Most crucial part of remote sensing satellite is the sensor. Two main classes of sensors are passive and active. In active sensors, energy is generated form within the sensor system and beamed outward to illuminate the target. The energy reflected back from the target is picked up by the sensor. Cost of such systems is higher than passive sensor systems. In passive sensors electromagnetic radiation received comes from an external source such as Sun and the reflected energy is again picked up by the sensor. Passive sensors are sensitive to clouds and haze. Thematic Mapper of Landsat and HRV of SPOT lie in the category of passive sensors, while SAR is an example of active sensor used for earth observation.
The payload sensor(s) design is crucial in defining mission's purpose. The sensor characteristics account for the entire payload's mission and the other space segment elements are really in service to the payload. Sensor design should flow from measurement requirements and is best performed as an iterative process between designers and the science community within the constraints set by fundamental physics, the state of the technology, and cost. Trade-off studies assess instrument design alternatives that can produce the required measurements within the constraints set by fundamental physics, the state of the technology, and cost. Advancement in sensor technology continue to improve performance, cost, size, mass, and power parameters to suit mission objectives. Here we will discuss the image acquisition part of the sensor its design and constraints. The physics of diffraction is a key factor that constrains sensor design, other are size, mass and power requirements. Beside these there are some other constraints which are necessary to be considered for the selection of senor components, material and calibration technique, like temperature coefficients, effect of radiation, and vibration effects etc. Here different techniques/approaches and constraints regarding the design of electro-optical imaging system are discussed. |
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