Inverse Synthetic Aperture Ladar Demonstration and Outdoor Experiments

Inverse synthetic aperture ladar(ISAL)operates at light wavelength and utilizes the synthetic aperture technique, which can obtain very high resolution two-dimensional or three dimensional image of a moving target and thus have many important applications for target detection and recognition. With a very short wavelength, 10000 times smaller compared with that of microwave radar, ISAL can get a high angle resolution with a small telescope in microseconds. However, ISAL is more sensitive to many errors, such as ladar vibration, atmospheric turbulence, moving target jitter, etc., which bring many difficulties to implement an ISAL equipment. In this article, we present an ISAL demonstration and some outdoor experimental results. The ISAL transmits wideband coherent laser which is created by modulating a phase coded signal onto a continuous laser waveform at 1550nm, and detects weak echoes reflected from moving targets by a coherent detection system. A modified phased gradient autofocus algorithm(MPGA)is utilized to suppress errors and improve image quality. The ISAL demonstration acquires high-resolution images of 3-centimeter with a distance about 200m.