Improved sensitivity performance of SWIR imager in a multispectral VIS/SWIR zoom camera for long-range surveillance tasks

Abstract

The multispectral sensor suite consists of a HD-TV camera sensitive in the visible (VIS) spectral range and a short wave infrared ( SWIR) camera channel in combination with an integrated laser range finder all through one common entrance pupil. The sensor suite is developed for long ranging surveillance applications. A significant reduction of the noise equivalent irradiance (NEI) of the SWIR imager in the multispectral VIS/SWIR sensor suite has been reached by a pitch reduction and corresponding optics F-number reduction of the SWIR channel. The pitch has been reduced from 20μm to 15μm and the F-number from F/7.0 to F/5.25, respectively. The visible channel has a F-number of F/2.6 with a 11- times optical zoom and provides the same field of view and focus position as the SWIR camera with the reduced pitch. The contributions from the pitch dependent dark current and read out noise levels in combination with the reduced F-number, increasing the resulting signal to noise ratio (SNR), are discussed. The optical design of the SWIR imaging path has been significantly improved with respect to the resulting modulation transfer function (MTF) performance, resulting in an improved resolution with respect to the initial configuration [1,2]. The optical coating designs of the two multispectral beam splitters for the separation of the visual (450nm – 680nm) from the SWIR spectral wavelength range (900nm – 1700 nm) and the separation of the included laser rangefinder (LRF) receiver channel at 1.57nm center wavelength have been improved with respect to the optical imaging performance. First electro-optical results of the improved multispectral sensor suite are discussed and compared with the original design.