A remote sensing platform is designed with a relatively narrow set of purposes in mind. Many important decisions must be made when designing a remote sensing technology. The type of sensor and its capabilities must be defined. The platform on which the sensors will be mounted must be determined. The means by which the remotely-sensed data is received, transmitted, and processed before delivery to its end user must be designed. All of these decisions are made based on knowledge of the target and the information about the target that is in demand, balanced by other factors such as cost, availability of resources, and time constraints. The end result of this process is a tool that is specifically designed to perform a task or a set of related tasks that will assist researchers in better understanding the process that is under investigation. 1.1
There are many applications of remote sensing, and each sensor is engineered for very specific purposes. The design and placement of a sensor is determined by the unique characteristics of the target that will be studied and the information that is required from the target. Each remote sensing application has specific demands on the amount of area to be covered, the frequency with which measurements will be made, and the type of energy that will be detected. Thus, a sensor must provide the spatial, spectral, and temporal resolution necessary to meet the needs of the application. Spatial resolution refers to the amount of detail that can be detected by a sensor. Detailed mapping of land use practices requires a much greater spatial resolution than observations of a large scale storm system. Thus, land use satellites such as Landsat generally have greater spatial resolution than global weather satellites. Spectral resolution refers to the width or range of each spectral band measured by a sensor. Detection of some phenomena, such as vegetative stress, requires a sensor with sensitivity in a narrow spectral band so that differences in the spectral signatures at a specific wavelength can be detected. Temporal resolution refers to the time interval between measurements. For some applications, such as monitoring the development of a severe thunderstorm, measurements are required at a frequency of a few minutes. Some applications, such as measuring crop production or insect infestations, require seasonal measurements, while others, such as geological mapping, require a single measurement. 2.0
Remote sensing platforms that position the sensor at the Earth's surface are called ground-based platforms. These systems are fixed to the Earth and the sensors are often standard tools used to measure environmental conditions such as air temperature, wind characteristics, water salinity, earthquake intensity and such. Ground-based sensors can be placed on tall structures such as towers, scaffolding, or buildings to elevate the platform. Ground-based sensors are generally less expensive to operate and maintain than air-borne or space-borne sensors, but they do not provide the aerial extent of the air-borne or space-borne platform. Ground-based sensors are often used to record detailed information about the surface, which is compared with information collected from air-borne or space-borne platform sensors. One example of ground-based remote sensing are sensors mounted on buoys that make real-time measurements of water temperature, salinity, wind speed, and wind direction. The buoys are anchored in a body of water (the target) and they transmit the results of each measurement to receiving stations to be processed. These sensors can be used to supplement or "ground truth" measurements made from air-borne or space-borne sensors. Ground-based remote sensing platforms can transmit data using ground-based communication systems, such as radio and microwave transmissions or computer networks. Some systems can store data on the platform, allowing...
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