Multispectral sensor using off-axis three-mirror reflective optics for airborne surveillance

This paper describes designing and testing the ground-base multi-spectral sensor using off-axis three-mirror reflective optics for imaging optics, and dichroic mirrors for separation of spectral bands. The off-axis three-mirror optics provides an obstruction free FOV (Field Of View) with a wide spectral range and high spatial resolution over a wide FOV. The three- mirror anastigmat consists of two aspherical mirrors and a spherical mirror. The design is configured for a telecentric flat focal plane. The dichroic mirrors separate spectral range into three visible bands, a near infrared band, an MWIR (Middle Wavelength InfraRed) band and an LWIR (Long Wavelength InfraRed) band. Relay optics is used to adjust multiplication factors for infrareds. The 10,000 element CCD sensors are used for three visible bands and the near infrared band. The 960 element HgCdTe linear arrays are used for the MWIR and the LWIR bands. The results of experiments show that the design goals are successfully achieved. Among them are a wide spectral band from 0.4 micrometer to 10 micrometer, with spatial resolution of 10 (mu) rad over 5.7 degrees FOV for visible and near infrared bands and 100 (mu) rad over 5.7 degrees for the MWIR and the LWIR bands. The overall MTF at the center of the FOV are more than 0.3 at Nyquist frequency for all bands.