large apertures are needed to achieve desired spatial resolution for earth observing sensors at microwave frequencies. To this end, our distributed aperture array technology dramatically reduces the SWaP of such sensors, thus enabling deployment of large radio frequency apertures on spaceborne platforms. The sensor performs optical upconversion of the upwelling microwave radiation to optical frequencies, using high-speed, broadband electro-optic mixers, and subsequent coherent optical reconstruction of the passive thermal microwave scene, without the need for bulky and power hungry digital correlation engines or substantial post-processing. Notably, the optical processing technique images all of the beams in the array concurrently, forming a real-time video stream of radiometric brightness temperatures. Herein, we describe a spaceborne, 1-D pushbroom passive millimeter wave sensor utilizing optical upconversion and aperture synthesis, at a nominal detection frequency of 36 GHz, and deployed on a 12U CubeSat for remote sensing and earth science applications.