Passive millimeter-wave imaging with compressive sensing

Passive millimeter-wave (PMMW) imagers using a single radio-meter, called single pixel imagers, employ raster scanning to produce images. A serious drawback of such a single pixel imaging system is the long acquisition time needed to produce a high-fidelity image, arising from two factors: (a) the time to scan the whole scene pixel by pixel and (b) the integration time for each pixel to achieve adequate signal to noise ratio. Recently, compressive sensing (CS) has been developed for single-pixel optical cameras to significantly reduce the imaging time and at the same time produce high-fidelity images by exploiting the sparsity of the data in some transform domain. While the efficacy of CS has been established for single-pixel optical systems, its application to PMMW imaging is not straightforward due to its (a) longer wavelength by three to four orders of magnitude that suffers high diffraction losses at finite size spatial wave-form modulators and (b) weaker radiation intensity, for example, by eight orders of magnitude less than that of infrared. We present the development and implementation of a CS technique for PMMW imagers and shows a factor-often increase in imaging speed. 1 Introduction Passive millimeter wave (PMMW) imaging has many applications , such as remote sensing of the Earth's resources, aircraft landing in optically obscure weather, and security point inspection of concealed weapons in humans. 1 The Earth's resources that may be sensed by passive MMWs include terrain mapping, soil moisture and polar ice mapping, ocean surface sensing, as well as atmospheric water vapor and temperature profiling as a function of altitude for climate modeling and weather sensing. 2 The underlying principle is the measurement of Planck's blackbody radiation of materials at millimeter wavelengths. The main advantage of passive MMW imaging is that it provides information about ground-based targets under all weather conditions; optical systems [visible and infrared (IR)], on the other hand, require clear atmospheric conditions for reliable operation. For example, the atmospheric attenuation of MMW frequencies at sea level is 0.07 to 3 dB∕km in drizzle and fog, whereas it is one to three orders of magnitude higher for optical frequencies (exceeding 100 dB∕km in foggy conditions).