CCD Based Multispectral Scanner

Charge Coupled Devices (CCD) are being used in a number of applications like Signal processing, memories and image sensors. This paper covers its application for the purpose of imaging. It has got many advantages over conventional imaging sensors. Energy reflected from different objects differs both in intensity and spectral distribution. For better recognition and identification of objects, their photographs in different spectral bands are required. The optomechanical scanners have a revolving mirror and detector elements for different spectral bands. In the optomechanical scanners, the decrease in dwell time affects the signal-to-noise ratio which can be improved either by increasing the collecting aperture or by using more sensitive detectors. The increase in collecting aperture causes enormous increase in the total weight of the scanner system. Charge Coupled Devices (CCD) image sensors have better sensitivity than the discrete detector elements. Use of linear CCD image sensors makes it possible to avoid the use of revolving mirror which is required in the optomechanical scanners. CCD image sensors have a wide spectral response, starting from UV to near infrared region. Their better sensitivity and wide spectral response make them specially suitable for multi-spectral imaging. An Airborne Multispectral Scanner using linear Charge Coupled Devices (CCD) image sensors and pyroelectric detector arrays has been described. It includes visible, near infra-red (IR) and thermal infra-red bands. CCD image sensors cover the visible and near IR bands while pyroelectric array is used for imaging in the thermal IR band. The video data is transmitted to ground in real time. The received data is recorded on a High Density Digital Tape Recorder (HDDT) and displayed on a monitor. It is aimed to obtain a resolution of 1 m at an altitude of 5 km.