Fig. 1. Schematic of RTL projection.

Fig. 2. Schematic of the RTL system. CM, concave mirror; EOM, electro-optic modulator; AOM, acousto-optic modulator; P, polarizer; M, mirror; NL, negative lens; Nd:YAG, neodymium-doped yttrium-aluminum-garnet laser; WP, wave plate; ND, neutral density filter; IPC, industrial personal computer; APD, avalanche photodiode; MMF, multimode fiber.

Fig. 3. Layout of the experimental setup. (a) Image of the test tower with a 100-mm-aperture telescope. (b) The target is fixed at an angle of 30° with the direction of light rotating on a rotary table. (c) The RTL system.

Fig. 4. (a) Image of two plates fixed on a translation stage. (b) Image of a plate (300mm×200mm) fixed on a precise rotating platform. (c) Echo waveforms of two plates with different spacing distances, i.e., 23, 25, 27, and 35 mm, over 10 km. (d) Echo waveforms of one plate (300mm×200mm) with different rotation angles, i.e., 0°, 10°, 20°, and 30°, over 10 km.

Fig. 5. (a) Projection data of WordArt target. Projections were taken at 1° intervals from 0° (one side forward) to 180° (another side forward). (b) Image reconstructed by the FBP algorithm with measured data. (c) Typical feature dimensions of the target.

Fig. 6. (a) Image reconstructed by the FBP algorithm with ROIs. (b) MTF curves of ROIs.

Fig. 7. (a) Equally sampled projection data with an interval of 5°. (b) Randomly sampled projection data with a sampling rate the same as the 5° uniform sampling. (c) Equally sampled projection data with an interval of 10°. (b) Randomly sampled projection data with a sampling rate the same as the 10° uniform sampling.

Fig. 8. Reconstruction results of fully and sparsely sampled data using the FBP algorithm, ART, and NLM algorithm.

Fig. 9. Evaluation of reconstruction performance using the metric (a) IE, (b) CC, (c) PSNR, and (d) SSIM. The reference image of the evaluation is a detailed and sharp image of the model.