The types of remote sensing data to be acquired depend on the type of information needed, the size and dynamics of the studied objects or phenomena. As previously mentioned, data acquisition is made possible through instruments called sensors that differ from each other by the way they function and their “capacities” (spatial, spectral and radiometric resolutions).
Remote sensing data can be acquired in the form of two-dimensional images when information with high spatial resolution is required, as is the case of the TM/Landsat image. Such images are also important when synoptic information about large areas such as those provided by meteorological satellites is desired (Figure).
Two-dimensional images can be acquired in different regions of the electromagnetic spectrum, such as visible, thermal, microwave, etc.; with channels with different spectral resolutions ranging from a few nanometers, as is the case of hyperspectral sensors, to panchromatic systems that integrate radiation across the entire visible spectrum.
Spectrometers are used to detect and measure the spectral content of an electromagnetic field. This type of information is important for identifying the chemical composition of objects. When studying the atmosphere, spatial aspects are less critical than when studying the earth’s surface, because the gradient of change in chemical composition is much smaller. Therefore, sensors for studying the chemical composition of the atmosphere do not need to have high spatial resolution, but they do need excellent spectral resolution.
In the case of studies of the earth’s surface, when there is an interest in knowing the chemical composition of rocks, for example, a good spatial resolution is essential, and in this case, the application of imaging spectrometers is recommended.
In many applications the spectral and spatial aspects are less important and what is needed are precise measurements of the strength of the electromagnetic field over a wide spectral region. An example of sensors used for this purpose are radiometers, including the Advanced High Resolution Radiometer that is on board the NOAA satellite. The NOAA Radiometer is designed to provide accurate temperature information. Therefore, the spectral resolution of the thermal channels is 1000 nm and the spatial resolution at the nadir is 1.1 km. But the radiometric resolution of the system, that is, its ability to measure small variations in the intensity of the radiance measured by the sensor, is quite high (10 bits).
In numerous applications, the information needed is the three-dimensional distribution of a given variable. In this case, sensors such as altimeters (provide information about the topography of the surface) and probes (provide the vertical distribution of temperature in the atmospheric column) are extremely useful.
References:
Campbell, James B., and Randolph H. Wynne. Introduction to remote sensing. Guilford Press, 2011.
Colwell, Robert N. “Manual of remote sensing.” (1985).
Lo, Chor Pang. “Applied remote sensing.” (1986): 60-60.
Cracknell, Arthur P. Introduction to remote sensing. CRC press, 2007.
