File Name: difference between passive and active sensors .zip
- Passive vs. Active Sensing
- A Comparison between Active and Passive 3D Vision Sensors: BumblebeeXB3 and Microsoft Kinect
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Platforms refer to the structures or vehicles on which remote sensing instruments are mounted. The platform on which a particular sensor is housed determines a number of attributes, which may dictate the use of particular sensors. These attributes include: distance the sensor is from the object of interest, periodicity of image acquisition, timing of image acquisition, and location and extent of coverage. There are three broad categories of remote sensing platforms: ground based, airborne, and satellite.
Passive vs. Active Sensing
So far, throughout this chapter, we have made various references to the sun as a source of energy or radiation. The sun provides a very convenient source of energy for remote sensing. The sun's energy is either reflected , as it is for visible wavelengths, or absorbed and then re-emitted , as it is for thermal infrared wavelengths. Remote sensing systems which measure energy that is naturally available are called passive sensors. Passive sensors can only be used to detect energy when the naturally occurring energy is available. For all reflected energy, this can only take place during the time when the sun is illuminating the Earth. There is no reflected energy available from the sun at night.
A Comparison between Active and Passive 3D Vision Sensors: BumblebeeXB3 and Microsoft Kinect
Another possibility to distinguish between earth observation satellites is to compare the sensors used. In general, there are passive sensors which measure the reflected sunlight or thermal radiation, and active sensors which make use of their own source of radiation. Active sensors for example Radar and laser scanners emit artificial radiation to monitor the earth surface or atmospheric features. Radars are imaging instruments while radar altimeters and scatterometers are non imaging. Radar is the abbreviation for Radio Detection and Ranging , a method for the detection and ranging of earth surface features. Radar satellites use short pulses of electromagnetic radiation in the microwave spectral range, therefore they do not depend on daylight and are hardly affected by clouds, dust, fog, wind and bad weather conditions. They measure the radar pulses reflected from the ground, analyse the signal intensity in order to retrieve information on the structure of the earth surface, and detect the elapsed time between pulse emission and return.
There are two main types of sensors used in remote sensing technology, active sensors and passive sensors. Difference between these two is quite small, however, leaves great impact on their functionality. As we learnt in primary school, sun constantly emits light energy and is only source of natural light for earth. Moreover, this energy is not observed by any component in solar system. Instead it is reflected to somewhere else. Just like the moon, it shines despite of not possessing its own light source. Measuring these emissions is useful for global satellite purposes.
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Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. Because of the recognized value of these measurements and because techniques are ever improving, several nations plan further radar missions to observe the land surface. Many more airborne radar remote sensing instruments have been developed to conduct studies on a regional scale, or as platforms for demonstrating future spaceborne techniques. Active microwave remote sensing has proven valuable across a number of science disciplines and practical applications, including geology, urban planning, agriculture and crop management, forestry and biomass assessment, hydrology and water resource management, weather forecasting, generation of topographic maps, sea ice mapping and glacier studies, earthquake and volcano studies, archaeological investigations, and post-disaster assessment.
If the sun disappeared, which type of sensor would miss it most? Would it be passive or active sensors? If you can answer this question, it will help you understand the concept of active and passive sensors in remote sensing.
Radars and lasers are breathtaking attributes of sci-fi movies no longer as it was just a few decades ago. These innovations have been widely used as types of sensors in remote sensing since science made a giant step ahead.
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