Resolution Tests with a TDI-Camera

Abstract

With Time Delay and Integration (TDI) detector arrays, high resolution space camera systems can be developed. The main advantage of TDI-detectors in comparison to conventional CCD-detectors is their very high responsivity which allows extremely short exposure times. This short exposure times on the other hand correspond to very fast data read out rates, e.g. at a ground sampling distance of 0.25 m from orbit height, a line read out frequency of approximately 27 kHz is required. To test the image quality of TDI cameras at these very high data read out frequencies laboratory tests with a "Dalsa TDI-Line Scan Camera CT-E2" were carried out. The TDI-detector array of 2048 elements with a single detector size of 13 x 13 mm², has 96 integrating steps and a radiometric resolution of 8 bit. A moving test pattern simulated the relative motion between space camera and earth surface. The processed images of the test pattern could be used to determine three bar resolving power in across and along flight direction, to derive the MTF curves and to obtain a value for the noise level. Furthermore the influence of slight deviations from the required read out frequency on the resolving power was investigated. The paper describes the laboratory experiment and presents the resolving power results.