Backlit droplet images are evaluated for droplet combustion experiments that have been performed on the International Space Station. The focus of the present analyses is on non-sooting or lightly-sooting droplets. The influences of diffraction, interference, and partial coherence on droplet images are considered via Fourier optics modeling. It is found that light diffraction at the droplet edge can contribute significantly to errors in droplet size measurements. Other error sources include background light variations and partial coherence effects. An image-processing algorithm is proposed to account for the effects of diffraction, partial coherence, and background light variations on measurements of droplet sizes.

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The method about how to distinguish the object from the standing wave, eliminate the wave patterns in CW THz images based on phase analysis is reported. The standing wave of CW THz images result from the interference of the wave-front reflected from the object and other optics in the system. Therefore, the information of the surface of the object and the background is included in the interference pattern of the images. Because the objects have different Phase Gradients from the background, they could be extracted from the image by utilizing the phase information of the interferential waves. The waves of the image can be removed with Election-pass filter, and the result of the filtering would not deteriorate the result because there is no object in the image. At last, the image of object and the image without standing wave can be fused together to make the image better for eyes. The scope of CW THz imaging's application can be extended and the quality of images can be improved by applying this approach.

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